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This work aims to study the effects of bionic spiral stacking sequence, impact energy and impactor shape on the impact resistance of laminates. The finite element model is established based on the stress failure criterion, progressive damage evolution, and the triangle traction‐separation law. The reliability of the finite element model is validated through rigorous comparison with experimental data. The study investigates the influence of laminate layup sequence, impact energy, and impactor shape on the impact resistance of laminates. The results show that during low‐speed impacts, laminate damage is primarily characterized by fiber breakage, matrix cracking, and delamination. Matrix cracking and delamination become more pronounced as the impact energy increases. The design of linear spiral ply and power function spiral ply has a positive effect on the impact resistance of laminates. The impact resistance of laminates is sensitive to the sharpness of the impactor and the level of impact energy. Higher impact energy and sharper impactor shapes lead to increased energy absorption in the laminate, resulting in more pronounced damage failure. Highlights: The impact resistance of bionic spiral composite laminates is studied.Three biologically inspired stacking sequences were designed.A numerical simulation method is proposed and verified.The low‐velocity impact characteristics of bionic laminates are revealed. [ABSTRACT FROM AUTHOR]

Structural behavior of precast concrete sandwich panels under low‐velocity drop weight impact is presented in this paper. Three types of concrete panels are considered namely, solid concrete panel (SCP), concrete sandwich panels containing recycled tire crumb rubber as core (CRSP), and expanded polystyrene foam as core (FSP). The panels are reinforced with steel mesh or steel fibers. A total of 12 panels are cast in this study. Six panels are reinforced using steel mesh, and the other six panels are reinforced using steel fibers. The impact test is carried out by dropping a weight from a varying height to input impact energy, which can cause various levels of damage for all specimens. The structural performance is discussed in detail, including failure modes, impact force, deflection, and strain. It is found that the core material greatly affects the structural response of the precast concrete panels. The sandwich panel containing recycled tire crumb rubber performed well in terms of rebounding force, permanent deflections, and damage behavior by partially absorbing the impact energy in both types of reinforced concrete panels. In CRSP and FSP, the maximum deflection to permanent deflection ratio rose from 1.19 in SCP to 2.67 and 2.01, respectively. A decrease of 70% in strain value from the first impact to permanent strain was recorded in CRSP when reinforced using conventional steel mesh. In comparison to its counterpart FSP, the CRSP exhibited a significantly smaller fracture width on the tension face as a result of the core's ability to dissipate impact energy, resulting in lower deflections and less damage to the panel. The CRSP reinforced with steel fibers demonstrated comparable performance to the counterpart FSP in terms of energy absorption and deflection reduction; however, it performed noticeably better than the SCP reinforced with steel fibers by reducing residual deflection by 51.8 mm. Consequently, recycled tire crumb rubber can be used as a sustainable alternative to traditional core materials in precast concrete panels. [ABSTRACT FROM AUTHOR]

Interfacial adhesion properties are a key factor affecting the mechanical properties of composites. It is a very effective way to improve the low‐velocity impact resistance of composites by improving the interfacial adhesion properties. To improve the fiber/matrix interfacial adhesion properties of GF/PA6 (glass‐fiber/polyamide 6) composites, polyethyleneimine (PEI) and γ‐aminopropyltriethoxysilane (KH550) were used to co‐modify GF together in this study. The GF/PA6 composites with different modifications of glass‐fiber (GF) were also prepared using a hot pressing process, and then their flexural strength, shear strength, pendulum impact strength, and low‐speed impact resistance were investigated. Next, the relationship between fiber/matrix interfacial adhesion and mechanical properties of GF/PA6 composites was investigated by combining x‐ray photoelectron spectroscopy, scanning electron microscopy, and x‐ray computed tomography test results. The results showed that the GF‐reinforced PA6 matrix composite with co‐modified GF by PEI and KH550 (PEI‐KH550‐GF/PA6) had the best mechanical properties, with flexural, shear, and pendulum impact strengths of 660.7 MPa, 53.1 MPa, and 261.6 kJ/m2, respectively. Furthermore, the low‐velocity impact resistance was measured in terms of stress peak, absorbed energy, residual stress, and damage extension, and the results showed that the low‐speed impact resistance of PEI‐KH550‐GF/PA6 composites was also substantially improved that the Fmax increased from 7402.1 to 10414.0 N. Highlights: Due to the poor surface activity of GF, in this experiment, GF was co‐modified with PEI and KH550 to achieve better fiber/matrix interfacial adhesion and successfully improve the mechanical properties of the composites;Different modification methods are used to improve the interfacial adhesion of the fiber/matrix interface. The relationship between the interface and impact strength of composites has been studied;The relationship between fiber/matrix interfacial adhesion and internal cracking in composites was investigated using X‐CT and SEM and other test results. [ABSTRACT FROM AUTHOR]

The present work highlights the benefits of matrix strengthening through the inclusion of hard particles within the resin‐impregnated woven Kevlar mat. Aluminium Oxynitride (ALON) particles are added to epoxy resin by 5, 10, and 15 volume percentages. The test coupons were developed through a hand‐lay‐up technique to estimate the low‐velocity impact resistance. The characterization was performed through EDAX and SEM to ensure the presence of the ALON particles and their homogenous distribution respectively. Low‐velocity testing is preferred to assess the capacity of the materials to rebound the incident energy. The damage assessment was made to estimate the material's stiffness. The compression after impact (CAI) was executed to observe the strength of the material after the impact. The post‐CAI micrographic observation reveals the delamination history. The results manifest that the ALON–rich coupon exhibits higher impact resistance to the scale of 33.33% than that of the ALON‐free coupon. The damage assessment and CAI results annunciate the lesser damage and higher compressive strength of ALON‐rich material respectively. The micrographic study studied after the CAI reveals the delamination and failure behavior. Additionally, explicit numerical assessment was conducted to validate the experimental results. A good agreement is attained between the experimental results and numerical predictions. The enriched stiffness of the synthesized material makes it a perfect candidate for structural application where the frequency of impact loading is high. Highlights: Development of ALON reinforced Kevlar‐Epoxy composites for low‐velocity impact applications.Evaluating the performance of developed composites under low‐velocity impact loading.Determining the optimal volume percentage of ALON in the composites.Studying the fractography of developed composites.Correlation between experimental and numerical studies. [ABSTRACT FROM AUTHOR]

To meet the lightweight requirements of advanced composite materials, the ultralightweight three‐dimensional (3D) braided spacer composites were designed and manufactured by ultra‐high molecular weight polyethylene (UHMWPE). The key structural effects of core column distances and core column heights on the static bending, compression, and low‐velocity impact properties of the composites were further investigated. Results indicated that the mechanical properties of 3D braided spacer composites was closely depended on their structural parameters. The flexure and compression of 3D braided spacer composites decreased with increasing core column distance and core column height. W1/H1 specimen showed the optimal bending and compressive performance. The maximum flexural strength and flexural modulus were approximately 54.77 MPa and 4.95 GPa, respectively. The low‐velocity impact properties were further investigated where the stiffness, energy absorption, and impact resistance of the composite decreased with increasing core column distance. The peak load and energy absorption of the W1 specimen were 2.39 kN and 7.99 J, respectively. While the low‐velocity impact properties increased with increasing core column distance. The H3 specimen exhibited the greatest stiffness, impact resistance and energy absorption with peak loads and energy absorption of 2.81 kN and 8.49 J, respectively. In addition, the macro morphology and scanning electron microscopy (SEM)micrographs were examined to investigate the damage morphology and failure mechanism of the composites. The main failure modes were matrix cracking, interface debonding, fiber buckling, and dislocation, as well as tilting, and failure of the core columns. This work provides guidance for structural design and engineering application of 3D lightweight braided spacer composite. [ABSTRACT FROM AUTHOR]

The rapid increase in use of polymer matrix composites in different industries underscores the need for reliable non‐destructive evaluation techniques to characterize small‐scale damage and prevent structural failure. A novel dielectric technique exploits moisture‐polymer interactions to identify and track damage, leveraging differences in dielectric properties between free and bound water. This technique has demonstrated the ability to detect low levels of damage, but the localization accuracy has not yet been evaluated. This work utilizes unsupervised machine learning to assess the technique's ability to identify the damage boundary following a low‐velocity impact event. Bismaleimide/quartz and E‐glass/epoxy laminates were impacted via drop tower to induce varying levels of damage, and subsequently inspected via dielectric technique at several moisture levels by weight. Resulting data was processed via k‐means clustering and the identified damage boundary was compared to a boundary obtained from backlit images and scanning electron microscopy. Accuracy was quantified using developed metrics for damage centroid and boundary identification. The technique averaged 93.9% accuracy in determining the damage center and 77.5% accuracy in identifying the damage boundary. Results indicated the technique's effectiveness across varying moisture levels, particularly in damage centroid identification. Localization accuracy was shown to be insensitive to moisture content, improving the technique's practical capabilities. Further analysis revealed potential for delineation of delaminations. Highlights: Low‐velocity impact of two material architectures.Damage boundary determined and validated via scanning electron microscopy.Detected damage site via dielectric technique compared to damage boundary.High technique accuracy revealed; >90% centroid localization accuracy.Potential for delamination delineation observed. [ABSTRACT FROM AUTHOR]

Highlights The integration of 3D‐printed cellular cores into sandwich composite structures for load‐bearing applications opens up innovative design possibilities while improving structural efficiency. However, ensuring effective energy dissipation under impact conditions without compromising structural integrity remains a challenge. This study investigates the energy absorption and failure mechanisms of 3D‐printed hexagonal honeycomb sandwich composite structures across three different PLA‐based core materials: polylactic acid (PLA), PLA–Carbon, and PLA–Wood, under dynamic and quasi‐static loadings. Material characterization was conducted via Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Failure modes were analyzed using optical microscopy. The results show that PLA–Wood composites demonstrated significant improvement in energy absorption, absorbing 9.22 J of energy at an impact energy of 11 J, compared to 8.49 J for PLA–Carbon while under in‐plane compression, PLA–Wood recorded an energy absorption of 8.74 J, significantly outperforming PLA–Carbon, which reached only 3.05 J. This improvement is attributed to enhanced interfacial adhesion between the wood filler and the PLA matrix, as confirmed by SEM and FTIR analyses. These findings highlight the critical role of filler compatibility in the structural integrity of 3D‐printed sandwich composites, indicating potential applications in the aerospace and automotive industries, where lightweight and durable materials are essential for improving performance. Dynamic and quasi‐static response of 3D‐printed hexagonal honeycomb cores. Material interactions affect energy absorption through plastic deformation of cores. PLA–Wood outperforms PLA–Carbon in absorbed energy due to filler compatibility. Dynamic loading causes localized core damage with short elastic recovery. Core failure mechanisms with long elastic recovery vary in quasi‐static tests. [ABSTRACT FROM AUTHOR]

Highlights In this study, experiments combined with finite element analysis (FEA) were used to investigate the damage mechanism of transverse low‐velocity impacts on three‐dimensional woven tubular composites (3DWTC) with different structures. The damage morphology after impact was observed using three‐dimensional microscopy and scanning electron microscopy (SEM). Three mesoscale models were constructed based on the authentic structure of the 3DWTC. Additionally, the effects of the structure type on the impact resistance, stress distribution, and damage morphology of 3DWTC were studied. The impact resistance of the shallow cross‐linked (SCL) structure is the strongest, according to the data. The structure that resists impacts the least is the through orthogonal (TO) structure. The greater the straightness of the warps in the structure, the density of the weft, the volume fraction, the greater the cooperative load‐bearing capacity of the warps and wefts, and the greater the speed of stress propagation. The wefts and inner warps are subjected to tensile forces at the point of impact. The outer warps are subjected to compression. The stresses are distributed in a cross‐shaped pattern. The straightened warp and weft parts of the TO serve a key structural role in load‐bearing. The warps of the SCL and the shallow‐crossed curved joint (SCCJ) structure serve a key structural role in the load‐bearing capacity. The impact resistance of 3DWTCs was investigated. The tensile state, stress propagation rate of 3DWTC were analyzed using the mesoscale model. The main load‐bearing components are revealed. The differences in damage morphology of 3DWTCs are analyzed. [ABSTRACT FROM AUTHOR]

This paper focuses on the mechanical response and viscoelastic properties of double‐blade composite stiffened structure (DCSS) under low‐velocity impact (LVI). Firstly, the impact resistance and viscoelastic behavior of the DCSS are revealed by LVI testing at four different locations using the same initial velocity. Next, the damage morphologies at the impact locations are observed with ultrasonic A‐ and C‐scan equipment and optical microscopy. At last, the DCSS containing impact damage is implemented for axial compression and the strain values of the DCSS surface are obtained using a strain testing system to reveal its residual properties and buckling behavior. The results show that there are significant differences in the impact damage modes at the four different locations. The maximum impact resistance is observed at location D, while location A has the opposite. The DCSS has a certain viscoelastic behavior at LVI and conforms to an exponential decay model. Moreover, position B presents interface debonding damage due to stiffness discontinuities at the flange and skin bonding and severely weakens the load carrying performance of the DCSS. Highlights: The impact resistance of different positions is analyzed by LVI experimental results.Viscoelastic properties exist at different impact locations and obey the exponential decay model.Impact damage alters the buckling load and residual strength of the DCSS.The damage mechanism of the triangular zone is revealed by damage morphology. [ABSTRACT FROM AUTHOR]

In challenging operational environments, Lithium‐ion batteries (LIBs) inevitably experience mechanical stresses, including impacts and extrusion, which can lead to battery damage, failure, and even the occurrence of fire and explosion incidents. Consequently, it is imperative to investigate the safety performance of LIBs under mechanical loads. This study is grounded in a more realistic coupling scenario consisting of electrochemical cycling and low‐velocity impact. We systematically and experimentally uncovered the mechanical, electrochemical, and thermal responses, damage behavior, and corresponding mechanisms under various conditions. Our study demonstrates that higher impact energy results in increased structural stiffness, maximum temperature, and maximum voltage drop. Furthermore, heightened impact energy significantly influences the electrical resistance parameters within the internal resistance. We also examined the effects of State of Charge (SOC) and C‐rates. The methodology and experimental findings will offer insights for enhancing the safety design, conducting risk assessments, and enabling the cascading utilization of energy storage systems based on LIBs. [ABSTRACT FROM AUTHOR]

This research proposes a novel sustainable composite using basalt (B), hemp (H) and polyurethane rubber (Pu) reinforced in nano clay functionalised epoxy matrix for sacrificial structural applications prone to low‐velocity impact (LVI). To this end, symmetric and asymmetric laminates such as HHHH, BBBB, BHHB, BHPuHB, BBPuHH and BPuBPuHPuH are fabricated using compression molding techniques and subjected to LVI at three different impact energies of 19.66, 39.39, and 59.05 J. The hemp fibers were treated with NaOH solution before fabrication. Material characterization such as X‐ray diffraction, Raman spectroscopy and morphological studies has been carried out. The impact and post‐impact properties of the proposed composites are experimentally evaluated and validated with the finite element (FE) results. The effect on the residual tensile strength degradation of laminates at different interlayers and energy levels is also investigated using the Caprino analytical model. The barely visible impact damages (BVID) are investigated through non‐destructive dye‐penetration tests, which facilitate easy identification of the prominent LVI damages like "Plateau" and "Cliff‐drop" impressions. Based on the impact energy absorption and residual tensile strength, proposed laminates followed BHPuHB > BBBB > BHHB > HHHH. The experimentation suggests that Polyurethane core laminates support maximum impact energy absorption by favoring a structural change in interlayers. Also, the residual tensile strength decreases as impact velocity increases. Highlights: Low‐velocity impact behavior of sustainable composites is experimented.Basalt, hemp and polyurethane rubber are reinforced in nano clay epoxy matrix.A FE framework to validate the experimentation is proposed.Dye penetrant NDT is adopted to investigate the damages.Morphological studies are conducted to understand LVI responses. [ABSTRACT FROM AUTHOR]

A multi‐stage fiber spreading process for the preparation of high‐performance continuous aramid fiber reinforced nylon 12 (CAF/PA12) composites was proposed in this paper. The effects of spreading rod crown radius, spreading rod axis height and traction speed on fiber impregnation effect and filaments properties were investigated. The fiber volume fraction of the prepared filament was approximately 30%. And the maximum tensile strength and modulus of the filaments were 839.89 MPa and 41.35 GPa, which were 34.36% and 34.30% higher than unspreading filaments, respectively. The influences of printing process parameters such as printing temperature, the combination of layer thickness and printing spacing on the transverse tensile properties of the specimens were studied. Printed specimens reached a transverse tensile strength and tensile modulus of 13.988 MPa and 1.293 GPa, respectively. The influences on low velocity impact properties of the specimens were also investigated in terms of impact energy and printing stacking sequences. Results revealed that the impact threshold energy of orthotropic ([0/90/0/90]2) specimens was 50 J. Quasi‐isotropic ([0/45/90/−45]2) specimens exhibited the superior impact resistance with an impact load of 4.939 kN. Macro‐ and micro‐matrix crack, surface buckling, fiber fracture and delamination were the main failure modes of the specimens. Highlights: A novel thermoplastic composite filament forming process was proposed, and the filament forming equipment was designed and manufactured.Continuous aramid fiber‐reinforced PA12 filaments with about 30% fiber content were prepared by orthogonal tests under different forming process conditions, which showed maximum tensile properties of 839.89 MPa and 41.35 GPa, respectively.Spreading multiplication was positively related to filament tensile properties, which was major affected by the axial height of the spreading rod.Transverse tensile strength (13.988 MPa tensile strength and 1.293 GPa tensile modulus) of printed specimens was investigated under different printing parameters.Fiber orientation had a significant effect on the low‐velocity impact properties. Micro‐ and macro‐matrix crack, surface buckling, fiber fracture and delamination were the main failure modes of the low‐velocity impact specimens. [ABSTRACT FROM AUTHOR]

Novel Stitched Foam‐filled Honeycomb Sandwich (SFHS) panels have been fabricated using vacuum‐assisted resin transfer molding to address the weak interfaces between the face sheets and the core in the Foam‐filled Honeycomb Sandwich (FHS) panel. The SFHS panels have shown better load‐bearing capacity and performance characteristics compared to FHS panel after Low‐Velocity Impact (LVI) tests. After the LVI test, MATLAB image processing was used to analyze the impact damage areas and failure mechanisms. In addition, Machine Learning regression algorithms were employed to predict the optimal amount of energy absorbed during low‐velocity impact testing of fabricated panels with a maximum impactor drop height of 700 mm. The results indicated that nylon yarn stitching significantly improved energy absorption and interfacial behavior compared to unstitched honeycomb panels. This research also revealed that SFHS1 panels with adjacent honeycomb cell stitching are more impact resistant, provide increased load carrying capacity, and are cost‐effective. These panels can be utilized by modern engineers to increase economy, durability, and functionality in industrial, automotive, and construction applications. Highlights: Stitched Foam Filled Honeycomb Sandwich (SFHS) panels, manufactured via resin transfer molding, and eliminates weak interfaces between the face sheets and core.SFHS panels outperformed unstitched panels in load‐bearing and energy absorption during low‐velocity impact, as confirmed by MATLAB image analysis showing reduced damage and failure.Machine learning algorithms particularly polynomial regression model predicted maximum absorption energy precisely with 99.9% accuracy, close to experimental results.SFHS panels can be used in automotive and industrial applications due to their through‐thickness stitching. [ABSTRACT FROM AUTHOR]

Highlights The outstanding mechanical performance and flowability of unidirectionally arrayed chopped strands (UACSs) give them an advantage in the manufacture of engineering structures with complex geometry. For the application of practical structures, the impact responses and damage evolution of material under low‐velocity impact must be investigated in advance. In this study, UACS laminates and continuous carbon fiber laminates with a stacking sequence of [0/90]4s and a thickness of 2 mm were fabricated for low‐velocity impact tests at 7, 11, 15, and 20 J. The impact responses and postimpact intralaminar damage area were analyzed according to the experimental results, including impact load responses and ultrasound C‐scan inspections. Moreover, to predict the damage evolution of the internal structure, the 3D finite element models were constructed in ABAQUS using a progressive damage model (PDM) through a user‐material subroutine VUMAT. Compared with continuous carbon fiber laminates, the dissipated energy of UACS laminates increases by approximately 10.64% and 57.37% for the 15 and 20 J, respectively. However, the intralaminar damage area of UACS laminates decreased by 29.96% and 28.16% at 15 and 20 J, respectively, since the discontinuous slits in UACS laminates can guide damage paths and suppress damage propagation. The regularly arrayed short fiber reinforced composite was studied. Revealed the low‐velocity impact responses and predicted the damage evolution. UACS and CFRP laminates have comparable impact performance. Illustrated the slits design can suppress the damage to a relatively small area. [ABSTRACT FROM AUTHOR]

The present study aimed to examine how the corrosive environment affected the low‐velocity impact (LVI) characteristics and damage mechanisms of thermoplastic polyamide fiber‐reinforced polymer (PFRP) composites. In this regard, composite specimens were subjected to corrosive environment containing 10 wt.% diluted HCl for one week and one month before LVI tests. To investigate the hostile effects of the corrosive environment on the composites, scanning electron microscope (SEM) coupled with energy‐dispersive X‐ray system (EDX) analyses were carried out, and thus variations in the elemental composition and damage mechanisms for the composites were determined. According to the examinations, it was discovered that the degradation in LVI responses, such as contact stiffness, bending stiffness, and peak force, increased with longer aging time, as expected. Furthermore, when the aging effect was assessed based on absorbed energy, the specimens exposed to a corrosive environment for one month exhibited the highest energy absorption compared to the control and 1‐week‐immersed ones. The degrading effect of the HCI environment appeared as higher damage severity on the composites, which was also detected from the SEM images. According to the SEM analyses, matrix cracks, corrosion pits, and local surface imperfections caused by ion exchange are detected in 1‐week‐immersed specimens, while more serious damage mechanisms such as fiber breakage and fiber pull‐out are noted in specimens exposed to corrosive environment for 1 month. Furthermore, approximately 6.33 wt.% CI was identified in the composites after 1 month of aging, which was associated with the hydrolysis triggered by rise in the composite's damage severity. Highlights: Aging effects in mechanical properties of PFRP composites were investigatedLVI tests were conducted to determine dynamic responses of aged compositesLonger aging time led to more severe damages such fiber rupture, delamination etc.PFRP composites absorbed at least 68% of impact energy. [ABSTRACT FROM AUTHOR]

Considering the nonlinearity of shear in the mechanics of composite materials, the increase of shear strength when the substrate interface is compressed, and the shear of the matrix itself, the Chang–Chang criterion is improved. The improved Chang–Chang criterion was used to establish a progressive damage model of low‐velocity impact of composites. The low‐velocity impact process of T700/EM134 composite laminates in the energy range from 5 to 10 J was compared by physical tests and finite element simulations, and the calculated impact response curves and material damage were in good agreement with the test results, which proved that the model of the improved criterion was suitable for the damage prediction of low‐velocity impact of composite laminates. Highlight: Consider various situations in composite material shearing.Improved based on the Chang–Chang criterion.Establishing a progressive damage model for low‐speed impacts.Comparison through physical experiments and finite element simulation.Prove that the improved criterion model is suitable for damage prediction. [ABSTRACT FROM AUTHOR]

Highlights The aim of this paper is to explore the effect of polyurethane foam filler on the out‐of‐plane compressive property and low‐velocity impact resistance of the orthogonal corrugated sandwich panel by experimental method. The results show that foam filling increases the energy absorption and specific energy absorption of the orthogonal corrugated sandwich panel by 64.75% and 38.22% under compressive load, respectively. Furthermore, during compression, the filled foam causes the core strut undergo pure buckling failure and gradually folds rather than brittle fracture. Under low‐velocity impact, the strengthening effect of foam filling on the first peak load of the load–displacement of the orthogonal corrugated sandwich panel decreases with the increase of impact energy, while the inhibition effect on the impactor drop increases with the increase of impact energy. The results can provide a reference for the design and optimization of foam‐filled hybrid sandwich structures. The compressive property and low‐velocity impact resistance of the foam‐filled orthogonal corrugated sandwich panel are tested. The effect of foam filling on the mechanical properties of the orthogonal corrugated sandwich panel is obtained by comparing the out‐of‐plane compressive response and low‐velocity impact response of the empty and foam‐filled orthogonal corrugated sandwich panel and foam sandwich panel. Foam filling can improve the load‐bearing property and energy‐absorbing capacity of the orthogonal corrugated sandwich panel and make it more stable progressive damage. [ABSTRACT FROM AUTHOR]

Highlights Carbon fibers woven‐ply reinforced polyether ether ketone (C/PEEK) thermoplastic composites are widely used in aerospace and high‐tech industries because of their exceptional resistance to low‐velocity impact. In this paper, experimental investigation is carried out to determine the low‐velocity impact performance of C/PEEK laminates at room temperature (RT) and high temperature (90°C and 150°C) environments. Both macroscopic and microscopic analyses are applied to examine the influence of temperature on the mechanical response and damage mode of the material. The attention of this investigation is on impact parameters such as maximum contact force, energy absorption rate, indentation depth, and damage mode. The findings show significant changes in material stiffness, rate of energy absorption, and indentation depth with rising temperature. Temperature variations have a notable effect on the PEEK matrix plasticity, C/PEEK composite interlaminar properties, crack initiation and propagation, and damage mode at the overlaps of warp and weft fibers, resulting in a transition from brittle to ductile failure. Experimental investigation is carried out to study the low‐velocity impact performance of C/PEEK. The effects of impact energy and environmental temperature on the low‐velocity impact performance of C/PEEK are investigated. The mechanism of how environmental temperature affects the damage mode of C/PEEK is investigated. [ABSTRACT FROM AUTHOR]

Highlights A voronoi user material subroutine (VUMAT) was developed using the three‐dimensional Hashin damage criterion and exponential nonlinear damage evolution method. An interlayer damage model based on the quadratic nominal stress (QUADS) criterion and B‐K fracture criterion was introduced, and a finite element model of Z‐pin reinforced composite laminates under low‐velocity impact was established. The low‐velocity impact behavior of Z‐pin reinforced composite laminates with different impact velocities (0.6 m/s, 0.4 m/s, and 0.3 m/s), different layup forms ([0°/90°]4 and [0°/45°/90°/−45°]2), and different Z‐pin spacing (4 mm, 8 mm, and 16 mm) was studied using ABAQUS. The results indicate that different layup forms have little effect on the low‐velocity impact behavior of Z‐pin reinforced composite laminates. The Z‐pin spacing has a significant influence on the low‐velocity impact behavior of Z‐pin reinforced composite laminates. When the impact velocity is 0.4 m/s, the specific energy absorption of composite laminates with Z‐pin spacing of 16 mm is 85.93% and 87.7% lower than that of composite laminates with Z‐pin spacing of 4 mm and 8 mm. As the Z‐pin spacing decreases (Z‐pin density increases), the impact resistance of Z‐pin reinforced composite laminates first increases and then decreases.• The low‐velocity impact of Z‐pin reinforced composite laminates was studied.• Analyzed the effect of layup forms of laminates on their impact behavior.• Explored the influence mechanism of Z‐pin spacing on the impact behavior.• Studied the energy absorption of different Z‐pin spacing under impact velocity. [ABSTRACT FROM AUTHOR]

Highlights This paper investigates a honeycomb sandwich structure that draws inspiration from the craft of origami. A specific folding pattern was applied to the honeycomb to create the origami‐based re‐entrant honeycomb (ORH), aimed at improving the energy absorption properties of the sandwich structure. The study on the energy absorption properties of structures under low‐velocity impact (LVI) utilized both experimental and numerical approaches. The energy absorption properties of the sandwich structure were examined by conducting LVI tests with different impact energy and then compared to the mechanical properties of the traditional re‐entrant honeycomb sandwich structures (TRHSS). Additionally, a refined finite element model has been established and its accuracy verified. Numerical studies were conducted to explore the effects of structural parameters on the energy absorption properties of ORH sandwich structure (ORHSS). The results show that the ORHSS exhibited a significant reduction in peak force when subjected to LVI, in contrast to the TRHSS. Furthermore, the ORHSS exhibit significant efficiency in energy absorption. Enhancing the wall thickness t$$ t $$ or folding angle V/H$$ V/H $$ can significantly improve the energy absorption properties of the ORHSS, thereby boosting the honeycomb's contribution to this process. This optimization results in an improved absorptive effect of the structure. The findings offer new recommendations for developing lightweight absorbent materials with potential applications across various industries. A novel composite sandwich structure serves as an efficient device for absorbing energy. This sandwich structure exhibits excellent cushioning and energy absorption capabilities. Changing geometric parameters can enhance the impact performance of the structure. A larger folding angle V/H$$ V/H $$ makes the core more prone to deformation. The greater the forward length V$$ V $$ of the ORH, the lower specific energy absorption (SEA) of the ORHSS. [ABSTRACT FROM AUTHOR]

The load‐bearing capacity and failure characteristics of composite structures are closely related to their dimensions. In this study, low‐velocity impact, ultrasonic non‐destructive testing, and compression after impact tests were conducted on composite laminates of varying widths to investigate the influence of size effects. Distinct impact response profiles and compression failure modes were characterized. The results indicate that under impact loading, the delamination threshold load (6700 N ~ 7200 N) and the knee‐point energy (40 J) are not affected by width. However, variations in width lead to differences in indentation depth, impact duration, peak load, delamination characteristics, and energy absorption. Furthermore, increasing impact energy further magnifies these differences. Under compression loading, wider laminates exhibit lower residual strength, with the influence of impact energy on residual strength decreasing as width increases. Importantly, the observed compression failure deformation mode transitions from localized buckling to widespread sub‐layer delamination‐induced compression failure. This suggests that changes in width alter the governing mechanical mechanisms of CAI failure. Consequently, the use of a single‐size laminate to represent both LVI and CAI processes is not recommended. Based on experimental results, the reliability of the equivalent damage method in predicting the residual compression strength of laminates of different widths was confirmed, providing valuable insights for practical engineering applications. Highlights: Assess the variations in the low‐velocity impact process of laminates with different widths.Evaluate the delamination damage of laminates after impacts by ultrasonic C‐scan techniques.Investigate the effect of variation in widths on the compression behavior of laminates after impact.Validate the feasibility of equivalent damage modeling for calculating residual strength. [ABSTRACT FROM AUTHOR]

The boundary condition is a very important factor when characterizing the impact performance of a material or a structure. However, its effect on fiber metal laminate (FML) has been rarely mentioned. In the present investigation, three levels of low‐velocity impact tests were conducted on the glass fiber reinforced aluminum laminate (Glare) under two different boundary conditions, one was that defined in ASTM D7136 and another one was self‐designed that has the same constraint area but different constraint degree. One basis of the experiments, finite element analyses were performed to gain a deeper understanding of the different damage mechanisms. With which another three boundary conditions were investigated for further considering the effect of constraint areas on both the impact and non‐impact sides, including that defined in another commonly used standard ASTM D5628 and two self‐designed cases. It was indicated that the boundary conditions influenced less the force and energy responses of Glare laminate, regardless of the impact damage levels, and hardly on the damage behavior as well when perforation was encountered. However, influences were obtained under lower and intermediate damage levels, and it was the constraint area on the rear side and constraint degree that played the dominant roles, respectively. The results achieved can provide suggestions for reasonably evaluating the low‐velocity impact performance of FML. Highlights: Comparisons were made between the low‐velocity impact behavior of Glare laminates under five different boundary conditions.Boundary conditions influenced hardly on maximum impact force and energy absorbed ratio, but evidently on damage behavior.Constraint area and constraint degree governed damage mechanism under lower and intermediate impact energies, respectively.Influence of boundary conditions on damage behavior disappeared when the impact energy was enough to perforate Glare laminate. [ABSTRACT FROM AUTHOR]

Short fiber reinforced polymers (SFRP) based on unidirectionally arrayed chopped strands (UACS) offer exceptional formability and great mechanical properties. To ensure its stability and safety in applications, it is crucial to enhance the impact performance of UACS laminates. This study investigated the low‐velocity impact (LVI) responses and damage evolution of UACS laminates with different slit sizes and continuous carbon fiber reinforced polymer (CFRP) laminates under various impact energies (4, 7, and 11 J). The curves of force and energy were recorded during LVI tests, and the post‐impact damage area was detected by the ultrasonic C‐scan technique. Moreover, a user‐defined subroutine VUMAT, containing a progressive damage model and a Johnson‐Cook constitutive model, was written to mimic the damage evolution. Based on experiments and numerical prediction, it was found that when the size was reduced from 25 to 5 mm, the vertical slits had the effect of suppressing delamination and could restrain the propagation of delamination, which explains the distinct difference in delamination area. Highlights: The effect of slit size on the impact behavior of UACS laminate was revealed.The damage mechanism was simulated with a progressive damage model.The novel UACS laminate exhibits excellent energy absorption capacity.The resistance of the slits greatly suppresses the delamination behavior. [ABSTRACT FROM AUTHOR]

This study reveals the impact resistance of shear thickening gel (STG) impregnated four‐layer regular angle interlocking fabrics (AIF) composites. The effects of STG parameters, including reaction time, reaction temperature, and reaction ratio, on the rheological characterization and mechanical properties of STG/AIF flexible composites were investigated. The results show that the increase in STG parameters accelerated the formation of BO crosslink bonds within the STG. The energy storage modulus of STG increased by three orders of magnitude for a reaction temperature of 230°C, a reaction time of 9 h, and a reaction ratio of 12.5%. STG had an obvious shear thickening effect. The coupling effect of STG and AIF increases the inter‐yarn friction. The shear thickening effect of STG and the deformation of AIF fabric synergistically absorbed the impact energy, and the energy absorption rate reached 95.6%. The material surface was not significantly damaged after the low‐velocity impact. The STG/AIF flexible composites showed excellent impact energy absorption properties. Highlights: A new high‐energy absorption and impact resistance composite was prepared.Increased STG reaction ratio and temperature promoted its internal reaction.B and O atomic interactions enhance the rheological properties of STG.STG and fabric synergistically improve the impact resistance. [ABSTRACT FROM AUTHOR]

In this paper, a new type of foldcore sandwich panel (tentatively called X‐type foldcore sandwich panel) is proposed by combining the X‐type corrugated sandwich panel and the Miura‐ori sandwich panel. The experimental specimens are prepared by using a glass fiber‐reinforced polymer. To systematically reveal the low‐velocity response mechanism and impact resistance of sandwich panels, a hemispherical impactor is used to impact panels. The effects of impact energy, impact position, diameter of tup, and impact mass on low‐velocity impact performance of X‐type foldcore sandwich panels are considered. The damage morphology, response process, and failure mechanism are analyzed under different working conditions. The results show that under the impact of 75 and 125 J, the impact resistance of the node is better than that of the base. Under 200 J impact, the impact resistance of the base is better than that of the node. Compared with the traditional foldcore sandwich panel, the new configuration reduces the impact resistance difference between two positions (node and base). Highlights: A new foldcore sandwich panel is proposed.The impact effect of energy, mass, position, and tup diameter is investigated.Damage morphology, response process, and impact resistance are analyzed.The new structure reduces differences in impact resistance. [ABSTRACT FROM AUTHOR]

With the help of the high‐speed camera and self‐designed fixture, it was investigated that the effects of the impactors in a variety of shapes on the mechanical behavior and failure mode of carbon fiber‐reinforced polymer (CFRP) tubes with a range of inner diameter during the low‐velocity impact (LVI) of four impact energies. Then, the three‐dimensional digital image correlation (3D‐DIC) system was carried out to monitor the damage evolution of the LVI‐damaged specimens under compressive and flexural loading. In addition, the residual compressive and flexural strength of all kinds of cases were compared and discussed. The results show that the increase in wall thickness can improve the LVI, compression‐after‐impact (CAI), and flexure‐after‐impact performance. The failure mode of compression changes to brittle fracture failure at the impact circumferential region. The CAI strength of the specimen damaged by a flat impactor is 23.89% less than that of a hemispherical one, but there is little difference in flexural loading. Highlights: Mechanical behavior on in & post LVI of CFRP tubes varying wall thickness and impactor.Due to point‐line contact for flat impactor, two peak forces are in the F‐D curves.LVI property and residual strength are improved with the increase of wall thickness.Compressive failure mode is brittle fracture at the impact circumferential area.Flexure‐after‐impact strength mainly depends on the no‐impact surface of tubes. [ABSTRACT FROM AUTHOR]

In this study, the effects of hybridizing carbon fibers with Kevlar fibers and incorporating multiwalled carbon nanotube (MWCNT) particles on low‐velocity impact, tensile, and flexural performance were evaluated experimentally. A manual lay‐up procedure followed by vacuum bag molding was used to construct hybrid composites (carbon and Kevlar) with and without MWCNTs, as well as hybrid composites with varying MWCNT weight ratios of carbon and Kevlar fiber reinforcements. When 0.1 wt% of MWCNT was added to the epoxy to enhance absorbed energy and peak load, the maximum improvements observed were 31% and 28%, respectively. The addition of MWCNTs by 0.5 wt% to the epoxy enhanced the flexural strength and flexural modulus by 66% and 41%, and by 5% with 0.1 wt% and 12.3% with 0.5 wt% MWCNT for tensile strength and tensile modulus, respectively. These improvements were observed in both tensile strength and tensile modulus. As for (C5K10C5), the maximum improvements in absorbed energy and peak load were observed to be 11.2% and 31%, respectively, corresponding to a 0.1 wt% MWCNT addition, whereas the maximum improvement in flexural strength and flexural modulus was 12.28% and 44%, respectively, with a 0.1 wt% MWCNT. These improvements in mechanical properties are primarily attributed to the enhanced stress transfer properties from fibers and nanoparticles to the matrix. This enhancement is a result of the strong interfacial interactions between epoxy and MWCNT nanoparticles. Highlights: MWCNT inclusion effects on mechanical properties of carbon/Kevlar hybrid composites.MWCNT inclusion effects on low‐velocity impact properties of Carbon/Kevlar hybrid composites.The effects of Kevlar and carbon stacking sequence with MWCNT incorporation were investigated. [ABSTRACT FROM AUTHOR]

In this paper, low‐velocity impact properties and impact damage responses of a novel type of 3D hybrid auxetic structures made from carbon fiber‐reinforced polymer (CFRP) laminates were investigated experimentally and numerically. The structures were first fabricated with three different rib's width ratios t1/t0, and then impacted with three different impact energies of 30, 40, and 50 J using a drop tower impact system equipped with a cylindrical impactor. The finite element (FE) models were built in ABAQUS/Explicit, and the Hashin criteria were applied to predict the failure of the structures. The contact force histories, energy histories, displacements, and failure modes were compared between the experiment and FE simulation at all three impact energy levels. The failure morphologies and mechanisms were obtained and studied. The impact testing results suggest that the 3D auxetic structure with a higher t1/t0 ratio can lead to higher peak contact force and sustain higher impact energy. The failure of the structure starts from the middle area and propagates to the upper and lower areas. This research provides a better understanding of the impact responses and failure modes of the 3D auxetic lattice structure, which can promote the potential applications of the auxetic materials. Highlights: Drop weight low‐velocity impact responses of 3D novel hybrid auxetic lattice structures are investigated through both experiment and finite element simulation.The effects of structural parameters on the impact performance of the 3D auxetic structures at different impact energy levels are analyzed.The failure morphologies and mechanisms of the 3D auxetic structures are studied. [ABSTRACT FROM AUTHOR]

This article reports a carbon fiber–reinforced plastic Kagome composite honeycomb sandwich structure reinforced with polymethacrylimide (PMI) foam (PKCSS). Low‐velocity impact performances on the node, rib, and two cell centers of the PKCSS were experimentally compared with those on a composite Kagome honeycomb sandwich (CKHS), and the failure mechanism of the PKCSS was investigated. The impact process was analyzed through an explicit numerical analysis using ABAQUS. A three‐dimensional Hashin failure criterion was introduced using the VUMAT subroutine. Results confirmed that the PKCSS exhibits higher impact and specific loads than the CKHS, with the maximum improvements of 69.7% and 39.5%, respectively, under 50‐J impact energy. As an uncrushable material, the PMI foam provides strong impact resistance during its plateau stage. This technology of cell filling can be used to fabricate lightweight all‐composite honeycomb sandwiches for potential use in ultrahigh engineering applications. Highlights: Cell filling is applied in an all‐composite Kagome honeycomb sandwich.The LVI performances of the PKCSS and CKHS are experimentally compared.C‐scanning is used to analyze the failure of the considered structures.The PKCSS's numerical model is established to investigate the impact process.The enhancement mechanism of the PMI foam is analyzed. [ABSTRACT FROM AUTHOR]

Experimental and simulation studies of the response of bonded‐repaired and scarf‐repaired carbon fiber‐reinforced polymer laminates under the low‐velocity impact (LVI) were carried out. The center‐ and eccentric‐repaired laminates were prepared for experiments. The experimental results verify the validity of the finite element model in terms of the force response and different modes of damage. The effect of impact energy and the variation of repair position on the impact response of the laminate was investigated based on the benchmark model. The bonded repaired laminates have higher peak impact forces and lower energy absorption than the scarf‐repaired laminates; the damage of the bonded repaired laminate is mainly intralaminar damage and delamination damage of the patch; the adhesive of the scarf repair is prone to failure, leading to poor impact resistance. The relative positions of the impact point and the patch determine the impact response of a laminate repaired at different locations. The impact point at the edge of the patch has a detrimental effect on the repaired laminate. The impact point vertical position near the bottom hole edge of the parent plate in the scarf‐repaired case harms the impact resistance of the laminate. Highlights: The low‐velocity impact response of bonded versus scarf‐repaired laminates was compared.Bonding repairs provide superior impact resistance to damaged laminates than scarf repairs.The risk of adhesive failure in scarf repair is significantly higher than in bonded repair.The relative position of the damage (repair) to the impact point critically influences the impact response.Impacts near the edge of the initial damage hole can cause severe damage to scarf‐repaired laminates. [ABSTRACT FROM AUTHOR]

In this study, the low‐velocity impact behavior of polymer composites produced separately by reinforcing with natural fiber fabrics such as linen, hemp, jute, and bamboo was investigated for three different thicknesses (2.5 ± 0.1, 5 ± 0.1, and 7.5 ± 0.1 mm) by vacuum infusion method. Low‐speed impact tests were performed at three different energy levels of 20, 35, and 50 J by striking the geometric center of the composite samples with a hemispherical impactor. The impact strengths of the composites were evaluated by comparing the contact force‐displacement, contact force‐time graphs, and impacted sample images. The types of damage occurring in each experimental sample were evaluated. Increasing the thickness had a positive effect on the impact strength of the composites. When the thickness of the composite plates increases, the peak contact force increases, the displacement decreases and capacity to carry impact loads increases due to the increased stiffness of the composites. However, except for the damaged 5 ± 0.1 mm thick bamboo and jute samples, the energy absorption ability of the samples generally increases with the increase of impact energy. Bamboo, jute, and hemp reinforced samples with a thickness of 2.5 ± 0.1 mm were completely perforated under 20 J impact energy. Also, it was determined that linen reinforced composites have the best impact resistance among natural fabric reinforced composites. Highlights: Low‐velocity impact behavior of natural fiber fabric reinforced PMCs was studied.The impact strength of PMCs increased as the thickness increased.Linen reinforced composites had the best impact resistance.The main damage modes are matrix cracking and delamination at low‐impact energies.As the impact energy increases, perforation and fiber breakage or separations are observed. [ABSTRACT FROM AUTHOR]

The global composite industry generates large quantities of waste which mostly ends up in landfills due to a lack of established end-use applications for multiple waste streams. The scrap from end-of-life (EoL) includes manufacturing waste such as dry chopped fiber tows, loose fibers, shredded fibers from fabric textile operations, cured/semi-cured prepregs, and fully cured composite structure waste from aircraft, automobiles, wind blades, boats, and pressure vessels. In this work, different composite waste streams were reduced to shredded intermediates, followed by simple blending, and subjected to wet compression molding to produce composite panels. The panels/plaques were tested for mechanical properties (flexure and impact), fiber-matrix wet-out, and property bounds. It was found that wet-compression molding was a viable and scaleable approach to produce recycled panels from EoL composites shredded scrap. Furthermore, full-scale size panels for use in truck bodies and intermodal shipping container flooring were manufactured and their impact resistance was tested using a drop weight impact test. They were tested both for high- and low-velocity load. In the case of high-velocity load, the average impact load was 14,673 N; the average absorbed energy was 101.6 J; the average elastic energy was 11.7 J and the impact resistance was 1065 J/m. In the case of the low-velocity drop weight impact test, it was found that the average impact load was 7877.358 N; the average absorbed energy was 9.718 J; the average elastic energy was 9.14 J, and the impact resistance was 184.1 J/m. The shredded composite was shown to be a candidate material for the manufacture of truck bodies and intermodal containers' flooring panels. Highlights • By using shredded intermediates from different composite waste streams, it is possible to manufacture composite panels. • Wet-compression process is an appropriate technique for manufacturing recycled fiber composite panels. • Regardless of the source of scrap, the mechanical properties of the produced composite panels were improved. • The recycling process technology can be transformed to commercial scale to produce full-size transportation flooring panels. • A product pathway is established in consideration of lower cost and improved recyclability. [ABSTRACT FROM AUTHOR]

Composite structures with a pure glass composite facesheet and an aluminum honeycomb core are widely used in aircraft interiors. Because impact-related problems are related to structural integrity and safety performance, the behavior of these structures under impact loading is critical. Due to their promising performance, lower cost, and low environmental impact, hybrid composites have recently become one of the most widely researched composite materials in the research field. This paper aims to investigate the impact behavior of nonhybrid glass and the glass partially replaced with a flax and kenaf hybrid composite facesheet caused by a low-velocity impact. The specimens were impacted with different impacted energies, such as 10, 20, and 30 J. All nonimpacted and impacted samples were tested and compared for postimpact flexural (three-point bending) behavior to analyze the residual strength of sandwich structures after impact. The results revealed that the hybrid composite face sheet outperformed the glass composite sandwich structure. The hybrid composite face sheet allowed the impactor to penetrate deeper, resulting in better energy absorption than the glass composite. Compared to nonimpacted specimens, the glass and hybrid face sheet combinations demonstrated comparable residual bending performance. Highlights • Experimental analysis shows the impact resistance (low-velocity impact test) and residual load-carrying capacity (three-point bending test) of glass and hybrid composite face sheets. • Hybrid face sheets show excellent energy-absorbing capability compared to glass one. • The residual flexural strength of the glass and hybrid composites was comparable to that of nonimpacted samples. • The peel strength achieved in this study using the pre-cure fabrication process was significantly higher than the peel strength achieved using prepreg face sheets. • Reinforcing the composite face sheet of the sandwich structure by partially replacing the glass with flax and kenaf fiber exhibited comparable performance. [ABSTRACT FROM AUTHOR]

The low-velocity impact (LVI) characteristics and compression after impact (CAI) properties of aircraft composite laminates under the influence of ultraviolet (UV) radiation were studied. Firstly, 0, 30, 60, 90 days of UV radiation experiments were carried out on the specimens to analyze the characteristics of the surface topography. Secondly, LVI experiments, the impact energies of 10, 17, and 25 J, were carried out on specimens to analyze the impact response laws and the characteristics of the impact instantaneous deformation. Finally, through CAI experiments and scanning electron microscope (SEM) techniques to clarify the influence mechanism of UV radiation on the residual compressive strength of specimens. The results showed that with the increase of UV radiation time, the shrinkage and erosion phenomena of the surface matrix and the exposure degree of the surface fibers were gradually increased, and the surface fibers were completely exposed after 90 days of radiation. At the same impact energy, with longer radiation time, the peak force gradually decreased (from 8673.86 to 7851.68 N at 17 J), the absorbed impact energy (from 9.48 to 11.13 J at 17 J) and maximum displacement (from 4.1 to 4.73 mm at 17 J) increased, the depth of pit on the impact surface decreased (from 0.213 to 0.14 mm at 17 J), and the internal damage projection area increased (from 906.68 to 1158.66 mm2 at 17 J). The compression damage of the specimens not exposed to/exposed to UV radiation was mainly fiber cracking/interlayer delamination, respectively. Highlights • Ultraviolet (UV) radiation makes the matrix of surface shrink, the fibers exposure increase. • The Stage II has obvious oscillation phenomenon in four stages of the lowvelocity impact process. • With prolonged UV radiation, the projected area of internal damage expands. • The residual compressive load increases with the increase of UV radiation time. [ABSTRACT FROM AUTHOR]

The present research investigates optimizing the impact resistance of functionally graded sandwich structures using experimental and numerical approaches. The low-velocity impact (LVI) responses of functionally graded sandwich composite (FGSC) with different configurations with skin material jute/rubber/jute (JRJ) and core material having epoxy and sea sand by volume fraction of sea sand at 0%, 10%, 20%, and 30%. Sandwich structures were impacted with LVI (5.89, 10.92, and 15.18 m/s), with the impactor dropped from heights of 0.5, 1, and 1.5 m with precompressed spring loads. FGSC samples are considered a deformable body, and the impactor is modeled as a rigid body using commercially accessible dynamic explicit software. The burnout test and weight method were used to test the core's gradience; both methods' results substantially matched, and the variance in gradation could be observed. The proposed sandwich structure characteristics are examined by energy absorption, peak force, energy loss percentage, and coefficient of restitution. Results showed that SC30S provides greater energy absorption and superior damage resistance when tested on LVI. To evaluate the accuracy of experimental findings in predicting the indentation behavior of the sandwich structure, the finite element analysis was used to compare with the experimental results. According to the examination of these proposed FGSC overall performance, they could potentially be employed as sacrificial materials for LVI applications like claddings to shield major structural components. The systematic approach used in this work serves as a standard for choosing and using FGSC effectively for LVI applications. Highlights • Low-velocity impact behavior of sandwich structures was investigated. • Combining flexible skin and epoxy core enhances energy absorption. • Based on impact energy levels, impact damage areas were determined. • Examined sandwich structure advantages in structural and aerospace uses. • In terms of time and cost, the numerical analysis method would be useful. [ABSTRACT FROM AUTHOR]

To investigate the failure mechanism of the composite T-joints subjected to low-velocity-impact (LVI) loading varying impact locations, a methodology composed of improved conventional vacuum-assisted resin infusion (VARI) and LVI testing based on ASTM D 7136 is developed and employed. Moreover, the simulation is conducted to mainly reveal the damage evolution of interlaminar delamination between web and web/skin laminate based on surfacebased cohesive behavior in the commercial software of Abaqus 2020. Further, the effect of LVI loading with various distances from the web laminate to the impact location on the mechanical property and failure mode of the composite T-joints are presented and discussed as well. By comparison, larger vertical cracks and higher residual tensile strength are found in the T-joints impacting the corner. However, the T-joints with the impact point near the corner have lower residual tensile strength and suffer more interlaminar delamination in the interface between web and skin, which is the most critical position of failure. Highlights • GFRP T-joints are manufactured by the vacuum-assisted resin infusion process with a newly designed mold. • The damage evolution in low-velocity-impact tests is presented via the quasi-static tests and finite element simulation. • Larger vertical cracks and higher residual tensile strength are found in the T-joints impacting the corner. • The T-joints with the impact point near the corner have lower residual tensile strength. • Interlaminar delamination in the interface between web and skin is the most critical factor of tensile failure. [ABSTRACT FROM AUTHOR]

Low‐velocity impact damage is one of the main defects of composite laminates, which seriously affects the bearing capacity and service life of composite laminates. Multiple impact experiments of carbon fiber/epoxy composite laminates were carried out under different impact energies. The finite‐element model was established according to the experimental conditions. The impact damage mechanism of laminated plates was studied by means of simulated damage cloud image, water immersion ultrasonic C‐scan, and computed tomography. The results showed that the matrix damage occurred mainly during the whole impact process, and the tensile damage of the matrix was dominant. As the number of impacts increased, the impact resistance of composite laminates decreased and the damaged area increased, with the second impact having the greatest influence on the degree of damage to the laminates; multiple impacts with low energy were easy to cause delamination at the top of the laminated plate. With the increase in impact energy, the damage at the bottom of the laminated plate was more serious, and the propagation mode of delamination damage in laminates changed from top‐bottom to bottom‐up. Highlights: Establishing a multiple impact finite‐element model for composites.Accurately predicting the impact mechanical response of composites.Revealing multiple impact damage evolution of composites by simulation. [ABSTRACT FROM AUTHOR]

Functionally graded (FG) composites reinforced by carbon nanotubes (CNTs) have received extensive attention due to their excellent mechanical properties. The impact responses of FG‐CNT nanocomposites are analyzed by the developed meshless method. The temperature‐dependent material properties are expressed by way of the extended rule of mixture. The kinematics of the composite plate is established on the basis of the first‐order shear deformation theory. The modified Hertzian contact law is adopted to evaluate the impact loading between the plate and the impactor. The dynamic balance equations of the plate are constructed and computed by the Systemic Smoothed Particle Hydrodynamics (SSPH) method with strengthened prediction ability. The impacting behaviors of the FG‐CNT nanocomposite plate, as well as the parametric effects, are analyzed by the developed model and the suitability is clearly demonstrated. Highlights: Impact of FG‐CNTRC is firstly solved by a self‐developed meshless SPH model.Strong capacity of the SPH impact model is clearly demonstrated.More CNTs close to the strike face would improve the impact resistance. [ABSTRACT FROM AUTHOR]

This study aims to quantify impact damage in laminated composites using acoustic emission (AE) and to verify the AE results with finite element (FE) method. Carbon fiber reinforced polymer (CFRP) composite specimens were subjected to quasi‐static out‐of‐plane indentation loading. A procedure, including feature extraction, feature selection, data dimensionality reduction, and data clustering using an evolutionary algorithm, that is, differential evolution (DE) optimization algorithm, was proposed to identify and quantify different damage mechanisms using AE. The AE results showed that the dominant damages were matrix cracking and delamination. For the quantitative evaluation of the AE results, the indentation test was simulated using the FE method. A FE model based on cohesive zone modeling and continuum damage mechanics was implemented to predict interlaminar and intralaminar damages. The quantity of the damaged elements associated with the matrix cracking and delamination was consistent with the AE results. This study showed the applicability of the AE for impact damage identification and quantification in composite structures. Highlights: Indentation damage in CFRP is experimentally quantified using the AE method.The DE algorithm is used to cluster the AE data.CZM and CDM are used to numerically model the damage.The AE clustering results are compared with the numerical results. [ABSTRACT FROM AUTHOR]

Design of automotive components with over‐molded short/continuous fiber reinforced thermoplastic composites necessitates understanding of their behavior under extreme outdoor conditions. The short, quasi‐isotropic and over‐molded short/continuous glass fiber reinforced polypropylene (PP) composite specimens were prepared as per standard and immersed in water until equilibration to study their relative moisture absorption characteristics and consequent mechanical behavior. As the absorbed moisture mostly occupied the interface between fiber and matrix in laminated composite inserts and moisture absorption of short fiber composite core is insignificant, the moisture absorption of over‐molded composites is just above 50% of that of laminated composites. The flexural, interlaminar shear and impact behavior of equilibrated composites is primarily governed by the quantum of imbibed moisture of composite materials. Optical analysis of failed moisture equilibrated over‐molded specimens showed a marginal delamination between plies of the inserts without any perceptible damage within the short fiber composite similar to dry as molded specimens. [ABSTRACT FROM AUTHOR]

This study exhibits the effect of different damage mechanisms on the mechanical behavior of composite laminates subjected to low‐velocity impact load. To achieve this, seven low‐velocity impact energies were applied to laminates with five different thicknesses and four unique stacking sequences. The extent of damage was quantitatively evaluated through contact measurements and ultrasonic C‐scan techniques. Numerical simulations, showing good agreement with experimental results, characterized the distribution and evolution of damage within the laminates. The findings reveal that when matrix and delamination damage are predominant, the dent depth increases slowly and is visually invisible, while the delamination area expands almost linearly. Conversely, When fiber damage prevails, the laminate absorbs more energy, leading to rapid increases in dent depth, the appearance of visible cracks, and the occurrence of sharp fluctuations with multiple peaks in contact force and displacement curves. Nonetheless, the delamination area and projection tend to be stable and unchanged. Furthermore, alterations in thickness and stacking sequence directly affect the damage characteristics and energy absorption properties. This research offers valuable theoretical insights and serves as a reference for enhancing the comprehension of the failure mechanism of laminates and optimizing their performance. Highlights: Demonstrate the utility of dent depth in identifying changes in damage mechanisms.Evaluate the delamination damage of laminates after impacts by ultrasonic C‐scan techniques.Reveal the regulation of impact response parameters for different damage mechanisms.Investigate the effect of variation in thickness on damage characteristics and energy absorption.Evaluate the impact resistance of laminates with different stacking sequences. [ABSTRACT FROM AUTHOR]

To understand the hybrid fiber enhanced impact‐resistance performance of composite laminates. In particular, the effects of different parameters, such as hybrid fiber ratios and plying modes, were investigated. The effects of UHMWPE short fibers (UHMWPESFs) fiber content and ply angle changes on the impact resistance of Carbon fiber/ultra‐high molecular weight polyethylene short fiber hybrid composite (CUFHRP) laminates were investigated in this article. The impact resistance of the CUFHRP laminate was tested by the drop weight test and residual strength test after impact. The results indicated that the peak load and absorption energy of the specimen with a fiber content of 15 g/m2 were the highest, reaching 6.543 kN and 16.51 J, respectively. Specimens with different ply modes of [0/−45/45/90]2s showed the most obvious effect on the maximum load. Its maximum load was 28.93% higher than that of the original sample. The critical damage threshold load of composite laminates is improved, and the impact resistance is strengthened. Highlights: Study to improve the impact resistance of the composite on the basis of the hybrid structure.Report the optimal parameters of the effects on the impact resistance of the composite, such as: hybrid fiber ratios and plying modes.Reveal the fundamental failure mode of hybrid structure composite laminates under low‐velocity impact. [ABSTRACT FROM AUTHOR]

Unidirectional fiber‐reinforced composite laminates have limited resistance to out‐of‐plane impact and are prone to structural integrity damage during service due to low‐velocity impact (LVI). In this study, the hot‐press fusion method was employed to repair the impact‐damaged unidirectional carbon fiber‐reinforced poly‐ether‐ether‐ketone (CF/PEEK) thermoplastic composites. No delamination or matrix cracking induced by impact was observed in the repaired specimens, as confirmed by ultrasonic scanning and digital microscope. In addition, the hot pressing treatment enables the fibers to be covered again by the resin matrix, which eliminates fiber pull‐out and fiber/matrix debonding. Afterward, typical responses of CF/PEEK composite laminates to re‐impact and post‐repair compression are presented in a comprehensive and detailed manner, and compared with the initial impact response and compression after impact (CAI) behavior. The effects of three impact energies and two stacking sequences are considered. The results indicate that quasi‐isotropic laminates are more susceptible to localized fracture damage upon re‐impact as the impact energy increases, due to initial fiber breakage, compared to orthotropic laminates. The hot‐press treatment enhances the compression residual strength of the specimen by 20%–30% compared to its state before repair. These studies offer technical insights into the application of the hot‐press fusion method to enhance the mechanical properties of composite laminates post impact damage. [ABSTRACT FROM AUTHOR]

This study presents an innovative approach utilizing Artificial Neural Network (ANN) strategies to evaluate the energy absorption capabilities of eco‐friendly rubber crumb/kenaf composites subjected to low‐velocity impact loads. The primary objectives of this research were to assess the energy absorption characteristics of these sustainable composites, understand their mechanical behavior under the impact, and provide valuable insights into their potential applications. To achieve these objectives, an experimental methodology was employed. Rubber crumb/kenaf composites with varying compositions were prepared, and low‐velocity impact tests were conducted using a drop‐weight impact testing apparatus to assess their energy absorption behavior and these parameters were used as inputs for training the ANN models. The weight percentage of waste tire rubber particle (WTRP), type of impactor and impact energies are considered as input data, whereas the absorbed energy is treated as the output. Through the advanced ANN strategies, accurate predictions of energy absorption performance were achieved for the rubber crumb/kenaf composites. The Levenberg–Marquardt optimisation algorithm with ten neurons and a tangent sigmoid activation function is used to train the ANN model. The trained ANN model is tested on an unseen dataset, different from the training data. It is shown to accurately predict the energy absorption characteristics of WTRP/KRE composites with a maximum error of 4.54%. The results revealed that the composite's energy absorption capabilities were influenced by the ratio of rubber crumb to kenaf, as well as the impact velocity. Additionally, the ANN models demonstrated excellent predictive capabilities, enabling efficient estimation of energy absorption behavior. The significance of these results lies in the potential applications of eco‐friendly rubber crumb/kenaf composites. By understanding their energy absorption characteristics, these composites can be effectively utilized in various industries. For instance, they could be employed in automotive parts manufacturing to enhance occupant safety during low‐velocity impact events. Furthermore, these composites can find applications in sports equipment, protective gear, and other impact‐prone products, contributing to sustainable and environmentally friendly materials. It is believed that by adopting the proposed ANN methodology, the experimentation costs and time can be significantly reduced without compromising the accuracy of the results. The obtained results provide valuable insights into the mechanical behavior of these sustainable composites and open avenues for their implementation in diverse industries where impact resistance is crucial Highlights: Development of sustainable Rubber crumb/kenaf compositesApplication of advanced ANN based predictive assessment of the impact responseParametric study of impactor shape and height of impact is performedThe damage mechanism contributing to energy absorption is micrographically studied [ABSTRACT FROM AUTHOR]

An experimental study is performed to explore the low‐velocity impact (LVI) and self‐healing behavior of carbon‐fiber‐reinforced‐polymer (CFRP) laminates reinforced by thermoplastic poly(ethylene‐co‐methacrylic acid) (EMAA) filaments. Firstly, differential scanning calorimetry (DSC), thermos‐gravimetric analysis (TGA) and dynamic mechanical analysis (DMA) are used to determine the process parameters. Thereafter, the unreinforced laminates and EMAA reinforced laminates are prepared via phased hot‐processing curing process. The LVI tests with four energy levels (5, 15, 25 and 35 J) are then carried out on the two types of specimens. In these energy cases, the peak‐force values of the reinforced specimens are 2.2%, 1.9%, 2.3% and 7.5% higher than those of the unreinforced ones, while the energy‐absorption‐rate values of the reinforced ones are 6.02%, 3.53%, 4.24% and 2.32% lower. The comparisons demonstrate the impact‐resistance enhancement of EMAA. Moreover, multiple LVI tests are performed on the unhealed and healed specimens. In 15 and 25 J cases, around 6.92% higher peak load and 4.58% lower absorbed energy are observed within the healed specimens, which is attributed to the healing effect. The healing mechanism is investigated by utilizing attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR), scanning electron microscope (SEM) and optical microscope (OM) technologies. It reveals that EMAA flows into the delaminations and cracks during the healing process, and thus accomplishing self‐healing behavior effectively. [ABSTRACT FROM AUTHOR]

Highlights In this study, a method was developed to detect impact damage and determine the damage propagation in increasing and repetitive impacts. The effect of nanographene additives on the propagation of delamination damage in the top face layer of a sandwich structure was investigated using the developed method. In addition, the effects of nanographene on visible (VID) or barely visible damage (BVID) formation were investigated, and the stiffness of the sandwich structures was evaluated. An ultrasonic C‐scan nondestructive testing was used to visualize the damage, and the numerical values of the damaged areas of the sandwich structures at different energy levels were determined using an image processing method. The obtained values were used in artificial neural network (ANN) training to estimate the impact energy at which the structural integrity of the sandwich structures was disrupted. It was observed that the nanographene additive was effective in maintaining rigidity of the sandwich structures and therefore, slowed the delamination damage progression in increasing and repeated impacts. The damage areas of the neat sandwich structures (NSS) and graphene nanoplatelets doped sandwich structures (GSS) structures at the first impact 5j energy level was 1004 and 811 mm2, respectively. At the first impact, 20% less damage occurred in the GNP‐doped sandwich structures. The increasing and repetitive last impact energies at the end of the neural network training were 5j + 35j in NSS and 5j + 50j in GSS. The method allows for a detailed examination of the damage progression of sandwich structures under increasing and repeated impact loads. Low‐velocity impact tests of Nomex honeycomb sandwich structures were performed. Damage formation and propagation in sandwich structures were investigated. The non‐destructive test C‐scan method was used to determine BVID. The damaged areas were determined using an image processing method. The damage areas were estimated using artificial neural networks. [ABSTRACT FROM AUTHOR]

This paper reports the low‐velocity impact performance of 3D auxetic composite embedded with re‐entrant triangle inclusions by both experiments and finite element (FE) simulations. Both auxetic and non‐auxetic samples were manufactured by embedding inclusions made from carbon fiber/epoxy laminates into silicone rubber matrix. The pure silicone rubber was also manufactured for comparison. All samples were subjected to low‐velocity impact with an impact energy of 147 J and an impact speed of 5.42 m/s and their impact load‐time and energy‐time curves were compared between the experimental results and FE simulation. The impact performances under different impact energies from 60 to 120 J were further investigated based on the validated FE models. The results show that the auxetic composites show better energy absorption capacity and impact resistance than non‐auxetic composites with the same number of inclusions at all energy levels. More inclusions can result in better impact resistance of auxetic composites when the impact energy is under 120 J. The auxetic composites possess 10% higher crash efficiency than non‐auxetic samples. The embedding of inclusions leads to easier damage of the composite under impact energy of 147 J. The research provides a better understanding on the impact performance of auxetic composites made from random inclusions. [ABSTRACT FROM AUTHOR]

This article investigates the effect of alternating the sequence of variable‐energy repeated low‐velocity impact on the residual strength of carbon fiber reinforced polymer (CFRP) laminates. Quasi‐isotropic CFRP specimens were impacted using three impact energy levels, that is, Low (L), Medium (M), and High (H). Every group, out of three groups in total, was impacted consecutively using one of three sequences: LMH, HML, and MLH. Delamination and its growth after each impact was quantified using a phased‐array ultrasonic probe. The impacted specimens were then subjected to compression after impact loading with in situ acoustic emission (AE) and digital image correlation (DIC) measurement. Mechanical results showed that the residual strength of the specimens was not significantly affected by alternating the impacts sequence. However, the AE, sentry function and DIC results revealed that the impact‐induced damage in HML configuration was activated much earlier than MLH, and the damage induced in LMH configuration was activated later than both. [ABSTRACT FROM AUTHOR]

The structural properties of braided composite laminates are significantly affected by the low‐velocity impact (LVI). In this paper, the impact resistance and damage tolerance of triaxial braid structure laminates at different positions were mainly studied. Three hybrid biaxial (B)/triaxial (T) braided composite structures of BBTT, BTTB, and TTBB were designed, and LVI test and post‐impact compression tests were carried out. The results show that the triaxial braided fabric with quasi‐isotropic on the impact side caused more significant matrix cracks along the axis yarn direction, and the matrix damage area and delamination area were larger. For triaxial braided ply with high curl levels, severe fiber fracture and relatively concentrated damage occurred first on the non‐impact side. Interestingly, triaxial braided fabrics exhibited better impact resistance in terms of mechanical response when distributed across the specimen surface. However, a global damage pattern appears at high energy levels, which seriously reduced the residual strength of the structure and showed the worst damage tolerance. The damage quantification analysis of cracks, dent depths, delamination and residual compressive strength caused by the LVI of hybrid shaft number braided laminates was carried out in this work, which provided a valuable reference for engineering failure analysis and rational structure optimization of composite laminates. [ABSTRACT FROM AUTHOR]

In this study, polyamide fibers, which stand out with their excellent plastic deformation and energy absorption capacity, were used as reinforcement materials, and in‐house manufactured composite specimens were subjected to low‐velocity impact (LVI), compression after impact (CAI) and tensile tests. Within this scope, one and two repeated drop tests were performed under 3 m/s velocity to determine LVI responses and how impact number affects the dynamic properties. CAI tests were also performed at a 1 mm/min crosshead speed, and mechanical properties for non‐impacted, one‐impacted, and two‐impacted specimens were determined. As a result of the outstanding plastic deformation capacity of thermoplastic fabrics, it is concluded that polyamide composites exhibited quite large strains. Furthermore, it was understood from the tensile responses that tensile stresses were carried by the thermoplastic fibers in two different regimes and significantly high toughness was obtained. Moreover, reductions in the maximum compression loads, critical buckling loads and axial stiffness were observed due to degradation in structural integrity after impact loads. Additionally, the utilization of recyclable thermoplastic polyamide fibers as reinforcement material instead of conventional reinforcement materials such as carbon and glass fibers provide more environmentally friendly products. [ABSTRACT FROM AUTHOR]