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• Analytical Method for Wafer Bonding Quality Assessment: The paper introduces an analytical method that connects external conditions such as normal pressure, planarity deviation, and impurity particle counts with key mechanical variables like wafer deflection and strain energy during the direct wafer bonding process. This is a significant advancement as previous research did not account for the impact of impurities on bonding quality. • Influence of Impurities on Bonding Process: The study establishes a mechanical model of the adhesive process that elucidates the relationship between impurity particle count and strain energy. It reveals how impurities affect wafer deflection and strain energy, showing nonlinear variations with changes in particle position. The results indicate that wafer curvature, thickness, and impurity count are critical factors determining deflection under specific pressures. • Theoretical Guidance for Practical Bonding: The proposed mechanical model, verified through finite element simulation, offers theoretical guidance for selecting adhesive materials and evaluating the feasibility of wafer bonding in industrial applications. It provides insights into the effects of initial wafer geometry, adhesive energy, and particle positions on successful bonding outcomes under applied external pressures. Direct wafer bonding technology has been widely used in the manufacturing of microelectromechanical systems (MEMS). The chip deflection and strain energy can be used to evaluate the bonding quality. Current research assumes that the wafer surface is perfectly clean and neglects the influence of impurities, lacking an analytical model to characterize the effects of external conditions (normal pressure, planarity deviation, impurity particle counts) on key mechanical variables (wafer deflection and strain energy) during the bonding process. In this paper, an analytical method is used to establish a bridge between external conditions and bonding variables. A mechanical model of the adhesive process is established, and the relationship between impurity particle count and strain energy is obtained. By considering the bonding pressure, chip geometry, and impurity particle count, analytical expressions for deflection and strain energy are derived, revealing the influence of external conditions and internal geometry on wafer deflection and strain energy. The results show that under certain pressure, the curvature and thickness of the wafer, as well as the impurity particle count, jointly determine the wafer deflection. The wafer deflection and strain energy exhibit nonlinear variations with changes in particle position. The correctness of the proposed model is verified through finite element simulation. This work provides a reference for judging wafer bonding with impurity particles in industrial applications. [ABSTRACT FROM AUTHOR]

Auxetic materials are attracting increasing interest due to their extraordinary or even abnormal mechanical properties. Different from the traditional truss-lattice structures, this paper proposes a series of novel auxetic plate-lattice structures with an excellent auxetic effect. Utilizing a dual-materials glue-free assembly design involving hyperelastic and plastic materials, these plate-lattices exhibit numerous advantages such as disassembly, assembly, replacement, recyclability, reusability, excellent energy absorption, high specific stiffness, and impact resistance performances. Quasi-static/dynamic tests and simulations are conducted to assess mechanical properties, including elastic constants, deformation modes, and mechanical responses. Simultaneously, the effect of the principal geometric parameter, concave angle, on the structural response was analyzed with various impact velocities. Findings suggest that the concave angle influences the structural elastic constants under compressive loading. The stress–strain response exhibits a distinct dual-plateau phenomenon. Taking the A65 (concave angle is 65°) configuration as an example, the stress on the second plateau is approximately 2.7 times that of the first plateau, significantly enhancing the structure's energy absorption capability. Under dynamic impact loadings, different configurations and varying impact velocities affect the structure's energy absorption performance. This paper introduces a series of assemblable plate-lattice structures with an auxetic effect, offering design insights and guidance tailored to the convenient transportation, unconventional structures, and rapid assembly needs of lightweight, impact-resistant mechanical metamaterials. [ABSTRACT FROM AUTHOR]

Fiber-reinforced plastic sandwich structures (FRPSSs) are increasingly used in marine applications thanks to their high levels of stiffness, lightweight, buoyancy and damage resistance to penetration and impacts. This paper investigates the effect of exposure to seawater conditions on mechanical behavior of FRPSSs with various core configurations loaded with indenters with different geometries. A new in-situ acoustic emission (AE) methodology is applied to monitor the moisture evolution process, while X-ray micro-computed tomography validated its influence on out-of-plane failure modes observed in quasi-static indentation experiments. Results indicate that AE velocity can effectively monitor the moisture uptake, serving as an in situ structural health monitoring approach. It was also revealed that the core configuration had a limited effect on moisture ingress. Samples exposed to sharp indentation exhibited the greatest decrease in load-bearing capacity (in excess of 50% in some cases) while that for blunt indentation was the lowest. This can be explained by reduced penetration forces resulting from matrix plasticization and degraded matrix/fiber interface, exacerbated by a smaller contact area. Also, early damage initiation and intensified damage progression were observed for sharp indenters after the seawater exposure. The core of FRPSSs significantly influenced localized damage in samples indented with conical and flat indenters, unlike those subjected to hemispherical ones. The seawater exposure adversely affected the energy absorption and penetration performance, enhancing macroscale damage mechanisms. These findings offer valuable insights for design and optimization of FRPSSs for marine applications. [ABSTRACT FROM AUTHOR]

Additive manufactured lattice structures offer great potential for impact resistance applications. They exhibit excellent energy absorption characteristics during the elasto-plastic deformation process, providing protection to internal devices. However, the mechanical response of lattice structures undergoes substantial variations during the deformation process, thereby imposing limitations on their energy absorption behavior. This study introduces a novel twist design to modify the energy absorption behavior of rectangular and hollow cylindrical lattice structures. Powder bed fusion was used to fabricate the twisted lattice structures. The study employed a combination of compressive simulations and experimental investigations to systematically explore the impact of the twist angle on the peak crushing force, energy absorption, and crash load efficiency of the structures. Adjusting the twist angle results in a reduction of the peak crushing force and a transition towards a stable loading profile during the deformation process. Moreover, the crash load efficiency is also reduced. The twist design concept presented in this paper provides insight into designing and optimizing lattice structures for energy absorption applications. [ABSTRACT FROM AUTHOR]

Nomex honeycomb cores have been widely used in composite sandwich panels. To accomplish meso-scale finite element modeling of these cores, cell wall mechanical properties are required, for which limited data are available. In this work, tensile testing was performed on Nomex paper, phenolic resin, and Nomex paper coated with phenolic resin. Flatwise tension and compression tests were also performed on two types of Nomex honeycomb cores. Test results were calibrated in finite element modeling to account for strain gage local stiffening effects and thickness normalization. Identified cell wall material properties were implemented in a honeycomb core finite element model and further calibrated by matching simulation results to manufacturer test data. The cells' double-wall thickness was also adjusted. These calibrations and adjustments led to an exact simulation match with test data. Numerically matching cell wall material properties depends on modeling sophistication and is subject to core test result variability and core construction differences among manufacturers. [ABSTRACT FROM AUTHOR]

In this paper, the aluminum foam sandwich (AFS) was obtained from foamable precursor sandwich (FPS) through a foaming process, in which the preparation of FPS was achieved by compound casting with hot rolling. The effects of rolling and foaming on the interface microstructures and mechanical properties were investigated. Furthermore, the interface bonding mechanisms and strengthening mechanisms were revealed. For FPSs, increasing the rolling pass increased the interface thermodynamic energy, which was beneficial to the achievement of a more effectively bonded interface. Meanwhile, the grains were refined, the fraction of low angle grain boundaries (f LGABs) and average geometrically necessary dislocation density ( ρ ¯ GND) at the interface increased, which collectively contributed to the enhancement of interface bonding strength and ductility. In the foaming process, although the interface thermodynamic energy led to a reduction in the original interface defects and an enhancement in elements diffusion at the pre-existing well-bonded interface, AFSs displayed lower interface bonding strength and ductility compared to their corresponding FPSs due to coarse grains, decreased f LGABs and ρ ¯ GND. Moreover, an analysis of interface strengthening mechanisms revealed that the increase of rolling pass for FPS resulted in an improvement in the interface bonding strength and ductility of the corresponding AFS. [ABSTRACT FROM AUTHOR]

• A topology optimization approach for porous scaffold is proposed. • The mechanical properties and mass transport characteristics are highly decoupled. • The elastic modulus and permeability are simultaneously maximized. • Large adjustment range of specific surface area and pore size are achieved. • Functional gradient scaffolds with adjustable local properties are designed. Design of tissue scaffolds in terms of multiple objectives such as mechanical and biological performances simultaneously remains challenging. In this paper, we present the development of a topology optimization approach that enables to design porous scaffolds with consideration of both mechanical and fluid properties simultaneously. The relationship between structural parameters, mechanical and mass transport properties was investigated, and then the scaffolds were optimized under the constraint of given pore size, porosity and specific surface area. Case studies on the optimized design of triply periodic minimal surface (TPMS) scaffolds were performed to illustrate the effective of our approach. Simulation and experimental results demonstrated that the proposed optimization approach fully decouples the mechanical and mass transport properties, specifically, under given porosities, the elastic modulus and permeability of optimized scaffolds ranged from 1.33 GPa to 16.7 GPa and 0.07 × 10−8 m2 to 1.62 × 10−8 m2, respectively. Three types of optimized gradient scaffolds were designed and they all exhibited significant functional gradients and high adjustability. The proposed approach decouples synergy and enables individual customization of multi-physics properties, providing practical guidance for gradient scaffolds with desired performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pseudo-ductility was achieved via glide of cut-tows in thick stiffener. • Optimal design of cut-tows in AGS was obtained under bending and tension. • Design limit of composite AGS was pushed with the method proposed in this paper. • Pseudo-ductile fracture induced by cut-tows provided repair window for AGS. Pseudo-ductile fracture in composite structures is desirable which can provide a window of detection for structural anomaly. Several design strategies had been investigated to induce pseudo-ductile fracture in thin composite laminates. However, the thickness of load bearing structures such as the grid stiffeners in advanced grid structures are ranged up to 30 mm. This paper presents an investigation into introducing pseudo-ductile fracture into a grid stiffener of representative thickness by implementing cut-tow design at the grids' intersection. Automated fibre placement permits the cutting, terminating and restarting layup of a tow which makes this design feasible. Experimental and numerical results showed the benefits of a cut-tows design is twofold. Firstly, improvements up to 42.4 % was achieved in mechanical strength due to the reduction in tow waviness at the grid's intersection. By varying the ratio and distribution of cut-tows, it is possible to achieve additional 55.9 % of pseudo-ductile displacement before fracture in thick section grid stiffeners under tension and bending loads. The enabling mechanism of pseudo-ductile fracture are discussed further using numerical modelling. [ABSTRACT FROM AUTHOR]

This paper proposes a numerical model to predict the pattern and features of the fracture surface and to understand the mechanisms and cause of the failure. Various fiber orientations of 0°, 90°, 0°/90° and ± 45° were utilized in the production of unidirectional glass-fiber-reinforced epoxy composites via the vacuum bagging technique. The mechanical properties of the manufactured composites were evaluated by measuring parameters including tensile strength, compressive strength, flexural strength and interlaminar shear strength. High-resolution scanning electron microscopy was used to examine the mechanisms of fracture in laminates. The mechanical properties of the composite material were found to be considerably improved when a unidirectional 0° fiber orientation was used, as compared to other fiber orientations. This was true for tensile, compressive, flexural and interlaminar shear loading modes. The composite laminates demonstrated several modes of breaking, including fibers pulling away from the matrix, holes in the matrix and river flow lines, depending on the direction of the fibers. The outcomes of the numerical simulation demonstrate a high level of fidelity with experimental findings. This study provides a valuable reference for predicting numerical analysis of the microstructure and mechanical properties. [ABSTRACT FROM AUTHOR]

In our previous papers we have described efficient and reliable methods of generation of representative volume elements (RVE) perfectly suitable for analysis of composite materials via stochastic homogenization. In this paper we profit from these methods to analyze the influence of the morphology on the effective mechanical properties of the samples. More precisely, we study the dependence of main mechanical characteristics of a composite medium on various parameters of the mixture of inclusions composed of spheres and cylinders. On top of that we introduce various imperfections to inclusions and observe the evolution of effective properties related to that. The main computational approach used throughout the work is the FFT-based homogenization technique, validated however by comparison with the direct finite elements method. We give details on the features of the method and the validation campaign as well. [ABSTRACT FROM AUTHOR]

• Multi-material printing interpenetrating phase composites with controlled mechanical properties. • Stable mechanical reponse for energy absorption, damage tolerance and fracture tougness. • Strengthening and toughening mechanisms of IPCs. Under external load, lightweight cellular solids are often associated with localized deformation that would lead to their catastrophic failure. Cellular solids are thus often infilled with a soft secondary material, constituting interpenetrating phase composites. Owing to highly interconnected porous architectures and controllable smooth surfaces, the triply periodic minimal surface structures based on interpenetrating phase composites are investigated in this paper. Samples are fabricated via polyjet multi-material printing, with the hard material taking on the primitive lattice and the soft material taking on its inverse. Quasi-static compression and three-point bending tests were performed on the fabricated composites. Results show that the combination of high stiffness, strength, and prolonged smooth plateau stress endows the composites to be promising for lightweight materials and energy absorbers. The designed composites can exhibit an excellent fracture toughness of 0.51 MPa•m1/2. Moreover, the designed interpenetrating architectures and stiff-contrast materials intrinsically control the strengthening and toughening mechanisms. The findings presented here demonstrate the potential to obtain enhanced mechanical properties by combining the advantages of the multi-material printing technique and interpenetrated design. [ABSTRACT FROM AUTHOR]

• Meso-scale simulations combining the damage of yarn, pure matrix, and debonding. • Systematic damage analyses of different oriented composites upon tension/bending. • Mechanisms leading to property differences of composites with different orientations. • The order of tensile damage mechanism is clearly identified. • Meso-macro models were combined for property prediction & design optimization. This paper investigates the tensile/bending mechanical properties, damage behaviors, and performance prediction of plain-woven composites with different orientations by numerical simulations and physical experiments. The mesoscopic model reproduces damage modes of yarn, pure matrix, and interfacial debonding by user-defined subroutine. On this basis, relevant physical experiments were conducted for comprehensive verification. Then, the influences of orientation on the mechanical properties of the composites and their tensile/bending damage processes were systematically analyzed, and meso-macro scale simulations were carried out for performance prediction and optimization design of multilayer composites. The results show that the tensile/bending strength of the composites decreases and the ductility increases with the increase of orientation angle, among which the ductility of 45° orientation is the best. The primary damage mechanism in tensile process is changed from fiber fracture and matrix cracking to yarns pullout and debonding damage. The orientation can change the primary damage mechanism and improve composite properties by changing the location, time, and degree of damage occurrence. In addition, meso-macro scale simulations can predict and optimize the properties of multilayer composites more efficiently and shorten the optimization design cycle of composites. [ABSTRACT FROM AUTHOR]

Negative Poisson's ratio honeycombs have been extensively studied due to their unique mechanical properties. In this paper, a novel negative Poisson's ratio honeycomb (NPH) is proposed by introducing a reinforced strut into the negative Poisson's ratio honeycomb (NPR). A finite element numerical model was constructed using Abaqus/Explicit, and the accuracy of the model was verified, and a series of researches were carried out. First, the mechanical properties of NPH at different angles were analyzed under different loading conditions, and the results showed that under the loading conditions of y-direction and x-direction, NPH-120 and NPH-105 had the best mechanical properties respectively. Subsequently, the mechanical properties of NPH at different velocities were studied. The research showed that the NPR effect of NPH was the most obvious under low-velocity impact, and as the velocity increased, the inertia effect increased, and NPH's deformation mode has changed. And the dynamic Poisson's ratio of NPH at medium-velocity is analyzed, and its energy absorption mechanism is analyzed through the deformation of subunits. Finally, the mechanical properties of NPH under different wall thicknesses were studied, and the mechanical properties of several typical reinforced supports and NPH-120 were compared. [ABSTRACT FROM AUTHOR]

Abstract: Sandwich cylindrical shells are the major components of aerospace structures. In this paper, an analytical investigation was carried out to examine the response of carbon fiber reinforced composite (CFRC) sandwich cylinders with lattice cores. An equivalent monocoque shell theory, was developed in this paper to predict mechanical behaviors of the quasi-isotropic sandwich cylinder, including the deformation and the multi-mode failure criterion. Five failure modes were suggested for the sandwich cylinder, including global buckling, face sheet mono-cell buckling/dimpling, face sheet local buckling, lattice rib crippling and strength failure. Using the suggested criterion, failure mode maps of the sandwich cylinder were acquired to instruct the design of the hierarchical sandwich cylinder with five geometrical variables. The method also correctly predicted the failure modes of the tested sandwich cylinder within acceptable errors. [Copyright &y& Elsevier]

Abstract: This paper uses a bio-inspired design strategy based on tree branch joints to improve the damage tolerance of co-cured composite T-joints. The design of tree branch joints at different length scales from the microstructural to the macro-length scale was investigated. X-ray computed tomography of a pine tree revealed three main features of tree branch joints which provide high structural efficiency and damage tolerance: integrated design with the branch embedded into the centre of the trunk; three-dimensional fibril lay-up in the principal stress directions; and variable fibril density to achieve iso-strain conditions through the joint connection. Research presented in this paper adapts the embedded structural feature of tree joints into a carbon/epoxy T-joint. The flange plies were embedded to 25%, 50% and 75% of the depth of the skin of the composite T-joint to mimic the design of tree branch joints. Experimental testing revealed that the bio-inspired T-joint design with integrated adherends had increased normalised inelastic strain energy (defined as ductility), increased normalised absorbed strain energy to failure, and higher load-carrying capacity following damage initiation (damage tolerance) compared to a conventionally bonded T-joint. However, these improvements were achieved at the expense of earlier onset of damage initiation in the T-joints. [Copyright &y& Elsevier]

The robotic filament winding (RFW) technology consists of an industrial robot that is equipped with a feed and deposition systems; they are suitable for placing a tape along the stress directions the part is subjected to during operation. RFW cell replaces the human operator that is the only system that has been previously used to manufacture complex shape parts. It represents an advantage as regards process control, repeatability and manufacturing times. The present work focuses on the family of structural parts whose shape may be obtained as a result of a full section sweeping along a closed non auto-intersecting 3D curve. The aim of the paper is to present a design methodology for the forming process of complex shape structural parts by RFW, in order to obtain structural homogeneity and fibre content uniformity, and so to demonstrate the potential of an innovative robotic cell for manufacturing these parts. [ABSTRACT FROM AUTHOR]

Abstract Recycling of construction and demolition waste (CDW) which contains materials with high resource value such as plastics, metals, wood, glass and concrete has been investigated in recent years due to tightening environmental legislation. Wood-plastic composites as an environmentally friendly material provide a possibility to enhance the recycling of material. The effect of the addition of CDW on the mechanical and moisture properties of WPC is studied in this paper. Three types of wood-plastic composites were manufactured with different amounts and composition of a CDW filler. Their properties were compared to the reference composite manufactured with virgin wood fibers and polypropylene as the polymer. It was found that the addition of the CDW filler weakened the mechanical properties of the composite generally, except for the fact that the Charpy impact strength was improved significantly. Minor variations in the composition of the CDW filler did not have an impact on the mechanical properties, but an increase in the amount of filler increased the deterioration of mechanical properties. For moisture properties, the addition of the CDW filler decreased the water absorption and thickness swelling of the composites. An increase in the filler content improved the thickness swelling more significantly than water absorption. [ABSTRACT FROM AUTHOR]

Abstract In recent years, a new class of composite reinforcements has gained considerable attention: 3D woven fabrics. Their advantages in terms of reducing preforming steps and their resistance to impact and delamination have been clearly proven. However, relationships between fabric structure and composite properties are still largely unknown. Numerical models on different length scales were developed that capture the mechanical behavior of fabrics and their composites. This paper reviews models for 3D woven fabrics in the dry state and discusses results that were achieved with parametric studies. Special attention is given to the determination of the initial configuration of the 3D woven fabric model. The multi-filament character of yarns is best depicted with meso-scale approaches that describe the sub-yarn behavior with realistic models. Developed models can be used for further investigations, e. g. the optimization of fabric structure and forming processes. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the influence of the off-axis angles on the flexure behaviors of three-dimensional (3D) woven carbon/epoxy composites. Four kind of samples with different angles, 0 degree, 30 degree, 45 degree and 90 degree, are experimentally tested via three-point bending method. The immersion focused ultrasound imaging and micro-computed tomography (Micro-CT) techniques are employed to investigate the deformation and damage mechanisms in the specimens fractured in bending. Results indicate that the stress-deflections of on-axis (0 degree and 90 degree) samples exhibit obvious quasi-brittle behaviors, whereas those of off-axis (30 degree and 45 degree) samples show important ductile features. Furthermore, the dominant failure mechanism of on-axis samples are identified to be inter-ply delamination and fiber bundle fractures, whereas those of off-axis samples are matrix cracks and tows debonding. [ABSTRACT FROM AUTHOR]

Abstract Due to its efficiency, Fiber Reinforced Polymers (FRP) jacketing has become a common practice for confining concrete columns that need increased axial strength, axial ductility or shear capacities. The presence of confining lateral steel in columns, when externally retrofitted with FRP, changes the mechanism of concrete behavior. The interaction between lateral and longitudinal steel and FRP jacketing redistributes stress concentrations in concrete and yields more complex effective confined area compared to that of plain concrete confined with either FRP or lateral steel alone. Square columns confined with lateral steel and FRP are not well-addressed in the literature compared to circular columns. Therefore, this research focuses on square columns confined with lateral steel and FRP sheets through reviewing existing models in the literature and benchmarking their performance against experimental cases of square columns using axial stress-strain diagrams. Moreover, statistical analysis conducted for theoretical peak strength and ultimate strain obtained from the available models highlight their comparative performance which can be further improved. Therefore, this paper proposes a new model that overcomes shortcomings found in the reviewed models and predicts peak strength and ultimate strain more accurately. [ABSTRACT FROM AUTHOR]

Abstract Stress distributions at interfaces of adhesive lap joints have been widely studied to optimize overall structural strength. However, these studies focussed mainly on the mechanics of adhesive layers. In this paper, a novel concept for a double lap adhesive joint is proposed by introducing a slot in its inner adherend. Numerical simulations employing a finite-element method are used to validate the proposed concept. The results show that the introduction of the slots can smooth the stress distributions along the edges of the interfaces between adhesive and adherend and reduce stress concentration near the cut-off ends of the joint. The results also show that the height of the slots has significant effects on alternating the interfacial stresses. Thus, the proposed concept provides a promising way to optimize double lap adhesive joints for enhanced strength with reduced weight. [ABSTRACT FROM AUTHOR]

This paper focuses on strengthening carbon fiber hierarchical composite square honeycomb structures (HCSH) by selecting high-modulus hierarchical phase and optimizing its thickness. HCSH have been manufactured from carbon fiber composite foam sandwich structures by a simple snap-fit and bonding method. The measured compressive and shear strengths are shown to be well predicted by micromechanics failure models of HCSH. Compared to the monolithic composite square honeycomb structures (CSH), the measured specific out-of-plane compressive strength of HCSH improves to approximately 330% and the specific shear strength improves to about 180%. Furthermore, the relationships between hierarchical phase modulus and its optimum thickness are developed to design the optimum HCSH. Carbon fiber HCSH are found to exhibit better mechanical properties than other cellular structures, and thus provide new opportunities for light-weight multifunctional sandwich structures. [ABSTRACT FROM AUTHOR]

Abstract: This research paper presents an experimental investigation into the sensitivity of the interlaminar properties of polymer laminates to long, narrow interlaminar galleries used in comparative vacuum monitoring (CVM). CVM is a structural health monitoring technique for the non-destructive detection of cracks in engineering materials. The paper examines the effect of CVM galleries on the mode I delamination toughness, interlaminar shear strength, and impact damage resistance of a carbon/epoxy laminate. It was found that the galleries improve the mode I delamination toughness by blunting and/or deflecting the crack tip; with the maximum improvement being double the toughness of the laminate free of galleries. The toughness increased with the diameter of the gallery up to a critical size, above which no further improvement was achieved. However, the composite is more prone to unstable delamination cracking in the presence of the galleries. The apparent interlaminar shear strength (ILSS) decreased at a linear rate with an increase in the diameter and volume fraction of galleries. The loss in ILSS is due to the reduction in the effective interlaminar load-bearing area caused by the galleries. Low-energy impact testing revealed that the galleries do not affect the impact damage resistance when below a critical diameter; however, above a threshold gallery size the impact resistance is degraded. This study shows that the incorporation of CVM galleries into laminates can have the added benefit of increased mode I delamination toughness, although the ILSS is degraded and the impact resistance is reduced by large galleries. [Copyright &y& Elsevier]

The incorporation of waste rubber into concrete has significant environmental value. However, a hydrophobic waste rubber surface results in poor adhesion to concrete, which damages the mechanical properties of concrete. In this paper, polyvinyl alcohol (PVA) is used to modify the waste rubber and the mechanical properties of PVA-modified waste rubber-filled cement paste are examined using digital image correlation (DIC) technology. According to the results, the addition of PVA increases the compressive strength and flexural strength of waste rubber-filled cement paste by 7.9%-15.4% and 12.7%-25.0% at the different curing ages with the content of waste rubber is 25%, respectively. In addition, the specimen exhibits higher integrity after complete destruction in the compressive strength and flexural strength tests as the waste rubber content increases. More importantly, DIC provides a good analysis of the full field displacement and strain in the compressive strength and flexural strength tests of PVA-modified waste rubber-filled cement paste. At the same time, DIC can accurately capture the generation and development of surface cracks on the specimen. The calculated results of the displacement and strain fields visually demonstrate the strengthening effect of PVA on the waste rubber-filled cement paste, especially the inhibition of crack development by PVA. [ABSTRACT FROM AUTHOR]

Steel plate bolted connections are frequently used in timber structures. However, these connections may incur durability problem due to the corrosion of the steel plates. This paper proposes using GFRP plate to replace steel plate in timber connections to mitigate the corrosion issue. The group effect of the proposed GFRP-timber bolted connection is studied. Tensile tests of GFRP-timber bolted connections were conducted considering a number of variables including bolt diameter, bolt pitch distance, bolt row number, bolt column number. The failure modes and the load–displacement curves of the connections were reported. Experimental results showed that the group effect of the GFRP-timber bolted connection is strongly affected by the bolt diameter and number of bolts, but little affected by bolt pitch distance. The effect of the number of bolt columns on the group effect was also discovered and quantified. The design equation of the timber bolted connection in Eurocode 5 was modified considering the effects of various parameters. The modified equation was then verified using the experimental data in this paper. Finally, detailed recommendations were provided for the design of the proposed GFRP-timber bolted connection. [ABSTRACT FROM AUTHOR]

In this paper, carbon nanofibers (CNFs) with high aspect ratio were dispersed into epoxy matrix via mechanical stirring and ultrasonic treatment to fabricate self-sensing CNFs/epoxy composites. The mechanical, electrical and piezoresistive properties of the nanocomposites filled with different contents of CNFs were investigated. Based on the tunneling conduction and percolation conduction theories, the mechanisms of piezoresistive property of the nanocomposites were also explored. The experimental results show that adding CNFs can effectively enhance the compressive strengths and elastic moduli of the composites. The percolation threshold of the CNFs/epoxy composites is 0.186 vol% according to the modified General Effective Media Equation. Moreover, the stable and sensitive piezoresistive response of CNFs/epoxy composites was observed under monotonic and cyclic loadings. It can be demonstrated that adding CNFs into epoxy-based composites provides an innovative means of self-sensing, and the high sensitivity and stable piezoresistivity endow the CNFs/epoxy composites with considerable potentials as efficient compressive strain sensors for structural health monitoring of civil infrastructures. [ABSTRACT FROM AUTHOR]

This paper presents the development of wood plastic composite manufactured from recycled polypropylene/polyethylene (r-PP/PE) blend reinforced with kenaf fibre. The r-PP/PE were sourced from rejected-unused diapers, which the plastic and absorbent gel were separated. The composite was prepared by varying the fibre loadings, at 0, 30, 40, 50, and 60 wt%. The composite was tested for flexural and impact tests followed by thermal and morphological analyses. The thermal analysis was performed by using differential scanning calorimetry technique, while the scanning electron microscopy was used for morphological analysis. It was found that the maximum flexural strength of the composite was at 30 wt% of kenaf fibre, meanwhile the maximum modulus was at 60 wt%. SEM morphology showed the failure mode from the impact fractures such as voids, fibre breakage and matrix cracking. From thermal analysis, the addition of kenaf fibre reduced the degree of crystallinity of the r-PP/PE but an improvement can be observed after the second step of heating and cooling. [ABSTRACT FROM AUTHOR]

During operational conditions, extreme environments combined with unexpected high loading rates can induce severe damages or, inclusively, premature fails. Therefore, this paper intends to study the effect of different hostile solutions on the longitudinal impact strength in order to establish design criterions. For this purpose, samples of GFRP composites were immersed into alkaline and acid solutions as well as distilled water. Variables like exposure time, temperature and concentration of the solution were analysed in detail. The effect of pre-damages was also studied for different pre-loads, where the severity of the damages introduced was quantified by acoustic emission. It was possible to conclude that, independently of the solution, the exposure time and temperature were determinant to decrease the tensile impact strength. Finally, the magnitude of the initial damage has a significant influence on the impact resistance. [ABSTRACT FROM AUTHOR]

The mechanical properties of artery stent are of key importance to the mechanical integrity and biomechanical performance reliability of stent-plaque-artery system. In this paper, making use of auxetic deformation features of chiral structures and mechanical benefits of structural hierarchy, two types of innovative chiral stents with auxetic properties are proposed: (a) anti-tetrachiral stent with circular and elliptical nodes; (b) hierarchical anti-tetrachiral stents with circular and elliptical nodes. Firstly, the in-plane mechanical properties of anti-tetrachiral structures are investigated theoretically, and uniaxial tensile experiments are performed for verification; Secondly, design procedures of anti-tetrachiral stent and hierarchical anti-tetrachiral stent with circular and elliptical nodes are elaborated. Effects of stent geometrical parameters on the tensile mechanical behaviors of these stents are studied with finite element analysis (FEA). It is found that the mechanical behaviors of anti-tetrachiral stent can be tailored through adjusting the levels of hierarchical structures and unit cell design parameters. Finally, the deformation of anti-tetrachiral and hierarchical anti-tetrachiral stents during stenting process are investigated with FEA. It is found that the proposed anti-tetrachiral and hierarchical anti-tetrachiral stents exhibit remarkable radial expanding abilities while maintaining axial stability, thus show promising performances for practical clinical applications. [ABSTRACT FROM AUTHOR]

As a novel type of reticulated structures, tensegrities have found various applications in science and engineering. In this paper, an ingenious assembly method is developed to construct large-scale tensegrities using truncated regular polyhedral tensegrities and prismatic tensegrities as elementary cells. The truncated polyhedral tensegrities with regular polygons on their surfaces are specified as islands, and the prismatic tensegrities are used as bridges to connect these polygons along different directions. This method allows us to construct many types of large-scale tensegrities satisfying the demands of the size and topology. Based on the node-on-node assembly scheme, Z-based truncated regular octahedral tensegrity and its matching quadruplex prismatic tensegrity are employed to produce representative examples with traditional and untraditional shapes. Their mechanical properties are evaluated from the viewpoints of self-equilibrium, stability, and mechanical responses. Our results help to manufacture demanded large-scale tensegrities with delicate mechanical properties, and may be beneficial to construct composite metamaterials. [ABSTRACT FROM AUTHOR]

This paper presents a study on the properties of sustainable high performance steel fiber-reinforced concretes that were manufactured with recycled concrete aggregates (RCA). Natural coarse aggregates were replaced by RCA derived from parent concretes with compressive strengths of 40 and 80 MPa at volume replacement ratios of 50% and 100%. High performance concretes (HPC) were manufactured using double hooked-end steel fibers added at a fiber volume fraction of 1%, and in some of the mixes 30% of ordinary Portland cement was replaced by slag. Along with their mechanical properties, the water absorption, electrical resistivity, and shrinkage of the concrete mixes were evaluated. The results indicate that HPC with desirable properties can be produced using RCA derived from a high-strength parent concrete. The addition of steel fibers significantly increases the mechanical properties of recycled aggregate concretes. Replacing natural aggregates with RCA of lower strength adversely affects the durability properties of the concrete. However, concretes produced with a higher quality RCA and those containing slag and steel fibers exhibit reduced water absorption and shrinkage compared to plain natural aggregate concrete. The findings of this research are highly promising for the development of HPC with reduced environmental impact. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental investigations of the tensile properties of different types of CFRP plates. Coupon specimens of low, normal and ultra-high modulus CFRP plates were prepared and tested under tensile loading. Four different strain rates were used, including one low strain rate and three high strain rates. Two methods of capturing strain were used: image correlation photogrammetry and foil strain gauges. The results showed a significant increase in the tensile strength, ultimate strain and elastic modulus for coupons under high strain rates. The CFRP coupons were prepared and tested in accordance with the ASTM3039-08 standards. Finite element analysis was performed and the results agreed very well with the experimental results. [ABSTRACT FROM AUTHOR]

The effect of ply thickness on the onset of intralaminar and interlaminar damage is extremely important for the structural response of laminated composite structures. This subject has gained particular interest in recent years due to the introduction in the market of spread-tow, ultra-thin carbon-fibre reinforcements with different configurations. In the present paper, an experimental test campaign was carried out to study the structural response of aerospace-grade plain weave spread-tow fabrics (STFs) of different areal weights. The results showed that, in spite of an apparent superior longitudinal tensile strength of the thick STF, the multidirectional thin-STF laminate exhibited an improved tensile unnotched strength over the thick-STF laminate, attributed to its damage suppression capability. However, damage suppression was also responsible for similar tensile notched strengths. In compression, the thin-STF laminate performed substantially better than the thick-STF laminate in both unnotched and notched configurations. Finally, a similar bearing response was obtained in both STF laminates, in spite of a slightly higher resistance of the thin-STF laminate to the propagation of subcritical damage mechanisms. [ABSTRACT FROM AUTHOR]

In this paper, the effects of FDM parameters (nozzle temperature, platform temperature, layer thickness, and printing speed) as well as annealing temperature on the mechanical properties of poly(ether ether ketone) (PEEK) were investigated through orthogonal experiments. And the tribological properties of PEEK were also studied before and after annealing. Results show that nozzle temperature and printing speed were main factors affecting the mechanical properties of PEEK, which was optimized to be 440 ℃ and 40 mm/s, respectively. The mechanical strength of PEEK was increased with increasing annealing temperature and reached the maximum at 300 ℃ with the sacrifice of elongation at break, and the ultimate tensile, flexural and compressive strength was increased by 36%, 54% and 21%, respectively. As for the tribo-properties, there appeared a minimum wear rate(1.37 × 10−6mm3/Nm) in 200 °C annealed PEEK when tested in parallel manner, combined influences of annealing and filament orientation were revealed, and appropriate annealing temperature was found to help enhance the formation of uniform and homogeneous transfer films on the counter steel surfaces. [ABSTRACT FROM AUTHOR]

The gap is one of the most common defects during the AFP process, which has a nonnegligible impact on the mechanical properties of laminates. This paper proposes a novel three-dimension reconstructive gap model based on the in-process serial layer scanned point clouds, which can characterizes the gap features inside the laminate and pre-determine the mechanical performance before the subsequent procedures. The measured point cloud will be transformed into eligible and processible formats and then be used to generate a finite element grid using the element-based material property assignment method. The local material properties and fiber orientation are defined by previously assigned classes and grid geometries respectively. The effect of gap size on the in-plane tensile strength and damage evolution of laminates is investigated and both the experimental and simulation results find that the ultimate strength and stiffness show a significant decrease with the increase of gap size. [ABSTRACT FROM AUTHOR]

To obtain a structure with excellent energy-absorbing ability, based on the traditional star-shaped honeycomb (SSH), a crossed star-shaped honeycomb (CSSH) was designed via evolving the horizontal and vertical walls of the honeycomb into crossed inclined walls. In this paper, the Poisson's ratio and Young's modulus of honeycomb under axial load are theoretically deduced, and a method is proposed to evaluate the deformation stability of honeycomb with the maximum deviation of unilateral horizontal strain (MDUHS). Numerical simulation is employed to verify the theoretical solution, and the in-plane mechanical properties and deformation behavior of CSSH are investigated in detail. The numerical simulation method in Abaqus software was verified by using quasi-static crush test data of 3D printed CSSH specimens. It is found that by changing the inclined angle θ 2 , CSSH can evolve into a positive Poisson's ratio(PPR), zero Poisson's ratio(ZPR), or negative Poisson's ratio structure(NPR), and Young's modulus is very sensitive to the difference between the opened angle θ 1 and the inclined angle θ 2 ; increasing θ 1 or decreasing θ 2 not only significantly improves the energy absorption capacity of the honeycomb but also facilitates the generation of a more pronounced double plateau region on the stress-strain curve; by changing the length of the crossed inclined wall, three improved CSSHs(ICSSH) can be obtained. Among them, by adjusting the length of the crossed inclined wall in the horizontal direction, the structure with the superior energy absorption capacity can be obtained. The structure with excellent deformation stability can be obtained through adjusting the length of the crossed inclined wall in the vertical direction. Results show that the performance of CSSH is better than that of SSH, with a specific energy absorption (SEA) of 245% higher than that of SSH. This work is expected to guide the design of new auxetic honeycombs with better energy absorption properties, and can also provide a reference for the optimization of honeycombs. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to investigate the failure mechanisms of carbon fiber reinforced composites (CFRP) single-lap bolted, bonded and hybrid bolted/bonded joints during compression. The failure process and the failure mechanisms of the compression tests were analyzed using field emission scanning electron microscope (FESEM) and acoustic emission (AE) technique. A novel method is proposed to obtain the relationship between the FESEM analysis and AE signals. The crack data is obtained by identifying, segmenting and quantizing FESEM images based on image processing technology. The final results give effective AE parameters for identifying crack damage in composite joints, and show the superiority of the proposed method. The research in this paper puts forward important suggestions for the application of AE technique in composites and fault diagnosis. [ABSTRACT FROM AUTHOR]

In this paper, 2D C/SiC z-pinned joint is prepared via chemical vapor infiltration. Effects of z-pin’s porosity on shear properties of z-pinned joint are investigated from the failure mode and the shear damage mechanisms. The results show that the average joint shear strength decreases asymptotically from 249.9 MPa to 97.2 MPa as the total porosity of 2D C/SiC z-pin increases from 14.4% to 27.3%. For each porosity, the joint shear strength is between the tensile strength and the in-plane shear strength of 2D C/SiC, which is rationalized by the rigid body sliding model of 2D C/SiC. Because high porosity leads to large rotational deformation of transverse fibers, a critical porosity about 17.7% is observed from shear-controlled failure to bending-controlled failure. A cohesive fracture model is developed to build the relation between the joint shear strength and the mechanical properties of 2D C/SiC. Very good accuracy is obtained. [ABSTRACT FROM AUTHOR]

This paper presents a fiber-based representative unit cell (fRUC) on the mesoscale to estimate the elastic constants of a three-dimensional (3D) needled carbon/carbon (C/C) composite through a hierarchical modeling scheme. The material variations due to needle-punching, including fiber dislocations, fiber distributions and matrix pockets, are precisely considered in the proposed fRUC model. A quarter-size mathematical model with a periodic boundary condition of a general mesh is established to perform the fRUC analysis by using interpolation functions. The predictive results from the fRUC are transitioned to a ply representative unit cell (pRUC) based on the developed analytical homogenization method. The proposed model agrees well with the experimental results, and the effects of microstructural parameters on the overall composite properties are discussed. The results allow great confidence in the reliable predictions of the effective properties and the damage and strength of 3D needled C/C composites. [ABSTRACT FROM AUTHOR]

This paper presents the preparation and characterization of nanocellulose coated woven jute/green epoxy composites. Waste jute fibers were used as precursor to purify and extract nanocellulose by chemical treatments. The prepared suspensions with 3, 5 and 10 wt% of nanocellulose were coated over jute fabric followed by preparation of composites by compression molding technique. The surface morphologies of treated jute fibers, jute cellulose nanofibrils (CNF), nanocellulose coated jute fabrics and fractured surfaces of composites were characterized by scanning electron microscopy (SEM). The crystallinity of jute fibers after different chemical treatments was measured by X-ray diffraction (XRD). The effect of nanocellulose coating over jute reinforcement on the tensile, flexural, fracture toughness and dynamic mechanical properties of prepared composites has been investigated. Fracture toughness was measured using single end notched bend (SENB) specimens and dynamic mechanical test was performed in three point bending mode. The results revealed the improvement in tensile modulus, flexural properties and fracture toughness except the decrease in tensile strength of nanocellulose coated woven jute/green epoxy composites as compared to uncoated jute composite. Dynamic mechanical analysis (DMA) results also showed the increase in storage modulus and reduction in tangent delta peak height of nanocellulose coated jute composites. [ABSTRACT FROM AUTHOR]

In this paper, a new radar-absorbing structure produced by electrical modification of glass fabric via the silver-sputtering coating technique is proposed. Although conventional radar absorbers are fabricated using a conductive carbon nanomaterial, such fabricated absorbers have many limitations in their electrical and mechanical performance. A thin and lightweight silver-coated glass-fabric microwave-absorbing structure (with a thickness of 1.82, 1.84 and 1.95 mm, respectively) having good microwave-absorbing performance in the X-band (8.2–12.4G Hz) was designed and fabricated without dispersing conductive carbon nanomaterials in the resin matrix. The morphology, element composition and phase identification of silver-coated glass fabrics were examined by SEM, EDS and XRD, respectively. In addition, interlaminar shear strength (ILSS) tests were conducted according to ASTM D 2344 to evaluate the mechanical performance of the proposed absorbers. Additionally, to design a thin broadband absorber using the silver-coated glass fabric, the absorbing performance of the proposed absorbers were analyzed from the C-band to the Ku-band (4–18G Hz), and the proposed broadband absorber showed excellent performance in the target frequency range. [ABSTRACT FROM AUTHOR]

The elasticity of carbon/carbon (C/C) composites is strongly dependent on the properties of pyrocarbon. Carbon planes of pyrocarbon prepared by the chemical vapor infiltration (CVI) method orient along the axial direction of fibers, leading to the anisotropy of pyrocarbon. This paper proposes a novel numerical model to accurately predict the effective elastic properties of C/C composites with anisotropic pyrocarbon. At first, the pore-pyrocarbon system is homogenized as an equivalent matrix. The equivalent matrix is then partitioned using a pyrocarbon micromorphology-based modified Voronoi tessellation method. Meanwhile, the cohesive elements are introduced to capture the interphase effect on the effective elastic properties of C/C composites. Regarding the prediction of the effective elastic properties of unidirectional C/C composites and short carbon fiber reinforced pyrocarbon (C sf /C) composites, the proposed model is validated by analytical and experimental results. Additionally, the results show that increasing interphase stiffness improves the effective elastic properties of C/C composites while an increase in porosity reduces the effective elastic properties of C/C composites. [ABSTRACT FROM AUTHOR]

• A kind of two-layer oblique honeycomb sandwich structure of flaky carbonyl iron powder/photosensitive resin composites with high precision was prepared by liquid crystal display (LCD) 3D printing method. • The structure is beneficial to improve the microwave absorption strength, and has the characteristics of light weight and low material consumption. • LCD 3D printing technology has the advantages of high precision, free forming and less time consumption. Carbonyl iron powder (CIP) is one of the most widely used magnetic loss absorbents due to its high saturation magnetization, strong wave absorption performance and low cost. However, CIP has a very high density (7.86 g/cm2) and requires a high addition amount (more than 50 wt%) when used as a microwave absorbing filler, which leads to high weight and low mechanical properties of the composite. Taking the diverse attenuation mechanisms during the electromagnetic energy conversion process into considerations, this paper designs a two-layer oblique honeycomb sandwich structure, which was prepared by liquid crystal display (LCD) 3D printing. This structure combines porous structure with strong absorbing materials to achieve strong electromagnetic wave (EMW) absorption performance at low concentrations and improve mechanical properties. When the inclined honeycomb core angle is 15° with only 15 wt% FCIP addition, the EMW absorption and mechanical properties of the composite are significantly improved compared with the full-filled structure. [ABSTRACT FROM AUTHOR]

• Increase in ultimate load up to 55 %. • Effective stiffness increased up to 51 %. • Optimum strength increase is obtained with pre-stressed implants. • Reinforcing with GFRP resulted in an up to 32 % increase in ductility. This paper brings results of the bending testing of oak-wood laminated elements for structural use. The bi-directional laminations were reinforced with six types of implants made of glass fibre reinforced polymer (GFRP), some of which were pre-stressed before embedding in epoxy resin. Previously we reported on improving the mechanical properties of oak-wood laminated elements using carbon fibre implants (CFRP). Although it proved as an efficient improvement of the mechanical properties, it also raised the question of the cost effect to the final product. Therefore, within the larger study on investigating effects of different reinforcement systems, we tested glass fibres reinforced polymer (GFRP) as an alternative. Results showed that the introduction of implants improved the effective stiffness between 4 and 51 % and the ultimate load to failure up to 55 %. Furthermore, not only that insertion of the GFRP layers significantly contributed to the strength and stiffness improvement, but the ductility of the elements increased up to 32 %. Pre-stressing of the glass fibres reinforced polymer implants in tension before their installation contributed to the strength increase to a much greater extent than the increase in the number of layers. The best reinforcement effect is obtained if two layers of pre-stressed GFRP are used. [ABSTRACT FROM AUTHOR]

Steel plate connection is popular in modern timber structures. However, the steel plate may be subjected to corrosion issue due to the presence of moisture in timbers. This paper proposes to replace steel plate with glass fiber reinforced polymer (GFRP) plate for connecting timber elements, so that the durability of the timber structure is expected to be improved. An experimental study is presented on the static and fatigue performances of the proposed GFRP-timber bolted connections. Variables including bolt diameter, number of bolt rows, number of bolt columns were selected to understand their effects on the static and fatigue behaviours of the connections. Failure modes, load–displacement curves, static bearing capacities, fatigue lives, stiffness degradations of the GFRP-timber bolted connections were reported. The residue bearing capacities of the connections were tested after the fatigue loading tests to assess the fatigue effect on the connection static behaviour. This study contributes to the understanding of the mechanical behaviour of GFRP-timber bolted connections. [ABSTRACT FROM AUTHOR]

Textiles have been used as preforms for high-performance composite materials. Fiber architecture of the preform has a decisive effect on mechanical properties of composite. As a kind of flexible reinforcement, textile preforms can deform easily in the manufacture process of complex shaped composite structures. Mechanical behavior of textile materials is specific due to their fibrous nature. The objective of this paper is to give an overview of the literatures dedicated to the mechanics of textiles used as composite preforms. Experimental test methods and mechanical models are reviewed. The experimental tests are categorized with respect to the type of load, including tension, compaction, bending, shearing and forming. Mechanical models of textile materials are classified into macro-scale continuum, discrete, semi-discrete and hybrid element models according to the scale of investigation and the numerical simulation method. The advantages and limitations of different approaches are discussed. [ABSTRACT FROM AUTHOR]

Mars has similar natural environments to Earth and is regarded as a potential candidate for human migration. Exploration to Mars has been a hotspot in major aerospace countries, and therefore bringing the national flag to Mars is an inevitable demand. A self-deployable mechanism inspired by the ancient papyrus scroll to demonstrate the national flag dynamically is proposed in this paper. The release device made of shape memory polymer composites, as the functional part, is analysed thoroughly from the perspective of material design, fabrication and experiments. Firstly, the mechanical properties of woven fabric composites are predicted theoretically, and the thickness of laminates is determined according to the mechanical requirement, fabrication technique and shape moulding method. Tensile and three-point bending tests were carried out to validate the analytical prediction and provide parameters for numerical simulation. Besides, shape fixation and recovery properties were studied by both simulation and experiments with consistent results. Additionally, the shape moulding method was modified by reheating and sustaining a high-temperature period after bending to obtain the designed pattern. This world's first application of shape memory polymer composites in Mars explorations is a milestone for both deep space exploration and advanced smart materials. [ABSTRACT FROM AUTHOR]

• Increase in ultimate load up to 55 %. • Effective stiffness increased up to 51 %. • Optimum strength increase is obtained with pre-stressed implants. • Reinforcing with GFRP resulted in an up to 32 % increase in ductility. This paper brings results of the bending testing of oak-wood laminated elements for structural use. The bi-directional laminations were reinforced with six types of implants made of glass fibre reinforced polymer (GFRP), some of which were pre-stressed before embedding in epoxy resin. Previously we reported on improving the mechanical properties of oak-wood laminated elements using carbon fibre implants (CFRP). Although it proved as an efficient improvement of the mechanical properties, it also raised the question of the cost effect to the final product. Therefore, within the larger study on investigating effects of different reinforcement systems, we tested glass fibres reinforced polymer (GFRP) as an alternative. Results showed that the introduction of implants improved the effective stiffness between 4 and 51 % and the ultimate load to failure up to 55 %. Furthermore, not only that insertion of the GFRP layers significantly contributed to the strength and stiffness improvement, but the ductility of the elements increased up to 32 %. Pre-stressing of the glass fibres reinforced polymer implants in tension before their installation contributed to the strength increase to a much greater extent than the increase in the number of layers. The best reinforcement effect is obtained if two layers of pre-stressed GFRP are used. [ABSTRACT FROM AUTHOR]

Thermoplastic laminates are increasingly used in the automotive industry, so it is essential to study convenient and effective repair technologies. In this paper, an adhesively bonded repair method based on 3D printed patches is proposed. Multiple types of patches were fabricated using 3D printing technique and traditional laminate cutting process, respectively. Two stacking sequence laminates including angle-ply and quasi-isotropic were utilized in this study. The mechanical properties of the repaired specimens were tested under tensile loading, and the strain distribution and damage process were monitored by digital image correlation (DIC) technique. The damage characteristics and failure mechanisms are analyzed. The results indicate that the load-bearing capacity of the open-hole laminates can be significantly improved through the repair method. Compared with traditional patches, the 3D printed patches show more excellent repair performance. Moreover, 3D printed patches are easier to manufacture and have a lower cost. This study can provide some insight for the repair of automotive lightweight components manufactured by polymer composites. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of thermal cycles on the structural integrity of a pultruded Glass Fibre Reinforced Polymer (GFRP). Through a critical review of current literature alongside a comprehensive experimental campaign, the material’s response to cyclic thermal loading has been ascertained, defined by the rate of degradation of its physical, mechanical and visco-elastic properties. Matching sets of both dry and soaked samples conditioned in distilled water for 224 days. Freeze–thaw cycling of both dry and soaked samples was conducted between 20 °C and −10 °C for a total of 300 cycles. Computed Tomography scanning (CT-scan) was undertaken to assess the microstructural physical changes throughout freeze–thaw cycling. After exposure, GFRP samples exhibited a minor decrease in glass transition temperature ( T g ) which indicated minor structural degradation. Dry GFRP sample’s mechanical response exhibited negligible changes in both tensile and in-plane shear properties. However, as a result of the higher induced thermal stresses, soaked samples showed a significant degradation of their tensile and shear strengths. Yet, the soaked material’s stiffness remained largely unaffected due to the potential reversible nature of plasticization, which acts to increase the material’s molecular mobility when initially moisture-saturated, but is later recovered as the soaked samples lose moisture throughout freeze–thaw cycling. [ABSTRACT FROM AUTHOR]