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In this study, a combination of theoretical analysis and experimental verification was used to investigate the effects of laser parameters and shock wave shape on the location of layer cracks in carbon fiber‐reinforced plastics specimens. Firstly, the propagation coupling process of trapezoidal, rectangular, and triangular pulses in the material was investigated based on the one‐dimensional stress wave propagation theory. The study analyzed the effects of shock wave pressure amplitude, pulse width, and other factors on the location of layer cracks in the material. Subsequently, laser impact experiments with varying energies and pulse widths were conducted on specimens of different thicknesses to investigate the impact of shock wave pressure amplitude and laser pulse width on the location of layer cracking. The results show that the theoretical analysis of triangular shock waves has broader applicability and can serve as a representative analytical model to describe single‐layer crack damage. Highlights: Laser impact experiments with various specimen thicknesses.Laser pulse width determines the initial location of inter‐laminar cracking.The applicability of the triangular pulsed layer cracking formula.The effect of laser energy on pulse amplitude. [ABSTRACT FROM AUTHOR]

Translation abstract Numerical simulation of concrete structures with mineral‐impregnated carbon fiber reinforcementThe bond behavior between reinforcement and concrete, as well as concrete damage, are crucial for the serviceability of structural elements. Due to the damage behavior of concrete and the nonlinear bond behavior, it is difficult to predict deformations, crack spacing, and crack openings in structures subjected to tensile and bending stresses. This study focuses on the experimental and numerical investigation of concrete structures reinforced with mineral‐impregnated carbon fibers (MCF). The objective of this work is to define and validate numerical models that allow for an accurate prediction of the load‐bearing, deformation, and cracking behavior of MCF‐reinforced elements. To achieve this objective, the study outlines the experimental uniaxial tension tests and a four‐point bending test that were specifically conducted for this research. Following the experimental investigations, the numerical models used in this study are defined and described. Finally, numerical models are evaluated based on their ability to reproduce experimental results. The authors aim to promote the utilization of MCF‐reinforced concrete structures in additional structural elements by defining and validating numerical models. [ABSTRACT FROM AUTHOR]

Background: Fiber-matrix debonding is a precursor for transverse cracking and several other types of damage in fiber composites. However, to date, there are limited experiment-based reports that study the fundamental mechanisms of fiber-matrix debonding. Objective: This work aims to uncover the governing mechanisms of fiber-matrix interface debonding by full-field measurements supplemented by numerical simulations. In particular, the application of a dual-vision image-based characterization approach on single glass macro fiber samples is discussed and proven useful in understanding the in-plane and out-of-plane debonding characteristics at the fiber-matrix interface. Methods: Full-field strain and displacement measurements based on digital image correlation are performed on model single-fiber composites. The use of a dual-vision system allows strain measurements in the vicinity of the fiber-matrix interface, also allowing for the identification of critical strain and stress values corresponding to the initiation and propagation of debonding damage. The experimental data are used to calibrate an inverse identification approach that outputs the shape of the debonded interface along the fiber length. Results: Full-field measurements allow for establishing correlations between local and global strain fields. Observation of debonding propagation along the fiber axis seems to be representative of the crack tunneling during the early stages of the failure process, i.e., when the crack tip is subjected to opening mode only. Conclusions: Side view measurements are useful as a first-order approximation of the debonding propagation velocity along the fiber axis but fail to provide accurate measurements for the debonding shape, esp. in areas where the crack is under a dominantly shear stress state. This issue can be resolved by full-field measurements coupled with computational simulations. [ABSTRACT FROM AUTHOR]

In the automotive industry, short glass fiber-reinforced thermoplastics are widely used under the hood and subjected to dynamic vibrations of the engine in multiple directions resulting in fatigue failure. Under fatigue loading, a significant portion of the strain energy is stored within the material, while the remaining portion is lost due to internal frictions and the damage occurrence. Internal friction results in heat generation, which in turn causes an increase in external temperature. This increase in temperature leads to thermal degradation of the polymer. Investigations on the cause of the stiffness drop are not widely available in the literature. Therefore, this study explores the source of the stiffness drop under biaxial fatigue loading of a polyamide 6,6 reinforced with 30 wt. % short glass fibers (PA66GF30) and distinguishes the contributions of thermal degradation and damage accumulation. The thermal evolution of the specimens was captured by means of thermography. In addition, the digital image correlation (DIC) technique was used to measure the in situ strain field during the fatigue. Despite the temperature stabilization being observed around the 10,000th cycle, the reduction in the stiffness continued until failure which was attributed to the mechanical damage accumulation and cyclic creep during the fatigue tests. Dynamic mechanical analyses (DMA) were carried out to quantify the stiffness drop with the varying temperature. From the results, it is seen that the damage accumulation and cyclic creep during the fatigue tests were responsible for the major part of the stiffness drop. Finally, scanning electron microscopy (SEM) inspection of the fracture surface was performed to identify fatigue damage mechanisms. Four unique features associated with the fatigue damage were identified: (1) debonding of fibers from the matrix, (2) polymer matrix crazing, and (3) cavitation and porosities, (4) pull out fiber ends and break on the fiber. [ABSTRACT FROM AUTHOR]

Background: This paper investigates the mechanical properties and failure behaviours of rivet-bonded hybrid joints composed of aluminium adherends and steel rivets under quasi-static tensile loading. Objective: The damage law of hybrid joints is studied to provide a reference for the design and manufacture of hybrid joints. Methods: Tensile tests were conducted on aluminium and steel specimens at various triaxial stress levels. The corresponding finite element model (FEM) was developed to verify the Johnson–Cook damage parameters of the studied metals. The hybrid joint considering the rivet forming process was constructed through FE modelling using the Johnson–Cook failure criterion and Cohesive Zone Model (CZM), which was then validated with the experimental results. Results: Experimental results of the hybrid joint showed that a typical two-stage failure: 1) the adhesive layer bears the majority of the load during the initial loading stage, and 2) the adhesive layer completely fails after reaching the peak load and the rivet solely bears the load subsequently. Conclusions: The riveting process did not cause damage to the adhesive layer, which ensured the reliability of the manufacturing techniques of the hybrid joint. And the yielding of rivets may buffer the immediate failure of hybrid joints. [ABSTRACT FROM AUTHOR]

Continuous fibre reinforced ceramic matrix composites (CMCs) are increasingly being employed in safety critical applications. As a result, their use in these applications requires the adoption of appropriate design methodologies that are able to consider their complex non-linear mechanical behaviour. In this paper, a simple but robust formulation for continuum damage model, thermodynamically consistent and written under plane stress condition, is proposed for a laminated 2D woven composite material. This model is implemented via the Classical Laminate Theory (CLT) extended to non-linear behaviour to predict the behaviour of different stacking sequences. In-plane tensile tests were performed on an oxide/oxide composite up to 1000 °C to fully identify the model. The procedure is described and used on tests at room temperature before being extended higher temperature tests. Finally, the law and its coupling with the CLT are validated by means of tests on quasi-isotropic and cross-ply laminates at different temperatures. [ABSTRACT FROM AUTHOR]

Methods used nowadays in forensic laboratories allow to stop some kinds of projectiles with degree of deformation which lets to use them for comparing traces to projectiles found on the crime scene. However they are not useful for every type of projectiles. Comparative physical tests are enough to indicate the best method for soft catching projectiles. For this aim point of view no modeling needed. The paper presents the results of ballistic tests of impact of chosen types of soft point projectiles into water. The behavior of projectiles of various shapes, with different kinetic energy, was analyzed. On the basis of the obtained results, the projectiles with the highest susceptibility to deformation were identified. Research works described in the paper were performed within the framework of the project Laboratory stand for stopping high-energy projectiles financed from the National Centre for Research and Development (Agreement no. DOB-BIO10/04/02/ 2019). The project is implemented in cooperation with Warsaw University of Technology, Military Institute of Armament Technology and Tebbex 2 since 2019 to 2022. [ABSTRACT FROM AUTHOR]

Due to the effects of manufacturing process, there are lots of distributed voids in the interior area of three‐dimensional (3D) woven C/SiC composites, leading to the difficulties in predictions of damage evolution and ultimate strength. In this work, the mesoscale geometry of 3D woven C/SiC composites is reconstructed based on the high‐resolution CT scanning, considering the yarn path, yarn profile, and void content. The CT‐based reconstructed model agrees well with the experimental observations. Then, the constitutive laws of mesoscale constituents and macroscale structure are established and implemented numerically by the user‐defined material subroutine UMAT. Finally, the established constitutive laws are applied for the reconstructed model, and the mesoscale and macroscale nonlinear progressive damage behavior of 3D woven C/SiC composite structures are predicted using the hierarchical multiscale method, which are also validated by the experiments. The established CT‐based multiscale computational scheme would be a potential tool for performance evaluation and design of composites. [ABSTRACT FROM AUTHOR]

This paper presents the mathematical derivation and numerical implementation of a novel regularized density-driven damage mechanics (D3M) model for simulating failure in concrete members. The novel idea behind the derivation of the approach is that damage is described as a function of the local change in material density. This choice is justified by the fact that the development of local damage directly corresponds to a reduction in local density since undamaged cementitious composites inherently have a higher density than the fluid or gas that occupies damaged regions. For this reason, devising numerical approaches that can predict the material behavior as a function of density could open up new possibilities for the prediction of the nonlinear behavior of concrete structures, as well as the derivation of novel testing procedures for the evaluation of strength by means of direct and indirect measures of density. In this context, a three-phase mesoscopic representation of concrete material is used, where coarse aggregate, mortar, and the interfacial transition zone are explicitly modeled to obtain a realistic representation of the material internal structure. The manuscript first presents the mathematical derivation of the model, with emphasis devoted to the regularization of the computational implementation. This paper then proceeds to demonstrate that the novel regularized D3M is insensitive to the mesh size chosen to represent the three material phases while also predicting realistic compression-to-tension strength ratios and damage patterns at failure. In addition, a parametric study is carried out to illustrate the effect of the relevant mechanical parameters on the observed response. Finally, the proposed model is validated by comparison with experimental results of 3-point bending tests on plain concrete beams of various sizes, also demonstrating that the regularized D3M is capable of predicting size effect in concrete members. [ABSTRACT FROM AUTHOR]

Due to its significant non-linear softening characteristics and its wide variety of use cases, concrete has received considerable attention for the modeling of its mechanical behavior. The non-linear simulation of linear concrete structures is often associated with mesh dependency, the resolution of which requires some form of regularization. While most of the past research has focused on tension energy regularization for better mesh-objectivity, the compression behavior has been partly left out, even though it may have a significant impact for particular applications. By starting from the failed attempt to simulate a pushout test from the literature, this paper focuses on the enhancements brought by the energetic regularization in compression to an isotropic damage model based on Mazars' equivalent strain. The resulting model is applied in three representative case studies where the enhanced mesh-objectivity is shown relative to the load–displacement behaviors and the damage patterns that are produced, and compared to those obtained by the classical model. [ABSTRACT FROM AUTHOR]

Due to its significant non-linear softening characteristics and its wide variety of use cases, concrete has received considerable attention for the modeling of its mechanical behavior. The non-linear simulation of linear concrete structures is often associated with mesh dependency, the resolution of which requires some form of regularization. While most of the past research has focused on tension energy regularization for better mesh-objectivity, the compression behavior has been partly left out, even though it may have a significant impact for particular applications. By starting from the failed attempt to simulate a pushout test from the literature, this paper focuses on the enhancements brought by the energetic regularization in compression to an isotropic damage model based on Mazars’ equivalent strain. The resulting model is applied in three representative case studies where the enhanced mesh-objectivity is shown relative to the load–displacement behaviors and the damage patterns that are produced, and compared to those obtained by the classical model.

Abstract The environment of deep in-situ occurrence is complex, and secondary dynamic disasters occur frequently. Exploring the dynamic constitutive models of coal at different depths is the foundation for deep resource development, which can help promote the safe and efficient mining of coal resources at different depths and reveal the mechanism of sudden dynamic disasters. Dynamic mechanical testing of coal at different depths of the Pingdingshan mine (China) was carried out using a split Hopkinson pressure bar system with confining pressure. On the basis of statistical damage theory, dynamic constitutive models of coal at different depths were explored, and the theoretical models were compared and verified using the experimental results. An expression relating to the infinitesimal element strength of coal and loading rate was derived, and the parameters σ 1dp , E d , and ε 1dp were determined. Inversion verification of the model showed that the experimental results agree well with the theoretical results prior to the peak stress. These research results are expected to be applied to the exploitation of deep resources, laying a foundation for the law of deep earth science and the construction of deep engineering.

Glass fiber reinforced polymer (GFRP) composites with chopped strand mat (CSM) and woven roving mat (WRM) reinforcements are widely used in high‐pressure piping due to their favorable strength‐to‐weight ratio. However, cyclic loading from vibrations and pulsating forces can induce internal microstructural damage, ultimately leading to performance degradation. A thorough understanding of this damage mechanism is imperative for its mitigation, necessitating a detailed examination. The present study aims to investigate the fatigue response and damage mechanisms in CSM and WRM composites subjected to tension‐tension cyclic loading. Scanning electron microscopy analysis of edge sections revealed the development of perpendicular microcracks in both composites. CSM composites exhibited fatigue cracks parallel to the loading direction and higher levels of parallel interface debonding compared to perpendicular matrix cracks. Finite element analysis of the representative volume element revealed the role of shear stress in the matrix in initiating parallel cracks, thereby explaining the damage initiation mechanism in CSM. These findings highlight the distinct damage mechanisms arising from the differing fiber arrangements in CSM and WRM composites, providing valuable insights for optimizing their performance under cyclic loading conditions. Highlights: Fatigue response of CSM and WRM was influenced by fiber orientation and weaving pattern.Perpendicular fibers were the most probable fibers to have their interface form a crack.Fatigue cracks parallel to the direction of loading were observed in CSM composites.Quantified the true 3D internal microstructural damages for the first time. [ABSTRACT FROM AUTHOR]

This research investigates the effects of fiber hybridization on the mechanical performance of carbon/flax bio‐hybrid laminates. The study comprised of manufacturing and analyzing five distinct composite laminates, comprising pure carbon and various carbon/flax configurations with symmetric and asymmetric layups. The laminates were subjected to uniaxial tensile and low‐velocity impact testing at energy levels from 30 to 75 J. Quantitative and qualitative analyses were conducted to assess the damage/failure patterns to determine the changes due to hybridization and stacking sequence. The experimental results revealed that integrating flax layers into different bio‐hybrid configurations significantly influences their strength, stiffness and impact resistance. One of symmetric layups, having uniform distribution of flax layers throughout thickness, demonstrated the most enhanced performance. To facilitate comprehensive comparison, two indices were developed: Composite‐Performance Index (CPI) and Cost‐Effectiveness Index (CEI). These indices indicate that bio‐hybrid configurations, optimally designed with appropriate number of evenly distributed flax layers, can match or surpass performance of pure carbon layup. The study concludes that incorporating flax into carbon fiber laminates can yield substantial benefits in impact performance with slight compromise in tensile strength and stiffness. However, the overall cost efficiency of bio‐hybrid composites is superior, considering both tensile strength and impact performance. Highlights: Effect of fiber hybridization on the mechanical performance of hybrid laminates was studied.Carbon/Flax composites exhibited slightly lower tensile strength compared to carbon‐based layup.Symmetric layups with evenly distributed flax layers showed enhanced impact performance.Cost efficiency of bio‐hybrid composites is superior for both tensile and impact performance. [ABSTRACT FROM AUTHOR]

This study explores the effects of laser pulse width and energy on CFRP laminates damage in laser bond inspection technology. Three testing programs were used, including varying laser energy while keeping pulse width constant, altering pulse width while maintaining constant power density, and modifying pulse width while keeping energy constant. The results show that when the pulse width remains constant, increased laser energy has a minimal effect on the initial damage location but leads to gradual interlayer delamination and fiber fracture propagation toward the impact surface. With constant laser energy, a specific threshold for pulse width is observed. When the laser pulse width is below this threshold, it exhibits a positive correlation with the damage characteristics of CFRP laminates, whereas when it exceeds this threshold, it shows a negative correlation. Power density correlates with damage when pulse width is constant, but there is no direct correlation when pulse width varies. Highlights: CFRP laminates underwent laser shock tests with varying pulse widths.Power density is positively correlated with damage under specific conditions.There exists a specific threshold for laser pulse width.In single‐sided laser shock, initial damage spreads within a specified range. [ABSTRACT FROM AUTHOR]

The bond behavior between reinforcement and concrete has a significant influence on the load‐bearing behavior and serviceability of the composite material. This paper focuses on the characterization of the bond behavior between fine‐grained concrete and mineral‐impregnated carbon‐fiber reinforcement. In this study, the influence of different bond lengths on local bond behavior was experimentally investigated. To predict the bond stress along the bond length, an analytical bond stress‐slip model was specified, and its model parameters were determined based on the experimental tests using an iterative approximation approach. Based on the defined bond stress‐slip model, a numerical bond model was developed and adjusted for the first time. A three‐dimensional (3D) finite element analysis (FEA) allows the simulation of the local bond stress along the bond length. Finally, the results of the 3D FEA were compared with the results of the experimental investigations to validate the developed numerical model. [ABSTRACT FROM AUTHOR]

Standard non-local gradient damage methodology for fatigue analysis has an intrinsic drawback of unusual widening of the damage zone. This causes a rapid growth of crack in the simulations which often violate experimental evidences. In order to tackle this undesirable behaviour, the localizing gradient damage methodology has been formulated for high cycle fatigue crack growth simulations. The framework comprises of coupling damage and elasticity through continuum mechanics, a fatigue damage law and an interaction function which reduces the influence of damaged regions on the surrounding locality. The present scheme prevents the spurious widening of the damage-band around the critically damaged area and therefore the non-physical growth of fatigue crack in the simulations is successfully countered. The developed framework is tested on various standard specimens under mode-I and mixed-mode high cycle fatigue loads. Nonlinear finite element analysis is used for this purpose. The discretized form of solver equations for the localizing framework is mathematically derived. Numerical examples show that the simulated crack-growth curves using proposed localizing framework agree closely with the experimental data and has a higher accuracy than the standard non-local framework. [ABSTRACT FROM AUTHOR]

This paper presents research concerning the numerical simulation of existing masonry buildings when subjected to pushover analysis. A nonlinear static analysis is undertaken using the commercial software ABAQUS standard, in which masonry structures are modelled using damage mechanics. To validate the chosen input parameters, this study compares two different approaches for static nonlinear modelling, the Finite Element Method (FEM) and the Equivalent Frame Method (EFM), for a simple masonry building. The two methods are compared using the guidelines from Part 3 of Eurocode 8. This study identifies the advantages and disadvantages of various modelling approaches based on the results obtained. The results are also compared in terms of capacity curves and damage distributions for the simple case study of a masonry building created to compare numerical methods. Subsequently, nonlinear pushover analyses with ABAQUS (FEM) were performed on the North Tower of Monserrate Palace, Portugal, in which the material parameters were calibrated by considering the results of dynamic characterisation tests conducted in-situ. Regarding the circular body of Monserrate Palace, the damage distribution of the structure is analysed in detail, aiming to contribute to the modelling of such structural configurations through the Equivalent Frame Method. [ABSTRACT FROM AUTHOR]

The effect of thermo-oxidative aging on mechanical properties is important to designing carbon fiber-reinforced composites serviced in long-term atmospheric environments. Here, we report the progressive bending damage behaviors of carbon fiber/epoxy 3D angle-interlock woven composites (3DAWCs) after thermo-oxidative aging. Three-point bending tests were conducted to characterize bending damage behaviors after different aging days. The electrical resistance change of 3DAWCs was also simultaneously measured with the two-probe method during three-point bending tests. Combining side image and digital image correlation (DIC) technology, we found that the bending strength and modulus deteriorated rapidly during thermo-oxidative aging. The strain distribution and progressive bending damage modes also changed significantly, i.e., a symmetrical strain distribution for the unaged specimens, while the existing interface cracks of the aged specimen changed this symmetry. The electrical resistance method (ERM) effectively identified the early-stage damages, and the first derivative of the rate of resistance change (FDC) revealed differences in the progressive damage modes of aged and unaged specimens. [ABSTRACT FROM AUTHOR]

This paper reports the damage mechanism of 30Cr1Mo1V rotor steel during thermal fatigue at 540°C. Detailed information on macro‐failure characteristics and micro‐failure mechanisms was revealed here. The results showed that both intragranular micro‐defects and intergranular micro‐crackings were formed during the fatigue process. The formation of intragranular micro‐defects was related to the dislocation tangle inside the ferrite sub‐grains, while the formation of intergranular micro‐cracking could be related to the weakening of atomic cohesion at the matrix/cementite interface. Eventually, the transgranular crackings occurred in the 30Cr1Mo1V steel. The morphology of these crackings presented an edge‐shaped discontinuity, which may propagate perpendicularly to the loading direction and cause the material to fracture. [ABSTRACT FROM AUTHOR]

The paper investigates the issue of post-impact fatigue damage of the 2060 aluminium–lithium alloy, a representative material of third-generation aluminium–lithium alloys extensively employed in the fuselage of C919 aircraft due to its notable attributes of high specific stiffness and strength. Initial impact damage is identified utilizing a residual stress–strain field obtained from a quasi-static simulation. Then, the continuum damage mechanics approach is applied to predict the fatigue life of the impacted 2060 aluminium–lithium alloy plates accounting for the combined effects of residual stress, plastic damage, and fatigue loading. A comparative analysis between calculated and experimental results is conducted to validate the efficacy of the proposed methodology. [ABSTRACT FROM AUTHOR]

Spread‐tow woven fabrics (STW) have attracted considerable attention because of their ultrathin structure and low porosity, which benefit the design and application of STW composites. Little is known about how the thickness relationship between the middle and surface layers affect the mechanical properties of sandwich structures. Therefore, this study developed an anti‐sandwich stitched composite with STW in the center and a nonwoven felt/STW hybrid on both sides. The interlayer shear behavior and damage mode transformation of STW composites with different middle‐layer thicknesses were studied using short‐beam shear tests, digital image correlation (DIC) full‐field strain nephograms and micro‐computed tomography (micro‐CT). The results showed that the anti‐sandwich structure improved the shear strength, particularly when the middle layer thickness was four times that of the surface layer. As the middle layer thickness ratio decreased, the synergistic effect of the anti‐sandwich structure was weakened, and the damage mode changed from ductile to brittle. Furthermore, the hybrid ratio of the STW/nonwoven fabric in the surface layer had little effect on the performance because of the good interfacial adhesion between the STW and nonwoven fabric. The anti‐sandwich structure that can improve the properties and stability of STW composites provides a reference for the structural design of STW composites in engineering applications. Highlights: An anti‐sandwich composite was developed by spread tow woven fabrics.Nine types of anti‐sandwich composite were designed and fabricated.The thickness of the middle layer affected the synergistic mechanisms.The optimal anti‐sandwich structure has a 4.59% increase in shear strength.The specific shear strength is 14.86% higher over pure spread tow laminates. [ABSTRACT FROM AUTHOR]

This paper presents the results of the experimental research on diamond-reinforced composites with WC–Co matrices enhanced with a ZrO2 additive. The samples were prepared using a modified spark plasma sintering method with a directly applied alternating current. The structure and performance of the basic composite 94 wt.%WC–6 wt.%Co was compared with the ones with ZrO2 added in proportions up to 10 wt.%. It was demonstrated that an increase in zirconia content contributed to the intense refinement of the phase components. The composite 25 wt.%Cdiamond–70.5 wt.%WC–4.5 wt.%Co consisted of a hexagonal WC phase with lattice parameters a = 0.2906 nm and c = 0.2837 nm, a cubic phase (a = 1.1112 nm), hexagonal graphite phase (a = 0.2464 nm, c = 0.6711 nm), as well as diamond grits. After the addition of zirconia nanopowder, the sintered composite contained structural WC and Co3W3C phases, amorphous carbon, tetragonal phase t-ZrO2 (a = 0.36019 nm, c = 0.5174 nm), and diamond grits—these structural changes, after an addition of 6 wt.% ZrO2 contributed to an increase in the fracture toughness by more than 20%, up to KIc = 16.9 ± 0.76 MPa·m0.5, with a negligible decrease in the hardness. Moreover, the composite exhibited an alteration of the destruction mechanism after the addition of zirconia, as well as enhanced forces holding the diamond grits in the matrix. [ABSTRACT FROM AUTHOR]

Silica-filled rubber composites exhibit nonlinear viscoelastic behavior depending on filler dispersion and matrix interaction. This study investigated the effects of silane treatment on dynamic mechanical properties of precipitated and fumed silica-reinforced polybutadiene rubber composites. The silane coupling agent improved filler dispersion and interfacial adhesion as characterized by microscopy and bound rubber content. Payne effect measurements showed enhanced storage modulus and network stability for silanized composites due to better filler networking. Cyclic tensile loading displayed reduced stress-softening in treated composites attributable to minimized damage formation. Modeling using Kraus and damage mechanics approaches provided quantitative correlations between the microstructure and magnitude of nonlinear response. The results demonstrate that silane treatment optimizes the viscoelastic performance of silica-filled rubber composites. [ABSTRACT FROM AUTHOR]

A novel damage tolerance design method of discrete interleaved toughening for laminated composite was proposed. In this paper, discrete thermoplastic Polyamide-6,6 (PA 66) films were deployed at between the selected adjected layers, and three toughening dimensions were considered. Besides, three impact positions of specimens were tested under 5 J, 10 J, and 15 J, respectively. The impact behavior and compression after impact (CAI) of specimens were discussed and compared. Experimental results showed that delamination damage was suppressed in the process of propagation outwards across the toughened region, and the path of delamination crack propagation was changed and swerved. Therefore, the delamination damage projected area (DDPA) of all specimens were reduced by 21.09%–62.85%, compared with the non-toughened plate (base plate). In addition, the finding demonstrated that CAI strength is influenced by the delamination position and DDPA. The proposed method could improve the CAI strength by suppressing delamination and swerving the propagation path of delamination. Moreover, the CAI strength of all toughened plates were improved by 16.35%–61.94% in contrast to the related base plates. [ABSTRACT FROM AUTHOR]

This study uses the finite element method (FEM) to investigate the effect of key structural parameters on the impact resistance of E-glass 3D orthogonal woven (3DOW) composites subjected to low-velocity impact. These structural parameters include the number of y-yarn layers, the path of the binder yarn (z-yarn), and the density of the x-yarn. Using ABAQUS, yarn-level finite element (FE) models are created based on the measured geometrical parameters and validated for energy absorption and damage behavior from experimental data gathered from the previous study. The results from finite element analysis (FEA) indicate that the x-yarn density and the binder path substantially influenced the composites' damage behavior and impact performance. Increasing x-yarn density in 3DOW leads to a 15% increase in energy absorption compared to models with reduced x-yarn densities. Moreover, as the x-yarn density increases, crack lengths at the back face of the resin matrix decrease in the y-yarn direction but increase in the x-yarn direction. The basket weave structure absorbs less energy than plain and 2 × 1 twill structures due to the less constrained weft primary yarns. These results underscore the importance of these structural parameters in optimizing 3DOW composite for better impact performance, providing valuable insights for the design of advanced composite structures. [ABSTRACT FROM AUTHOR]

In structural engineering, composite patch repairs are widely used to address cracked structures. However, their behavior under thermo-mechanical loading remains complex and less understood. This study examines the repair of a center-cracked plate subjected to both mechanical and thermo-mechanical environments, using finite element analysis in ANSYS. The repair effectiveness is evaluated using the Stress Intensity Factor (SIF) at the crack tip. Findings reveal that increased temperature substantially elevates SIF values. Boron/epoxy patches are most effective under mechanical loading, yielding the lowest SIF, while graphite/epoxy patches excel under thermo-mechanical loading due to their lower Coefficient of Thermal Expansion (CTE). Patch thickness influences SIF differently based on loading conditions; thicker patches decrease SIF under mechanical loading but increase it under thermo-mechanical loading. Furthermore, adhesive defects, particularly at the crack tip, markedly increase the risk of adhesive failure, especially under thermo-mechanical conditions. This research underscores the significant impact of temperature variations on the efficiency of structural repairs, contributing to a deeper understanding of composite patch repair performance in cracked structures.

AbstractThis study delves into mechanical engineering by investigating damage mechanisms and reinforcement strategies in notched structures. Our research centers on enhancing structural integrity through a localized heat treatment technique applied at the notch before uniaxial tensile stress testing. Central to our approach is Functionally Graded Material (FGM), defined by volume fractions that specific exponents modulate. The innovation lies in treating the interface between the base metal and the heat-affected zone (HAZ). We introduce a novel meshing-based grading technique that facilitates elastoplastic behavior and allows for the gradation of damage properties. This technique is particularly noteworthy as it obviates the need for complex subroutines or FORTRAN compilation. Our methodology employs a mesh model with independent elements, each characterized by a volume fraction gradient to accurately represent the graded material’s behavior. The behavioral model is anchored in the Von Mises equivalent stress flow theory, and tensile tests inform the material properties of steel and the HAZ. The results of our investigation are presented through force-displacement curves, which critically evaluate our reinforcement technique. Moreover, using the eXtended Finite Element Method (XFEM) in our meshing approach has proven particularly effective in delineating structural behavior post-fissure initiation, showcasing its superiority in capturing the nuances of crack propagation and structural separation. [ABSTRACT FROM AUTHOR]

Composite structures are vulnerable to delamination under out‐of‐plane loading due to the absence of reinforcing fibers in the thickness direction. This paper introduced the interlaminar basalt fiber veil technique to improve the interlaminar fracture toughness of basalt fiber‐reinforced thermoplastic composite laminates. The reinforcement effect of the basalt fiber veil on GIC of composite laminates was investigated by a double cantilever beam (DCB) test. The toughening effect, damage morphology, and the basalt fiber veil toughening mechanism were analyzed by mechanical response, optical photos, and scanning electron microscopy (SEM). It was found that the basalt fiber veil could significantly inhibit the propagation of interlaminar cracks. Compared to the unreinforced specimen, the maximum load of basalt fiber veil‐reinforced laminate was increased by 73%, the average platform load was increased by 72.7% and the GIC was increased by 157%. Highlights: Improvement of GIC of basalt fiber‐reinforced thermoplastic laminates by basalt fiber veil.The toughening mechanism for the basalt fiber veil.The GIC of the fiber veil‐reinforced laminate was 157% higher than the unreinforced laminate. [ABSTRACT FROM AUTHOR]

This paper studies the mechanical properties of the 2-D tri-axial braided composite. A volume element is established, so that the classical laminate plate theory and the series-parallel model can be adopted to study a bi-directional stress--strain response. Failure criteria are given and the failure strength is determined. The finite element simulation is used to verify the reliability of the present theoretical model. [ABSTRACT FROM AUTHOR]

Fatigue failure is the main problem affecting the safety of structural members. It is of great engineering significance to predict the fatigue life accurately. Based on the damage evolution model with mean stress correction, a numerical method for fatigue life prediction considering both crack initiation and propagation was established combined with finite element method. To verify this method, fatigue tests and numerical simulations of aluminum alloy plates with holes under different stress levels were carried out. The results show that the crack propagation process and the fatigue lives can be effectively predicted by the proposed fatigue numerical method, and the error band of the predicted lives is less than two times. [ABSTRACT FROM AUTHOR]

In the present investigation, we constructed a novel mathematical model of a one-dimensional thermoelastic semiconducting solid sphere based on the L-S model to study the photothermal interaction. Within this work, we applied two considerations: the mechanical damage variable, and rotation with constant speed. The bounding surface of the sphere has been thermally loaded by ramp-type heating. Laplace transform has been applied, and its inversions have been computed numerically. The numerical results of the temperature increment, carrier density increment, strain, displacement, stress, have been represented in figures with various values of the damage mechanics variable, ramping time parameter, and rotation angular velocity parameter. The ramping time parameter has significant effects on all the studied functions, while the damage and rotation have limited effects on the thermal waves and significant effects on the mechanical waves. [ABSTRACT FROM AUTHOR]

A reliable approach based on an entropy-damage model for assessing remaining useful fatigue life is presented. Two damage models are presented and evaluated to assess their effectiveness in predicting remaining useful life. The first model focuses on reduced toughness caused by fatigue degradation, while the second is based on accumulating entropy during fatigue loading. The entropy-based approach employs infrared thermography to anticipate entropy accumulation and damage status. Outcomes reveal that the entropy-driven technique offers enhanced precision. Moreover, its damage growth rate remains consistent, regardless of the number of cycles leading to failure, ensuring a more stable tracking of damage evolution. It successfully predicts the remaining useful life and can treat variable load sequencing without knowing the loading history. An extensive set of experimental results with carbon steel 1018 are presented to illustrate the utility of the approach. [ABSTRACT FROM AUTHOR]

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To accurately predict the behavior and mechanical damage of sheet metal during hot forming process, the use of advanced thermomechanical modeling and precise identification of the constitutive parameter are required. This paper proposes a novel identification approach for constitutive parameters that relies on multiple regression and the shape index of experimental data curves. This approach is used to determine the material constants associated with the Johnson-Cook material and failure models for steel and aluminum sheets. Therefore, the obtained results approve the applicability and high accuracy of the identification procedure for the damage and the constitutive parameters of sheet metal, which allows for substantial time savings. Furthermore, to evaluate the formability of sheet metal, experimental forming tests at various temperatures were conducted. The identification process enhances the prediction of forming results, as shown by the fact that the numerical simulation of Erichsen and square die hydroforming tests using identified Johnson-Cook parameters agreed with the results of these tests carried out at different forming conditions. Moreover, the thickness measurement shows the ability of the developed model to properly predict the thickness of deformed shapes.

Abstract The establishment of mechanical models of rocks can provide crucial guidance to the surrounding rocks stability analysis in the rock engineering. According to statistical damage theory and Mohr–Coulomb strength criterion, the Logistic model is used to yield the damage evolution equation and further establish statistical damage constitutive model for describing the whole failure process of rocks. Then, the rationality of the proposed damage model is proved by comparing with the different test curves, and damage evolution laws are summarized into four stages, including: slow-growth stage, rapid-growth stage, constant-speed-similar growth stage and speed-reducing growth stage. Physical meanings of model parameters $${r}{\prime}$$ r ′ and $$m$$ m are also discussed. Finally, to verify the application of this proposed model, this damage constitutive model is developed and implemented to simulate the tunnel excavation and analyze the stability of surrounding rocks by using Fortran, python and Abaqus. The displacement data on site is used to prove the superiority of proposed damage constitutive model compared with the existing ones in Abaqus. The research outcomes presented in this paper can also provide useful references for the theory and application of rock mechanics.

In a corrosive environment with coupled dry-wet-sulfate action, concrete structures are susceptible to erosion by sulfate ions, which seriously affects the safe operating life. To forecast the operational lifetime of concrete below the influence of the dry-wet cycle and sulfate erosion environment, four different admixtures of polypropylene fiber: 0, 0.6, 0.9, and 1.2 kg/m 3, were incorporated into concrete specimens, and indoor accelerated tests were designed to observe the macroscopic and microscopic deterioration law analysis of concrete specimens; using the precept of damage mechanics, the damage of concrete under solubility cycle was established. The damage evolution equation of concrete under freeze-thaw cycles was established and the operational life of concrete was predicted. The results showed that the overall mass loss rate of concrete specimens increased with the number of tests, and the relative energetic modulo decreased with the number of tests; the pore change pattern, microstructure, and internal material composition of specimens under different working conditions were obtained by using NMR scanning technique, SEM electron microscope scanning technique and XRD physical phase analysis technique. The damage evolution equation shows that adding a certain amount of polypropylene fiber to concrete can improve the working life of concrete under dry and wet connected sulfate assault.

Acoustic emission (AE) technology provides a novel approach for studying the damage and fracture behavior of wood‐plastic composites (WPCs) during their application process. This method allows rapid and precise analysis of the mechanical properties of materials, which is a significant advancement for the emerging WPC industry. Hence, a blend of waste floor sanding powder (FSP) and rice husk (RH) reinforced recycled high‐density polyethylene (Re‐HDPE) was prepared by the extrusion method. The AE technique, scanning electron microscopy, and finite element method (FEM) were used to analyze the damage and fracture behavior of the composite materials under a three‐point bending test. The results indicated that the bearing capacity of RH/Re‐HDPE composites was slightly higher than that of FSP/Re‐HDPE composites. The AE technique can better illustrate the damage evolution and fracture process of composites and determine the damage degree and mode. Matrix cracking and deformation were more pronounced in the FSP/Re‐HDPE composites. Fiber breakage and delamination were more prominent in the RH/Re‐HDPE composites. In addition, repeated loading caused irreversible damage to the composite. The increase in temperature led to the attenuation of the AE signal and a decrease in matrix strength. However, when the temperature reached a certain point, the cumulative AE ringing count increased again because the higher temperature improved the fiber–matrix interface strength, which partially canceled out the negative effect. In addition, Abaqus was used for simulation analysis, and the running results coincided with the experimental value. Highlights: RH/Re‐HDPE and FSP/Re‐HDPE are sustainability and low‐cost composites.AE can determine the degree and mode of damage of WPC at different temperatures.The AE curves of RH/Re‐HDPE and FSP/Re‐HDPE all pass through four stages.Heating reduced the matrix strength and improved the interface strength of WPC.The results of FEM were consistent with the experimental results. [ABSTRACT FROM AUTHOR]

This work was dedicated to the simulation of fiber composite structures consisting of carbon fibers and mineral impregnation. The aim of this study was to generate a micromodel that predicts the properties of a mineral-impregnated carbon fiber reinforcement. The numerical characterization was based on the discrete microscopic modeling of the individual phases using a representative volume element. In addition, the stochastic nature of the fiber strength, the anisotropic damage mechanisms of the brittle matrix, and the non-linear bonding behavior between the filaments and the matrix were considered in the material models. The material models were adjusted based on the literature sources and our own experimental investigations. This was followed by the validation of the representative volume element, quantifying the evolution of stiffness and damage under longitudinal tensile loading. The numerical results of material stiffness, as well as the tensile strength of the representative volume element, were compared with the results of the experimental investigations. To verify the robustness of the numerical model, significant model parameters were subjected to a sensitivity analysis. [ABSTRACT FROM AUTHOR]

Quantifying fault severity is a critical part of rolling bearing health management. There are numerous methods for evaluating the severity of rolling bearing faults that utilize various signals to predict the remaining useful life (RUL). However, the fault severity assessment methods based on digital twins still cannot accurately track the fault evolution. To address this issue, this paper proposes a data/physics-driven digital twin model for predicting the RUL of rolling bearings. Firstly, using theoretical damage mechanics, the evolution of fatigue damage of rolling bearings throughout their entire life cycle is described, for which a spalling fatigue evolution model is constructed. Secondly, fatigue defects predicted by the spalling fatigue evolution model are introduced into a dynamic model to construct a bearing high-fidelity model. Thirdly, a local-to-global dynamic updating framework is designed for the interactive coupling of real-time monitoring data of rolling bearings and corresponding simulated data, as well as updating the high-fidelity model parameters. Finally, a neural network is used to predict the RUL of rolling bearings. The approach is verified using test data of rolling bearings. The results demonstrate that the proposed digital twin model can more accurately address the problem of RUL prediction of rolling bearings. The remaining useful life prediction process of rolling bearing is based on digital twin. [ABSTRACT FROM AUTHOR]

In this research, a nonlinear model is presented to explore the seismic response of concrete arch dams. This model is much more simplified and efficient in comparison with plastic-damage models. It can represent softening, hardening and stiffness degradation of concrete due to load reversal. Additionally, it is able to predict the final and residual strength of the structure in softening with good accuracy. Employing different scale factors to monitor the failure of the dam, this model is used to analyze the nonlinear response of Morrow Point arch dam. The dam-reservoir interaction is considered with modified Westergaard's approach, and the dam body is modeled with second order 20-node isoparametric elements. Moreover, two different damping algorithms are included to evaluate their impact on nonlinear analysis. It is concluded that the employed model can predict realistic crack patterns through the dam body, and it can be a good replacement for other time consuming and complicated models. In addition, it is shown that the damping algorithm plays a significant role in the nonlinear dynamic analysis of concrete arch dams. [ABSTRACT FROM AUTHOR]

This work proposes a numerical investigation on the effects of damage on the structural response of Reinforced Concrete (RC) bridge structures commonly adopted in highway and railway networks. An effective three-dimensional FE-based numerical model is developed to analyze the bridge's structural response under several damage scenarios, including the effects of moving vehicle loads. In particular, the longitudinal and transversal beams are modeled through solid finite elements, while horizontal slabs are made of shell elements. Damage phenomena are also incorporated in the numerical model according to a smeared approach consistent with Continuum Damage Mechanics (CDM). In such a context, the proposed method utilizes an advanced and efficient computational strategy for reproducing Vehicle-Bridge Interaction (VBI) effects based on a moving mesh technique consistent with the Arbitrary Lagrangian-Eulerian (ALE) formulation. The proposed model adopts a moving mesh interface for tracing the positions of the contact points between the vehicle's wheels and the bridge slabs. Such modeling strategy avoids using extremely refined discretization for structural members, thus drastically reducing computational efforts. Vibrational analyses in terms of damage scenarios are presented to verify how the presence of damage affects the natural frequencies of the structural system. In addition, a comprehensive investigation regarding the response of the bridge under moving vehicles is developed, also providing results in terms of Dynamic Amplification Factor (DAFs) for typical design bridge variables. [ABSTRACT FROM AUTHOR]

Continuous fiber-reinforced silicon carbide composites have received significant attention due to their high-temperature mechanical stability. However, their widespread implementation has been hindered by intricate fracture mechanisms and limited toughness. This study presents a real-time approach for identifying damage type in 2.5D SiCf/SiC composites and highlights the significant impact of minor eccentric loading angle on the fracture behavior and mechanical properties using acoustic emission (AE). Even a slight degree of eccentric loading angle can significantly alter the fracture behaviors, leading to a significant increase in fracture toughness. The fracture damage evolution law of 2.5D SiCf/SiC under varying eccentric loading angles was investigated with the help of the AE damage identification, fracture morphology and finite element analysis. These findings provide valuable insights for multi-axis stress analysis of 2.5D high-performance composites.