Damage Propagation Research Articles

Compressive behavior of hierarchical brick‐and‐mortar structures obtained by fused deposition modeling

AbstractNature is a never‐ending fount of inspiration to solve engineering problems. In light of this, the goal of this work is to propose and study structures that mimic materials found in nature, more specifically nacre. These structures were designed to be manufactured using fused deposition modeling since this is an accessible way to reproduce complex geometries. The manufactured biomimetic materials were tested in uniaxial compression in two different directions. In addition, an elastoplastic numerical analysis was used to better understand the compressive behavior of the studied structures. The comparison between experimental and numerical analysis reveals that the overall behavior results from two competing mechanisms, that is, an increase in stiffness due to strain‐hardening and a stiffness decay promoted by damage propagation. Moreover, it was possible to see that the structures continue to bear load while they retain the structural integrity, which is dominated by the crushing strength of each type of structure.Highlights Additive manufactured nacre‐inspired structures were proposed. Influence of different geometries in the compressive behavior was assessed. Behavior was linked to competition between strain‐hardening and damage growth. Load‐bearing capacity was related to the structural integrity of elements. The crack deflection mechanism was identified in some specimens.

Torsional progressive damage mechanisms in 3-D braided carbon fiber/epoxy resin composite tubes

3-D braided composites are a promising material for manufacturing tubular structures. However, a thorough understanding of their damage mechanisms under torsion is required to maximize their potential applications. The present work constructed a multiscale equivalent model, integrating mesoscopic and homogeneous structures to reveal torsional behavior of 3-D braided carbon fiber/epoxy resin composite tubes. The cumulative failure process, spatial stress distribution and interface damage were calculated to illustrate stress transfer and damage initiation and propagation. It is found that stress varies on the surface and internally within the representative unit cell (RUC). The yarns experience both axial tension parallel to the direction of torsion and axial compression perpendicular to the direction of torsion. The stress difference between them leads to damage initiation and propagation. Interfacial cracking as main damage mode hinders the stress transfer between resin and fiber bundles. The results show that the braided yarn path, axial stress dispersion in two directions and localization of damage effectively impede the torsional damage propagation.

Synergistically improving the edge-on impact damage resistance of composite laminates using multi-scale CNF/Z-pin toughening

Edge-on impact damage of composite structures has drawn significant attention from the engineering and academic communities because of the much more notorious damage caused than that by out-of-plane impacts. However, research focusing on improving the edge-on impact resistance of these structures has been limited. This paper proposed a synergistic toughening approach involving multi-scale carbon nanofiber (CNF) and Z-pin to improve the composite laminates' edge-on impact damage resistance. Through analysis of mechanical response, C-scan, optical and Scanning electron microscopy (SEM) photographs of unreinforced, CNF-reinforced, Z-pin-reinforced and CNF/Z-pin-reinforced laminates, the failure mechanisms of the four types of laminates and the synergistic toughening mechanism of CNF/Z-pin were revealed. The results show that the synergistic toughening of CNF/Z-pin could weaken the negative effects caused by Z-pin implantation and that CNF has the potential to increase the damage initiation energy threshold of the laminate. Furthermore, the toughening effect of Z-pin was significantly greater than that of CNF in damage propagation. Specifically, at 50 J impact energy, the damage area of CNF/Z-pin, Z-pin and CNF-reinforced laminates was reduced by 50.5 %, 39.8 %, and 8.3 %, respectively, compared to unreinforced laminates.

Experimental and Numerical Investigation of Prepreg-RTM Co-Curing Molding Composite Bolted T-Joint under Bending Load.

A set of polymer composite bolted T-joints with a novel configuration consisting of an internal skeleton and external skin was fabricated using a prepreg-RTM co-curing molding process. Experiments were conducted to study their mechanical properties under a bending load. A finite element model with a polymer resin area between the skin and skeleton was established and verified by the experimental results. Then, the damage propagation process and failure mechanism of the joint and the influence of three factors related to the layer characteristics of the skin and skeleton were investigated by the validated models. The results show that the bending stiffness and the yield limit load of the novel composite T-joint are 0.81 times and 1.65 times that of the 2A12 aluminum T-joint, respectively, while at only 55.4% of its weight. The damage of the joint is initiated within the resin area and leads to the degradation of the joint's bending performance. The preferred stacking sequence of the skeleton is [0/+45/90/-45]ns when primarily subjected to bending loads. The decrease in the bending performance is within 5% of the inclining angle of the skeleton, less than 12 degrees. The more 90° layers in the skin, the better the bending performance of the joints, while the more 0° layers, the poorer the bending performance.

I-FENN with Temporal Convolutional Networks: Expediting the load-history analysis of non-local gradient damage propagation

In this paper, we demonstrate for the first time how the Integrated Finite Element Neural Network (I-FENN) framework, previously proposed by the authors [1,2], can efficiently simulate the entire loading history of non-local gradient damage propagation. To achieve this goal, we first adopt a Temporal Convolutional Network (TCN) as the neural network of choice to capture the history-dependent evolution of the non-local strain in a coarsely meshed domain. The quality of the network predictions governs the computational performance of I-FENN, and therefore we perform an extended investigation aimed at enhancing them. We explore a data-driven vs. physics-informed TCN setup to arrive at an optimum network training, evaluating the network based on a coherent set of relevant performance metrics. We address the crucial issue of training a physics-informed network with input data that span vastly different length scales by proposing a systematic way of input normalization and output un-normalization. We then integrate the trained TCN within the nonlinear iterative FEM solver and apply I-FENN to simulate the damage propagation analysis. I-FENN is always applied in mesh idealizations different from the one used for the TCN training, showcasing the framework’s ability to be used at progressively refined mesh resolutions. We illustrate several cases that I-FENN completes the simulation using either a modified or a full Newton–Raphson scheme, and we showcase its computational savings compared to both the classical monolithic and staggered FEM solvers. We underline that we satisfy very strict convergence criteria for every increment across the entire simulation, providing clear evidence of the robustness and accuracy of I-FENN. All the code and data used in this work will be made publicly available upon publication of the article.

A Numerical Method for Unstable Propagation of Damage in Fiber-Reinforced Plastics with an Implicit Static FE Solver

Finite element analyses of the propagation of damage such as fiber compressive failure and delamination have greatly contributed to the understanding of failure mechanisms of fiber-reinforced plastics owing to extensive studies on methodologies using Continuum Damage Mechanics and Fracture Mechanics. Problems without the need for consideration of inertia, such as Double-Cantilever Beam tests, are usually solved by implicit FE solvers, and explicit FE solvers are appropriate for phenomena that progress with very high velocity such as impact problems. However, quasi-static problems with unstable damage propagation observed in experiments such as Open-Hole Compression tests are still not easy to solve for both types of solvers. We propose a method to enable the static FE solver to solve problems with unstable propagation of damage. In the present method, an additional process of convergence checks on the averaged energy release rate of damaged elements is incorporated in a conventional Newton–Raphson scheme. The feasibility of the present method was validated by two numerical examples consisting of analyses of Open-Hole Compression tests and Double-Cantilever Beam tests. The results of the analyses of OHC tests showed that the present method was applicable to problems with unstable damage propagation. In addition, the results from the analyses of DCB tests with the present method indicated that mesh density and loading history are not significantly influential to the solution.

What is the Initiating Reaction for the Lipid Radical Chain Reaction System That Can Induce Ferroptotic Cell Death at the Lower Oxygen Content?

The neural cell death in cerebral infarction is suggested to be ferroptosis-like cell death, involving the participation of 15-lipoxygenase (15-LOx). Ferroptosis is induced by lipid radical species generated through the one-electron reduction of lipid hydroperoxides, and it has been shown to propagate intracellularly and intercellularly. At lower oxygen concentration, it appeared that both regiospecificity and stereospecificity of conjugated diene moiety in lipoxygenase-catalysed lipid hydroperoxidation are drastically lost. As a result, in the reaction with linoleic acid, the linoleate 9-peroxyl radical-ferrous lipoxygenase complex dissolves into the linoleate 9-peroxyl radical and ferrous 15-lipoxygenase. Subsequently, the ferrous 15-lipoxygenase then undergoes one-electron reduction of 13-hydroperoxy octadecadienoic acid, generating an alkoxyl radical (pseudoperoxidase reaction). A part of the produced lipid alkoxyl radicals undergoes cleavage of C-C bonds, liberating small molecular hydrocarbon radicals. Particularly, in ω-3 polyunsaturated fatty acids, which are abundant in the vascular and nervous systems, the liberation of small molecular hydrocarbon radicals was more pronounced compared to ω-6 polyunsaturated fatty acids. The involvement of these small molecular hydrocarbon radicals in the propagation of membrane lipid damage is suggested.

Load-Carrying Capacity of Thin-Walled Composite Columns with Rectangular Cross-Section under Axial Compression.

The aim of the current study was to determine the load capacity of composite columns subjected to axial compressive load. The subjects of the study were two types of columns with a rectangular cross-section, with different edge lengths. The tested columns had a closed cross-section. Four different fiber arrangements were analyzed for both cross-sections studied. The research was realized using interdisciplinary methods to determine the mechanism of damage to the composite material, with particular emphasis on damage initiation and propagation. Experimental tests were realized on a testing machine, the analysis was carried out with an acoustic emission system, and image analysis using visual assessment system of deflections of the walls of the structure. In addition, a number of numerical analyses were realized based on advanced modeling techniques for fiber-reinforced composites. A comparative analysis of both quantitative and qualitative results is presented for both analyses. The innovation of the presented research lies in the development of a custom method for modeling structures made of composite material with special emphasis on the failure phase. This will allow to accurately reflect the modeling of thin-walled structures with closed cross-section subjected to loading in a complex stress state.

The effect of fibre orientation on fatigue crack propagation in CFRP: Finite fracture mechanics modelling for open-hole configuration

The demand to capture translaminar crack growth under fatigue loading scenarios led this work contribution to carry out the Finite Fracture Mechanics (FFM) method in fatigue damage growth and the application of the Paris model to generate the translaminar damage propagation prediction. The purpose of this study is to analyse the effect of fibre orientation on translaminar crack propagation rate using the FFM model, which includes cycle damage increment estimation and fractographic analysis. The results confirm the feasibility of FFM in predicting crack growth and estimating life under cyclic loading. However, C-scan analysis and the revised crack propagation direction are critical in determining the realistic crack length, considering adhesive failure along the fibre direction. Additionally, this work contribution is also related to the application of the Paris model (based on dL/dN vs ΔK) to generate the translaminar damage propagation prediction model. The most dominant damage mechanism was the splitting pattern, which changed the aspect of failure for each laminate architecture as a function of fibre orientation. The laminate with multidirectional fibre orientation exhibited higher resistance to translaminar crack propagation due to the growth of splitting and delamination in multiple directions. The fibre orientation changed the propagation path, which influenced the fracture toughness and crack propagation rate behaviour.

Micromechanics in Mg alloys: Role of hard Al2RE precipitates

The influence of hard Al2RE phases (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) on the overall and local deformation as well as damage mechanism of Mg alloys has been studied by using a crystal plasticity model based on dislocation density with a brittle damage criterion. Microcracks that lead to swift damage initiation and propagation throughout the matrix have been predicted. It has been found that the hard Al2RE with higher elastic modulus enhances the damage resistance of the Mg matrix, which was confirmed by fracture SEM/EDS characterizations and phase-field damage simulation. This discovery provides valuable insights for designing Mg alloys with both high stiffness and enhanced damage resistance.

Mesoscopic mechanical study on quasi-static compression of coral aggregate seawater concrete after high temperature exposure

Coral aggregate seawater concrete (CASC) is a pioneering concrete made by blending and curing coral reefs, coral sands, cement, mineral admixtures, chemical additives, and seawater. The investigation of its mechanical properties is important for both theoretical and engineering purposes. This paper aims to investigate the quasi-static mechanical properties of CASC after exposure to high temperatures using a combined approach of experiments and numerical simulations. The simulation uses LS-DYNA software and a three-dimensional random aggregate mesoscopic model to analyze the process of concrete damage and crack propagation. Various mechanical parameters such as peak stress, peak strain, and compressive strength after exposure to different temperatures are calculated. The simulation results show that under quasi-static uniaxial compressive loading, microcracks initiate within the mortar and interfacial transition zone (ITZ) of CASC. These cracks then propagate through the coarse aggregates, leading to aggregate failure and the disintegration of the concrete structure. The macroscopic damage traits of CASC specimens reveal concentrated damage in the central region. As the temperature increases during heat treatment, the severity of damage to CASC specimens also increases. However, as the strength grade increases, the damage condition of CASC tends to improve.

Degradation analysis of dynamic properties for plain concrete structures under mixed-mode fracture conditions via an improved cohesive crack approach

The present work investigates the crack-induced degradation of the dynamic characteristics in plain concrete elements subjected to mixed-mode fracture conditions. Specifically, a discrete fracture model, based on an inter-element cohesive approach, has been improved and implemented into a 2D finite element framework to evaluate the progressive variation of the static and dynamic properties as the damage level increases. The obtained numerical results highlight the effectiveness of the proposed model in determining the load-carrying capacity and the degradation of natural vibration frequencies during damage propagation, demonstrating its applicability in the framework of structural health monitoring.

A phase field-immersed boundary-lattice Boltzmann coupling method for fluid-structure interaction analysis

Fluid-structure interaction (FSI) is critical in numerous engineering and scientific applications. This paper presents a numerical model for FSI simulations that integrates the lattice Boltzmann method (LBM) for fluid dynamics, the phase field method (PFM) for structural deformation and fracture, and the immersed boundary method (IBM) for fluid-solid coupling. The fluid employs an explicit time integration scheme with a smaller time step than the solid, which uses an implicit time integration scheme, satisfying the CFL condition. During the synchronization of fluid-solid interaction information, a multi-substep strategy is applied. The IBM is implemented using the iterative velocity method for boundary treatment. This approach facilitates the information transfer between domains with different time steps, enhancing the coupling accuracy through iterative computation. The effectiveness of the improved immersed boundary-lattice Boltzmann (IB-LBM) has been verified by the classical cylindrical flow case, which effectively prevents the particle penetration phenomenon and improves the calculation accuracy. The phase field-immersed boundary-lattice Boltzmann method (PF-IB-LBM) is subsequently deployed to simulate the deformation of an aluminum plate under hydrostatic pressure and the aftermath of a dam-break impact on an elastic plate. Verification of the coupling method substantiates its feasibility and efficacy. In addition, the proposed PF-IB-LBM is implemented to simulate the entire process of structural deformation and failure in response to fluid dynamics, which further confirms its capability to predict discontinuous mechanical behaviors such as damage and crack propagation under intricate fluid flows. The results emphasize the flexibility and efficiency of the proposed approach, providing a robust framework for solving more complex scenarios in engineering FSI problems.

Damage Monitoring of Regularly Arrayed Short-Fiber-Reinforced Composite Laminates under Tensile Load Based on Acoustic Emission Technology.

Carbon-fiber-reinforced polymer (CFRP) composites are widely used in lightweight structures because of their high specific strength, specific modulus, and low coefficient of thermal expansion. Additionally, the unidirectionally arrayed chopped strand (UACS) laminates have excellent mechanical properties and flowability, making them suitable for fabricating structures with complex geometry. In this paper, the damage process of UACS quasi-isotropic laminates under tensile load was tested using acoustic emission detection technology. The mechanical properties and damage failure mechanism of UACS laminates were studied combined with finite element calculation. By comparing and analyzing the characteristic parameters of acoustic emission signals such as amplitude, relative energy, and impact event, it is found that acoustic emission behavior can accurately describe the damage evolution of specimens during loading. The results show that the high-amplitude signals representing fiber fracture in continuous fiber laminates are concentrated in the last 41%, while in UACS laminates they are concentrated in the last 30%. In UACS laminates, more of the damage is caused by matrix cracks and delamination with medium- and low-amplitude signals, which indicates that UACS laminates have a good suppression effect on damage propagation. The stress-strain curves obtained from finite element analysis agree well with the experiment results, showing the same damage sequence, which confirms that the model described in this research is reliable.

Analyzing the Sound of Materials: Application of Acoustic Emission Technique for Monitoring Material Behavior

During the last years, some concerns have arisen in relation to the outcome of mechanisms of failure in composite materials according to its mechanical behavior. Such interest resulted in the development of new complex structures in order to enhance its mechanical resistance and the controlling of damage processes. Nevertheless, it is imperative to understand the degree of mechanical performance that these materials can achieve when under external stresses. In this regard, applying Acoustic Emission (AE) technique is widely known as a very effective technology for identifying and monitoring damage progression on different kind of materials and structures providing valuable information. AE is a non-destructive technique (NDT) capable of detecting micro damage initiation and propagation along several types of failure modes such as reinforcement/matrix interfacial debonding, matrix cracking, delamination, fracture, etc. This paper examines applications of AE regarding to composite materials where fracture processes are generally more complex and data interpretation is correspondingly more difficult. Finally, in order to continuously improve the reliability of this technique, several researches have advanced its trustworthiness through innovations in AE technology. Some perspectives are discussed.

Localizing gradient damage model for anisotropic materials: Focusing on timber

This paper presents a new damage model for transversely isotropic materials, with special focus on timber. The model proposed in this study is formulated by employing the localized gradient form of continuum damage theory. The model accounts for anisotropic damage through two damage variables, delineating damage parallel and perpendicular to the grain, representing isotropic damage within the cross-sectional plane. The conditions assumed in this work pertain to loading scenarios that occur within the plane. An additional fourth-order tensor transformation is incorporated to facilitate the conversion between the global and local reference frames, allowing for arbitrary spatial orientations of the material matrix. In this work we concentrate on damage arising from tensile and shear stresses. The model is implemented as a consistent linearized coupled (monolithic) problem.The performance verification of the model relies on numerous numerical examples, incorporating experimental benchmark problems. The outcomes demonstrate that the suggested damage model adeptly captures both the initiation of failure and the propagation of damage.

Study of the Effect of NaOH Treatment on the Properties of GF/VER Composites Using AE Technique.

The purpose of this study is to use acoustic emission (AE) technology to explore the changes in the interface and mechanical properties of GF/VER composite materials after being treated with NaOH and to analyze the optimal modification conditions and damage propagation process. The results showed that the GF surface became rougher, and the number of reactive groups increased after treating the GF with a NaOH solution. This treatment enhanced the interfacial adhesion between the GF and VER, which increased the interfacial shear strength by 25.31% for monofilament draw specimens and 27.48% for fiber bundle draw specimens compared to those before the GF was modified. When the modification conditions were a NaOH solution concentration of 2 mol/L and a treatment time of 48 h, the flexural strength of the GF/VER composites reached a peak value of 346.72 MPa, which was enhanced by 20.96% compared with before the GF was modified. The process of damage fracture can be classified into six types: matrix cracking, interface debonding, fiber pullout, fiber relaxation, matrix delamination, and fiber breakage, and the frequency ranges of these failure mechanisms are 0~100 kHz, 100~250 kHz, 250~380 kHz, 380~450 kHz, 450~600 kHz, and 600 kHz and above, respectively. This paper elucidates the fracture process of GF/VER composites in three-point bending. It establishes the relationship between the AE signal and the interfacial and force properties of GF/VER composites, realizing the classification of the damage process and characterizing the mechanism. The frequency ranges of damage types and failure mechanisms found in this study offer important guidance for the design and improvement of composite materials. These results are of great significance for enhancing the interfacial properties of composites, assessing the damage and fracture behaviors, and implementing health monitoring.

Time-dependent damage development during creep in carbon woven-ply polyphenylene sulfide laminates above the glass transition temperature

In order to understand the coupling between time-dependent behaviours (viscoelasticity, viscoplasticity) and damage mechanisms within carbon woven-ply polyphenylene sulfide (C/PPS) thermoplastic composites subjected to creep loadings at T > Tg (Glass transition temperature), it is necessary to develop experimental protocols adapted to high temperature conditions. To this aim, the present study combines different complementary techniques (acoustic emission, edge replication, fractographic analysis, tomography) allowing in-situ analyses of the damage mechanisms that coexist and interact during the different phases of creep-type loadings. These techniques provide information to quantify and dissociate the different material behaviours (viscoelasticity, viscoplasticity, damage). Two main damage mechanisms are identified: intra-bundle cracking and inter-bundle cracking leading to extensive meta-delamination. Image analyses based on morphological operations allow the evaluation of the surface cracking density (intra- and inter-strand) from edge replicas. At macroscopic scale, the thermo-mechanical response is little influenced by the viscous behaviour of angle-ply C/PSS laminates though their thermo-mechanical behaviour is mainly driven by the PPS matrix. At micro and mesoscopic scales, the results clearly show the onset and propagation of time-dependent damage in C/PPS specimens. By implementing this protocol, the acoustic emission monitoring associated with the quantification of the cracking density proved to be relevant and complementary to study the coupling between viscous effects and damage within C/PPS laminates subjected to high temperature loading.

Efficient design of composite honeycomb sandwich panels under blast loading

Hybrid composite honeycomb sandwich structures (HCHSS) were employed due to high specific strength and stiffness and higher impact resistance property required for the aerospace and defence fields. The numerical modelling of the efficient HCHSS was developed for the core, front and back face plate using the C3D8R elements to determine the realistic failure behaviour for the honeycomb sandwich structure. The ConWep blast simulation loading was applied for the HCHSS. Advanced composite materials were used for the blast analysis of the HCHSS (carbon/epoxy, graphite/epoxy, woven basalt fibres/polypropylene and woven Kevlar fibres/polypropylene). The damage initiation and damage propagation based progressive damage modelling was developed and implemented in the VUMAT code for composite materials to determine the actual failure behaviour of the HCHSS. The face sheets used in this model were of a stainless-steel alloy AL-6XN. The sandwich structure was subjected to blast loads of 1, 2 and 3 kg of TNT and their performance was compared w.r.t both front and back-face deflection. The effectiveness of sandwich panels was further examined by altering the thickness of the core. Fibre-metal laminates (FML) were used in place of the steel face sheets in the panel in order to minimise its mass, and a thorough analysis of the panel’s mass in relation to its peak deflection was carried out. Upon analysing the results, it was noted that the panel with the basalt fibre reinforced polymer (BFRP) core gave the best results compared to other composite materials. For a blast load of 3 kg TNT, the peak back face deflection (PBFD) of HCHSS with a BFRP core decreased by 10.64%, 7.61% and 4.75%, respectively, compared to panels with CFRP, GFRP, and KFRP cores. The peak deflection of the panel decreased as the BFRP core thickness increased. The energy absorption capacity of the panel also increased with increasing thickness. Additionally, it was found that panels with BFRP cores and KFRP-steel laminate face sheets provided the optimum balance of strong blast resistant performance and light weight. Compared to the metallic (steel) sandwich panel, the mass of the sandwich panel with KFRP-steel laminate face sheets and BFRP core was reduced by 33%, but at the same time, its PBFD increased by almost 50%.

Fracture mechanism of carbon fiber-reinforced thermoplastic composite laminates under compression after impact

Thermoplastic carbon fiber-reinforced plastics (CFRPs) are increasingly utilized in the aerospace industry owing to their beneficial properties and enhanced formability relative to thermoset CFRPs. Despite the extensive use of these materials, studies focusing on compression after impact (CAI) tests with impact energies exceeding 20 J for thermoplastic CFRPs remain scarce. This study examines CAI tests on quasi-isotropic laminates of thermoplastic CFRP, subjected to a low-velocity impact energy of 27.04 J. For comparison, quasi-isotropic laminates of thermoset CFRP were subjected to a low-velocity impact energy of 36.5 J. These tests reveal that the CAI strength of both materials is comparable, notwithstanding the lower fiber volume fraction in the thermoplastic CFRP. Further, this research incorporates a finite element (FE) analysis to investigate the damage mechanisms in thermoplastic CFRP. The FE model, integrating interlaminar damage observed during the impact tests, accurately predicted the relationship between compressive stress and strain, correlating closely with the experimental outcomes. It was observed that both interlaminar and intralaminar damage propagation were constrained until the point of maximum compressive stress. Prior to reaching this maximum, a region of elevated compressive stress in the fiber direction was noted in the 0° layer near the non-impacted side. These findings indicate that the compressive stress in the fiber direction in the 0° layer adjacent to the non-impacted side is pivotal in dictating the final failure, which determines the CAI strength of thermoplastic CFRP laminates.