Matrix Failure Research Articles

Lap-shear strength and fracture behavior of CFRP/3D-printed titanium alloy adhesive joint prepared by hot-press-aided co-bonding

Multimaterial structures comprising carbon fiber reinforced plastics (CFRPs) and titanium alloys can be widely utilized in the aerospace and automotive industries to achieve optimal weight reduction and reliable structures. In this study, three-dimensional-printed titanium (3DP-Ti) adherends prepared using selective laser melting were co-bonded with woven-fabric carbon fiber reinforced phenolic matrix composite by hot pressing. Upon controlling the scanning speed and path, the 3DP-Ti adherends were prepared with various porosities and macrostructures on their surfaces, and the influences of these surface structures on the lap-shear strengths and fracture morphologies of the 3DP-Ti adherends were investigated. The lap-shear tests of the lap-shear joints with flat 3DP-Ti and pyramidal-macrostructured 3DP-Ti displayed the cohesive failure of the phenolic resin matrix. In contrast, the specimen with cylindrical macrostructure exhibited CFRP fracture and delivered the highest bond strength of 20.6 MPa, which was 18–64% greater than the strength of the lap-shear joint with the conventional Ti alloy plate and 3DP-Ti adherends with flat surface and pyramidal macrostructure. The major possible mechanisms behind the failure mode transition and the highest bond strength included the mechanical interlocking between the cylindrical macrostructure and CFRP.

Failure of a hollow-fibre shower filter device to prevent exposure of patients to Pseudomonas aeruginosa

Pseudomonas aeruginosa in hospital water is a risk for invasive infection. Point-of-use (POU) filters are used to reduce patient exposure to the organism, and hollow-fibre filters are becoming more popular. However, retrograde colonization of the filter mechanism may contaminate the effluent. To assess the efficacy of POU filter head (polysulfone; hollow-fibre matrix) shower filters in preventing the exposure of high-risk patient groups to P.aeruginosa. Pre-flush (opening the outlet and collecting the first 100mL of water) samples were analysed to measure P.aeruginosa contamination from 25 shower outlets (∼21% of all showers on the six wards), with and without a hollow-fibre filter. P.aeruginosa was measured in a subset of outlets harbouring P.aeruginosa (sampling period 19th August 2019 to 10th January 2020). Water from all 25 showers was heavily colonized [>300colony-forming units (cfu)/mL] with P.aeruginosa at the showerhead. P.aeruginosa was found in 32% (8/25) of post-filter shower water effluent samples with a geometric mean of 4x106cfu/mL (N=4) (6.8x104-2x108). Filters were sampled at 15-150 days of use (median 15 days), with 26% (6/23) of filter units becoming colonized before the expiry date. POU filter showerhead units may not be effective in preventing exposure of vulnerable patients to P.aeruginosa in hospital water due to retrograde contamination (external contamination of the showerhead passed back to the filter cartridge itself) or failure of the hollow-fibre filter matrix. Reliance should not be placed on the use of hollow-fibre filters to protect patients from exposure to P.aeruginosa without repeated microbiological monitoring.

A three-dimensional micromechanical model for simulating ply crack formation in laminates under in-plane tensile loading

Micromechanical models were established to simulate ply cracking in [0/90/0] laminates under tension. A new user-defined material model was developed within a finite element framework to capture inelastic deformation of the matrix and local cavitation-induced and ductile failure. A damage model was used to capture corresponding post-peak behaviour. Representative volume elements (RVEs) of laminates were generated, where the fiber and matrix constituents were explicitly represented in the 90° ply. The experimentally verified simulations revealed local matrix failure onset was governed by brittle cavitation, while subsequent microcracking was influenced by local ductile failure. The model accurately captured the delay in first full ply crack formation for laminates with thinner plies. The role of thermal residual stress, ply constraints, and fiber volume fraction on ply crack formation were investigated. The associated effective energy release rate was predicted and can be used for predicting ply crack multiplication in meso- or macro-scale models.

Experimental and numerical damage analysis of low-velocity drop weight impact of polyethylene self-reinforced composite laminates for transportation applications

This study covers a low-velocity impact property analysis of Polyethylene self-reinforced composites (PET-HDPE/HDPE SRC)through experimental and numerical methods emphasizing the influence of interfacial properties. Self-reinforcing a polymer material has gained a lot of attention due to maximum exploration of their light density characteristics with better chemical compatibility and interfacial adhesion of matrix and reinforcement, resulting in higher fuel efficiency. Reusability of self-reinforced thermoplastic composites even without separating their constituent materials has been observed to be aiding the circular economy strategies. The study aimed to analyze the peak load characteristics, energy-absorbing characteristics, and damage response of these materials processed through the hot compaction technique and subjected to a drop mass impact test. Fractographic visual inspection, optical macrographs, Scanning electron microscopy analysis, and through transmission ultrasonic C-scan were employed to study the damage evolution and failure mechanisms under the low-velocity impact. Three levels of impact energy were included in the test matrix, and initiation of the damage, nature of the matrix, interface debonding, matrix and fibre failures could be identified through the inspection of the damage cross-section at the impact eye. A finite element model developed through commercial FEA packages (Abaqus) was utilized for the complex mechanisms of damage and failure. Weak interfacial adhesion due to the self-lubricating nature of the polyethylene fibre surface contributed to the fibre pull out during the drop weight impact. A qualitative analysis and correlation of the nature of surface damage and internal damage were also studied, which are the factors that are necessary for the development of cargo containers and marine/aerospace ultralight luggage applications.

Analysis of multiple impact tests’ damage to three-dimensional four-directional braided composites

Abstract This article was designed with a plurality of impact tests of three-dimensional four-directional braided composites, and the impact response of specimen impacted by a circular punch was studied. Ultrasonic C-scanning was used to detect the internal damage area to study the damage propagation process under multiple impact loads. The finite-element software ABAQUS was used to model the meso-structure of three-dimensional four-directional braided composites. Based on material characteristics, the three-dimensional Hashin damage criterion was used for the fiber bundle, and the maximum stress criterion was used for the matrix to judge the material damage. Combined with test and simulation results, the failure mode and damage evolution process of the specimen under multiple impact loads were studied. The results showed that the impact resistance of the three-dimensional woven composite material is affected by the braided angle. The larger the braided angle of the specimen, the better the impact resistance. The damaged area of the large braided angle material expanded to the periphery, and the damaged area of the small braided angle material was primarily developed in the longitudinal direction. The failure modes of the specimen during the impact process were primarily a longitudinal tensile failure of fiber bundles, transverse tensile failure and transverse compression failure of fiber bundles and matrix.

Numerical Assessment on the Fatigue Behavior of Composite Open‐Hole Tensile Specimens

AbstractThis paper deals with the fatigue failure of composite coupon characterized by circular hole and subjected to tensile cyclic loading conditions. A limited sensitivity analysis has been performed to study the onset and propagation of intralaminar damages, in terms of fibers and matrix failure. The residual strength material properties degradation model, proposed by Shokrieh and Lessard, has been implemented in the FEM code ANSYS Mechanical and employed to study the damages induced by stress concentrations and assess the effects of the stacking sequence and the geometrical parameters on the fatigue damage.

Study on Thermo-oxidative Aging Mechanism of Air Spring Rubber Cord Composites

To study the thermo-oxidative aging mechanism of air spring rubber cord composites, observe the changes in surface micro-morphology, study the thermo-oxidative aging mechanism of air spring rubber cord composites, observe the changes in surface micro-morphology, infrared spectrum, quality, hardness, and mechanical properties during the process of thermo-oxidative aging, and analyze the aging mechanism. The results show that the micro-morphological changes of the rubber surface of the rubber cord composites go through two stages: at 0-72 h, the rubber surface The results show that the micro-morphological changes of the rubber surface of the rubber cord composites go through two stages: at 0-72 h, the rubber surface develops from no cracks to a large number of cracks; at 96-336 h, the rubber surface changes from a cracked state. The size of the crack on the rubber surface affects the rate of change of IRHD hardness. The larger the crack, the greater the hardness growth rate, otherwise the opposite. In the aging process, the rubber is in a state of dynamic development. The increase of cross-linking density causes changes in microscopic The increase of cross-linking density causes changes in microscopic morphology and accessible volume, which affects the IRHD hardness. The aging mechanism is more complicated. Material failure is dominated by the failure of the rubber matrix.

Three-dimensional failure behaviour of L-shaped laminated composite with wrinkles and defects

In this paper, three-dimension failure behaviour of L-shaped composite beam with manufacturing defects was studied under four-point bending test condition. First, X-ray computed tomography scan was performed for L-shape laminated composite beam specimen to detect manufacturing defects such as voids, pre-delamination, and wrinkles or ply waviness. The scan images were then converted to three-dimensional volumetric entity through image processing, from which finite element mesh was generated with the detected defects directly incorporated. Next, three-dimensional progressive failure analysis was performed for the finite element model of the L-shaped laminate composite simulating four-point bending test condition with delamination and matrix failure in 90 degree plies accounted for by using cohesive zone modelling. The predicted maximum load was well matched to that obtained by tests validating the analysis modeling. Then a series of parametric studies were performed to investigate the effect of defect size and location on the failure load and delamination propagation pattern. It was found that the maximum load reduction was the largest when the pre-defect was located at the center of the symmetrical portion of the L-beam. In addition, the maximum load and delamination development behavior varied significantly depending on the interlayer and in-plane position of the pre-defect.

Low-velocity impact studies on Kevlar/Epoxy composites reinforced with carboxyl functionalized Graphene

The addition of nanoparticles as fillers improves the properties of polymer matrix composites. In this work functionalized Graphene Platelets are added to Kevlar-reinforced epoxy composites and their mechanical properties such as tensile, short beam strength and low-velocity ballistic response are evaluated. For comparison, composites prepared with 0.25, 0.5, and 0.75 wt% filler addition was compared with the condition of no filler addition. The fractured samples were examined to understand the failure mechanisms involved. The results indicated that the sample with 0.5 wt% had superior tensile, shear and energy-absorbing characteristics. A lower reinforcement weight percentage (0.25%) was unable to effectively transfer the loads while higher reinforcement percentage (0.75%) showed premature failures due to agglomeration. At the optimum reinforcement, a sufficient amount of nano-fillers passes through the matrix and the functionalization assists in good fiber–matrix adhesion through surface bonding. This leads to high interfacial properties giving high resistance to impact motion. In addition, the nanoparticles in the matrix phase help in matrix toughening giving resistance to cracking. This is evident from the micro and macroscopic fracture images which show a high fiber interaction and the least matrix failure. The lower damage area and the higher fiber pullouts also indicate the effectiveness of 0.5 wt% reinforcement.

A 3-D numerical modeling for prediction of mixed failure characteristics in composite single lap joints with hybrid adhesive layer

In general, the fracture of composite single lap joints (SLJ) may be induced by various combination of individual failure types such as adhesive and adherend failure. In this work, a 3-D numerical method is established in order to consider the mixed failure characteristics of the cohesive failure in adhesive layer, the delamination failure and the failure of fiber and matrix in composite adherend. A 3-D mixed-mode continuum damage model is applied for the simulation of cohesive failure in adhesive layer. The delamination failure is predicted by the cohesive zone model (CZM) at interlayer of plies adjacent to the adhesive layer, and orthotropic elastic model and Hashin criterion is used for the mechanical response of fiber and matrix. Some examples are considered in order to validate the current numerical method for composite SLJs with single and functionally graded adhesive layer. Also, these examples show the coupled failure characteristics details in the composite SLJs with various stacking sequences.

Multi-scale study on interfacial bond failure between normal concrete (NC) and ultra-high performance concrete (UHPC)

It is a promising way to strengthen and repair the damaged normal concrete (NC) structure with ultra-high performance concrete (UHPC), and the interfacial performance between NC and UHPC is a critical issue. This paper aims to reveal the debonding failure performance between UHPC (repair material) and NC (substrate material) under tensile loading and shear loading. A multi-scale analysis method is established to simulate the mechanical behavior of the NC-UHPC interface, considering the complex interface geometry on the meso-scale. The failure of NC matrix is described by the elastic-plastic damage model in form of coupled gradient-enhanced damage evolution, the interface is represented by the cohesive zone model (CZM), and the UHPC is characterized by the second-order mean-field homogenization (MFH) method. After extracting the roughness characteristic parameters of the tested interfaces, the representative volume element (RVE) corresponding to the roughness is established, the load transfer and the debonding failure behavior are investigated, and the effective traction-separation law (TSL) is obtained. Finally, the tensile and the shear separation mechanisms of the NC-UHPC interface are revealed, and the effects of the roughness and strength of the interface on the macro shear and tensile strength are evaluated. Both the interface roughness and the substrate concrete strength have positive effects on the mechanical properties of the interface.

Extracellular biomolecular free radical formation during injury

ObjectiveDetermine if oxidative damage increases in articular cartilage as a result of injury and matrix failure and whether modulation of the local redox environment influences this damage.Osteoarthritis is an age associated disease with no current disease modifying approaches available. Mechanisms of cartilage damage in vitro suggest tissue free radical production could be critical to early degeneration, but these mechanisms have not been described in intact tissue. To assess free radical production as a result of traumatic injury, we measured biomolecular free radical generation via immuno-spin trapping (IST) of protein/proteoglycan/lipid free radicals after a 2 J/cm2 impact to swine articular cartilage explants. This technique allows visualization of free radical formation upon a wide variety of molecules using formalin-fixed, paraffin-embedded approaches. Scoring of extracellular staining by trained, blinded scorers demonstrated significant increases with impact injury, particularly at sites of cartilage cracking. Increases remain in the absence of live chondrocytes but are diminished; thus, they appear to be a cell-dependent and -independent feature of injury. We then modulated the extracellular environment with a pulse of heparin to demonstrate the responsiveness of the IST signal to changes in cartilage biology. Addition of heparin caused a distinct change in the distribution of protein/lipid free radicals at sites of failure alongside a variety of pertinent redox changes related to osteoarthritis. This study directly confirms the production of biomolecular free radicals from articular trauma, providing a rigorous characterization of their formation by injury.

Delamination buckling of a laminated composite shell panel using cohesive zone modelling

Abstract Laminated composite shell panels take part in several engineering structures. Due to their complex nature, failure modes in composites are highly dependent on the geometry, direction of loading and orientation of the fibers. However, the design of composite parts is still a delicate task because of these fiber failure modes, which includes matrix failure modes or other so-called interlaminar interface failure such as delamination, that corresponds to the separation of adjacent layers of the laminate as a consequence of the weakening of interface layer between them. In this work, impact-induced delamination represented as a circular single delamination is investigated, as it can reduce greatly the structural integrity without getting detected. Furthermore, attention is focused on its effect upon the post-buckling response and the compressive strength of a composite panel. The delamination buckling was modelled using the cohesive element technique under Abaqus software, in order to predict delamination growth and damage propagation while observing their effects on the critical buckling load.

A failure model for the analysis of cross-ply Non-Crimp Fabric (NCF) composites under in-plane loading: Experimental & numerical study

In the present work, a set of physically-based failure criteria are applied to a cross-ply Non-Crimp Fabric (NCF) composite. The proposed criteria account for the stitch reinforcement and the induced in- and out-of-plane fibre misalignment. A distinction between matrix and fibre failures in tension and compression is introduced, while the in-plane shear non-linear response is directly incorporated to the model as well. The constitutive model is associated with an energy-based damage mechanics method, which consists of five in-plane damage variables per layer level. Within this study, a novel approach to obtain the effective longitudinal stiffness of the composite, as a function of the in- and out-of-plane misalignment, is described. An experimental study characterises the internal structure and the mechanical response of the composite in tension, compression, in-plane shear and Mode I & II interlaminar fractures. In this paper, validation examples for the failure criteria, implemented in Abaqus/Explicit as a VUMAT subroutine, are presented. Tensile, in-plane shear and compressive responses are modelled at a coupon level with continuum shell elements and correlate well with the experimental data. Fibre misalignment, mainly out-of-plane, had a strong influence on the compressive modulus and strength of the composite.

Energy-Based Approach for Studying Fibre-Reinforced Concrete Subjected to Impact Loading

In general, concrete behaves differently when the load is applied at a different speed, i.e. concrete’s mechanical parameters are strain-rate sensitive. There is a need for an experimental method that should meet several criteria such as removal or accurate description of boundary conditions, simplicity, affordability and reproducibility of the experiments. The main goal of this study is the design, assembly and optimisation of the experimental apparatus and procedure to carry out the impact testing. Using this apparatus, an experimental study was conducted. The main aspect of this experimental method is the elimination of rigid supports, which could negatively affect the obtained results. Measured data are acquired using specifically designed measuring devices and analysed using a computer script. Four concrete mixtures were examined ranging from high-strength concrete to ultra high-performance concrete. Quasi-static experiments were also carried out for comparison. A clear difference in quasi-static and impact performance of the materials was observed. Different trends for different compositions of the tested concrete specimens were apparent. Higher fibre content specimens generally showed higher strain-rate sensitivity and the highest strain-rate sensitivity was observed in combination with the two strongest concrete matrices. This was most probably related to fibre anchoring, as complete fibre pullout before premature matrix failure was critical. The newly designed measuring apparatus greatly improves the speed and precision of conducting the impact experiments. It can be successfully used for a relatively quick and simple comparison of materials when designing concretes for withstanding elevated strain-rate loading.

Molecular dynamics simulations on the mechanical properties of gyroidal bicontinuous Cu/Ni nanocomposites

Metallic nanocomposites with high strength and extensive plasticity have attracted intensive scientific interest. Herein, molecular dynamics simulations are performed to explore the mechanical responses of bicontinuous Cu/Ni nanocomposites with a representative isotropic gyroidal architecture. The effect of volume fraction of constitute phase on the mechanical properties is discussed. Tensile results show that Cu/Ni interface acts as a barrier to dislocation propagation, causing the dislocation activity of nanocomposite occurring in the individual matrixes. The dislocation activity is more pronounced in the soft Cu phase and the crack propagates in Cu matrix rather than along the Cu/Ni interface, resulting in the breakage of material occurring in Cu phase for all nanocomposites. After the failure of Cu matrix, the remaining Ni matrix can still bear the applied load alone. The modulus and strength of Cu/Ni nanocomposites are higher than those of individual constitute phases and even the sum of two matrixes. Similar to nanoporous materials, Cu/Ni nanocomposites obey the power relations between mechanical properties and volume fraction. The research further gives an atomic insight into the mechanical responses and associated deformation mechanisms of metallic bicontinuous nanocomposites.

A simplified reinforcement and fracture mechanism analysis model of epoxy nanocomposites based on finite element simulation

Understanding the reinforcement and fracture mechanism of polymer matrix nanocomposites is crucial for the design of high-performance composite materials. By taking boron nitride@boronate polymer core-shell nanoparticles modified epoxy resin nanocomposites (EPNCs) as an example, a reinforcement and fracture mechanism analysis model of nanocomposites was established through the combination of experiments and simulations. Instead of the traditional programming method by using the external language, a new modeling method was introduced with the help of Digimat. The results indicated that the interface force between (within) EP matrix and nanoparticles, the shell thickness and nanoparticle content play important roles in the reinforcement and fracture of EPNCs. The bending strength increases with the raising of particle content, but decreases with the increasing of shell thickness. The simulated results were consistent with the experiments. The interface force evolves according to the order of interfaces within particles and their shell > matrix-shell > matrix interior. A proper interfacial force can make interfacial debonding and matrix failure occur at the same time, thus improving both the strength and toughness of nanocomposites. This model construction will provide theoretical guidance for nanocomposites design and the clarification of reinforcement mechanism. • Cross-examination of analytical, numerical and experimental results is conducted. • Appropriate interface, thin shell and particle content play important roles in composites reinforcement mechanism. • Finite element evaluation of core-shell nanoparticles reinforced epoxy resin composites wais established.

Explicit Analysis of Nonuniform Irradiation Swelling Pressure Exerting on Dispersion Fuel Matrix Based on the Equivalent Inclusion Method.

Under irradiation, dispersion nuclear fuel meat consists of a three-phase composite of fuel particles surrounded by an interaction layer dispersed within a metal matrix. Nonuniform swelling pressures are exerted on the matrix, generated by irradiation swelling of the fuel particles. As these are considerable, they can cause matrix failure, but they are difficult to calculate. In this paper, taking into account thermal expansion, nonuniform fission pores and the interaction layer, nonuniform irradiation swelling pressure has been formulated, based on the equivalent inclusion method. By means of doubly equivalent transformations, a porous fuel particle, surrounded by an interaction layer, which is under irradiation, can be simplified as a homogeneous particle with the eigenstrain. With the aid of Green’s function, nonuniform irradiation swelling pressure can be numerically analyzed. The simulation results of swelling pressures are in good agreement with numerical calculations. Furthermore, several simplified examples have been given to investigate the factors of influence and the impact mechanisms. Conclusions are drawn that nonuniform irradiation swelling pressure can be analyzed numerically and adopted to explore matrix failure. It is identified that the number and locations of fission pores inside a fuel particle are key factors for nonuniformity of swelling pressures. The volatility of swelling pressures is aggravated by burnup, while the average values of swelling pressures are intensely affected by temperature. This work provides a perspective to investigate the strength and integrity of dispersion fuel meat under high burnup.

A novel approach to consider triaxial tensile stresses within the framework of a failure criterion

AbstractFor use in micromechanical simulations of continuous fiber reinforced polymers, a more general form of the paraboloid failure criterion by Stassi‐D'Alia for matrix failure was developed with explicit consideration of the hydrostatic tension strength. Regarding polymers, limits for hydrostatic tensile strength based on isotropic linear elasticity could be derived. The comparison of the newly developed extended paraboloid criterion with experimental data for yielding as well as for material separation (fracture) shows good agreement.

Identification of fracture damage characteristics in ultra-high performance cement-based composite using digital image correlation and acoustic emission techniques

The study of fracture mechanism and damage of ultra-high performance fiber reinforced cement-based composite (UHPFRCC) is of great significance for material performance evaluation and nondestructive structural health monitoring. In this paper, three-point bending fracture tests of UHPFRCC with fiber content of 1% and 2% were carried out, and the digital image correlation (DIC) and acoustic emission (AE) technique were used to monitor the fracture simultaneously. The microcrack area of UHPFRCC1 (UHPFRCC with 1% fiber content) decreases gradually with the loading process, and the microcrack area of UHPFRCC2 (UHPFRCC with 2% fiber content) increases first and then decreases with the loading process. The macrocrack area of UHPFRCC1 and UHPFRCC2 increases gradually with the same growth trend. The matrix failure and fiber/matrix debonding behavior of UHPFRCC were identified effectively based on the unsupervised k-means clustering method, and the fiber/matrix debonding behavior was obvious when the AE amplitude was greater than 60 dB. Meanwhile, the clustering results are also verified by the evolution of FPZ length. Finally, an efficient identification model of UHPFRCC matrix failure and fiber/matrix debonding behavior based on supervised KNN algorithm is proposed, which provides theoretical support for nondestructive structural health monitoring in practical engineering.