Damage Evolution In Composites Research Articles

On the experimental determination and prediction of damage evolution in composites via cyclic testing

This study introduces a novel approach to obtaining and predicting damage evolution laws using quasi-static cyclic testing within the framework of continuum damage mechanics. To achieve this, a comprehensive set of characterization and parameter identification tests was performed. Carbon-epoxy specimens were manufactured using the filament-winding technique, and these laminates were tested using a universal testing machine. Digital image correlation was employed in all experiments to capture strain fields, and an alternative method utilizing the combined loading compression device is presented to obtain mechanical properties. Once the material was characterized, cyclic tests were conducted, including [Formula: see text], [Formula: see text], and [Formula: see text] tensile tests, and shear v-notch tests. These aim to determine damage evolution laws for both conditions, pure and coupled stress states. From these tests, values for damage onset and threshold were obtained and used to define four new parameters. These parameters permit the estimation of degradation relationships for any arbitrary orientation without requiring additional tests. This approach was tested as the proof-of-concept within the positive range of transverse tension and in-plane shear stress domain. The obtained results are promising, justifying its extension to other failure mechanisms. While acknowledging its limitations, this new approach holds potential for implementation in the analysis of progressive failure in fiber-reinforced composite materials, possibly in conjunction with established failure criteria and computational tools, mainly in the finite element method domain.

Open-hole fatigue testing of UD-GFRP composite laminates containing aligned CNTs using infrared thermography

The present study aims to characterize the open-hole fatigue (OHF) behavior of unidirectional glass fiber-reinforced polymer matrix (UD-GFRP) epoxy composites containing aligned multi-walled carbon nanotubes (MW-CNTs) locally reinforcing the composite in the vicinity of the hole. The performance of these multi-scale composites has been compared with that of composites containing randomly oriented MW-CNTs around the hole. UD-GFRP containing neat epoxy (without MW-CNTs) as a matrix were the control samples in the study. Infrared thermography has been used to investigate the damage evolution in composites during the OHF tests. MW-CNTs, aligned perpendicular to the loading direction, improved the fatigue strength of the UD-GFRP composites by over 12% compared to the control samples. Fractography results are also presented in support of the findings from fatigue testing. Infrared thermography is presented as a method to rapidly determine the high cycle fatigue strength of the OHF specimens.

The investigation on dynamic damage evolution and energy absorption of FML pin joints with different ply stacking sequences

With fiber reinforced composites widely applied in aerospace, the crashworthiness aspects for aircraft have been an important part of the design. Fiber metal laminate (FML) is a kind of hybrid composite fabricated by fiber reinforced plastic composites and metal layers, showing a potential application on energy absorption. In this work, the damage evolution and energy absorption of FML pin joints are investigated comprehensively. The configurations of FML pin joints with constant geometric parameters are designed to avoid net-tension damage failure in the experiments. The damage evolution processes of specimens are captured by a high-speed camera, and the surface strain is calculated by Digital Image Correlation (DIC) method. Abaqus/Explicit solver is adopted to simulate the mechanical responses of FML pin joint considering ductile damage of metal, damage evolution of composites, and delamination of the interface. The results indicate that the initial dynamic ultimate bearing strength of FML incorporate notable contribution from inertia effects. The average bearing strength associated with energy absorption efficiency is related to the ply stacking sequence of composites. The fiber direction of laminates should be perpendicular to the movement direction of pin as much as possible under the premise that the initial ultimate bearing strength satisfies the design requirement. The results obtained in this work provide comprehensive design guidance for the improvement of crashworthiness in the composite fuselage.

Damage evolution and failure mechanism of three-dimensional braided composite subjected to varied high strain-rate loadings

Three-dimensional (3D) braided composite exhibit the excellent integrity of a braided structure, which gives the composites the advantages of high-impact damage tolerance, excellent delamination resistance, and high fatigue resistance. They have been widely used in the fields of aerospace and transport. Composites are always subjected to high strain-rate loading in these application cases. Braided composites show significantly different damage evolution under varied high strain-rate loadings. A bridge which can connect the strain rate variation to the different damage evolution of composites is urgently needed for composite strength design. This research demonstrated how the strain rate variation induced the change of damage evolution and failure mode of 3D braided composite. A high-speed camera system was used to capture damage process information. A micro-scale rate-dependent finite-element model (FEM) was established to study the underlying mechanisms. The results show that the velocity gap between yarns and resin becomes more obvious at higher strain-rate loading. Damage morphology of composites under lower strain rate resulted from the higher transverse stress at the output-bar area. Higher strain-rate loading induces plastic deformation, which occurs earlier in composites. The deformation distributes more haphazardly under higher strain-rate loading. Optimizing suggestions are given to improve the impact resistance of 3D braided composites.

The anti‐oxidation mechanism of SiCf/SiC–B4C modified with Al2O3 in wet atmosphere based on machine learning

AbstractTo study the anti‐oxidation mechanism of SiCf/SiC–B4C modified with Al2O3 in wet atmosphere, the damage evolution of composites after oxidation was explored by unsupervised machine learning technology (k‐means). Results display that the mean feature values of cluster‐1 (some small cracks in oxidation layer and matrix as well as fiber debonding) in composites modified with Al2O3 are larger than that in virgin after oxidation. Meanwhile, as the oxidation time increases, the concentrated area of cluster‐2 (fiber breakage, cracks in axial and transverse yarns) in both composites gradually shifts toward the direction of high mean feature values. Because Al2O3 can protect the BN from oxidation, the increase of peak frequency and risetime of composites modified with Al2O3 is less than that of virgin. Moreover, the proportion of cluster‐3 (big transverse matrix cracks) in composites modified with Al2O3 is always more than that of virgin. Based on the research results, the corresponding relationship between each damage behavior and each cluster is thoroughly built.

In-situ real-time imaging of subsurface damage evolution in carbon fiber composites with shearography

Carbon fiber composites are complex material systems comprising components of different length scales. It is important to understand the interactions of these components and their influence on the overall mechanical properties of the composites for development of new or improved composite materials. However, it is challenging to experimentally image the damage evolution in composites with existing tools. In this paper, we apply shearography technique for real-time in-situ imaging of subsurface damage evolution in carbon fiber composites during open-hole tensile (OHT) tests. Due to its high sensitivity to out-of-plane displacement derivative, shearography can record the initiation and growth of subsurface defects in real-time. Comparison with digital image correlation shows that shearography can provide better defect imaging results. The shearography technique provides a convenient and high-sensitive solution to visualize damage evolution in carbon fiber composites during mechanical tests.

Extended mean-field homogenization of viscoelastic-viscoplastic polymer composites undergoing hybrid progressive degradation induced by interface debonding and matrix ductile damage

In this contribution, a probabilistic micromechanics damage framework is presented to predict the macroscopic stress–strain response and progressive damage in unidirectional glass-reinforced thermoplastic polymer composites. Motivated by different failure modes observed experimentally, the damage mechanism in the vicinity of the fibers (namely, the interphase) is characterized by initiating and growing voids. The mechanisms can be formulated through a Weibull probabilistic density function. In contrast, the ductile progressive degradation of matrix initial stiffness is analyzed via the continuum damage theory. To accommodate different damage mechanisms in the matrix and the interphase, a three-phase Mori-Tanaka (MT) method and transformation field analysis approach (TFA) are established within a unified framework that allows simulation of both ductile and discrete damages in different phases. Moreover, the rate-dependent viscoelastic and viscoplastic response of the polymer matrix phase is modelled through a phenomenological model consisting of four Kelvin-Voigt branches and a viscoplastic branch under the thermodynamics framework. The reliability and efficiency of the modified mean-field damage model, based on TFA and Mori-Tanaka scheme, are assessed by comparing the simulated stress-strain response against full-field Abaqus simulations under both unidirectional and multiaxial nonproportional loading paths at different loading rates. The developed model provides an efficient alternative to the finite-element based full-field homogenization schemes or other mean-field micromechanics techniques that may be compared, as well as a framework for a potential extension of the theory for simulating damage evolution in composites with random reinforcement orientations.

An explicit–implicit combined model for predicting residual strength of composite cylinders subjected to low velocity impact

Composite structures are susceptible for low velocity impact, which leads to the reduction of the residual strength. In present paper, an explicit–implicit combined model based on stress-based failure and damage evolution laws is introduced for predicting residual strengths of composite cylinders subjected to low-velocity impact. The whole-process of damage evolution in composites can be explored by using direct damage state at the end of impact for residual strength analysis instead of traditional equivalent method. Then the proposed model is implemented by user-defined subroutines and Python scripting language in ABAQUS. VUAMT and UMAT subroutines are used for explicit impact analysis and implicit residual strength analysis, and Python scripting language is applied for damage data linking between the explicit–implicit modules. Relatively consistent experimental data and numerical results for the low velocity impact behaviors and residual tensile strength in T300/YH69 laminates validate the current model. Finally, residual strengths of composite cylinders after impact consisting of five impact energies are numerically explored. The residual burst pressure after impact and damage mechanism withstanding internal pressure of cylinders are predicted. The fiber damage caused by impact loading at hoop layers is determined as the dominant influencing mechanism affecting the residual strength of composite cylinders.

Effects of carbon nanotubes on open-hole carbon fiber reinforced polymer composites

Properties and damage evolution of open-hole carbon fiber-reinforced composite laminates without/with MWCNTs during tensile damage were monitored by a complementary technology combining acoustic emission, digital image correlation and finite elements analysis. Meanwhile, the AE signals can be post-processed by fuzzy C-Means. It was concluded that adding amount of MWCNTs can reduce the stress concentration, improve the strength and fracture interface stiffness of laminate specimens and prevent the evolution of micro-cracks. The AE signals are concentrated in three areas: 23-74 kHz (matrix cracking), 82-120 kHz (fiber pull-out and delamination), 120-190 kHz (fiber breakage), respectively. An enhancement of properties of materials is obtained correspondingly due to the addition of MWCNTs into matrix. The number and amplitude of AE signals corresponding to matrix cracking produced by the specimen without MWCNTs are much larger than that of the specimen with MWCNTs, indicating that the damage degree of matrix cracking for the specimen without MWCNTs is more serious. The properties and damage evolution of composites can be studied from experimental research and numerical simulation, respectively.

Acoustic Emission Based on Cluster and Sentry Function to Monitor Tensile Progressive Damage of Carbon Fiber Woven Composites

Understanding the tensile failure mechanisms in carbon fiber woven composites based on the acoustic emission (AE) technique is a challenging task. In this study, the mechanical behaviors of composites were studied under uniaxial tensile loading. Meanwhile, the internal damage evolution process in composites was monitored by AE and the recorded AE signals were analyzed. To achieve the dominant damage mechanisms in composites, five AE parameters such as rise time, duration, energy, peak amplitude, and frequency were selected for cluster analysis by a k-means algorithm. The results show that AE signals can be divided into three clusters based on microscopic observations and frequency range. The three clusters correspond to three kinds of damage modes such as matrix cracking, fiber/matrix debonding, and fiber breakage. In addition, the sentry function (SF) was adopted to investigate AE signals originated from the internal damage evolution in composites. It was found that the drop in the SF curve corresponds to the serious damage of the composites.

Strain rate-dependent mechanical behavior of quasi-unidirectional E-glass fabric reinforced polypropylene composites under off-axis tensile loading

To make a better use of quasi-unidirectional fabrics in structural application, the strain rate-dependent tensile behavior of quasi-unidirectional E-glass fabric reinforced polypropylene composites was studied. Monotonic tensile tests were firstly performed on 10°, 20° and 90° off-axis samples of composites. The experimental results show that both mechanical properties and nonlinear stress-strain behavior of composites are dependent of strain rate. A regression function is adopted to describe the variation in overall mechanical properties with the imposed strain rate. A strain rate-dependent coupled damage-plasticity model is built for quasi-unidirectional composites. The damage variables and plastic parameters in the proposed model are determined through cyclic loading-unloading tensile tests and can be represented as a function of the imposed strain rate. In addition, the damage mechanism of composites is observed to evolve with strain rate. Increasing strain rate can hinder the initiation and evolution of damage in composites.

Temperature-dependent response of quasi-unidirectional E-glass fabric reinforced polypropylene composites under off-axis tensile loading

Abstract The temperature-dependent off-axis tensile behavior of quasi-unidirectional E-glass fabric reinforced polypropylene composites has been investigated both experimentally and constitutively in this paper. The nonlinearity in composites under off-axis loading is shown to be a combination of damage and plasticity regardless of temperature. A nonlinear constitutive model is established to predict the temperature-dependent nonlinear stress-strain curves of composites, in which the accumulation of plastic strain and evolution of damage in composites are described by the plasticity and damage theories, respectively. A full suite of temperature-dependent plastic and damage parameters in the model are determined through cyclic loading-unloading tests.

Fatigue damage diagnostics and prognostics of composites utilizing structural health monitoring data and stochastic processes

The procedure of damage accumulation in composites, especially during fatigue loading, is a complex phenomenon of stochastic nature which depends on a number of parameters such as type and frequency of loading, stacking sequence, material properties, and so on. Toward condition-based health monitoring and decision making, the need for not only diagnostic but also prognostic tools rises and draws increasing attention in the last few years. To this direction, we model the damage evolution in composites as a doubly stochastic hidden Markov process that manifests itself via structural health monitoring observations, that is, acoustic emission data. The damage process is modeled via an extension of the classic hidden Markov models to account for nonhomogeneity, that is, age dependence in state transitions. The observations come from acoustic emission data recorded throughout fatigue testing of open-hole carbon–epoxy coupons. A procedure that utilizes multiple observation sequences from a training dataset and estimates in a maximum likelihood sense the optimal model parameters is presented and applied in unseen data via a cross-validation rationale. Diagnostics of the most likely health state determination, average degradation level, and prognostics of the remaining useful life are among the capabilities of the presented stochastic model.

A Numerical Method for Simulating the Microscopic Damage Evolution in Composites Under Uniaxial Transverse Tension

In this paper, a new numerical method that combines a surface-based cohesive model and extended finite element method (XFEM) without predefining the crack paths is presented to simulate the microscopic damage evolution in composites under uniaxial transverse tension. The proposed method is verified to accurately capture the crack kinking into the matrix after fiber/matrix debonding. A statistical representative volume element (SRVE) under periodic boundary conditions is used to approximate the microstructure of the composites. The interface parameters of the cohesive models are investigated, in which the initial interface stiffness has a great effect on the predictions of the fiber/matrix debonding. The detailed debonding states of SRVE with strong and weak interfaces are compared based on the surface-based and element-based cohesive models. The mechanism of damage in composites under transverse tension is described as the appearance of the interface cracks and their induced matrix micro-cracking, both of which coalesce into transversal macro-cracks. Good agreement is found between the predictions of the model and the in situ experimental observations, demonstrating the efficiency of the presented model for simulating the microscopic damage evolution in composites.

Plasticity dependent damage evolution in composites with strain-gradient effects

A unit cell approach is adopted to numerically analyze the effect of reinforcement size on fracture evolution in metal matrix composites. The matrix material shows plastic size-effects and is modeled by an anisotropic version of the single parameter strain-gradient (higher-order) plasticity model by Fleck and Hutchinson (2001). The fracture process along the fiber–matrix interface is modeled using a recently proposed cohesive law extension, where plasticity affects the fracture process as both the average as well as the jump in plastic strain across the interface are accounted for Tvergaard et al. (2013). In this study the reinforcement is assumed perfectly stiff and consequently only one new cohesive material parameter is introduced. Results are shown for both conventional isotropy as well as plastic anisotropy with higher-order material behavior. Due to fiber–matrix decohesion a sudden stress-drop is seen in the macroscopic stress–strain response curve, which defines the failure strain of the composite. It is shown, that decreasing the value of the new cohesive material length parameter will monotonically decrease the failure strain. On the other hand, the material length scale parameter of the matrix affects the failure strain in a non-monotonic manner. Depending on the degree of anisotropy a maximum failure strain is predicted for a length scale corresponding to 10–15% of the reinforcement radius.

Progressive damage in satin weave carbon/epoxy composites under quasi-static punch-shear loading

Damage evolution in composites during a high velocity impact is difficult to observe. In this work, quasi-static punch-shear (QS-PS) tests were conducted in an effort to determine damage that could develop during a penetrating impact event. Eight satin weave carbon/epoxy composite samples were fabricated and tested under different load levels. Load-displacement (P-δ) curves were obtained and type and extent of damage were identified in two/three dimensions using optical microscopy and X-ray computed tomography. Corresponding displacements at which the damage occurred were marked on the P-δ plots. A finite element analysis (FEA) was performed using the ABAQUS/Explicit commercial package with a progressive damage model to simulate experimental observations. It is found that the load pattern of the plate changes from local shearing to overall bending, which corresponds to the inflection stage of the P-δ curve. The final failure is caused by major delamination and fibre breakage due to shear and tensile stresses developed during the QS-PS tests.

Microstructure-Based Numerical Simulation of the Tensile Behavior of SiCp/Al Composites

Modeling and prediction of the damage evolution in particle reinforced composites is a complex problem. Microstructure characters such as the particle morphologies, sizes, and distribution significantly affect the damage evolution in composites. A numerical simulation has been performed to investigate the damage evolution of SiCp/AA2009 composites. Tensile deformation in SiCp/AA2009 composites was simulated using the microstructure-based model constructed from the metallograph. Matrix damage, particle cracking, and interface debonding were simulated combining the ductile damage model, the normal stress criterion, and the maximum stress ratio criterion. The simulation results show that under tensile loading, damage initiates at the interface, and then propagates along the weakest direction. The simulation microstructures agree well with experimental results in which interface debonding, particle cracking, and matrix damage co-exist. In addition, the effects of component properties on the damage evolution are examined for various situations.

Damage and fracture in fabric-reinforced composites under quasi-static and dynamic bending

Fabric-reinforced polymer composites used in sports products can be exposed to different in-service conditions such as large deformations caused by quasi-static and dynamic loading. Composite materials subjected to such bending loads can demonstrate various damage modes – matrix cracking, delamination and, ultimately, fabric fracture. Damage evolution in composites affects both their in-service properties and performance that can deteriorate with time. Such behaviour needs adequate means of analysis and investigation, the main approaches being experimental characterisation and non-destructive examination of internal damage in composite laminates. This research deals with a deformation behaviour and damage in carbon fabric-reinforced polymer (CFRP) laminates caused by quasi-static and dynamic bending. Experimental tests were carried out to characterise the behaviour of a CFRP material under large-deflection bending, first in quasi-static and then in dynamic conditions. Izod-type impact bending tests were performed on un-notched specimens of CFRP using a Resil impactor to assess the transient response and energy absorbing capability of the material. X-ray micro computed tomography (micro-CT) was used to analyse various damage modes in the tested specimens. X-ray tomographs revealed that through-thickness matrix cracking, inter-ply and intra-ply delamination such as tow debonding, and fabric fracture were the prominent damage modes both in quasi-static and dynamic test specimens. However, the inter-ply damage was localised at impact location in dynamically tested specimens, whereas in the quasi-static specimens, it spread almost over the entire interface.

Sensing of Damage in Glass Fiber Composites by Adding Carbon Nanotubes

Advanced fiber-reinforced polymer composites are known to possess outstanding specific strength and stiffness and their use in structural applications continues to expand. Most structural composites are susceptible to the formation of micro-scale damage in polymer matrix under adverse conditions which has significant implications on the durability and performance of fiber composites. Thus, it is imperative to detect the initiation and evolution of damage in composites long before their catastrophic failure. In this report, our recent research in sensing of micro-crack in matrix in situ and in real time for glass fiber composites was reviewed. Carbon nanotubes were dispersed into glass fiber composites by three roll mill technique. A resistance parameter was utilized to quantitatively characterize damage initiation and propagation. Damage mechanisms and development were investigated under tension, fatigue loadings. This research demonstrates the feasibility and benefits of electrical resistance measurements in the sensing of micro-scale damage for fiber composites using carbon nanotubes and offers the potential for in-service health monitoring of composite structures.

High-Fidelity Analyses of Composites at Various Length Scales with Discrete Damage Representations

High-fidelity strength prediction of composites requires advanced numerical methods that can explicitly resolve the multiple damage processes and their nonlinear coupling at various scales. Nonlinear fracture models such as cohesive zone models are critical for damage descriptions and need to be properly embedded in a numerical framework so that correct coupling between different damage process zones can be guaranteed. This paper reviews the recent developments in advanced numerical methods that have the potential to address the important issue of progressive damage evolution in composites. Candidate FE-based numerical methods, including X-FEM, A-FEM, and phantom node methods, are reviewed and their capabilities in handling the multiple damage coupling in composites are assessed. Successful simulations of composites at various scales using the framework of A-FEM are presented and the numerical and material issues associated with these high-fidelity analyses are highlighted. Finally, we address the question of how to integrate all these different scale analyses into a single multiscale numerical framework by using the Arlequin coupling method.