Intralaminar Damage Research Articles

Flexural response of composite beams made by Automated Fiber Placement process: Effect of fiber tow gaps

Automated Fiber Placement is one of the well-established composite fabrication techniques in both aerospace and automotive industries. However, new types of defects may be formed during the fiber steering due to replacing the prepreg sheets with the prepreg fiber tows. These defects can be a source of both intralaminar and interlaminar damages, which reduce the mechanical performance of the final products. Although the effect of these defects on the performance of the composite structure, especially the in-plane behavior can be found in the literature, there is still a lack of knowledge in the study of the mechanical performance of the composite structures with manufacturing induced defects. In the present study, the effect of automated manufacturing induced gaps on the mechanical response and failure of the Quasi-isotropic Carbon/Epoxy thin beams under out-of-plane loading is investigated. For this purpose, three-point bending tests are carried out on both short and standard beams to measure the interlaminar shear strength and flexural stiffness/strength of the composite beams with the gaps. The results are then compared with the results of the baseline sample (the one with no defect). Furthermore, Finite Element simulations are used to examine the stress distribution and also damage initiation and propagation of the composite beams under out-of-plane loading in the presence of the gaps. It is shown that the material scaling at the inhomogeneity area, which is widely used in the literature for Finite Element simulation of the composite structure with the gaps, is not sufficient for all scenarios of the loading and thickness scaling might also be applied to the models.

Simulation of progressive failure in laminated composites under variable environmental conditions

This paper presents the development, calibration and finite element implementation of a novel set of phenomenological equations describing the effect of temperature and moisture on the stiffness, strength and toughness properties of fibre-reinforced plastics. An extension of the classical Zhurkov's kinetic approach is proposed to describe the effect of temperature and moisture on the ply-level matrix-dominated strength properties. The phenomenological equations are implemented into a finite-element simulation framework, consisting of a smeared crack approach for modelling intralaminar and translaminar failure, coupled with a bi-linear cohesive zone approach to describe delamination onset and progressive growth. The modelling approach is calibrated by means of experimental data in the open literature for the carbon-epoxy material IM7/8552. Validation case studies for the simulation strategy include quasi-isotropic short beam shear coupons and open-hole specimens subject to tension. It is demonstrated that the proposed simulation framework provides a comprehensive quantitative description of the role played by environmental effects in terms of development and interaction of intralaminar, interlaminar and translaminar damage processes.

Progressive damage analysis of composite laminates subjected to low-velocity impact using 2D layer-wise structural models

The present work deals with the progressive damage analysis of composite laminates subjected to low-velocity impact. We develop a numerical model using higher-order structural theories based on the Carrera Unified Formulation (CUF) with Lagrange polynomials and resulting in a 2D refined layer-wise model. To model damage, we use a combination of the continuum damage-based CODAM2 intralaminar damage model to account for fibre and matrix damage within the ply, and cohesive elements to account for delamination between successive composite plies. We carry out numerical assessments for the case of a linear elastic composite plate subjected to impact, to compare the current framework with standard approaches based on 3D finite element (FE) analysis. We, then, consider the elastoplastic analysis of a bimetallic laminated plate to compare the performance of the proposed layer-wise model and 3D-FE approaches, for the case of nonlinear impact analysis. The final assessment considers progressive damage due to low-velocity impact, and the results are compared with available literature data. The numerical predictions show a good correlation with reference experimental and simulation results, thus validating the current framework for impact analysis of composite structures. Comparisons of the proposed layer-wise structural models with those based on 3D finite elements demonstrate the improved computational efficiency of the CUF models in terms of model size and analysis time.

A stacked sublaminate-based damage-plasticity model for simulating progressive damage in composite laminates under impact loading

We present a simple, efficient and easy-to-use finite element (FE) model for the simulation of progressive damage in quasi-isotropic IM7/8552 carbon fibre reinforced composites under low velocity impact loading. The sub-laminate based continuum-discrete model in the commercial FE software LS-DYNA consists of built-in tools to facilitate modelling and analysis. The coupled plastic-damage material card MAT81 describes intralaminar damage in tension and compression which is calibrated using digital image correlation in over-height compact tension and compact compression tests to extract damage properties such as strain softening curves and size of the failure process zone. The cohesive interface formulation is virtually calibrated leading to realistic zones of delamination. The proposed model was applied to a wide range of impact loadings and compared to results obtained from experimental testing and high-fidelity FE models. Besides the good correlation between simulation and experiments, we demonstrate how to quantify different energy dissipation mechanisms during impact events.

Finite element analysis and acoustic emission monitoring of progressive failure of corrugated core composite structures

The present work investigates the progressive failure in a corrugated core type CFRP composite structure under out-of-plane compression and four-point-bending tests. The structure has a novel geometry where unidirectional prepreg is used for both the corrugated core and the facesheets, which are manufactured together in a single process. Acoustic Emission (AE) registration is applied during the four-point-bending test and the k-means++ clustering algorithm is used to group the similar AE events and provide reliable correlations with failure modes. Test results are complemented with finite elements progressive failure analysis in which Hashin’s failure criterion and Cohesive Zone Model are utilized to predict the intralaminar and interlaminar damage modes respectively. The model is validated by comparing it with load–displacement curves and observed failure modes during the tests. Analysis of AE results reveals failure modes during four-point bending test and provides reliable evidence which is in good agreement with the predictions of the finite element model.

On the Modelling Aspect of Low-Velocity Impact Composite Laminates

Composites suffer a degradation of structural stiffness due to various types of impact loading resulting in damage which is difficult to observe from the surface of the structure. The paper deals with the finite element model (FEM) to study the possible modelling procedures in low-velocity impact (LVI) and failure mechanism of carbon fiber reinforced polymer (CFRP) composite laminate of CCF300/epoxy and its structural responses. In finite element calculation, a proposed three-dimensional progressive damage model is used to determine the intralaminar damage, whereas the cohesive contact formulation is employed to analyse the interlaminar damage. The failure model performances are validated and verified based on different boundary conditions while maintaining the impact energy. Through simulation, the variation in boundary conditions significantly changes the structural responses and energy absorption of the laminates. It is hoped this study will be a great tool in determining the different composite impact scenarios.

An anisotropic cohesive phase field model for quasi-brittle fractures in thin fibre-reinforced composites

Thin unidirectional-tape and woven-fabric composites are widely utilized in the aerospace and automotive industries due to their enhanced fatigue life and damage resistance. Providing high-fidelity simulations of intra-laminar damage in such laminates is a challenging task both from a physics and a computational standpoint, due to their complex and largely quasi-brittle fracture response. This is manifested by matrix cracking and fibre breakage, which result in a sudden loss of strength with minimum crack openings; subsequent fibre pull-outs result in a further, although gradual, strength loss. To effectively model this response, it is necessary to account for the cohesive forces evolving within the fracture process zone. Furthermore, the interaction of the failure mechanisms pertinent to both the fibres and the matrix necessitate the definition of anisotropic damage models.We propose a cohesive phase-field model to simulate intra-laminar fracture in fibre reinforced composites. To capture damage anisotropy, distinct energetic crack driving forces are defined for each pertinent composite damage mode together with a structural tensor that accounts for material orientation dependent fracture properties. The material degradation is governed by a 3-parameter quasi-quadratic degradation function, which can be calibrated to experimentally derived strain softening curves. The proposed damage model is implemented in Abaqus and is validated against experimental results.

Analysis on failure mechanism of CFRP double-tap interference-fit joint

Composite interference-fit joints have attracted much attention because they can effectively reduce the stress concentration around the holes during loading. In this paper, the load-bearing mechanism and strength of a typical double-lap structure under static load are studied through experiment and finite element method. In order to eliminate the influence of bending moment and other factors, a special fixture was designed to study the damage failure mechanism of CFRP interference fit joint under pure tension. The finite element model of CFRP interference fit double lap structure considering both intralaminar and interlaminar damages was established with ABAQUS user subroutine and cohesive element. The damage propagation mechanism during loading process is revealed and the ultimate bearing strength is predicted by comparing the results of experiment and finite element model.

A mesoscale modelling approach of glass fibre/Elium acrylic woven laminates for low velocity impact simulation

This study presents a numerical mesoscale approach to simulate the damage and failure mechanisms of woven laminated composites under low velocity impact loading conditions. First, some measurements were made on samples to obtain a realistic reproduction of the microstructure. This allows relating failure mechanisms in composite laminates with their geometry and topology. A three-dimensional Hashin criterion was developed to investigate the impact behaviour, by accounting for both intralaminar and interlaminar damages. Four failure modes were considered relatively to fibre damage initiation in tension and compression and Puck criteria was employed to capture the initiation of the yarn’s matrix damage. The matrix surrounding undulated yarns were taken into account by an elastoplastic behaviour with maximum-stress failure criteria. Good correlation between numerical and experimental results demonstrated the robustness and the accuracy of the proposed multiscale approach.

Modeling of damage behavior of carbon fiber reinforced plastic composites interference bolting with sleeve

Interference-fit is getting increasing attentions in the aerospace field owing to its excellent enhancement on the sealing and fatigue life of composites assembly, but the severe damage around the hole caused by installation is still a huge challenge. In this paper, a three-dimensional anisotropic non-linear progressive damage model based on continuum damage mechanics was developed to reveal the damage mechanism of carbon fiber reinforced plastic (CFRP) composites interference bolting with sleeve. The proposed model adopted strain-based failure criteria and non-linear damage evolution law to predict damage initiation and propagation of composite laminates. A cohesive model taking into account the traction-separation constitutive response was employed to capture the delamination behavior between the composite plies. The elastoplastic model was utilized to characterize the sleeve's deformation behavior. Numerical simulations of different installation modes are performed and compared with experiments. The inserting load, damage modes and damage positions predicted by the proposed model agree well with the experimental results. Moreover, it is also verified that the interference installation of sleeved fasteners can remarkably reduce the intra-laminar damage and avoid the inter-laminar delamination of composite laminates compared to the conventional bolt.

A numerical-experimental assessment on a composite fuselage barrel vertical drop test: Induced damage onset and evolution

Crashworthiness is the ability of a structure to withstand a crash event ensuring the safety of its passengers. The aim of this work is to investigate the damage onset and evolution in a composite fuselage barrel undergoing a vertical drop test on a rigid surface. The mechanical behaviour of the barrel has been assessed by means of a Numerical-Experimental study. Indeed, the experimental data from a full scale barrel test, performed at the CIRA facilities, have been used in conjunction with numerical results, obtained by means of an advanced 3D FEM model, to investigate, in detail, the deformations and the damage development during the crash event. The adopted three-dimensional numerical model, based on an explicit FE formulation, uses Continuum Shell elements and CDM to take into account the onset and the evolution of the intra-laminar damages in each subcomponent of the investigated composite fuselage barrel. The obtained numerical results have been compared with experimental data in terms of accelerations, displacements and deformations to provide a preliminary validation of the adopted FEM model. A special attention has been given to sub-components which demonstrated to mainly influence the global mechanical behaviour of the investigated composite fuselage barrel during the experimental test.

Effects of environmental exposure on the mechanical properties of composite tidal current turbine

In order to meet the growing demand for energy and also to fight against global warming, Renewable Marine Energies (RME) appeared as a great opportunity for a real ecological and industrial choice. Tidal current turbines are used to extract this energy and installed on the seabed at locations where the nozzle can be prone to the accidental impact and critical loads. The principal objective of this research is to investigate the effects of environmental exposure on the mechanical properties of composite tidal current turbine, the most advanced features currently available in finite element (FE) Abaqus/Explicit have been employed to simulate the behavior of the composite nozzle under static and dynamic loading conditions. To investigate this situation, a parametric analysis is conducted which deals with the effect of velocity and geometry of the impactor. The mechanical behavior has been analyzed as both kinematic effect due to deflection of the composite structure and dynamic effect caused by the interaction between the impactor and the hydrodynamic and hydrostatic pressures over the loading. The stress and the deformation distribution are presented. On the other hand, damage modeling was formulated based on Hashin criteria for intra-laminar damage. This has been accomplished by forming a user-created routine (VUMAT) and executing it in the Abaqus software.

Analysis of boundary condition in modelling the low-velocity impact carbon-fiber reinforced polymer composite laminates

The effect of modelling strategy on boundary condition and impact energy of low-velocity impact laminate has been investigated. The paper deals with the finite element model (FEM) to study the structural responses of carbon fibre reinforced polymer (CFRP) composite laminate of CCF300/epoxy. In FE calculation, a proposed three-dimensional progressive damage model is used to determine the intralaminar damage, while cohesive contact formulation is employed to analyse the interlaminar damage. The failure model performances are validated and verified based on different boundary conditions and impact energies. Through experiment and simulation, it can be said that variation in boundary condition as well as impact energy, significantly change the force-time, displacement-time, energy-time, and load-displacement histories.

In-situ imaging of inter- and intra-laminar damage in open-hole tension tests of carbon fibre-reinforced composites

This paper investigates damage progression during Open-Hole Tension (OHT) test of carbon fibre-reinforced composites with different Quasi-Isotropic (QI) layups. Digital Image Correlation (DIC) and in-situ edge microscopy are utilized simultaneously to detect damage on the specimen’s surface and in the inner plies, respectively. It is found that damage does not always initiate in the 90° plies, but also in the surface 45° plies, depending on the orientation of the adjacent ply. DIC resulting strain field on the surface does not necessarily have the same butterfly-shape concentration around the hole, in all layups. Some laminates show large free edge delaminations at 45°/90° interfaces. This study adds in-situ evidences to the existing data on damage during OHT test of QI laminates, providing quantitative and comparative information on different damage modes, and reveals new features of the damage phenomena.

Effect of friction and shear strength enhancement on delamination prediction

This study considers the intra-laminar damage mode in composite structures and its effect on delamination prediction. The progressive damage models for matrix cracking and fibre failure in ABAQUS, based on Hashin's model, are only available for shell elements. The results presented here show that the predicted matrix cracking based on the damage model presently available in ABAQUS diverges from experimental results. A new model based on strain failure criteria, which can be used with both shell elements and 3D solid elements, has been developed. The effect of friction coefficient and enhancement factor on the delamination lobes within the delamination area was investigated, and it is shown that the intact zone can be captured in laminate [03/903]s and [903/03]s subjected to low-velocity impact, by using an enhancement factor of η = 0.75, and friction coefficient [Formula: see text], together with the new model proposed here.

A unified numerical approach for the simulation of intra and inter laminar damage evolution in stiffened CFRP panels under compression

Thin-walled composite structures operating in the post-buckling regime needs a thorough understanding of their stability behavior and failure mechanisms. For the accurate prediction of the collapse loads, one needs to account for the damage evolution precisely. In the current study, we have proposed a unified and generic numerical modeling approach that accounts for both the intra and inter-laminar damage modes in stiffened CFRP panels. A 3D finite element based progressive damage model (PDM) is proposed to simulate the collapse behavior of the single blade stiffened composite (SSC) CFRP panels with and without embedded de-bonding defects under uniaxial compression loading. A user-defined material subroutine based on 3D Hashin failure criteria is developed in Abaqus software to study the evolution of intra-laminar damages in SSC panel. Further, the skin-stiffener bonded interface, the inter-laminar interfaces in the skin, stiffener, including the noodle region, is modeled using the cohesive zone elements to simulate the de-bonding/delamination growth. The stability response and collapse load results obtained using the proposed PDM are compared with the experimental observations. Also, the damage evolution, failure mechanisms, the ultimate load, and the corresponding displacement data obtained from the developed PDM are validated with the experimental estimates. A comprehensive damage assessment involving the ultrasonic C-scans, infrared thermograms, and micrographic study is also carried out to supplement the PDM predictions. Thus, the proposed PDM is generic in terms of damage studies and can be used for investigating the collapse behavior of CFRP panels with multiple stiffeners.

Prediction of residual burst strength for composite pressure vessels after low velocity impact

Composite pressure vessels have been widely used for high-pressure hydrogen storage. This paper aims to study the residual burst strength of composite pressure vessels after low velocity impact. An explicit-implicit combined model using strain-based three-dimensional failure theory is employed for numerical analysis, which is implemented by ABAQUS user-defined subroutines VUAMT, UMAT and ABAQUS-Python scripting language. Impacted-induced damage including the intralaminar fiber and matrix damage, and interface delamination is directly imported to the residual strength analysis to explore the whole-process damage mechanisms by using current model. For composite pressure vessels, the mechanical responses and damage behaviors of intralaminar damage and interface delamination at six impact energy are explored. After impact, the damage evolution under internal pressure for vessels is discussed. By comparison, the numerical results are basically consistent with experimental results. Besides, the effects of impact direction of strip impactor and liner type on the low velocity impact responses and residual burst strength are explored. By studying the influence of impact energy, liner type and impact direction systematically, it shows that fiber damage on the hoop layers caused by impact load can reduce the residual burst strength for current composite pressure vessels.

An experimental study on the influence of intralaminar damage on interlaminar delamination properties of laminated composites

Coupling between intralaminar and interlaminar damage plays a significant role in accurately predicting delamination and final failure. However, insufficient experimental data are available for models of this phenomenon. In this paper, we proposed a two-step experiment on cross-ply laminates to quantitatively study the influence of in-plane strain on the interlaminar fracture toughness. First, we performed a tensile test on the [02/902]s cross-ply laminates to introduce various extents of intralaminar damage. Next, we bonded a backing adherend of [06] plies to the cross-ply, so we could probe the delamination properties through a subsequent double cantilever beam (DCB) test. We identified the effective fracture toughness Gc,eff by the compliance calibration method. We found that intralaminar damage promotes fiber bridging in the transverse direction, which finally influence the out-of-plane properties significantly.

Investigation of the impact and post-impact behaviour of glass and glass/natural fibre hybrid composites made with various stacking sequences: Experimental and theoretical analysis

In the present work, impact and post-impact response of thermoset composite laminates manufactured from glass, flax, jute fabrics and their hybrid combinations (glass/jute and glass/flax) made with various stacking sequences was studied. The low-velocity impact response of these laminates was investigated by drop-weight impact tests at different energy levels (20–50 J). Additionally, their post-impact behaviour was studied by compression after impact tests, measuring their residual compressive strength. Impact test results showed that glass composites had higher impact resistance than natural and hybrid composites. Moreover, the hybrid composites with glass fabric layers in the exterior resulted in better impact resistance compared to composites where glass fabric layers were placed in the interior with flax or jute fabrics. It was also observed that natural and hybrid composites absorbed more energy than that of glass composites between 20 and 40 J. Glass composites exhibited higher compression and compression after impact strength than natural and hybrid composites. However, hybrid composites had higher compression after impact strength retention (%) than glass composites due to less fibre damages. The numerical analysis was also conducted to simulate the intra-laminar damages and delamination failures. Good agreement was observed between numerical and experimental results.

Modelling damage in fibre-reinforced thermoplastic composite laminates subjected to three-point bend loading

It is important to account for nonlinearity in the deformation of a thermoplastic matrix, as well as fibre fracture and matrix cracking, when predicting progressive failure in unidirectional fibre-reinforced thermoplastic composites. In this research, a new high-fidelity model approach is developed incorporating elastic-plastic nonlinearity. In order to validate the model, three-point bend experiments were performed on composite specimens, with a lay-up of [03/903]2s, to provide experimental results for comparison. Digital Image Correlation (DIC) was employed to record the strain distribution in the composite specimens. The developed intralaminar damage model, which is implemented as a user defined material (VUMAT in Abaqus/Explicit) subroutine, is then combined with a cohesive surface model to simulate three-point bend failure processes. The simulation results, including the load-displacement curves and damage morphology, are compared with the corresponding experimental results to assess the predictive capability of the developed model. Good agreement is achieved between the experimental and numerical results.