Intralaminar Damage Research Articles

Comparison of two progressive damage models for studying the notched behavior of composite laminates under tension

Two continuum damage models with different underlying assumptions are investigated to assess their predictive capabilities and limitations with respect to progressive intra-laminar damage in notched IM7/8552 CFRP composite laminates under tension.The recently modified continuum damage model, CODAM2, implemented in LS-DYNA is compared to a Ladevèze-based damage model, ABQ_DLR_UD, implemented as a user-material model (VUMAT) in Abaqus/Explicit. Fundamental similarities and differences between the two models are first investigated by various single element simulation case studies before assessing their predictive capabilities at the more global coupon level. Over-height Compact Tension (OCT) tests with dispersed and blocked lay-ups as well as a wide range of scaled Center-Notched Tension (CNT) specimens are used to evaluate characteristic damage-related quantities such as strength, post-peak behavior and fracture energies. Experimental data are also used to further validate the two different meso-scopic damage models.The results of this study clearly demonstrate the layups, geometries and loading conditions that are suitable for applying intra-laminar damage models with confidence to this class of CFRP material system. Conversely, the study shows limitations of the continuum damage modeling techniques and suggests strategies that can be used to address these drawbacks.

Transition from buckling to progressive failure during quasi-static in-plane crushing of CF/EP composite sandwich panels

Global buckling failure should be avoided when designing a structure with the requirement of crashworthiness performance. This study characterises the quasi-static in-plane crushing of CF/EP composite sandwich panels by tailoring their bevel angles. A finite element model was developed describing the interlaminar and intralaminar damage of a composite sandwich panel; this model was validated by in-plane compression experiments. A numerical analysis and compression experiments were then performed to determine the responses and failure modes in the CF/EP composite sandwich panels with various bevel angles. The results showed that the global buckling-to-progressive failure transition under compression occurred in the composite sandwich panels when the bevel angle reached a critical value. A microscopic analysis showed that the composite sandwich panels with buckling failure behaviours exhibited an apparently classical post-buckling transverse shearing mode, while those with progressive failure presented individual lamina bending with inward and outward fronds. This study provides some useful data for the design of the crashworthiness of a sandwich composite panel by introducing a progressive failure mode.

Multi-scale modelling of dynamic progressive failure in composite laminates subjected to low velocity impact

This paper aims to investigate the structural mechanical responses and progressive damage behaviors of composite laminates subjected to low velocity impact. First, a three-dimensional multi-scale model based on micromechanics of failure (MMF) criterion with new damage evolution laws is introduced for intralaminar damage, which considers the different mechanical behaviors of the microscopic constituents for fiber and matrix. The macroscopic damage variables of the new damage evolution laws are directly evaluated by the degraded elastic parameters of the microscopic constituents calculated from representative volume elements (RVEs). Second, by using this multi-scale approach, the relationship between macroscopic stress and microscopic stress is established by stress amplification factors (SAFs) through the RVEs using ABAQUS-PYTHON scripting language. The proposed model is implemented by the user-defined material subroutine VUMAT built on ABAQUS/Explicit platform, and the bilinear cohesive model in ABAQUS is employed to capture the onset and progression of interlaminar delamination. Finally, impact numerical simulation for the impact force-time/central displacement curves and energy dissipation is performed on three composite laminates with different layup patterns. Relatively good agreements are achieved between the experimental and numerical results, which validates the effectiveness of the multi-scale model.

Numerical analysis of intralaminar damage evolution on various composite laminates

The paper presents the numerical modelling of progressive damage distribution on the layers of various configurations of composite laminates (cross-ply, angle-ply, balanced laminate and quasi-isotropic laminate) under tensile loading. The purpose of the paper is to study the effect of the stacking sequence and fibre orientation angles on the damage propagation on multi-layered composites. These damage initiations do not necessarily imply a complete loss of structural integrity of the composite laminate. Additional load can be supported due to the stress redistribution over the fibres. A post-critical analysis is carried out, in order to analyse the integrity or the degradation state of the layers of composite laminates. The progressive failure analysis is performed in ANSYS Composite Prep/Post, to enable the investigation of damage initiation and damage evolution on each ply with various fibre orientations of the composite laminates. The intralaminar failure is initially detected based on a failure criterion and the post-critical analysis is evaluated based on a damage evolution law. The results are presented in terms of representative tensile displacements, which lead to damage initiation and damage evolution on the layers of the analysed composite laminates. Moreover, the laminas with different fibre orientations are investigated for progressive loading steps, from the first local failure to the total collapse. The obtained results show that the damages distribution on the plies of the composite laminates are strongly influenced by the fibre orientations, but also by the interaction with the other laminas and stacking sequence.

Determination of the longitudinal compressive strength of a CFRP ply through a tensile test on a laminate

In this study, an innovative test is proposed to identify the longitudinal compressive strength of a unidirectional ply. The key idea consists in designing a laminate that, when subjected to a tensile loading, fails by compressive failure in its central 90°-ply, due to the Poisson effect, without any prior damage. Six specimens have been tensile tested to failure. No intra-laminar matrix damage could be detected before the final failure. Fibre kinking in the 90°-ply is observed experimentally in the failed specimens. This damage mechanism, located in the gauge section of the specimens, leads to the final failure. A fast computational identification method is used to determine the longitudinal compressive stress and strain within the 90°-ply at failure, from this specific tensile test. The identified average failure properties are consistent with those obtained through conventional compression tests, but the associated scattering is much lower. Consequently, this innovative method leads to an increase in the design allowable, resulting in higher performance designs.

Barely visible impact damage assessment in laminated composites using acoustic emission

Despite the key advantages of Fiber Reinforced Polymer (FRP) composites, they are susceptible to Barely Visible Impact Damage (BVID) under transverse loadings. This study investigates BVID in two quasi-isotropic carbon/epoxy laminates under quasi-static indentation and Low-Velocity Impact (LVI) loadings using Acoustic Emission (AE). First, the evolution of interlaminar and intralaminar damages is studied by analyzing the AE signals of the indentation test using b-value and sentry function methods. Then, the specimens are subjected to the LVI loading and the induced damages are compared with the indentation test and the percentage of each damage mechanism is calculated using Wavelet Packet Transform (WPT). In consistent with the mechanical data, ultrasonic C-scan and digital camera images of the specimens, the AE results show a considerable similarity between the induced BVID under quasi-static indentation and LVI tests. Finally, the obtained results show that AE is a powerful tool to study BVID in laminated composites under quasi-static and dynamic transverse loadings.

Open hole and filled hole progressive damage and failure analysis of composite laminates with a countersunk hole

Countersunk holes are used in bolted joints for creating non-protruding smooth surfaces. As a first step towards a detailed progressive damage and failure analysis of bolted joint configurations, a new model referred to as the Intra-inter crack band model (I2CBM) is used to study open hole tensile/compressive and filled hole tensile/compressive progressive damage and failure. The I2CBM is a unified approach for modeling intralaminar and interlaminar progressive damage and failure in polymer matrix composites. 3D finite elements in the I2CBM formulation can be adapted for modeling individual lamina elements or to model interface delamination elements. A path for communication between the intralaminar and interlaminar failure mechanisms is enabled in the model to overcome limitations associated with homogenized element modeling and to capture complex interactions in a physically correct manner. A non-local crack spacing method is implemented for tracking matrix cracks. Comparisons between test results and I2CBM predictions for the open hole tensile/compressive and filled hole tensile/compressive cases with a countersunk hole configuration are discussed. The effect of bolt pretension on the filled hole failure analysis case is also presented and the failure mechanisms are discussed.

Finite Element Simulation of Interlaminar and Intralaminar Damage in Laminated Composite Plates Subjected to Impact

Abstract Here In this study, the composite laminates subjected to transverse impact with consideration interlaminar and intralaminar damage based on Cohesive Zone Model (CZM) and Progressive Damage Model (PDM) are investigated by numerical analysis using ABAQUS commercial finite element code. The delamination in stacking ply with the same fiber orientation is considered as interlaminar damage and the delamination in an inner layer of any cluster is ignored. Hashin criterion is used for intralaminar damage initiation and evolution without using any subroutine. First, the appropriate procedure for delamination on composite specimen was suggested based on CZM approach in double cantilever beam to verify the intralaminar damage simulation. Then by considering several case studies with different impact energies, the results of present simulation is verified with the relevant and available experimental results and numerical references in the existing literature. According to the available experimental results the present simulation results are more acceptable and accurate than the results of similar numerical works, especially in higher impactor velocity.

Progressive damage modeling and interface delamination of cross-ply laminates subjected to low-velocity impact

In this study, Hashin failure criteria were enhanced with Puck’s action plane concept to develop a user material model that can accurately predict the damage development inside the composite laminate when it is subjected to low-velocity impact. A simple cross-ply laminate [0/90]s was chosen to demonstrate the applicability of the material model. Experiments were also performed to observe the real behavior of the laminate. A good correlation between the experiment and simulation results was obtained in terms of peak force and displacement. However, the model under-predicted the absorbed energy, but the discrepancy decreased with the increase in impact energy. Moreover, the interface delamination study was performed by comparing the signatures in post-impact samples of the experiment and numerical simulation. It was observed that the experimentally detected delamination area was closely predicted by the simulation. It was further noticed that the top interface delamination increases faster than bottom interface delamination. Furthermore, the total energy absorbed by the laminates in intralaminar and interlaminar damage modes and friction effects were found to be closely matching with the final absorbed energy of the laminate. Hence, it was seen that the developed finite element model was able to closely capture the behavior occurring in experiments.

A strain-rate-dependent damage model for evaluating the low velocity impact induced damage of composite laminates

Low velocity impact (LVI) has always been a potential threaten to composite structures. This out-of-plane dynamic impact load easily leads to a dramatic increase of the strain state in the material transverse plane, which can affect the dynamic stress state and damage evolution of the composite laminate, especially for LVI with a relatively high energy. However, the strain rate effect was always neglected in existing investigations, thus introducing inevitable errors in numerical predictions for engineering practices. To accurately capture the failure process of composite laminates under LVI, a three-dimensional strain-rate-dependent damage model was proposed. This model was composed of three parts: a modified stress–strain relationship for composites under a dynamic stress state; a strain-rate-dependent progressive damage model to evaluate the intra-laminar damage; and a cohesive zone model to examine the inter-laminar delamination. LVI tests with different impact energies were conducted to provide validating data. It is shown that the numerical results from the strain-rate-dependent damage model are highly consistent with the experimental outcomes. The contact force history curves, intra- and inter-laminar damage evolution process are found to be strain rate dependent, and thus the numerical errors predicted by the strain-rate-independent damage model significantly increase with the increment of the applied impact energy, which is unacceptable in practice for LVI with relatively high impact energies.

Finite element analysis of composite laminates subjected to low-velocity impact based on multiple failure criteria

Progressive damage models based on continuum damage mechanics are used in combination with cohesive elements to explore the effect of three different failure criteria including Chang-Chang, Hashin and Puck criteria, on the structural response and the failure mechanisms of composite laminates subjected to low-velocity impact. Three different failure criteria and damage evolution laws based on equivalent strain are used for intralaminar damage models, and the delamination is simulated by the bilinear cohesive model based on quadratic criteria. A new numerical optimization method combining analytical approximation and Golden section Search has been applied in Puck criteria to search the fracture plane. Numerical analysis is performed on two composite laminates specimens with different materials, layups and impact energy to study the impact force-time, force-displacement and absorbed energy, computational cost, as well as the damage evolution behaviors of fiber, matrix and delamination. The numerical results with three different failure criteria show acceptable accord with available experimental data, which validate the accuracy of the proposed damage model. Moreover, this research can be helpful to select appropriate failure criteria in the progressive failure analysis of composite laminates under low velocity impact.

Finite element analysis of dynamic responses of composite pressure vessels under low velocity impact by using a three-dimensional laminated media model

This paper aims to study dynamic structural responses and failure mechanisms of composite pressure vessels subjected to low velocity impact. First, a three-dimensional laminated media model based on sub-laminate theory is introduced for intralaminar damage, where Puck's failure criteria and strain based damage evolution laws for fiber and matrix are used. The impact responses of composite pressure vessels can be calculated based on sub-laminates and the fiber and matrix damage are predicted based on each ply by using this approach. Second, the proposed laminated media model is implemented using ABAQUS/Explicit user-defined material subroutine VUMAT by the time stepping algorithm and the bilinear cohesive model is employed to simulate interlaminar delamination. Finally, numerical simulations are performed to study the impact force-time/central displacement curves and intralaminar damage and interlaminar delamination features for composite pressure vessels at three different impact energy. Detailed energy dissipation mechanisms due to intralaminar dynamic progressive failure, interlaminar delamination and deformation of liner are also discussed. By comparison, relatively good agreement is achieved between the experimental and numerical results by using the three-dimensional laminated media model.

Experimental and numerical investigation on the crashworthiness of a composite fuselage sub-floor support system

Abstract In the present paper, advanced numerical methodologies have been adopted to investigate the structural behaviour of a composite subcomponent for aerospace applications subjected to quasi-static compression and dynamic loads. The analysed structural component, made of laminated carbon fibres reinforced polymers, is part of the floor support system in the cargo area of a commercial aircraft. The inter-laminar and intra-laminar damage onset and propagation has been preliminary monitored under a quasi-static compressive displacement application. Then, the effects on the structural integrity of two impact energy levels have been analysed: 42 J energy has been applied to study the dynamic behaviour in an elastic linear rate while 585 J energy has been considered to assess the crashworthiness behaviour. The adopted numerical model has been validated by comparisons between the numerical results and analytical mass-spring model results and experimental data in terms of stiffness, strain, and ultimate load. The simultaneous assessment of numerical results and experimental data has allowed to provide a comprehensive insight on the damage onset and propagation leading to the structural collapse of the investigated sub-floor support system.

A Study on the Failure Mechanisms of Composite Laminates Simultaneously Impacted by Two Projectiles

With most studies concentrated on the single point isolated impact events, this work mainly investigates the failure mechanisms of composite laminates simultaneously impacted by two projectiles over low energies. A 3D intralaminar damage model combining continuum damage mechanics to analyze the in-ply damage and cohesive interface elements to simulate the delamination are applied to model the damage evolution of E-glass/epoxy composites simultaneously impacted by two projectiles. The damage model is incorporated into the Abaqus/Explicit by the subroutine VUMAT. A comparison between the simulated predictions and the experimental observations of laminates impacted by one projectile is made to verify the reasonability of the damage model applied. The simulation results indicate that the delamination initiation is not largely affected by the impact energy and the number of the projectiles. As the combined effects of the two projectiles on the laminate, the intersection of matrix damage areas in plies and the connection of delamination regions at interfaces, largely decrease the overall stiffness of the laminate and result in more serious damage.

Reduction of slamming damage in the hull of high-speed crafts manufactured from composite materials using viscoelastic layers

For high-speed crafts, the shift to new materials was initially driven by a need to obtain lighter, stronger vessels, with complex geometries and adapting the mechanical properties of the material to the needs of the design. A new experimental set-up has been designed to reproduce the slamming impacts in small samples of the material, at different velocities and impact energies. Ultrasonic C-scan inspection of each of the prepared specimens has been conducted to evaluate its quality level and the absence of porosity zones. After a certain number of cycles of impacts, each panel was removed and inspected again to assess damage evolution, and the micromechanisms of interlaminar and intralaminar damage propagation. Damage levels have been correlated to residual strengths using AITM-0010 test method for determination of compression strength after impact. It is shown how is possible to effectively mitigate the damage by slamming by inserting a viscoelastic layer into the GFRP panels. The structured combination of a polymer with high deformation capacity with domains of a second, rigid polymer, dampens the impacts and delays the damage progression, improving the dissipation of impact energy, thus protecting the structure of the hull and increasing the service life of the high-speed crafts.

Influence of stiffener configuration on post-buckled response of composite panels with impact damages

In this paper, the effect of T, I and J stiffer configurations on post-buckling response of composite stiffened panels with impact damage is investigated through experiments and numerical simulations. Two identical panels in all three configurations were designed and manufactured. Each panel has four stringers of the same type. All panels were designed to have a skin buckling load of 92 kN ± 5 kN and weight of 1.45 kg ± 0.05 kg to separate the effect of impact damage irrespective of stiffener type. One panel from each configuration is impacted with 50 J energy above stiffener flange from skin side to create a Barely Visible Impact Damage (BVID) and followed by a compression test till collapse. A comparative study between pristine and impacted panels is presented. The effect of impact damage on buckling load, post-buckling response, collapse load and end-shortening were investigated. Moreover, finite element numerical models were developed for all panels which include intra-laminar and inter-laminar damage initiation and growth models. Impact damage area measured from ultrasonic C-scan was modelled in commercial finite element software Abaqus®. Failure modes in pristine and impacted panels such as disbond, tearing of stiffener web and locations from experiments are discussed and validated by numerical simulations.

Clustering of interlaminar and intralaminar damages in laminated composites under indentation loading using Acoustic Emission

This study focuses on the clustering of the indentation-induced interlaminar and intralaminar damages in carbon/epoxy laminated composites using Acoustic Emission (AE) technique. Two quasi-isotropic specimens with layups of [60/0/-60]4S (is named dispersed specimen) and [604/04/-604]S (is named blocked specimen) were fabricated and subjected to a quasi-static indentation loading. The mechanical data, digital camera and ultrasonic C-scan images of the damaged specimens showed different damage evolution behaviors for the blocked and dispersed specimens. Then, the AE signals of the specimens were clustered for tracking the evolution behavior of different damage mechanisms. In order to select a reliable clustering method, the performance of six different clustering methods consisting of k-Means, Genetic k-Means, Fuzzy C-Means, Self-Organizing Map (SOM), Gaussian Mixture Model (GMM), and hierarchical model were compared. The results illustrated that hierarchical model has the best performance in clustering of AE signals. Finally, the evolution behavior of each damage mechanism was investigated by the clustered AE signals with hierarchical model. The results of this study show that using AE technique with an appropriate clustering method such as hierarchical model could be an applicable tool for structural health monitoring of composite structures.

Progressive Analysis of Bearing Failure in Pin-Loaded Composite Laminates Using an Elasto-Plastic Damage Model

Bearing failure of composite laminate is very complicated due to the complexity of different failure mechanisms and their interactions. In this paper, an elasto-plastic damage model is built up to describe the process of failure in composite laminates subjected to bearing load. Non-linear behavior of composite before failure is taken into consideration by using a modified Sun-Chen one parameter plasticity model. LaRC05 failure criteria are employed to predict the initiation of failure and the evolution of failure is described by a CDM based stiffness degradation model. Both theory and some application issues like parameter determination are discussed according to phenomenon of experiments. The model is firstly validated by several experiment results of unidirectional laminate and then applicated into the progressive analysis of bearing failure in pin-loaded multidirectional laminates, both intralaminar and interlaminar damage are taken into consideration. The result of finite element analysis is compared with experiment results; it shows good agreements in both mechanical response and progress of failure, so the model can be evaluated to be effective and practical in bearing failure analysis of composite laminates.

A model of low-velocity impact damage assessment of laminated composite structures

Laminated composites have important applications in modern aeronautical structures due to their extraordinary mechanical and environmental behaviour. Nevertheless, aircraft composite structures are highly vulnerable to impact damage, either by low-velocity sources during maintenance or high-velocity sources during in-flight events. Even barely visible impact damage induced by low-velocity loading, substantially reduces the residual mechanical performance and the safe-service life of the composites structures. Despite the extensive research already carried out, impact damage of laminated composite structures is still not well understood and it is an area of on-going research. Numerical modelling is considered as the most efficient tool as compared to the expensive and time-consuming experimental testing. In this paper, a finite element model based on explicit dynamics formulations is adopted. Hashin criterion is applied to predict the intra-laminar damage initiation and evolution. The numerical analysis is performed using the ABAQUS® programme. The employed modelling approach is validated using numerical results found in the literature and the presented results show an acceptable correlation to the available literature data. It is demonstrated that the presented model is able to capture force-time response as well as damage evolution map for a range of impact energies.

A numerical study on the energy-absorption of fibre metal laminate conical frusta under quasi-static compression loading

The energy-absorption (EA) of fibre metal laminate (FML) conical frusta under quasi-static compression loading is studied by performing virtual test. A progressive deterioration model combined with the conventional shell model is initially employed to simulate collapse behaviors of composite wrapped aluminium conical (CWAC) frusta. To sufficiently understand collapse behaviors, the stacked shell model is used to reproduce intralaminar damage and delamination. The numerical models are validated with available experimental results and the collapse behaviors of aluminium wrapped composite conical (AWCC) frusta are detailedly discussed. The effects of conical frusta with single and hybrid materials towards EA are investigated. The triggering mechanisms including inward and outward chamfer triggers, and convex and concave plug-type triggers are studied to better induce collapse modes of FML conical frusta. Results show that the stacked shell model has better predictive ability of collapse behaviors. The only difference between experiment and simulation is that the initial load is not perfectly captured due to specific conical profile, complex failure modes and hybrid fibre metal materials. The FML conical frusta with appropriate hybrid materials, such as AWCC frusta, present a higher EA capacity with an increase of 28.7% in SEA. The outward chamfer trigger and convex plug-type trigger can effectively improve EA of FML conical frusta.