Damage Model and Progressive Failure Analyses for Filament Wound Composite Laminates

Recent improvements in manufacturing processes and materials properties associated with excellent mechanical characteristics and low weight have made composite materials very attractive for application on civil aircraft structures. However, even new designs are still very conservative, because the composite failure phenomenon is very complex. Several failure criteria and theories have been developed to describe the damage process and how it evolves, but the solution of the problem is still open. Moreover, modern filament winding techniques have been used to produce a wide variety of structural shapes not only cylindrical parts, but also “flat” laminates. Therefore, this work presents the development of a damage model and its application to simulate the progressive failure of flat composite laminates made using a filament winding process. The damage model was implemented as a UMAT (User Material Subroutine), in ABAQUS^TM Finite Element (FE) framework. Progressive failure analyses were carried out using FE simulation in order to simulate the failure of flat filament wound composite structures under different loading conditions. In addition, experimental tests were performed in order to identify parameters related to the material model, as well as to evaluate both the potential and the limitations of the model. The difference between numerical and the average experimental results in a four point bending set-up is only 1.6 % at maximum load amplitude. Another important issue is that the model parameters are not so complicated to be identified. This characteristic makes this model very attractive to be applied in an industrial environment.     

复合材料层合板准静态压痕损伤研究

本文对复合材料层合板准静态横向压缩特性损伤进行了研究.在损伤模拟过程中采用机体开裂和分层扩展判据,分类考虑了不同的损伤形式,通过修正损伤层的材料常数来模拟层板损伤所造成的局部刚度下降对横向压痕过程的影响.损伤模拟结果与超声C扫描的结果吻合较好.     

A Global–Local Numerical Model for the Prediction of Impact Induced Damage in Composite Laminates

Delamination and other damage mechanisms, such as matrix cracks, fibre-matrix debonding and fiber failure can appear as a consequence of impact events with foreign objects under in service conditions and maintenance operations. These phenomena are seldom analyzed together without discussing how the interferences between the different damage mechanisms can influence their evolution under different loading conditions. The present work is focused on the development of a specific numerical procedure, able to take into account the failure modes interaction in composite laminated structures subject to a low velocity impact. As a matter of fact, a very fine mesh refinement is required to correctly evaluate the stress state where the impact induced damage onsets. Hence, in order to reduce the computational cost without compromising the accuracy of results, a global/local approach, characterized by a very refined mesh in the critical impact region interacting with a coarser mesh in the rest of the geometrical domain, has been implemented in the FE model. In the present work, Multi-Point-Constraints (MPC) has been used to link the refined local domain to the coarse global domain without using transition meshes. The implementation and the analyses have been performed in the ABAQUS® FE environment.     

Improvement of Progressive Damage Model to Predicting Crashworthy Composite Corrugated Plate

To predict the crashworthy composite corrugated plate, different single and stacked shell models are evaluated and compared, and a stacked shell progressive damage model combined with continuum damage mechanics is proposed and investigated. To simulate and predict the failure behavior, both of the intra- and inter- laminar failure behavior are considered. The tiebreak contact method, 1D spot weld element and cohesive element are adopted in stacked shell model, and a surface-based cohesive behavior is used to capture delamination in the proposed model. The impact load and failure behavior of purposed and conventional progressive damage models are demonstrated. Results show that the single shell could simulate the impact load curve without the delamination simulation ability. The general stacked shell model could simulate the interlaminar failure behavior. The improved stacked shell model with continuum damage mechanics and cohesive element not only agree well with the impact load, but also capture the fiber, matrix debonding, and interlaminar failure of composite structure.     

Impact Damage to Composite Laminates: Effect of Impact Location

Accidental impact loading of Composite laminates during manufacture and in-service can occur in different locations including near the edge or on the edge of a composite structure. This paper describes investigation of the effect of impact to composite laminates and compares the damage arising from central, near edge and on edge impact events. The damage tolerance of impact damaged laminates using both compression and tension tests has been measured. These results reveal the different damage mechanisms arising from different locations of impact. These different damage mechanisms have been investigated using X-Ray computed tomography. Impact on the edge of composite laminates is found to lead to smaller damage area, but more fibre failure; the severity of this damage is not revealed in standard compression after impact tests.     

Micromechanical Modeling of Impact Damage Mechanisms in Unidirectional Composite Laminates

Composite laminates are susceptible to the transverse impact loads resulting in significant damage such as matrix cracking, fiber breakage and delamination. In this paper, a micromechanical model is developed to predict the impact damage of composite laminates based on microstructure and various failure models of laminates. The fiber and matrix are represented by the isotropic and elastic-plastic solid, and their impact failure behaviors are modeled based on shear damage model. The delaminaton failure is modeling by the interface element controlled by cohesive damage model. Impact damage mechanisms of laminate are analyzed by using the micromechanical model proposed. In addition, the effects of impact energy and laminated type on impact damage behavior of laminates are investigated. Due to the damage of the surrounding matrix near the impact point caused by the fiber deformation, the surface damage area of laminate is larger than the area of ??impact projectile. The shape of the damage area is roughly rectangle or elliptical with the major axis extending parallel to the fiber direction in the surface layer of laminate. The alternating laminated type with two fiber directions is more propitious to improve the impact resistance of laminates.     

T700/6421复合材料层板低速冲击后损伤特性

对未增韧及增韧后的T700/6421复合材料层板进行了低速冲击实验,讨论了表面凹坑深度(D)、表面凹坑直径(R)、冲击后压缩强度(CAI)及冲击能量(E)的关系,并通过记录冲击过程中的接触力与时间的变化分析了冲击时的损伤过程。实验结果表明,增韧后的复合材料其更容易出现深凹坑及更大的表面凹坑直径,更容易实现目视明显可见损伤(VID)的效果,并通过分析冲击历程响应发现:低速冲击过程中复合材料层板起始产生分层损伤时的时间与冲击能量并没有必然的联系。     

碳纤维复合材料层合板低速冲击损伤应力分析

目的 为掌握碳纤维复合材料板在低速冲击载荷作用下的损伤规律,延缓失效破坏,对其冲击损伤的应力状态进行研究。方法 基于ABAQUS平台,建立碳纤维复合材料层合板低速冲击有限元模型,采用Hashin失效准则和VUMAT用户子程序,对碳纤维复合材料层合板的冲击过程进行数值模拟,同时考虑层合板层内与层间失效,以此来研究低速冲击条件下复合材料的损伤机理,分析冲击损伤过程中的应力变化趋势,讨论应力的分布状态。重点研究铺层角度及铺层距离冲头远近对应力的影响。结果 不同角度铺层的应力传播轨迹均沿着纤维方向和垂直于纤维方向同时扩展,应力均先增加至极限值而后迅速下降;铺层角度越大,板料的承载能力越弱,0°铺层的极限应力为1 432 MPa,而90°铺层的极限应力降至1 206 MPa;离冲头越远的铺层应力越小,达到峰值的时间更早且率先下降,说明远离冲头的铺层更早发生失效。结论 揭示了碳纤维层合板在低速冲击载荷作用下的应力状态及其对损伤的影响规律,能够为复合材料层合板零件设计提供参考。     

模糊评价法表征复合材料层合板低能量冲击行为

通过模糊综合评判的方式,建立复合材料低能量冲击表面损伤与其失效的数学判据。复合材料受到冲击后的表面损伤是冲击程度最直观的表现,因此,对复合材料冲击行为的分析,应基于其表面损伤来进行。本研究选择的观测工具为超景深显微镜,观测、探究了复合材料试样受到冲击后的表面损伤情况,建立损伤程度与材料冲击门槛值之间的数值关系。经实验验证,该数值关系可以精确判断材料是否失效。同时也验证了不同厚度的复合材料,其失效时的表面损伤有某些共同特性,本文给出的判据可以在树脂基复合材料中通用。     

离位增韧复合材料层合板准静态压入实验研究

采用准静态压入(Quasi-Static Indentation, QSI)实验方法对"离位"增韧复合材料层合板和未增韧层合板进行了实验研究.分析了QSI实验中层合板的损伤破坏过程,并对两类层合板的实验结果进行了对比分析.结果表明:"离位"增韧技术能够有效提升复合材料层合板的低速冲击损伤阻抗性能;准静态压入实验中,接触...     

A Higher Order Synergistic Damage Model for Prediction of Stiffness Changes due to Ply Cracking in Composite Laminates

A non-linear damage model is developed for the prediction of stiffness degradation in composite laminates due to transverse matrix cracking. The model follows the framework of a recently developed synergistic damage mechanics (SDM) approach which combines the strengths of micro-damage mechanics and continuum damage mechanics (CDM) through the so-called constraint parameters. A common limitation of the current CDM and SDM models has been the tendency to over-predict stiffness changes at high crack densities due to linearity inherent in their stiffness-damage relationships. The present paper extends this SDM approach by including higher order damage terms in the characterization of ply cracking damage inside the material. Following the SDM procedure, predictions are aided by suitable micromechanical computations of crack opening displacements. A nonlinear SDM model is developed and applied for multiple classes of composite laminate layups. Stiffness predictions for damaged laminates using the developed model are compared with the experimental data for cross-ply ([0m/90n]s), angle-ply ([±θm/90n]s), off-axis ([0/±θ4/01/2]s) and quasi-isotropic ([0/90/±45]s) laminates. A comparison with current linear damage models showcases the usefulness of the proposed nonlinear SDM approach.     

碳纤维增强复合材料含孔层合板损伤破坏分析研究进展

综述了碳纤维增强复合材料含孔层合板损伤破坏以及应力分析的研究进展，介绍了几种含孔层合板的破坏准则和分析含孔层合板损伤破坏的二维以及三维模型，展望了有待于进一步研究的问题。     

A Progressive Damage Model for unidirectional Fibre Reinforced Composites with Application to Impact and Penetration Simulation

The computationally efficient simulation of the progressive damage behaviour of continuous fibre reinforced plastics is still a challenging task with currently available computer aided engineering methods. This paper presents an original approach for an energy based continuum damage model which accounts for stress-/strain nonlinearities, transverse and shear stress interaction phenomena, quasi-plastic shear strain components, strain rate effects, regularised damage evolution and consideration of load reversal effects. The physically based modelling approach enables experimental determination of all parameters on ply level to avoid expensive inverse analysis procedures. The modelling strategy, implementation and verification of this model using commercially available explicit finite element software are detailed. The model is then applied to simulate the impact and penetration of carbon fibre reinforced cross-ply specimens with variation of the impact speed. The simulation results show that the presented approach enables a good representation of the force-/displacement curves and especially well agreement with the experimentally observed fracture patterns. In addition, the mesh dependency of the results were assessed for one impact case showing only very little change of the simulation results which emphasises the general applicability of the presented method.     

Micromechanical Analysis of Interphase Damage for Fiber Reinforced Composite Laminates

In the present study, the initiation and evolution of the interphase damage and their influences on the global stress-strain relation of composite laminates are predicted by finite element analysis on a micromechanical unit cell model. A thin layer of interphase elements is introduced and its stress-strain relation is derived based on a cohesive law which describes both normal and tangential separations at the interface between the fiber and matrix. In addition, a viscous term is added to the cohesive law to overcome the convergence difficulty induced by the so-called snap-back instability in the numerical analysis. The matrix behavior is described by a recently developed nonlinear viscoelastic constitutive model. As application examples, glass fiber/epoxy unidirectional laminates under off-axis loadings are analyzed. One-quarter of the unit cell is used in the analysis accounting for the geometrical symmetry of the model, and the corresponding periodic boundary conditions for combined global shear and normal loading are derived. Results show that the initiation and evolution of the interphase damage can be well simulated and the predicted global stress-strain responses are in good agreement with the experimental results.     

Simulating Initial and Progressive Failure of Open-Hole Composite Laminates under Tension

A finite element (FE) model is developed for the progressive failure analysis of fiber reinforced polymer laminates. The failure criterion for fiber and matrix failure is implemented in the FE code Abaqus using user-defined material subroutine UMAT. The gradual degradation of the material properties is controlled by the individual fracture energies of fiber and matrix. The failure and damage in composite laminates containing a central hole subjected to uniaxial tension are simulated. The numerical results show that the damage model can be used to accurately predicte the progressive failure behaviour both qualitatively and quantitatively.     

铜离子注入T700/6421复合材料层板低速冲击损伤的研究

对T700/6421复合材料层压板进行铜离子注入,改变其表面性能,使得低速冲击损伤表面目视勉强可检(BVID).用TEM观察离子注入深度、形貌及分布情况,对离子注入前后的复合材料进行了显微硬度的测定,并进行了落锤冲击试验,结果表明:离子注入后的复合材料显微硬度明显增加,受低速冲击后,表面更容易出现深凹坑,表面目视可检损伤更容易实现,冲击后压缩强度增加,从冲击过程的动态力学响应特性可以得知,离子注入后的复合材料受冲击时分层起始载荷有所提高,最大接触力也有相应增加.     

A Graphical Method Predicting the Compressive Strength of Toughened Unidirectional Composite Laminates

The in-plane shear and compressive properties of unidirectional (UD) HTS40/977-2 carbon fibre-toughened resin (CF/TR) laminates are investigated. Scanning Electron microscopy (SEM) and optical microscopy are used to reveal the failure mechanisms developed during compression. It is found that damage initiates by fibre microbuckling (a fibre instability failure mode) which then is followed by yielding of the matrix to form a fibre kink band zone that leads to final fracture. Analytical models are briefly reviewed and a graphical method, based on the shear response of the composite system, is described in order to estimate the UD compressive strength. Predictions for the HTS40/977-2 system are compared to experimental measurements and to data of five other unidirectional carbon fibre reinforced polymer (CFRP) composites that are currently used in aerospace and other structural applications. It is shown that the estimated values are in a good agreement with the measured results.     

Matrix-Dominated Damage in Notched Cross-Ply Composite Laminates: Experimental Observations

The matrix-dominated damage in three highly transparent notched cross-ply laminates with double-edge-semicircular notches were experimentally investigated under a monotonously increasing quasi-static tensile load. A newly designed computer controlled digital camera-video recorder system was successfully used to record the real time damage development due to the enhanced stresses around the notches. The damage states were quantitatively characterised as a function of the nominal strain or stress. It was observed that the notches have significant influences on the formation and propagation of the matrix-dominated subcritical damage. The damage states, which depend on the type of the laminate and the size of the notches, appeared to be highly reproducible. Instead of the conventional longitudinal cracks (splits) and the free-edge delamination in unnotched specimens, notch-induced splits (NISs) and notch-induced delamination (NID) were observed. The notches speed up the transverse damage growth in the areas near the notches, both in density and in length. The ultimate strength of the laminates with different notch size is significantly different, due to the diversities of the final failure mechanisms. The notch size and the laminar thickness are two key parameters determining the mode of the matrix damage and the final failure mechanisms of the laminates.     

纤维增强层合板低能冲击损伤机理分析

针对复合材料低能冲击损伤机理研究不足的现状,应用复合材料层合板三维逐渐累积冲击损伤预测方法,对3种不同铺层顺序的T300/BMP-316层合板的低能冲击过程进行了详细分析,研究了其损伤在各层中的分布规律,并结合层合板的应力等值线图,分析了基体开裂及分层的损伤机理,研究认为基体开裂产生主要由垂直于纤维方向的拉应力达到一定值后,基体和纤维的形变不协调引起的;冲击背面附近和冲击正面附近的分层,分别是由基体开裂和相邻层的弯曲刚度不协调引起的。     

A Plane-Stress Damage Model for Vectran Laminated Composite

Applied Composite Materials - The aim of this paper is to present a plane-stress damage model based on the Classical Lamination Theory (CLT), developed for polymer fibre-based composite. The...