含孔复合材料层合板逐渐损伤破坏分析

采用逐渐损伤模型有限元技术对含复合材料层板损伤破坏规律进行了研究，编制了面向对象的后处理软件，为损伤累积，损伤扩展与破坏以及损伤类型与模式的预测和研究提供了先进手段，并针对含孔T30／KH304复合材料层板进行了数值模拟和试验研究，研究表明，采用二维逐渐损伤模型及分析方法，以及所发展的后处理模拟分析软件能够较好地模拟含孔层合板的损伤破坏规律和位移－载荷的响应规律，以豚预测层合板的损伤类型，破坏模式和破坏强度，得到了一些有意义的结论。     

Recent developments on damage modeling and finite element analysis for composite laminates: A review

Under complex environments such as continuous or cyclic loads, the stiffness degradation for the laminated composites such as the carbon fiber reinforced polymer matrix composites is an important physical and mechanical response to the damage and failure evolution. It is essential to simulate the initial and subsequent evolution process of this kind of damage phenomenon accurately in order to explore the mechanical properties of composite laminates. This paper gives a comprehensive review on the general methodologies on the damage constitutive modeling by continuum damage mechanics (CDM), the various failure criteria, the damage evolution law simulating the stiffness degradation, and the finite element implementation of progressive failure analysis in terms of the mechanical response for the variable-stiffness composite laminates arising from the continuous failure. The damage constitutive modeling is discussed by describing the evolvement of damage tensors and conjugate forces in the CDM theory. The failure criteria which interpret the failure modes and their interaction are compared and some advanced methods such as the cohesive theory which are used to predict the damage evolution properties of composites are also discussed. In addition, the solution algorithm using finite element analysis which implements progressive failure analysis is summarized and several applicable methods which deal with the numerical convergence problem due to singular finite element stiffness matrices are also compared in order to explore the whole failure process and ultimate load-bearing ability of composite laminates. Finally, the multiscale progressive failure analysis as a popular topic which associates the macroscopic with microscopic damage and failure mechanisms is discussed and the extended finite element method as a new finite element technique is expected to accelerate its practical application to the progressive failure analysis of composite laminates.     

弯曲载荷下机织复合材料T型接头渐进失效分析

根据树脂传递模塑(RTM)成型的缎纹机织复合材料T型接头的结构特征和纤维布局特点, 基于ANSYS有限元数值分析平台, 建立符合其真实结构的几何模型和有限元分析模型。基于渐进失效强度预测方法的基本思想, 使用有限元计算软件ANSYS的参数化设计语言(APDL)开发相应的程序, 实现改进形式的Hashin失效准则。采用合适的最终失效评价方法, 建立二维机织结构复合材料T型接头受弯曲载荷时的渐进失效预测方法, 能够有效地模拟从初始加载到最终失效过程中机织复合材料T型接头结构的力学响应及损伤的萌生与发展, 并预测结构的静强度。      

Illustrations of a microdamage model for laminates under oxidizing thermal cycling

Degradations initiated near the edges of a laminate can have a significant effect on its state of degradation, even at the core. Indeed, results from the literature show that laminates which have the same stress state at the core can have completely different states of degradation, even far away from the edges. The paper discusses the influence of the edge effect on damage initiation and propagation for a specific example. A computational micromechanical approach to the degradation of laminated composites was developed recently at LMT-Cachan. This is a hybrid approach in which, depending on the scale, the mechanisms are described using continuous damage mechanics or finite fracture mechanics. Initially developed for static loading, this technique is being extended to fatigue and environmental effects. The aim of this paper is to illustrate the capability of such an approach to take into account major observations during cyclic loading in an oxidizing atmosphere, even when edge effects are significant.     

Modelling VARTM process induced variations on bending performance of composite Omega beams

Finite element simulation with cohesive contact is presented, to correlate the vacuum assisted RTM process and the bending performance of Omega beams. The model considers the process induced variations, including part thickness, resin rich pockets and voids. The bending performance prediction relies on cohesive contact to model delamination initiation and propagation. Computing efficiency is achieved by mesh scaling. The modelling approach applies to three variations of Omega beams with the different mode-mixture ratios. The finite element predictions result in a high degree of agreement with the experimental measurements.     

缝合泡沫夹芯复合材料低速冲击的多尺度数值方法

为了发展缝合泡沫夹芯复合材料低速冲击损伤的多尺度分析方法, 建立了缝合泡沫简化力学模型, 将缝合泡沫等效为缝线树脂柱增强的正交各向异性芯材, 其材料参数由各组分性能及所占体积分数根据均一化理论计算得出; 同时, 建立冲击试验有限元模型, 通过界面元模拟面板与芯材之间的层间分层。采用GENOA渐进损伤分析模块对缝合结构冲击动态响应过程进行数值模拟, 并将计算结果与试验记录进行对比分析。结果表明: 缝合可以减小面板破坏面积, 抑制面板与泡沫分层的扩展; 但缝纫会对结构造成初始损伤, 较高的缝合密度使芯材刚度增加, 不利于泡沫结构的缓冲吸能。数值模拟结果与试验记录吻合良好, 验证了多尺度分析方法的正确性。     

考虑纤维缠绕形态的复合材料结构拉伸承载行为

纤维缠绕复合材料的纤维束具有交叉起伏形态特征,该形态对复合材料结构的力学行为有显著的影响。本文采用数值仿真和实验手段研究了纤维缠绕复合材料平板结构的拉伸力学行为。实验方面,开展纤维缠绕复合材料平板的准静态拉伸实验,通过数字图像相关技术(DIC)监测其表面应变场的演化过程,研究交叉起伏特征对载荷-位移曲线和应变分布特征的影响;数值分析方面,构建包含纤维缠绕形态的介观有限元模型,基于3D Hashin失效准则开展渐进损伤过程模拟,并引入了复合材料的剪切非线性行为。选取层合板结构为参照组,同时开展实验和数值分析。实验结果表明:对于层合结构,缠绕结构的整体刚度更低,失效位移更大,失效载荷基本相同,且缠绕结构菱形特征单元中部纤维交叉起伏区域存在明显的应变集中现象。所构建的有限元模型和实验结果吻合较好,呈现出纤维起伏区域的应变集中、失效起始和扩展行为。      

Finite Element Analysis of Micromechanical Progressive Failure Properties of Glass Fiber/Phenolic Resin Composites by Monte Carlo Simulation

Journal of Failure Analysis and Prevention - This paper studies the micromechanical progressive failure properties of glass fiber/phenolic resin composites by finite element analysis and...     

Impact damage response of natural stitched single lap-joint in composite structures

In this paper the damage behaviour of natural stitched composite single lap-joints are investigated under low velocity impact loading conditions. For this study, the laminated hybrid composite beams were pinned using Flax yarns before curing process. The Charpy impact test was chosen to study the energy absorbing capability of single lap composite joints. Composite beams were fabricated from combination of glass/epoxy and carbon/epoxy composites. It was shown that composite beams which are stitched through the thickness are able to absorb more energy in comparison with adhesive bonded composite joints in the hybrid composite beams. The Charpy impact test of stitched composite single lap joint was also simulated by finite element analysis using software LS-DYNA and the results verified with relevant experimental data.     

Progressive failure analysis of laminated composite with hole under flexural loading

Abstract

Understanding the progressive failure of laminated composite plays an important role in the structural integrity analysis of a structure. Continuum damage mechanics-based approach is one of the powerful tools to analyze the failure of laminated composite structures. The present paper investigates the damage evolution and progression in laminated composites with a hole under flexural loading. The presence of high-stress concentrations along with the free edge stresses at the vicinity of the hole in laminated composite leads to complex failure mechanisms. The influence of the change in thickness and lamina configuration on the strength characteristics is presented.     

Investigation of prepreg bonded composite single lap joint

Adhesive bonded single lap joint has been used extensively in laminated composite structures. Using neat resin adhesives, however, the joint strength is comparatively low and the fabrication time is long. In order to increase the joint strength and reduce the fabrication time, two types of fiber pre-impregnated (prepreg) composites were used to bond composite single lap joints. Test specimens were prepared per ASTM D 3165-95 standard. Ninety days of accelerated conditioning using seawater and ultraviolet radiation were conducted to investigate the long-term performance of prepreg bonded single-lap joint in an offshore environment. The shear strength of various specimens was obtained using tension tests. Two types of neat resin bonded specimens were also used for comparisons. Finite element analysis was implemented to justify test results. Parameters affecting the load carrying capacity of prepreg bonded composite single lap joints were investigated based on finite element analysis results.     

A linear finite element model to predict processing-induced distortion in FRP laminates

Manufacturing processes for laminated composites often produce parts whose dimensions do not match the mold from which they were made. This distortion is commonly referred to as ‘spring-in’. The amount of spring-in can depend on many factors including the manufacturing process (cure temperature, resin bleed, and applied pressure), the part (geometry, material, thickness, cure shrinkage, thermal expansion and layup sequence), and the tool (surface, thickness and thermal expansion). Much of the current work devoted to spring-in relies on extensive resin characterization. While this approach has been reasonably successful, it does little to assist the designer using material systems that have not been fully characterized (which is not always possible or feasible). This study considers the ability of a linear elastic finite element model to describe and quantify many of the factors contributing to spring-in. The aim of this study is to show that spring-in can be accurately predicted without a complete resin characterization. Numerical predictions based on relatively simple mechanical tests were observed to compare favorably with experimental measurements. Spring-in was dominated by thickness shrinkage, which contributed approximately 3/4 of the measured distortion. The mold stretching contribution diminished with thickness and was negligible for parts thicker than 2.5 mm (0.1 in.). While the material system at hand did not exhibit a fiber volume fraction gradient, its effects were included in the formulation of the model. For materials that have reported a gradient, it was found to account for approximately 10% of the part spring-in.     

Assessment of a composite beam finite element based on the proper generalized decomposition

In this paper, a finite element based on the Proper Generalized Decomposition (PGD) is presented for the analysis of bi-dimensional laminated beams. The displacement field is approximated as a sum of separated functions of x (axial coordinate) and z (transverse coordinate). This choice yields to an iterative process that consists of computing a product of two one-dimensional functions at each iteration. The capability and the behavior of the PGD approach are shown on isotropic beam with different slenderness ratios. A second and fourth-order expansion with respect to the thickness are considered. Mechanical tests for thin/thick laminated and sandwich beams are presented in order to evaluate the two approaches. They are compared with elasticity and 2D finite element reference solutions.     

Compressive response of Z-pinned woven glass fiber textile composite laminates: Experiments

In the first of this two part sequel, experimental results pertaining to the compressive response and failure of Z-pinned S-Glass fiber, plain-weave laminated composites are presented. These experiments are motivated by a need to understand the effect of Z-pinning on the strength and stiffness of these composites. A series of experiments are performed based upon density of the Z-pins and the diameter of the Z-pins. It is concluded that the damage zone around a Z-pin plays an important role in influencing the stiffness and strength of the Z-pin composite. In part 2 of this sequel, a 3D finite element (FE) based numerical model (based upon the composite microstructure acquired from scanning electron micrograph-SEM images) are used to capture details of the observed failure mechanisms and to provide predictions of the stiffness and strength of the composite.     

The effects of geometric parameters on the failure strength for pin-loaded multi-directional fiber-glass reinforced epoxy laminate

A numerical and experimental study was carried out to determine the failure of mechanically fastened fiber-reinforced laminated composite joints. E/glass–epoxy composites were manufactured to fabricate the specimens. Mechanical properties and strengths of the composite were obtained experimentally. Tests have been carried out on single pinned joints in [0/90/0]_s and [90/0/90]_s laminated composites. A parametric study considering geometries was performed to identify the failure characteristics of the pin-loaded laminated composite. Data obtained from pin-loaded laminate tests were compared with the ones calculated from a finite element model (PDNLPIN computer code). Damage accumulations in the laminates were evaluated by using Hashin's failure criteria combined with the proposed property degradation model. Based on the results, ply orientation and geometries of composites could be crucial for pinned laminated composite joints.     

Analytical simulation of strength size effect in composite materials

This paper presents a theoretical analysis of the strength size effect associated with the length, width and thickness of laminated composites. The presented expressions for prediction of the reliability, use the Equal Load Sharing Rule (ELS Rule) which are determined by sequential multi-step failure of single lamina or sublaminate. The developed equations are validated using two sets of experimental data obtained from published data. The influence of the length, width, and thickness on the ultimate strength of laminated composites is demonstrated. Strength size effect is analyzed for the in-plane strength parameters. The developed size effect equations are implemented in a user-defined subroutine UMAT in the finite element code ABAQUS to demonstrate their applicability in numerical analysis.     

复合材料厚壁圆筒的损伤问题

基于连续介质损伤力学理论,引入表征材料内部微细缺陷的损伤变量,导出了三维复合材料厚壁圆筒的损伤模型,预测该结构内各处的损伤过程;针对不同损伤模式,推导出包含不同结合力和损伤变量的损伤扩展准则;利用三维有限元分析软件模拟计算出结构损伤破坏的全过程,分析了复合材料圆筒的损伤模式与破坏机理,以及能量变化关系。     

复合材料层合板低速冲击逐渐累积损伤预测方法

针对复合材料层板在冲击载荷下,各种损伤的产生和扩展是一个随载荷、时间和空间而演变的过程,发展了复合材料层合板低速冲击逐渐累积损伤预测方法.采用刚度退化技术和改进的Chang-Chang失效准则、显式有限元法来模拟复合材料层合板受到低速冲击下逐渐损伤过程.使用所发展的方法分析了[0m/90n/0m]铺层的复合材料层合板在低速冲击过程中的逐渐损伤扩展,结果表明本文的方法能较好地模拟复合材料层板在低速冲击下的损伤扩展及变形过程,计算结果与实验结果吻合较好;对不同冲击能量下层合板损伤扩展研究表明,冲击能量与分层损伤面积成线性关系.     

Determination of Fracture Parameters for Multiple Cracks of Laminated Composite Finite Plate

A predictive method for estimation of stress state at zone of crack tip and assessment of remaining component lifetime depend on the stress intensity factor (SIF). This paper discusses the numerical approach for prediction of first ply failure load (F_L), progressive failure load, SIF and critical SIF for multiple cracks configurations of laminated composite finite plate using finite element method (FEM). The Hashin and Chang failure criterion are incorporated in ABAQUS using subroutine approach user defined field variables (USDFLD) for prediction of progressive fracture response of laminated composite finite plate, which is not directly available in the software. A tensile experiment on laminated composite finite plate with stress concentration is performed to validate the numerically predicted subroutine results, shows excellent agreement. The typical results are presented to examine effect of changing the crack tip distance (S), crack offset distance (H), and stacking fiber angle (θ) on F_L, and SIF .     

Damage analysis of laminated composites using a new coupled micro‐meso approach

In this study, the simplicity and strong physical meaning of micromechanics approach and capability of mesomechanics approach for damage analysis of structures with complex loadings are employed to develop a new micro‐meso approach. For this purpose, a new micromechanics model is developed to predict the matrix cracking initiation and evolution in laminated composites. These damage initiation and evolution are replaced with the damage criteria and flow rule in the continuum damage approach, respectively. The results of this procedure are used in the FEM damage analyses of laminated composites to predict constitutive response of layered composites. It is shown that, the predicted stress distribution and strain energy in a lamina unit cell are in good agreement with the finite element results. Furthermore, it is shown that the predicted stress–strain behaviours are in good agreement with the available experimental results for various laminates with different lay‐ups.