基于弹塑性损伤本构模型的复合材料层合板破坏荷载预测

在连续损伤力学和塑性力学框架内,建立一个同时考虑塑性效应和损伤累积导致材料属性退化的复合材料弹塑性损伤本构模型。基于最近点投影回映算法,开发本构模型的应变驱动隐式积分算法以更新应力及与解答相关的状态变量,并推导与所开发算法相应的数值一致性切线刚度矩阵,保证有限元分析采用NewtonRaphson迭代法解答非线性问题的计算效率。采用断裂带模型对已开发的本构模型软化段进行规则化,以减轻有限元分析结果的网格相关性问题。对损伤变量进行粘滞规则化,并推导出相应的粘滞规则化数值一致性切线刚度张量,解决了在有限元隐式计算程序中采用含应变软化段本构关系的数值分析由于计算困难而提前终止的问题。开发包含数值积分算法的用户材料子程序UMAT,并嵌于有限元程序Abaqus v6.14中。通过对力学行为展现显著塑性效应的AS4/3501-6V型开口复合材料层合板的渐进失效分析,验证本文提出的材料本构模型的有效性。结果显示,预测结果与已报道的试验结果吻合良好,并且预测精度高于其他已有弹性损伤模型。表明已建立的弹塑性损伤本构模型能够准确预测力学行为,展现显著塑性效应的复合材料层合板的破坏荷载,为其构件和结构设计提供一种有效的分析方法。     

基于剪切非线性三维损伤本构模型的复合材料层合板失效强度预测

基于连续损伤力学,建立了同时考虑复合材料剪切非线性效应和损伤累积导致材料属性退化的三维损伤本构模型。模型能够区分纤维损伤、基体损伤和分层损伤不同的失效模式,并定义了相应损伤模式的损伤变量。复合材料层合板层内纤维初始损伤采用最大应力准则判定,基体初始损伤采用三维Puck准则中的基体失效准则判定,分层初始损伤采用三维Hou准则中的分层破坏准则判定,为了计算Puck失效理论中的基体失效断裂面角度,本文提出了分区抛物线法,通过Matlab软件编写计算程序并进行分析。结果表明,与Puck遍历法和分区黄金分割法对比,本文提出的分区抛物线法有效地降低了求解断裂面角度的计算次数,提高了计算效率和计算精度。推导了本构模型的应变驱动显式积分算法以更新应力和解答相关的状态变量,开发了包含数值积分算法的用户自定义子程序VUMAT,并嵌于有限元程序Abaqus v6.14中。通过对力学行为展现显著非线性效应的AS4碳纤维/3501-6环氧树脂复合材料层合板进行渐进失效分析,验证了本文提出的材料本构模型的有效性。结果显示,已提出的模型能够较准确地预测此类复合材料层合板的力学行为及其失效强度,为复合材料构件及其结构设计提供一种有效的分析方法。      

A new damage model for composite laminates

Aircraft composite structures must have high stiffness and strength with low weight, which can guarantee the increase of the pay-load for airplanes without losing airworthiness. However, the mechanical behavior of composite laminates is very complex due the inherent anisotropy and heterogeneity. Many researchers have developed different failure progressive analyses and damage models in order to predict the complex failure mechanisms. This work presents a damage model and progressive failure analysis that requires simple experimental tests and that achieves good accuracy. Firstly, the paper explains damage initiation and propagation criteria and a procedure to identify the material parameters. In the second stage, the model was implemented as a UMAT (User Material Subroutine), which is linked to finite element software, ABAQUS™, in order to predict the composite structures behavior. Afterwards, some case studies, mainly off-axis coupons under tensile or compression loads, with different types of stacking sequence were analyzed using the proposed material model. Finally, the computational results were compared to the experimental results, verifying the capability of the damage model in order to predict the composite structure behavior.     

A micromechanical composite approach for finite element crashworthiness simulation

The present article deals with micromechanical composite modeling. Both analytical and computational micromechanics approaches are described as well as micromechanical modeling of damage. Based on micromechanics of failure theory, a user subroutine including a progressive damage algorithm is programmed for finite element analysis. Three theory-experiment correlations of tubes under a three-point bending test have been carried out using the bi-phase material model developed along with this project. These studies include three-ply schedules.     

复合材料多钉斜削搭接连接强度预测与累积损伤研究

该文基于三维逐渐损伤理论,采用ANSYS的二次开发语言,建立了复合材料层合板多钉斜削搭接结构的三维有限元模型,考虑接触状态非线性和累积损伤过程非线性,并用牛顿-拉普森非线性迭代算法,对复合材料多钉斜削搭接结构从初始失效到最终失效的过程进行可视化模拟并对其连接强度进行了研究;数值模拟计算结果与文献结果进行比较,验证了本模型的正确性。分析结果得到:斜削程度不同、几何尺寸不同,连接结构的失效扩展过程不同;并且不同铺层失效形式不同;在一定程度上,随着斜削程度的降低,优化了钉载分配,初始失效载荷和最终失效载荷有所升高,提高了连接效率。     

Auto‐adaptive multiblock cycle jump algorithm for fatigue damage simulation of long‐span steel bridges

An algorithm is developed for fatigue damage evolution simulation of long‐span steel bridges based on continuum damage mechanics (CDM) in this study. The progressive fatigue damage from local component damage evolution to entire structural failure is simulated with nonstandard varying block cycle length, which is automatically obtained during computation to speed up fatigue evolution simulation without user intervention. In this paper, progressive fatigue damage evolution of the Stonecutters cable‐stayed bridge due to vehicle loading is simulated by using the proposed algorithm and the bridge model. It shows that the algorithm is effective, and it can improve the computational efficiency of fatigue damage simulation of a large‐scale steel bridge.     

3D constitutive model of anisotropic damage for unidirectional ply based on physical failure mechanisms

A 3D anisotropic continuum damage model is developed for the computational analysis of the elastic–brittle behaviour of fibre-reinforced composite. The damage model is based on a set of phenomenological failure criteria for fibre-reinforced composite, which can distinguish the matrix and fibre failure under tensile and compressive loading. The homogenized continuum theory is adopted for the anisotropic elastic damage constitutive model. The damage modes occurring in the longitudinal and transverse directions of a ply are represented by a damage vector. The elastic damage model is implemented in a computational finite element framework, which is capable of predicting initial failure, subsequent progressive damage up to final collapse. Crack band model and viscous regularization are applied to depress the convergence difficulties associated with strain softening behaviours. To verify the accuracy of the damage model, numerical analyses of open-hole laminates with different lay-up configurations under tension and compression were performed. The numerical predictions were compared with the experimental results, and satisfactory agreement was obtained.     

A comprehensive implicit substepping integration scheme for multisurface plasticity

A complex elastoplastic model requires a robust integration procedure of the evolution equations. The performance of the finite element solution is directly affected by the convergence characteristics of the state-update procedure. Thereby, this study proposes a comprehensive numerical integration scheme to deal with generic multisurface plasticity models. This algorithm is based on the backward Euler method aiming at accuracy and stability, and on the Newton–Raphson method to solve the unconstrained optimization problem. In this scenario, a line search strategy is adopted to improve the convergence characteristics of the algorithm. The golden section method, an exact line search, is considered. Also, a substepping scheme is implemented to provide additional robustness to the state-update procedure. Therefore, this work contributes to computational plasticity presenting an adaptive substep size scheme and a consistent tangent modulus according to the substepping technique. Finally, some numerical problems are evaluated using the proposed algorithm. Single-surface and novel multisurface plasticity models are employed in these analyses. The results testify how the line search and substepping strategies can improve the robustness of the nonlinear analysis.     

Accelerating cyclic plasticity simulations using an adaptive wavelet transformation based multitime scaling method

Cyclic finite element simulations of complex materials, for example, polycrystalline metals, are widely used to study fatigue failure due to plasticity and damage. Typically, this requires the simulation of a large number of cycles to failure for accurate determination of evolving deformation variables. Modeling cyclic deformation using conventional methods of time integration in semidiscretization techniques can however be computationally challenging. Single time scale integration methods typically follow the high frequency characteristics and discretize each cycle into a number of time steps over which integration is performed. To overcome this computational challenge, the wavelet transformation‐based multitime scale (WATMUS) method proposed in an earlier work by the authors is advanced and validated in this paper to perform accelerated finite element simulations of materials undergoing rate‐dependent plasticity for large number of cycles. Specifically, the WATMUS algorithm is integrated with crystal plasticity finite element method to perform accelerated simulations of polycrystalline alloys. The WATMUS methodology is also endowed with adaptive capabilities to optimally construct the wavelet basis functions and determine coarse‐scale cycle steps. Accuracy and efficiency of the WATMUS methodology is conclusively demonstrated by comparing the results with cyclic single‐time scale crystal plasticity finite element simulations performed on image‐based microstructure of titanium alloys. Copyright © 2012 John Wiley & Sons, Ltd.     

Progressive failure modeling of woven fabric composite materials using multicontinuum theory

Failure of composite materials often results from damage accumulation in the individual constituents (fiber and matrix) of the composite. At times, damage may even be limited to a single constituent. The ability to accurately predict not only ultimate strength values but also intermediate constituent level failures is crucial to the success of introducing composite materials into demanding structural applications.In this paper, we develop two progressive failure models for the analysis of a plain weave composite material. The formulations are based on treating the weave as consisting of separate but linked continua representing the warp fiber bundles, fill fiber bundles, and pure matrix pockets. Retaining constituent identities allows one to access constituent (phase averaged) stress fields that are used in conjunction with both a stress based and damage based failure criterion to construct a nonlinear progressive failure algorithm for the woven fabric composite material. The MCT decomposition and the nonlinear progressive failure algorithm are incorporated within the framework of a traditional finite element analysis.The constituent based progressive failure algorithm combined with both the stress based and damage based failure criteria are compared against experimental data for a plain weave, woven fabric composite under various loading conditions. The analytical results from the damage based approach show a marked improvement over the stress based predictions and are in excellent agreement with the experimental data.     

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.     

Damage model and implementation in nonlinear dynamic problems

Microcracking, damage and subsequent softening in materials introduce higher levels of nonlinearity than those for materials characterized by nonlinear elastic or classical plasticity models. Hènce, implementation of such advanced models that allow for the foregoing effects require special considerations in terms of the analysis of the characteristics of the model, convergence during plastic deformations, and time integration schemes that consider the nonlinearity.This paper describes a damage model, a special scheme involving drift correction and the generalized time finite element (GTFEM) scheme for time integration for dynamic analysis. The main objective is to examine the model and develop schemes that can lead to consistent and reliable predictions from computational procedures. Toward this aim, (1) the damage model is analyzed with respect to its convergence behavior with mesh refinement, (2) a special drift correct scheme is implemented for the plasticity based model, (3) the generalized time finite element method (GTFEM) is implemented in the nonlinear dynamic finite element procedure for time integration and compared with the Newmark method, and (4) the damage model, the drift correction scheme and the GTFEM are verified by solution of representative static and dynamic problems involving a material (concrete) that experiences damage and softening, including verification with respect to behavior of concrete in the laboratory.     

含纤维波纹缺陷复合材料层合板的损伤分析

纤维波纹是复合材料层合板制备过程中的一种常见缺陷,会导致其刚度和强度显著下降,有效地预测含波纹缺陷复合材料层合板的失效强度具有显著的意义。基于此,本文采用解析的方式分别构造了纤维波纹呈正弦起伏与余弦起伏状的复合材料层合板模型。利用该模型,以Tsai-Wu准则作为失效判据,研究了一种含纤维波纹的碳纤维/环氧树脂复合材料层合板在受压情况下的损伤演化过程,得到了碳纤维/环氧树脂复合材料层合板的初始损伤强度。与有限元方法计算得到的损伤位置和损伤强度非常吻合,验证了本文算法的正确性。另外,相比于有限元方法,本文所述计算方法具有模型构造简单、计算效率高等优点,便于快速分析和确定含纤维波纹缺陷复合材料层合板的损伤位置与损伤强度。      

Computationally efficient modelling of the fatigue behaviour of composite materials

Fatigue of composite structures is a complex process involving several types of failure. Existing approaches either neglect this complexity or require large computational effort. In this work, a simple progressive damage model including strength and stiffness degradation is implemented into finite element (FE) software. To reduce computational time, the major part of stress calculations is carried out by classical lamination theory. At single points of time, FE analysis is employed to support these calculations. The simplified model is tested against a reference model using FEA after each load cycle. Calculations are set up for a tensile specimen and a cap profile with quasi-isotropic layup. The simplified model using CLT is shown to be in good agreement with the reference while significantly reducing computational time.     

Progressive damage and nonlinear analysis of pultruded composite structures

This study combines a simple damage modeling approach with micromechanical models for the progressive damage analysis of pultruded composite materials and structures. Two micromodels are used to generate the nonlinear effective response of a pultruded composite system made up from two alternating layers reinforced with roving and continuous filaments mat (CFM). The layers have E-glass fiber and vinylester matrix constituents. The proposed constitutive and damage framework is integrated within a finite element (FE) code for a general nonlinear analysis of pultruded composite structures using layered shell or plate elements. The micromechanical models are implemented at the through-thickness Gaussian integration points of the pultruded cross-section. A layer-wise damage analysis approach is proposed. The Tsai–Wu failure criterion is calibrated separately for the CFM and roving layers using ultimate stress values from off-axis pultruded coupons under uniaxial loading. Once a failure is detected in one of the layers, the micromodel of that layer is no longer used. Instead, an elastic degrading material model is activated for the failed layer to simulate the post-ultimate response. Damage variables for in-plane modes of failure are considered in the effective anisotropic strain energy density of the layer. The degraded secant stiffness is used in the FE analysis. Examples of progressive damage analysis are carried out for notched plates under compression and tension, and a single-bolted connection under tension. Good agreement is shown when comparing the experimental results and the FE models that incorporate the combined micromechanical and damage models.     

Multicontinuum Failure Analysis of Composite Structural Laminates

Damage in a composite typically begins at the constituent level and may, in fact, be limited to only one constituent in some situations. Accurate predictions of constituent damage at points in a laminate provide a genesis for progressively analyzing failure of a composite structure from start to finish. In this article we develop an efficient constituent-based failure analysis for composite structural laminates. Continuum-based (phase-averaged) constituent stress and strain fields are computed in a finite-element environment without a computational time penalty. Constituent stress-based failure criteria are developed and used to construct a progressive failure algorithm in which one constituent is allowed to fail while the other constituent remains intact, e.g., matrix cracking. The proposed failure algorithm was used to predict failure of a variety of laminates under uniaxial and biaxial loads. The results were shown to be superior to comparable single-continuum failure analyses and in good agreement with experimentally determined failure loads.     

含离散源损伤复合材料加筋板的拉伸特性

通过对含有离散源损伤的复合材料加筋板的拉伸试验和有限元模拟,研究了离散源损伤的损伤扩展与破坏特性。结果表明:复合材料加筋板的离散源损伤用穿透蒙皮切断桁条的切口来模拟是合适的,蒙皮上的穿透切口前端有很高的应力集中,桁条被切断导致加筋板传力路线改变;基于Hashin失效准则的渐进损伤有限元数值模拟方法,可以有效地模拟含切口加筋板的宏观损伤扩展和破坏过程,计算结果与试验值吻合较好。