Post Buckling Progressive Failure Analysis of Composite Laminated Stiffened Panels

The present work deals with the numerical prediction of the post buckling progressive and final failure response of stiffened composite panels based on structural nonlinear finite element methods. For this purpose, a progressive failure model (PFM) is developed and applied to predict the behaviour of an experimentally tested blade-stiffened panel found in the literature. Failure initiation and propagation is calculated, owing to the accumulation of the intralaminar failure modes induced in fibre reinforced composite materials. Hashin failure criteria have been employed in order to address the fiber and matrix failure modes in compression and tension. On the other hand, the Tsai-Wu failure criterion has been utilized for addressing shear failure. Failure detection is followed with the introduction of corresponding material degradation rules depending on the individual failure mechanisms. Failure initiation and failure propagation as well as the post buckling ultimate attained load have been numerically evaluated. Final failure behaviour of the simulated stiffened panel is due to sudden global failure, as concluded from comparisons between numerical and experimental results being in good agreement.     

冲击后含损伤复合材料格栅加筋板的后屈曲

采用数值分析方法研究了冲击后含损伤的复合材料格栅加筋板的后屈曲特性。基于Mindlin 一阶剪切理论和Von Karman 大挠度理论, 建立了冲击后蒙皮内含分层损伤复合材料格栅加筋板后屈曲分析的有限元方法; 分析中同时考虑了蒙皮和肋骨中纤维断裂、基体开裂等损伤累积造成的刚度的退化和蒙皮分层子板间的闭合接触效应, 为含损伤复合材料格栅加筋板的后屈曲特性研究提供了一种有效的数值分析方法。分析结果表明, 蒙皮分层面积较大时, 格栅加筋板出现蒙皮分层上子板的局部屈曲后仍然具有较强的继续承载能力, 而在后屈曲分析中, 应考虑损伤累积对格栅加筋结构承载能力的影响; 采用非线性虚拟界面元可成功处理分层子板间的闭合接触效应。      

复合材料加筋板低速冲击损伤的数值模拟

建立了复合材料加筋板在横向低速冲击载荷作用下的渐进损伤有限元模型。该模型考虑了复合材料加筋板受低速冲击时的纤维断裂、基体开裂及分层脱粘等五种典型的损伤形式, 在层内采用应变描述的失效判据, 结合相应的材料性能退化方案, 通过编写VUMAT用户自定义子程序以实现相应损伤类型的判断和演化。在层间以及筋条与层板间加入界面元, 模拟层间区域的情况, 结合传统的应力失效判据和断裂力学中的能量释放率准则来判断分层损伤的起始和演化规律。通过对数值模拟结果与实验数据的比较, 验证了模型的合理性和有效性。同时探讨了不同位置、不同冲击能量以及含初始损伤(脱粘)等因素对复合材料加筋板低速冲击性能的影响。     

Multiscale finite element modeling of failure process of composite laminates

A multiscale nonlinear finite element modeling technique is developed in this paper to predict the progressive failure process for composite laminates. A micromechanical elastic–plastic bridging constitutive model, which considers the nonlinear material properties of the constituent fiber and matrix materials and their interaction and the damage and failure in fibrous composites at the fiber and matrix level, is proposed to represent the material behavior of fiber-reinforced composite laminates. The micromechanics constitutive model is employed in the macroscale finite element analysis of structural behavior especially progressive failure process of the fiber-reinforced composites based on a 4-node 24-DOF shear-locking free rectangular composite plate element.     

J型加筋壁板结构轴压试验及承载能力数值预测

设计了复合材料J型加筋板轴压试验件形式和加载方式,试验研究了其承载能力和破坏形式,讨论了轴压下复合材料加筋板件承载能力预测的有限元建模和分析方法,数值分析了加筋板屈曲和后屈曲模式,结果表明如果不考虑损伤累积对结构承载能力的影响,预测值将明显偏高;而通过引入逐步破坏准则,考虑了基体破坏、纤维基体剪切失效以及纤维断裂等损伤累积对结构承载能力的影响,可以提高数值预测精度。     

含分层损伤复合材料加筋层合板的动承载能力

采用有限元方法研究了含穿透分层损伤复合材料加筋层合板的动力响应和承载能力。根据复合材料层合板一阶剪切理论, 推导了复合材料层合板单元的刚度阵和质量阵列式;同时采用Adams 应变能法与Rayleigh阻尼模型相结合的方法, 构造了相应的阻尼阵列式;为了防止在低阶模态中分层处出现的上、下子板不合理的嵌入现象, 建立了含分层损伤复合材料加筋层合板动力分析中分层分析模型和虚拟界面联接模型。并采用Tsai提出的刚度退化准则和动力响应分析的精细积分法, 对在动荷载作用下含分层损伤复合材料加筋层合板结构进行了破坏和承载能力分析。通过典型算例分析, 分别讨论了外载频率、分层深度、筋的位置以及破坏过程中刚度退化对含损伤复合材料加筋层合板动力响应特征和承载能力的影响, 得到了一些具有理论和工程价值的结论。     

含脱粘损伤的复合材料加筋板压缩破坏渐进损伤数值分析

本文提出了基于连续损伤力学的复合材料层合加筋壁板渐进损伤分析模型。该模型采用界面单元模拟筋条和壁板之间的连接界面,连接界面和复合材料层板分别采用Quads准则和Hashin准则作为失效判据,基于内嵌连续损伤状态变量的材料刚度退化方案,采用非线性有限元方法,研究了复合材料加筋壁板在压缩载荷下的破坏过程,分析了结构相应失效模式的细观失效机理。数值分析结果与实验数据吻合较好,证明该方法的合理性和有效性,并详细探讨了界面单元关键参数和层板铺设角度对加筋壁板结构力学响应的影响规律,得到了一些富有价值的结论。     

压缩载荷下复合材料整体加筋板渐进损伤非线性数值分析

建立了考虑脱粘的复合材料整体加筋板渐进损伤有限元分析模型。该模型采用界面单元模拟筋条与壁板之间的连接界面, 连接界面和复合材料层板分别采用Quads准则和Hashin准则作为失效判据, 基于ABAQUS软件, 建立了含连续损伤状态变量的材料刚度退化方案。基于该模型, 采用非线性有限元方法研究了压缩载荷下复合材料整体加筋壁板在考虑初始几何缺陷时的破坏过程, 分析了结构相应失效模式的细观损伤机制; 详细讨论了轴向刚度比对结构承载能力及破坏模式的影响。结果表明: 考虑脱粘损伤的有限元模型能有效模拟加筋板的破坏过程; 在加筋板铺层设计合理的情况下, 增加筋条与壁板刚度比能有效提高加筋板截面单位面积的承载能力。      

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。      

Compressive Behavior of 3D Woven Composite Stiffened Panels: Experimental and Numerical Study

The structural behavior and damage propagation of 3D woven composite stiffened panels with different woven patterns under axial-compression are here investigated. The panel is 2.5D interlock woven composites (2.5DIWC), while the straight-stiffeners are 3D woven orthogonal composites (3DWOC). They are coupled together with the Z-fibers from the stiffener passing straight thought the thickness of the panel. A “T-shape” model, in which the fiber bundle structure and resin matrix are drawn out to simulate the real situation of the connection area, is established to predict elastic constants and strength of the connection region. Based on Hashin failure criterion, a progressive damage model is carried out to simulate the compressive behavior of the stiffened panel. The 3D woven composite stiffened panels are manufactured using RTM process and then tested. A good agreement between experimental results and numerical predicted values for the compressive failure load is obtained. From initial damage to final collapse, the panel and stiffeners will not separate each other in the connection region. The main failure mode of 3D woven composite stiffened panels is compressive failure of fiber near the loading end corner.     

带口盖加筋复合材料壁板剪切性能

采用试验和有限元方法研究了带口盖加筋复合材料壁板的剪切性能。在带口盖加筋复合材料壁板有限元模型的基础上, 去掉口盖, 对不带口盖的大开口加筋复合材料壁板进行了有限元模拟分析, 以此研究口盖对带口盖加筋复合材料壁板的影响。试验和数值计算结果表明: 当达到屈曲载荷时, 带口盖加筋复合材料壁板各个区域同步发生屈曲, 最终破坏位置位于加强筋条以外的复合材料壁板区域; 去掉口盖后, 结构的刚度以及承载能力降低, 结构的应力集中点以及损伤起始位置均发生变化, 破坏时失稳形式无明显变化, 均为局部失稳。      

湿热环境下考虑累积失效和分层损伤AGS结构的稳定性

对湿热环境下考虑累积失效和分层损伤的先进复合材料格栅加筋结构(AGS)的稳定性进行了数值分析。基于一阶剪切理论和Von Karman非线性变形假设建立了含分层损伤复合材料 A GS结构的有限元模型,并推导了考虑温度和湿度效应的AGS结构有限元列式,同时给出了材料破坏准则。通过典型算例讨论了湿热环境、累积失效及分层损伤等因素对复合材料AGS结构稳定性的影响,数值结果表明当上述因素导致结构的屈曲模式发生突变时,其对 A GS结构稳定性能的影响是不容忽视的。     

A Multiscale Progressive Failure Modeling Methodology for Composites That Includes Fiber Strength Stochastics

A multiscale modeling methodology was developed for continuous fiber composites that incorporates a statistical distribution of fiber strengths into coupled multiscale micromechanics/ finite element (FE) analyses. A modified twoparameter Weibull cumulative distribution function, which accounts for the effect of fiber length on the probability of failure, was used to characterize the statistical distribution of fiber strengths. A parametric study using the NASA Micromechanics Analysis Code with the Generalized Method of Cells (MAC/GMC) was performed to assess the effect of variable fiber strengths on local composite failure within a repeating unit cell (RUC) and subsequent global failure. The NASA code FEAMAC and the ABAQUS finite element solver were used to analyze the progressive failure of a unidirectional SCS-6/ TIMETAL 21S metal matrix composite tensile dogbone specimen at 650°C. Multiscale progressive failure analyses were performed to quantify the effect of spatially varying fiber strengths on the RUCaveraged and global stress-strain responses and failure. The ultimate composite strengths and distribution of failure locations (predominately within the gage section) reasonably matched the experimentally observed failure behavior. The predicted composite failure behavior suggests that use of macroscale models that exploit global geometric symmetries are inappropriate for cases where the actual distribution of local fiber strengths displays no such symmetries. This issue has not received much attention in the literature. Moreover, the model discretization at a specific length scale can have a profound effect on the computational costs associated with multiscale simulations.     

Micromechanical modeling of interface damage of metal matrix composites subjected to transverse loading

A three-dimensional finite element micromechanical model was developed to study effects of thermal residual stress, fiber coating and interface bonding on the transverse behavior of a unidirectional SiC/Ti–6Al–4V metal matrix composite (MMC). The presented model includes three phases, i.e. the fiber, coating and matrix, and two distinct interfaces, one between the fiber and coating and the other between coating and matrix. The model can be employed to investigate effects of various bonding levels of the interfaces on the initiation of damage during transverse loading of the composite system. Two different failure criteria, which are combinations of normal and shear stresses across the interfaces, were used to predict the failure of the fiber/coating (f/c) and coating/matrix (c/m) interfaces. Any interface fails as soon as the stress level reaches the interfacial strength. It was shown that in comparison with other interface models the predicted stress–strain curve for damaged interface demonstrates good agreement with experimental results.     

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。      

Stress and Failure Analysis of Brittle Matrix Composites. Part I: Stress Analysis

Damage initiation in brittle matrix composites with ultimate strain of the matrix less than that of the fiber under longitudinal tensile load takes place with the formation of cracks in the matrix. This is followed by debonding at the fiber-matrix interface and fiber fractures depending on the properties of the interface. Study of the various failure mechanisms of the composite has a prerequisite the analysis of the stress field around matrix cracks, fiber-matrix disbonds, fiber failures, etc. In the present work stress analysis for a cylindrical element of matrix with a single fiber and two matrix annular cracks perpendicular to the fiber direction under longitudinal tensile load takes place. The results of the finite element stress analysis are used to predict the overall tensile stress-strain curve of the composite which is compared with the predictions based on a modified shear lag analysis. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

基于连续介质损伤力学的复合材料层合板低速冲击损伤模型

基于连续介质损伤力学（CDM）方法,建立了分析复合材料层合板低速冲击问题的三维数值模型。该模型考虑了层内损伤（纤维和基体损伤）、层间分层损伤和剪切非线性行为,采用最大应变失效准则预测纤维损伤的萌生,双线性损伤本构模型表征纤维损伤演化,基于物理失效机制的三维Puck准则判断基体损伤的起始,根据断裂面内等效应变建立混合模式下基体损伤扩展准则。横向基体拉伸强度和面内剪切强度采用基于断裂力学假设的就地强度（in-situ strength）。纤维和基体损伤本构关系中引入单元特征长度,有效降低模型对网格密度的依赖性。层间分层损伤情况由内聚力单元（cohesive element）预测,以二次应力准则为分层损伤的起始准则,B-K准则表征分层损伤演化。分别通过数值分析方法和试验研究方法对复合材料典型铺层层合板四级能量低速冲击下的冲击损伤和冲击响应规律进行分析,数值计算和试验测量的接触力-时间曲线、分层损伤的形状和面积较好吻合,表明该模型能够准确地预测层合板低速冲击损伤和冲击响应。     

离位增韧复合材料加筋板三点弯曲试验研究与数值分析

为研究离位增韧对复合材料加筋板结构承载性能的影响,首先,分别对未离位增韧和离位增韧复合材料帽型长桁加筋板进行了三点弯曲试验,比较了2种加筋板的初始分层载荷、极限载荷以及试验现象;然后,利用ABAQUS建立了三维渐进失效模型,考虑长桁-蒙皮界面和复合材料层合板的失效,对界面的分层机制和蒙皮的失效过程进行了分析。结果表明:有限元结果与试验结果吻合较好,离位增韧仅能略微提高界面的初始分层载荷,但对极限载荷有较大提升;在分层起始阶段I型拉伸模式占主要作用,随着分层不断扩展,II型剪切模式占比持续增加,而剪切模式的高韧性正是离位增韧界面具有良好性能的重要原因。所得结论表明离位增韧界面有良好的抗剥离性能,且在剪切方向上的表现尤为突出。     

阻尼夹芯复合材料加筋板的振动分析与数值模拟

以阻尼夹芯复合材料加筋板为研究对象,依据一阶剪切变形理论(FSDT)和Hamilton原理,推导板和加强筋的应变能、动能表达式,采用变分原理建立控制微分方程,根据相关边界条件和傅里叶级数求解方程。建立了ANSYS阻尼夹芯复合材料加筋板的有限元模型,该模型考虑到阻尼夹芯复合材料加筋板中阻尼材料与纤维预浸料间的结合方式,用模态应变能有限元数值模拟方法研究了结构的动力学性能,并通过对数值模拟结果与理论解的比较,验证了模型的合理性和有效性。探讨了不同的筋条尺寸、不同的筋条数量、不同的筋条分布方式对阻尼夹芯复合材料加筋板动力学性能的影响,得出了阻尼夹芯复合材料加筋板的一阶模态频率和损耗因子随不同参数的变化曲线,其结论为阻尼夹芯复合材料加筋板的优化设计提供参考。