正交铺设陶瓷基复合材料单轴拉伸行为

采用细观力学方法对正交铺设陶瓷基复合材料单轴拉伸应力-应变行为进行了研究。采用剪滞模型分析了复合材料出现损伤时的细观应力场。采用断裂力学方法、 临界基体应变能准则、 应变能释放率准则及Curtin统计模型4种单一失效模型确定了90°铺层横向裂纹间距、 0°铺层基体裂纹间距、 纤维/基体界面脱粘长度和纤维失效体积分数。将剪滞模型与4种单一损伤模型结合, 对各损伤阶段应力-应变曲线进行了模拟, 建立了复合材料强韧性预测模型。与室温下正交铺设陶瓷基复合材料单轴拉伸应力-应变曲线进行了对比, 各个损伤阶段的应力-应变、 失效强度及应变与试验数据吻合较好。分析了90°铺层横向断裂能、 0°铺层纤维/基体界面剪应力、 界面脱粘能、 纤维Weibull模量对复合材料损伤及拉伸应力-应变曲线的影响。      

单向C/SiC陶瓷基复合材料基体失效机制与强度预测

采用细观力学方法对单向C/SiC陶瓷基复合材料的基体失效机制进行了研究。利用剪滞理论模型和临界基体应变能(CMSE)准则预测了C/SiC陶瓷基复合材料受拉时基体开裂失效过程,获得了单向C/SiC陶瓷基复合材料基体开裂段的应力-应变曲线。并将扩展有限元法(XFEM)用于该开裂过程的模拟,得到了对应的应力-应变曲线。研究结果表明,采用剪滞理论模型、CMSE和采用XFEM得到的计算结果与相关的实验结果三者能较好地吻合,证明了计算方法的有效性。     

界面脱粘对正交铺设SiC/CAS复合材料基体开裂的影响

采用细观力学方法研究了正交铺设SiC/CAS复合材料在单轴拉伸载荷作用下界面脱粘对基体开裂的影响。采用断裂力学界面脱粘准则确定了0°铺层纤维/基体界面脱粘长度, 结合能量平衡法得到了主裂纹且纤维/基体界面发生脱粘(即模式3)和次裂纹且纤维/基体界面发生脱粘(即模式5)的临界开裂应力, 讨论了纤维/基体界面剪应力、 界面脱粘能对基体开裂应力的影响。结果表明, 模式3和模式5的基体开裂应力随纤维/基体界面剪应力、 界面脱粘能的增加而增加。将这一结果与Chiang考虑界面脱粘对单向纤维增强陶瓷基复合材料初始基体开裂影响的试验研究结果进行对比表明, 该变化趋势与单向SiC增强玻璃陶瓷基复合材料的试验研究结果一致。     

双向等轴拉伸载荷下二维编织陶瓷基复合材料的应力-应变行为预测

将二维编织结构简化为(0°/90°)s正交铺层结构。采用含损伤变量的剪滞分析理论,解得双向等轴拉伸载荷下,0°层和90°层开裂后各层的应力分布;基于随机基体裂纹演化理论,随机纤维损伤和最终失效理论,确定了0°层和90°层沿纤维方向的应力-应变关系,以及切线拉伸模量与施加载荷之间的关系;然后,将切线拉伸模量代入正交铺层结构的剪滞分析中,进而预测出二维编织陶瓷基复合材料在双向等轴拉伸载荷下的应力-应变关系。预测结果表明:在双向等轴拉伸载荷下,二维编织陶瓷基复合材料的横向和纵向应力-应变曲线基本相同,与单向加载时的应力-应变曲线相近。     

2D-SiC/SiC复合材料拉伸加卸载行为

为了研究国产2D-SiC/SiC复合材料的拉伸损伤行为以及低周循环载荷作用下的力学性能,通过试验和建立加卸载细观力学模型,对其拉伸加卸载行为进行了探讨。建立了单向连续纤维增强陶瓷基复合材料加卸载细观力学模型,得到了初始加载、卸载和重新加载时的应力-应变关系;利用断裂统计方法得到了基体裂纹数随应力变化的关系和复合材料失效判断条件。经过应力转化,将该模型应用于国产二维编织SiC/SiC复合材料。对单向加载试件,采用正交试验方法和最小二乘法得到基体Weibull模量和界面剪切阻力,通过控制材料失效强度与试验结果一致,得到纤维Weibull模量。由上述参数确定的2D-SiC/SiC复合材料拉伸循环加卸载应力-应变曲线与实测曲线吻合很好。通过Matlab编程得到2D-SiC/SiC复合材料单向加载时基体开裂过程图。结果表明,2D-SiC/SiC复合材料失效时,基体裂纹分布相对比较均匀;基体裂纹数随应力单调增加,未出现持平段,表明材料失效时,基体裂纹还没有达到饱和。     

连续石墨纤维增强铝基复合材料准静态拉伸损伤演化与断裂力学行为

针对连续石墨纤维增强铝基(CF/Al)复合材料,采用三种纤维排布方式的代表体积单元(RVE)建立了其细观力学有限元模型,采用准静态拉伸试验与数值模拟结合的方法,研究了其在轴向拉伸载荷下的渐进损伤与断裂力学行为。结果表明,采用基体合金和纤维原位力学性能建立的细观力学有限元模型,对轴向拉伸弹性模量和极限强度的计算结果与实验结果吻合良好,而断裂应变计算值较实验结果偏低。轴向拉伸变形中首先出现界面和基体合金损伤现象,随应变增加界面发生失效并诱发基体合金的局部失效,最后复合材料因纤维发生失效而破坏,从而出现界面脱粘后纤维拔出与基体合金撕裂共存的微观形貌。细观力学有限元分析结果表明,在复合材料制备后纤维性能衰减而强度较低条件下,改变界面强度和刚度对复合材料轴向拉伸弹塑性力学行为的影响较小,复合材料中纤维强度水平是决定该复合材料轴向拉伸力学性能的主要因素。     

界面对纤维增强陶瓷基复合材料拉伸性能的影响

建立了桥联纤维细观力学模型, 研究了界面对纤维增强陶瓷基复合材料拉伸模量及强度的影响。分别引入纤维应力均匀系数和界面脱粘率作为界面完全脱粘和局部脱粘条件下界面性能的表征参数。研究表明, 应力均匀系数及界面脱粘率越大, 材料模量越低, 而断裂时纤维所承担的应力越高。基于混合率给出了拉伸强度表达式, 同时也分析了基体裂纹分布、界面脱粘和纤维拔出对强度的影响。计算结果表明, 本文强度模型给出的预测值与试验值吻合较好。      

三维针刺C/C复合材料面内压缩失效行为研究

通过研究三维针刺C/C复合材料面内压缩失效行为,发现应力-应变行为包括起始段的非线性滞弹性、线弹性、非线性损伤及应力下降失效4个阶段,循环加载-卸载实验表明线弹性阶段应力-应变行为的重复性好,而非线性损伤阶段则与加载历程有关。面内压缩失效主要是端部分层脱粘和分层劈裂,受纤维/基体界面结合强度影响较大。     

陶瓷基复合材料单纤维拔出过程分析

纤维埋入长度是单纤维拔出试验能否成功的关键因素之一,本文采用载荷位移曲线离散化方法将单纤维拔出过程离散为主要细观失效模式控制的不同阶段,建立了包含泊松效应影响的复合材料单纤维拔出力学模型,得到各阶段的载荷分布和位移分布。采用能量平衡失效准则建立了界面脱粘长度与外载荷的关系,针对SiC／RBSN陶瓷基复合材料,分析不同纤维埋入长度情况下,泊松比、界面摩擦系数等载荷位移曲线的影响。     

二维编织陶瓷基复合材料偏轴拉伸力学性能预测

基于二维编织C/SiC复合材料的细观结构,建立了碳纤维丝/热解碳界面/SiC基体和纤维束/表层SiC基体两种尺度下的细观单胞模型,通过有限元方法计算碳纤维丝/热解碳界面/SiC基体模型的等效弹性常数和强度,然后代入纤维束/表层SiC基体模型中计算,并引入Tsai-Wu失效准则,考虑不同失效模式的损伤,建立了二维编织C/SiC复合材料的渐进损伤模型,模拟了其偏轴拉伸应力-应变行为。针对该模型,阐述了二维编织C/SiC复合材料单胞模型在复杂应力状态下其纤维束的损伤过程。数值模拟结果与实验数据吻合较好,验证了模型的有效性,为该种材料的力学性能分析提供了一种有效方法。     

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.     

Meso-Scale Progressive Damage Behavior Characterization of Triaxial Braided Composites under Quasi-Static Tensile Load

Based on continuum damage mechanics (CDM), a sophisticated 3D meso-scale finite element (FE) model is proposed to characterize the progressive damage behavior of 2D Triaxial Braided Composites (2DTBC) with 60° braiding angle under quasi-static tensile load. The modified Von Mises strength criterion and 3D Hashin failure criterion are used to predict the damage initiation of the pure matrix and fiber tows. A combining interface damage and friction constitutive model is applied to predict the interface damage behavior. Murakami-Ohno stiffness degradation scheme is employed to predict the damage evolution process of each constituent. Coupling with the ordinary and translational symmetry boundary conditions, the tensile elastic response including tensile strength and failure strain of 2DTBC are in good agreement with the available experiment data. The numerical results show that the main failure modes of the composites under axial tensile load are pure matrix cracking, fiber and matrix tension failure in bias fiber tows, matrix tension failure in axial fiber tows and interface debonding; the main failure modes of the composites subjected to transverse tensile load are free-edge effect, matrix tension failure in bias fiber tows and interface debonding.     

Modeling Loading/Unloading Hysteresis Behavior of Unidirectional C/SiC Ceramic Matrix Composites

The loading/unloading tensile behavior of unidirectional C/SiC ceramic matrix composites at room temperature has been investigated. The loading/unloading stress–strain curve exhibits obvious hysteresis behavior. An approach to model the hysteresis loops of ceramic matrix composites including the effect of fiber failure during tensile loading has been developed. By adopting a shear-lag model which includes the matrix shear deformation in the bonded region and friction in the debonded region, the matrix cracking space and interface debonded length are obtained by matrix statistical cracking model and fracture mechanics interface debonded criterion. The two-parameter Weibull model is used to describe the fiber strength distribution. The stress carried by the intact and fracture fibers on the matrix crack plane during unloading and subsequent reloading is determined by the Global Load Sharing criterion. Based on the damage mechanisms of fiber sliding relative to matrix during unloading and subsequent reloading, the unloading interface reverse slip length and reloading interface new slip length are obtained by the fracture mechanics approach. The hysteresis loops of unidirectional C/SiC ceramic matrix composites corresponding to different stress have been predicted.     

An Approach to Estimate Interface Shear Stress of Ceramic Matrix Composites from Hysteresis Loops

An approach to estimate interface shear stress of ceramic matrix composites during fatigue loading has been developed in this paper. By adopting a shear-lag model which includes the matrix shear deformation in the bonded region and friction in the debonded region, the matrix crack space and interface debonding length are obtained by matrix statistical cracking model and fracture mechanics interface debonding criterion. Based on the damage mechanisms of fiber sliding relative to matrix in the interface debonded region upon unloading and subsequent reloading, the unloading counter slip length and reloading new slip length are determined by the fracture mechanics method. The hysteresis loops of four different cases have been derived. The hysteresis loss energy for the strain energy lost per volume during corresponding cycle is formulated in terms of interface shear stress. By comparing the experimental hysteresis loss energy with computational values, the interface shear stress corresponding to different cycles can then be derived. The theoretical results have been compared with experimental data of three different ceramic composites.     

三维五向编织复合材料渐进损伤分析的数值方法

基于连续损伤理论, 推导了含损伤裂纹的正交各向异性材料的应力-应变关系。建立了考虑界面脱粘破坏的三维五向编织复合材料细观体胞模型, 并将有限元网格尺寸和单元裂纹尺寸引入损伤演化方程。采用Hashin准则和von-Mises准则分别判断纱线与基体的初始损伤, 结合Eshelby-Mori-Tanaka方法确定材料的刚度退化系数。利用ANSYS有限元软件对材料进行渐进损伤分析, 得到了材料在单向拉伸作用下的应力-应变曲线和极限强度。计算结果表明, 轴纱为材料的主要承力部分, 小编织角材料的破坏模式主要为纱线的拉伸断裂, 界面破坏情况较为严重。模拟计算结果与实验结果吻合较好。     

A modeling study on residual stress-induced interfacial debonding and stress–strain behavior of weakly bonded UD composites

Residual stress-induced interfacial debonding and its influence on stress–strain behavior of unidirectional fiber-reinforced brittle matrix composites with weak interface were studied using mini-composite model by means of the two-dimensional shear lag analysis combined with a Monte Carlo method. Damages (fracture of fiber, matrix and interface) were accumulated intermittently, resulting in serrated stress–strain curve. In this process, the residual stresses changed the strain, order and location of occurrence of damages, and consequently the shape of stress–strain curve and strength of composite. Under the existence of compressive and tensile axial residual stresses in fiber and matrix, respectively, the fracture of the matrix and the debonding from the fracture-ends of matrix were enhanced, while the fracture of fiber and the debonding from the fracture-ends of fiber were suppressed. The residual stress-induced premature fracture of the matrix, followed by debonding, reduced the strength of composite.     

ECC单轴受拉损伤本构模型研究EI北大核心CSCD

通过单轴拉伸试验,讨论了PVA纤维体积掺入量和水胶比对工程用水泥基复合材料(ECC)受拉力学性能参数(开裂应变、开裂应力、峰值应变、峰值应力、极限应变以及应力-应变关系曲线)的影响规律。基于此,从损伤力学的角度讨论了ECC在单轴受拉过程的开裂前阶段、应变硬化阶段以及应变软化阶段的损伤演化机制。进而,基于ECC受拉损伤演化机制提出ECC受拉损伤本构模型,并给出模型相关参数的计算方法,分析表明:该文提出损伤模型得到的ECC受拉损伤演化曲线能更为合理的描述ECC的损伤演化全过程。最后,该文损伤模型计算的ECC受拉应力-应变关系曲线和试验曲线对比结果表明,所提出的模型能够合理的描述ECC受拉非线性应力-应变关系特征,且具有良好的精度。