On One Two-Level Model in the Mesomechanics of Compression Fracture of Cracked Composites

The article is devoted to a two-level model in the mesomechanics of compression fracture of composites with cracks. Consideration is given to fiber-laminated panels with an opening compressed along the fibers so that two cracks propagate from the opening edge in a direction perpendicular to the loading axis. The previous results obtained by the author in the three-dimensional theory of stability of deformable bodies and nonclassical fracture mechanics are used to create the above-mentioned two-level model     

Convexity of the Strain-Energy Function in a Two-Scale Model of Ideal Fabrics

A two-scale model is used to generate the macro-scale constitutive response of a sheet of woven fabric from a micro-scale model of interacting yarns regarded as crossed elasticae in contact. The model furnishes a macro-scale strain-energy function for an orthotropic membrane idealized as being weak in shear compared to the extensional resistance of material curves representing the yarns. The operative Legendre–Hadamard inequality for the membrane is derived and shown to be satisfied by a suitably relaxed version of the computed strain-energy function.     

高温下C/SiC复合材料弯曲断裂性能实时测试和微观结构表征分析

采用先驱体浸渍裂解法制备三维编织的C/SiC复合材料,利用自主研发的高温散斑制作技术和改进的三维变形光学测试系统,基于数字图像相关技术测试原理,在高温小尺度下实时表征分析C/SiC复合材料的力学性能。运用X射线衍射和扫描电子显微镜测试分析了材料高温氧化情况、显微组织结构及裂纹扩展情况。研究表明:温度对C/SiC复合材料的性能有很大的影响。随着温度的升高,材料由脆性断裂逐渐转变为韧性断裂;材料的断裂韧性由7.98±0.12MPa·m~(1/2)减小到2.76±0.11MPa·m~(1/2),断裂强度从251.40±2.71MPa减小到86.94±1.82MPa。本文为掌握C/SiC复合材料的高温失效机理提供了一种有效的实验测试技术和方法。     

On Some Nonclassical Problems of Fracture Mechanics Taking into Account the Stresses Along Cracks

The paper reports on the results from analysis of some nonclassical fracture problems that allow for stresses along cracks. The results have been obtained by the author and his collaborators at the Institute of Mechanics (Kiev) since 1980     

复合材料Ⅰ型层间断裂韧性GIC和初始裂纹长度

从经典梁理论和弹性基础上的正交各向异性梁理论出发，分析了梁的弯曲剪切效应和弹性基础对用双悬臂梁试件测得的复合材料层合板Ⅰ型层间断裂韧性Ｇ＿（ＩＣ）的影响，发现当试件的初始裂纹长度较短时，剪切效应和弹性基础对Ｇ＿（ＩＣ）的影响是显著的，建议将初始裂纹长度取５０毫米。实验结果表明，初始裂纹长度由２０毫米增加到５０毫米时，测得的Ｇ＿（ＩＣ）值的离散系数降低２０％～４０％，数据趋于稳定，分散性减小。     

压电压磁复合材料中正六边形孔边裂纹的反平面断裂问题

基于线性磁电弹性理论,利用Schwarz-Christoffel(CS)变换技术和Stroth公式,首次系统研究了压电压磁复合材料中含带两个不对称裂纹的正六边形孔口问题在部分渗透磁电边界条件下的解析解.当忽略磁场时,磁电非渗透裂纹和磁电渗透裂纹两种极端情况下的解析解答可退化为文献已有研究结果.数值结果揭示了正六边形孔口尺寸、裂纹长度以及力电载荷和磁载荷对能量释放率的影响规律.研究结果表明：减小孔口边长和裂纹长度可以提高材料的可靠性;机械载荷总是促进裂纹扩展;在磁电非渗透和磁电部分渗透边界条件下,负电场和负磁场会延缓裂纹的扩展,而正电场可以增强或阻碍裂纹的扩展,这取决于所施加的电场和磁场的强度以及机械载荷的水平;在磁电渗透边界条件下,电场和磁场对裂纹的扩展没有影响.     

反平面剪切作用下双材料滑动界面的细观力学模型

非理想粘结界面对多相材料力学性能具有重要影响。对于双材料间含众多随机分布微裂纹的界面，宏观上可以等效为连续损伤的弱界面，其两侧的面力连续而位移有间断。只有切线方向的位移间断，而法线方向位移连续的弱界面称之为滑动界面。在反平面剪切的作用下，我们证明了对于含有随机分布微裂纹的弹性双材料界面在宏观上等效为线弹簧型滑动界面，并获得了滑动界面柔度的一般表达式。利用Mori—Tanaka方法和广义自洽方法，我们研究了滑动界面柔度系数和微裂纹密度的关系。对这两种方法所得的结果进行比较发现，Mori—Tanaka方法得到的界面柔度比广义自洽方法得到的界面柔度大。当裂纹密度比较小时，这两种方法求得的界面柔度很接近。两种方法的结果都表明，界面柔度随裂纹密度的增加而增加。Mori—Tanaka方法比广义自治方法求解更为简便。     

Analyzing the Laws of Stable Subcritical Growth of Cracks in Polymeric Materials on the Basis of Fracture Mesomechanics Models. Theory and Experiment

The laws of stable crack growth are analyzed using fracture mesomechanics models for polymeric materials under long-term subcritical tension. A review is given of experimental and theoretical studies of crack-tip process zones. The studies were conducted using physical and mechanical methods and fracture mesomechanics models, allowing for the structural and rheological features of process zones. Theoretical and experimental results on the behavior of process zones are generalized and the theory of stable crack growth in viscoelastic polymers, which assumes the autonomy of the process zone during crack development, is justified     

混合边界多裂隙体在简谐变温场作用下的断裂问题（张开型）

给出了无限平面作用有简谐变化的点热源时的位移场、应力场基本解、用间接法构造出混合边值多裂隙体在简谐变温场作用下的热断裂问题的边界积分方程,并离散求解.数值结果表明,该方法求解多裂隙体的简谐热断裂问题精度好,计算工作量少.文中计算了含边界裂缝的平板、含三条平行裂缝的平板在简谐变温场作用下缝端应力强度因子的变化过程,并与实验结果进行了比较,两者吻合良好.     

含裂纹梁刚塑性动态断裂的非线性线弹簧模型分析

用非线性线弹簧模型分析了带裂纹梁的刚塑性动态断裂问题.在塑性势理论基础上,建立了全塑性状态下的弹簧本构关系,并用此关系导出带裂纹梁刚塑性动态断裂分析的基本方程,计算了在冲击载荷作用下,裂纹梁的动态断裂响应.     

层状磁电复合材料界面共线裂纹平面问题分析

本文研究了面内电磁势载荷作用下双层压电压磁复合材料中共线界面裂纹问题．考虑了压电材料的导磁性质和压磁材料的介电性质,引入了界面电位移和磁感强度的连续性条件．利用Fourier 变换得到一组第二类Cauchy 型奇异积分方程．进一步导出了相应问题的应力强度因子、电位移强度因子和磁感强度强度因子的表达式,给出了应力强度因子的数值结果．结果表明电磁载荷会导致界面裂纹尖端I、II 混合型应力奇异性,同时还伴随着电位移和磁感强度的奇异性．比较了双裂纹左右端的应力强度因子,发现在面内极化方向上施加面内磁势载荷时共线裂纹内侧尖端区域的两个法向应力场发生互相干涉增强．     

Mesomechanics of fatigue fracture for polycrystals with macroconcentrators

Fatigue fracture of aluminum alloys is analyzed from analysis of time-spatial mesoscale substructures. The behavior involves many stages at the mesoscale and translational–rotational movement of the bulk structure element in addition to fragmentation. Mesofragments on a trajectory of the fatigue crack were also studied.     

三维网络结构增强复合材料磨损模型的研究

考虑网络结构增强体特殊的拓扑结构因素和弹性模量影响,利用复合材料磨损率最小化和最大化假设,建立了网络结构增强复合材料的磨损模型,同时制备了不同体积分数的Si3N4陶瓷增强Al-Mg合金复合材料,并将其磨损试验结果数据拟合到模型中.结果表明,所建立的模型可以反映复合材料增强相的体积分数、复合材料的弹性模量和磨损率之间的数学关系,证明复合材料的摩擦磨损率随增强相体积分数的增加而逐渐降低,当体积分数超过45%～50%时,磨损率随增强相体积分数的增加而逐渐增大.该模型不同于Khruschov模型和Zum-Gahr 模型,其关系不遵循线性规则.与增强体复合材料的磨损试验数据拟合表明,该模型能够较好地反映网络结构增强复合材料的磨损性能,具有一定普遍性.     

Fracture of Plates with an Inclined Edge Crack under Tension

The paper discusses experimental results on tension fracture of D16AT plates with an inclined crack with and without local buckling. The influence of crack geometry (initial length and crack angle) on fracture kinetics and strength of the plates is studied. Also the effect of local buckling on the fracture characteristics is evaluated     

碳纤维增强树脂基复合材料压缩失效机理研究

为分析基体性质和纤维铺设方式对碳纤维树脂基复合材料(CFRP)压缩性能的影响,设计两种基体（耐高温环氧树脂基体和PA6 基体） 和两种碳纤维铺设方式[[45/0/-45/90]s和[45/-45]2s],共4 类盒型碳纤维试件．采用轴向压缩实验,研究低应变速率下碳纤维复合材料的极限载荷、压缩量和刚度等力学性能．研究表明试件的失效形式主要由基体性质决定,损伤区域及裂纹方向主要由碳纤维铺设方式决定．利用X射线显微镜(XRM)对试件典型的损伤区域进行三维扫描,并对扫描图像进行重构与渲染,获得破坏区域的内部损伤细节．根据损伤扫描结果,得到材料内部的损伤类型及破坏程度．归纳所获得的损伤测试特征,分析不同类型试件压缩时的损伤规律与失效机理．     

Deformation Characteristics of Laminar Composites under Nonlinear Strains

It is shown that the type of governing relations in a composite can change, namely, a laminar composite formed by layers of physically linear materials under nonlinear strains should be described by nonlinear Hooke's law. Local stresses can be not proportional to elastic constants of the layers under nonlinear strains.     

Fracture of a Semi-Bounded Composite Material with a Near-Surface Penny-Shaped Crack under Compression

International Applied Mechanics - The nonclassical problem of fracture mechanics for a near-surface crack is solved in the case of small distances between the free surface and the crack plane. The...     

骨料对混凝土材料冲击压缩行为的影响

利用大尺寸Hopkinson压杆，以实验数据为依据，研究了四种不同骨料尺寸的普通混凝土材料和两种不同配比的钢纤维增强混凝土材料在冲击载荷下的压缩强度，从唯象的角度分析了骨料性质及其粒径对混凝土材料动态压缩性能的影响及可能的力学机理，为在工程上更好地利用混凝土材料提供一定的理论和实验的支持。     

压缩载荷作用下岩石类材料的断裂模式研究

为了解岩石类材料在压缩条件下的裂纹扩展规律,本文对含有内部倾斜裂纹的石膏板试件进行了双轴压缩实验. 研究表明:在通常情况下岩石裂纹按I 型张拉模式扩展,但随着裂纹表面摩擦系数μ和围压与纵向荷载比值λ的提高,翼裂纹扩展的偏转角随之减少.当裂纹表面摩擦系数和围压与纵向荷载比值足够大时,例如,μ=0.83和λ=0.315,岩石裂纹按Ⅱ型剪切模式扩展.然而,当裂纹表面摩擦系数和围压与纵向荷载比值进一步增加时,石膏板试件将发生强度破坏.本文提出了一个理论模型用以解释和描述这一实验现象.