基于有限断裂力学的准脆性材料断裂与疲劳特性研究

In the engineering structure, there are a large classes of quasi- brittle materials, whose mechanical properties have size effect. With the increasement of structural elements size , considering the size effect on fracture and fatigue properties of the elements under the static and cyclic loading is of great importance on structural design for safety and durability.In the project,a new kind of failure criterion in the framework of Finite Fracture Mechanics is introduced for characterization the failure of quasi-brittle materials.A finite distance in front the crack tip is assumed to be not a material constant but a structural parameter.Its value is determined by a condition of consistency of both energetic and stress approaches.An experimental investigation on the properties of the fracture process zone (FPZ) in such materials is recorded by using the digital image correlation (DIC) technique；At the same time, the size of FPZ , the crack opening displacement in the FPZ is determined accurately. In order to check its soundness, an application to the strength prediction for three point bending tests （or open hole strength of laminate composite ）of various relative crack depths and of different sizes is performed under static or fatigue loads，the accuracy of the calculation method will be compared with cohesive zone model and double K model under such simple boundary conditions and loads. the effectiveness and general of the algorithm will be further proved by strength of the complex defects(such as V notch or ellipse hole) boundary condition.The size effect of mechanical properties will be given by "finite distance"

在工程结构中包含了一大类力学性能具有尺寸效应的准脆性材料，随着大型和超大型结构的不断增加，在结构设计中考虑尺寸效应对静载与循环载荷下构件断裂与疲劳性能的影响对结构的安全性与耐久性有重要意义。本项目拟提出一类新的失效准则，该准则基于有限断裂力学框架来表征准脆性材料的失效，裂缝扩展的有限距离假设为结构参数而非材料参数，其值由能量与应力（应变）相匹配条件确定。借助于数字图像相关技术跟踪这些组成材料的断裂过程区、同时准确测定断裂过程区尺寸和裂缝张开位移.利用含不同长度裂缝的三点弯曲梁（或不同开孔层压板）在静力与疲劳荷载下的强度试验来验证该原理的有效性，和粘聚模型与双K准则等对比在这些简单几何边界条件和载荷条件下算法的精确度。利用提出的失效准则进行解析和边界元分析计算，与更复杂的孔口（如V型或椭圆型）边界条件下强度试验对比说明算法的一般性和有效性.利用"有限距离"概念描述对这类材料力学性能尺寸效应。

在工程结构中包含了一大类力学性能具有尺寸效应的准脆性材料，随着大型和超大型结构的不断增加，在结构设计中寻求不考虑尺寸效应的断裂性能评价理论与方法对结构的安全性与耐久性有重要意义。本项目提出了一类新的失效准则，该准则基于有限断裂力学框架来表征准脆性材料的失效，裂缝扩展的有限距离假设为结构参数而非材料参数，其值由能量与应力（应变）相匹配条件确定。借助于数字图像相关技术跟踪这些组成材料的断裂过程区、同时准确测定断裂过程区尺寸和裂缝张开位移.利用不同材料及不同类型缺陷 的三点弯曲梁在静力荷载下的强度试验来验证该原理的有效性， 和粘聚模型与双 K 准则等对比在这些简单几何边界条件和载荷条件下算法的精确度。利用提 出的失效准则进行解析和自制试件及参考文献中的试验结果，在验证新准则的通用性的同时得到了提取材料抗拉强度、断裂韧性的新方法.利用"有限距离"概念过程区长的研究对这类材料力学性能尺寸效应。 这些测试和分析只需要常规实验室的小试样及实验中得到的最大荷载，而不依赖于峰值后的软化曲线，因此所建立的断裂准则与分析方法很适用于在工程设计中使用。