Mesh-independent discrete numerical representations of cohesive-zone models

The importance of the cohesive-zone approach to analyse localisation and fracture in engineering materials is emphasised and ways to incorporate the cohesive-zone methodology in computational methods are discussed. Until recently, numerical implementations of cohesive-zone models have suffered from a certain mesh bias. For discrete representations this is caused by the initial mesh design, while for smeared representations it is rooted in the ill-posedness of the rate boundary value problem that arises upon the introduction of decohesion. A proper representation of the discrete character of cohesive-zone formulations which avoids any mesh bias is obtained by exploiting the partition-of-unity property of finite element shape functions. The recently developed cohesive segments method, which is well-suited for simulating the entire process of crack nucleation, growth and coalescence is reviewed. The effectiveness of this approach is illustrated by some examples for crack nucleation and growth in heterogeneous materials and for fast crack growth.     

Two field multibody method for periodic homogenization in fracture mechanics of nonlinear heterogeneous materials

This paper presents a new computational approach dedicated to the fracture of nonlinear heterogeneous materials. This approach extends the standard periodic homogenization problem to a two field cohesive-volumetric finite element scheme. This two field finite element formulation is written as a generalization Non-Smooth Contact Dynamics framework involving Frictional Cohesive Zone Models. The associated numerical platform allows to simulate, at finite strain, the fracture of nonlinear composites from crack initiation to post-fracture behavior. The ability of this computational approach is illustrated by the fracture of the hydrided Zircaloy under transient loading.     

On the Fracture Models Determined by the Continuum-strong Discontinuity Approach

The paper focuses on the Continuum Strong Discontinuity Approach (CSDA) to fracture mechanics, and the traction-separation cohesive laws induced from continuum dissipative models as their projections onto the failure interface. They are compared with the cohesive laws commonly used for the fracture simulation in quasi-brittle materials, typically concrete. Emphasis is placed in the analysis of the mechanical stress-strain states induced by the CSDA into the fracture process zone: first when the damage mechanism is initiated and, after, when the cohesive model determines the crack response. The influence of the material parameters, particularly the fracture energy and the initial continuum softening modulus, in the obtained phenomenological responses is also analyzed. Representative numerical solutions of fracture problems are finally presented.     

颗粒增强复合材料非理想界面刚度和有效模量的理论估计

采用内聚力模型(CZM)描述颗粒增强复合材料(PRCs)颗粒/基体非理想界面的力学行为,采用细观力学的Mori-Tanaka(M-T)方法和稀释解方法研究非理想界面刚度对该复合材料有效模量的影响。结果表明:复合材料某一体积含量下的有效模量和其颗粒/基体非理想界面刚度之间存在单调递增的关系曲线。同一复合材料不同体积含量的有效模量和非理想界面刚度关系曲线存在一个临界交点(CP),该点对应的临界界面刚度控制着颗粒体积分数对有效模量的影响。研究了基体和增强相的力学性能以及增强颗粒的尺寸对CP点临界界面刚度的影响。采用有效模量-界面刚度关系曲线,结合实验测得的有效模量,提出了估算PRCs的非理想界面刚度的方法,进而估计了复合材料的宏观有效模量。