锥头籽晶对DKDP晶体生长和损伤阈值的影响

籽晶是影响DKDP晶体生长和光损伤阈值的一个重要因素。采用传统降温法,分别利用Z片和锥头作为籽晶,从氘化程度为85%的溶液生长了DKDP晶体,并选取部分样品进行3倍频光损伤阈值测试。实验证明,DKDP晶体可以在不同籽晶下基本实现稳定生长,锥头籽晶所得DKDP晶体对晶体损伤阈值提高有积极作用且能有效缩短生长周期。     

A micromechanical model of distributed damage due to void growth in general materials and under general deformation histories

We develop a multiscale model of ductile damage by void growth in general materials undergoing arbitrary deformations. The model is formulated in the spirit of multiscale finite element methods (FE ²), that is, the macroscopic behavior of the material is obtained by a simultaneous numerical evaluation of the response of a representative volume element. The representative microscopic model considered in this work consists of a space‐filling assemblage of hollow spheres. Accordingly, we refer to the present model as the packed hollow sphere (PHS) model. A Ritz–Galerkin method based on spherical harmonics, specialized quadrature rules, and exact boundary conditions is employed to discretize individual voids at the microscale. This discretization results in material frame indifference, and it exactly preserves all material symmetries. The effective macroscopic behavior is then obtained by recourse to Hill's averaging theorems. The deformation and stress fields of the hollow spheres are globally kinematically and statically admissible regardless of material constitution and deformation history, which leads to exact solutions over the entire representative volume under static conditions. Excellent convergence and scalability properties of the PHS model are demonstrated through convergence analyses and examples of application. We also illustrate the broad range of material behaviors that are captured by the PHS model, including elastic and plastic cavitation and the formation of a vertex in the yield stress of porous metals at low triaxiality. This vertex allows ductile damage to occur under shear‐dominated conditions, thus overcoming a well‐known deficiency of Gurson's model. Copyright © 2012 John Wiley & Sons, Ltd.