裂纹扩展速度对焦散线的影响和动态应力光学常数的测定

本文从焦散线形成原理的数学描述出发,用扩展裂纹尖端附近的应力分量表达式,在前人工作的基础上,作了详细的数值计算。特别分析了裂纹扩展速度对焦散斑和初始曲线的形状、大小的影响,为测量扩展裂纹尖端的动态应力强度因子K_1~d提供了依据,并通过拟合得到了以裂纹扩展速度为参量的修正因子表达式。本文还提出了一种测定透明材料动态应力光学常数的方法,并用这一方法测定了有机玻璃的动态应力光学常数。     

含裂纹三点弯曲梁起始扩展的动态分析

本文利用高速摄影捕捉含裂纹三点弯曲梁在冲击下裂纹扩展过程，借助动态焦散线对裂纹尖端初始曲线范围内的应力第二不变量分布进行了试验研究，并通过Ｄｅｔ．－准则对动载下裂纹起始扩展的条件和方向进行了分析。结果表明：裂纹扩展的实际方向与理论预测相一致；Ｄｅｔ．－准则与焦散线相结合在动态断裂力学研究中具有广泛的使用价值     

爆炸应力波作用下裂纹与孔洞的动态焦散线分析

将高速摄影技术与动态焦散线方法相结合，研究了爆炸应力波对裂纹、空孔的作用历史，记录了环绕它们的动态焦散斑图，给出了爆炸应力场中裂纹尖端复合应力强度因子的时间依赖关系以及空孔周围应力场分布的瞬态变化过程，为固体介质的爆破机理研究提供了新方法。     

Experimental caustics analysis in fracture mechanics of anisotropic materials

The originally developed reflection method of caustics is presented for application to cracks in mechanically anisotropic materials such as fiber-reinforced composites. The derived solutions for the combination of crack-opening modes I and II show that the size of the dark spot depends on the load intensity, whereas its shape depends strongly on the mechanical properties of the material, the orientation of the crack tip and the mixed-mode mixture. The evaluation of optical effects is possible using the diameter-measuring method or the advanced multipoint overdeterministic data reduction method. To find the exact position of caustics, the experimental images are analyzed by the simple boundary value method and a more sophisticated differential method, which is accomplished by shifting the real image onto the gradient image. The standard experimental testing procedure is performed for cracks oriented 0 deg, 45 deg and 90 deg to the material axes in carbon-fiber-reinforced polymer composites.     

Experimental study on crack curving propagation in bending beams under impulsive load

Dynamic fracture behaviour of crack curving in bent beams has been investigated. In order to understand the propagation mechanism of such cracks under impact, an experimental method is used that combines dynamic photoelasticity with dynamic caustics to study the interaction of the flexural waves and the crack. From the state change of the transient stresses in polymer specimen, the curving fracture in the impulsively loaded beams is analyzed. The dynamic responses of crack tips are evaluated by the stress intensity factors for the cracks running in varying curvature paths under bending stress wave. The project supported by the National Natural Science Foundation of China and the Scientific Commission of Yunnan Province of China     

Diffraction of a Plane Discontinuos Wave in Layered Anisotropic Elastic Media

The problem of transformation of the front of a plane longitudinal shock wave by curvilinear interfaces of layered anisotropic elastic media with different mechanical properties is considered. To solve the nonlinear Snell equations, the approach based on a synthesis of the Newton method and the algorithm of parametric continuation of a solution is used. The cases of focusing and scattering of rays by convex and concave interfaces of layered composite media and by convex lenses are investigated. Numerical examples are given for various ratios between the parameters of the elastic media.     

A study on caustic method in cracked plate under symmetric bending

Based on Chun-Tu Liu's result for Reissner's plate, an equation of caustics in cracked plate under symmetric bending was obtained. The shape and the distribution of light intensity of the caustic curve were discussed in detail. The relation between the stress intensity factor (SIF) and the size of the caustic curve was found by numerical method, and a simple and accurate experimental method for evaluating SIF in plate under bending was proposed.     

Propagation of laser beams and caustics in crystals

We investigated the propagation and transformation of laser beams and the formation of caustics in particular directions, including optical axes of crystals. We found a direct connection between the particular directions and the curvature of wave surfaces that is determined by the symmetry and optical properties of the crystals. We demonstrated that caustics in particular directions are characterized by a degree of the curvature degeneracy and are described by particular solutions of the corresponding nonlinear equations. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 491–498, July–August, 2007.     

Time-Domain Mapping of Electromagnetic Ray Movement Inside Anisotropic Spherical Resonator

This paper presents the analytical proof of Time-Domain Mapping Method for the spherical resonator made up of uniaxial crystal. In this way, the main types of caustics inside the spherical resonator made up of uniaxial crystal, which were investigated numerically before, are confirmed analytically. It is engraved that the problem of the ray flow inside the spherical resonator can be reduced to the problem of the ray flow inside metal cavity shaped as spheroid.     

Hybrid numerical methods in static and dynamic fracture mechanics

In this article, the concept of the hybrid numerical methods is clarified. On the basis of this concept, various hybrid numerical methods used in static and dynamic fracture mechanics are classified into five categories: (i) hybrid experimental–numerical methods, (ii) hybrid numerical–experimental methods, (iii) hybrid analytical–numerical methods, (iv) hybrid numerical–analytical methods, and (v) hybrid numerical–numerical methods. Features of each category of hybrid numerical method are presented with pertinent numerical results.