动、静裂纹作用偏置效应的动焦散冲击实验

为了研究冲击荷载作用下脆性材料中运动裂纹与静止裂纹的相互作用,选取动态载荷下断裂行为与岩石材料类似且本身光学特性较好的有机玻璃（PMMA）作为实验材料,试件尺寸为220 mm×50 mm×5 mm,采用激光切割制作长度5 mm的预制裂纹和长度10 mm的静止裂纹,预制裂纹位于试件的底部边缘中心,静止裂纹的中心位于试件水平轴线。将静止裂纹偏置距离作为单一变量,采用数字激光动态焦散实验系统对含不同缺陷的PMMA进行三点弯曲实验,并结合几何分形理论研究不同偏置距离下运动裂纹的分形规律。实验结果表明：存在预制裂纹与静止裂纹的临界偏置距离（6 mm）,该条件下裂纹轨迹对应的分形维数值最大,裂纹轨迹的规则程度最低,裂纹破坏形态最复杂。当预制裂纹与静止裂纹的偏置距离在0～6 mm时,裂纹Ⅰ起裂后垂直向上扩展一段距离,与静止裂纹交汇,并停滞一段时间后发生二次起裂,直至贯穿试件,偏置距离和交汇点竖向坐标值呈近似线性函数关系。偏置距离的存在不会影响裂纹Ⅰ的起裂时间和应力强度因子,但会显著减小裂纹Ⅱ的动态应力强度因子,且停滞时长随偏置距离的增大而逐渐缩短。当偏置距离大于临界偏置距离时,运动裂纹不再与静止裂纹交汇而是呈拱状向试件上边缘扩展直至贯穿,裂纹的起偏时间、起偏位置也会出现明显的滞后现象。

     

Thermoelastic-numerical hybrid analysis of holes and cracks in composites

An effective thermoelastic-numerical hybrid method is demonstrated for obtaining stress information on, and adjacent to, geometric discontinuities in orthotropic composites. This includes determining stress intensity factors. The technique involves evaluating the stress functions from measured thermoelastic data around the external boundary of a subregion containing the geometric discontinuity of interest. Knowing the stress functions, stresses throughout the subregion surrounding the geometric discontinuity, and stress intensity factors, are available.     

Stress-intensity distributions for corner cracks emanating from open holes in plates of finite width

A series of frozen stress photoelastic tests is carried out in the present investigation. Linear Elastic Fracture Mechanics is used to analyze the problem of a part-through corner crack at an open hole in a plate of finite width loaded in tension. The photoelastic modeling capability of three-dimensional subcritical crack growth problems is assessed. This is achieved by comparing monotonically grown flaw shapes in epoxy models with crack profiles relative to fatigue crack propagation tests in a different material. Photoelastic stress-intensity factor distributions are checked against numerical results obtained for quarter elliptical geometries. The dependence of stress intensity factors on flaw shape is also discussed.     

Electromagnetoelastic problem for a plate with holes and cracks

The methods of complex potentials, conformal mappings, and least squares are used to solve a plane problem of electromagnetoelasticity for a plate with holes and cracks. Numerical solutions are found for a ring and a disk with a crack under internal concentrated forces or electric charges as well as electric potentials applied to the boundaries     

正交异性平面内的椭圆孔或裂纹系问题

应用Ｆａｂｅｒ级数展开和各向异性体平面问题复应力函数的方法，对于含有任意个椭圆孔或裂纹的正交异性平面，给出了孔周应力场解或孔附近裂纹应力强度因子解，其特例与前人结果一致．     

切槽孔爆破动态力学特征的动焦散线实验

应用爆炸加载的透射式动焦散线测试系统,分析了有机玻璃切槽孔爆破模型的裂纹动态特征变化规律。比较了不同切槽角度、切槽深度的定向断裂裂纹尖端的扩展长度、扩展速度和动态应力强度因子。初步探讨了切槽爆破的动态效应,研究表明切槽孔爆破早期裂纹破坏模式为爆炸拉应力波作用下的I型快速扩展裂纹,裂纹尖端拉应力集中积聚的较大应变能维持了爆炸裂纹进一步扩展,裂纹尖端扩展后期表现为P波、S波共同作用下的复合型扩展特征。切槽角为60时获得的定向断裂效果最好,合理切槽深度为炮孔半径的1/4～1/2。     

反平面圆形夹杂和多圆孔多裂纹相互作用问题

动用复变函数及积分方法方法求解了反平面圆形夹杂和多圆孔多裂纹相互作用问题。为解决该问题,建立了两种类型的基本解。利用叠加原理和所得的基本解没圆孔和裂纹表面取待定的基本解密度函数,可得一组Ｆｒｅｄｈｏｌｍ积分方程,通过积分方程组的数值求解,可以得到密度函数的离散值,进而得到应力强度因子。     

Determination of stress intensity factors at the tips of cracks growing from loaded holes in finite anisotropic plates

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 171–177, March–April, 1990.     

Thermal stress state near edge cracks in a plane with elliptical holes

S. P. Timoshenko Institute of Mechanics of National Academy of Sciences of Ukraine, Kiev. Poltava Agricultural Institute, Poltava. Translated from Prikladnaya Mekhanika, Vol. 31, No. 11, pp. 90–96, November, 1995.     

Problems of electromagnetoelasticity for a half-plane and a strip with holes and cracks

The methods of complex potentials, conformal mappings, Cauchy integrals, and least-squares are used to develop a method for determining the electromagentoelastic state (EMES) of a multiply connected half-plane, with the boundary conditions on the straight-line boundary satisfied exactly. The method underlies an approximate method for determining the EMES of a strip with arbitrarily arranged holes and cracks. The dependence of the EMES on the geometrical parameters of a strip with a circular hole or a crack is analyzed     

Stress wave fields in plates weakened by curvilinear holes with edge cracks

The dynamic fracture of plates weakened by holes with edge cracks and subjected to impulsive loading is studied using the dynamic photoelastic method. The time dependences of the stress intensity factors and the crack growth rate are examined for three models of plates with circular holes and edge cracks __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 2, pp. 79–84, February 2006.     

Integral equations for any configuration of curved cracks and holes in an elastic strip

Summary A method is presented to deal with the problems of an elastic strip weakened by cracks and holes of any configuration and geometry. The solution in terms of complex potentials is given by integrals over the cracks and holes with integrands expressed in terms of determined functions (Green) and an unknown density function (t). A singular integral equation for the complex density function (t) is derived for the problem. The appropriate Green's functions are derived from the solution for the problem of an uncracked strip subjected to a concentrated force or a dislocation. The integral equation is solved numerically for a strip in tension with an internal circular arc crack.

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Integralgleichungen für beliebige Konfigurationen von gekrümmten Rissen und Löchern in einer elastischen Scheibe

Übersicht Eine Methode wird dargestellt, welche zur Lösung von Problemen einer unendlichen elastischen Scheibe endlicher Breite mit Rissen und Löchern beliebiger Konfiguration und Geometrie geeignet ist. Die Lösung in Form von komplexen Spannungsfunktionen wurde mit Hilfe von Integralen über den Rissen und Löchern gegeben. Die Integranden wurden mit Hilfe von bekannten Funktionen (Green) und einer unbekannten Dichtefunktion (t) ausgedrückt, für welche eine singuläre Integralgleichung abgeleitet wurde. Die geeigneten Greenschen Funktionen wurden von der Lösung des Problems der entsprechenden Scheibe ohne Risse, welche mit einer Einzelkraft belastet wird oder eine Versetzung enthält, hergeleitet. Die singuläre Integralgleichung wurde numerisch für eine Scheibe endlicher Breite mit einem Kreisbogenriß im einachsigen Zugspannungsfeld gelöst.

     

任意多孔多裂纹板的裂纹闭合接触分析

基于摩擦接触问题的数学规划解法，采用各向异性体平面弹性理论中的复势方法，建立了含多椭圆孔及裂纹群有限大各向异性板，在任意载荷作用下裂纹闭合或局部闭合问题的有效分析方法。通过在可能闭合的裂纹边界引入互补变量函数并将其展成Fourier级数形式，以Faber级数为工具，应用保角映射技术和最小二乘边界配点法，导出无卸载情况下裂纹面摩擦接触的线性互补模型，并通过算例验证了方法的有效性。数值结果表明，由于采用级数解描述板应力场和位移场，该方法具有较高的计算精度和效率，便于研究裂纹闭合对应力强度因子等断裂参数的影响。     

The method of caustics for static plane elasticity problems

By use of the complex stress function analysis of Muskhelishvili-Kolosov and conformal mapping procedures the general governing equations of the method of caustics or shadow spot technique have been developed for optically isotropic and anisotropic materials in static plane elasticity theory. Special cases of caustics formed about cutouts, cracks, and various singular regions in static elastic stress fields are obtained upon specialization.