双K断裂模型粘聚韧度KcIc实用插值计算方法

为了配合《水工混凝土断裂试验规程》在工程界的推广使用,提出了双K断裂模型中在临界状态时分布在虚拟裂缝上的粘聚力σ(x)产生的粘聚韧度KcIc的二元拉格朗日插值计算方法,进而由准脆性材料韧度三参数定律计算了混凝土起裂韧度KiInci。与粘聚韧度KcIc积分计算和简化计算方法的比较,表明此插值计算方法具有很高的精度,计算过程简化,使用计算器即可实现,便于工程人员实际使用。     

混凝土双K断裂参数计算的半解析有限元法

混凝土裂缝扩展的双$K$断裂准则，用于描述混凝土结构裂缝的起裂、稳定扩 展和失稳断裂. 其相应的双$K$断裂参数(起裂断裂韧度$K_{\rm IC}^{\rm ini} $和失 稳断裂韧度$K_{\rm IC}^{\rm un}$)一般通过简便的试验和基于虚拟裂缝扩展粘 聚力的解析方法确定. 利用平面扇形域哈 密顿体系的方程，通过分离变量法及共轭辛本征函数向量展开法，以解析的方法推导出基于混 凝土虚拟裂缝扩展线性粘聚力模型的平面裂缝解析元列式. 将该解析元与有限元相结合，构成 半解析的有限元法，可求解任意结构几何形状的混凝土平面裂缝双$K$断裂参数的计算问题. 数值计算结果表明半解析有限元法对该类问题的求解是十分有效的.     

An experimental method for determining dynamic fracture toughness

The boundary and loading conditions in many dynamic fracture test methods are frequently not well defined and, therefore, introduce a degree of uncertainty in the modeling of the experiment to extract the dynamic fracture resistance for a rapidly propagating crack. A new dynamic fracture test method is presented that overcomes many of these difficulties. In this test, a precracked, three-point bend specimen is loaded by a transmitter bar that is impacted by a striker bar fired from a gas gun. Different levels of energy can be imparted to the specimen by varying the speed and length of the striker to induce different crack growth rates in the material. The specimen is instrumented with a crack ladder gage, crack-opening displacement gage and strain gages to develop requisite data to determine toughness. Typical data for AISI 4340 steel specimen are presented. A simple quasi-dynamic analysis model for deducing the fracture toughness for a running crack from these data is presented, and the results are compared with independent measurements.     

选取最大载荷为岩石KIC测试中临界载荷的合理性研究

本文对选取最大载荷为岩石 K_(IC)测试中临界载荷的合理性从理论上和实验上进行了研究,结果表明,选取最大载荷为岩石 K_(IC)测试中的临界载荷是合理的,正确的。     

岩石断裂韧度试样CCNBD临界应力强度因子的全新数值标定

国际岩石力学学会（ISRM）提出的用人字型切槽巴西圆盘（Cracked Chevron Notched Brazilian Disc—CCNBD）测试岩石I型断裂韧度所必需的量纲为一的临界应力强度因子Y＊min的精度需要进一步改进。本文对CCNBD试样的Y＊min进行了系统的重新标定,CCNBD的几何参数有效范围为0.44≤αB≤1.04、0≤α0≤0.69、0.4≤α1≤0.8。采用有限单元法对CCNBD做三维数值分析,得到了435种CCNBD试样的Y＊min值标定结果;在此基础上全面修正了CCNBD试样Y＊min计算公式中u和v的取值表;给出了不用查表直接确定CCNBD试样Y＊min值的近似表达式,该表达式计算结果与标定结果的相对误差绝对值在1.87%以内。对于ISRM建议的CCNBD标准试样的Y＊min值：ISRM标定值0.84比本文结果0.957小12.2%;分片合成法标定值0.947比本文结果小1.0%;子模型法标定值0.943比本文结果小1.5%。本文特别强调了任何CCNBD试样Y＊min的取值必须在它对应的上限和下限所限定的范围内,这一要求对判断Y＊min标定值是否合理是很重要的。     

A stencil-like volume of fluid （VOF） method for tracking free interface

A stencil-like volume of fluid （VOF） method is proposed for tracking free interface. A stencil on a grid cell is worked out according to the normal direction of the interface, in which only three interface positions are possible in 2D cases, and the interface can be reconstructed by only requiring the known local volume fraction information. On the other hand, the fluid-occupying-length is defined on each side of the stencil, through which a unified fluid-occupying volume model and a unified algorithm can be obtained to solve the interface advection equation. The method is suitable for the arbitrary geometry of the grid cell, and is extendible to 3D cases. Typical numerical examples show that the current method can give ＂sharp＂ results for tracking free interface.