Subcritical propagation of cracks is a warning sign of fracture.If such propagation is detected at an early stage,timely maintenance measures can be taken to prevent the failure of structures.To detect the subcritical...Subcritical propagation of cracks is a warning sign of fracture.If such propagation is detected at an early stage,timely maintenance measures can be taken to prevent the failure of structures.To detect the subcritical propagation of a crack,the crack needs to be monitored continuously in a long term, which is not realistic under certain conditions.However,cracks in concrete dams can be monitored continuously by dam monitoring to offer possible detection for subcritical propagation.In this paper, with measured crack openings from dam monitoring,a state equation for characterizing crack development is established based on the grey system theory.The relation between the stability of the equation and the subcritical crack propagation is investigated,then a criterion is proposed for detecting subcritical propagation.An example demonstrates the validity of the criterion and its potential for practical application.展开更多
采用铜-焊料-铜双悬臂梁焊接试件,利用联动夹具和非接触式引伸计,对锡铅焊料Sn63Pb37和无铅焊料Sn Ag Cu305进行了25℃温度下的I型断裂实验,得到了焊料I型断裂时的载荷-张开位移曲线,观察了焊料的起裂、裂纹扩展、断裂等实验现象,采用...采用铜-焊料-铜双悬臂梁焊接试件,利用联动夹具和非接触式引伸计,对锡铅焊料Sn63Pb37和无铅焊料Sn Ag Cu305进行了25℃温度下的I型断裂实验,得到了焊料I型断裂时的载荷-张开位移曲线,观察了焊料的起裂、裂纹扩展、断裂等实验现象,采用双材料弹性基柔度法,计算了焊料的I型能量释放率.实验结果表明,两种焊料的初始能量释放率基本相同,均为800~900 N/m,但无铅焊料有较长的亚临界裂纹扩展阶段,其开裂载荷约为最大载荷的80%左右;能量释放率饱和值比初始值高1. 4倍,表现出更好的抵抗裂纹扩展的特性.展开更多
基金Supported by the National Natural Science Foundation of China(Grant Nos.50909041,50879024,50809025,50539010,50539110)the National Supporting Program(Grant Nos.2008BAB29B03,2008BAB29B06)the Natural Science Foundation of Hohai University(Grant No.2008426811)
文摘Subcritical propagation of cracks is a warning sign of fracture.If such propagation is detected at an early stage,timely maintenance measures can be taken to prevent the failure of structures.To detect the subcritical propagation of a crack,the crack needs to be monitored continuously in a long term, which is not realistic under certain conditions.However,cracks in concrete dams can be monitored continuously by dam monitoring to offer possible detection for subcritical propagation.In this paper, with measured crack openings from dam monitoring,a state equation for characterizing crack development is established based on the grey system theory.The relation between the stability of the equation and the subcritical crack propagation is investigated,then a criterion is proposed for detecting subcritical propagation.An example demonstrates the validity of the criterion and its potential for practical application.
文摘采用铜-焊料-铜双悬臂梁焊接试件,利用联动夹具和非接触式引伸计,对锡铅焊料Sn63Pb37和无铅焊料Sn Ag Cu305进行了25℃温度下的I型断裂实验,得到了焊料I型断裂时的载荷-张开位移曲线,观察了焊料的起裂、裂纹扩展、断裂等实验现象,采用双材料弹性基柔度法,计算了焊料的I型能量释放率.实验结果表明,两种焊料的初始能量释放率基本相同,均为800~900 N/m,但无铅焊料有较长的亚临界裂纹扩展阶段,其开裂载荷约为最大载荷的80%左右;能量释放率饱和值比初始值高1. 4倍,表现出更好的抵抗裂纹扩展的特性.
