一、引言许多世纪以来,人们为了了解构件在使用过程中损坏的原因,曾进行过许多研究,然而一些不呈任何塑性变形的脆性断裂仍经常出现。特别是高强度材料的制成,以及应力分析技术的进步,允许减小安全系数,提高工作应力。但另一方面会使材料对裂纹的抗力减小,使构件中原有缺陷发展成裂纹的机会增大,以致飞机、大型转子、装甲车辆、大炮、贮存罐、承压容器、管道、焊接船舶、宇航结构等经常发生灾难性的脆断事故。这就引起了人们对断裂现象的研究。通过对大量事故的研究发现: I. INTRODUCTION For many centuries, many studies have been conducted to understand the causes of damage to components during use. However, some brittle fractures without any plastic deformation often occur. In particular, the manufacture of high-strength materials, as well as advances in stress analysis techniques, allow the safety factor to be reduced and work stress to be increased. On the other hand, it will reduce the resistance of the material to the crack and increase the chances of the original defects in the component being cracked. As a result, aircraft, large rotors, armored vehicles, artillery, storage tanks, pressure vessels, pipes, Aerospace structures and other disastrous crises often happen. This caused people to study the phenomenon of fracture. Through a large number of accidents found that: