由于科学技术的不断进展,机械零件和结构的尺寸愈来愈大,材料的强度水平日益提高,焊接技术广泛应用,而机器服役时的工作环境更为恶化(如低温、辐照、腐蚀介质等),从而使一些按传统强度设计应该是很安全的构件发生了低应力脆断,造成了不少灾难性事故。事故分析表明,一切低应力脆性断裂都是由材料的裂纹失稳扩展造成 Due to the continuous advancement of science and technology, the size of mechanical parts and structures is getting larger and larger, the strength level of materials is increasing day by day, welding technology is widely used, and the working environment of machines is deteriorated (such as low temperature, irradiation, corrosive medium, etc. ), So that some of the components designed according to traditional strength should be very low-stress brittle fracture, causing a lot of catastrophic accidents. Accident analysis shows that all the low-stress brittle fracture is caused by the instability of the crack propagation