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长期以来,人们认为只要构件上的工作应力σ_1不超过许用应力[σ],就能保证构件在使用过程中不会发生突然断裂事故。这就是传统的设计思想,即对塑性材料对脆性材料在一般情况下,这样设计的构件是安全的。但是,这种设计思想却不能解释某些高强度和超高强度材料在使用过程中出现的重大的工程断裂事故——低应力脆断。随着断裂力学的兴起和发展,使得设计人员打破了传统的设计思想,而把构件内部的裂纹大小和构件的工作应力以及断裂韧性三者定量地联系起来,因而为工程构件(特别是火箭发动机壳体、飞机结构、压力容器、电站设备、机车和桥梁等)的安全设计和选材原则提供了新的理论基础。断裂韧性是材料抵抗裂纹失稳扩展能力的度量,
For a long time, people think that as long as the work on the component stress σ_1 does not exceed the allowable stress [σ], we can ensure that the components in the process of using a sudden rupture failure. This is the traditional design philosophy, that is, the plastic material on the brittle material under normal circumstances, the design of the components is safe. However, this design concept can not explain the major engineering failure occurred during the use of some high-strength and ultra-high-strength materials - low stress brittle fracture. With the rise and development of fracture mechanics, designers broke the traditional design idea, and quantitatively linked the crack size inside the component with the working stress and the fracture toughness of the component, so that the engineering components (especially the rocket engine Shell, aircraft structure, pressure vessels, power plant equipment, locomotives and bridges, etc.) provide a new theoretical basis for safety design and material selection principles. Fracture toughness is a measure of the material’s ability to resist crack propagation.