一、问题的提出在电厂设备中使用的紧固件和联接件,例如汽轮机汽缸及锅炉主蒸汽管道用的螺栓,为了保证联接强度并具有很高的密封效果,在工作中需要承受很大应力。在恒定的总变形条件下,随时间的延长,螺栓内部的弹性变形部分转变为非弹性变形,从而使内部应力逐渐下降。应力的下降减弱了螺栓的紧固作用,会使联接部位松动,承受高压的容器或壳体联接处漏气,引起故障。因此,在设计中必须考虑到螺栓材料在初始应力下工作一定时间后的剩余应力,以便正确地设计螺栓的工作应力。另一个应力松弛的典型示例是水泥预制 First, the issue put forward Fasteners and fasteners used in power plant equipment, such as the steam turbine cylinder and the boiler main steam pipe bolts, in order to ensure the strength of the joint and has a high sealing effect, in the work need to withstand great stress . Under constant total deformation, with the passage of time, the internal elastic deformation of the bolt is transformed into inelastic deformation, so that the internal stress gradually decreases. The reduction of stress reduces the tightening effect of the bolt, loosens the connection part, and leaks at the connection of the container or the shell under high pressure, causing the failure. Therefore, the design of the bolt material must be taken into account in the initial stress after working a certain period of time the residual stress in order to properly design the working stress of the bolt. Another typical example of stress relaxation is cement prefabrication