基于累积损伤的结构系统时变刚度可靠性分析

Time-dependent stiffness reliability analysis of the structural system based on the cumulative damage

基于累计损伤的结构系统时变刚度可靠性分析,对设计寿命期内结构系统刚度可靠性指标的影响非常重要.根据疲劳载荷造成的累积损伤对材料极限应力的影响,结合材料强度与弹性模量之间的关系,给出了结构构件在基于累积损伤下剩余弹性模量的表达式,并导出了在外载作用下刚度失效时安全余量的具体表达式.采用改进的一次二阶矩方法求解可靠性指标,用改进的分枝限界法寻找主要失效模式,然后用PNET法计算结构系统可靠性.数值算例表明,结构系统在设计寿命内虽然满足了系统疲劳可靠性的要求,但随着使用寿命的增加,结构系统刚度可靠性下降,当疲劳载荷循环次数大于一定值时,结构系统结构刚度可靠性不能满足设计要求.因此,该方法为设计人员综合考虑结构系统可靠性提供理论依据.

The time-dependent stiffness reliability analysis of structural system, which is based on cumulative damage, is very important for the influence on the stiffness reliability index of structural system in the design life. According to the influence of cumulative damage caused by fatigue load on ultimate stress and combining the relation of material strength and elastic modulus, the expression of residual elastic modulus with the form of cumulative damage and the safety margin expression of the stiffness failure when the structures bear fatigue load are given. The reliability index is calculated by advanced first order second moment reliability method, the significant failure modes are identified by the advanced branch and bound method, and the reliability of structural system is evaluated by PNET method. A numerical example indicates that the fatigue reliability index of structural system can fulfill the demand of fatigue reliability in the design life, but the stiffness reliability index of structural system descends with the increase of the service life, and the stiffness reliability index doesn＇t fulfill the demand of the design when the service life is larger than a certain value. Therefore, the method mentioned in this paper provides a theoretical basis for designers to consider the reliability of the structural system synthetically.