船体结构表面裂缝在应力腐蚀耦合作用下的扩展机理数值研究

用数值方法研究了船体表面微裂缝在海水腐蚀以及外荷载耦合作用下扩展的机理.实验表明,在给定材料和腐蚀环境的条件下,外荷载越小,微裂缝扩展并最终导致材料断裂破坏过程越长;但当荷载小于某个值(门槛值或称疲劳极限)时,这种延迟的腐蚀断裂破坏现象可以避免.为研究方便,文中假设了在腐蚀环境中工作的材料为各向同性材料.根据数值计算结果,共发现了三种可能的裂缝扩展形式,并证实了导致腐蚀疲劳断裂临界条件的存在性.最后通过计算,针对不同材料以及不同环境条件,勾勒出导致腐蚀疲劳断裂相应的临界条件曲线.

Fracture Mechanism Maps for Crack Growth Driven by Stress-Assisted Corrosion in Ship Structures

A front-tracking finite element method is used to compute the evolution of a crack-like defect that propagates by stress driven corrosion in ship structures, assumed as an isotropic, linear elastic solid.Experiments have shown that for a given material and ambient environment,the lesser the applied stress, the longer the time to fracture. However, when the applied stress decreases to a threshold level, known as a fatigue limit or a stress corrosion limit, failure of the solid can be avoided. Through the numerical simulations reported in this paper,three possible behaviors for the flaws are observed and the existence of a threshold stress level is confirmed.Finally,by computations, fracture mechanism maps showing the range of values of parameters required to cause crack blunting or sharpening are attained, i.e., a map of fatigue limits corresponding to various conditions.