疲劳损伤演化的机理及损伤演化律

Mechanism of Fatigue Damage Evolution and the Evolution Law

疲劳是由材料内部的损伤演化导致的,但损伤演化的机理目前尚不清楚。根据原子运动的热扰动,当原子的活性能大于某一临界值时,原子将从原平衡位置逃逸并产生空穴。当材料受循环应力作用时,因原子平衡位置的变化而导致热扰动所产生的空穴不能完全相互湮灭,从而形成缺陷或导致其发展。这一观点不仅可以说明疲劳损伤演化的机理,而且可以把损伤演化速率与原子逃逸过程的速率联系起来,从而可以提出一种具有机理性依据的疲劳损伤演化律的一般形式。这种形式的损伤演化律,是与已知的金属材料损伤寿命关系相一致的。讨论并给出对称循环下损伤演化律的具体形式,并依据该演化律讨论损伤的累加方式。

It is well known that fatigue is induced by the internal damage evolution of material. However the mechanism of damage evolution remains unclear yet. From the thermal disturbance of atomic motion, when the active energy of an atom is greater than a certain critical value, the atom will escape from its original equilibrium position and thereby a void will be generated. Under cyclic loadings, the voids generated by the thermal disturbance cannot be completely annihilated, so that the damage will be initiated or accumulated. From this view, the mechanism of damage evolution can be well explained, and the damage accumulation rate can be theoretically related to the rate of the statistical process of atomic escape. Therefore, this view provides the way to set up the damage evolution law with theoretical foundation. The evolution law based on this mechanism can well indicate the already known damage-life relationships of metals. Taking the experimental relationships between the damage and fatigue life under symmetrical cyclic loadings with different stress amplitudes into account, the damage evolution law is deduced in details. Furthermore, the accumulating rule of darnage is also discussed on the basis of the proposed damage evolution law.