Al双晶体的晶界疲劳效应

通过Al双晶体疲劳试验,研究了晶界对循环变形和疲劳裂纹扩展的影响。实验结果表明,晶界疲劳效应集中体现于晶界影响区,表现为不相容塑性应变在该区内产生内应力,并由此可激发次级滑移,甚至产生晶界裂纹;在常幅循环应力下,随超Ⅰ阶段裂纹逐渐接近晶界,裂纹分叉、前沿碎裂,扩展速率降低,直至在晶界影响区中央达到一最小值。本文提出了晶界诱发裂纹顶端屏蔽机制,并以此解释了上述超Ⅰ阶段裂纹对微观组织敏感的扩展行为。

EFFECT OF GRAIN BOUNDARY ON FATIGUE BEHAVIOUR OF Al BICRYSTALS

The effect of grain boundaries on cyclic deformation and fatigue crack growth in aluminum bicrystals has been studied.The effect of a grain boundary is restricted in a narrow area, termed as grain boundary affecting zone(GBAZ),where the incompatible plastic strain treats internal stress which conversely promotes inhomogeneous slip in the area and grain boundary cracking.As an extended stage I crack initiated from a notch approaches the grain boundary under a constant cyclic stress,the crack front branches splits into several pieces, meanwhile,the growth rate of the crack reduces to a minimum value at the center of the GBAZ.Such microstructure-sensitive growth of extended stage I cracks is mainly attributed to the grain boundary-induced crack tip sheilding.