Influence of foreign-object damage on crack initiation and early crack growth during high-cycle fatigue of Ti-6Al-4V
Influence of foreign-object damage on crack initiation and early crack growth during high-cycle fatigue of Ti-6Al-4V
复制标题
DOI：
10.1016/s0013-7944(00)00045-x
复制
发表时间：
2000-10-01
影响因子：
5.4
通讯作者：
Ritchie, RO
中科院分区：
文献类型：
--
作者：
Peters, JO;Ritchie, RO
这项工作的目的是提供一种合理的方法来确定存在异物损伤(FOD)时高周疲劳(HCF)的极限条件。本研究重点研究了模拟FOD对典型涡轮叶片加工的Ti-6Al-4V合金表面小裂纹萌生和早期扩展的影响。利用3.2nlm直径钢球高速(200~300m/S)撞击疲劳试件表面模拟疲劳裂纹扩展，发现裂纹萌生时间提前，疲劳疲劳抗力显著降低。早期裂纹萌生和随后的近门槛裂纹扩展主要受到与FOD压痕相关的应力集中和损伤区存在小微裂纹(仅在较高冲击速度下才能看到)的影响。此外，从疲劳强度退化的角度评估了FOD诱导的压痕位置的塑性变形对残余应力和微观组织损伤的影响。结果表明，POD引发的裂纹，其尺寸与微结构尺寸相当，可以在与1 Mpa根m相似的K量级的外加应力强度范围内扩展，即对于尺寸比微结构尺寸大的裂纹(“连续尺寸”裂纹)，大约比Ti-6Al-4V中的“最坏情况”门槛应力强度范围小两倍。相应地，对于FOD引发的失效，必须在存在微结构小裂纹的情况下定义HCF的临界条件，提出了北川-高桥图，其极限条件为应力集中修正的10(7)周疲劳极限和“最坏情况”增量K次疲劳门槛，作为抗FOD引起的HCF失效的设计基础。(C)2000爱思唯尔科学有限公司。保留所有权利。
The objective of this work is to provide a rationale approach to define the limiting conditions for high-cycle fatigue (HCF) in the presence of foreign-object damage (FOD). This study focused on the role of simulated FOD in affecting the initiation and early growth of small surface fatigue cracks in a Ti-6Al-4V alloy, processed for typical turbine blade applications. Using high-velocity (200-300 m/s) impacts of 3.2 nlm diameter steel spheres on the flat surface of fatigue test specimens to simulate FOD, it is found that the resistance to HCF is markedly reduced due to earlier crack initiation. Premature crack initiation and subsequent near-threshold crack growth is primarily affected by the stress concentration associated with the FOD indentation and the presence of small microcracks in the damaged zone (seen only at the higher impact velocities). Furthermore, the effect of residual stresses and microstructural damage from FOD-induced plastic deformation at the indent sites are assessed in terms of fatigue strength degradation. It is shown that POD-initiated cracks, that are of a size comparable with microstructural dimensions, can propagate at applied stress-intensity ranges on the order of Delta K similar to 1 MPa root m, i.e., a factor of roughly two less than the "worst-case" threshold stress-intensity range in Ti-6Al-4V for a crack of a size large compared to microstructural dimensions (a "continuum-sized" crack). Correspondingly, for FOD-initiated failures, where the critical condition for HCF must be defined in the presence of microstructurally small cracks, the Kitagawa-Takahashi diagram, with the limiting conditions of the stress-concentration corrected 10(7)-cycle fatigue limit and the "worst-case" Delta K-TH fatigue threshold, is proposed as a basis for design against FOD-induced HCF failures. (C) 2000 Elsevier Science Ltd. All rights reserved.