Fatigue Strength of Ti-6Al-4V Alloys Containing Small Artificial Defects

Abstract

The effects of small defects on the fatigue strength of Ti-6 Al-4V were investigated in tension-compression fatigue tests.specimens (Series A). Another series of specimens (Series B) were prepared to investigate the effect of a burr or a pre-crack which was introduced at the edge of the artificial hole. For Series A specimens, the fatigue limit was defined as the threshold for crack initiation from the edge of the hole. For Series B specimens, the fatigue limit was defined as the threshold for crack propagation from the burr or the tip of the pre-crack fatigue limit of Series A specimens, but the model accurately predicted the fatigue limit defined by crack-growth threshold for Series B specimens. In addition it was noted that the presence of abun resulted in a decrease in fatigue life, since the bun facilitated the crack initiation process.

A practical expression for evaluating the small shear-mode fatigue crack threshold in bearing steel

“…8, the exponent representing the crack size dependence is likely to be close to 1/3 for the crack size regime l = 0.005-0.3 mm ( ffiffiffiffiffiffiffiffiffi ffi area p of 0.02-1 mm). Similar trends in crack size dependence have been confirmed for other materials (e.g., hard steels [43,44], low-carbon steels [41][42][43], titanium alloys [50], etc.). The value of DK th plateaus as the transition to the large crack regime is approached, where linear elastic fracture mechanics (LEFM) is applicable under a small scale yielding condition.…”

“…Although the values for DK IIth and DK IIIth obtained in this study are dependent on the crack size and the crack-face interference, no significant difference between the tendencies of these values is observed, supporting the conclusion of Murakami et al Therefore, combining Eqs. (2)-(4), the threshold SIF ranges for mode II and III cracks are expressed by The three constants A, B and C can be determined by the least squares method using the data shown in Table 1 The crack size dependence of the fatigue limit associated with mode I fatigue cracks has been investigated by many researchers [23,[41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57]. For example, Frost [47] and Kobayashi and Nakazawa [49] proposed the following formula: r n w l ¼ constant, where r w is the fatigue limit of the material and l is the length of the twodimensional crack.…”

Effect of defects on the fatigue limit of Ni‐based superalloy 718 with different grain sizes

“…It has been reported that for various metallic materials, the fatigue limit as a crack‐growth threshold can accurately be predicted by the parameter model . This model states that Δ Κ th at a stress ratio of −1 depends on the size of the initial crack or defect and the hardness of the material, expressed by the following equation: The unit is MPa for Δ Κ th .…”

Effect of small defect orientation on fatigue limit of carbon steels

“…Fatigue strength of metallic materials is deteriorated by a variety of small defects, for example, non‐metallic inclusions, cavities, microstructural irregularities and cracks . Thus, the effect of small defects has been a major concern for fatigue researchers for many years.…”

“…Fatigue strength of metallic materials is deteriorated by a variety of small defects, for example, non-metallic inclusions, 1-11 cavities, [12][13][14][15][16] microstructural irregularities 17,18 and cracks. [19][20][21] Thus, the effect of small defects has been a major concern for fatigue researchers for many years. In the 1980s, Murakami and Endo approached this problem in terms of fracture mechanics and proposed the ffiffiffiffiffiffiffiffi ffi area p parameter model that provides a quantitative estimation of the fatigue limit deteriorated by small defects.…”