Papers by Keyword: Crack Growth Resistance

Abstract: Rotating bending fatigue tests were carried out to investigate the influence of grain size on the resistance to crack growth of Ni-base super alloy, Inconel 718, using the materials with grain sizes of about 20, 50,100 and 200 たm, at room temperature. The larger grain size, the smaller crack growth rate, though the static strength was decreased with increase in grain size. The growth rate of a small crack was uniquely determined by the term ja na (Small crack growth law), where ja and a are the stress amplitude and the crack length, respectively, and n is a constant. The resistance to crack growth among materials was evaluated based on the law and showed a good correlation with tensile strength jB, meaning that fatigue life can be predicted by using only j B BB.

Abstract: This paper reports the results of a numerical study concerning the influence of local brittle zones intersecting the crack front on the fracture behaviour of welded joints. This work was performed using the numerical simulation of the three point bending test of weld samples with different amount of brittle structures at the crack front. Using 3D finite element discretization it was possible to simulate welded samples with very small fractions of brittle zone at the crack front, such as 5 %. Comparing the results of samples with increasing proportion of brittle zone it was observed a significant decrease in the crack growth resistance with increasing amounts of brittle material. This decrease in crack growth resistance was obtained even for samples with very small amounts of brittle material at the crack front.

Abstract: The crack growth resistance of the Al-Zn-Mg-Cu alloy forgings in overaged condition was investigated with three industrially produced alloys, which showed differences in the microstructures governed by compositional variations. Fatigue-crack propagation experiments were conducted at ambient temperature and variations in crack growth rates (da/dN) as a function of applied stress intensity range (ΔK) were related to the characteristics of microstructures, including coarse intermetallic (IM) particles and precipitates. It appears that the crack growth rate increases systematically with an increase of the impurity level, which in turn increases the amount and size of large Fe- and Si-containing IM particles while decreases their spacing. That degradation in resistance to crack growth was attributed to the acceleration of the crack initiation and propagation by coarse IM particles were confirmed by in-situ SEM observation of the fracture process. The observed anisotropy in fatigue behavior was caused by the anisotropy in coarse IM particle orientation.