Dependence of stress frequency on fatigue crack initiation in orthotropic material

✍ Scribed by H. Sakamoto; S. Takezono

• Publisher: Elsevier Science
• Year: 1990
• Tongue: English
• Weight: 857 KB
• Volume: 36
• Category: Article
• ISSN: 0013-7944
• DOI: 10.1016/0013-7944(90)90295-r

✦ Synopsis

Tbe effect of stress frequency on fatigue crack initiation in 99.5% pure titanium plate, which has remarkable strain rate dependence in the plastic region and notable orthotropy, was studied. Fatigue crack initiation tests were carried out under three kinds of stress frequencies (0.2, 1 and 20 Hz). The test specimens were cut out from the rolling direction and the transverse to rolling direction of the plate. An anisotropic elasto/visco-plastic analysis was performed by the use of the orthotropic elasto/visco-plastic overlay model, and the comparison between the cycles to crack initiation and the &co-plastic strain range at notch root obtained by the analysis was made. The results obtained in this study are summarized as follows: (1) It was found from the experiment that the cycles to fatigue crack initiation depended on the cutting out direction of the specimen because of the anisotropy of titanium plate, and were approximately in proportion to f* (n > 0), where f is the stress frequency. (2) A parameter closely related to the fatigue crack initiation in orthotropic material is the v&o-plastic strain range strain range at the notch root, and the cycles to fatigue crack initiation is approximately in inverse proportion to the nth power of the visco-plastic strain range at the notch root. (3) The effect of stress frequency on fatigue crack initiation may be. explained by the variation of v&o-plastic strain range at notch root based on the strain rate dependence and the anisotropy of the material.