Fatigue crack propagation under step variation of stress frequency in orthotropic material

✍ Scribed by H. Sakamoto; S. Takezono

• Publisher: Elsevier Science
• Year: 1988
• Tongue: English
• Weight: 824 KB
• Volume: 31
• Category: Article
• ISSN: 0013-7944
• DOI: 10.1016/0013-7944(88)90088-4

✦ Synopsis

The effect of variation of stress frequency on fatigue crack propagation in 99.5% pure titanium, which has remarkable strain rate dependence in the plastic region and anisotropy, was studied. Fatigue crack propagation tests were carried out under four stress frequencies: two constant stress frequencies (f = 20 Hz, 0.02 Hz) and two stress frequencies changed step-wise (f = 20 -+ 0.02 Hz, 0.02 4 20 Hz). The test specimens were cut out from roiling direction and transverse direction to rolling of the plate. An orthotropic elasto/visco-plastic analysis of fatigue crack propagation was performed by the use of the orthotropic visco-plastic model, and the comparison between the change of crack propagation rate due to variation of stress frequencies and the visco-plastic strain behavior at the crack tip calculated by the analysis was made. The results obtained in this study are summarized as follows: (1) It was found from the experiments that the crack propagation rate changed characteristically depending on cutting out direction of the specimen caused by anisotropy of titanium plate and on the variation of stress frequency. (2) A parameter closely related to the fatigue crack propagation rate is the visco-plastic strain range at the crack tip. (3) The effect of variation of stress frequency on the fatigue crack propagation rate may be explained by the variation of the visco-plastic strain range at the crack tip based on an anisotropic visco-plasticity of the materials.