Papers by Author: Sotomi Ishihara

Abstract: Recently, due to increasing popularity of the magnesium alloys, many studies on corrosion resistance of the magnesium alloys have been reported to improve their corrosion resistance. However, it is not clarified yet whether an electrochemical polarization curve or a corrosion rate is a good measure for the corrosion fatigue resistance or not. In the present study, corrosion fatigue tests, the weight loss test, and measurement of the electrochemical polarization curve were performed in 3% sodium chloride solution using both the extruded and the rolled Mg alloys. It was clarified that there are no differences in the corrosion fatigue lives between the extruded and the rolled Mg alloys, though they have different corrosion resistance. So, it was concluded that the corrosion fatigue characteristic does not correspond well with the trend in corrosion resistance.

Abstract: . In this study, fatigue tests were carried out using a diecast Mg alloy AZ91 to study the distribution of fatigue lives under constant stress amplitudes. During the fatigue process of the diecast Mg alloy, cracks initiated from the casting defect within inside of the specimen, and then propagated prior to final failure of the specimen. Distributions of fatigue lives at the constant stress amplitudes can be represented by the Weibull distributions. The scatter in the distribution of fatigue lives becomes larger at the lower stress amplitude of 80 MPa as compared with those at the higher stress amplitudes. There is a common relationship regardless of the stress amplitudes between the initial maximum stress intensity factors Kimax and fatigue lives Nf. The lower Kimax, the longer Nf becomes. Integrating the fatigue crack propagation law from the initial maximum stress intensity factor Kimax to the fatigue fracture toughness Kfc, the relation Kimax vs. Nf can be successfully evaluated.

Abstract: Fatigue tests were performed in laboratory air using extruded Ti-6Al-4V to determine the effect of microstructure on S-N curve, and the crack initiation and crack propagation behavior of the alloy. A modified linear elastic fracture mechanics approach was used in the analysis of the short crack propagation behavior to predict the S-N curve and the crack propagation curve. The predictions agreed well with the experimental results.

Abstract: In the present study, fatigue experiments were conducted using two kinds of extruded magnesium alloys with different extrusion ratios. Effect of the extrusion ratio on fatigue lives and crack propagation behavior was studied in detail. There was no dramatic effect of the extrusion ratio on fatigue life, fatigue limit and crack propagation behavior.