P-SC327-4 FOD を有する Ti-6Al-4V 合金の残留応力測定と疲労限度評価

概要

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In order to investigate the effects of Foreign Object Damage (FOD) on fatigue strength of Ti-6Al-4V alloy, the FOD was simulated by shooting a steel ball with a diameter φ=4.7mm onto specimen surface at a velocity of 90m/s using a compressed-air gun facility. Tension-compression fatigue tests clarified that the fatigue limit of the specimen having shot marks (FOD) was 56% lower than that of smooth specimen without FOD. Fracture origins of the specimen having shot marks were at the bottom of the shot mark in all specimens. The fatigue limit of the specimen having a shot mark (FOD) was evaluated quantitatively from the viewpoint of the following factors, (1) residual stress distribution inside and vicinity of the shot mark, (2) work hardening related with plastic deformation at the bottom of the shot mark and cyclic softening at the stress amplitude of fatigue limit, and (3) the size of shot mark which acts as a detrimental defect. A narrow beam with size □100μm×100μm using the synchrotron radiation facility at SPring-8 was used for the measurement of the residual stress distribution. The fatigue limit of the specimen having a FOD can be predicted within 10% error by the √<area> parameter model.
2002-03-07