Relationship between X-ray residual stress near crack and crack opening/closing behavior controlling fatigue crack propagation in Ti-6Al-4V alloy
Torii Tashiyuki; Toi Norihiko; Nakano Kohji; Honda Kazuo
Abstract:There are very few reports concerning X-ray residual stress measurements near the fatigue crack for Ti-6Al-4V alloys. The residual stress near the crack was measured by an X-ray method for the annealed materials of Ti-6Al-4V alloys and their aging treatment materials, in which the X-ray residual stress was confirmed to exist by comparing with loading stresses under tension. The compressive residual stress, measured in the wake of the propagating fatigue crack, was larger in the aging treatment material. In addition, the crack opening displacement was measured along the real fatigue crack, which was different from the theoretical one. This made it possible to evaluate the effective stress intensity factors Keff depending on the residual stress near the fatigue crack. The fatigue crack propagation rate under the same Keff value was smaller in the annealed than in the aging treatment material. This was probably related not only to the zigzag crack path in the annealed material, but also to the heavier plastic deformation accompanying the large compressive residual stress in the aging treatment material. Key Words:fatigue, crack propagation, fracture mechanics, residual stress, crack closure, crack opening displacement, stress intensity factor, titanium alloy