A. Inoue, T. Sekigawa, K. Oguri, Mitsubishi Heavy Industries, Ltd., Nagoya, Japan
Shot peening is widely used to increase fatigue properties of aircraft metallic parts. Due to the continuous demand to improve fuel efficiency, possible weight reduction process of metal parts is still very important. Therefore we try to apply Fine Particle Shot Peening (FPSP), which was developed and applied mainly in the Japanese automobile industry, to enhance fatigue properties of aircraft parts more than conventional Shot Peening (SP). Rod shape fatigue coupons made of aluminum alloy 7050-T7451 were shot peened by fine ceramic media of less than 2 mil in diameter and also by conventional shot media of S230. The shot peening Almen intensity of FPSP and SP were about 0.004N and 0.006A, respectively. Tensile fatigue test was performed in axial loading (R=0.1). Fatigue life after SP was increased by several times, while that after FPSP was increased more than one order of magnitude compared with SP. The surface after FPSP consists of continuous fine dimples and the surface roughness was almost unchanged for 63 and 125 μ-inch coupons. Fracture surface observation by SEM revealed that fatigue cracks after FPSP nucleate at the subsurface layer, which indicated the high compressive residual stress near the surface although the value of the compressive stress by FPSP was almost the same as that of SP. Furthermore smooth surface morphology must be effective to prevent crack initiation from the surface. The experimental fatigue lives coincided with the calculated fatigue lives by the crack propagation equation with surface roughness as preliminary existing crack and residual stress. The calculations as well as the experiments indicate that the s ‚“mooth surface morphology by FPSP with high compressive stress at very near surface creates superior fatigue property compared with SP. This study has been conducted in NEDO (New Energy and Industrial Technology Development Organization) project.
Summary: Shot peening is widely used to increase fatigue properties of aircraft metallic parts. Due to the continuous demand to improve fuel efficiency,
possible weight reduction process of metal parts is still very important. Therefore we try to apply Fine Particle Shot Peening (FPSP), which was developed and applied mainly in the Japanese automobile industry, to enhance fatigue properties of aircraft parts more than conventional Shot Peening (SP). Rod shape fatigue coupons made of aluminum alloy 7050-T7451 were shot peened by fine ceramic media of less than 2 mil in diameter and also by conventional shot media of S230. The shot peening Almen intensity of FPSP and SP were about 0.004N and 0.006A, respectively. Tensile fatigue test was performed in axial loading (R=0.1). Fatigue life after SP was increased by several times, while that after FPSP was increased more than one order of magnitude compared with SP. The surface after FPSP consists of continuous fine dimples and the surface roughness was almost unchanged for 63 and 125 ƒÊ-inch coupons. Fracture surface observation by SEM revealed that fatigue cracks after FPSP nucleate at the subsurface layer, which indicated the high compressive residual stress near the surface although the value of the compressive stress by FPSP was almost the same as that of SP. Furthermore smooth surface morphology must be effective to prevent crack initiation from the surface. The experimental fatigue lives coincided with the calculated fatigue lives by the crack propagation equation with surface roughness as preliminary existing crack and residual stress. The calculations as well as the experiments indicate that the s ‚“mooth surface morphology by FPSP with high compressive stress at very near surface creates superior fatigue property compared with SP. This study has been conducted in NEDO (New Energy and Industrial Technology Development Organization) project.
