Akira Tange

Study on warm shot peening for suspension coil spring

Warm Shot Peening is a shot peening process within warm temperature range. However, the effect of warm shot peening to fatigue strength was not certain and no substantial study has been made. The requirements of coil spring with higher fatigue strength and sag resistance have been increasing to obtain the mass saving of vehicle. While several new spring materials have been developed in recent years, the essence of those developments were to make the strength(hardness) of spring higher, so-called high strengthened spring. As for high strengthened spring, the shot peening process becomes further essential to relieve the increased notch sensitivity due to higher strength. However, for the shot peening process to high strengthened spring, the shot with higher hardness is also required. This can decrease the life of both shot and shot peening equipments. Warm shot peening under the tempering temperature may become one solution to those problems, because the hardness of spring can be temporarily reduced only during the shot peening process. In this paper, the following experimental results concerned with the effect of warm shot peening, are summarized. 1. The relation between spring fatigue life and hardness under one warm shot peening temperature. 2. The relation between spring fatigue life and shot peening temperature. 3. Effects of residual stress, coverage, and surface hardness to fatigue life.

Improvement fatigue limit of steel containing a small crack‐like surface defect by overload effect

Purpose – Surface defects reduce fatigue strength and may greatly reduce component reliability, particularly in pressure vessel weld regions, springs, and other applications. The fatigue strength of components, and thus their reliability, can be substantially increased by tensile overloading prior to use. The purpose of this paper is to investigate the effect of tensile overload on small cracks by applying a tensile overload to steel plates containing semicircular slits that simulate small surface cracks and by determining the degree of increase in the fatigue strength. The effect of tensile overload on the apparent fatigue threshold stress intensity factor range (ΔKth) was also investigated.Design/methodology/approach – A tensile overload stress of 1,000 or 1,200 MPa was applied once to all test pieces. Then, bending fatigue tests were conducted with a stress ratio R=0.1. The slit region was subjected to applied cyclic tensile stress by four‐point bending throughout the fatigue test. A test specimen to w...

Effect of Shot Peening on Fatigue Limit of Surface Flawed Sample

The effects of shot peening on the fatigue strength of specimens having a semicircular notch of varied surface length, 2a (aspect ratio=1.0), are investigated. In the case of un-peened specimens, the fatigue limit of specimens having a notch of a=0.05mm was equal to that of the un-notched specimens. However, the fatigue limit of a=0.3mm was 46% smaller than that of the un-notched specimens. On the contrary, in the case of peened specimens, the fatigue limit of a=0.2mm was equal to that of the un-notched specimens and furthermore, that of a=0.3mm was only 5% smaller than that of the un-notched specimens. Multiple non-propagating cracks were observed in a peened specimen after fatigue testing. The stress intensity factor of the maximum non-propagating crack size was corresponding to that of a=0.2mm notch. In other words, shot peening increases fatigue limit and decreases the likelihood that a surface flaw will result in failure. The experimental data agree well with the calculation results. This study would be industrially useful for the decision of allowable defect size.Copyright