Shot peening process is a cold performed function to enhance the mechanical properties which is widely used in many industries. This process introduces compressive residual stress which was proven to increase the fatigue life, geometry stability and corrosion resistance. However, the benefit of the residual stress is still unstable due to the relaxation during the operation. This paper will study on the trend of the relaxation of residual stress against cyclic loading as well as the change in the hardness. The material used in this study is carbon steel ASTM A516/ SA 516 Grade 70. Shot peening process with steel shots was applied to the samples to introduce compressive residual stress in the samples. Cyclic load was applied to samples after shot peening process with low load of 52Mpa (20% of Yield Strength) and high load of 208Mpa (80% of Yield Strength). The measurement of residual stress using X-Ray diffraction and hardness test was done on the samples to study the trend of the relaxation of residual stress and the change in hardness values. The result shows that more relaxation of residual stress occurs if the applied cyclic load is higher. The change of hardness trend is found non-sequenced in this study due to random coverage of shot peening.
ASTM A516 Grade 70 is widely used in the industrial sector as it provides very good mechanical properties in tough conditions. The main usage of this material is in moderate and low operating services. This paper focuses on the effect of shot peening process on ASTM A516 Grade 70 on improving the mechanical properties and fatigue life of the material. Samples have been shot peened with steel shot to induce compressive residual stress. Hardness, tensile and fatigue test as well as microstructure were done on the samples before and after shot peening process to study the effects on mechanical properties. The result shows that there is an increment in every test after shot peening process. There is a slight increment of 0.47% in hardness value, 0.39% increment in tensile strength and 6.78% increment in fatigue life of the material after shot peening process applied. The slight increment in every result was due to the low intensity of the shot peening process. Result also shows that the shot peening process compressed the molecules closer to each other as can be seen under SEM. Therefore it was proven that in this study, there is a very significant improvement in mechanical properties and fatigue life by shot peening process on ASTM A516 Grade 70 Steel.
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