Investigation of Fatigue Damage Effect on Elastic Properties of 304 SS using Small Punch Test

Small Punch testing on miniaturized thin discs is a powerful technique for evaluation of different mechanical properties of materials. The load-deflection curve originated from small punch test can be partitioned into four distinct regimes which the first part is the elastic bending deformation associated with local surface micro-yielding. The slope of load-deflection curve in the elastic regime and load value at the end of elastic domain in small punch test can be related to the Young’s modulus and the Yield strength of material respectively. In the present study some small punch tests are performed under constant displacement rate on virgin 304 SS at room temperature and the results are compared to conventional tension test to investigate the aforementioned relation. Also samples for tension test and small discs for the small punch test are cut out from specimens which were experienced tension-tension axial fatigue loading. It is shown that the increment of fatigue damage subsequently decreases the maximum load and the slope of deflection curve in the elastic regime. Finally the relation between the extent of fatigue cycles and the degradation of Young’s modulus and Yield strength due to cyclic loading is investigated. Utilizing this finding, small punch is proposed to assess the degradation of elastic mechanical properties of in-service components by considering the linear relationship between tension test and small punch test of virgin 304 SS and subsequently the relation of Small Punch test of virgin and damaged 304 SS.