Experimental investigation on fracture properties of material by small punch test at room and cryogenic temperature

In this study, small punch tests are conducted to investigate the fracture behavior of 304 stainless steel using unnotched and pre-notched specimens at room temperature and deep cryogenic temperature in liquid nitrogen. The mechanical properties of the material are discussed through the force-displacement relationship. The fracture surface of the specimen after the test is observed using a scanning electron microscope to examine the fracture characteristics of the steel. The obtained results show a negative rate-sensitivity in both maximum force and displacement at maximum force at room temperature. This behavior is attributed to a mixed fracture mechanism involving both ductile and brittle failure. Meanwhile, at deep cryogenic temperature, the mechanical properties and fracture behavior of the investigated material can be improved considerably, especially at higher strain rates, with significant increases in both strength and ductility. Notably, a positive rate-sensitivity in displacement at the maximum force can be obtained from the test conducted at deep cryogenic temperature. This enhancement is likely due to the facilitated formation of martensite during the small punch test at low temperature.