Comparison study of small punch test, hydraulic bulge test and uniaxial tensile test for typical pressure vessel CrMo steel

Small specimen testing methods offer valuable insights into the mechanical properties of materials when specimen size is limited. Various small specimen methods have been applied, but their differences and correlations are poorly understood. This study compares small punch test (SPT), hydraulic bulge test (HBT), and uniaxial tensile test (UTT) for the typical pressure vessel CrMo steel, focusing on strain distribution, stress state, and fracture mechanism. The SPT shows an “M” shape strain distribution, with the strain concentrating on the contacting area between ball and specimen, leading to the ductile fracture at the near biaxial tension stress state. The HBT presents the inverted “V” shape strain distribution, with fracture occurring in the central region of specimen at the biaxial tension stress state. Based on membrane theory, the theoretical derived correlation models of SPT and UTT, as well as HBT and UTT, were developed for the tensile strength, providing effective approaches to predict tensile mechanical properties by SPT and HBT. The novelty of this paper is revealing the differences and correlations among SPT, HBT and UTT, and demonstrating the efficiencies of SPT and HBT as alternative testing methods to UTT for mechanical properties in the conditions of very limited materials.