Mechanical characterization of resin materials using small punch test

Abstract

The small punch test (SPT) is a miniature test that utilizes small-diameter disk specimens, typically around 10mm in diameter. This study investigated the conversion equations proposed for determining the tensile properties of metallic materials using the SPT for their applicability to resin materials. The test specimens included thermoplastic resins such as polyamide 6 (PA6), polyethylene terephthalate (PET), polycarbonate (PC), polytetrafluoroethylene (PTFE), and thermosetting resins such as epoxy (EP) and phenol (PF). The maximum loads obtained from the SPT were found to be in the order of PC, PET, PA6, PF, EP, and PTFE, which significantly differs from the order of tensile strength. The 0.2% proof stress conversion from the SPT was determined by using the intersection point of the SP curve and a parallel line offset from the initial thickness, and the load was obtained by displacing the initial slope of the SP curve by a factor of t/10. In the SPT results for EP, the displacement velocity dependence was confirmed, as was observed in the tensile test. However, the increase in strength in response to the displacement velocity was higher for the conversion value obtained from the SPT than that from the uniaxial tensile test. This difference is presumed to be due to the uniaxial stress in the tensile test, whereas the SPT is multiaxial stress, and the sensitivity to displacement velocity differs.