The Use of a Small Punch Test Procedure to Determine Mechanical Properties

A small ball-punch-on-rectangular-specimen design was developed to test materials such that cracking occurs along a desired orientation. Energy to fracture is determined from the punch load and displacement, which are measured continuously during the test. A three dimensional ¼ finite element model was formulated to simulate the punch test. The calculated load-displacement and stress-strain curves compared reasonably well with the experimental results. The plastic strain distribution was consistent with the observed location of fracture, and the reduction in thickness was also in agreement with measurements taken from deformed test specimens. Room temperature and 250 °C tests were performed on a SA106 grade B steel for two orientations, C-L and L-C. Empirically, the punch test's energy to break results showed a correlation with fullsize JIc results. The test method can also be used to determine the Ductile-to-Brittle-Transition-Temperature (DBTT) behavior of steel. An ASTM A533, grade B material was tested to -180 °C and the typical DBTT behavior, relative to Charpy test results, was observed. Although the technique described in this paper shows some correlations with JIc and the DBTT, the scatter is larger than results for full-size specimens.