Fracture toughness estimation of ductile materials using a modified energy method of the small punch test

The fracture property estimation of ductile materials with small volumes at room temperature was performed experimentally and analytically in this study. A modified energy method of the small punch test (SPT) was applied to estimate fracture toughness based on the membrane stretch analysis. The effective strain was assumed to be the average value of center strain and contact boundary strain. To overcome the problem involved in strain calculation by microscopic observation, one relatively simple correlation which related effective fracture strain to displacement was proposed. The results obtained by the modified energy model and conventional experiment were in good agreement. Furthermore, a three-dimensional finite element model was established successfully. The influence of ball diameter and center hole diameter in the lower die on the SPT was analyzed by detailed discussion. Finally, the applicability and accuracy of the modified energy model based on the SPT were proved. An economic, effective energy method can be obtained from the present study to assess the properties of in-service components and micrometer scale materials.