Test Of Material J_R Curve By Continuous Ball Indentation Technology

The continuous ball indentation method can estimate strength and fracture toughness of material in service. In this paper, fracture toughness tests and the continuous ball indentation tests were carried out on seven kinds of materials. The deformation of the specimens after the indentation test have been observed. The damage of the specimens after the indentation test have been observed. At the same time, the fracture toughness of materials have been gotten after processing the indentation test data by using the critical indentation energy(CIE) model which is based on associating the indentation test work with the needed energy for the material to crack. The fracture toughness got from indentation test have been compared with fracture toughness got from conventional test, the empirical correlation has been applied between the effective elastic modulus Ed got from indentation test and unloading compliance C got from single-sample unload compliance method. The main achievements are as follows:(1) The fracture toughness of materials have been gotten using the CIE model. By comparing fracture toughness got from different ball indentation test plan and fracture got from toughness routine test, we found that the error is relatively small when the indenter diameter is 1.5875 mm,2.5 mm and 3.175 mm respectively with the 0.2 mm depth.(2) The stress and deformation of the sample in the process of ball indentation test have been studied. The deformation of the specimens after the indentation test have been observed on the 3d scanning instrument, and statistical elastic have been done to know the recovery of the test specimen. we found that the elastic recovery percentage is smaller with bigger indenter diameter and depth. At the same time, we found that the accumulation degree of sample was not very obvious, all stack heights were below 20 microns. The sample have been cut open after the ball indentation test,and we observed successive holes and "wings" holes with SEM.(3)The similarity of ball indentation method and single-sample unload compliance method were analyzed, the empirical correlation has been applied between the effective elastic modulus Ed got from indentation test and unloading compliance C got from single-sample unload compliance method. Then, the JR curve of materials have been gotten using the indentation test data.