Influence of the Friction Coefficient Value on the Disk Microspecimens Punching Diagram Taking into Account the Fracture Process

Abstract

Determining changes in mechanical characteristics, such as yield strength and tensile strength, of structural materials during their service life under the influence of operating loads and the working environment is a very important task of ensuring reliable and safe operation of working equipment. The use of uniaxial tensile tests for this purpose is not always possible because of the limited availability of material for the manufacture of specimens and the inevitable disruption of structural integrity. Therefore, indirect control methods are being developed, one of which is the small punch test method. The essence of this method consists in punching of a fixed specimen by a spherical indenter with recording the load-displacement curve. Mechanical characteristics are determined by the parameters of this diagram using correlation dependencies. In improving the methods for determining the mechanical characteristics of small punch test, there is a need to use numerical modeling, one of the parameters of which is the friction coefficient in contact pairs. The purpose of this work was to investigate the influence of the friction coefficient on the punching diagram in the numerical simulation of the disk microspecimen deformation process, taking into account the fracture process. The Gurson–Tvergaard–Needleman (GTN) model was used to account for the fracture process. According to the study results, it was found that when the coefficient of friction changes from 0 to 0,36, the punching diagrams at the stages of elastic and elastic-plastic deformation of the specimen do not differ significantly. When the maximum load value is reached, there is a discrepancy in the punching diagrams. It was found that an increase in the friction coefficient leads to a decrease in the maximum load and the punching depth upon failure. The difference between the maximum load values is 27 %, the penetration depth is 14 %. It was determined that the closest to the experimental load-displacement curve was the curve determined by numerical simulation with a friction coefficient equal to 0, 18.