The significance of specimen displacement definition on the mechanical properties derived from Small Punch Test

Abstract

The different displacements definitions used for describing the Small Punch Tests (SPT) material response were thoroughly reviewed. For that purpose, an instrumented experimental setup allowing determining the specimens top or bottom displacement together with the machine cross head displacement was designed. The effects of the machine and load train compliances on the respective displacements values were carefully evaluated. The significance of the different displacements definitions was demonstrated by proposing two alternative procedures for assessing the specimen thickness evolution and by revising the definition of the load associated with the determination of the material yield stress from SPT. To facilitate the systematic study of the influence of the different parameters that might be affecting the test, a finite element (FEM) analysis tool was developed. The results obtained from FEM simulations show that even using a constitutive model that does not include damage initiation it is possible to adequately reproduce the SPT load vs. displacement response curve to near maximum load and also the diametral profiles of the deformed specimens. The FEM analysis indicate the arbitrary character of the different proposals for determination of the load for yield stress estimation with them corresponding to different degrees of plastic deformation of the specimen.