Determination of creep properties of P91 by small punch testing

Abstract

Small punch creep testing was conducted to determine creep properties of P91 at 873 K. The procedure followed the European Code of Practice for Small Punch Tests. Results of small punch creep test and finite element analysis were compared and discussed. Based on the results, a practical method was proposed to determine the parameters of Norton creep law more conveniently for material which obey this law. The validity of the proposed method was verified and it is shown that the parameters of the Norton creep law can be determined from only one experimental curve directly.     

Evaluation of the mechanical properties of SS-316L thin foils by small punch testing and finite element analysis

Thin foils having thickness values of 200 μm and less are commonly applied in the food industries, medical applications and more. Small punch technique (SPT) is a promising mechanical testing method for specimens thicker than 250 μm, in which a formulation correlating the measured parameters to standard tensile properties was previously reported. The current research is focused, for the first time, on the correlation between SPT and tensile mechanical properties of SS-316L thinner specimens in the range of 100–200 μm. It is demonstrated by finite-element-analysis, that the mechanical response of thin foils having thicknesses in the range of 25–500 μm can be divided into three categories. For specimens thicker than 300 μm, thin plate bending equations that were applied previously for thick specimens, are still valid, while for thinner specimens this theory fails to provide adequate correlation between SPT and tensile yield stress. For specimens thinner than 50 μm it was identified that equations derived from membrane solution should be employed rather than classical plate theory. For intermediate thickness values in the 50–300 μm range, a “transition-zone” was identified between plate and membrane-like mechanical responses. For the lower region, 50–100 μm, an analytical expression correlating the measured SPT parameters and the tensile yield stress is currently proposed.     

Investigation the effect of crystal orientation of nickel‐based single crystal superalloys on bending creep tests

The relationship between the three points bending creep test and the uni‐axial creep test on the single crystal superalloy was investigated by using crystal plasticity slip theory with a three‐dimensional (3D) finite element model. The purpose of the present work is to build the relationship between bending creep and conventional uni‐axial tensile creep in determining crystallographic creep parameters for face centered cubic (FCC) nickel‐based single crystal superalloys. To this aim, the bending creep performed on [001]‐, [011]‐, and [111]‐oriented nickel‐based single crystal superalloys were respectively investigated, and the data was compared with those obtained with uni‐axial tensile creep counterparts. It shows that the determination of crystallographic creep stress exponent is independent of crystallographic orientations, and the results agree reasonably well between bending creep test and uni‐axial tensile creep test. The findings may shed some light on understanding of the crystal structures and its time‐dependent deformation mechanisms with the bending creep method.