New Algorithm to Determine the Yield Stress from FIMEC Test

Abstract

The indentation test is one of the most common techniques for the mechanical characterization of materials. Different tests have been standardized, depending on punch geometry and indentation parameters, and different models have also been set up to predict indentation hardness and to estimate uni-axial mechanical properties for all the geometries (cone, wedge, pyramid, sphere, etc.). A flat-ended cylindrical indentation technique (FIMEC) has been developed by one of the present authors. FIMEC employs a cylindrical punch with diameter ranging from 3.0 to 0.5 mm and gives pressure-penetration curves from which yield stress and elasticity modulus can be determined. The specific characteristics of FIMEC are: 1-the high simplicity of the apparatus; 2-the possibility to get information about the local material properties on a scale large enough to include many grains (data represent bulk characteristics and are not influenced by those factors which dramatically affect micro-and nanoindentation tests); 3-the large versatility in industrial applications such as the control of welding quality, 4-the on-line monitoring of forging or extrusion processes etc.. This paper describes a new algorithm developed to calculate the yield stress from FIMEC curves. To assess the reliability of the method, it has been tested on several metals of known characteristics and the scattering of data with respect those from tensile tests resulted to be within ±7%.