Material Testing in Support of the Development and Calibration of Material Models for Forming Simulations

Abstract

Material testing at various strain rates, temperatures and loading conditions provides data that is used for the development and calibration of constitutive equations (material models) that are utilized in numerical simulations of sheet metal forming. In general, the testing can be divided into characterization tests and validation tests. In characterization tests basic material properties (e.g. yield stress, ultimate stress, failure strain) are determined from a test in which a material coupon is loaded under a well-defined condition (stress, strain rate, temperature, etc.). The data is used for determining the values of parameters in plasticity and failure models. In validation tests a material specimen or a small component is loaded with a more complicated, but well defined, loadings. The test is numerically simulated and the calculated quantities (forces, deformation, failure, temperature, etc.) are compared with measurements. The recent development of the Digital Image Correlation (DIC) technique for full-field measurement of deformation has extended the useful data that can be extracted from traditional characterization tests and provide means for developing new experiments that can be used for obtaining more accurate material models. This paper reviews the advantages of using DIC in traditional tests and presents several new recently developed testing configurations for material coupons and small components. Many of these tests have been used during in the development of a failure surface that gives the equivalent plastic strain to failure as a function of stress triaxiality and the Lode parameter.