Recent Developments in Material Testing for Characterization of Materials (Deformation and Failure) for LS-DYNA Materials Models

摘要

Several new testing methods that have been recently developed for mechanical characterization (deformation and failure) of materials are presented. The data from these tests is used for the development and calibration of material models (constitutive relations) in LS-DYNA. The first method involves the use of Digital Image Correlation (DIC) in tests that are used for generating data needed for the MAT224 model. In these tests specimens with different geometries are loaded and DIC measurements are used for determining the equivalent failure strain as a function of stress triaxiality and Lode parameter. The second testing method is a shear test for sheet metals. The experiment is done by using a flat notched specimen in a tensile apparatus. The shear strain is measured by using DIC within and on the boundary of the notch. The third development is a dynamic punch test in which the deformation of the specimen is measured continuously with 3-D DIC. The fourth is a high strain rate tensile testing technique for Kevlar cloth and Kevlar yarn in a tensile Split Hopkinson Bar (SHB) apparatus. The Kevlar cloth/yarn is attached by specially designed adaptors that keep the impedance constant. In addition to the traditional method of determining the specimen's strain from the recorded waves in the bars the strain is also measured with DIC. The fifth development is an apparatus for testing at intermediate strain rates in compression. In this apparatus the specimen can be deformed at strain rates ranging from 20 s-1 to 200 s-1. The apparatus is a combination of hydraulic actuator and a long (40 m) transmitter bar. The stress in the specimen is determined from the stress wave and the strain and strain rate is determined by using DIC. The results show very clean (no ringing) stress strain curves.