Strain decoupling for the real time strains measured during welding process

Abstract

Stress during welding is of high interest while complex due to the high gradient transient thermal effect. All published literatures studied it by finite element simulations. For the first time, the authors tried to derive the stress history based on measured temperature and in-plane strains. However, the measured strains were the total strains consisted of coupled thermal, elastic and plastic strains. To determine the stress based on the constitutive equations, measured total strains should be decoupled. Three in-plane strain (strain X, strain Y and shear strain XY) histories which were general strain history during welding process were utilized for illustrating the strain decoupling process. Thermal strain was first determined by the measured temperature history. To separate the elastic strain and plastic strain, the sum of mechanical strain determined by subtracting thermal strain from total strain was divided into three stages: compression, recovery and tension. Yielding was detected at both the compression and tension regions using von Mises' yielding criteria. Similar to cyclic tension/compression testing, same amount of elastic strain will be recovered before the tension region starts. All material properties used were temperature dependent, and a plane stress condition was assumed since welding was applied on thin steel plates. © The Society for Experimental Mechanics, Inc. 2014.