Determination of mechanical properties in the heat-affected zone of a dissimilar metal weld

Welded joints generally consist of two base materials joined by filler material which has melted and resolidified. The interface region between base and filler, where the base material has not melted, but has experienced a change in microstructure, is called the heat affected zone (HAZ). Welding dissimilar metals creates chemical and temperature gradients in the HAZ. Subsequent post weld heat treatment enhances chemical diffusion. In the case of chromiun-molybdenum steels, a carbon denuded, "soft" zone is created at the base/filler interface. The zone is distinct, but measures less than 1 mm transverse to the weld. The soft zone cannot be accurately reproduced in a larger specimen and therefore, must be tested in the weld. Tested in the weld, the soft zone is in a three dimensional stress state caused by specimen non-homogeneity.; This study develops an iterative method to extract the uniaxial stress-strain curve of a microstructurally distinct zone tested in a three dimensional stress state. Boundary conditions are known and resultant displacement fields are obtained using moire interferometry (an optical technique producing high resolution, full field displacement data, which can be converted to strain). The constitutive relation (uniaxial stress-strain curve) is unknown. It is obtained from an iterative scheme which postulates the constitutive relation, uses this relation in a finite element model and compares the computed strain fields to those derived from the moire displacement fields. Iterations are performed until computational and experimental strain fields match.; The resultant uniaxial stress-strain curve is verified by using it to model a different soft zone specimen, testing the specimen with moire interferometry and comparing computational strain fields with experimental strain fields. The uniaxial stress-strain curve is verified everywhere except a small portion of the curve just above yield stress. Based on the success of the soft zone analysis, the iterative method is recommended to determine the uniaxial stress-strain curve of small, highly constrained zones surrounded by materials of known mechanical properties. It is particularly useful for dissimilar metal weld specimens because HAZ microstructures must be tested in the weld.