13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Modeling of deformation and failure behavior of dissimilar resistance spot welded joints under shear, axial and combined loading conditions Sebastian Burget1,*, Silke Sommer1 1 Crash-Safety, Damage Mechanics, Fraunhofer-Institute for Mechanics of Materials IWM, 79108 Freiburg, Germany * Corresponding author: Sebastian.Burget@iwm.fraunhofer.de Abstract This paper presents the modeling of deformation and failure behavior of dissimilar resistance spot welded joints (RSW) between hot-stamped ultra-high strength (22MnB5) and microalloyed (HC340LAD) steels. To determine the deformation and failure behavior of the different material zones of the weld, tensile and shear specimens, which were cut from the base metals, the weld nugget and heat treated sheets were tested and modeled using the Gologanu-Leblond model coupled with the fracture criteria of Thomason and Embury. The joints were modeled using detailed 3-dimensional finite element models taking into account the different weld zones, i.e. base metal (BM), heat affected zones (HAZ) and weld metal (WM), their dimensions and their mechanical properties. Simulations of the spot welded joints’ behavior under shear, axial and combined axial and shear loading were carried out and compared to experimental results such as force vs. displacement curves, load bearing capacities, fracture mode and fracture locations. Maximum loads and force vs. displacement curves from experiments and simulations showed good agreements for all loading situations examined. Despite of its superior strength compared to the microalloyed steel, pull-out fracture of the joints took place in the coarse grain HAZ of the hot-stamped ultra-high strength steel in experiments and simulations. Keywords Resistance spot welding, Mechanical properties, Combined loading, Failure criterion, Ultra-high strength steel 1. Introduction With several thousands of spot welds in a body-in-white, spot welding still represents the most widely used thermal joining process in steel-based automotive production. With the development of hot-stamped ultra-high strength steels, new light-weight potentials have been created, that combine thin steel sheets and thereby reduce weight, with a simultaneous optimization of passive safety requirements. To implement these potentials joining technologies have been adapted to ensure a combination of optimized material and joint strength. At present hot-stamped manganese-boron steels (22MnB5) are widely used, especially for load-bearing structural components in parts of the passenger cabin, where deformation and intrusion should be kept at a minimum. To increase the reliability and accuracy of crash-simulations failure of the joints has to be taken into account using simplified models like solid or beam elements [1][2][3] in combination with simplified mostly force based failure criteria depending on the occurring axial and shear loads acting on the joints. To identify the model parameters of such criteria, failure of the joints can be characterized experimentally under different loading situations, as e.g. shown in [4][5]. For different welding parameters, which lead to a change in the joints’ geometry in terms of different diameters of the weld nugget and the heat-affected zone [6], the procedure has to be repeated to determine the load bearing capacities of each particular joint. In this work the deformation, fracture and load bearing capacity of dissimilar spot welds between hot-stamped and microalloyed steels is investigated in detailed finite-element simulations in several loading situations such as pure shear and pure axial loading as well as combined axial and shear loading. Material data for the modeling of the different material zones of the weld were obtained in tensile, notched tensile and double notched shear tests. The material models calibrated based on these tests are used for the simulation of experiments on spot-welded tensile-shear, KS2- and coach-peel specimens.
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