Jiwoong Ha

DYNAMIC FAILURE OF A SPOT WELD IN LAP-SHEAR TESTS UNDER COMBINED LOADING CONDITIONS

This paper is concerned with the evaluation of the dynamic failure load in the lap-shear tests of a spot weld. Dynamic lap-shear tests of a spot weld in SPRC340R were conducted with different tensile speeds ranging from 5×10-5 m/sec to 5.0 m/sec. Dynamic effects on the failure load of a spot weld are examined based on the experimental data. Experimental results indicate that failure strength increases with increasing loading rates. Finite element analyses of dynamic lap-shear tests were also performed considering the failure of a spot weld. A spot weld is modeled with a beam element and dynamic failure model is utilized in order to describe the failure of a spot weld in the simulation. The failure loads obtained from the analyses are compared to those from the lap-shear tests. The comparison shows that the failure loads obtained from the analyses are close in consistence with those obtained from the experiments.

Failure Characteristics of Spot Welds of AHSS under Quasi-static Conditions

This paper is concerned with the failure characteristics and the failure load of spot welds of AHSS under combined axial and shear loading conditions. A testing fixture and a specimen are newly designed to impose the pure-shear load acting on a spot weld. The testing fixture and the specimen proposed by Song et al. [1] are used to impose the combined axial and shear load at the loading angle from 0° to 75° on a spot weld. Using those testing fixtures and specimens, failure tests of the spot weld of TRIP590 1.2t, DP780 1.0t, and DP980 1.2t are conducted with seven different conditions of combined loading. Based on the experimental results, failure loads and failure behaviors of a spot weld of AHSS are investigated with respect to the different loading angles. Failure loads of the spot weld obtained from failure tests are interpolated to construct the Song and Huh’s failure model [2], which facilitates the failure description of a spot weld in the macroscopic finite element analysis of autobody crashworthiness.

Compatible finite element modelling of laser welded region for crash analysis of autobody assemblies

Abstract This paper proposes a compatible modelling method for finite element analysis of the laser welding for autobody assemblies in the crash analysis. The fracture modes of a laser weld were investigated for application to finite element modelling. A single laser weld in a stitch shape was modelled by a cluster of beam elements or hexahedron elements. The model was then applied to a cross tension test and a lap shear test under the quasi‐static loading condition both experimentally and numerically. Finite element analyses were carried out with respect to the element type, the number of elements and the panel mesh size. The numerical result was compared with experimental results under the same condition. Analysis results demonstrate that the load acting on the laser welded element is accurately calculated by the change of the element type and the location of welded constrains. The method proposed provides a guideline for accurate finite element modelling of the laser welded region for the crash analysis of vehicles.

Effect of Tensile Speed on the Failure Load of Laser Welding under Combined Loading Conditions

This paper is concerned with the failure characteristics and the failure loads of laser welds in a SPRC340 1.2t steel sheet under combined normal and shear loading conditions. The quasi-static and dynamic failure tests were carried out under nine different combined normal and shear loads including a pure-normal load and a pure-shear load. Especially for the pure-shear condition, a testing fixture was newly designed in order to evaluate the strength of a laser-welded region fabricated by the same welding condition as a two-layered lap joint. The failure load and the failure behavior of laser welds were investigated in each loading condition. Dynamic effects on the failure load of laser welds, which are critical for structural crashworthiness, were also examined based on the experimental data. In order to evaluate the effect of the strain rate on the failure contour of laser welds under the combined normal and shear loads, the failure loads measured from the experiment were decomposed into two components along the normal and shear directions.