Construction of a Failure Model of Spot Welds Using Lap-Shear Tests

This paper proposes an alternative methodology to construct a dynamic failure model of spot welds under combined axial and shear loading conditions for auto-body crash analyses performing cross-tension tests and lap-shear tests which are substitution of pure-shear tests. To construct a failure model of a spot weld proposed by Song and Huh, failure tests of spot welds with an imposed angle to the weldment have to be carried out at an interval of 15° from 0° to 90°. In the general case, it was suggested that the β value of 1.45 from the results of the failure load of cross-tension tests and pure-shear tests can be used for constructing their failure model. However, the scheme is not practical because of difficulties in making pure-shear specimens with the same welding conditions of two-sheet spot weld because the pure-shear specimen is generally prepared with three-sheet spot weld. In order to substitute lap-shear tests for pure-shear tests, correlation of failure loads between the pure-shear test and the lap-shear test is investigated with stress distribution that is approximated around a nugget at the failure point of a spot weld. Actual tests show that the correlation equation of the failure load between the two tests can be expressed as a linearly proportional function. Failure loads and failure behaviors of the spot weld through the finite element analyses with the failure model constructed by the alternative methodology are investigated in order to verify the validation of the methodology proposed in this paper.