Dynamic Separation of Resistance Spot Welded Joints: Part II—Analysis of Test Results and a Model

Abstract

The ultimate strength of resistance spot welded joints fabricated from a wide range of steel grades, weld button size, and sheet thickness are reported for lap-shear and cross-tension specimens subjected to quasi-static and impact loading conditions. Test data are analyzed with respect to energy, impact speed, and loading rate. Loading rate is identified as a critical, test system independent parameter to reflect the strain rate sensitivity of the steels. An equation is fitted to the ultimate strength test data as a function of loading rate which is proposed to predict the separation of spot welded joint under dynamic loading. The model is validated by test data from open literature generated from other type of specimens and/or dynamic test conditions.

Dynamic Separation of Resistance Spot Welded Joints: Part I—Experiments

“…The first term in equations (3)(4)(5) is the gravitational force of the drop weight imposed upon the system (corresponding to V=0). It is shown later that the effect of the first term is negligible relative to the second term in typical tests using a drop weight system.…”

“…It is shown later that the effect of the first term is negligible relative to the second term in typical tests using a drop weight system. In a horizontal impact system using high speed projectile as the striker, equations (3)(4)(5) are also valid after deleting the first term (or setting g=0).…”

“…In reference [2], fracture mechanisms were revealed and an engineering failure criterion was developed for lap-shear and crosstension test specimens under quasi-static, uniaxial or mixed mode loading conditions. In these current papers, Part I and Part II [3], we report results on the impact or dynamic separation of spot welded specimens.…”

“…The challenges are twofold, namely, (a) how to perform appropriate tests, and (b) what dynamic parameter(s) can be selected from the test data such that the strain rate sensitivity can be reflected and transferred to numerical crash simulation of vehicle structure for safety design. Part I addresses challenge (a) and Part II [3] will address (b).…”

“…Spot weld test data is presented as examples. Interpretation of the test data, identification of an appropriate dynamic parameter, development of a test-facility independent dynamic fracture model and verification are reported in Part II [3] of the investigation.…”