Study on precise weld diameter validations by comparing destructive testing methods in resistance spot welding

The torsion test is rarely used for resistance spot-welded joints since they are not subjected to torsion in applications. Normal, shear, and/or peel loads are usually the main stresses. Extensive scientific investigations in the context of Kunsmann’s dissertation date back more than 50 years. These investigations are still the basis of ISO 17653 and the German guideline DVS 2916-1. Recent scientific investigations only use torsion tests, but do not describe the reason for its use. A decisive advantage of the torsion test over the other standardized destructive testing methods lies in the types of fracture modes that occur and the properties of the fracture surfaces. Torsional loading results in either interfacial or button-pulled fracture modes. No material residues occur on the fracture surfaces for ductile and advanced high-strength steels. Hence, the measurement of weld diameter is achievable with minimal constraints, resulting in reduced variability and facilitating objective assessments of spot welds. This article delineates these attributes through a comparative analysis of various destructive testing methods employing statistical approaches. Additionally, the article expounds on the design concept of the developed rig for conducting torsion tests on spot welds.