Temperature Dependency of Spot Welded Joint Strengths

Abstract

This investigation, as the preliminary stage of investigations for static and fatigue strengths of spot welded joints under especial circumstances: various temperature and/or corrosion circumstances, treats the temperature dependency of spot welded joint strengths.
Specimen materials used are mild steel sheets and high strength steel sheets (45 kg class and 80 kg class) of 0.8 mm thickness. Tests were carried out under temperature circumstances of three kinds of -20°C, room temperature and 100°C.
Main conclusions obtained in this investigation are as follows:
(1) Tensile shearing strengths of spot welded joints decrease with the increase of temperature for all steels and this dependency on temperature is alike as that of tensile strength of mother sheet.
(2) Fatigue strengths for spot welded joint decrease with the increase of temperature for all steels, but the degree of the decrease is a little in comparison with that of mother sheet.
(3) Fatigue strengths of spot welded joints in steels with different tensile strengths are almost the same, under various temperature circumstances in this investigation.
(4) Temperature dependency of fatigue strengths of spot welded joints has a rather strong correlation with one of tensile shearing strength of spot welded joint and in addition also has a correlation with one of tensile strength of mother sheet.
(5) The fatigue cracks at 100°C for mild steel initiate in the position far away from the nugget and propagate in outer direction from the nugget, which is different from usual initiation positions and propagation paths.