Investigation of Fatigue Strength Behaviour in Dual Weld S420 Steel Joints Fabricated at a Close Proximity

There is insufficient information available in existing welding standards, codes and specifications regarding the implications of having two or several adjacently fabricated weld joints in close proximity. This has introduced fatigue life performance uncertainties, due to a lack of understanding of the inherent behaviour of weld joints in the presence of adjacent welds. Hence, it is vital to investigate the fatigue life performance and obtain quantitative data for future assessments. This experiment has been designed using six welded, and one unwelded, S420G2+M 500 × 300 × 15 mm structural steel plate. Two of these plates were used for fatigue testing, having 44 mm and 12 mm between the adjacent weld toes. These distances were less than normally recommended in standards codes and specifications. The preparation of the samples was conducted in accordance with ASTM E466-15 for homogenous materials subjected to high-cycle fatigue. The experiment was not able to detect any detrimental effect by having welds in close proximity using this specific preparation method and weld setup. The weld metal and corresponding heat-affected zones had a higher fatigue strength than that of the surrounding base material. All tested specimens failed in the base metal. The material and welding method did not seem to introduce any degrading effect on the weld joint. Important to note is that the fabrication method required a surface roughness of 0.2 µm and had likely introduced an outer layer of compressive residual stresses at yield point level 50 µm into the surface and bottom surfaces of the specimens. This might have improved the resistance to crack formation in the surface. The residual stress was obtained by using ultrasonic stress measurement technique and x-ray diffraction presented in a parallel study by the same authors.