In this study, in order to investigate the fatigue characteristics of the spot welded joints using the high strength steel, fatigue tests were conducted and internal fatigue crack behavior around the spot area was observed in detail. Test results showed that spot welded joints had the low fatigue strength compared with the tensile strength of base metal and spot welded joints. Moreover, it was clarified spot welded joints used in this study require many cyclic loading to initiate the fatigue crack. Furthermore their fatigue crack propagation indicates the similar behavior in major part of life independently of the stress level.

3-Dimensional Observation of Fatigue Crack Propagation on Spot Welded Joints using High Strength Steel

In this paper, fatigue tests were carried out under the repeated two-step and random loading condition using the spot welded joints which had the base metal categorized into 590MPa class in order to consider the effect of their loading condition on fatigue characteristics of the joints. As the results of fatigue tests under the repeated two-step loading condition, it was found that the fatigue limit of the spot welded joints was vanished. Therefore, we found that it was necessary to consider the effect of the damage caused by the loading below the fatigue limit on the fatigue damage of the spot welded joints. When the random loading fatigue tests were carried out, it was confirmed that evaluation of the cumulative damage value considered with the mean loading effect had validity though the result of them considered without it indicated the un-conservative estimation. Thus, it was necessary to estimate the mean loading effect on the cumulative damage value of the spot welded joints under the random loading condition. Moreover, for considering the local mean stress involved with the deformation of the spot welded joints, it will be achieved to make the precise cumulative damage value evaluation.

Establishment of the Fatigue Cumulative Damage Evaluation Based on the Applied Load for the Spot Welded Joints Using 590 MPa-Class Automobile Steel

Tensile–shear test blanks were fabricated using high strength and low carbon steel sheets with three diﬀerent strength levels by a resistance spot welding (RSW) procedure. The nugget sizes were cha...

https://www.jstage.jst.go.jp/article/qjjws/37/4/37_152/_pdf

Effects of material strength levels and nugget sizes on fatigue behaviour of resistance spot welded steel sheets

https://www.jstage.jst.go.jp/article/kikaia1979/76/770/76_KJ00006666060/_pdf

3-Dimensional Observation of Fatigue Crack Propagation on Spot Welded Joints Using High Strength Steel

The relation between the total fatigue life and the fatigue crack initiation life of a single spot weld tensile shear specimen was determined. Based on the results, the reason why the initial stress intensity factor could control the toota fatigue life was discussed. During the investigation, the methods of determination of fatigue crack initiation at the spot weld were developed, and related phenomena were elocidated.

Relation between the total fatigue life and the fatigue crack initation life of a spot weld.

The behavior of fatigue crack growth in the single spot weld tension shear specimens was studied by experimental and analytical fracture mechanics. Variation of the shape and size of fatigue fracture surfaces was observed and measured by beach mark techniques, and crack growth rate was determined. The crack growth rate in the plate thickness direction was related with the stress intensity factors which were detemined by the analyses of a plate with a semi-elliptic surface crack by the influence function method and the super-position method.

Masatoshi Shinozaki

Papers

Relation between the total fatigue life and the fatigue crack initation life of a spot weld.

A fracture mechanics study on the fatigue crack growth at the spot weld joint.