Fatigue strength of steel sheet adhesive joints was investigated. From the results of the fatigue tests, it was obtained that the fatigue strength of the tensile-shear adhesive joints was much higher than that of the T-type tension adhesive joints. Stress distributions on adhesive layer have been analyzed by theoretical analysis method. All of the data obtained by the fatigue tests fell almost on one S/N curve, in spite of the differences of joints type and plate thickness, if the equivalent stress(Mises stress) range of the adhesive layer at the periphery of the end of the jointed part obtained by theoretical analysis was taken as the ordinate of S/N curve.
Since the fatigue strength and rigidity of adhesive bonded joints can be higher than the spot welded joints in the weight-saving structures, it is expected that the structural adhesive joints will be employed more in the automobile body structure.[1]-[3] For assuring the introduction of this joint more into the automobile body structures, the durability and reliability of the structural adhesive joints must be established. But, we now have little data on the durability and reliability, especially, fatigue of the adhesive bonded joints of the steel sheets used in the automobile body structure. Though it is required unifyingly to estimate the fatigue strength of the joints to design the adhesive joints, such a method has not been established, because the adhesive joints have an interface in bi-material, steel sheet and adhesive layer, and evaluation of the fatigue strength of the bi-material is more difficult than the homogeneous material.
In the present research to be reported, the fatigue tests on two kinds of typical adhesive joints of steel sheet, tensile-shear(TS) and T-type tension(TT), were carried out to clear the property of fatigue strength. The stress distributions in the adhesive layer of the adhesive joints have been analyzed by the theoretical analysis [4]-[6] and most results of the fatigue tests were able to be well described by the maximum Mises' equivalent stress values obtained by the analysis.