The previous report has shown the relationship between the arrangement of spot welds as one of design factors and the strength of multiple spot-welded joints under the static load.
Succesively, for the same purpose, the repeated tensile-shear load test was carried out for multiple spot-welded Alclad heat-treatable Al alloy joints with various arrangements.
As the result of this study, the relationships between the fatigue strength and the spacing, number and arrangement of spot-welded joints have been obtained. Basing upon these results, moreover, a method of determining the strength of multiple spot-welded joints by the simple joints have been found. That is, the stress concentration factor for the fatingue strength of multiple joints K_mn is give as follows.
K_mn=rK_1n+(1-r)K_1n'
K_1n and K_1n' are stress concentration factors obtained through the fatigue test on simple joints. r is the load-share ratio among the rows of multiple joints.

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The susceptibility to stress corrosion cracking in hydrogen sulfide-water system was studies on two commercial 80 kg/mm² high strength steel plates and some weld metals. Here weld metals were prepared by submerged arc welding method using experimental bonded fluxes and commercial wires for low alloy steels. The susceptibility to cracking was tested by failure time on specimens loaded in tension and exposed to 0.5% acetic acid solution to which hydrogen sulfide was added. Furthermore a experiment on hydrogen embrittlement was conducted on commercial 80 kg/mm² high strength steel plates. Hydrogen sulfide-water system was used in this experiment too.
The test results were as follows :
(1) Poor resistance of test materials to cracking is accompanied by relatively high nickel content (0-2% Ni in test meterials).
(2) Lower susceptibility of annealed (600°C) weld metals was attained by increasing Molybdenium and Chromium content up to about 2%. (Test materials contain about up to 5% Cr and 2% MO)
(3) The test steel plate which was relatively susceptible to cracking was seemed to be more sensitive to hydrogen embrittlement than the less susceptible one.

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