The purpose of this paper is to present some design data obtained from experiments on the statical and fatigue strengths of plug welding of thin steel sheets, extensively.used in the manufacture of roll ing stock at present. This investigation consisted of three different groups of experiments.
Group 1 experiments. In this group of experiments, the plug weld test specimens were prepared by three welding operators, two of whom were qualified as 1st class operators and the other a 2nd class operator. Two kinds of medium coated electrodes and one kind of thin coated electrode were used.
Group 2 experiments. 28 weding operators, consisting of 1st and 2nd class operators, welded the test specimens under working conditions using medium coated electrodes which gave satisfactory results in Group 1 experiments.
Group 3 experiments. The fatigue strength of plug welds under repeated loading wag compared with that for riveted joints of comparable statical strength.
In these experiments two types of test specimens were prepared and tested. Type A specimens consisted of a 2.3 mm base steel on which a 3.2 mm steel sheet with two plugs was welded on. Type B specimens consisted of a 6mm thick base steel on which a 2.3mm thick steel sheet with two plugs was welded on. The diameter of the plug was 10mm and all welding was done in the vertical position.
The results obtained are as follows :
(1) In both Group 1 and Group 2 experiments, the strength of plug welds of 3.2mm sheet welded on 2.3mm sheet was weaker than that of 2.3 mm sheet welded on 6mm sheet. The strength of type A specimens was about 80% of type B specimens.
(2) The average strength of one plug weld was 1938 kg for type A and 2398 kg for type B specimens.
(3) Comparing the results of Group 1 and Group 2 tests, the strength of plug welds by the same operator gave different values depending on the care of welding. The strength of plug welds under working conditions was about 20% less than when welding was carefully done.
(4) The following results were obtained from the fatigue tests:
(a) For the riveted joints, the fatigue strength is about 54% of the statical strength.
(b) For the plug weld joints, the fatigue strength is about 35% of the statical strength.
(c) The strength of plug welded joints is about 2/3 of riveted joints under repeated loading, both types of joints having the same strength under statical load.
The results for Group 3 experiments are those obtained from a small number of test specimens and further investigation is desirable.
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