216 THE APPLICATION OF ELECTRIC WELDING 



The general arrangement of the apparatus is shown in Fig. 2, Plate 148, and a 

 typical example of the results obtained is given in Fig. 6, Plate 149, which shows 

 clearly the stresses at which the welded and unwelded bars will withstand a very 

 large number of repetitions of stress. 



In the second series of alternating stress experiments flat plates were used 

 of three thicknesses, viz., ^ inch, ^ inch and J/^ inch. These specimens were tried 

 in groups of four, each group consisting of one plain, one butt welded, one lap welded 

 and one lap riveted plate. The specimens, which were about 14 inches long by 5 

 inches broad, were clamped along the short edges, so that the distance between the 

 fixed lines was 12 inches. Each plate was also clamped, near the middle, to the end 

 of a pillar, which by means of a crank arm was caused to oscillate and to bend the 

 specimen equally up and down by adjustable amounts (the maximum total move- 

 ment in any of the experiments tried was 5/16 inch). The machine was run at vari- 

 ous revolutions (not exceeding 90 per minute), and the number of repetitions at 

 which the specimen parted was observed. 



The type of apparatus used in these tests is illustrated in Fig. i, Plate 150, and 

 typical results obtained are illustrated in Figs, ya and yh, Plate 149, in which the 

 ordinates represent total displacement from normal position, i. e., 2/16 inch means 

 1/16 inch up and 1/16 inch down. 



Minor tests of various kinds were undertaken, of which the principal ones had 

 reference to the suitability of the welded material to withstand such bending and 

 shock stresses as might occur in the shipbuilding yards. The experim.ents on bend- 

 ing consisted of doubling the welded plate over a circular bar of diameter equal to 

 three times the plate thickness and comparing the results with those of the plate of 

 the same material, but unwelded. 



Figure 8, Plate 149, shows the results obtained from the bending tests, from 

 which it will be noticed that the angle at which fracture occurred decreases rapidly 

 with increased thickness of plate. 



In the impact tests heavy weights were dropped from various heights on to 

 the welded portion of a plate 5 feet long and 2 feet 6 inches in breadth, the weld be- 

 ing across the plate parallel to the shorter edge. The deflections were noted and the 

 condition of the weld was examined after each blow. 



Other tests to determine the relative value of welding and caulking under ten- 

 sion and the relative bearing value of a riveted or welded lug attachment are shown 

 in Plates 151 and 152. In the former, two plates are attached at right angles by an 

 angle lug with closely spaced rivets and the angle caulked on both edges, similar to 

 the boundary angles of a watertight or oiltight bulkhead. The object of the test was 

 primarily to ascertain at what stress the "tightness" of the attachment was destroyed 

 as compared with that of the welded attachment. The results indicated are very 

 striking. 



The test shown in Plate 152, in which a direct shearing force was applied to the 

 lug attachment, indicates the relative values as between riveting and welding a lug 

 attachment for such work as bracket connections. 



