218 THE APPLICATION OF ELECTRIC WELDING 



4. Minor Tests: — 



(a) Welded specimens are not capable of being bent (without fracture) over 

 the prescribed radius to more than about 80 degrees with ^-inch plate, reducing to 

 some 20 degrees where the thickness is i inch. Unwelded material under the same 

 conditions can be bent through 180 degrees. 



(b) Welded plates can withstand impact with a considerable degree of suc- 

 cess ; a half-inch plate of dimensions already quoted sustained two successive blows 

 of 4 cwt. dropped through 12 feet, giving a deflection of 12 inches on a length of 

 about 4 feet 6 inches without any signs of fracture in the weld. 



5. Chemical and Microscopic Analysis: — 



(a) Chemical analysis — 



The electrode was practically identical with mild steel, but there was a greater 

 percentage of silicon. 



The material of the weld after deposition was ascertained to be practically pure 

 iron, the various other contents being carbon, 0.03 ; silicon, 0.02, phosphorus, 0.02 ; 

 and manganese, 0.04 per cent respectively. 



(b) Microscopic examination — 



The material of the weld is practically pure iron. 



The local effect of heat does not appear to largely affect the surrounding ma- 

 terial, the structure not being much disturbed at about 1/16 of an inch from the 

 edge of the weld. The amount of disturbance is still less in thin plates. 



The weld bears little evidence, if any, of the occurrence of oxidation. 



With welds made as for these experiments, i. e., with flat horizontal welding, a 

 sound junction is obtained between the plate and the welding material. 



6. Strength of Welds (large specimens) : — 



(a) Butt welds have a tensile strength varying from 90 to 95 per cent of the 

 tensile strength of the unwelded plate. 



(&) Lap ivelds. — With full fillets on both edges the ultimate strength in ten- 

 sion varies from 70 to 80 per cent of that of the unwelded material. 



With a full fillet on one edge and a single run of weld on the other edge the re- 

 sults are very little inferior to those where a full fillet is provided for both edges. 



(c) Riveted lap joints. — For plates of about >4 inch in thickness, the specimens 

 averaged about 65 to 70 per cent of the strength of the unperforated plate. 



Typical examples of the statical strength of large specimens of riveted and 

 welded joints are given in the following table : — 



