TO SHIP CONSTRUCTION. 217 



It will be observed that the welded lug is notched out at its mid-length and the 

 welding applied only at the ends and in way of the notch. 



Many other practical tests of this nature were made, but the foregoing are 

 perhaps of greatest interest. 



The chemical and micrographical examination followed the ordinary practice. 



SUMMARY OF EXPERIMENTAL RESULTS. 



1. Modulus of Elasticity and Approximate Elastic Limit: — 



(a) In a welded plate the extensions in the region of the weld are sensibly the 

 same as for more distant portions of the unwelded plate. 



(b) With small welded specimens containing an appreciable proportion of 

 welded material in the cross-sectional area, the relation between extension and 

 stress is practically the same, up to the elastic limit, as for similar unwelded material. 



(c) The elastic limit (or the limiting stress beyond which extension is not ap- 

 proximately directly proportional to stress) appears to be slightly higher in welded 

 than in unwelded material. 



(d) The modulus of elasticity of a small test piece, entirely composed of ma- 

 terial of the weld, was about 11,700 tons per square inch as compared with about 

 13,500 tons for mild steel and about 12,500 tons for wrought iron. 



2. Ultimate Strength and Ultimate Elongation: — 



(a) The ultimate strength of welded material with small specimens was over 

 100 per cent of the strength of the unwelded steel plate for thicknesses of y^ inch, 

 and averaged 90 per cent for plates of }i and i inch in thickness. 



(b) Up to the point of fracture the extensions of the welded specimens are not 

 sensibly different from those of similar unwelded material. 



(c) At stresses greater than the elastic limit, the welded material is less ductile 

 than mild steel, and the ultimate elongation of a welded specimen when measured 

 on a length of 8 inches only averages about 10 per cent as compared with 25 to 30 

 per cent for mild steel. 



3. Alternating Stresses: — 



(o) Rotating specimens (round bar) — 



Unwelded turned bars will withstand a very large number of repetitions of 

 stress (exceeding, say, 5 millions) when the range of stress is not greater than from 

 loj^ tons per square inch tension to 10^/2 tons per square inch compression. 



Welded bars similarly tested will fail at about the same number of repetitions 

 when the range of stress exceeds ±6% tons per square inch. 



(&) Stationary test pieces (flat plate) — 



Butt welded specimens will withstand about 70 per cent of the number of repe- 

 titions which can be borne by an unwelded plate. 



Lap welded plates can endure over 60 per cent of the number of repetitions 

 necessary to fracture a lap riveted specimen. 



