Strength of Welds

Static and fatigue strength of welded joints, as well as impact toughness of the weld and HAZ metals were evaluated. Mechanical properties of welded joints of alloy T110 are adduced in Table 7. 

Welding of Al-Mg alloys decreases the welded joint strength by 20 to 50 MPa and the ductility by 50%. Strength of welded joints for AMF2 and AMF3 alloys is about 95% that of the base metal and for AMF5 and AMF6 alloys somewhat less. 

The strength of weld lines in injection-molded articles is generally weaker than that of the bulk. This is due to the incomplete entanglement of polymer chains at the two impinging fountain flow fronts in the mold cavity. When the two flow fronts meet in the cold cavity, the molecular orientation at the interface remains parallel to the weld line as evidenced by the frozen-in molecular orientation found in the molded article under proper injection-molding conditions... 

In all cases, the strengths of the welds increase as temperature decreases and the elongations (with the weld at the center of the 2 in. gage length) generally remain about the same or increase as temperature decreases. These results also indicate that the minitnum strengths of welds in the nonheat-treatable alloys are the same as the minimum tensile strengths of annealed plate of the respective alloys. 

Strength of Welds (non coder Permissible unit stress lor fillet welds made with coated welding rod is 14,000 lbs per square inch, taking into consideration that practically every fillet weld is subject to shear... 

Another cause of failure in PP artefacts is the poor quality of the weld lines. Weld lines are inherent weak positions due to the poor frsion of the material at molecular level. However, the strength of welds can be maximised by favourable moulding conditions such as sufficiently high melt temperature, high tool temperature, heated metal inserts and fast injection times. Similarly to other plastics, more attention should be paid to filled or reinforced grades of PP. 

Untersuchungen zur Betriebsfesigkeit von geschweiKten Offshore-Konstruktionen in Meerwasser (Investigations on the service strength of welded offshore constructions in seawater) (in German)... 

Teng, J.G. Rotter, J.M. (1991) The strength of welded steel silo hoppers under filling and flow pressures. J. Struct. Eng., ASCE, 117(9), 2567-2583. 

Fig. 12.19 Influence of type and weld profile on fatigue strength of welds (modified from [23])...

Maddox S.J. An introduction to fatigue of welded joints, improving the fatigue strength of welded joints. TWI (1983)... 

Maddox, S.J. Fatigue strength of welded structures. Abington, Camtoidge (1991)... 

Haangsen, P.J. Improving the strength of welded joints. In Almar-Naess, A. (ed.) Fatigue Handbook. Tapir, Trondheim (1985)... 

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