TWI Industrial Member Report Summary 656/1998
S J Maddox and C A Moura Branco*
Although there are well established fatigue design rules for welded joints in steels, they are based largely on fatigue data obtained from tests on manual metal arc (MMA) welds. Such welds, and indeed welds made by the other production arc welding processes, are known to contain inherent flaws at the toes, which have a very significant effect on fatigue performance. However, the flaws are thought to be far less severe, or even absent altogether, in tungsten inert gas (TIG) and plasma welds, due to the quiescent nature of these processes. Thus, it can be expected that joints welded by these processes will display superior fatigue strengths.
The greatest potential for the use of TIG and plasma welding is in the joining of sections less than 10mm thick. This may introduce an additional benefit from the fatigue viewpoint, since fatigue strength is expected to increase with decrease in plate thickness.
- To confirm that the fatigue performance of TIG and plasma welds is superior to that of corresponding welds made by other production arc welding processes.
- To quantify the potential benefit of reduced thickness in terms of increased fatigue strength.
- To provide fatigue design guidance for a range of welded joints made by TIG or plasma welding.