Aluminium Design and Construction John Dwight

failure plane in the HAZ, close to the weld deposit, for which the
limiting stress is taken as the basic parent value factored by k z1 .
With welds in 7xxx material, carrying transverse tension, a check is
also needed for possible failure at the dip in HAZ (point A in figure 6.2).
For this we take k z =k z3 .
6.7 COMPARISON WITH ONE-INCH RULE
It has already been stated that the most useful HAZ treatment for general
use in design is the simple, but conservative, one-inch rule. In many
situations, the softened region is relatively small and any slight overestimate
of its extent, through employing the one-inch rule, is justified
by the simplicity. But there are other cases where HAZ effects cause a
more serious drop in the resistance of a member, perhaps 10 or 20%.
For these, the one-inch rule becomes too pessimistic, and something
better is then needed if an economic section is to be arrived at. Our RD
method is proposed as a more scientific alternative.
Figure 6.18 shows two beam sections for which relevant parameters
are as follows:
Alloy 6082-T6
Welding process MIG
Limiting stress po 260 N/mm2 Softening factor kz 0.60.
Included against each section is a bar-chart showing how the ratio M c /M cg
varies, depending on which HAZ method is used, where M c =calculated
Figure 6.18 Effect of HAZ softening on calculated resistance for two members in bending.
Comparison of proposed RD method and the one-inch rule. RD method: N=normal thermal
control; S=strict thermal control.
Copyright 1999 by Taylor & Francis Group. All Rights Reserved.