Aluminium Design and Construction John Dwight

The problem is to decide on a suitable value of the parameter s for
such welds. An instinctive procedure might be to consider a section
transverse to the axis of the weld, and determine s in the same way as
for a long straight joint of the same geometry, using the data in Table
6.2. This is not acceptable. In practice, the whole of an attachment
weld, or all of one pass, will be laid non-stop without pause. The resulting
heat flow, which is complex, would have to be determined on a one-off
basis using a specialist computer program or else experimentally, neither
of which may be practicable. The only sure thing is that the heat flow,
and hence the pattern of softening, will be more unfavourable than that
based on a straight weld.
The designer, therefore, should first calculate the value of s for an
equivalent long straight weld of the same size, and then increase this
by a suitable factor to allow for all the imponderables. For lack of hard
data, we would suggest an arbitrary increase of 25% in the value of s,
although this may be pessimistic when applied to a very short attachment
weld (connection of a small lug, say).
With a wide attachment, the precise amount that the HAZ projects
at either side is relatively unimportant, since it forms only a small part
of the total affected width. The penetration into the thickness is more
critical. If a small attachment weld is used on a relatively thick member,
the HAZ penetrates only part way into the thickness, leading to a much
smaller area of HAZ than that based on full penetration such as would
be predicted by the one-inch rule.
6.5.10 Definition of an isolated weld (10A-rule)
For an isolated single-pass weld, it is permissible to use the more favourable
HAZ parameters based on strict thermal control, even when only normal
control is specified. How do we define ‘isolated’? The following ‘10Arule’
for so doing is derived from Rosenthal’s heat-flow equations [22].
Referring to Figure 6.17, weld Y may count as isolated provided that:
A p 10A zp (6.7)
where A p =cross-section area of plate on the heat-path from any
neighbouring weld (X) to the weld considered (Y), as measured from
the nearest point in each weld, and A zp =section area of that part of the
nominal HAZ at weld X that lies in the interconnecting plate, measured
from the nearest point in weld X.
Figure 6.17 Check for an isolated weld, ‘10A-rule’.
Copyright 1999 by Taylor & Francis Group. All Rights Reserved.