Thermal Tensioning Effects.
The basic principle of the whole cross-
section thermal tensioning effect is shown in Fig. 1. Two curves (
σ
x1
and
σ
x2
)
of thermal stress distributions are created by a preset heating with the
temperature profiles (
T
1
and
T
2
)
correspondingly on the thin plate. In this
case, the thermal tensioning effect is defined as the value of
σ
∗
x
in the plate
edge of
Y
= 0
where the weld bead will be applied. For a given
σ
∗
x
, the
greater temperature gradient
∂T
1
∂Y
>
∂T
2
∂Y
, the higher will be the induced
maximum value of compressive stress
−
σ
1x
max
. An optimized temperature
curve can be calculated mathematically for an estimated value
σ
∗
x
while the
value
−
σ
x
max
is kept below the yield stress.
As an active in-process control method, thermal tensioning techniques
have been improved at BAMTRI and is more widely acknowledged as
Low Stress No-Distortion (LSND) welding methods for thin materials
(Refs. 9, 10). It is worthwhile to note, that the LSND welding techniques
as active in-process control methods are replacing the formerly adopted
passive measures for buckling removal after welding in most cases in
aerospace engineering in China.
The thermal tensioning effects can be classified into two categories: one
is created in an whole cross-section of plate (whole cross-section thermal
tensioning) using additional heating and cooling as mentioned above, the
other is created in a localized zone limited to a near arc high temperature
area within a certain isotherm induced solely by welding arc without any
additional heating (localized thermal tensioning). For the localized thermal
Fig. 1. Basic principle of whole cross-section thermal tensioning effect
94 ISSN 0236-3941. Вестник МГТУ им. Н.Э. Баумана. Сер. “Машиностроение”. 2005. № 4
