PNNL-13501 - Pacific Northwest National Laboratory

Figure 2. Schematic of experimental apparatus and photo of
sample tested
surrounding the fractures were characterized using a
strain grid analysis system. This system determined the
magnitude of strains that developed in the specimen in the
region around the failure. Each of the originally 2.54 mm
square grids characterized in the area surrounding fracture
were identified as necked if the nodes near the failure
showed elevated levels of local strain (necking) in the
grid, or the fracture had penetrated under (undercut) the
grid surface. These types of forming limit definitions
must be defined and applied in the finite element analysis
in order to accurately capture the material limits of
formability.
Welding Experiments and Modeling
The experimental fixture shown in Figure 3 was
constructed for use in validating the weld modeling. An
automated TIG welding system was used to provide
accurate control of the welding parameters (electrode
speed, welding current, and voltage). Their parameters
were recorded at selected intervals and used as inputs to
the finite element weld models.
Figure 3. Experimental fixture for use in validating the weld
modeling
Welds were performed in the circumferential direction on
6-inch outside diameter by 0.125-inch wall thickness
6061-T6 aluminum tubing. Thermocouples were located
at various distances from the weld. The weld was also
monitored with strain gauges located opposite the weld.
Data were recorded to characterize the temperature profile
and development of distortions in the tube. Data were
also recorded periodically during cool down after the
weld was completed. The gross distortion in the tube was
measured at the end of the test for comparison with the
modeling results.
Finite element analyses of the experimental welds on the
aluminum tubes were performed using MARC analysis.
A three-dimensional shell model representing the tube
was constructed. The weld was modeled in two steps, a
thermal analysis followed by a structural analysis with the
loading provided by the temperatures from the thermal
analysis. The heat input to the thermal model was based
on the voltage, current, and electrode speed used during
the experiment. Figure 4 shows the comparison of the
analytically determined temperatures with the
thermocouple data. Strains from the structural model
were compared to the strain gauge data taken during the
test. The final distortion was then compared with the
experimentally determined deformation.
Temperature (C)
Temperature (C)
300
250
200
150
100
50
0
00:00.0 02:00.0 04:00.0 06:00.0 08:00.0 10:00.0
Time (min:sec:tenths)
300
250
200
150
100
50
0
00:00.0 02:00.0 04:00.0 06:00.0 08:00.0 10:00.0
Time (min:sec:tenths)
Summary and Conclusions
T/C 1
T/C 2
T/C 3
T/C 5
T/C 6
T/C 8
T/C 9
Loc 1
Loc 2
Loc 3
Loc 5
Loc 6
Loc 8
Loc 9
Figure 4. Comparison of the analytically determined
temperatures with the thermocouple data
We developed computational methods and simulation
tools for predicting weld durability of hydroformed thinwalled
aluminum alloy extrusions and tube assemblies
Design and Manufacturing Engineering 177