Final Welding Report.pdf (15.2 MB)
It doesn't look much like a final report, it's really more of a final conclusion, and I think the number of samples tested (5 of 27 welds) is just abominable if you ask me, but here you go.
Plaintext follows, for those who don't want to suck down 15MB for a random PDF.
Document wrote: Goals/Purpose
Arc welding in microgravity conditions is poorly understood, and is plagued by numerous
problems. Our research was intended to examine these phenomena and find ways to counteract
them. This was predominantly achieved by varying the welder's operating parameters.
Tests/Results
Weld samples for zero, lunar, and Martian gravity were analyzed using a Vickers Hardness Test.
Each weld sample was cut along the width of the weld and placed in a sample tray. The Vickers
Hardness Number (VHN) was found experimentally by testing each weld at five points along the
weld-aluminum interface and taking the average of the five measured values. This average
Vickers Hardness number was used as the official value for weld hardness. The VHN can also be
obtained by dividing an applied load P by the surface area S of the indentation made by the test,
or as according to Eq. 1.
VHN = P/S (1)
As shown in Table 1, the zero gravity samples showed considerably less hardness than the weld
sample taken at Earth gravity (1.0 g). Sample 2-5 came closest to the Earth-gravity control with
an average hardness of approximately 77.76. While the first two zero-gravity welds were much
softer, sample 2-5 holds some promise that zero-gravity welds might achieve hardness very close
or equal to an Earth-based weld. Sample 2-8, created in lunar gravity, also had an average VHN
of 77 which was close to the 1 g control VHN of 83.3. The Martian weld exhibited a VHN
greater than the 1 g control weld.
(yeah, the formating is messed up, I don't know how to fix it.Code: Select all
0 g VHN 1 g VHN Lunar VHN Martian VHN Sample Point* S2-2 S1-7 S2-5 S1-2 S2-8 S2-9 1 69.9 84.3 92.3 68.7 86.5 87 2 66.4 74.1 71.5 83.3 81.7 86.5 3 68.7 67.2 75 90 55.9 72.8 4 73.3 54.5 74.6 79.7 81.7 88.8 5 70.3 46.8 75.4 94.8 79.2 91.7 Avg. VHN 69.72 65.38 77.76 83.3 77 85.36 *Sample points are 5 mm apart Table I: VHN of welds for various gravitational conditions
Martian gravity is approximately one-third the gravity of Earth. As a result, the same
detrimental effects as lunar gravity should have been observed on the Martian weld. However,
according to Table 1, the Martian weld had a harder average VHN than the 1g control weld.
Furthermore, the VHN at each point along the sample was harder than those points on the 1g
control weld. The reasons for such a strange result, at this point, are unknown.
The zero-g welds were generally softer than the 1-g weld due to lack of gravitational attraction.
This caused the weld to lift from the surface of the material, rather than settle as it would in 1-g
conditions. This lack of gravitational attraction also caused poor penetration and porosity. This
is further shown in the wide range of individual hardness values that were obtained during the
VHN Test.
Each zero-g sample exhibited a varied range of hardness. For sample S1-7 the hardness varied
from 84.3 at point 1, 67.2 at point 3, and 46.8 at point 5. The overall, decreasing value of the
VHN along the interface demonstrates the non-uniformity of the weld due to the aforementioned
lack of gravitational attraction. As shown in Table 1, sample S2-5 had the closest average VHN
to that of the 1-g control weld with point one exhibiting a VHN of 92.3. This one point, taken by
itself, shows that if proper weld geometry is maintained, zero-gravity welds could be as hard as
welds in Earth gravity. However, other points, such as 3 and 4 on S2-5, were much softer than
the 1g weld at the same points. Further research is required to determine the proper techniques
to maintain the correct geometry and material characteristics.
Each sample above was examined under a microscope to analyze the porosity of the weld
material. The samples were also inspected for cracks on the underneath surface due to high
temperature effects. At least three snapshots were taken of each sample: two on each side of the
weld interface and one at the top of the weld. Figures 1 through 6 show the porosity
comparisons of the samples inspected.
[snip images and descriptions]
Through inspection, the weld samples from micro-, lunar, and Martian gravity tend to be more
porous than the Earth gravity control weld. This is partially due to the lack of gravity, therefore
not allowing the air in the molten metal to escape. More porous welds will not be as strong, so
this could pose a problem for welding in space without further studies.
