Lower thrust structure S/N 0000001 static structural test evaluation report Page: 49 of 53
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V. EVALUATION AND CONCLUSIONS
1. Structural Integrity
Results of all loading conditions indicated that the lower thrust
structure successfully withstood the static loads applied to simulated expected
NERVA boost and operational flight loads. The maximum stress level at any measured
point occurred at the weld joint between the cylinder and the PV flange ring. At
station 106 the meridional stress of 44,180 psi on the outer surface (see Figure 13)
were recorded, primarily as a result of high bending stresses caused, significantly,
by the weld mismatch and by distortion which ranged from .030 in. to .100 in.
(Figure 11 shows this mismatch condition, which is considered undesirable). It is
significant to note that, in spite of this inelastic condition, the permanent
strain of 615 micro-inches/inch was considerably less than the limit value of .2%
Stress distribution around a reinforced hole, as shown in Figure 25,
is similar to that expected in a flat plate under uniaxial tension loading. Stress
at the edge of this heavily reinforced hole was approximately twice as great as that
in the skin. For the circular shaped, reinforced, holes shown in Figures 27 and 28,
the stresses in the skin and reinforcement were high and were of the same order of mag-
nitude. The greatest strain on the part was measured at location 151 on the inside
edge of the hole (Figure 25). This 3300 micro-inches/inch strain resulted in an
uniaxial stress of 39,160 psi and a permanent strain of 1840 micro-inches/inch,
which is slightly less than the limit value of .2%. Although, compared to the
doubler type, the circular-rim type reinforcement was more effective in reducing
the stress concentration factor at the hole, both types satisfied the yield design
The stresses at the weld joining of the cylinder to the frustrum-
cylinder flange (shown in Figure 17) were also significant when the pitch actuator
load was tension (Case 6). At location 130 the meridional stress on the inner surface
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Lower thrust structure S/N 0000001 static structural test evaluation report, report, April 1, 1965; Sacramento, California. (https://digital.library.unt.edu/ark:/67531/metadc1024652/m1/49/: accessed March 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.