Design and Stress Analysis of Extraterrestrial ... - The Black Vault

Iftesting continues, as shown in Fig. 1.250, creep stage III
ends in material rupture. I Stress at which rupture 6dccrA will
depend upon the material, the testing time, and the temperature,.
Limitingivalue 6f ;:ress at which sample rupture appears in' a
ist perioddof time is ctlled the stress-rupture strength of the
mdtekial and is designated by ator at (the subscript T indicates
I • the operating time bsfore rupture). This time is usually 100, 1000,
5600i 10,000 h and is determined-by both the design operatinf time
sand thee capabilitieS of the test machine on which these values are
'achieved. The superscript t indicates the sample testing temperature
S • since' it is the second factor, after operatingtime, which determines
S! o the value of the -strength limit of a given material.
In-many: cases of stress-analysis, Just aS 'the Strength limit
a 8 6f a standard strain diagram, the stress-rupture strength is a
criterion. for the operational capability of a design. The principal
diff6eence'-between st'ress-rupture strength and strength limita
''lies in its dependence on operatin. time. In the same way as ,raph
) 0 t 1= f (T) is plo'tted in determinihg.creep limit, so graph
ýCot
is plotted in determining stress-rupturi strength as a function
Figure 1.28c shcws a typical stress-
of mater3tal operating time.
rupture strength-curve.
The suppiy" of stress-rupture strength is determined similarly
to the supply with short-term loading:
' 1.... .- , (1.23)'
where amax is the maximum stress in a part or the maximum.intensity
of stresses under a complex stressed state (see below). Since in
logarithmic coordinates the graph showing the dependence of 'tressrupture
Strenh h on time is linear, the dependence of time before
Srupture on' s-ress-rupture strength .Ls exponential:
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