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

Plastic deformations in the latter case can, achieve such
significant values that we can not disregard them where it Is
important to conserve the geometric dimensions of an it'em.
To evaluate the supporting power of material operating for a
long time under elevated temperatures, it would be best to take
the deformation diagram of this material under conditions of actual
operating time and temperature. However, machines for experiments
under such conditions would have to be built. The conditions themselves
cannot be a limitless quantity; some tests cannot be set up at all.
Therefore, tests are carried out on the simplest niachines. Constant
pull P is applied to a sample and elongation and rupture stress ar(
measured as a function of time and temperature. As a result of svch
tests: we can plot curves a = f(T) at t = const or a f(t) at T =
= const (Fig. 125a, b).
60 F
S• ~~~=C~llst ' •gt~
Kt
'C-
\ L
P'1
-1>-pI
S~c)
a) b)
Fig. 1.25.
Typical creep dlt;,.;am.
However, it is best to obtain the function e f(T), wihich we
call the creep curve (Fig. 1.25c).
If stresses are low and the i:kme for taking the deformation
diagram is short, relative el.ongatin :f a rod will be deterviined
from formula e = a/E = P/EF.
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