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MACHINE DESIGN  An
211
PROBLEM 21
Statement:
Figure P21 shows stressstrain curves for three failed tensiletest specimens.
All are plotted
on the same scale.
(a)
Characterize each material as brittle or ductile.
(b)
Which is the stiffest?
(c)
Which has the highest ultimate strength?
(d)
Which has the largest modulus of resilience?
(e)
Which has the largest modulus of toughness?
Solution:
See Figure P21 and Mathcad file P0201.
1.
The material in Figure P21(a) has a moderate amount of strain beyond the yield point, P21(b) has very little, and
P21(c) has considerably more than either of the other two.
Based on this observation,
the material in Figure P21(a)
is
mildly ductile
, that in P21(b)is
brittle
, and that in P21(c) is
ductile
.
2.
The stiffest material is the one with the grearesr slope in the elastic range.
Determine this by dividing the rise by
the run of the straightline portion of each curve.
The material in Figure P21(c) has a slope of 5 stress units per
strain unit, which is the greatest of the three.
Therefore,
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This note was uploaded on 04/26/2010 for the course MAE 3242 taught by Professor N/a during the Spring '10 term at University of TexasTyler.
 Spring '10
 N/A
 Machine Design, Strain, Stress

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