ME
401 -Machine Design
Assignment 2
How
much torque can a 0.500 inch diameter bar carry before failure? Failure is
l0pb
1.
defined as either yielding
or
fracture -which ever comes first.
How
will
the
following materials fail (yield
or
fracture)? What failure theory(s) would be
appropriate
to
apply
to
these? Hint, see appendix, including A-24.
a)
ASTM
class 20 gray
cast
iron
b) AISI 1040
HR
2.
Using a factor
of
safety
of3
against yielding,
what
is the minimum yield strength
I()~
required for apart
to
carry aload
of
cr
x=
l20MPa,
cry
= - 100MPa and
'txy
=
50MPa
applied at a point?
Use
both the maximum shear stress theory and maximum
distortion energy theory -and compare (briefly discuss) the difference.
3. Design a round bar based
on
the
criteria in the following table. "Design" for this
problem means selecting a specific material (including heat treating
if
any) and
determining
the
diameter.
You
must also select an appropriate factor
of
safety.
IOr
fs
Assume this part
if
for a bridge, failure will cause significant damage
to
the bridge
but will
not
cause it
to
collapse, there is a sign
on
the bridge that says
"maximum
allowable vehicle weight is 30,000 pounds (only
two
vehicles could fit
on
the bridge
at the same time), and
the
load criterion (#2) is based
off
of
a total load
of
60,000
pounds
on
the bridge.
I,
# Criteria Priority Description
II
1 Withstand operation at temperatures between -20°F
to
160°F Essential
1
2
il
Withstand static load
of
15,000 lb. Axial, near
continuous. Essential
II
3 20 inches long Essential
14
Low
weight
High
Less is better
16
Low
cost Desired Less is
better
Problem 4 is
on
the backside.
