ENB215 Lecture Fundamentals of Mechanical Design
Assessment Weighting
Computational Scheme 50% 20%
Hand Drawing 10%
Solid Model 10%
Design and Build Competition
Performance of the device 30%
Features of the device 20%
Report 20%
Final Exam (Open book) 50% 50%
What is a machine?
A combination of resistant bodies arranged so that
by their means the mechanical forces of nature can
be compelled to do work accompanied by certain
determinate motions.
Review
∫
Not be confused with the area moment of inertia
Parallel axis theorem
If cgis a mass moment of inertia about some axis “aa” thru the centroid (cg) of a body then the moment of
inertia about an axis “bb” which is parallel to “aa” and some distance “d” away is given by.
( )
This same theorem also works for area moments of inertia in the same way.
More generally where k is called the radius of gyration which can be thought of as the radius where all
the mass could be concentrated (relative to the axis of interest) to give the same moment of inertia I that the
body with distributed mass has.
For a solid cylinder:
For a hollow cylinder:
( )
( )
R = Radius
M=Mass This intuitively seems like it should be ( ) but
K=Radius of Gyration that is not the case.
1 Week 1 Tuesday, 27 August 2013 ENB215 Lecture Fundamentals of Mechanical Design
Factors of safety
( )
Hookes Law
V = Poisson’s ratio (~0.3 for most metals) Material Strength
Static Load –a stationary load that is gradually applied 1. S =Yield strength in tension
y
having an unchanging magnitude and direction 2. S ysield strength in shear
Failure – a part is permanently distorted and will not 3. S u Ultimate strength in tension
function properly. A part has been separated into two or

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