Lecture 1
Introduction to AME and
Review some of the important principles of
statics
Objectives
To understand the need to take
Analysis of Machine elements course.
Review of statics needed to
determine forces in members of
simple structures.
Why Study AME
Common Machine Elements
Why Study AME
All
Machine Elements have
some functions
Shape ,Size (Geometry)
Material
Ex: Propeller shaft of car
Function : to transmit the drive
Which one of the following
force generated by the engine to
cross sections should I choose.
the axles.
As a designer you know the
functional requirement of a
machine element
Your job is to find the shape , size
How do I decide the
and material of the machine element
dimensions of the chosen
so that it performs its required function
cross section
without failure.
Are there any rules based on which I can decide
the shape ,size, material of a machine element.
Why Study AME
This course familiarizes you with the fundamental concepts which are
needed to decide the shape ,size and material of a machine element .
A thorough understanding of the fundamentals of this subject is of vital
importance because many of the formulas and rules of design cited in
engineering codes are based upon the principles of this subject.
This foundational course in
mechanical
engineering
explores various indignities
(stretching,
squeezing,
twisting, and bending) to
which mechanical structures
can be subjected, and their
Review of statics
Mechanics : science which describes and predicts
the conditions of rest or motion of bodies under
the action of forces
Mechanics of rigid bodies (Statics and dynamics)
Statics and dynamics are devoted primarily to
the study of the external effects upon rigid bodies
that is, bodies for which the change in shape
(deformation) can be neglected.
Mechanics of deformable bodies
deals with the internal effects and deformations that
are caused by the applied loads.
Mechanics of fluids
Deals with the fluids at rest and in motion under the
action of forces
Review of statics
Types of Loads:
External loads : Surface Loads
Surface forces are caused by the direct
contact of one body with the surface of
another
If this area is small in comparison with the
total surface area of the body, then the
surface force can be idealized as a single
concentrated force, which is applied to a
point on the body
If the surface loading is applied along a
narrow strip of area, the loading can be
idealized as a linear distributed load,
w(s)
The resultant force of w(s) is equivalent to
the area under the distributed loading
curve, and this resultant acts through the
centroid C or geometric center of this area.
Review of statics
Types of Loads:
External loads : Body Forces.
A body force is developed when
one body exerts a force on another
body without direct physical
contact between the bodies.
Examples include the effects
caused by the earths gravitation or
its
electromagnetic
field.
Review of statics
Types of Loads:
Support reactions :
The surface forces that develop at the supports
or points of contact between bodies are called
reactions
As a general rule, if the support prevents translation in
a given direction, then a force must be developed on
the member in that direction. Likewise, if rotation is
prevented, a couple moment must be exerted on the
member.
Review of statics
Supports and reactions
Review of statics
Equations of Equilibrium
Equilibrium of a body requires both a balance of forces, to
prevent the body from translating or having accelerated
motion along a straight or curved path, and a balance of
moments, to prevent the body from rotating. These
conditions can be expressed mathematically by two vector
equations
3D Vector
form
For a Coplanar
forces : 2D Scalar
form
3D Scalar
form
Review of statics
Free body diagram :
free-body diagram is a complete
specification of all the known and
unknown forces that act on the body.
Problem
Consider the structure shown in Fig. 1.1, which was
designed to support a 30-kN load. It consists of a boom AB
with a 30 x 50-mm rectangular cross section and a rod BC
with a 20-mm-diameter circular cross section.
These are connected by a pin at B and are supported by
pins and brackets
at A and C, respectively.
1. Draw free body diagram
of the structure.
2. Obtain all the support
reactions.
