Part 1 Statics and strength of
materials
1
The effects of forces on materials
At the end of this chapter you should be
able to:
- define force and state its unit
- recognise a tensile force and state relevant
practical examples - recognise a compressive force and state
relevant practical examples - recognise a shear force and state relevant
practical examples - define stress and state its unit
- calculate stressσ fromσ=
F
A- define strain
- calculate strainεfromε=
x
L- define elasticity, plasticity, limit of propor-
tionality and elastic limit - state Hooke’s law
- define Young’s modulus of elasticityE
and stiffness - appreciate typical values forE
- calculateEfromE=
σ
ε- perform calculations using Hooke’s law
- plot a load/extension graph from given
data - define ductility, brittleness and malleabil-
ity, with examples of each - define rigidity or shear modulus
- understand thermal stresses and strains
- calculates stresses in compound bars
1.1 Introduction
Aforceexerted on a body can cause a change in
either the shape or the motion of the body. The unit
of force is thenewton,N.
No solid body is perfectly rigid and when forces
are applied to it, changes in dimensions occur. Such
changes are not always perceptible to the human
eye since they are so small. For example, the span
of a bridge will sag under the weight of a vehicle
and a spanner will bend slightly when tightening
a nut. It is important for engineers and designers to
appreciate the effects of forces on materials, together
with their mechanical properties.
The three main types of mechanical force that can
act on a body are: (i) tensile, (ii) compressive, and
(iii) shear