Page 12 - Mechanical Engineer's Data Handbook

II Strengths of materials

1.1 Types of stress

Engineering design involves the correct determination dimensional stress is dealt with, although many cases
of the sizes of components to withstand the maximum of three-dimensional stress combinations occur. The
stress due to combinations ofdirect, bending and shear theory is applied to the special case of shafts under
loads. The following deals with the different types of both torsion and bending.
stress and their combinations. Only the case of two-

I. I. I Direct, shear and bending stress
Tensile and compressive stress (direct stresses)

load P
Stress o=-=-
area A
extension
x
Strain e= original length =z Shear stress
Stress a PL
- -Young's modulus, E. Thus E =- P
Strain e Ax Shear stress T = -
A

Shear strain 4=:, where G=Shear modulus
G

Note: A is parallel to the direction of P.

Poisson's ratio
strain in direction of load
Poisson's ratio v=
strain at right angles to load
6BIB eB
-- I P
-
~L/L=<
Note: $e, is positive, eB is negative.