Shear Deformation
Shear deformation occurs when an object changes shape because forces are applied to it and does not just become longer or shorter.
The force F produces a deformation of the shape. If the cross sectional area of the top is given by A, the Shear Stress,and Shear Strain are given byrespectively.
If the object undergoing deformation is elastic, the Shear Stress is proportional to the Shear Strain. The constant of proportionality is called the Shear Modulus, denoted by G:Some values of Shear Modulus are given in the table below for various materials.
Material 
Shear Modulus (Pa) 
Aluminium 

Steel 

Glass 

Bone 

Rubber 

Quartz 

Wood 
The Shear Modulus is about one third the value of Young's Modulus for similar materials.