Fastenings and Shear stress

Fastenings and Shear stress,Fastenings and Shear stress,Fastenings and Shear stress,Fastenings and Shear stress

Fastenings

Engineering fastenings such as rivets, bolts, the different kinds of machine screws and setscrews, self-tapping screws and hinge pins are frequently subjected to shear loading. Shear loading occurs when equal and opposite parallel forces act on a component. Direct loading tends to cause failure perpendicular to the direction of loading whereas shear loading tends to cause failure parallel to the direction of loading. Direct loading and its effects have already been dealt with (and we will now examine the effects of shear loading (Figure 1.54

Shear stress

Shear stress , is a measure of the intensity of loading over the sheared area A.

Shearing forces tend to distort the shape of a component as shown in Figure 1.55.

Shear strain , is a measure of the deformation which the shearing force produces. It is the ratio of the displacement of the sheared surfaces to the distance between them.

The angle , is called the angle of shear. Its tangent is equal to the shear strain

(Shear modulus or (Modulus of rigidity

When an elastic material is subjected to shear loading, the displacement x of the sheared surfaces is proportional to the load F, which is applied. Also the shear stress is proportional to the

shear strain . A graph of shear stress against shear strain is a straight line, as shown in Figure 1.56, whose gradient for a given material is always found to be the same. It gives a measure of the elasticity or

‘stiffness’ of the material in shear and is known as its Shear Modulus, G. In older text books you might find that it is called the Modulus of Rigidity

Substituting the expressions for shear stress and shear strain from    equations previous  

It will be noted that several of the above formulae are similar to those derived for direct stress and strain and theModulus of Elasticity but they should not be confused. The symbols F, A, l and x have different meanings when used to calculate shear stress, shear strain and shear modulus. Furthermore, the values of Modulus of Elasticity E, and ShearModulus G, are not the same for any given material. With mild steel, for example, E=210GNm 2 whilst G=85GNm 2