C1.1 Normal and Shear Stress

What is stress

Imagine if you stretch a rubber block by pinching it. Although you applied a point load at both ends of the block, the entire cross-section of the block stretches. The distribution of force across the whole cross-sectional area is what we call stress.

distributed force equals stress

C1.1 Normal and Shear Stress

What is stress

Imagine if you stretch a rubber block by pinching it. Although you applied a point load at both ends of the block, the entire cross-section of the block stretches. The distribution of force across the whole cross-sectional area is what we call stress.

distributed force equals stress

Normal stress

Normal stress occurs when the force applied is in the same direction as the stress:

schematic of normal stress acting on block

normal stress formula

Note:

F is the normal force applied
A is the cross-sectional area
Pa or Pascal is the SI unit for stress
Sign: σ is +ve when in tension, -ve when in compression

Shear stress

Shear stress occurs when a shear force is applied instead of a normal force:

schematic of shear stress acting on block

shear stress formula

Note:

V is the shear force applied
A is the cross-sectional area
Has the same Pa unit for shear stress
Sign: +ve or -ve does not matter for now, but will be important when we come to stress transformation

Let’s look at an example now.

Normal stress

Normal stress occurs when the force applied is in the same direction as the stress:

schematic of normal stress acting on block

normal stress formula

Note:

F is the normal force applied
A is the cross-sectional area
Pa or Pascal is the SI unit for stress
Sign: σ is +ve when in tension, -ve when in compression

Shear stress

Shear stress occurs when a shear force is applied instead of a normal force:

schematic of shear stress acting on block

shear stress formula

Note:

V is the shear force applied
A is the cross-sectional area
Has the same Pa unit for shear stress
Sign: +ve or -ve does not matter for now, but will be important when we come to stress transformation

Let’s look at an example now.