Engineering Studies Full Course Notes

Resource Description

CIVIL STRUCTURES

STRESS & STRAIN

SHEAR STRESS: It is a measure of the internal reaction of a shearing force.

If the shear plane runs perpendicularly across the object, the shear area will be the cross-sectional area. But if the shear force punches a hole through the object, the area used will be the circumference of the circle/s multiplied by the thickness of the material.

fs= P/A

f=shear stress

P=load

A= shear area

ENGINEERING AND WORKING STRESS: 

Engineering stress is calculated with the load always divided by the original cross sectional area. This stress does not take into account the falling cross-sectional area.

Working stress is usually less than the yield stress and UTS. The ratio of working stress to one of the other two values is called the Factor of Safety and it is an important consideration in designing equipment. Safe working stress is always less than the elastic limit of the material.

Yield stress is the stress where there is a marked increase in strain without corresponding increased in stress. It is always greater (though by a small amount) than the elastic limit, but less than the UTS.

Proof stress is the amount of stress necessary to bring about a certain amount of permanent strain in a material. Used as a measure of a yield on materials that does not show a yield point.

Toughness is the measure of the ability of a material to absorb energy. They are the opposite of brittle materials and can be found by the area under the curve (i.e. larger the area, the tougher the material).

Hooke’s Law may be stated as follows “Stress is proportional to strain up to the elastic limit”. It simply means that any increase in stress will bring about a proportional amount of strain