What is shear force?

Take a chalk and try to bend it..

What happens

After certain loading its breaks, right ?

This event/action (i.e.breaking of chalk) is known as shear and the force/stress associated with it is called as shear force/stress.

So any event consist of breaking the material is a shear.

Now as the chalk is brittle material it breaks with very little loading and almost no bending.

But what happens in case of ductile material or semi ductile materials like concrete.

In that case , the ductile material doesn't break easily instead it bends (like bending of rcc beam) but after some time the concrete shears. Obviously it doesn't fall apart, instead there is a crack formation in Concrete member (also known as shear cracks)

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Hope This Helped..