Explain the classification of longitudinal stress?

Explanation

Longitudinal stress can be classified into two types, tensile stress and compressive stress.
Tensile stress : Internal force on the two sides of `Delta A` may pull each other, i.e., it is stretched by equal and opposite forces. Then , the longitudinal stress is called tensile stress.
Compressive stress : When forces acting on the two sides of `Delta A` push each other, `DeltaA` is pushed by equal and opposite forces at the two ends. In this case, `DeltaA` is said to be under compression. then , the longitudinal stress is called compressive stress.