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Strain and stress in metals

When an object is subjected to force, temperature change, etc., its shape and size will change relatively. This relative deformation is called strain. When metal is rolled, forged, pressed and drawn, such as wire winding, lamp holder stamping, etc., the metal will be deformed.

Before deformation, the layout of molecules (atoms) in the object is adapted to the thermal equilibrium state of the object. During deformation, the layout of molecules or atoms will change, so that the object will leave its original equilibrium state. Therefore, there will be a force that causes the object to return to equilibrium. These internal forces that appear during deformation are called internal stress. The stresses that interact on both sides of any cross section inside the object are called normal stress or normal stress when they are perpendicular to the cross section, and shear stress or shear stress when they are tangent to the cross section.

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