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Definition of Strain

To define strain let us first understand what stress is. Stress is the property of a body to resists any deformation due to any load or external force. 

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Stress is the internal force produced in the body to oppose external force. Deformation is done in the shape or the dimensions ft he body by stress. This deformation produced is known as strained. So definition of strain is deformation caused by stress. 

Different types of strain are tensile strain, compressive, shear strain and volumetric strain.Here is strain formula for different types of strain are given in following subtopics. Here e denotes strain. Tensile strain: tensile strain is the deformation produced in the length of a material when force is acted upon it such that its length increases. et = change in length/ original length = (final length – initial length)/ (initial length) = dL/L dL is change or increment in length of a piece of material and L is initial length of the material. 

Compressive strain: this is the deformation in length again when force acts on a material such that its length = change in length/ original length = (initial length – final length) / initial length = dL/LdL is change or decrement of length of a material and L is original length of the material.Shear strain: deformation in the shape of a body such that a plane is displaced from its original position parallel to itself and relative to the parallel planes of that body. es = tan ? since ? is very small or negligible. where ? is the angle of distortion which is also known as shear angle.Volumetric strain: deformation produced in the volume of a body by volumetric stress is known as volumetric strain. ev = change in volume/ original volume = (V – Vo)/ V = dV/Vunits of strainStrain is a unit less quantity as you can see in the formula both denominator and denominator have same units which cancels out. 

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But sometimes strain units are also given as m/m or inch/inch. The strain produced in a body is very small so the strain units are also expressed as µm/m etc.stress strain relationship equation is given as: E = stress/ strainhere E is modulus of elasticity and for tensile and compressive stress it is known as young’s modulus of elasticity. Unit of E is equal to unit of stress (N/m2) since strain is dimension less quantity. Shear stress strain relationship example is given here: E =