Question

The stress-strain curves vary from material to material. These curves help us to understand how a given material deforms with increasing loads. From the graph, we can see that in the region between O to A, the curve is linear. In this region, Hooke's law is obeyed. The body regains its original dimensions when the applied force is removed. In this region, the solid behaves as an elastic body.

The ratio of stress and strain, called modulus of elasticity, is found to be a characteristic of the material. Experimental observation shows that for a given material, the magnitude of the strain produced is same whether the stress is tensile or compressive. The ratio of tensile (or compressive) stress (σ) to the longitudinal strain (ε) is defined as Young's modulus and is denoted by the symbol Y. Y = Stress (σ)/Strain (ε) = (F/A)/(ΔL/L) = F × L/(A × ΔL) Since strain is a dimensionless quantity, the unit of Young's modulus is the same as that of stress i.e., N m-2 or Pascal (Pa)

Assertion: On elastic bodies, though we apply force and experience elongation, it is a general practice to plot stress versus strain instead of plotting force versus elongation graph. Reason: Stress versus strain plotting makes the graph independent of the geometry of the sample body and reflects only the material property.

Draw stress and strain curve. Explain the various region or points that are necessary to understand this graph (i) Proportional Limit (ii) Elastic Limit (iii) Yield Point (iv) Ultimate Stress Point (v) Fracture or Breaking Point.