Figure shows the relationship between tensile stress and strain for a typical material. Below proportional point A, stress is directly proportional to strain which means Young's moudulus (Y) is a constant. In this region the material obeys Hooke's law.

Provided the strain is below the yield point 'B' the material returns to its original shape and size when the force is removed. Beyond the yield point, the material retains a permancnt deformation after the stress is removed. For stresses beyond the yeld point, the material exhibit plastic flow, which means that it continues to elongate for little increases in the stress. Beyond C a local constriction occurs. The material fractures at D (i.e. breaking point). The graph below shows the stress-strain curve for 4 different materials.

Material which is most brittle is

Options

A. Material-I
B. Material-II
C. Material-III
D. Material-IV

Answer

C

Explanation

Material which breaks just after proportional point.