Question

Describe the micro-mechanism of fracture of (a) brittle material and (b) ductile material. (c) What is the difference between typical fracture surfaces of brittle and ductile materials?

Answer 1

(a) Brittle material micro mechanism

When the load is applied on the brittle material small crack is develope in the brittle material and after removal of load, cracking is still continued. Because brittle material is a crystalline material and crack/fracture can occurs by small cleavage due to tensile stress which is acting normally to crystalline plane .

Here is the steps of mechanism of fracturing :-

• frist of all a flaw is developed in brittle material due to applied tensile force

• As the load increased the size of crack is also increased.

• At the critical crack the material will fail due to sudden cracking.

(b) Ductile material micro mechanism

In ductile material large deformation takes place after fracture of material.

Here is machanism of fracturing:-

•first a small plastic deformation is formed at area where maximum stress is developed.

• after that a micro crack is form due to shear stress at above point location.

• finally the elastic energy generated through this process allows elongation of crack.

(C) Difference between typical fracture surfaces of brittle and ductile material

1. Brittle materials cross section area will not change after failure but Cross sectional area of ductile material is reduced after failure.
2. Brittle material failure surface is mostly rough and uneven crystalline texture type but Ductile material surface is cup- cone types.