12 In crvaline mater s the defects marly re plastic deform b

12 In crvaline mater s the defects marly re- plastic deform (b) Precipitates 1.3 The Ginth theory of britt fracture pontu- dua Movement of d b Diaolution of prec Growth of smal longation a mate 1.4 The a Fatigue (c Yield 1.5. Refining the grain structure of an can significantly alter its: (a) Yield stress and shear modulus (b) Yield stress and fracture toughness (c) Fracture toughness and shear stifiress

Solution

1. Permanent deformation of solid when even the applied stresses are removed is a sign of plastic deformation.(a)

2. In crystalline materials the defects mainly responsible for plastic deformation are dislocations(c).

3. The griffth theory of brittle fracture postulates that the fracture is due to growth of small cracks(c).

4. The gradual elongation of a material under constant load is called creep(b).

5. Refining the grain structure of an alloy can significantly alter its yield stress and shear modulus(a).