Number of pages: 2

AP] ABDUL KALAM TECHNOLOGICAL UNIVERSITY
THIRD SEMESTER M.TECH DEGREE EXAMINATION, JUNE / JULY,

Mechanical Engirieering

(Machine Design)

01ME6110 Fracture Mechanics
Max. Marks : 60 Duration: 3 Hours

(Answer any two from each module)
Unless otherwise specified material properties may be assumed appropriately.

Part A
| (೩) What kind of singularity describes a stress field near the vicinity of a crack tip in
LEFM?
What is Irwin's contribution related to crack tip? (3)
| (b) Why edge crack is more dangerous than centre crack of the same length a? Write down
Kl for both edge crack and centre crack in an infinite plate. (3)

| (©) Determine the critical crack length in a centre cracked large size plate, loaded in
Mode-l, if the critical stress intensity factor is 7OMPa(m) and applied stress 15 1001/83

(3)
2(a) Write down the values of strain energy density of a ductile material including plasticity
and compare with that of brittle material. (3)

2(b) Draw an R- curve with crack length and explain why resistance of crack growth increases with
increase in crack length? (3)

2(c) Stress function for mode --|| = ‏بد‎ Rez . Find out the second derivative of(b ۷۰۸۲.۲۷ . (3)

3(a) Write down mode | stresses in an infinite plate with a centre crack (3)

3(b) A large plate of 36mm thickness with an edge crack ofa = 26mm length is pulled very slowly
under the displacements control loading. At the displacement of 4.8mm, when the recorded
load is 2000N, the crack starts growing . At a = 38.4 mm, the crack is arrested and the load
decreases to 1 200N. Determine the critical energy release rate. (6)

Part - 3

4(a) How does fatigue crack originates on a smooth surface ? (3)

4(b) Compare the plastic zone size between Irwin and Dugdale model. Write
down the effective crack length using Irwin's model.