53103-mt----creep, Fatigue & Fracture Mechanics

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Code No: 53103/MT M.Tech. – I Semester Supplementary Examinations, September, 2008 CREEP, FATIGUE & FRACTURE MECHANICS (Machine Design) Time: 3hours

Max. Marks:60 Answer any FIVE questions All questions carry equal marks ---

1.a) b) 2.a) b)

Explain in detail of the ductile/brittle transition temperatures for notched and unnotched components. Discuss the equivalence of energy approach and stress intensity approach. Explain the phenomena of Tresca and Von mises criteria. A 3-D state of stress is as follows σ x = 50 Mpa σ y = 10Mpa σ z =-20 Mpa

ζ xy =-15Mpa and ζ yz = ζ zx 0. (i) (ii) (iii)

Determine the principal normal and shear stresses. Determine the direction cosines for each principal normal stress axis Determine the octahedral normal and shear stress.

3.a) b)

Explain the different methods of measuring KIC. Explain the phenomenon of crack tip plasticity.

4.

Explain the following: (a) J-integral approach (b) Fail state and safe life design approaches.

5.a)

Discuss with neat sketches of microstructural models of crack initiation under fatigue stages I, II and III crack growth. Explain the cyclic work hardening and softening.

b) 6.a) b)

Explain and state the developments in using rain flow counting methods to recreate fatigue standard spectra. Enumerate the factors affecting the fatigue life of weldments. Contd…..2.,

Code No: 53103/MT 7.a) b) 8.

::2::

Discuss the mechanical model for representation of creep in engineering materials. Write a note on creep-fatigue interactions. Write a short notes on the following: (a) Creep integrals (b) Basquin’ law (c) R-curve analysis. ******