1
Seat No.: Enrolment
GUJARAT TECHNOLOGICAL UNIVERSITY
ME SEMESTER I EXAMINATION WINTER 2018
Subject Code: 3710801 Date: 03/01/2019
Subject Name: Advanced Machine Design
Time: 02:30 PM to 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1

Draw and explain the rheological models for plastic deformation and their responses to different strain inputs.
07

Describe the modified Coulomb-Mohr theory.
07
Q.2

The stresses at a point in a body are:
fx 91 MN/m2, fy 21 MN/m2, fxy (shear stress) 84 MN/m2, yield point stress 280 MN/m2.
Find the factor of safety:
1. By the maximum shear stress theory. 2. By the distortion energy theory.
07

Explain design procedure for finite life.
Explain design procedure for infinite life.
07
OR

Discuss the Strain Vs Life Curve for variable load.
Explain fatigue crack propagation and life estimation for variable amplitude stress.
07
Q.3

Explain Manson's method.
Define: Notch sensitivity Stress concentration
07

Estimate the life of a shaft mm made of alloy steel for which fut 550 MPa. The bending stress at the most critical section has been determined to be 180MPa.
Assume CF 0.85, Kf 1.585.
07
OR
Q.3

Explain following term in detail:
Crack propagation criteria.
Stress intensity factor.
07

A cold drawn steel bar is to withstand a tensile preload of 36.3 kN and a fluctuating tensile load varying from 0 to 72.60 kN. The bar has a geometric stress concentration factor of 2.02 corresponding to a fillet whose radius is 4.75 mm. Determine the size of the bar for an infinite life and a factor of safety of 2. The material properties are fyp 588.0 N/mm2, fut 700 N/mm2. Assume surface finish factor 0.73, load factor 0.85, average value of material constant 0.25 and endurance limit 0.5 x ultimate stress.
07
Q.4

Explain the following:
Effect of crack strength of ductile material.
Different between Hydrostatic and Hydrodynamic lubrication system.
07

Calculate the time to rupture at 650°C and 100MPa stress for a Mo-0.25%V steel, according to the Larson-Miller and Sherby-Dorn, if this alloy underwent rupture in 20hrs when tested in tension at the same stress level at a temperature of 750°C. Assume Q 460 kJ/mol.
07
OR
Q.4

Explain the following:
Factor affecting the fracture of material.
Define: Failure due to fatigue Failure due to creep.
07
2

What are the failure criteria for structural component for justified life? Explain any one with case study.
07
Q.5

Discuss about different mode of lubrication for mechanical rotating part and gives practical example of them.
07

A cylindrical pressure vessel is constructed from a long, narrow steel plate by wrapping the plate around a mandrel and then welding along the edges of the plate to make an helical joint (see figure-1 below). The helical weld makes an angle 55° with the longitudinal axis. The vessel has an inner radius r =1.8m and a wall thickness t 20mm. The material is steel with a modulus E=200GPa and a Poisson's ratio ν=0.30. The internal pressure is 800kPa.
Calculate the following quantities for the cylindrical part of the vessel:
The circumferential and longitudinal stresses σ1 and σ2 respectively. The maximum in-plane and out-of-plane shear stresses. The circumferential and longitudinal strains ε1 and ε2 respectively and The normal stress σw and shear stress τw acting perpendicular and parallel, respectively, to the welded seam.
Figure-1
OR
Q.5

Explain the following:
Different mode of energy dissipation in material.
Define: True stress True strain.
07

What is surface fatigue? Derive expression for size of contact patch and static stress distribution in cylindrical contact.
07