Subject Code: BME502
Subject Name: Machine Design
Course: B.Tech (Semester V)
Maximum Marks: 70
Duration: 3 Hours
Exam Year: 2024–25
Sections: A, B, and C
SECTION A – Short Answer Questions (2 × 7 = 14 Marks)
Attempt all questions briefly.
a. Explain preferred numbers in machine design. b. Define bearing characteristic number.
c. Describe: (i) Helix angle of a helical gear
(ii) Addendum circle of a gear
d. What is pitch point in gear design? e. What is a foot-step bearing?
f. State the function of a piston in an I.C. engine. g. What is an octane number?
SECTION B – Medium-Length Questions (7 × 3 = 21 Marks)
Attempt any three of the following.
Write short notes on: Notch sensitivity
Stress concentration Endurance stress
Fatigue failure
Design an eccentrically loaded lap riveted joint for a steel bracket (25 mm thick, P=50kNP = 50 kNP=50kN, e=400mme = 400 mme=400mm, C=100mmC = 100 mmC=100mm,
τperm=65MPaτ_{perm} = 65 MPaτperm=65MPa, σc=120MPaσ_c = 120 MPaσc=120MPa) — determine rivet size.
A pair of helical gears (20 T pinion, 100 T gear, 720 rpm,
αn=20°α_n = 20°αn=20°, β=25°β = 25°β=25°, mn=4mmm_n = 4 mmmn=4mm, b=40mmb = 40 mmb=40mm, Sut=600MPaS_{ut} = 600 MPaSut=600MPa, BHN=300BHN = 300BHN=300)
— determine power-transmitting capacity considering a velocity factor and safety factor = 2.
Derive the dynamic load rating capacity of a rolling contact bearing under variable load.
For a four-stroke diesel engine cylinder, BP=5kWBP = 5 kWBP=5kW, N=600rpmN = 600 rpmN=600rpm, IMEP=0.5MPaIMEP = 0.5 MPaIMEP=0.5MPa:
(i) Bore & stroke (ii) Liner thickness (iii) Head thickness
(iv) Stud size, number, and pitch.
SECTION C – Long / Analytical Questions (7 × 5 = 35 Marks)
Attempt one part from each question.
Q3. Design for Strength and Fatigue
a. A steel plate (Sut=440MPaS_{ut} = 440 MPaSut=440MPa), subjected to completely reversed axial load = 30 kN (see fig. on page 2).
Given: q=0.8q = 0.8q=0.8, reliability = 90%, FOS = 2, size factor = 0.85.
→ Find thickness for infinite life.
OR
b. Why are alloy steels used in machine design? How are engineering materials classified?
Q4. Shaft Design and Keys
a. A solid circular shaft is subjected to Mb=3000N⋅mM_b = 3000 N·mMb=3000N⋅m, T=10000N⋅mT = 10000 N·mT=10000N⋅m, material = 45C8 steel, Sut=700MPaS_{ut} = 700 MPaSut=700MPa, Sus=500MPaS_{us} = 500 MPaSus=500MPa, FOS = 6.
→ Determine shaft diameter.
OR
b. Write short notes on:
(i) Spline (ii) Feather key (iii) Woodruff key (iv) Keyway.
Q5. Spur and Worm Gear Design
a. Design a spur gear speed reducer for a compressor (7.5 kW, 1000 rpm motor → 250 rpm output, C.D. = 250 mm, 20° pressure angle, steel 50C4).
(i) Design the gears and specify dimensions.
(ii) Calculate dynamic load using Buckingham’s equation (Grade 6).
OR
b. A worm drive transmits 15 kW at 2000 rpm to 75 rpm, triple-thread worm, dw=65mmd_w = 65 mmdw=65mm, zg=90z_g = 90zg=90, m=6mmm = 6 mmm=6mm, φ=20°φ = 20°φ=20°, μ = 0.10.
→ Find:
(i) Tangential force on worm (ii) Axial thrust & separating force (iii) Efficiency of worm drive.
Q6. Bearings
a. Explain:
(i) Zero-film bearing (ii) Thin-film bearing (iii) Thick-film bearing
(iv) Dynamic load rating capacity.
OR
b. A journal bearing for a steam engine:
Load = 3 kN, d=75mmd = 75 mmd=75mm, L=75mmL = 75 mmL=75mm, N=1600rpmN = 1600 rpmN=1600rpm, c=0.1mmc = 0.1 mmc=0.1mm, Tamb=15.5°CT_{amb} = 15.5°CTamb=15.5°C, oil = SAE 10, μ60°C=0.014kg/m⋅sμ_{60°C} = 0.014 kg/m·sμ60°C=0.014kg/m⋅s.
→ Find heat generated and heat dissipated.
Q7. IC Engine Components
a. Design a cast-iron piston for a single-acting four-stroke engine:
D=100mmD = 100 mmD=100mm, L=125mmL = 125 mmL=125mm, pmax=5MPap_{max} = 5 MPapmax=5MPa, IMEP=0.75MPaIMEP = 0.75 MPaIMEP=0.75MPa,
mechanical efficiency = 80%, fuel=0.15kg/bhp⋅hrfuel = 0.15 kg/bhp·hrfuel=0.15kg/bhp⋅hr, CV=42×103kJ/kgCV = 42×10^3 kJ/kgCV=42×103kJ/kg, N=2000rpmN = 2000 rpmN=2000rpm.
→ Assume suitable data and design piston dimensions.
OR
b. Explain the functions of piston components:
(i) Ribs (ii) Piston rings (iii) Piston skirt (iv) Piston pin.
Key Topics to Prepare
Design fundamentals: Stress concentration, fatigue, endurance limit
Shaft & key design: Torque, bending, combined loading
Gears: Spur, helical, worm — velocity ratio, dynamic load, Buckingham equation
Bearings: Lubrication regimes, load rating, heat balance
Fasteners: Rivets, welded & bolted joints
IC Engine parts: Piston, cylinder, liner, head design
Material selection: Alloy steels, properties, design factors
Design for fatigue & reliability
Study Tips
Revise standard formulas — torque equations, gear tooth strength, dynamic load (Buckingham), fatigue stress.
Draw clear diagrams — gear tooth geometry, bearings, riveted joints, piston design.
Practice numericals — rivet design, shaft diameter, gear power transmission.
Understand material properties — SutS_{ut}Sut, SytS_{yt}Syt, SeS_{e}Se, and their relation in design.
Learn empirical correlations for thermal and fatigue design (e.g., Goodman and Soderberg lines).
