(SEM V) THEORY EXAMINATION 2024-25 MACHINE DESIGN

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).