Machine Design Important Questions for R20 JNTU Students
Machine Design is one of the most practical and concept-heavy subjects in the mechanical engineering syllabus. It focuses on designing mechanical components like shafts, gears, bearings, springs, couplings, fasteners, and welded joints.
For R20 JNTU students, understanding machine design fundamentals is essential not just for semester exams but also for GATE, PSU, and job interviews. This blog provides unit-wise important questions, formulas, and preparation tips to help you master the subject effectively.
Machine Design Important Questions for R20 JNTU Students
Unit 1: Design Fundamentals & Material Selection
Key Theory Questions
Define machine design and explain its objectives.
Differentiate between design, manufacturing, and analysis.
Explain the types of design – adaptive, creative, and developmental.
What are the steps in machine design process?
Define factor of safety and its significance.
Explain design stress, yield stress, and ultimate stress.
What are the different design considerations in machine elements?
Define static, impact, and fatigue loading.
Explain design for strength, rigidity, and wear.
What are the criteria for material selection?
Explain the properties of engineering materials.
Define endurance limit and S-N curve.
What is creep and stress relaxation?
Discuss the design procedure for ductile materials.
Explain the concept of preferred numbers (R5, R10, R20 series).
What is ergonomic design and why is it important?
Define interchangeability and standardization.
Explain design optimization and its benefits.
What is reliability in design?
Define working stress and nominal stress.
Numerical Focus Areas
Calculation of factor of safety under static and dynamic loads.
Stress–strain diagram interpretation.
Material property comparison for selection.
Design stress using failure theories.
Key Formulas
Factor of Safety (FoS):
FoS = σ_y / σ_wEndurance Limit:
σ_e = 0.5 × σ_ult (approx. for steels)Mean Stress:
σ_m = (σ_max + σ_min)/2Stress Amplitude:
σ_a = (σ_max − σ_min)/2
Unit 2: Design for Static and Variable Loads
Key Theory Questions
Define static loading and variable loading.
What are the different failure theories in design?
Explain maximum principal stress theory.
Define maximum shear stress theory.
Explain distortion energy theory (von Mises).
Discuss fatigue failure and its stages.
Define mean, alternating, and maximum stresses.
Explain Soderberg, Goodman, and Gerber criteria.
Define stress concentration factor (Kt).
Explain methods to reduce stress concentration.
What is fatigue strength?
Explain cumulative damage theory (Miner’s law).
Define impact energy and its importance in design.
Explain endurance strength modification factors.
What are notch sensitivity and its effects?
Numerical Focus Areas
Solving Soderberg, Goodman, and Gerber equations.
Finding factor of safety for variable loads.
Calculating stress concentration using charts.
Fatigue life prediction for shafts and springs.
Key Formulas
Soderberg Criterion:
σ_a/σ_e + σ_m/σ_y = 1/FoSGoodman Criterion:
σ_a/σ_e + σ_m/σ_ult = 1/FoSGerber Criterion:
(σ_a/σ_e)² + (σ_m/σ_ult)² = 1/FoSFatigue Ratio:
Rf = σ_e / σ_ult
Unit 3: Design of Joints and Fasteners
Key Theory Questions
Classify different types of joints.
Explain cotter joint and its applications.
Describe knuckle joint with a neat sketch.
Define threaded fasteners and their standards.
What is bolt of uniform strength?
Differentiate between riveted and welded joints.
Explain failure modes in riveted joints.
What are butt and lap joints?
Explain eccentric loading on riveted joints.
Define pitch, lead, and thread angle.
Discuss locking devices for nuts and bolts.
Explain power screws and their efficiency.
What is self-locking condition in screws?
Discuss design of welded joints for torsion.
Define efficiency of riveted joint.
Numerical Focus Areas
Design of cotter and knuckle joints for axial load.
Bolt and nut design for direct and eccentric loads.
Riveted joint efficiency problems.
Power screw torque and efficiency calculations.
Key Formulas
Efficiency of Riveted Joint:
η = (Strength of joint) / (Strength of plate)Torque in Power Screw:
T = (W × d_m / 2) × (tan(α + φ))Lead angle:
tan(α) = L / (π d_m)Weld Strength:
P = τ × Throat × Length
Unit 4: Design of Shafts, Keys, and Couplings
Key Theory Questions
Define shaft and its functions.
What are materials used for shafts?
Derive the torsion equation.
Explain hollow vs solid shaft design.
Define rigidity modulus (G).
Discuss design of shafts for combined bending and torsion.
Define key and its types.
Explain sunk key, woodruff key, and splines.
What is coupling and its purpose?
Describe rigid and flexible couplings.
Explain design procedure for muff and flange coupling.
Define torsional rigidity and angle of twist.
Explain failure modes of keys.
What is BIS code used for shaft design?
Numerical Focus Areas
Torque and power transmission in shafts.
Combined bending and torsion stresses.
Key dimensions and shear stress checks.
Flange coupling bolt design
Key Formulas
Torsion equation:
T/J = τ/r = Gθ/LPower transmitted:
P = (2πNT)/60Equivalent bending moment:
M_e = √(M² + T²)Shear stress in key:
τ = 2T / (d × l)
Unit 5: Design of Springs and Bearings
Key Theory Questions
Define spring and its types.
Explain helical compression spring design.
What are leaf springs and their applications?
Define stiffness and spring index.
What is Wahl factor and why is it used?
Explain energy stored in springs.
Describe design procedure for helical spring.
Define bearing and its classification.
Explain journal bearing and rolling element bearing.
Define bearing characteristic number (Sommerfeld number).
Explain lubrication regimes in bearings.
Define bearing modulus.
Discuss types of bearing failures.
Explain selection of bearings from manufacturer catalogues.
Numerical Focus Areas
Deflection and stiffness of helical springs.
Spring constant (k) and stress analysis.
Bearing life and load rating calculations.
Dynamic load capacity and life equations
Key Formulas
Spring stiffness:
k = Gd⁴ / (8D³N)Shear stress in spring:
τ = 8WD / (πd³)Energy stored:
U = ½ WδBearing life:
L10 = (C/P)³ × 10⁶ revolutions
Unit 6: Design of Gears and Brakes
Key Theory Questions
Explain gear tooth terminology.
Differentiate between spur, helical, bevel, and worm gears.
Define gear module, addendum, and dedendum.
What is Lewis equation for beam strength of gear tooth?
Explain dynamic load in gears.
Define wear load and bending load.
Explain AGMA equations.
What is brake and its types?
Define block, band, and disc brakes.
Explain self-locking condition in brakes.
Derive torque equation for band brake.
Discuss design of clutch and brake lining materials.
Define thermal capacity of brakes.
Numerical Focus Areas
Design of spur gear teeth for strength.
Gear ratio and module selection.
Braking torque and efficiency calculations.
Band and block brake problems.
Key Formulas
Lewis equation:
σ = Ft / (b × Y × π × m)Tangential load:
Ft = 60 × P / (2π × N × r)Torque in brakes:
T = (W × r)Self-locking condition:
μr ≥ h
Practice Numerical Questions
Design a solid shaft to transmit 20 kW at 250 rpm, with τ_allow = 40 MPa.
Calculate mean and max stresses for fluctuating load of 200–500 N.
Determine bolt diameter for a cotter joint subjected to 50 kN load.
A helical spring carries 500 N load with 10 coils, G = 80 GPa. Find wire diameter.
Find torque transmitted by a muff coupling.
Compute bearing life for C = 25 kN, P = 5 kN.
Find power transmitted by a spur gear pair at 1200 rpm.
Preparation Tips for R20 JNTU Machine Design Exam
Focus on problem-solving – almost 60% of marks are numericals.
Memorize all formulas and note where to apply them.
Use diagrams while answering theory questions for full marks.
Study previous year papers – many design problems repeat.
Practice IS code–based questions from textbook (V.B. Bhandari).
Always check units and assumptions in numericals.
Conclusion
Machine Design builds the bridge between theory and application in mechanical systems. Understanding how to safely and efficiently design components like shafts, bearings, and springs is crucial for every engineer.
For R20 JNTU mechanical students, mastering these Machine Design Important Questions ensures strong exam performance, technical confidence, and a better foundation for GATE, ESE, and real-world engineering roles.
