Download Machine Design Elements Board Ultimate Exam and more Exams Technology in PDF only on Docsity!
Exam
Question 1. Which material property is defined as the maximum stress a material can sustain before permanent deformation occurs? A) Yield strength B) Ultimate tensile strength C) Hardness D) Toughness Answer: A Explanation: Yield strength marks the transition from elastic to plastic behavior; beyond this stress permanent deformation begins. Question 2. The ratio of lateral strain to axial strain in a material under uniaxial loading is called: A) Young’s modulus B) Poisson’s ratio C) Shear modulus D) Bulk modulus Answer: B Explanation: Poisson’s ratio (ν) quantifies the transverse contraction relative to axial extension. Question 3. For a ductile material, which failure theory predicts yielding first under a complex state of stress? A) Maximum normal stress (Rankine) B) Maximum shear stress (Tresca) C) Modified Mohr theory D) von Mises (distortion energy) Answer: B Explanation: The Tresca criterion states yielding begins when the maximum shear stress reaches the material’s shear yield stress. Question 4. In a rotating shaft, the critical speed is primarily associated with which phenomenon?
Exam
A) Torsional buckling B) Lateral (whirling) vibration C) Axial thrust load D) Thermal expansion Answer: B Explanation: Critical speed occurs when the shaft’s natural lateral frequency coincides with the rotational speed, causing whirling. Question 5. A gear with a pressure angle of 20° and a base circle radius of 50 mm will have a tooth thickness at the pitch circle of approximately: A) 25 mm B) 31 mm C) 36 mm D) 42 mm Answer: B Explanation: Tooth thickness at pitch = (π·m)/2 where m = module; using geometry for standard 20° pressure angle gives roughly 31 mm for the given dimensions. Question 6. The factor that reduces the endurance limit of a steel component due to surface finish is known as: A) Size factor (k_s) B) Load factor (k_L) C) Surface factor (k_a) D) Temperature factor (k_T) Answer: C Explanation: The surface factor (k_a) accounts for polishing, machining, or roughness, lowering the fatigue limit. Question 7. According to the Goodman fatigue criterion, a component subjected to a mean stress σ_m = 100 MPa and alternating stress σ_a = 150 MPa will be safe if its ultimate tensile strength S_u is:
Exam
C) Lubrication distribution D) Noise generation Answer: B Explanation: Chordal action causes the chain to deviate from a perfect circle, affecting effective pitch and load distribution. Question 11. For a ball bearing operating at 2000 rpm with a dynamic load rating C = 500 kN, the basic rating life L_10 (in million revolutions) is approximately: A) 2.5 × 10⁴ B) 5.0 × 10⁴ C) 1.0 × 10⁵ D) 2.0 × 10⁵ Answer: C Explanation: L_10 = (C/P)^3 × 10⁶ revolutions; assuming equivalent radial load P ≈ 100 kN gives (5)^3 × 10⁶ = 125 × 10⁶ ≈ 1.0 × 10⁵ k rev. Question 12. The Reynolds equation is fundamental to which type of bearing lubrication analysis? A) Boundary lubrication in plain bearings B) Hydrodynamic lubrication in journal bearings C) Elastohydrodynamic lubrication in gear contacts D) Mixed lubrication in rolling bearings Answer: B Explanation: Reynolds equation describes pressure distribution in a thin fluid film, essential for hydrodynamic journal bearing design. Question 13. The coefficient of fluctuation of speed (C_f) for a flywheel is defined as: A) (ω_max − ω_min)/ω_avg B) (ω_max + ω_min)/2ω_avg C) (ω_max × ω_min)/ω_avg²
Exam
D) (ω_max / ω_min) Answer: A Explanation: C_f = (Δω)/ω_avg quantifies speed variation; lower C_f yields smoother operation. Question 14. In a threaded fastener, the “thread pitch” is: A) The distance between adjacent thread crests measured axially B) The angle of the thread flank C) The diameter of the minor thread D) The length of the engaged thread portion Answer: A Explanation: Pitch is the axial distance from one crest to the next; it determines lead for single‑start threads. Question 15. A self‑locking power screw must satisfy which condition relating the lead angle λ and the coefficient of friction μ? A) tan λ > μ B) tan λ = μ C) tan λ < μ D) λ = 0° Answer: C Explanation: For self‑locking, the friction angle φ (tan φ = μ) must exceed the lead angle, i.e., tan λ < μ. Question 16. In a bolted joint loaded in shear, the shear stress is calculated using: A) σ = F/A_t where A_t is tensile stress area B) τ = F/A_s where A_s is shear area of the bolt shank C) σ = F/(πd²/4) where d is bolt diameter D) τ = F/(πd²/4) where d is bolt diameter Answer: B
Exam
Explanation: K_w adjusts the spring rate for curvature and helix angle, reflecting the increased stress over a straight coil. Question 20. Which of the following best describes the operating principle of a centrifugal clutch? A) Friction plates engage under hydraulic pressure B) Magnetic particles align under a magnetic field C) Shoes expand outward due to centrifugal force to engage a drum D) A cone lock engages with a mating cone when speed rises Answer: C Explanation: Centrifugal clutches use rotating shoes that swing outward with speed, pressing against a drum to transmit torque. Question 21. In a band brake, the effective frictional force is increased by: A) Using a wider band only B) Adding a second band in series (differential configuration) C) Reducing the coefficient of friction D) Decreasing the wrap angle Answer: B Explanation: A differential (double‑band) brake doubles the frictional force for the same input pressure, enhancing braking capacity. Question 22. The Lame equation for thick‑walled cylinders is used to determine: A) Buckling load of a column B) Radial and hoop stresses due to internal pressure C) Torsional shear stress distribution D) Bending stress in a beam Answer: B Explanation: Lame’s solution gives σr and σθ as functions of inner and outer radii for thick‑walled pressure vessels.
Exam
Question 23. According to ISO 286, a tolerance grade “H7” for a 50 mm shaft indicates: A) Upper deviation = +0 μm, lower deviation = −30 μm B) Upper deviation = +30 μm, lower deviation = 0 μm C) Upper deviation = +0 μm, lower deviation = −50 μm D) Upper deviation = +50 μm, lower deviation = 0 μm Answer: B Explanation: H7 for a 50 mm nominal size provides a tolerance of +0/−30 μm (upper deviation zero, lower deviation – 30 μm). Question 24. The basic hydraulic formula Q = C_d A √(2ΔP/ρ) expresses flow rate Q as a function of: A) Discharge coefficient, orifice area, pressure drop, and fluid density B) Pipe length, viscosity, and pressure gradient C) Pump speed, impeller diameter, and fluid bulk modulus D) Valve opening time and accumulator volume Answer: A Explanation: The orifice flow equation includes discharge coefficient C_d, area A, pressure differential ΔP, and fluid density ρ. Question 25. In a welded butt joint subjected to axial tension, the critical stress for failure is governed by: A) The shear strength of the filler metal B) The tensile strength of the parent material in the heat‑affected zone C) The compressive strength of the weld metal D) The fatigue limit of the weld toe Answer: B Explanation: The weakest region under tension is usually the heat‑affected zone, where material properties are degraded.
Exam
B) Reduce the allowable stress for notched components C) Adjust the yield strength for temperature effects D) Account for creep deformation Answer: B Explanation: K_f > 1 amplifies nominal stress to reflect stress concentration effects on fatigue life. Question 30. In a planetary gear system, if the sun gear is the input, the carrier is the output, and the ring gear is fixed, the gear ratio is: A) 1 + (N_r/N_s) B) N_r/N_s C) N_s/N_r D) (N_s + N_r)/N_s Answer: A Explanation: With ring fixed, the carrier speed = (1 + N_r/N_s) × input speed, giving the stated ratio. Question 31. The primary advantage of a tapered roller bearing over a plain ball bearing is: A) Higher radial load capacity only B) Ability to support combined radial and axial loads C) Lower friction coefficient D) Simpler mounting Answer: B Explanation: Tapered rollers can handle significant axial components in addition to radial loads. Question 32. The Soderberg line for fatigue design is considered the most conservative because it: A) Uses the ultimate tensile strength as the limiting value B) Employs the yield strength for alternating stress limit C) Incorporates the endurance limit only D) Assumes zero mean stress
Exam
Answer: B Explanation: Soderberg uses yield strength for alternating stress, which is lower than ultimate or endurance limits, making it conservative. Question 33. In a worm gear set, the efficiency is typically lower than that of spur gears because: A) The worm material is softer B) Sliding contact causes higher friction losses C) The worm has a larger number of teeth D) The gear ratio is always less than 1 Answer: B Explanation: Worm–gear meshes involve extensive sliding, leading to higher friction and lower efficiency. Question 34. The term “backlash” in gear terminology refers to: A) The angular difference between input and output shafts B) The clearance between mating teeth allowing relative motion C) The increase in tooth thickness due to wear D) The dynamic load factor in gear design Answer: B Explanation: Backlash is the intentional or unavoidable clearance that permits gear teeth to move without interference. Question 35. The fatigue strength reduction factor for a welded joint under bending compared to pure tension is approximately: A) 0. B) 0. C) 0. D) 0. Answer: B
Exam
Question 39. The primary failure mode of a leaf spring under repeated loading is: A) Tensile fracture at the clamped ends B) Buckling in the middle span C) Fatigue cracking at the stress concentration near the clamps D) Creep deformation at the center Answer: C Explanation: Repeated bending creates high cyclic stresses near the clamps, leading to fatigue cracks. Question 40. In a double‑acting hydraulic cylinder, when the fluid pressure on the rod side is 5 MPa and the rod area is 200 mm², the retracting force generated is: A) 1 kN B) 5 kN C) 10 kN D) 20 kN Answer: C Explanation: Force = pressure × area = 5 MPa × 200 mm² = 5 N/mm² × 200 mm² = 1000 N = 10 kN. Question 41. The stress‑strain curve of a ductile material exhibits a distinct “yield plateau.” This plateau is associated with: A) Strain hardening B) Elastic deformation C) Plastic deformation at nearly constant stress D) Necking Answer: C Explanation: After the elastic limit, the material yields and deforms plastically with little increase in stress, forming the plateau. Question 42. A keyway in a shaft transmits torque by:
Exam
A) Shear in the key only B) Bearing stress on the shaft surface only C) A combination of shear in the key and bearing stress on the shaft/keyway surfaces D) Torsional stress in the shaft only Answer: C Explanation: Load is shared: shear stress in the key and compressive bearing stress between key and keyway. Question 43. The “critical speed” of a shaft is proportional to: A) √(GJ/ρA L⁴) where G is shear modulus, J polar moment, ρ density, A area, L length B) (GJ/ρA L²) C) √(EI/ρA L²) D) (EI/ρA L⁴) Answer: A Explanation: For transverse vibration, ω_cr ≈ √(π⁴EI/(ρAL⁴)). Using torsional stiffness (GJ) yields a similar form; option A captures the proportionality. Question 44. In a splined shaft, the load is transferred primarily through: A) Adhesive bonding B) Interference fit C) Contact pressure on the splines’ flanks (bearing) D) Shear of the spline material only Answer: C Explanation: The spline teeth bear against each other, transmitting torque through bearing pressure on the flanks. Question 45. The term “hydrostatic bearing” differs from a “hydrodynamic bearing” in that: A) Hydrostatic bearings require external pressurization of the fluid film B) Hydrostatic bearings operate only at high speeds
Exam
Answer: C Explanation: Modified Mohr (or Mohr‑Coulomb) incorporates both normal and shear stresses with material‑specific coefficients. Question 49. In a flexural (bending) spring, the stress distribution across the cross‑section is: A) Uniform B) Linear, zero at the neutral axis and maximum at the outer fibers C) Parabolic, with maximum at the neutral axis D) Exponential, decreasing from the surface inward Answer: B Explanation: Bending stress varies linearly from zero at the neutral axis to σ = My/I at the outer fibers. Question 50. The “burst pressure” of a thin‑walled cylindrical pressure vessel is given by: A) P = 2tσ_h / D B) P = tσ_h / D C) P = σ_h / (2t/D) D) P = σ_h D / (2t) Answer: A Explanation: For thin walls, hoop stress σ_h = P D/(2t); solving for P yields P = 2tσ_h / D. Question 51. In a belt drive, the “effective tension ratio” (T1/T2) is increased by: A) Using a larger pulley diameter only B) Increasing the coefficient of friction between belt and pulley C) Decreasing the belt width D) Adding a second belt in parallel Answer: B Explanation: Higher friction allows a larger tension differential before slip, raising the effective tension ratio.
Exam
Question 52. The primary design parameter that controls the life of a roller bearing under oscillating loads is: A) The static load rating C₀ B) The dynamic load rating C C) The bearing’s lubrication temperature D) The number of revolutions per minute Answer: B Explanation: The dynamic load rating C correlates to fatigue life under variable loads. Question 53. A “self‑aligning ball bearing” differs from a standard ball bearing because: A) It uses cylindrical rollers instead of balls B) It incorporates a two‑row design with a common sphere allowing angular misalignment C) It has a larger inner diameter D) It is lubricated by grease only Answer: B Explanation: Self‑aligning bearings have an outer ring with a spherical raceway, permitting shaft misalignment. Question 54. In a hydraulic system, cavitation is most likely to occur when: A) The fluid temperature is very low B) The pump inlet pressure drops below the vapor pressure of the fluid C) The flow rate exceeds the pump’s rated capacity D) The discharge valve is completely closed Answer: B Explanation: Cavitation happens when local pressure falls below vapor pressure, forming vapor bubbles that collapse downstream. Question 55. The “Wöhler curve” is another name for:
Exam
D) The ratio of pitch diameter to base circle diameter Answer: B Explanation: Contact ratio >1 ensures continuous tooth engagement; it is the average number of tooth pairs in contact. Question 59. When designing a bolted joint for preload, the torque required to achieve a specified preload is calculated using: T = K F_i d where K is the torque coefficient, F_i is the desired preload, and d is nominal bolt diameter. Answer: (Explanation integrated) The equation directly relates torque, preload, and bolt size; the torque coefficient accounts friction. Question 60. In a gear pair, the “pitch line velocity” (v) is given by: v = π d n / 60 where d is pitch diameter (mm) and n is speed (rpm). Answer: This expression calculates the linear speed of the tooth at the pitch circle, essential for dynamic analysis. Question 61. For a thin‑walled pressure vessel, the longitudinal stress σ_l is: σ_l = P r / (2t) where P is internal pressure, r is inner radius, t is wall thickness. Answer: Longitudinal stress is half the hoop stress in thin cylinders, derived from equilibrium of forces. Question 62. The “Mohs hardness” scale is primarily used to: A) Compare tensile strengths of metals B) Rank resistance to indentation among minerals and some engineering materials C) Determine the elastic modulus of polymers D) Evaluate fatigue life of alloys Answer: B Explanation: Mohs hardness quantifies scratch resistance; though not typical for metals, it is a standard mineral scale.
Exam
Question 63. In a clutch with uniform wear theory, the friction torque is proportional to: A) The average pressure times the mean radius B) The square of the mean radius only C) The pressure distribution exponent D) The number of friction plates only Answer: A Explanation: Uniform wear assumes constant wear across the surface, leading to torque = (2/3) μ p R² π N, where p is pressure and R mean radius. Question 64. The “effective modulus” used in calculating contact stress for a ball‑on‑flat contact is: 1/E' = (1 − ν₁²)/E₁ + (1 − ν₂²)/E₂ Answer: This combines material properties of both bodies to determine the reduced modulus for Hertzian contact. Question 65. In a pneumatic cylinder, the speed of the piston is directly proportional to: A) The square root of the supply pressure B) The supply pressure itself (assuming constant flow) C) The inverse of the supply pressure D) The cube of the supply pressure Answer: B Explanation: For a flow‑controlled cylinder with constant flow rate, piston speed v = Q/A and Q ∝ pressure for a given valve; thus speed ∝ pressure. Question 66. The “factor of safety” (FoS) based on yield strength for a component under static load is calculated as: FoS = σ_y / σ_actual Answer: Using yield stress as the allowable limit provides a margin against plastic deformation. Question 67. In a planetary gear set, the “carrier” typically carries:
