27 real Machine Design questions from the Mechanical Core bank, as asked in Indian campus drives and tech interviews. Every question has a verified answer and an AI-tutor explanation on placd — free to start.
1. What is Factor of safety?
Junior
A.conservative fatigue design line joining the endurance limit to yield strength on the mean-stress axis, preferred for ductile parts
B.initial tightening keeps mated parts clamped so external load is shared between bolt and members in proportion to stiffness, improving bolt fatigue life
C.ratio of failure stress (yield for ductile, ultimate for brittle materials) to the allowable working stress
D.bearing characteristic (r/c)²·μN/p that governs hydrodynamic film thickness and friction and marks the change from boundary lubrication
A.Factor of safety — correction applied to helical spring shear stress for wire curvature and direct shear, larger for a lower spring index
B.Factor of safety — bearing characteristic (r/c)²·μN/p that governs hydrodynamic film thickness and friction and marks the change from boundary lubrication
C.Factor of safety — ratio of failure stress (yield for ductile, ultimate for brittle materials) to the allowable working stress
D.Factor of safety — friction coefficient 2π²(μN/p)(r/c) for a lightly loaded concentric journal bearing, the starting point of bearing friction analysis
5. Which term means: "stress amplitude below which steel survives an unlimited number of fully reversed cycles, roughly half the tensile strength up to 1400 MPa"?
A.Endurance limit — gear tooth bending strength modelled as a cantilever beam, Wt = σ·b·m·Y with the form factor Y rising with tooth count
B.Endurance limit — friction coefficient 2π²(μN/p)(r/c) for a lightly loaded concentric journal bearing, the starting point of bearing friction analysis
C.Endurance limit — correction applied to helical spring shear stress for wire curvature and direct shear, larger for a lower spring index
D.Endurance limit — stress amplitude below which steel survives an unlimited number of fully reversed cycles, roughly half the tensile strength up to 1400 MPa
8. Which term means: "conservative fatigue design line joining the endurance limit to yield strength on the mean-stress axis, preferred for ductile parts"?
A.Maximum principal stress theory — gear tooth bending strength modelled as a cantilever beam, Wt = σ·b·m·Y with the form factor Y rising with tooth count
B.Maximum principal stress theory — correction applied to helical spring shear stress for wire curvature and direct shear, larger for a lower spring index
C.Maximum principal stress theory — stress amplitude below which steel survives an unlimited number of fully reversed cycles, roughly half the tensile strength up to 1400 MPa
D.Maximum principal stress theory — Rankine's criterion suited to brittle materials such as cast iron, where failure is by fracture rather than yield
A.gear tooth bending strength modelled as a cantilever beam, Wt = σ·b·m·Y with the form factor Y rising with tooth count
B.correction applied to helical spring shear stress for wire curvature and direct shear, larger for a lower spring index
C.friction coefficient 2π²(μN/p)(r/c) for a lightly loaded concentric journal bearing, the starting point of bearing friction analysis
D.initial tightening keeps mated parts clamped so external load is shared between bolt and members in proportion to stiffness, improving bolt fatigue life
A.Wahl factor — correction applied to helical spring shear stress for wire curvature and direct shear, larger for a lower spring index
B.Wahl factor — gear tooth bending strength modelled as a cantilever beam, Wt = σ·b·m·Y with the form factor Y rising with tooth count
C.Wahl factor — friction coefficient 2π²(μN/p)(r/c) for a lightly loaded concentric journal bearing, the starting point of bearing friction analysis
D.Wahl factor — bearing characteristic (r/c)²·μN/p that governs hydrodynamic film thickness and friction and marks the change from boundary lubrication
A.Lewis equation — bearing characteristic (r/c)²·μN/p that governs hydrodynamic film thickness and friction and marks the change from boundary lubrication
B.Lewis equation — gear tooth bending strength modelled as a cantilever beam, Wt = σ·b·m·Y with the form factor Y rising with tooth count
C.Lewis equation — correction applied to helical spring shear stress for wire curvature and direct shear, larger for a lower spring index
D.Lewis equation — initial tightening keeps mated parts clamped so external load is shared between bolt and members in proportion to stiffness, improving bolt fatigue life
A.Rankine's criterion suited to brittle materials such as cast iron, where failure is by fracture rather than yield
B.initial tightening keeps mated parts clamped so external load is shared between bolt and members in proportion to stiffness, improving bolt fatigue life
C.friction coefficient 2π²(μN/p)(r/c) for a lightly loaded concentric journal bearing, the starting point of bearing friction analysis
D.conservative fatigue design line joining the endurance limit to yield strength on the mean-stress axis, preferred for ductile parts
20. Which term means: "initial tightening keeps mated parts clamped so external load is shared between bolt and members in proportion to stiffness, improving bolt fatigue life"?
A.Preloaded bolted joint — initial tightening keeps mated parts clamped so external load is shared between bolt and members in proportion to stiffness, improving bolt fatigue life
B.Preloaded bolted joint — Rankine's criterion suited to brittle materials such as cast iron, where failure is by fracture rather than yield
C.Preloaded bolted joint — stress amplitude below which steel survives an unlimited number of fully reversed cycles, roughly half the tensile strength up to 1400 MPa
D.Preloaded bolted joint — correction applied to helical spring shear stress for wire curvature and direct shear, larger for a lower spring index
A.initial tightening keeps mated parts clamped so external load is shared between bolt and members in proportion to stiffness, improving bolt fatigue life
B.ratio of failure stress (yield for ductile, ultimate for brittle materials) to the allowable working stress
C.stress amplitude below which steel survives an unlimited number of fully reversed cycles, roughly half the tensile strength up to 1400 MPa
D.bearing characteristic (r/c)²·μN/p that governs hydrodynamic film thickness and friction and marks the change from boundary lubrication
23. Which term means: "bearing characteristic (r/c)²·μN/p that governs hydrodynamic film thickness and friction and marks the change from boundary lubrication"?
A.Sommerfeld number — friction coefficient 2π²(μN/p)(r/c) for a lightly loaded concentric journal bearing, the starting point of bearing friction analysis
B.Sommerfeld number — bearing characteristic (r/c)²·μN/p that governs hydrodynamic film thickness and friction and marks the change from boundary lubrication
C.Sommerfeld number — stress amplitude below which steel survives an unlimited number of fully reversed cycles, roughly half the tensile strength up to 1400 MPa
D.Sommerfeld number — correction applied to helical spring shear stress for wire curvature and direct shear, larger for a lower spring index
26. Which term means: "friction coefficient 2π²(μN/p)(r/c) for a lightly loaded concentric journal bearing, the starting point of bearing friction analysis"?
A.Petroff's equation — conservative fatigue design line joining the endurance limit to yield strength on the mean-stress axis, preferred for ductile parts
B.Petroff's equation — gear tooth bending strength modelled as a cantilever beam, Wt = σ·b·m·Y with the form factor Y rising with tooth count
C.Petroff's equation — correction applied to helical spring shear stress for wire curvature and direct shear, larger for a lower spring index
D.Petroff's equation — friction coefficient 2π²(μN/p)(r/c) for a lightly loaded concentric journal bearing, the starting point of bearing friction analysis
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