NCEES Mechanical Engineering PE Exam 2 — Questions and Answers
Question 1: On the NCEES PE Mechanical exam, what does 'fatigue limit' (endurance limit) represent for a steel component?
- The maximum single-cycle load before fracture
- The stress amplitude below which a material can theoretically withstand infinite load cycles without failure (Correct answer)
- The yield strength under dynamic loading
- The stress at 50% of ultimate strength
Correct answer: The stress amplitude below which a material can theoretically withstand infinite load cycles without failure
The endurance limit (Se) is the stress amplitude below which a ferrous material can endure an essentially unlimited number of loading cycles without fatigue failure.
Question 2: In the NCEES PE Mechanical exam, what is the purpose of the 'Miner's rule' in fatigue analysis?
- To calculate shaft deflection under multiple loads
- To linearly accumulate damage fractions from variable amplitude stress cycles (Correct answer)
- To determine bearing selection based on life cycles
- To size gear teeth for bending fatigue
Correct answer: To linearly accumulate damage fractions from variable amplitude stress cycles
Miner's rule (cumulative damage theory) sums the ratios ni/Ni for each stress level, predicting fatigue failure when the sum reaches 1.0.
Question 3: For the NCEES PE Mechanical exam, which type of bearing is best suited for handling both radial and axial (thrust) loads simultaneously?
- Cylindrical roller bearing
- Deep-groove ball bearing (Correct answer)
- Needle roller bearing
- Thrust washer
Correct answer: Deep-groove ball bearing
Deep-groove ball bearings can carry both radial and moderate thrust loads simultaneously due to their geometry, making them the most versatile and widely used bearing type.
Question 4: On the NCEES PE Mechanical exam, what does the AGMA bending stress equation for gear teeth primarily check?
- Pitting resistance of the tooth flank
- Root bending fatigue strength of the gear tooth (Correct answer)
- Gear tooth deflection under load
- Thermal capacity of the gear mesh
Correct answer: Root bending fatigue strength of the gear tooth
The AGMA bending equation calculates the tensile bending stress at the root of the gear tooth and compares it to the material's allowable bending stress to prevent tooth breakage.
Question 5: In the NCEES PE Mechanical exam, what is 'thermal resistance' in heat transfer analysis?
- The resistance of a material to thermal shock
- An analogy to electrical resistance representing the opposition to heat flow (Correct answer)
- The maximum temperature a material can sustain
- The ratio of conduction to convection heat transfer
Correct answer: An analogy to electrical resistance representing the opposition to heat flow
Thermal resistance (R = L/kA for conduction, 1/hA for convection) allows complex heat transfer problems to be solved using electrical circuit analogies.
Question 6: For the NCEES PE Mechanical exam, which fluid property governs the Bernoulli equation's applicability?
- The fluid must be compressible
- The fluid must be inviscid (frictionless) and incompressible along a streamline (Correct answer)
- The fluid must be turbulent
- The fluid must be non-Newtonian
Correct answer: The fluid must be inviscid (frictionless) and incompressible along a streamline
Bernoulli's equation applies to steady, inviscid, incompressible flow along a streamline, where energy losses due to viscosity and density changes are negligible.
NCEES Mechanical Engineering PE Exam 2
On the NCEES PE Mechanical exam, what does 'fatigue limit' (endurance limit) represent for a steel component?