Machine Elements Test Questions
For a biaxial stress condition, if the most positive principal stress is 50,000 psi and the other non zero principal stress is -25,000 psi, what is the safety factor based on the maximum shear stress theory if the yield strength in tension of the material is 100,000 psi? A. 1.33 B. less than 1.0 C. 1.25 D. 1.10
A
If the first mechanical failure of a new gear transmission design exhibits a Weibull distribution, what would be a reasonable probability of failure after 65 weeks of operation if the minimum time to the first failure is 50 weeks, the characteristic time is 80 weeks, and the Weibull slope of the failure distribution is 2.0? A. 22.1% B. 47.6% C. 36.8% D. 12.2%
A
If the population of a set of numbers describes a certain attribute of a design, what is the best method to assess the type of distribution from which the set of numbers was taken? A. plotting of the numbers estimated median rank against its magnitude or other statistical parameter and examining for trends B. Monte Carlo simulation C. least squares curve fitting D. calculating the mean and standard deviation of the set of numbers and comparing it against the appropriate value in the cumulative normal distribution data table
A
Residual stresses are A. stresses that remain in the material after the load has been removed because of localized yielding. B. stresses that exhibit a gradient across the beam section during bending. C. stresses that reside in the material due to other external environmental conditions such as temperature. D. stresses that cause the uniform plastic deformation.
A
The fully corrected endurance strength of a material is 65,000 psi. The tensile strength is 120,000 psi and the yield strength is 80,000 psi. The load stress varies between 10,000 and 12,000 psi. No stress concentrations are present in the design. What is the safety factor based on infinite life assuming no yielding during the first load cycle using the Goodman theory A. 6.67 B. 3.53 C. Zero, the material yields on the first load cycle. D. 9.34
A
The horizontal axis of the Manson Coffin fatigue failure diagram is A. log strain reversals to failure B. log stress cycles to failure C. log stress D. log strain
A
The percent reduction of area material property is most closely related to A. ductility of the material B. size of the material test specimen C. low temperatures during material loading D. compression of the test specimen
A
The shear yield strength of a material that can be described by the von Mises static failure theory is what percentage of the yield strength of the material? A. 58% of the yield strength B. 63% of the yield strength C. 50% of the yield strength D. 42% of the yield strength
A
The slope of the plastic portion of the log stress versus log strain curve on a log-log plot from uniaxial tensile test data is most likely to be A. significantly less than 45 degrees but greater than zero B. significantly more than 45 degrees but less than 90 degrees C. approximately 45 degrees D. approximately horizontal (zero degrees)
A
The stress magnitude in the vicinity of a geometric stress concentration from a significant load applied to the part has a high chance of having a magnitude above the yield strength in a ductile metal. A. No because once the stress reaches the yield point the ductile material will yield, thereby relieving the stress in this region. B. Yes because the material is elastic. C. Yes because the abrupt change in the geometry causes the materials stiffness to increase thereby increasing the stress in that region. D. No because there will be little or no stress in this region subjected to the load because the volume of material in this region is small.
A
What is your best estimate of the crack growth rate if the change in stress intensity during the fatigue loading is 80 ksi in^(1/2) for a material with crack growth properties of n = 3.0 and A = 6.9 x 10^(-10) in/(cycle-ksi-in^(1/2)) A. 3.5 x 10-4in/cycle B. 3.5 x 10-3 in/cycle C. 3.5 x 10-6 in/cycle D. 3.50 in/cycle
A
What statistical distribution type would you most expect to describe the fatigue lives of steel roller bearings? A. Weibull B. Poisson C. Log Normal D. Exponential
A
When determining the shaft loading from gear forces, which gear type mesh produces no loads on the shaft that tends to deflect the shaft laterally? A. all gear meshes will deflect the shaft laterally B. hypoid gear C. bevel gear D. involute gear
A
When vibration is present, the power screw A. may overhaul if self-locking was based on static loads. B. is not affected. C. may self lock if over hauling was based on static loads. D. will not operate because of the sudden increase in friction between the nut and thread.
A
Which bearing type is commonly used as the benchmark to compare load (radial and thrust) and life capacity of all other types of ball bearings? A. Deep groove ball bearing B. Double row ball bearing C. Angular contact ball bearing D. Filling notch ball bearing
A
Which is the closest C_10 catalog load rating to be used if the reliability is 90%, the design life is 10 million revolutions, and the design load is 500 lbf for a roller bearing? A. 977 lbf B. 1077 lbf C. 742 lbf D. 1233 lbf
A
Which is the primary reason for a separator to be used in a rolling contact bearing? A. To keep the rolling elements from touching one another B. To minimize bearing fatigue failure C. To keep the rolling elements evenly spaced around the raceway to avoid rotational unbalance in the bearing D. To evelnly distribute the lubricant within the bearing to the rolling elements
A
Which machine element will have the largest angular deflection constraint when used with a shaft to transfer torque power? A. universal coupling B. keys and keyway C. gear mesh D. rolling element bearing
A
Which static failure theory allows for higher principal load stress magnitudes in both the first and fourth quadrant of the principal stress plane when the absolute magnitudes of the yield strength in tension and compression are not equal? A. Maximum Normal Stress Theory B. von Mises Failure Theory C. Modified Mohr Theory D. Coulomb Mohr Theory
A
Which teeth are larger in profile for gears with the same pitch diameter? A. module = 6.35 B. diametral pitch = 12 C. diametral pitch = 6 D. module = 3.175
A
A major advancement in ball bearing development and design was caused by the need for A. reliable bearings in automobiles. B. reliable bearings in bicycles. C. reliabile bearings in airplanes. D. reliable bearings in railroads.
B
A shaft that is integral to the prime mover to be connected to another shaft through a coupling to transmit power to a machine is called a A. head shaft B. stub shaft C. line shaft D. jack shaft
B
Consider a round metal bar loaded only in tension. The force distribution exerted on the bar is normally distributed with a mean force of 10,000 lbf and a standard deviation of 100 lbf, the distribution of the cross-section's area is normally distributed with a mean area of A = 1.0 in2 and a standard deviation of 0.1 in2, and the distribution of the yield strength of the material is normally distributed with a mean yield strength of Sy = 11,000 psi and a standard deviation of 1,000 psi. What is the probability that the axial tensile stress developed in the bar will exceed the yield strength? A. Less than 9.0% B. Greater than or equal to 20.0% but less than 28% C. Greater than 9.0% but less than 20.0% D. 28% or greater
B
Consider the case where a shaft is supported by two bearings between which a gear is centered. The gear transfers the power out of the shaft. A prime mover is connected to one end of the shaft outboard of one of the support bearing with an aligned coupling. Which region of the shaft is subjected to the highest bending stress? A. The outer surface of the shaft near the coupling B. The outer surface of the shaft near the gear on the coupling side C. The outer surface of the shaft near the gear opposite the coupling side. D. The outer surface of the shaft near the support bearings
B
For two spur gears to mesh together correctly, which of the following is not required? A. Both must have the same pressure angle B. Both must have the same face width. C. Both must have the same diametral pitch D. Both must have the same dedendums.
B
If a shaft is supported by two ball bearings, it is common practice to allow both bearings to support the thrust load instead of one bearing. A. Having only one ball bearing support the thrust load might overload the bearing. B. The above statement is incorrect. One ball bearing should always be mounted to support thrust loads in either direction. C. The reason is the mountings of two ball bearings can always be matched to take equal amounts of the thrust loads. D. The reason is thermal expansion of the shaft would cause thrust loads on the ball bearings to cancel each other.
B
If there are three identical rolling element bearings supporting a shaft each supporting identical radial loads, what reliability would be used to select the bearings if the overall reliability of the shaft bearing system needed is 97%? A. 94.090% B. 98.899% C. 91.267% D. 99.967%
B
If we use the Maximum Shear Stress Theory, the shear yield strength of the material is predicted to be what percentage of the tensile yield strength of the material? A. 53% B. 50% C. 47% D. 58%
B
Sturges Rule is used to A. determine the approximate minimum number of data values that should appear in any range to effectively reveal the best distribution exhibited by the data. B. determine the approximate maximum number of ranges that can be used to effectively reveal the best distribution exhibited by the data. C. determine the approximate minimum number of ranges that can be used to effectively reveal the best distribution exhibited by the data. D. determine the approximate maximum number of data values that should appear in any range to effectively reveal the best distribution exhibited by the data.
B
The AFBMA C_10 load rating for rolling element bearings is based on a failure percentage of A. 99% B. 10% C. 90% D. 50%
B
The R.R. Moore Rotating Beam Machine A. applies a zero mean fatigue axial load to the test specimen. B. applies a zero mean fatigue bending load to the test specimen. C. applies a fatigue impact load to test specimens. D. creates rotating bending test specimens
B
The local stress concentration factor used in the analysis in a stress concentration region of the design subjected to fatigue loading is usually A. higher than the theoretical stress concentration factor for a ductile steel B. lower than the theoretical stress concentration factor for a ductile steel C. the same as the theoretical stress concentration factor for a ductile steel
B
The maximum normal stress theory is used most often to predict failure of A. materials that yield considerably before fracture B. brittle materials that fracture and have a high compressive ultimate strength C. materials that yield somewhat before fracture D. materials that yield and have identical absolute magnitudes for tension and compression yield strengths
B
The modification of the endurance strength due to push-pull loading versus rotating bending loading is due to the fact that A. stress concentrations are not as important with push-pull loads B. more material volume is subjected to higher stresses with the push-pull mode C. none of the three choices is correct D. load eccentricity in the push-pull mode tends to induce extra bending stresses
B
The sun gear in an epicyclic gear train has 28 teeth. Each of the four planet gears has 17 teeth. The ring or annulus gear has 62 teeth. The sun gear and ring gear have the same axis of rotation. If the sun gear is held fixed and the ring gear is rotated at 60 rpm, what is the angular speed of the arm? A. 34.6 rpm B. 41.3 rpm C. 22.7 rpm D. 60 rpm
B
The vertical axis of the Manson Coffin fatigue diagram is A. log stress B. log strain C. log strain reversals to failure D. log cycles to failure
B
When the lubricant provided to a journal bearing has no external pressure source, the journal bearing is defined as A. elastrodynamic lubrication B. hydrodynamic lubrication C. hydrostatic lubrication D. elastrostatic lubrication
B
Which torque transfer element generally has the lowest torque transfer capacity if all are of comparable size? A. Key B. Set-Screw C. Spline D. Pin
B
A spall associated with a rolling element bearing is A. an errosion in the bearing raceway surface due to wear. B. flattening of the bearing raceway. C. a small rough area on the bearing raceway surface due to a chip of material breaking out. D. a small indentation or dent in the bearing raceway surface due to an impact load.
C
An oil with a low viscosity index means A. a low viscosity compared to a standard viscosity set by the industry B. a small change in viscosity with changes in temperature C. the viscosity goes through a large change with changes in temperature. D. the viscosity is high compared to other oils of the same type.
C
Brittle fracture of metals is more closely related to which condition? A. high temperature B. thin cross sections C. high normal stresses D. high shear stresses
C
If the fracture toughness magnitude stays below the stress intensity magnitude developed at a crack created by the load A. there will only be yielding of the material B. there will be facture after substantial additional crack growth. C. there will be an immediate fracture. D. there will never be a fracture.
C
The mean stress during a rotating bending fatigue test is A. varies depending on the distance from the centerline of the test specimen B. one-half of the maximum positive normal cyclic stress C. none of the listed answers D. one-half of the largest negative cyclic normal stress
C
Two bearings of the same bore size with designations of 12 and 02 differ only in A. both thickness and outside diameter B. none of the answers C. thickness (axial width) D. outside diameter
C
When the comparative tensile and compressive yield strengths of a ductile metal are roughly equal in magnitude, which static failure theories are most often used? A. von Mises failure theory and linearized Mohr theory B. Maximum normal stress and linearized Mohr theories C. Maximum shear stress theory and von Mises failure theory D. Modified Mohr theory and maximum shear stress theory
C
Which gear mesh is the least noisy (most quiet)? A. spur gear mesh B. straight bevel gear mesh C. hypoid gear mesh D. spur idler gear mesh
C
Which group of fracture toughness data is the most difficult to find in the literature? A. Mode I and Mode III B. Mode I and Mode II C. Mode II and Mode III
C
Which of the listed dynamic failure theories best matches ductile steel fatigue failure data for non mean stress fatigue loading? A. von Mises theory B. Goodman theory C. Gerber theory D. Sodeberg theory
C
Which static failure theory is least conservative when in a biaxial stress condition, when both non zero principal stresses are positive? A. Linearized Mohr Theory B. Maximum Shear Stress Theory C. von Mises Failure Theory D. Maximum Normal Stress Theory
C
Yielding of the material is more closely related to which of the following conditions? A. thick cross sections B. low temperatures C. plastic deformation D. impact loads
C
All rolling element bearings loaded with static loads supporting a rotating shaft and properly lubricated will eventually fail by A. compression yielding of the raceway surface B. tensile yielding of the raceway surface C. none of the above D. fatigue fracture
D
Estimate the remaining life in revolutions of an 0-2 series 30 mm angular contact ball bearing already subjected to 200,000 revolutions with a radial load of 12 kN. The basic load rating of this bearing is C10 = 20.3 kN with and L10 life of 1,000,000 cycles. A. 1,434,000 cycles remaining B. 434,000 cycles remaining C. infinite number of cycles remaining D. 4,641,000 cycles remaining
D
The actual Manson-Coffin fatigue failure line on a log strain versus log 2N is A. a continuous line that is concave down. B. a straight two segment line with the line segment to the right have a steeper slope than the line segment to the left C. a straight two segment line with the line segment to the left have a steeper slope than the line segment to the right D. a continuous line that is concave up.
D
The major failure type stress generated in a rolling element bearing under load is A. Contact normal stress at the raceway surface B. Contact shear stress at the raceway surface C. Contact normal stress below the raceway surface D. Contact shear stress below the raceway surface
D
The maximum allowed alternating stress (the mean stress is zero) in a steel shaft under load designed to last a maximum of 1,800,000 revolutions A. can exceed either but not both the yield strength and the fully corrected endurance strength of the shaft material. B. can not exceed either the yield strength or the fully corrected endurance strength of the shaft material. C. can only exceed the yield strength of the shaft material. D. can only exceed the fully corrected endurance strength of the shaft material.
D
Which of the four items listed below generally has the highest torque transfer capacity when used with a shaft? A. Round Tapered Pin through a tranverse hole in the shaft B. Set Screw C. Key using a sled runner keyway D. Splines
D
Who did the pioneering work and tests that included a coefficient of friction in the analysis of journal bearing torque? A. Beauchamp B. Tower C. McKee D. Petroff
D
If proper lubrication is not maintained in a journal bearing, the bearing failure mode will be fatigue
False
If the center distance between two external spur gears is increased by a small amount above the sum of the radii of the two pitch circles, the teeth will not mesh correctly.
False
Needle bearings are used in designs that have bearing mounting restrictions requiring only a small axial length available on the shaft for mounting of the bearing.
False
Straight bevel gears do not produce thrust loads on shaft support bearings
False
T or F: Generally, a key/keyway system is designed to fail due to shear stresses in the keyway
False
T or F: If a data population exhibits a log normal distribution, the log mean of that population is the natural log of the arithmetic mean of the population
False
T or F: In shaft design, it is required that the cross section geometry of the shaft be known at all locations along the shafts length in order to check adequacy of the design with respect to the strength of the shaft material
False
T or F: One of the major criticisms of Miner's Rule is that the Miner sum has been experimentally shown to be greater than 1.0 in some cases. For the metals that do exhibit a Miner sum greater than 1.0, the use of this Miner sum of 1.0 would reduce the reliability of the design.
False
T or F: Round tapered pins through a transverse tapered hole in a shaft are recommended when large amounts of torque must be transmitted from the shaft to a torque transfer element such as a gear
False
T or F: The classic S-N diagram for all ductile metals exhibits a distinct plateau at the higher number of load cycles.
False
T or F: The log mean of a log normal distribution is found by taking the log of the arithmetic mean of the values within the data set.
False
T or F: The theory behind linear elastic fracture mechanics originated because the actual theoretical strength of materials like glass was found to be lower than measured strength.
False
The bearing diameter must always be slightly smaller than the journal diameter in a properly designed journal bearing
False
The face width of a gear is directly related to the diametral pitch of the gear
False
The power screw collar only contributes a frictional resistance torque when the power screw is lowering the load.
False
The velocity ratio of two meshing gears is also the same as the ratio of the two base circle diameters of the two gears
False
Worm gears will not produce radial loads on the shaft support bearings.
False
T or F: The Manson-Coffin equation gives the relationship between total strain and fatigue life
False, alternating strain amplitude versus load reversals
T or F: The surface roughness fatigue correction factor is governed only by the manufacturing process.
False, process and material's strength
Hobbing is a term describing the milling of gear teeth
True
In journal bearing design, the clearance is determined by the difference in the bearing and journal radial dimensions.
True
Interference can be eliminated between two meshing involute gears by stubbing the teeth on the larger gear which will also decrease the contact ratio of the gear mesh.
True
T or F: A Monte Carlo Simulation is used to reveal the distribution of a complex calculation made up of differently distributed parameters.
True
T or F: A circumferential groove in a shaft designed to be used in conjunction with a snap ring to axially locate a rolling contact bearing's inner ring must be analyzed as a stress concentration.
True
T or F: A crack existing in a material will extend when the energy necessary to produce crack surface area is less than the elastic energy stored in the material.
True
T or F: A rotating shaft transmitting a constant torque that is transferred into the shaft by a coupling and transferred out of the shaft by a gear must always be analyzed for fatigue failure.
True
T or F: Axles are not used to transmit power and rotary motion.
True
T or F: Elastrohydrodynamic lubrication is a type of lubrication most likely to be found with rolling element bearings using oil as a lubricant.
True
T or F: Finite life for wrought steel is defined as any number of cycles lower than 10^6 cycles.
True
T or F: If the location of the largest stress in a rotating shaft experiences a low alternating stress compared to the mean stress, the shaft is more likely to yield first due to any over loads (the overload will have the same ratio of alternating stress to mean stress as the lower magnitude stress) rather than develop any growing fatigue cracks.
True
T or F: Mean stress will affect the fatigue life of a steel part
True
T or F: Neuber's Rule is used to calculate an estimation of the true alternating stress in the region where a stress concentration exists.
True
T or F: Shafts transmitting thrust loads must also be checked for possible column buckling when the bearing supports are at the ends of the shaft.
True
T or F: Stress is assumed not to be proportional to the load's magnitude only with contact stress.
True
T or F: The condition of stress, either plane stress or plane strain, will affect a material's fracture toughness.
True
T or F: The critical shaft speed is the lowest rotational speed a shaft can be rotated where the rotating unbalanced forces do not excite a natural frequency in the shaft.
True
T or F: The intersection of the two straight asymptote lines used to create the Manson Coffin diagram represents a life below which the plastic strain controls the fatigue life.
True
Tapered roller bearings are designed to also support thrust loads.
True
Can a linear elastic material have a Poisson's ratio of 0.487?
Yes
A general trend has been developed and graphed between the bearing characteristic number and the coefficient of friction which can be used to help establish the overall dimensions of the journal bearing.
true
The designer does not have precise control over the coefficient of friction in the design of a journal bearing even with careful selection of the journal and bearing materials.
true
The journal part of a journal bearing is the rotating component
true
Worm gears are less efficient than spur gears
true
