Load rating and rolling contact fatigue
.
1.
Which statement is untrue?
The Brinell hardness is the ratio of applied load and the curved surface area of indentation left in the surface of the test piece.
In the Rockwell hardness test the hardness value is derived from the depth of indentation under prescribed load.
The Vickers hardness is the ratio of applied load and the pyramid surface area of indentation left in the surface of the test piece.
Exact conversion of the hardness scales is possible when regarding the type of material.
2.
Which statement is untrue?
The dynamic load rating of deep groove ball bearings is higher than the static load rating.
Doubling the load on a deep groove ball bearing will reduce the fatigue life with a factor 8.
The static load rating of a hybrid ball bearing with ceramic balls is higher than one with steel balls.
Elastic shakedown positively affect the dynamic load rating of roller bearings.
3.
Which statement is untrue?
The plasticity index is a dimensionless parameter indicating whether the asperities in contact mainly deform elastic, elastic-plastic or plastic.
In polymer - metal contacts the plasticity index is usually small, indicating elastic behavior.
In polymer - metal contacts the real contact area increases less than proportional to the load.
The asperities in metal-metal contacts usually deform purely plastic.
4.
Which statement is untrue?
Between intermeshing evolute gear teeth pure rolling takes place (no slip).
The surface durability of gear teeth is based on the Hertzian contact pressure at the pitch circle.
The permissible contact stress is derived from material tests and relative influence factors.
The repetitive loading of the gear teeth may result in surface fatigue, despite the fact that the Hertzian contact stresses remain below the elastic limit of the gear materials.
5.
Which statement is untrue?
According to Hertz theory the surface area of a nominal point contact is proportional to F^(2/3).
In the case of plastic deformation the contact area of a nominal point contact is proportional to F
Initial inelastic yielding in nominal point contacts starts at the surface in the centre of the contact.
Hertz theory is based on two contacting semi-infinite bodies.
6.
Calculate the effective contact radius R’ of the Hertzian contact formed between a ball of diameter d=10mm rolling over a plane surface.
R’ = 5 mm
R’ = 2.5 mm
R’ = 10 mm
R’ = 1.25 mm
7.
Which statement is true?
The surface roughness expressed in Ra, Rm or Rt is
independent of the shape of the asperities and independent of the wave length of the roughness profile.
dependent on the shape of the asperities and independent of the wave length of the roughness profile.
dependent on the shape of the asperities and dependent on the wave length of the roughness profile.
independent of the shape of the asperities and dependent on the wave length of the roughness profile.
8.
Calculate the Center Line Average or Ra value and the arithmetic mean or Rq roughness of a block shaped profile with an amplitude 0.5 um and a periodicity of 2 um.
Ra=0.25 um, Rq=0.5 um
Ra=0.25 um, Rq=0.25 um
Ra=0.5 um, Rq=0.5 um
Ra=0.5 um, Rq=0.25 um
9.
Which statement is true? The maximum rotational speed of hybrid ball bearings with ceramic balls is higher than with steel balls because
Ceramic balls have lower density (lower mass).
Ceramics have higher modulus of elasticity.
Ceramics have lower density and higher modulus of elasticity.
Ceramics have lower density and lower modulus of elasticity.
10.
The prescribed hardness of a Cam and rolling follower should be 500HBW. The measured hardness is 10% less. Calculate the effect of the lower hardness on the life expectancy for fatigue. The life expectancy is reduced by about
10%
20%
30%
50%