Material selection.
 

1.	Which statement is untrue? Measures to extend the life duration of roller guides are
	Selecting materials of high hardness.
	Super finishing the contacting surfaces.
	Introducing compressive stresses by micro peening or carburizing.
	Applying a thin hard coating.

2.	Which statement is untrue? A large hardness ratio between boundary lubricated metal – metal surfaces in sliding motion is favorable
	because of metallurgical incompatibility.
	because of good wear resistance with respect to two body abrasion.
	because of good embedability for abrasives.
	because edge pressures are leveled out.

3.	High performance plastics, engineering plastics and general purpose plastics in tribological applications are classified on the basis of their
	low friction.
	hard wearing properties.
	High service temperature.
	high strength.

4.	Calculate the load capacity of a polymer sliding bearing. Consider a bearing with a shaft diameter D=20mm, a relative bearing length L/D=1, sliding velocity v=0.5 m/s, coefficient of friction μ=0.3, maximum temperature increase of 100 K and a heat flow resistance from the contact to the environment of R=6.25 K/W.
	F = 50 N
	F = 100 N
	F = 200 N
	F = 400 N