In the study of tribology, what are the theoretical considerations behind the Stribeck curve, and how do different lubrication regimes affect the friction and wear characteristics of interacting surfaces under varying load and speed conditions? 3
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The curve shows how µ changes as operating conditions move surfaces through boundary, mixed and full-film (hydrodynamic or elastohydrodynamic) lubrication regimes. Show more…
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7.13 The highly loaded cam, shown below, has a minimum radius of 10 [mm] and is 20 [mm] wide. It is subjected to a load of 4 [kN]. The cam rotates against a convex stationary follower that has a radius of 40 [mm]. The sliding speed at the point of contact is approximately 0.1 [m/s]. The cam is lubricated with oil that has a dynamic viscosity of ̐ = 1.44 [Pas] at the operating temperature and a pressure-viscosity coefficient of 2.810⁸ [Pa⁻¹]. The material of both the cam and follower has a modulus of elasticity E = 2.0710¹¹ [Pa] and Poisson's ratio ̑ = 0.3. Estimate the surface roughness of the cam and the follower necessary to prevent the occurrence of scuffing. (Ans. ̒ = 0.0768 [μm]) R₁ = 40 mm R₂ = 10 mm 7.14 Assuming the coefficient of friction μ = 0.05 for problem 7.13, calculate the oil temperature increase after 1 [min] of operation. For simplicity, assume that all heat remains in the cam, follower, and oil, that the coefficient of friction is independent of temperature, that the temperature of the cam, follower, and oil is the same, and that the total heat capacity of the assembly is C = 200 [J/K]. Assume that the cam and follower are adiabatic. (Ans. ΔT = 6°C)
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5. Petroff's Equation and Petroff's Law, respectively, are given by the formulas shown below. The figure shows journal bearing test results. (a) Petroff's Equation is accurate under what conditions? (b) What does the line DE represent? (c) What does the line AB represent? (d) What does point C represent? (e) Briefly discuss stability of lubrication with respect to this figure. (f) Give average values for f for: unlubricated surfaces, surfaces with boundary lubrication, and surfaces with thick-film lubrication.
A reciprocating type ball-on-disc tribometer was used to measure the tribological behavior of the thermally sprayed cobalt oxide coatings against the alumina (Ø 6.35 mm) counterface. After wear testing at high temperatures, the average area of the wear track was 400 µm², measured by a white light microscope. The following parameters were used for sliding wear testing: Parameters Values Applied load (N) 5 Sliding velocity (cm/s) 3.14 Test frequency (Hz) 1 Track length (mm) 10 Total sliding cycles 5000 Total sliding distance (m) 100 Determine the wear volume in mm³ that was removed during the sliding process and the specific wear rate (mm³/N.m).
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