PEARSON ETEXT ENGINEERING MECH & STATS
15th Edition
ISBN: 9780137514724
Author: HIBBELER
Publisher: PEARSON
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Students have asked these similar questions
20-4-2025
Exam-2-Tribology
Q1: What are the assumptions of hydrodynamic lubrication theory:
Q2: Explain with sketch the cycle or process of engine lubrication system-pressurized
lubrication system
Q3: A short bearing is designed to operate with an eccentricity ratio = 0. 7. The journal
diameter is 60 mm, and its speed is 1300 r.p.m. The journal is supported by a short
hydrodynamic bearing of length L/D = 0. 5, and clearance ratio C/R = 103. The radial load
on the bearing is 9800 N.
a. Find the Sommerfeld number.
b. Find the minimum viscosity of the lubricant for operating at ε = 0.7
c. Select a lubricant if the average bearing operating temperature is 70°c
Q4: Two parallel circular disks of 100 mm diameter have a clearance of Imm between them.
Under load, the downward velocity of the upper disk is 2 m/s. At the same time, the lower disk
is stationary. The clearance is full of SAE 40 oil at a temperature of 60°c.
a. Find the load on the upper disk that results in the instantaneous…
Tribobolgy
15/2022
Monthly Exam.
Automobile Eng. Dert
2nd Semster/3rd class
Max. Mark: 100%
7. Viscosity of multi-grade oils
(a) Reduces with temperature
(c) is less sensitive to temperature
(b) Increases with temperature
(d) None of the above
8. In a hydrodynamic journal bearing if eccentricity ratio = 1, it means
(a) Journal/shaft is subjected to no load and the rotational speed is very high.
(b) Journal is subjected to no load and the rotational speed is moderate
(c) Journal is subjected to very light load and the rotational speed is very high.
(d) Journal is subjected to very high load and the rotational speed is negligible.
Q4/ The journal speed of a 100mm diameter journal is 2500 rpm. The journal is supported by
a short hydrodynamic bearing of length L=0.6D, eccentricity ratio = 0.75 and a clearance
ratio C/R=0.001. The radial load on the bearing is 10 kN. The lubricant is SAE 30, and the
operating temperature of the lubricant in the bearing is 700C.
1- Assume…
1 of 2
Monthly Exam.
Automobile Eng. Dert
2nd Semster/3rd class
Max. Mark: 100%
Q1/A/ Compare between the long and short journal bearings
B/ With the help of Stribeck's curve, discuss different regimes of lubrication.
C/ Explain the importance of Tribology in the design of different machine elements
Q2 /A/ According to the SAE viscosity grading system all engine oils are divided into two
classes: monograde and multi-grade. Compare between them?
B/What are the differences between grease and Synthetic oils
C/ Explain the effect of eccentricity ratio & with respect to hydrodynamic journal bearing.
Q3/A/ What are the major factors which affect the selection of lubricants?
B/What are the criteria to classify sliding bearings?
C/ Answer of the following:
1. According to the SAE viscosity classification, the oil (SAE 40) is lower viscosity than the
oil (SAE 20) at the same temperature. (True or False)
2. For a slow speed-highly loaded bearing, used oils of high viscosity; while for high-speed…
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