GATE Past Year Questions: Bearings
Q1: For a ball bearing, the fatigue life in millions or revolutions is given by L = (c/P)n, where P is the constant applied load and c is the basic dynamic load rating. Which one of the following statements is TRUE? [GATE ME 2024]
(a) n = 3, assuming that the inner racing is fixed and outer racing is revolving.
(b) n = 1/3, assuming that the outer racing is fixed and the inner racing is revolving
(c) n = 3, assuming that the outer racing is fixed and inner racing is revolving
(d) n = 1/3, assuming that the inner racing is fixed and outer racing is revolving
Ans: (c)
L = (C/P)n x 106 rev
n = 3 for ball bearing
n = 10/3 for roller bearing
Q1: A shaft AC rotating at a constant speed carries a thin pulley of radius r = 0.4m at the end C which drives a belt. A motor is coupled at the end A of the shaft such that it applies a torque Mz about the shaft axis without causing any bending moment. The shaft is mounted on narrow frictionless bearings at A and B where AB = BC = L = 0.5m. The taut and slack side tensions of the belt are T1 = 300N and T2 = 100N, respectively. The allowable shear stress for the shaft material is 80 MPa. The selfweights of the pulley and the shaft are negligible. Use the value of π available in the on-screen virtual calculator. Neglecting shock and fatigue loading and assuming maximum shear stress theory, the minimum required shaft diameter is _______ mm (round off to 2 decimal places). [GATE ME 2022 SET-2]
Ans: 23.6 to 24.2
Mₘₐₓ = 400 × L = 400 × 0.5 × 10³
= 200 × 10³ N·mm
Tₘₐₓ = Mz
= (T₁ - T₁) × r
= (200 × 0.4) × 10³
Tₘₐₓ = 80 × 10³ N·mm
Here section-B is critical due to loading,
Critical particle :
According to maximum shear stress theory,
⇒ d = 23.94 mm
Q2: A shaft of length L is made of two materials, one in the inner core and the other in the outer rim, and the two are perfectly joined together (no slip at the interface) along the entire length of the shaft. The diameter of the inner core is di and the external diameter of the rim is do, as shown in the figure. The modulus of rigidity of the core and rim materials are Gi and Go, respectively. It is given that do do = 2di and Gi = 3Go. When the shaft is twisted by application of a torque along the shaft axis, the maximum shear stress developed in the outer rim and the inner core turn out to be τo and τi, respectively. All the deformations are in the elastic range and stress strain relations are linear. Then the ratio τi/τo is ______ (round off to 2 decimal places). [GATE ME 2022 SET-2]
Ans: Given Gi = 3Go, do = 2di, li = lo, θi = θo (It is a rigid joint)
Find Ti/To =?
τmax(in core) = 
Try yourself: Which of the bearings given below SHOULD NOT be subjected to a thrust load? [2016,Set-3]
Try yourself: Two identical ball bearings Pand Q are operating at loads 30 kN and 45 kN respectively. The ratio of the life of bearing P to the life of bearing Q is [2011]
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Try yourself: A Journal bearing has a shaft diameter of 40 mm and a length of 40 mm. The shaft is rotating at 20 rad/s and the viscosity of the lubricant is 20 mPa.s. The clearance is 0.020 mm. The loss of torque due to the viscosity of the lubricant is approximately [2008]
Try yourself: A natural feed Journal bearing of diameter 50 mm and length 50 mm operating at 20 revolution/sec. carries a load of 2.0 kN. The lubricant used has a viscosity of 20 mPa.s. The radial clearance is 50 mm. The Sommerfield number for the bearings is [2007]
Try yourself: A ball bearing operating at a load F has 8000 hours of life. The life of the bearing, in hours, when the load is doubled to 2F is [2007]
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Try yourself: Spherical roller bearings are normally used [1992]
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Try yourself: The expected life of a ball bearing subjected to a load of 9800 N and working at 1000 rpm is 3000 hours. What is the expected life of the same bearing for a similar load of 4900 N and speed of 2000 rpm? [1987]
FAQs on GATE Past Year Questions: Bearings
| 1. What are the different types of bearings used in mechanical engineering? |  |
| 2. How do you calculate the load capacity of bearings? | |
| 3. What is the significance of bearing life in mechanical systems? | |
| 4. What factors should be considered when selecting a bearing for a specific application? | |
| 5. How can improper lubrication affect bearing performance? | |
