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Bearing Design in Machinery Episode 2 Part 8

Tham khảo tài liệu 'bearing design in machinery episode 2 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | static radial capacity Cor. In Manufacturers catalogues this value is based on a limit stress of 4.2 GPa 609 000 psi for 52100 steel and 3.5 GPa 508 000 psi for 440C stainless steel. The static radial capacity Cor is based on the peak load Wmax on one rolling element as well as additional transient and momentary overload on the same rolling element during start-up and steady operation. At these ultimate pressure levels the assumption of pure elastic deformation is not completely correct because a minute plastic irreversible deformation occurs. For most applications the microscopic plastic depression does not create a noticeable effect and it does not cause a significant microcracking that can reduce the fatigue life. However in applications that require extremely quiet or uniform rotation a lower stress limit is usually imposed. For example for bearings in satellite antenna tracking actuators a static stress limit of only 2.2 GPa 320 000 psi is allowed on bearings made of 440C steel. This limit is because plastic deformation must be minimized for accurate functioning of the mechanism. 12.4 THEORETICAL LINE CONTACT If a load is removed there is only a line contact between a cylinder and a plane. However under load there is an elastic deformation at the contact and the line contact becomes a rectangular contact area. The width of the contact is 2a as shown in Fig. 12-11. The magnitude of a half-contact width can be determined by the equation 12-2a Fig. 12-11 Contact area of a cylinder and a plane. Copyright 2003 by Marcel Dekker Inc. All Rights Reserved. Here the dimensionless load IF is defined by W W LEeqRx 12-2b The load W acts on the contact area. The effective length of the cylinder is L and Eeq is the equivalent modulus of elasticity. In this case Rx is an equivalent contact radius which will be discussed in Sec. 12.4.2. For a contact of two different materials the equivalent modulus of elasticity Eeq is determined by the following expression 2 c 1 _ V2 1 _ v2