tailieunhanh - Engineering Tribology 2E Episode 9

Tham khảo tài liệu 'engineering tribology 2e episode 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 336 Engineering Tribology If the contacting solids are of the same material then their thermal constants are also the same and the above equation can be written as T _ p W - I . 740 2l 2b .5 K pơ .5 . or in terms of the reduced radius of curvature R and Young s modulus E as T _ p UA .5 - UB .5 k W T TE T25 K pa .5 2l R where E is the reduced Young s modulus Pa . For two solids of the same material E Ea 1 - u A2 Eb 1 - u B2 R is the reduced radius of curvature of the undeformed surfaces m . or in terms of maximum contact pressure as T maxc p Pm W K pơ .5 - UB .5 R T5 E where pmax is the maximum contact pressure Pa . Although the procedure outlined does not always provide precise values of the temperature distribution over the entire interface between contacting solids it greatly facilitates the physical interpretation of frictional temperatures. For example consider a pin-on-disc machine with the pin and the disc manufactured from the same material. Since the pin is stationary low speed conditions of heat transfer apply whereas high speed conditions apply to the disc. The interfacial temperature of the disc will be very much lower than that of the pin since the disc is constantly presenting fresh cool material to the interface. Hence the temperature distribution at the interface will be mostly determined by the heat flow equations in the disc 44 49 . Another example of this effect which is more closely related to EHL is the difference in frictional temperatures between a large and a small gear-wheel when meshed together. The maximum flash temperature rise is located towards the trailing region of the contact and its location depends on the Peclet number as shown in Figure 47 . The maximum flash temperature distribution for high speed conditions in circular contacts is shown in Figure 44 . it can be seen that the maximum temperature is about Tfmax and occurs at the centre of the trailing edge of the contact. it .