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Tham khảo tài liệu 'friction and lubrication in mechanical design episode 1 part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 130 Chapter 5 Figure 5.6 shows a plot of these relationships for tữ tL 0.25 0.5 and 0.75 respectively. The principle of superposition can be applied to determine the surface temperature rise for any given function of heat flux. It can be determined either as a summation or an integration of the effect of incremental step inputs that convolute the given function. An illustration of this is the study of the effect of applying the same total quantity of heat input with a triangular flux with the same maximum value but with different slopes Sj and s2 during the increase and decrease phases respectively. Using the integration approach therefore t 0 - i0. AĨ 0 1.12Ố - dx J Jkpc 0 AT i i 1.12S - dx- 1.12S2 dx J y kpc J yjkpc 0 0 t k Figure 5.8 Temperature rise as a function of time on the surface of a steel slab subjected to constatn flux q for different periods . Thermal Considerations in Tribology 131 Figures 5.7-5.11 show plots of the surface temperature history for 9 4 1 ị and 5 respectively. Figure 5.12 shows the maximum surface temperature as a function of S1 S2 for the same total heat flow max. It can be seen from Fig. 5.12 that the highest surface temperature rise occurs as the ratio Sị S2 decreases. If the heat flux function is determined from experimental data and is difficult to integrate the temperature rise can be obtained by summing the effects of incremental steps that are constructed to convolute the function as illustrated in Fig. 5.13. Better accuracy can be obtained as the number of steps increases. The temperature rise at the surface for this case can be calculated as t ti - t2 1 2 3. t li - _ 1.12 AT V7 - h s kpc 112 4 I A T 22 V I 42 - 41 7 - 2 1 12 4 s A T 22 41 h 2 4i 5 7 2 yjkpc1 0 2 4 6 6 to Time sec Figure 5.7 Temperature rise on the surface of a steel slab due to a total heat input q applied at different rates to h 0.1 . 3.0 1.5 Figure 5.8 Temperature rise on the surface due to a total heat input q applied at different rates t i 0.2 .
