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16_ch 07 Mechanical Design budynas_SM_ch07

16_ch 07 Mechanical Design budynas_SM_ch07 -...

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Chapter 7 193 x ( mm (rad) F.E. Model Full F.E. Model 0 0.001 4260 0.001 4270 0.001 4160 140 0.000 1466 0.000 1467 0.000 1646 315 0.001 3120 0.001 3280 0.001 3150 The main discrepancy between the results is at the gear location ( x = 140 mm) . The larger value in the full model is caused by the stiffer 55 mm diameter step. As was stated earlier, this step is not as stiff as modeling implicates, so the exact answer is somewhere between the full model and the simpliﬁed model which in any event is a small value. As expected, mod- eling the 30 mm dia. as 35 mm does not affect the results much. It can be seen that the allowable slopes at the bearings are exceeded. Thus, either the load has to be reduced or the shaft “beefed” up. If the allowable slope is 0.001 rad, then the max- imum load should be F max = (0 . 001 / 0 . 001 46)7 = 4 . 79 kN. With a design factor this would be reduced further. To increase the stiffness of the shaft, increase the diameters by (0 . 001 46 / 0 . 001) 1 / 4 = 1 . 097, from Eq. (7-18). Form a table: Old d , mm 20.00 30.00 35.00 40.00 45.00 55.00 New ideal d , mm 21.95 32.92 38.41 43.89 49.38 60.35 Rounded up d , mm 22.00 34.00 40.00 44.00 50.00 62.00
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