东大机械设计考试样卷

(1)     For a tight bolted connection with transverse load, the bolt is carried by     . f[ GH  
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C. shear stress and tensile stress   D. shear stress or tensile stress wQb")3dw  
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(2)     For a tight bolted connection with axial tensile load F and preload , the resultant tensile force in the bolt is       . s['F?GWg  
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(3)     If the performance grade of a bolt is 6.8, then the yield limit stress of the bolt material is       MPa. 6VolT y@(x  
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A. 600       B. 800       C. 680       D. 480 &of %;>$>M  
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(4)     The lubricating method of a journal bearing is dependent on     . ~zRUJ2hD!  
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(5)     For a hydrodynamic radial journal bearing, the valid method for increasing is to     . zdyS"H}  
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C. decrease     D. replace lubricating oil with lower viscosity E~2}rK+#)  
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(6)     For a hydrodynamic radial journal bearing, the relative clearance is the ratio of     . >T.U\,om7  
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A. diametral clearance and journal diameter   B. radial clearance and journal diameter  (8@._  
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D. minimal clearance and journal diameter $4>K2  
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(7)     The axial preloading for rolling bearings is for _______. LEc%BQx  
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A. increasing loading capacity     B. decreasing noise }7X85@jC  
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C. improving running precision   D. avoiding shaft displacement QlSZr[^v  
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(8)     The inner ring and outer ring of the     bearing are separable. [j eZZB  
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A. deep-groove ball   B. self-aligning ball   C. tapered roller   D. self-aligning roller :a0qm.EN  
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(9)     In an important application, if the reliability of rolling bearings is increased to 95%, then the relation between the dynamic load rating relative to 95% reliability to the basic dynamic load rating C is _______. H^B/ '#mO  
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(10)   For a cylindrical helical compressive spring, the maximal shear stress on spring wire happens at the ______. Zc{
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(11)   For a cylindrical helical compressive spring with working coils being 12, if the number of working coils is decreased by 3, then spring stiffness is _____. L V?- g  
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A. decreased to 3/4 of the original value   B. decreased to 9/16 of the original value C^2Tql  
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(12)   For a static balanced rigid rotor, its mass center is     located at the rotating axis. f-k%P$"X&  
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(13)   Shown in the figure is a cylindrical cam with uniform material, accurate manufacture and installation. When it rotates round the axis A-A, the cam is under the state of _________. MQG(n+c  
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A. static imbalance   B. static balance   C. complete imbalance   D. dynamic balance p[!&D}&6h  
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(14)   The installation of flywheel in machinery is to       . U6t>UE6k  
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A. eliminate speed fluctuation     B. realize steady running pV9$Vg?-H  
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C. decrease speed fluctuation     D. balance the inertia forces \xlelsmB*  
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(15)   In order to decrease the flywheel weight, the flywheel should be installed on the       。 ^RAs t1q7  
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A. equivalent link               B. crankshaft with lower rotating speed jdiH9]&U  
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C. crankshaft with higher rotating speed   D. spindle of machinery M4w,J2_8MK  
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2.     (7 points) In a tight bolted connection with axial tensile load, both the preload and the axial working load are constant. If the metal gasket between the connected components is replaced by a leather one, explain, with force-deformation diagram, the changes of the resultant tensile force in the bolt and residual compressive force on the connected components. uD0T()J.P5  
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3.     (10 points) Shown in the figure are the four structure schemes of the moving pulley shaft system in a lifting device. In each structure scheme, the lifting load is constant; the shaft diameter, shaft material and method of heat treatment are the same, respectively. C&|K7Zp0v  
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(1)   Determine the loads carried by the shaft and shaft types in each structure scheme. 7f] qCZ<0V  
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(2)   Determine the stresses on the shaft and their changing characteristics in each structure scheme. [ s4|+  
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(3)   Compare the strength difference of the four shafts. ^'\JI  
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4.     (8 points) Shown in the figure is a transmission layout for a belted conveyer. The arrangement for speed reduction is as follows: 1(motor)→2(chain drive)→3(gear reducer)→4(belt drive)→5(conveyer). Point out the unreasonable aspects of the arrangement and give a correct order represented with the drive number. <6Y|vEo!N  
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5.     (15 points) Shown in the figure, a helical gear shaft is supported by a pair of angular contact ball bearings (7208AC) with ; the radial loads acting on the bearings are , ; the externally axial load on the shaft is ; the rotating speed of the shaft is . n}b{u@$  
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(1)   Find the axial forces on the two bearings: , . R?zlZS.~  
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(2)   If , find the equivalent dynamic loads of the two bearings: , . A_l\ij$Y  
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(3)   Find the bearing lives: , . ~j>
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6.     (15 points) In a gear train shown in the figure, , , , , , , , , , the rotating direction of the gear 1 is as shown in the figure. Find both the magnitude and the direction of . Op8Gj `  
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7.     (15 points) Shown in Fig. (a) is the dynamically equivalent model of a mechanical system. The equivalent resistant moment of force is a given function of the rotating angle shown in Fig. (b) with the period . The equivalent driving moment of force is constant. The equivalent moment of inertia of the system is (constant). The average rotating speed of the equivalent link is . *z6A ~U  
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(1)   Find the equivalent driving moment of force. :R +BC2x  
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(2)   Find the coefficient of speed fluctuation , maximal rotating speed and minimal rotating speed of the equivalent link. Tc!n@!RA|  
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(3)   If the allowable coefficient of speed fluctuation is , find the minimum moment of inertia of the flywheel on the crankshaft A of the equivalent link. !SE  
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8.     (15 points) Point out all the mistakes in the shaft system shown in the figure and explain them with brief words.