东大机械设计考试样卷

(1)     For a tight bolted connection with transverse load, the bolt is carried by     . ]JR2Av  
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C. shear stress and tensile stress   D. shear stress or tensile stress Wn{MY=5Y  
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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       . 6p9 {z42  
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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. #KNl<V+c}1  
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A. 600       B. 800       C. 680       D. 480 Vr@tSc&  
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(4)     The lubricating method of a journal bearing is dependent on     . on;>iKta9  
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A. average intensity of pressure p   B. circle velocity of journal v   C. pv   D. Gr>CdB>~+  
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(5)     For a hydrodynamic radial journal bearing, the valid method for increasing is to     . XG!6[o;  
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C. decrease     D. replace lubricating oil with lower viscosity N:CQ$7T{ j  
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(6)     For a hydrodynamic radial journal bearing, the relative clearance is the ratio of     . PxQQfI>  
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A. diametral clearance and journal diameter   B. radial clearance and journal diameter PU[<sr#,  
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C. minimal clearance and diametral clearance `qYii
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D. minimal clearance and journal diameter [& Z- *a  
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(7)     The axial preloading for rolling bearings is for _______. a5R. \a<q  
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A. increasing loading capacity     B. decreasing noise /a<UKh:A[  
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C. improving running precision   D. avoiding shaft displacement [^?i<z{0C  
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(8)     The inner ring and outer ring of the     bearing are separable. c|JQ0] K  
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A. deep-groove ball   B. self-aligning ball   C. tapered roller   D. self-aligning roller ]{q=9DczG(  
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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 _______.
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A.     B.     C.     D. uncertain 4r` I)  
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(10)   For a cylindrical helical compressive spring, the maximal shear stress on spring wire happens at the ______. _B#x{ii  
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C. center of spring wire     D. arbitrary position on spring wire g- wE(L  
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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 _____. Pg8boN]}  
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A. decreased to 3/4 of the original value   B. decreased to 9/16 of the original value W{.:Cf9  
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(12)   For a static balanced rigid rotor, its mass center is     located at the rotating axis. \t1#5  
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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 _________.
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A. static imbalance   B. static balance   C. complete imbalance   D. dynamic balance 8tR6.09'  
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(14)   The installation of flywheel in machinery is to       . >*gf
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C. decrease speed fluctuation     D. balance the inertia forces {$[0YRNk u  
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(15)   In order to decrease the flywheel weight, the flywheel should be installed on the       。 Gdb0e]Vt+  
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A. equivalent link               B. crankshaft with lower rotating speed "?6*W"N9  
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C. crankshaft with higher rotating speed   D. spindle of machinery M5+R8ttc  
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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. jWxa [>  
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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. ug`Jn&x!  
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(1)   Determine the loads carried by the shaft and shaft types in each structure scheme. J]*?_>"#8  
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(2)   Determine the stresses on the shaft and their changing characteristics in each structure scheme. +N:M;uTS  
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(3)   Compare the strength difference of the four shafts. ?O e,  
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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. ?wS/KEl=O  
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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 . /F6=iHK(l  
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(1)   Find the axial forces on the two bearings: , . )o8]MWT\;  
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(2)   If , find the equivalent dynamic loads of the two bearings: , . q
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(3)   Find the bearing lives: , . 9W<I~  
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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 . .'
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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 . 4|ryt4B  
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(1)   Find the equivalent driving moment of force. b{C3r3B8  
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(2)   Find the coefficient of speed fluctuation , maximal rotating speed and minimal rotating speed of the equivalent link. sglYT!O  
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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. ef\Pu\'U  
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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.