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主题 : 东大机械设计考试样卷
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楼主  发表于: 2007-11-14   

东大机械设计考试样卷

(1)     For a tight bolted connection with transverse load, the bolt is carried by     . z\>ZgRi~n  
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A. shear stress             B. tensile stress 4ULdf|oP"  
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C. shear stress and tensile stress   D. shear stress or tensile stress |k]fY*z(  
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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       . D[` ~=y(  
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A.   B.   C.   D. ^(KDtc  
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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. <4TF ]5  
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A. 600       B. 800       C. 680       D. 480 b{;LbHq+G  
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(4)     The lubricating method of a journal bearing is dependent on     . 9&{HD  
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A. average intensity of pressure p   B. circle velocity of journal v   C. pv   D. `t+;[G>ZE  
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(5)     For a hydrodynamic radial journal bearing, the valid method for increasing is to     . G$2Pny<!  
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A. increase relative clearance     B. increase oil supply ,r; E[k@  
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C. decrease     D. replace lubricating oil with lower viscosity /!U(/  
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(6)     For a hydrodynamic radial journal bearing, the relative clearance is the ratio of     . oSl}A,aQ(  
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A. diametral clearance and journal diameter   B. radial clearance and journal diameter seb/rxb  
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C. minimal clearance and diametral clearance AR c   
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D. minimal clearance and journal diameter v)nBp\fjxp  
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(7)     The axial preloading for rolling bearings is for _______. %&wi@ *#  
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A. increasing loading capacity     B. decreasing noise zr wzI+4  
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C. improving running precision   D. avoiding shaft displacement QN#tj$x  
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(8)     The inner ring and outer ring of the     bearing are separable. e@PY(#ru  
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A. deep-groove ball   B. self-aligning ball   C. tapered roller   D. self-aligning roller M$} AJS%8  
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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-eHX3c7  
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A.     B.     C.     D. uncertain _jaB[Q=By  
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(10)   For a cylindrical helical compressive spring, the maximal shear stress on spring wire happens at the ______. N w/it *f  
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A. inner side of spring coil   B. outer side of spring coil #V y:6O  
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C. center of spring wire     D. arbitrary position on spring wire Lc(eY{CY  
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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 _____. (UZ].+)s  
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A. decreased to 3/4 of the original value   B. decreased to 9/16 of the original value PgsG *5WQ  
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C. not changed         D. increased to 4/3 of the original value  hRqr  
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(12)   For a static balanced rigid rotor, its mass center is     located at the rotating axis. w17CZa 6  
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A. certainly       B. not always       C. certainly not u,]qrlx{  
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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 _________. uvi&! )x  
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A. static imbalance   B. static balance   C. complete imbalance   D. dynamic balance _/YM@%d  
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(14)   The installation of flywheel in machinery is to       . x+v&3YF  
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A. eliminate speed fluctuation     B. realize steady running lHE \Z`  
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C. decrease speed fluctuation     D. balance the inertia forces :k2 J &@8  
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(15)   In order to decrease the flywheel weight, the flywheel should be installed on the       。 uH#X:Vne  
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A. equivalent link               B. crankshaft with lower rotating speed /v.<h*hxWy  
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C. crankshaft with higher rotating speed   D. spindle of machinery Pfd%[C/vdm  
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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. 4\j1+&W   
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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. \_+Af`  
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(1)   Determine the loads carried by the shaft and shaft types in each structure scheme. "T}HH  
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(2)   Determine the stresses on the shaft and their changing characteristics in each structure scheme. YLV$#a3  
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(3)   Compare the strength difference of the four shafts. 7f~7vydZ}  
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(a)             (b)           (c)             (d) WhV>]B2+"  
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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. Rs 0Gqx  
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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 . 'gz@UE1  
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(1)   Find the axial forces on the two bearings: , . YZ+<+`Mz<  
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(2)   If , find the equivalent dynamic loads of the two bearings: , . ?I#zcD)w  
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(3)   Find the bearing lives: , . 5nG$6Hw  
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6.     (15 points) In a gear train shown in the figure, , , , , , , , , , the rotating direction of the gear 1 is as shown in the figure. Find both the magnitude and the direction of . ZKa.MBde  
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7.     (15 points) Shown in Fig. (a) is the dynamically equivalent model of a mechanical system. The equivalent resistant moment of force is a given function of the rotating angle shown in Fig. (b) with the period . The equivalent driving moment of force is constant. The equivalent moment of inertia of the system is (constant). The average rotating speed of the equivalent link is . ^ cn)eA  
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(1)   Find the equivalent driving moment of force. L;0ZB=3n  
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(2)   Find the coefficient of speed fluctuation , maximal rotating speed and minimal rotating speed of the equivalent link. F$FCfP7  
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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. .h2K$(/  
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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.
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