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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. SuR+Vv
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(4) The lubricating method of a journal bearing is dependent on . {EjzJr>
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(7) The axial preloading for rolling bearings is for _______. ?@^gpVK{
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(8) The inner ring and outer ring of the bearing are separable. "[sr0 'g:
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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 _______. y:Ag mr
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(10) For a cylindrical helical compressive spring, the maximal shear stress on spring wire happens at the ______. RJ-J/NhWyI
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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 _____. %6x3 G
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(12) For a static balanced rigid rotor, its mass center is located at the rotating axis. [4-u{Tu
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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 _________. BPu>_$C
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(15) In order to decrease the flywheel weight, the flywheel should be installed on the 。 @_?
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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. #e;\Eap
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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. \'40u|f
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(1) Determine the loads carried by the shaft and shaft types in each structure scheme. *tda_B
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(2) Determine the stresses on the shaft and their changing characteristics in each structure scheme. ivbuS-f =r
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(3) Compare the strength difference of the four shafts. A8R}W=
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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. Te~"\`omJ3
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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 . U q&n e 1
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(1) Find the axial forces on the two bearings: , .
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(2) If , find the equivalent dynamic loads of the two bearings: , . (
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(3) Find the bearing lives: , .
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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 . sZPPS&KoP3
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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 . 0V"r$7(}
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(1) Find the equivalent driving moment of force.
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(2) Find the coefficient of speed fluctuation , maximal rotating speed and minimal rotating speed of the equivalent link. H`njKKdR
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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. s&iM.
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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.
