(1) For a tight bolted connection with transverse load, the bolt is carried by . ;17E(tl
dm\F
A. shear stress B. tensile stress <}C
o
Qz
?1~` *LE
C. shear stress and tensile stress D. shear stress or tensile stress R`NYEptJ
ejSji-Qd
(2) For a tight bolted connection with axial tensile load F and preload , the resultant tensile force in the bolt is . 9 P l
Wf+cDpK
A. B. C. D. >FeX<L
h79}qU
(3) If the performance grade of a bolt is 6.8, then the yield limit stress of the bolt material is MPa. ` 'DmDg
k
= >oO9`
A. 600 B. 800 C. 680 D. 480 4>wP7`/+y
Zu*F#s!tUI
(4) The lubricating method of a journal bearing is dependent on . Y`~Ut:fZ
<
$D`Z-6
A. average intensity of pressure p B. circle velocity of journal v C. pv D. N=V==Dbu-
OAgniLv
(5) For a hydrodynamic radial journal bearing, the valid method for increasing is to . AP3a;4Z#
y6g&Y. :o
A. increase relative clearance B. increase oil supply A kq2 d;
/!0={G
C. decrease D. replace lubricating oil with lower viscosity { a =#B)6
z<MsKD0Q
(6) For a hydrodynamic radial journal bearing, the relative clearance is the ratio of . [*Z;\ 5&P
(Lb bc+1m
A. diametral clearance and journal diameter B. radial clearance and journal diameter D, k6$`
_qF+tm
C. minimal clearance and diametral clearance dn& s *
})'B<vq
D. minimal clearance and journal diameter M`0V~P`^
d9k0F
OR1
(7) The axial preloading for rolling bearings is for _______. kXViWOXU^
[C Y9^N
A. increasing loading capacity B. decreasing noise P?%s
#I:
xw.A #Zb\_
C. improving running precision D. avoiding shaft displacement ~?l |
[
1 v y* {D
(8) The inner ring and outer ring of the bearing are separable. C2!|OQ9A2
aHD]k8 m z
A. deep-groove ball B. self-aligning ball C. tapered roller D. self-aligning roller <]o
x;-56
[DuttFX^x
(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 _______. W" scV@HKu
<|HV. O/!
A. B. C. D. uncertain #`^ }PuQ
[+^1.N
(10) For a cylindrical helical compressive spring, the maximal shear stress on spring wire happens at the ______. GC-5X`Sq
Y/F6\oh
A. inner side of spring coil B. outer side of spring coil I^.Om])
Cp\6W[2+B
C. center of spring wire D. arbitrary position on spring wire y
R qL9t
_;"il%l=1
(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 _____. PI { bmZ
x>K Or,f
A. decreased to 3/4 of the original value B. decreased to 9/16 of the original value 3l~^06D
&C_j\7Dq
C. not changed D. increased to 4/3 of the original value m!!/Za
MpT8" /.]A
(12) For a static balanced rigid rotor, its mass center is located at the rotating axis. hgG9m[?K
r `=I
A. certainly B. not always C. certainly not L(6d&t'|-R
gT. sj d
(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 _________. b=C*W,Q_#
ZvM(Q=^
A. static imbalance B. static balance C. complete imbalance D. dynamic balance qz_7%c]K[
LE Nq_@$
_;S- x
J3V=
46Yc
(14) The installation of flywheel in machinery is to . ;?Tbnn Wn
6_o*y 8s.
A. eliminate speed fluctuation B. realize steady running s[>,X#7 y
C^Yb\N}S
C. decrease speed fluctuation D. balance the inertia forces ?FZ HrA
P= BZ+6DS
(15) In order to decrease the flywheel weight, the flywheel should be installed on the 。 =ZznFVJ`={
Evq IcZ
A. equivalent link B. crankshaft with lower rotating speed y-b%T|p9
WDYeOtc
C. crankshaft with higher rotating speed D. spindle of machinery tKuwpT 1Qc
Tk[ $5u*,
e)k9dOR
8NJqV+jn)t
2. (7 points) In a tight bolted connection with axial tensile load, both the preload and the axial working load are constant. If the metal gasket between the connected components is replaced by a leather one, explain, with force-deformation diagram, the changes of the resultant tensile force in the bolt and residual compressive force on the connected components. t>RY7C;PuS
3pROf#M
%IA\pSE
~vhE |f
O:R*rJ
FX&~\kmV'j
1-uxC^u?|#
?=7 cF
:pY/-Cgv
+o{R _
> >)b
'c
2wg5#i
8'[7
)I=
eK =xrk
re?,Wext\
/Iy]DU8
^mDe08.
%b
ou lVg];
HZB>{O
Sq V},
(t
K||*u
(N6 i4
g6
sf
qL|8
k,6f
&#x
"Yv_B3p
.G XBc
Gr'
CtO
h 8S. x)
orpri O|qD
[A~xy'T
3. (10 points) Shown in the figure are the four structure schemes of the moving pulley shaft system in a lifting device. In each structure scheme, the lifting load is constant; the shaft diameter, shaft material and method of heat treatment are the same, respectively. ZohC
P
CS5?Ti6
(1) Determine the loads carried by the shaft and shaft types in each structure scheme. (O?.)jEW(.
faX #**r
(2) Determine the stresses on the shaft and their changing characteristics in each structure scheme. Jb@
V}Ul$
@Zu5Vp J
(3) Compare the strength difference of the four shafts. ) 1f~ dR88
K~{$oD
7!
?0?#U0(;u
Ad8n<zt|
(a) (b) (c) (d) ;>yxNGV`
2DtM20<>
Egp/f |y
mt{nm[D!Xp
u@UMP@"#
x b~yM%*c
|(E
FY\
O)*+="Rg
uA Jx.>$b
?m}s 4a
4y?n
[/M/
M*, -zGr
,{u
yG:
A@[o;H }XP
5|j<`()H
:
Lv;^My
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. 5y [Oj^
D9=KXo^
t7Iv?5]N
|!3DPA(_
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 . w !-gJmX>
8B
K(4?gC
(1) Find the axial forces on the two bearings: , . %9F([K
?} tFN_X"
(2) If , find the equivalent dynamic loads of the two bearings: , . q s6]-
x_N'TjS^{
(3) Find the bearing lives: , . &tLgG4pd
kX7C3qdmt
nLZTK&7}
A5I)^B<(
s 8jV(P(O
_ @NL;w:!
X 8a/ ` Y,
3=P]x ;[ba
NqazpB*
# Yj 1w
'6iEMg&3
jjB~ G^n
O~#!l"0 L+
K( c\wr\6
Fx_z 6a
|PCm01NU!
VX0 %a@ur
`_Zg3_K.dS
wY{-BuX v
;s = l52
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 . E1 aHKjLQ
e\`&p
Tj` ,Z5vy
>-RQ] ?^
lBL ARz&c#
,GhS[VJjR
YlJ@XpKM
CAig ]=2'
\j}ZB<.>
\_VA 5 0
$lfn(b,
GE:vp>>}`
7. (15 points) Shown in Fig. (a) is the dynamically equivalent model of a mechanical system. The equivalent resistant moment of force is a given function of the rotating angle shown in Fig. (b) with the period . The equivalent driving moment of force is constant. The equivalent moment of inertia of the system is (constant). The average rotating speed of the equivalent link is . w _
"E*9
}1L4 "}L.
(1) Find the equivalent driving moment of force. [ :
n'k
&T?RZ2
(2) Find the coefficient of speed fluctuation , maximal rotating speed and minimal rotating speed of the equivalent link. kr ^P6}'
T$)^
gHS
(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. L:$ ,v^2
Y #ap*
/Iu 1L#
kf\PioD8
b"<liGh"n-
:[.vM
6fE7W>la
4B8 oO
5 9
T 8r
)W,aN)1)
@(EAq<5{
XAD- 'i
W]$w@.oW[
CCs%%U/=
:I.mGH!^
p %up)]?0
\i>?q
|"q5sym8Y_
rm'SO JVA
M><yGaaX/
nUaJz
Pl
j.[.1 G*("
q^@Q"J =v
^ x ]r`b
Po+.&7F
%_H<:uGO%
pHGY Q;:L
x
`eo"5.$
4!{KWL `A
n1ZbRV
^cC,.
Fdw
c1(R
uP:S
)N{Pw$l_
(Bb5? fw
PudS2k_Qv
@Rze|
T.
6xmZXp d!
e-/&$Qq
r.=K~A
KJUH(] >F
C\3rJy(VJ
/|m2WxK)
8. (15 points) Point out all the mistakes in the shaft system shown in the figure and explain them with brief words.
