Archive of Applied Mechanics 71 (2001) 221±232 Ó Springer-Verlag 2001
Temperature and stress analysis of an elastic circular cylinder in contact with heated rigid stamps F. Ashida
Summary The present paper discusses a plane strain problem of transient thermoelasticity in a circular cylinder which is in partial contact with two heated rigid stamps, in the case where the coef®cient of relative heat transfer on the contact surface of the cylinder is different from that on the traction-free surface. A ®nite difference method with respect to the time variable and Airy's thermal stress function is employed to analyze the temperature and thermoelastic ®elds. The problem is formulated in terms of two dual-series equations derived not only from the thermal boundary conditions but also from the mechanical boundary conditions. Since the radial, hoop and axial stresses have singularities at the end of the contact surface of the cylinder, the stress singularity coef®cients are de®ned and then the relationship among these three coef®cients is also obtained. Finally, numerical results are illustrated graphically. Key words stress singularity, asymmetric contact, circular cylinder, thermoelasticity, plane strain
1 Introduction When a structural body in contact with another body is subjected to a thermal load, stresses produced in the body concentrate at the end of the contact surface. The stress concentration may lead to a crack at the end of the contact surface so that the structural body may fracture. Evaluation of the stress concentration is very important for the safety of the structural body in service. Therefore, many papers have dealt with various thermoelastic contact problems, [1, 2]. Among the recent investigations in thermoelastic contact, [3] discussed uniqueness and continuous dependence of solutions to a contact problem of thermoelasticity. Steady thermoelastic contact problems in an elastic half-space and a rigid body were solved in [4], [5] and [6]. Papers [7] and [8] investigated the stress singularity in bonded dissimilar materials, while [9] analyzed a steady thermoelastic contact problem in two plates with bolted joints by means of a ®nite element method. In papers [10], [11] and [12] axisymmetric contact problems of steady thermoelasticity with frictional heating were studied on the assumption that the shearing stress on the contact surface was negligible. However, the models analyzed in these papers are semi-in®nite bodies, semi-in®nite quarter bodies and plates with ¯at surfaces. In contrast, thermoelastic contact problems in circular cylinders have attracted little attention. Axisymmetric contact problems in isotropic circular cylinders inserted into rigid rings were solved in [13±15], while similar problems in transversely isotropic circular cylinders inserted into rigid rings were analyzed in [16±18]. Although there are many structural systems whose components are in asymmetric contact with other bodies, an asymmetric contact problem of thermoelasticity in a circular cylinder has not been analyzed. The present paper deals with a plane strain problem of transient thermoelasticity in a circular cylinder which is in partial contact with two heated rigid stamps. It is assumed that the coef®cient of relative heat transfer on the contact surface of the cylinder is different from that on the traction-free surface. This problem is analyzed by means of a ®nite difference formulation with respect to a time variable as well as of Airy's thermal stress function. Stress singularity coef®cients are derived from the radial, hoop and axial stresses. Numerical results for Received 3 March 2000; accepted for publication 12 July 2000 F. Ashida Department of Electronic and Control Systems Engineering, Shimane University, Matsue 690-8504, Japan e-mail:
[email protected]
221
the temperature, radial displacement, radial stress and stress singularity coef®cient are illustrated graphically.
222
2 Analysis Let us analyze a transient thermoelastic problem in a circular cylinder which is in partial contact with two heated rigid stamps without friction, as shown in Fig. 1. In order to simplify the analysis of this problem, it is presumed that the thermal and mechanical conditions of the cylinder are symmetric with respect to x and y axes. Therefore, we only have to analyze the thermal and elastic ®elds in the ®rst quadrant. Moreover, assuming that the cylinder and rigid stamps are long and the heating temperature distributes uniformly in the axial direction, this problem can be reduced to a plane strain problem. 2.1 Temperature field It is assumed that the cylinder, initially at uniform zero temperature, is suddenly subjected to heating temperature on the contact surface. Then, the initial and boundary conditions for the temperature ®eld are given by T 0 at t 0 ;
1
T;r h1 T h1 T0 q
h; T;r h2 T 0;
0 h < h0 ; h0 < h p2 ;
on r a ;
2
where T is temperature, t is time, h1 and h2 are coef®cients of relative heat transfer on the contact and traction-free surfaces, T0 denotes constant temperature, q
h is a prescribed function assumed to be
q
h q
h q
p
h ;
and the comma denotes partial differentiation with respect to variable. The temperature is governed by Fourier's heat conduction equation
r2 T j 1 T;t ;
3
where j is thermal diffusivity and
r2
o2 r or2
1
o r or
2
o : oh2
Since it is dif®cult to solve the governing equation (3) under the initial and boundary conditions (1) and (2) by means of the Laplace transform technique, a ®nite difference formulation with respect to the time variable, [17], is introduced. The time variable is given by
Fig. 1. Geometry of a circular cylinder in asymmetric contact with two rigid stamps
j X
tj
Dtk ;
4
k1
where Dtk are time differences. The temperature is expressed as
Tj
j X
wjk DTk ;
5
k1
where DTk are temperature differences and
wjk djk
1
223
w
j 1k Dtk djk ; Dtk Dtj
6
in which djk is Kronecker's delta. Considering the initial condition (1), Eqs. (3) and (2) become
r2
DTj
DTj 0 ; jDtj
7
DTj ;r h1 DTj Dj q
h;
DTj ;r h2 DTj 0;
0 h < h0 ; h0 < h p2 ;
on r a ;
8
where
Dj h1 T0
1
d1j
j 1 X
wjk Dk :
9
k1
The solution for Eq. (7) is taken to be
DTj
1 X n0
A2nj I2n
sj r cos
2nh ;
10
where A2nj are unknown coef®cients, In
r are the modi®ed Bessel function of the ®rst kind and
1 sj p : jDtj
11
Substituting Eq. (10) into Eqs. (8), a dual-series equation is obtained 1 X n0 1 X n0
U2nj E2nj cos
2nh Dj q
h; E2nj cos
2nh 0;
0 h < h0 ;
p h0 < h ; 2
12
where E2nj are unknown coef®cients related to the unknown coef®cients A2nj and U2nj are known coef®cients as follows:
E2nj
2n h2 I2n
sj a sj I2n1
sj a ; A2nj a
U2nj
2n h1 aI2n
sj a sj aI2n1
sj a :
2n h2 aI2n
sj a sj aI2n1
sj a
13
14
In order to solve Eqs. (12), we introduce the following series, which identically satis®es the second of Eqs. (12)
1 h0 X
1l xlj fJ2l2
2nh0 J2l
2nh0 g ; 1 dn0 l0
E2nj
15
where xlj are new unknown coef®cients and Jl
h are the Bessel functions of the ®rst kind. Substituting Eq. (15) into the ®rst of Eqs. (12) and applying the series
q
h
1 X n0
224
q2n cos
2nh;
4 q2n
1 dn0 p
Zh0 q
h cos
2nhdh ;
16
0
and
cos
2nh
1 X m0
em cos
2mbJ2m
2nh0 ;
h ; em 2 b sin h0 1
dm0 ;
17
the following in®nite system of simultaneous algebraic equations is obtained:
h0
1 X
1l xlj
l0
Dj
1 X n0
1 X U2nj fJ2l2
2nh0 J2l
2nh0 g n0
q2n Z2m
2nh0 ;
1 dn0
Z2m
2nh0
m 0; 1; 2; . . . ;
18
where
Z2m
c
m 3fJ2m
c
J2m4
cg
m 1fJ2m4
c
J2m8
cg :
19
Therefore, the unknown coef®cients xlj can be determined by solving the linear equations (18) numerically. Finally, substituting Eqs. (10) and (15) into Eqs. (5) and (13), respectively, the temperature is given by
Tj
j X k1
wjk
1 X n0
A2nk I2n
sk r cos
2nh ;
20
where
A2nj
P l h0 a 1 l0
1 xlj J2l2
2nh0 J2l
2nh0 :
1 dn0 f
2n h2 aI2n
sj a sj aI2n1
sj ag
21
2.2 Thermoelastic field The plane strain problem of transient thermoelasticity in a circular cylinder which is in partial contact with two rigid stamps, as shown in Fig. 1, can be analyzed by means of Airy's thermal stress function. Applying the ®nite difference formulation, Airy's thermal stress function vj at t tj is expressed as vj
j X k1
wjk Dvk ;
where Dvk are governed by
22
r2 r2
Dvj
aE 1
m
r2
DTj ;
23
in which a is the coef®cient of linear thermal expansion, E is the Young's modulus and m is the Poisson's ratio. The stress components are expressed in terms of Airy's thermal stress function as follows:
rrrj r 2 vj;hh r 1 vj;r ; rhhj vj;rr ; 2
rrhj r vj;h
24 1
r vj;hr :
225
The admissible solution for Eq. (23) is taken to be
Dvj
1 X
(
cos
2nh
n0
aE 1
I2n
sj r r2n2 r2n A2nj F G 2nj 2nj 2n 2 a2n a s2j m
) ;
25
where F2nj and G2nj are unknown coef®cients. Substituting Eq. (25) into Eqs. (22) and (24), the stress components are obtained as follows:
rrrj
) I2n
sk r I2n1
sk r A2nk 2n
2n 1 wjk cos
2nh 1 m sk r
sk r2 n0 k1 # r 2n r 2n 2 2
n 1
2n 1F2nk ; 2n
2n 1G2nk a a
rhhj
j X
"
1 X
(
! 2n
2n 1 A2nk I2n
sk r wjk cos
2nh 1 1 m
sk r2 n0 k1 # r 2n r 2n 2 ; 2n
2n 1G2nk 2
n 1
2n 1F2nk a a j X
"
1 X
rzzj m
rrrj rhhj rrhj
(
aE
aE
) I2n1
sk r sk r
aETj ; "
1 X
27
28
) 2n 1 I2n1
sk r 2 wjk n sin
2nh I2n
sk r A2nk 1 m sk r
sk r2 n0 k1 # r 2n r 2n 2
2n 1F2nk :
2n 1G2nk a a j X
26
aE
(
29
The radial displacement is derived from the radial strain as
( ) " j 1 X 1m X aE 2nI2n
sk r I2n1
sk r urj wjk cos
2nh r A2nk E 1 m sk r
sk r2 n0 k1 # r 2n r 2n 2 2
n 1 2mF2nk 2nG2nk : a a
30
It is assumed that the cylinder is in smooth contact with two rigid stamps without friction and the rigid stamps are ®xed. In this case, the mechanical boundary conditions are taken to be
rrhj 0 on r a ; urj 0; 0 h < h0 rrrj 0; h0 < h p2
31 on r a :
32
Substituting Eq. (29) into Eq. (31), we have
"
1
G2nj
2n
1
(
aE
2n 1F2nj
1
m
A2nj
I2n1
sj a 2n 1 2 I2n
sj a sj a
sj a
)# :
33
Substitution of Eqs. (30) and (26) into Eqs. (32) leads to a dual-series equation
226
1 X
X2n L2nj W2nj cos
2nh 0
0 h < h0 ; n0
1 X n0
L2nj
34
p cos
2nh 0
h0 < h ; 2
where L2nj are unknown coef®cients related to the unknown coef®cients F2nj , and X2n and W2nj are known coef®cients as follows:
L2nj
2n 1 2F2nj
aE 1
m
A2nj
I2n1
sj a ; sj a
35
1 mf1 2m 4n
1 mga ;
2n 1
2n 1E I2n1
sj a 2
1 maA2nj : sj
X2n W2nj
36
In order to solve Eqs. (34), we introduce the following series, which identically satis®es the second of Eqs. (34):
L2nj
1 2h0 X ylj J2l
2nh0 ; 1 dn0 l0
37
where ylj are new unknown coef®cients. Substituting Eq. (37) into the ®rst of Eqs. (34) and applying the series given in Eq. (17), the following in®nite system of simultaneous algebraic equations is obtained:
2h0
1 X l0
ylj
1 X X2n J2l
2nh0 n0
1 dn0
Z2m
2nh0
1 X n0
W2nj Z2m
2nh0 ;
m 0; 1; 2; . . . :
38
Therefore, the unknown coef®cients ylj can be determined by solving the linear equations (38) numerically. Substituting Eqs. (33), (35), (37) and (20) into Eqs. (26)±(28), the radial, hoop and axial stresses on the surface of the cylinder are expressed by
rrrj ra
j 1 X H
h0 h X h l ; q wjk
1 ylk T2l h0 l0 1 h2 =h20 k1
rhhj ra
j X k1
" wjk
1 H
h0 h X h l q
1 ylk T2l h0 1 h2 =h20 l0 1 aE X A2nk cos
2nh I2n
sk a 1 m n0
39
# I2n1
sk a ; 2
2n 1 sk a
40
rzzj ra
"
1 2mH
h0 h X h wjk q
1l ylk T2l h 2 2 0 k1 1 h =h0 l0 1 aE X A2nk cos
2nh I2n
sk a 1 m n0
j X
I2n1
sk a 2
2n 1m sk a
# ;
41
where H
h is the Heaviside's unit step function and Tl
h are Tchebycheff's polynomials of the ®rst kind. Expressions (39)±(41) indicate that the radial, hoop and axial stresses have singularities at the end of the contact surface of the cylinder. In order to evaluate the strength of these singularities, the following stress singularity coef®cients are introduced:
s h rrrj ; rhhj ; rzzj ra : Krj ; Khj ; Kzj lim 2 1 h!h0 h0
42
Substituting Eqs. (39)±(41) into Eq. (42), we have j
Krj Khj
1 X Kzj X wjk
1l ylk : 2m l0 k1
43
2.3 Exact solution When a coef®cient of relative heat transfer on the contact surface of the cylinder is identical with that on the traction-free surface, namely h1 h2 h, the exact solution is obtained by employing the Laplace transform technique as follows: ( ) 1 1 r 2n X X T cos
2nh T2n T2nm J2n
bm r ;
44 a n0 m1 1 Kz X
1l yl ; Kr Kh 2m l0
45
where
T2n
haT0 q2n ; 2n ha
2
T2nm
2n haJ2n
bm a
4n2
2haT0 q2n e jbm t ; b2m a2 h2 a2 J2n
bm a
bm a J2n1
bm a 0 ;
and yl are the solutions for the linear equations when W2nj in Eqs. (38) are replaced by the following coef®cients:
(
W2n
1 X T2n J2n
bm a 2
2n ha
1 maa T2nm 2n 1 b2m a2 m1
) :
3 Numerical results The following dimensionless quantities are introduced for convenience in the presentation of numerical results: jtj Tj ; Bi ahi ; Tj ; 2 a T0
1 muij
1 mrikj
1 mKij ; rikj ; Kij : uij aa
1 mT0 aET0 aET0 r r ; a
tj
227
For an illustrative example, the heating temperature distribution and the Poisson's ratio are assumed to be
q
h H
h0
h;
m 0:3 ;
and the time variable tj is given by j 1
4
tj 10 6
j 23 24
tj 10 228
2
j 75 5
tj 10
j 7
j 1±6;
3
j 7±22;
j 47 28
1
tj 10 16
j 23±46;
tj 10
j 47±74;
j 75 :
It is necessary to examine the convergences of the in®nite series P involving P1the formulations P1 such as Eqs. (18) and (38). The upper limits of in®nite series of 1 no ; n0 0 and l0 are P P 1 1 0 represented by N; N and L, where n0 and n0 0 denote the in®nite series of the left- and right-hand sides of Eqs.(18) and (38) respectively. The temperature at the center of the contact surface of the cylinder as well as the radial stress singularity coef®cient was calculated for various upper limit numbers of the in®nite series for B1 B2 1 and 2h0 30 . The ®nite difference results for the temperature at the centre of contact surface of the cylinder as well as the radial stress singularity coef®cient are shown in Tables 1 and 2 and compared to the exact solutions. These tables show that the in®nite series converge for N 45000; N 0 7500 and L 80 in the case of temperature and for N 45000, N 0 7500 and L 95 in the case of radial stress singularity coef®cient at a reasonable rate, and then the ®nite difference results agree quite well with the exact solutions. Figures 2±4 illustrate the distributions of the temperature, radial displacement and radial stress on the surface of the cylinder at selected Fourier's numbers for B1 10, B2 1 and 2h0 30 . Figures 5 and 6 illustrate how the range of the contact region in¯uences the temperature distribution on the surface of the cylinder as well as the radial stress singularity Table 1. Effects of upper limit numbers of in®nite series on ®nite difference results for temperature at the center of contact surface of the cylinder in the case of 2h0 30 and B1 B2 1 Fourier's number tj
Upper limits of series N
N0
L
10
45000 50000 40000 45000 45000 45000 45000
7500 7500 7500 8000 7000 7500 7500
80 80 80 80 80 85 75
0.03461 0.03461 0.03461 0.03476 0.03436 0.03436 0.03360
0.10610 0.10610 0.10610 0.10630 0.10576 0.10576 0.10473
0.03520
0.10681
Exact solution
3
10
2
100
101
102
0.23211 0.23212 0.23212 0.23237 0.23171 0.23170 0.23044
0.34123 0.33976 0.34031 0.34205 0.33941 0.34040 0.33871
0.36879 0.36879 0.36878 0.36908 0.36831 0.36831 0.36684
0.36884 0.36884 0.36884 0.36913 0.36837 0.36836 0.36690
0.23298
0.34144
0.36816
0.36816
10
1
Table 2. Effects of upper limit numbers of in®nite series on ®nite difference results for radial stress singularity coef®cient in the case of 2h0 30 and B1 B2 1 Fourier's number tj
Upper limits of series N
N0
L
10
45000 50000 40000 45000 45000 45000 45000
7500 7500 7500 8000 7000 7500 7500
95 95 95 95 95 100 90
0.00283 0.00284 0.00283 0.00283 0.00284 0.00285 0.00280
0.00334 0.00334 0.00334 0.00285 0.00336 0.00328 0.00326
0.00292
0.00348
Exact solution
3
10
2
100
101
102
)0.06056 )0.06059 )0.06052 )0.06053 )0.06060 )0.06063 )0.06003
)0.28503 )0.28513 )0.28479 )0.28480 )0.28528 )0.28487 )0.28207
)0.35629 )0.35644 )0.35603 )0.35599 )0.35662 )0.35610 )0.35268
)0.35644 )0.35658 )0.35617 )0.35614 )0.35676 )0.35625 )0.35283
)0.06126
)0.28831
)0.35633
)0.35633
10
1
229
Fig. 2. Temperature distributions on the surface of the cylinder
Fig. 3. Radial displacement distributions on the surface of the cylinder
Fig. 4. Radial stress distributions on the surface of the cylinder
230 Fig. 5. Effect of the range of the contact region on temperature distributions on the surface of the cylinder
Fig. 6. Effect of the range of the contact region on radial stress singularity coef®cients
coef®cient for B1 10 and B2 1. In these ®gures, the dotted and broken lines represent the numerical results for B1 B2 1 and B1 B2 10, respectively. Figures 2±4 and 6 show that the temperature, radial displacement, radial stress and radial stress singularity coef®cient for B1 10 and B2 1 are much larger than those in both cases of B1 B2 1 and B1 B2 10. It is seen from Fig. 3 that the radial displacement is negative for small Fourier's number, and then turns to positive for large Fourier's number. Conversely, as shown in Fig. 4, the radial stress in the neighbourhood of the end of contact surface is positive when Fourier's number is small, and then turns to negative as time proceeds. Figures 5 and 6 show that the temperature and radial stress singularity coef®cient increase according to the range of the contact region. Now, it is seen from Fig. 2 that when 2h0 30 and tj 1, the temperature on the tractionfree surface of the cylinder for B1 B2 1 is higher than that in the case of B1 B2 10, because the quantity of the heat transfer by convection on the traction- free surface increases according to Biot's number on its surface. A similar trend applies to the radial displacement and radial stress singularity coef®cient, as it evident from Figs. 3 and 6. Figures 7 and 8 illustrate how Biot's numbers on the contact and traction-free surfaces have in¯uence on the radial stress singularity coef®cient for the case of 2h0 30 . The radial stress singularity coef®cient increases with increasing Biot's number on the contact surface, but decreases with increasing Biot's number on the traction-free surface, because the quantity of the heat transfer by convection increases according to the each Biot's number.
231 Fig. 7. Effect of Biot's number at the contact surface of the cylinder on radial stress singularity coef®cient
Fig. 8. Effect of Biot's number at the tractionfree surface of the cylinder on radial stress singularity coef®cient
In the present problem, the cylinder is assumed to be in complete contact with the rigid stamp without friction, and so Eqs. (2), (31) and (32) are given. As shown in Figs. 3 and 4, these boundary conditions bring about the curious result that the radial displacement is negative and the radial stress is positive near the end of contact surface of the cylinder, when Fourier's number is very small. If separation between the cylinder and rigid stamp is acceptable to the boundary conditions, we can deduce that separation occurs at the end of rigid stamp and then the stress singularity does not appear, while the radial displacement near the end of the contact surface is negative. In this case, the stress singularity is considered to occur after the radial displacement near the end of the contact surface has turned from negative to positive. Therefore, positive and negative of the stress singularity coef®cient shown in Fig. 6 indicate the behavior of elastic deformation near the end of the contact surface.
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