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Shear creep behaviour of elastomeric adhesives
Shear creep behaviour of elastomeric adhesives S. Wasserman, H. Dodiuk and S. Kenig (State of Israel Armament Development Authority) Received 29 January 1992; accepted ~n revised form 2 August 1992
The shear creep behaviour of elastomeric adhesives has been investigated at various temperatures, loading stresses and adhesive thicknesses. Three adhesive types were included m the study: two polysulphides, one silicone and one polyurethane elastomer. The creep comphance of the two polysulphide adhesives could be described by an Arrhentus-type relationship incorporating time, temperature and stress. The silicone and polyurethane adhesives, on the other hand, showed an mitial creep response followed by a long period of zero creep over the ranges of temperature and load studied.
Key words: elastomer~c adhesives; creep; shear loading; temperature, stress, adhesive thickness
Elastomenc adhesives are widely used in joints where relatively large deformations arise due to the exerted or developing stresses One of the most common cases is related to thermally induced strains, when large differences in the thermal expansion coefficients of a muhi-matenal joint result in associated thermal stresses The so-called "thermal mismatch" may lead to failure in extreme cases and to unacceptable movement of components in less severe cases_ Mounting and fixing of opucal components (windows, lenses) to metallic frames or other substrates could be realized by adhesives, provided the joint IS properly designed to absorb changes in the thermally reduced strains of its components. The use of an adhesive may result in an economic and simple solution compared w~th its counterpart based on mechamcal fastening However, special attention should be addressed to selection of the correct adhesive to yield a thermal stress-free system Due to their low elastic modulus, elastomenc adhesives are specially suited for such systems. In a typical case where a Schott BK-7 glass having a thermal expansion coefficient (a) of 7 X 10-6°C -I IS bonded to aluminium, a = 23 X 10-6°C -I, large thermal strains develop due to the relatively large difference ~n a (Aa = 16 × 10-6°C -I) (Data for linear thermal expansion coefficients were taken from Schott's Optical Glass Manual for BK-7 glass, and from Perry's Handbook of Chemical Engineenng for the metal_)
If a thermal stress-free system is desired, an elastomeric layer of several milhmetres thickness is needed Such joints, under externally exerted mechanical loads, may result m large static deformations and, more severely, in creep Creep ~n polymeric materials and elastomers has been widely studied I-3. For apphcauons revolving elastomeric adhesives, however, there are almost no Investigations reported and consequently the design of such joints is limited Hence the present study IS aimed at investlgatlng and characterizing the shear creep behaviour of elastomenc adhesives Four different adhesives are included in the study, two types of twocomponent po[ysulphide, a two-component silicone e[astomer and a two-component polyurethane A special fixture was adopted and developed to study creep ~n the shear mode, where creep was characterized under various temperatures, loads and adhesive thicknesses
Experimental Chromic acid ano&zed 2024 alummlum (according to MIL-A-8625C) served as joint substrates Four different e[astomenc adhesives were stud~ed, as detailed m Table 1 Two were based on polysulphide and had different curing agents, one comprised an elastomeric silicone and the fourth was based on polyurethane The thickness of the adhesive layer, which was vaned
0 1 4 3 - 7 4 9 6 / 9 2 / 0 4 0 2 5 7 - 0 5 © 1992 Butterworth-Hememann Ltd INT.J ADHESION AND ADHESIVES VOL 12 NO. 4 OCTOBER 1992
257
Table 1.
S u m m a r y of adhesives tested
Adhesive
Type
Manufacturer
Curing cond~tMons
PR 380
Two-component polysulph~de, PbO2 catalysed
Product Research Corporat=on
48 h at room temperature + 2 0 h at 55°C
PR 1750
Two-component polysulphide, MnO 2 catalysed
Product Research Corporation
48 h at room temperature + 2 0 h at
R'IV 560
Two-component sd=cone rubber
General Elecmc
PR 1535
Two-component polyurethane
Product Research Corporation
70°C Room temperature curing 16 h at room temperature + 16 h at
60°C
between 0 5 and 2.5 mm, was controlled by a p p r o p n a t e spacers. In the present study the joints under stress were shear joints according to ASTM D-10024, subjected to a constant load. A schematic representation of the test specimen appears m Fig. 1 The test fixture for shear creep was based on that described in ASTM 22905. which deals with tensile, compressive and flexurat creep of plastics. A fixed load was applied to each specimen, see F~g 2, and the shear deformation of the joint was determined by measuring the displacement between two holes, one situated in each alumintum substrate, using a Mitutoyo measuring device The toad was retained until the specimen failed or creep had ceased. Shear creep strain was determined according
Anchoring hole
;©
Bonded - area
O We,ght
\
~©
hanging hole
Measured d~stance
to'
a
(l)
e = AL/d
/2
where AL is the measured displacement under constant load and d is the original thickness of the adhesive, see Fig. 3. The applied shear stress, which was varied in the range 1.5-3.5 kg cm -2, was determined from the applied load (W) and the bonded area (,4). Measurements were taken every day during the initial stages of the tests and every seven days
Anchorln0 ----/
© Teflon tape (for fixed
\ot
Mylar strips (spacers f o r fixed adhestve fhLckness)
\
,
We=oht
AI 2 0 2 4 " ~ substrofe J
b Fig 2
(a) Measurement of sheer strata, (b) loading of test speCimen
a A 1 2 0 2 4 sul~trafe (1) ,,
---r__L
, A 1 2 0 2 4 substrate 121
b Fig. 1
258
Test specwnen (a) lower plate w=th spacer. (b) s=de vmw
INT.J.ADHESION A N D ADHESIVES OCTOBER 1 9 9 2
thereafter. Expenments were conducted at three temperatures - - ambient, 45°C and 70°C - - using a temperature-controlled oven for elevated temperature testing. Each experimental set-up (adhesive, temperature. stress, adhesive thickness) was carried out in duplicate, thus the reported results are the average of two
e -
I
F~g 3
(2)
where e0 ts the mmal strain on loading, e ,s the umedependent strata, t is the ume elapsed from tmtial loading, and m and n are empirical constants. Whde n ~s independent of stress and temperature, m Is stressand temperature-dependent Alperstein e t a L 7 used Fmdley's equation to study compression creep of polyurethane foams To study the effect of stress and temperature on creep behavlour the appropriate relationship between the former parameters and m has to be established. Zaslawsky ~ extended Findley's equation to include an expressmn for the temperature and stress through m as follows
d (3"
At hme f
At hrne 0
n
eO = m t
Shear displacement
m
= A~[I
(3)
exp(-KT)]
-
Results and discussion
where A and K are empirical constants, ~ is the applied stress and T is absolute temperature Combining Equations (2) and (3) the relationship between the creep strain (c), time ( t ) , stress (a) and temperature (T) is gwen by:
Tensile and shear creep are commonly characterized by three regions 6 The first reg=on is one of high creep rate, the second ~s ty,p~fied by a constant rate of creep and m the third the creep rate increases to the point where failure occurs F~ndley6 suggested that the tensile creep of polymers could be represented by the empirical equation
l
80
e -
o Room temperature ,-, 45oc
eo = Ao[I
-
exp(-KT)]t
(4)
n
o 45 °C z~ 70°C
60
~J
440
20 /k
0
0
I0
0
a
0
20
30
0
40
5
I0
15
20
b o 45°C 70°C 06 0.2
O t
O2 0
0 C
0
r I0
0
0
I
I
20
30
Tt me (days)
40
0
d
0
I0
20
30
40
T, me (days)
F~g 4 Creep response of adhesives as a function of temperature and stress (a) PR 3 8 0 , 1 5 mm th,ck. 1 5 kg cm -2, (b) PR 1 7 5 0 , 2 O0 mm thick, 2_0 kg cm -2, {c) RTV 5 6 0 , 0 5 mm thick, 1 5 kg cm -2, (d) PR 1535, 2 O0 mm th=ck. 2 0 kg cm -2
INT.J.ADHESION A N D ADHESIVES OCTOBER 1 9 9 2
259
D u n n g the course of the study an attempt was made to analyse the experimental results according to Equation (4) First. shear strains were calculated according to Equauon (I) e0 was taken as the shear strain measured after one day of loading. Charactedsuc creep curves for the four elastomeric adhestves at two temperatures and a single stress level are given in Fig 4 The two polysulphide adhestves exhibit typical creep behavlour. the curves demonstrating a constant creep rate As can be observed, temperature has a sigmficant effect on creep in shear loading of polysulphides: this is slmtlar to results reported for tensile creep 6 The creep curves of the silicone and polyurethane adhesives represent a different behav~our - - a high creep rate in the initial penod of loading followed by a zero creep rate at long loading times Again, temperature has a pronounced effect on the creep levels attained. The polyurethane adhesive has a somewhat outstanding feature As illustrated in F~g 4(d) two levels of zero shear creep are obtained, indicating the existence of two different creep mechanisms at short and at long loading times To generalize results according to Equation (2), the variation of shear strata with time was plotted on a logarithmic scale for the two polysulphide adhesives (see Figs 5(a) and 5(b)), at various loading stresses and temperatures. As can be dLstingmshed from Fig 5, the curves are linear on a loganthmic scale indicating conformance to Findley's equation (Equation (2)) Thus the parameters m and n m Equation (2) were determined from Figs 5(a) and 5(b), and are gwen in Table 2. As expected, the exponent n for the two polysulphides studied has been found to be independent of temperature and stress levels, giving values of 1.22 for PR 380 and 0_60 for PR 1750 The parameter m varied with temperature and apphed stress The same basic results were reported for tenstle creep of rigid thermoplastics 6 and compressive creep of polyurethane foams 7 To quantify the effects of temperature and stress on the shear creep of the polysulphlde adheswes, Equation (4) was used. It was found for PR 380 adhesive that K = - 0 136 K - I and A = - 3 3 × 10--'t~ cm 2 kg -~ K -t fitted the experimental results, while tbr PR 1750 adhesive the respective values of K and A were -0.038 K -I and -0.185 × 10-6 cm 2 kg -i K -i
lO
re, 1 5 kg crn "2
i t
o
Room f e m p e r o l ' u r e , 3 0 k g c m -2
A
4 5 ° C , t 5 kgcm - z
i
o ol
a
1 I0
i
I0
I I00
m
uJ
I 5 k g c m -2
00I
b
o
" ~ 5 = C , 3 0 k g c m -2
•
7 0 ° C , I 5kg cm -2
B
7 0 ° C , 3 0 kgcm -2
I
I
I0
I00 Time (doys)
Fig 5 Logartthmm creep response of (a) PR 3 8 0 and tb) PR 1 7 5 0 adhestves
Table 2. Findley's equation parameters for PR 380 and PR 1 7 5 0 Adhestve
Temperature (°C)
Stress (kg cm -1)
m (day -1)
n
PR 380
Room temperature 45
15 3.0 1.5
0 021 0 045 0.32
1.21 1.14 1.31
PR 1750
45 45 70 70
1.5 3.0 1.5 3.0
0.048 0.078 0.085 0 27
0.57 0 62 0 70 0 70
Conclusions
The shear creep behaviour of four adhesive elastomers was investigated. It was established that Findley's equation modified by Zaslawsky describes the creep in shear loading of the two polysulphide adhesives studied. Results indicated that constant shear stress applied on the polysulphides, especially at elevated temperatures, caused continuous creep and consequently displacement of the bonded substrates, The MnO2 catalysed polysulphide (PR 1750) resists creep better than the PbO2 catalysed polysulphide (PR 380). The two other adhesives studied exhibited enhanced resistance to applied shear stress at elevated temperature The silicone rubber demonstrated low creep levels and zero creep rate following initial creep.
260
INT.J.ADHESION AND ADHESIVES OCTOBER 1992
The polyurethane adhesive exhibited s~mllarly low creep values Two creep regions were identified as a function of loading time. attributed to two creep mechanisms
References 1 2 3 4
5
Sk=est, I 'Handbook of Adhesrves" (Van Nostrand Reinhold Company, 1975) Dsrnus=s, A "Sea~ants"(Reinhold Pubhshmg Corp, 1960) Seymour, R B "Po/ymers for Engmeenng Apphcattons" (ASM International, 1987) 'Strength properties of adhes=ves =n shear by tenston loading (metalto-metal) ASTM D-1002-73 (American Society for Testing and Materials, 1973) 'Standard method for tensile, compressive and flexural creep and creep rupture of plastics' ASTM 2290 (American Soc=et'yfor Testing and Matenals, 1973)
6 7 8
Fmdley, W N S P E J 1 6 ( 1 9 6 0 ) p57 Alperstem, D, Nerk=s, M , Kenig, S and S=egmann, A Polyrn Composttes 5 No 2 (1984) p 155 Zaslawsk'y, M SPE J 24 (1968) p 62
Authors The authors are with the State of Israel Armament Development Authority, PO Box 2250 (Dept 27), Halfa 31021, Israel Correspondence should be directed to Dr Dodiuk.
INTJ ADHESION AND ADHESIVES OCTOBER 1992
261
The shear creep behaviour of elastomeric adhesives has been investigated at various temperatures, loading stresses and adhesive thicknesses. Three adhesive types were included m the study: two polysulphides, one silicone and one polyurethane elastomer. The creep comphance of the two polysulphide adhesives could be described by an Arrhentus-type relationship incorporating time, temperature and stress. The silicone and polyurethane adhesives, on the other hand, showed an mitial creep response followed by a long period of zero creep over the ranges of temperature and load studied.
Key words: elastomer~c adhesives; creep; shear loading; temperature, stress, adhesive thickness
Elastomenc adhesives are widely used in joints where relatively large deformations arise due to the exerted or developing stresses One of the most common cases is related to thermally induced strains, when large differences in the thermal expansion coefficients of a muhi-matenal joint result in associated thermal stresses The so-called "thermal mismatch" may lead to failure in extreme cases and to unacceptable movement of components in less severe cases_ Mounting and fixing of opucal components (windows, lenses) to metallic frames or other substrates could be realized by adhesives, provided the joint IS properly designed to absorb changes in the thermally reduced strains of its components. The use of an adhesive may result in an economic and simple solution compared w~th its counterpart based on mechamcal fastening However, special attention should be addressed to selection of the correct adhesive to yield a thermal stress-free system Due to their low elastic modulus, elastomenc adhesives are specially suited for such systems. In a typical case where a Schott BK-7 glass having a thermal expansion coefficient (a) of 7 X 10-6°C -I IS bonded to aluminium, a = 23 X 10-6°C -I, large thermal strains develop due to the relatively large difference ~n a (Aa = 16 × 10-6°C -I) (Data for linear thermal expansion coefficients were taken from Schott's Optical Glass Manual for BK-7 glass, and from Perry's Handbook of Chemical Engineenng for the metal_)
If a thermal stress-free system is desired, an elastomeric layer of several milhmetres thickness is needed Such joints, under externally exerted mechanical loads, may result m large static deformations and, more severely, in creep Creep ~n polymeric materials and elastomers has been widely studied I-3. For apphcauons revolving elastomeric adhesives, however, there are almost no Investigations reported and consequently the design of such joints is limited Hence the present study IS aimed at investlgatlng and characterizing the shear creep behaviour of elastomenc adhesives Four different adhesives are included in the study, two types of twocomponent po[ysulphide, a two-component silicone e[astomer and a two-component polyurethane A special fixture was adopted and developed to study creep ~n the shear mode, where creep was characterized under various temperatures, loads and adhesive thicknesses
Experimental Chromic acid ano&zed 2024 alummlum (according to MIL-A-8625C) served as joint substrates Four different e[astomenc adhesives were stud~ed, as detailed m Table 1 Two were based on polysulphide and had different curing agents, one comprised an elastomeric silicone and the fourth was based on polyurethane The thickness of the adhesive layer, which was vaned
0 1 4 3 - 7 4 9 6 / 9 2 / 0 4 0 2 5 7 - 0 5 © 1992 Butterworth-Hememann Ltd INT.J ADHESION AND ADHESIVES VOL 12 NO. 4 OCTOBER 1992
257
Table 1.
S u m m a r y of adhesives tested
Adhesive
Type
Manufacturer
Curing cond~tMons
PR 380
Two-component polysulph~de, PbO2 catalysed
Product Research Corporat=on
48 h at room temperature + 2 0 h at 55°C
PR 1750
Two-component polysulphide, MnO 2 catalysed
Product Research Corporation
48 h at room temperature + 2 0 h at
R'IV 560
Two-component sd=cone rubber
General Elecmc
PR 1535
Two-component polyurethane
Product Research Corporation
70°C Room temperature curing 16 h at room temperature + 16 h at
60°C
between 0 5 and 2.5 mm, was controlled by a p p r o p n a t e spacers. In the present study the joints under stress were shear joints according to ASTM D-10024, subjected to a constant load. A schematic representation of the test specimen appears m Fig. 1 The test fixture for shear creep was based on that described in ASTM 22905. which deals with tensile, compressive and flexurat creep of plastics. A fixed load was applied to each specimen, see F~g 2, and the shear deformation of the joint was determined by measuring the displacement between two holes, one situated in each alumintum substrate, using a Mitutoyo measuring device The toad was retained until the specimen failed or creep had ceased. Shear creep strain was determined according
Anchoring hole
;©
Bonded - area
O We,ght
\
~©
hanging hole
Measured d~stance
to'
a
(l)
e = AL/d
/2
where AL is the measured displacement under constant load and d is the original thickness of the adhesive, see Fig. 3. The applied shear stress, which was varied in the range 1.5-3.5 kg cm -2, was determined from the applied load (W) and the bonded area (,4). Measurements were taken every day during the initial stages of the tests and every seven days
Anchorln0 ----/
© Teflon tape (for fixed
\ot
Mylar strips (spacers f o r fixed adhestve fhLckness)
\
,
We=oht
AI 2 0 2 4 " ~ substrofe J
b Fig 2
(a) Measurement of sheer strata, (b) loading of test speCimen
a A 1 2 0 2 4 sul~trafe (1) ,,
---r__L
, A 1 2 0 2 4 substrate 121
b Fig. 1
258
Test specwnen (a) lower plate w=th spacer. (b) s=de vmw
INT.J.ADHESION A N D ADHESIVES OCTOBER 1 9 9 2
thereafter. Expenments were conducted at three temperatures - - ambient, 45°C and 70°C - - using a temperature-controlled oven for elevated temperature testing. Each experimental set-up (adhesive, temperature. stress, adhesive thickness) was carried out in duplicate, thus the reported results are the average of two
e -
I
F~g 3
(2)
where e0 ts the mmal strain on loading, e ,s the umedependent strata, t is the ume elapsed from tmtial loading, and m and n are empirical constants. Whde n ~s independent of stress and temperature, m Is stressand temperature-dependent Alperstein e t a L 7 used Fmdley's equation to study compression creep of polyurethane foams To study the effect of stress and temperature on creep behavlour the appropriate relationship between the former parameters and m has to be established. Zaslawsky ~ extended Findley's equation to include an expressmn for the temperature and stress through m as follows
d (3"
At hme f
At hrne 0
n
eO = m t
Shear displacement
m
= A~[I
(3)
exp(-KT)]
-
Results and discussion
where A and K are empirical constants, ~ is the applied stress and T is absolute temperature Combining Equations (2) and (3) the relationship between the creep strain (c), time ( t ) , stress (a) and temperature (T) is gwen by:
Tensile and shear creep are commonly characterized by three regions 6 The first reg=on is one of high creep rate, the second ~s ty,p~fied by a constant rate of creep and m the third the creep rate increases to the point where failure occurs F~ndley6 suggested that the tensile creep of polymers could be represented by the empirical equation
l
80
e -
o Room temperature ,-, 45oc
eo = Ao[I
-
exp(-KT)]t
(4)
n
o 45 °C z~ 70°C
60
~J
440
20 /k
0
0
I0
0
a
0
20
30
0
40
5
I0
15
20
b o 45°C 70°C 06 0.2
O t
O2 0
0 C
0
r I0
0
0
I
I
20
30
Tt me (days)
40
0
d
0
I0
20
30
40
T, me (days)
F~g 4 Creep response of adhesives as a function of temperature and stress (a) PR 3 8 0 , 1 5 mm th,ck. 1 5 kg cm -2, (b) PR 1 7 5 0 , 2 O0 mm thick, 2_0 kg cm -2, {c) RTV 5 6 0 , 0 5 mm thick, 1 5 kg cm -2, (d) PR 1535, 2 O0 mm th=ck. 2 0 kg cm -2
INT.J.ADHESION A N D ADHESIVES OCTOBER 1 9 9 2
259
D u n n g the course of the study an attempt was made to analyse the experimental results according to Equation (4) First. shear strains were calculated according to Equauon (I) e0 was taken as the shear strain measured after one day of loading. Charactedsuc creep curves for the four elastomeric adhestves at two temperatures and a single stress level are given in Fig 4 The two polysulphide adhestves exhibit typical creep behavlour. the curves demonstrating a constant creep rate As can be observed, temperature has a sigmficant effect on creep in shear loading of polysulphides: this is slmtlar to results reported for tensile creep 6 The creep curves of the silicone and polyurethane adhesives represent a different behav~our - - a high creep rate in the initial penod of loading followed by a zero creep rate at long loading times Again, temperature has a pronounced effect on the creep levels attained. The polyurethane adhesive has a somewhat outstanding feature As illustrated in F~g 4(d) two levels of zero shear creep are obtained, indicating the existence of two different creep mechanisms at short and at long loading times To generalize results according to Equation (2), the variation of shear strata with time was plotted on a logarithmic scale for the two polysulphide adhesives (see Figs 5(a) and 5(b)), at various loading stresses and temperatures. As can be dLstingmshed from Fig 5, the curves are linear on a loganthmic scale indicating conformance to Findley's equation (Equation (2)) Thus the parameters m and n m Equation (2) were determined from Figs 5(a) and 5(b), and are gwen in Table 2. As expected, the exponent n for the two polysulphides studied has been found to be independent of temperature and stress levels, giving values of 1.22 for PR 380 and 0_60 for PR 1750 The parameter m varied with temperature and apphed stress The same basic results were reported for tenstle creep of rigid thermoplastics 6 and compressive creep of polyurethane foams 7 To quantify the effects of temperature and stress on the shear creep of the polysulphlde adheswes, Equation (4) was used. It was found for PR 380 adhesive that K = - 0 136 K - I and A = - 3 3 × 10--'t~ cm 2 kg -~ K -t fitted the experimental results, while tbr PR 1750 adhesive the respective values of K and A were -0.038 K -I and -0.185 × 10-6 cm 2 kg -i K -i
lO
re, 1 5 kg crn "2
i t
o
Room f e m p e r o l ' u r e , 3 0 k g c m -2
A
4 5 ° C , t 5 kgcm - z
i
o ol
a
1 I0
i
I0
I I00
m
uJ
I 5 k g c m -2
00I
b
o
" ~ 5 = C , 3 0 k g c m -2
•
7 0 ° C , I 5kg cm -2
B
7 0 ° C , 3 0 kgcm -2
I
I
I0
I00 Time (doys)
Fig 5 Logartthmm creep response of (a) PR 3 8 0 and tb) PR 1 7 5 0 adhestves
Table 2. Findley's equation parameters for PR 380 and PR 1 7 5 0 Adhestve
Temperature (°C)
Stress (kg cm -1)
m (day -1)
n
PR 380
Room temperature 45
15 3.0 1.5
0 021 0 045 0.32
1.21 1.14 1.31
PR 1750
45 45 70 70
1.5 3.0 1.5 3.0
0.048 0.078 0.085 0 27
0.57 0 62 0 70 0 70
Conclusions
The shear creep behaviour of four adhesive elastomers was investigated. It was established that Findley's equation modified by Zaslawsky describes the creep in shear loading of the two polysulphide adhesives studied. Results indicated that constant shear stress applied on the polysulphides, especially at elevated temperatures, caused continuous creep and consequently displacement of the bonded substrates, The MnO2 catalysed polysulphide (PR 1750) resists creep better than the PbO2 catalysed polysulphide (PR 380). The two other adhesives studied exhibited enhanced resistance to applied shear stress at elevated temperature The silicone rubber demonstrated low creep levels and zero creep rate following initial creep.
260
INT.J.ADHESION AND ADHESIVES OCTOBER 1992
The polyurethane adhesive exhibited s~mllarly low creep values Two creep regions were identified as a function of loading time. attributed to two creep mechanisms
References 1 2 3 4
5
Sk=est, I 'Handbook of Adhesrves" (Van Nostrand Reinhold Company, 1975) Dsrnus=s, A "Sea~ants"(Reinhold Pubhshmg Corp, 1960) Seymour, R B "Po/ymers for Engmeenng Apphcattons" (ASM International, 1987) 'Strength properties of adhes=ves =n shear by tenston loading (metalto-metal) ASTM D-1002-73 (American Society for Testing and Materials, 1973) 'Standard method for tensile, compressive and flexural creep and creep rupture of plastics' ASTM 2290 (American Soc=et'yfor Testing and Matenals, 1973)
6 7 8
Fmdley, W N S P E J 1 6 ( 1 9 6 0 ) p57 Alperstem, D, Nerk=s, M , Kenig, S and S=egmann, A Polyrn Composttes 5 No 2 (1984) p 155 Zaslawsk'y, M SPE J 24 (1968) p 62
Authors The authors are with the State of Israel Armament Development Authority, PO Box 2250 (Dept 27), Halfa 31021, Israel Correspondence should be directed to Dr Dodiuk.
INTJ ADHESION AND ADHESIVES OCTOBER 1992
261