(kg/ cm2) (lb / in.2)
500
32
119
41
400
0
Tem( erature
p
C)
29
24
44
60
300
16
200
76F
8
100
0
0
0
100
200
300
400
Elongation (%)
Figure 11. Karpati's (1972a) results showing the effect of temperature on
the nominal stresspercentage elongation response of silicone butt joint
seal specimens.
Rubber elasticity models have been used with
eral research programs are illustrated in Figures
finite-deformation numerical analysis techniques
11 through 16. These examples from the literature
to model the large deformation behavior of seals.
have been chosen to demonstrate the nature of the
responses of seals formed from a variety of ma-
Figure 10 shows results generated by Catsiff et al.
terials under a range of conditions. The first ex-
(1970b) using finite element approximations for
ample is Karpati's (1972a) joint extension experi-
plane strain sections of silicone butt joint seals.
ments showing the effect of temperature on sili-
The stress distribution and deformed configura-
cone butt joint seal specimens with dimensions of
tions in Figure 10 illustrate a quantitative predic-
1.3 1.3 cm in the cross section and with a length
tion of the response, and demonstrate the insight
of 5.1 cm. The material of the supporting bars was
into the response behavior that can be obtained
aluminum. The test results are depicted in Figure
through such analysis. In particular, the high stress
11. As Karpati suggested, below 50% extension of
level at the corner reveals the critical zone within
the joint and 350 kPa (50 psi) of nominal stress,
the structure, and suggests that adhesive failure
there was little effect of temperature upon the seal
would likely occur in this area if failure stresses
responses, except that slightly stiffer responses
are reached. The use of these techniques requires
were observed at the 42C (44F) and 51C
an appropriate calibration of the hyperelastic ma-
(60F) temperatures. For this material the effect
terial model, however, which has not always been
of temperature was primarily evident at much
the case. For example, Holland (1990) calibrated a
higher deformations of the seals. This observation
hyperelastic model with results from structural
is consistent with the low glass transition tem-
property tests rather than material property tests,
perature of silicone. The effect that the deformation
evidently presuming that the structural responses
rate has on the response is shown in Figure 12 for
represented homogeneous behavior.
tests at 23C (10F) and 22C (72F) (Karpati
Other analysis techniques, particularly ana-
1972b). Here is seen a more pronounced effect on
lytical solutions based on small-strain elasticity
the stiffness below 50% extension, relative to the
theory, have been developed to investigate the ef-
negligible effect of temperature, with the higher
fect of the material volume change behavior on
deformation rates resulting in stiffer specimens.
the stress distribution within a joint seal when the
As a comparison, Karpati's (1973) results from poly-
seal is constrained to have zero width change. Such
sulfide model seals are illustrated in Figure 13.
techniques would apply to the response of a seal
Again results at two temperatures are shown
to thermal and other volume change mechanisms.
(34C and 23C), at the different deformation
Wu (1982) has reviewed these techniques.
rates indicated, which in this case reflect a signifi-
Responses of model seals from experimental
cant stiffening of the seal response from the higher
work on building and pavement sealants from sev-
14
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