Bloch, Ricardo (1976) Viscoelastic behavior of filled and unfilled elastomers in moderately large deformations. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-02202004-115154
A constitutive model was developed for the description of the viscoelastic (time-dependent) behavior of soft rubberlike materials in moderately large deformations. The model assumes that time shift invariance is preserved in such deformations. Hence, the Boltzmann superposition integral remains valid and time-dependent behavior can be described by incorporating a nonlinear stress-strain law into it. The elastic potential of Blatz, Sharda, and Tschoegl, which is based on a generalized measure of strain, was used for this purpose.
A slightly plasticized styrene-butadiene copolymer rubber (SBR) was subjected to various modes of deformation in simple tension. The experimental data were compared with the theoretical predictions of the model. The agreement was unprecedentedly good.
In the course of this work a curious anomaly was discovered in the behavior of emulsion polymerized compression molded dicumylperoxide cured SBR. This material showed lack of time shift invariance in the region of very small strains in which elastomers generally follow a linear stress-strain law. Normally, non-preservation of time shift invariance is linked with stress-strain nonlinearity. In the anomalous SBR the former effect can be studied free of interference from the other.
To test the applicability of the model to filled elastomers, experiments were made on both crosslinked and uncrosslinked SBR filled with a high-structure carbon black. The model, and several generalizations of it, failed to predict the behavior of the filled materials in response to small (theoretically infinitesimal) deformations superposed on a finite stretch. Such experiments may be considered looked upon as sensitive probes with which the behavior of the material may be explored in large deformations. The superposition tests confirmed that in carbon black filled rubbers there exists a network of secondary aggregates of the filler particles which is held together by Van der Waals forces. This network imparts to the filled rubber a thixotropic character with a rebuilding time of about 15 minutes at room temperature. Successful prediction of the properties of such a filled system must await the development of a new constitutive model which incorporates the thixotropic behavior.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Degree Grantor:||California Institute of Technology|
|Division:||Chemistry and Chemical Engineering|
|Major Option:||Chemical Engineering|
|Thesis Availability:||Public (worldwide access)|
|Defense Date:||1 March 1976|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||25 Feb 2004|
|Last Modified:||26 Dec 2012 02:31|
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