ABSTRACT
The subject of rheology is very important for both polymers and polymeric composites. This is true for two reasons. Firstly. flow is involved in the processing and fabrication of such materials in order to make useful objects. Thus. fluid rheology is relevant to polymer processing and determines stress levels in operations such as extmsion. calendering, fiber spinning, and film blowing. Similarly, rheology influences residual stresses, cycle times. and void content in composite processing operations such as bag molding. compression molding. and injection molding. Clearly. a quantitative description of polymer and composite rheology is essential for developing models of the various polymer processing operations; these models can be employed for process optimization and for predicting the onset of flow instabilities. ln the use of polymers, though, it is generally the
mechanical properties thai are important Mechanical behavior, however. is influenced by rheological behavior, and this is the second important reason for studying polymer rheology. For example, molecular orientation has dran1atic effects on the mechanical properties of molded objects, fibers, and films. For shortfiber composites. fiber orientation plays the role of molecular orientation in unfilled systems. The kind and degree of molecular or fiber orientation are largely determined by the rheological behavior of the polymer and the nature of the flow in the fabrication process.
