propriate combinations of temperature and extrusion ratio. The extrusion technique was somewhat faster than the drawing method.

The importance of the entanglements was emphasized by the next development, which occurred in a European industrial laboratory. The density of entanglements and the morphology were optimized by converting the polymer solution to a gel before solid-state processing. Gelling sets the molecular topology of the chain entanglements. High-modulus fibers are produced when the gel is drawn to a high ratio.

The gel-and-draw technique has been commercialized by an American corporation, following an extensive in-house development program. A new polymer fiber with distinctive properties has appeared in the marketplace. The starting material is cheap, the process technology is relatively inexpensive, and the modulus and strength are superior. The fundamental information developed early in academic laboratories was essential to the industrial research, which led to successful development and commercialization of the fibers.

OPPORTUNITIES FOR THE FUTURE

The final section of this appendix is devoted to some selected areas in which research in materials processing might have a significant impact in the not-too-distant future.

Computers, Modeling, and Simulation

The rapid development of fast and versatile computers provides opportunities for significant improvements in materials processing technologies. On-line computational control of process parameters can lead to major improvements in product quality and performance as well as to increased efficiency and reduced costs. The union of computers and processing technology already has appeared in some industrial sectors, and greater effort is anticipated in the future. Processing technologies as different as steelmaking, crystal growth, fabrication of integrated circuits, near-net-shape forming, and rapid solidification might benefit greatly from full use of this capability.

To take advantage of this opportunity, major advances will be required in modeling and simulation, characterization of materials behavior during processing, and sensor technology to monitor process inputs and material response. Materials processing typically involves unusual and sometimes extreme conditions of temperature, pressure, strain rate, flow velocity, or other material or system parameters. The phenomena that occur during materials processing are generally complex and highly nonlinear; they must be modeled with considerable precision in order for the numerical results to be meaningful.



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