A. Brent Strong

Incremental Forming of Large Thermoplastic Composites

Incremental forming is a new manufacturing method designed to create large thermoplastic composite laminate structures. These large laminates can be made utilizing small to medium sized equipment. The equipment and the operating parameters for successful incremental forming were developed. Thermoplastic laminate parts were made utilizing the incremental forming method and the properties were compared to parts of the same shape made using matched die molding. The areas of comparison were mechanical properties, physical qualities (surface quality), and uniformity of manufac ture The results revealed that the incremental forming process created parts of high mechanical integrity, excellent physical quality and good uniformity.

Postforming of Thermoplastic Composite I-Beams

The use of composite materials for structural members has been restricted by the lack of data on the use of these composites, by the inherent brittleness of many of these materials, and by the expensive manufacturing methods associated with their fabri cation. This study examines a new process to postform a constant cross section structural section (I-beam) from a straight section to a bent or contoured section. The structural pieces were tested for stiffness and compared with finite element analysis to determine the net change, if any, due to the bending. Statistical analysis of these results indicated that the bending procedure had little or no significant effect on the stiffness of the samples. This process may, therefore, result in a method of using preformed, standard shaped composite structural members and postforming those members for specific applications.

A new technique to improve adhesion of polyaramid fibers to thermoplastic

A novel technique has been developed to increase interfacial adhesion be tween organic fibers and thermoplastics. The technique consists of exposing the fiber to a radio frequency plasma discharge and then immediately coating the fiber with thermo plastic while still in the vacuum environment of the plasma reactor. Increased adhesion has been shown using a polyaramid fiber (Kevlar 49) and a polycarbonate resin (Lexan 121). An oxygen plasma exposure of 4.1 seconds at 24 Watts increased interfacial shear strength by 18 % as evaluated using the critical filament length technique. The plasma ex posure had no measurable effect on the filament tensile strength or the surface roughness. It is thought that the enhanced adhesion is due to the presence of covalent bonds formed at the interface when free radicals on the fiber are quenched by the thermoplastic.

Electrical sensing of shelf-cure properties of polymeric prepreg materials

Most polymeric thermoset materials change (cure) slowly as they lie in storage; a prime example of this is composite prepreg materials. These changes are generally vitrification, and are not readily observable using some of the standard cure-monitoring methods, such as DSC and FTIR, which sense mainly the gelation process. Evidence of this observation is presented, along with the successful results of an effort to monitor this shelf-cure process using a simplified resistivity meter.