Paul J. Biermann

Project summary: applied research on remotely queried embedded microsensors

This paper describes the final results of the Applied Research in Remotely-Queried Embedded Microsensors program. The program developed wireless and battery-less embedded strain/temperature gages suitable for embedding in aerospace and other composite structures. The program culminated in a working remotely queried strain rosette/temperature gage and testing of the device in several composite applications. The US Office of Naval Research funded this program to consolidate progress made in earlier programs towards self- contained microsensors.

Characterization of a peek composite segmental bone replacement implant

A composite material of polyetheretherketone and short, chopped E-glass fibers was used to produce a segmental bone replacement implant. Problems with current metallic implants include stress-shielding of the surrounding bone and subsequent loosening of the implant. A better match between the bulk material properties of the implant and the bone it replaces can decrease the occurrence of these problems. Composite materials were chosen because their properties can be tailored to match the requirements. Material selection was accomplished with the aid of modeling software, which predicted the composite properties based on its composition and fiber directional parameters. Prototype parts were completed through a series of in-house molding and machining processes. Sections complete with an embedded metallic porous surface were tested to measure the strength of the attachment of the surface. The molded parts were characterized both destructively and nondestructively. The results of tensile tests performed on molded parts were comparable to those using commercially supplied samples. The fiber orientation was measured to verify the random positioning of fibers throughout the part, as assumed in the initial material selection. Ultrasonic C-scanned images confirmed that the molded parts had a very low density of air pockets or voids.

End-of-cure sensing using ultrasonics for autoclave fabrication of composites

The objective of this work was to demonstrate the use of ultrasonics to determine the end-of-curve for autoclave cured, graphite/epoxy composite laminates. The fundamental benefit of this work will be understanding when to complete the temperature hold and cool down the autoclave and, therefore, consistently produce composite laminates with the desired material properties. An additional benefit is the ability to follow the changing viscosity of the resin during the initial part of the cure. The general approach to this program involved using pulse-echo ultrasonics to measure the transit time for longitudinal ultrasonic waves to pass through a graphite/epoxy composite laminate during cure. Sixteen, 32 and 64 ply (0/90)s graphite/Fiberite 934 epoxy panels were fabricated and cured to various end-of-cure conditions. Additionally, panels with various starting conditions were run. Sound speed was calculated using the panel thickness divided by the measured transit time.