This study provides a detailed consideration of five manufacturing options that are used to produce aerospace sandwich panels used in secondary structure. The structural performance of each of the manufacturing options is considered along with a cost analysis. By considering the traditional preimpregnated (prepreg), autoclave-cured process, the sources of cost have been investigated, and it has been shown that by removing a portion of the large labor content and the autoclave cure, in favor of an oven-only cure, it would be possible to make significant savings. Monitoring the time to manufacture representative full-scale sandwich panels using the five manufacturing options has shown that by using a resin film infusion (RFI) oven cure, a 30% reduction in time to production is possible. To make an initial assessment of the comparative structural performance of laminates produced using the five manufacturing options, this article also presents results of material quality, in-plane and out-of-plane loading tests. The results of these tests show that the laminates produced using RFI are comparable in quality and performance to laminates produced using the current aerospace industry standard prepreg/autoclave process.

This paper describes the design of a test rig to apply a representative pressure load to full-scale composite sandwich secondary aircraft structure. A generic panel was designed with features to represent those in composite sandwich secondary aircraft structure. To provide full-field strain data from the panels, the test rig was designed for use with optical measurement techniques such as thermoelastic stress analysis (TSA) and digital image correlation (DIC). TSA requires a cyclic load to be applied to a structure for the measurement of the strain state, therefore the test rig has been designed to be mounted on a standard servo-hydraulic test machine. As both TSA and DIC require an uninterrupted view of the surface of the test panel, an important consideration in the design is facilitating the optical access for the two techniques. To aid the test rig design a finite element (FE) model was produced. The model provides information on the deflections that must be accommodated by the test rig, and ensures the stress and strain levels developed in the panel when loaded in the test rig would be sufficient for measurement using TSA and DIC. Finally, initial tests using the test rig have shown it to be capable of achieving the required pressure and maintaining a cyclic load. It was also demonstrated that both TSA and DIC data can be collected from the panels under load, which is used to validate the stress and deflection derived from the FE model.

All rights reserved. No part of this publication may be reproduced in any form or by any means, without the prior written permission of the Prestressed Concrete Institute. N ineteen seventy-nine was the 25-year Silver Jubilee of the founding of the Prestressed Concrete Institute. CONTENTS Part 6-Early History of Prestressed 163 Concrete in Colorado 'Ed Thwaits is now 85 years old and fives quietly in Denver, Colorado.

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