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REPAIR ASPECTS OF COMPOSITE AND 39 ADHESIVELY BONDED AIRCRAFT STRUCTURES Anton L. Seidl 39.1 INTRODUCTION 39.1.1 MANUFACTURABILITY AND MAINTAINABILITY OF COMPOSITE AIRCRAFT STRUCTURE To the manufacturer, weight reductions, struc- tural requirements, manufacturability and production costs have long been obvious pri- orities. Only recently, however, and only as a consequence of persistent user demands, have maintainability and repairability been added to this list. From the operator’s perspective, nevertheless, composite structures continue to be a mixed blessing. Clearly, and despite state- ments being heard to the contrary, the industry would be loath to give up the many obvious advantages gained through the use of composites and revert to all-metal airplanes. However, the maintenance problems associ- ated with composites cannot be underestimated and may well be regarded as the weak link in the new technology chain. 39.1.2 METAL REPAIRS COMPARED WITH COMPOSITE REPAIRS Compared to the relative simplicity of conven- tional metallic structures, composites are replete with complexities that continue to baf- fle and confuse maintenance workers trained only in the traditional, i.e. metalworking, skills. The glossary of terms alone, as used by Handbook of Composites. Edited by S.T. Peters. Published in 1998 by Chapman & Hall, London. ISBN 0 412 54020 7 the composites industry, is an unfamiliar lan- guage to the uninitiated. Inspectors are often at a loss when attempting to describe a condi- tion they perceive as a defect; the words simply do not exist in their standard lexicon. It is intuitively clear to even the casual observer that repairs using mechanically fastened con- ventional materials can be effected quickly, under almost any atmospheric conditions, and with minimal investments in tooling, raw materials, and training. In contrast, repairing even relatively minor damage on composite structure requires an array of non-conven- tional materials, highly skilled and experienced technicians, special tooling and equipment, access to production drawings (to locate and interpret the many hidden features characteristic of composite structures), a con- trolled environment in terms of temperature and humidity, time-consuming preparatory work, cold storage of shelf-life limited and occasionally hazardous materials, lengthy resin cure cycles, post-repair NDT, and legally mandated record-keeping and follow-up activities. 39.1.3 COMPOSITE REPAIRS: AN AIRLINE PERSPECTIVE The aim and purpose of this presentation is to highlight the principal aspects of composite structure repairs from an airline perspective. An attempt will be made to: 1. describe some of the more common defects and conditions encountered in service;
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858 Repair aspects of composite and adhesively bonded aircraff structures 2. give a brief summary of common mainte- 3.
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