Design allowables for composite aerospace structures
Recent developments in aircraft design have seen the Airbus A380 and the Boeing Dreamliner employ significant amounts of advanced composite materials. There is some thought however, und the motivation for this current work, that these materials continue to suffer a weight penalty. In this work tests...
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University of Surrey
2012
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| Online Access: | http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604017 |
| Summary: | Recent developments in aircraft design have seen the Airbus A380 and the Boeing Dreamliner employ significant amounts of advanced composite materials. There is some thought however, und the motivation for this current work, that these materials continue to suffer a weight penalty. In this work tests required to generate design allowables which accommodate environmental effects and holes arc performed on Carbon/epoxy quasi-isotropic laminatcs. The test data is treated statistically to provide B-basis allowables for each specimen type and condition. It was seen that the notched specimens (coupons containing a centrally placed through hole) displayed significantly less scatter in strength than unnotched specimens. This is significant when considering the widespread use of deterministic knock-down factors as an alternative route to obtain design allowables which accommodate environmental effects and/or holes. This results in an over-conservative design allowable being employed in subsequent structural design calculations. The possibility for using notched coupons to determine design allowables was explored using the COG (Critical Damage Growth) model. This showed that. given two of the three parameters. the unnotched and notched strength, and fracture toughness the variation in strengths could be reasonable predicted. This leads to a more representative design allowable by maintaining the statistical nature of the B-basis allowable. During the statistical treatment of the test data it was also seen that although current aerospace guidelines recommend a particular distribution model (i.e. the Wcibull distribution) this can also leads to an artificially reduced design allowable. These findings suggest that the use of notched specimens can lead to a reduced development test programme and reduced structural weight. |
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