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Composites: Part A 40 (2009) 164–175

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Composites: Part A
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Experimental study of the low-velocity impact behaviour of primary sandwich structures in aircraft
Joris Leijten *, Harald E.N. Bersee, Otto K. Bergsma, Adriaan Beukers
Department of Design and Production of Composite Structures,Faculty of Aerospace Engineering, Technical University Delft, Kluyverweg 1, 2629 HS Delft, The Netherlands

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The susceptibility of sandwich structures to localised (impact) damage is one of the main reasons why the sandwich concept is not yet used in large primary aircraft structures of airliners. The objective of this work is to experimentally investigatethe damage tolerance of representative composite sandwich panels for primary aircraft structures. Instrumented low-velocity impact tests were performed on sandwich specimens consisting of carbon Non-Crimp Fabric/epoxy facings and a Rohacell (PMI) foam core. Both internal and external damage resulting from these impact events was evaluated. The foam core material has a considerable influence on theamount of damage detected by ultrasonic TTU C-scan. CAI tests however showed that this core damage has no significant influence on the residual compressive strength of the specimens. Ó 2008 Elsevier Ltd. All rights reserved.

Article history: Received 22 April 2008 Received in revised form 15 September 2008 Accepted 29 October 2008 Available online xxxx Keywords: B. Impact behaviour B. Mechanicalproperties B. Damage tolerance D. Non-destructive testing

1. Introduction Sandwich structures are applied in various areas, ranging from civil engineering and road transport (composite trailers) to marine and aerospace applications. The degree of integration and structural efficiency of these sandwich structures varies however. In the construction of trailers for instance, sandwich panels aremainly applied for thermal insulation and weight reduction in case of solid structural design. In marine applications, foam-core sandwich panels are applied for multiple reasons. Besides the reduced structural weight, sandwich panels can result in a nonmagnetic hull with a low acoustic and thermal signature, which can be key features in naval shipbuilding. In addition, maintenance costs are reducedby the application of non-corrosive materials [1]. A special feature of sandwich materials in modern yachts is the use of a foam-filled double hull, resulting in an unsinkable structure. In contrast to marine applications, sandwich structures are currently still at a lower level of functional and structural integration in the aerospace industry. In case of airliners, the use of sandwich structuresis limited to aerodynamic fairings, covers, doors and control surfaces [1]. Closed cell foam is also applied in the hat profiles on the rear pressure bulkheads of the Airbus A340 and A380, but merely as a manufacturing aid [2]. Even though the high potential of sandwich structures is well acknowledged [2–4], their use in large primary aircraft structures has not yet been established. The conceptionthat sandwich struc* Corresponding author. E-mail address: (J. Leijten). 1359-835X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.compositesa.2008.10.019

tures are susceptible to localised damage is one of the main reasons for this [4–6]. Furthermore, new technologies must compete with the current highly developed metal aircraft structures,making the introduction of these new materials slightly more difficult. New technologies must therefore offer significant advantages over the existing technology in order to compensate the development costs [3]. Sandwich structures consisting of composite facings and foam core material are believed to have an added value for primary aircraft structures by not only fulfilling mechanical, but also...
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