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Hamburg, Germany

Mittelstedt C.,ELAN GmbH
25th Technical Conference of the American Society for Composites and 14th US-Japan Conference on Composite Materials 2010 | Year: 2010

In composite laminated structures, severe interlaminar stress fields may arise in the vicinity of geometrical discontinuities such as holes, corners, notches, cracks, as well as near material discontinuities like free-edge interfaces between dissimilar laminate layers. The latter problem class is usually referred to as the so-called free-edge effect. Mainly evoked by the differing elastic material properties of two adjacent dissimilar laminate layers, the free-edge effect is characterized by significant (and possibly even singular) three-dimensional stress fields at the free edges of composite laminates that rapidly decay with increasing distance from the free edge, until in the inner laminate regions sufficiently remote from the free edge (usually at a distance more or less equal to the laminate thickness), an unperturbed stress field according to Classical Laminate Plate Theory (CLPT) is recovered. Such interlaminar stress concentrations are of highest practical importance since typical composite materials such as fiber-reinforced plastics only exhibit rather weak interlaminar strength properties. Consequently, free-edge stress fields may lead to premature failure of the laminate due to interlaminar failure modes like e.g. delamination fracture. Initiated by the classical seminal and wayleading work by Pipes and Pagano [1] in 1970 (even though one of the first works in this field has been published by Hayashi [2] in 1967) the free-edge effect has had a very rich research tradition since more than 40 years and a virtually uncountable number of publications is available. In an effort to give an overview over the main analysis aspects of the free-edge effect, this paper summarizes a selection of relevant works in this field. The main emphasis is put on the kind of employed methodologies, the underlying assumptions and the modelling aspects in the reviewed investigations with a bias towards closed-form or semi-analytical methods. The paper closes with a summary of current research on free-edge effects, and an outlook (which only represents the author's opinion and which is surely far from being complete) on future investigations is attempted. Source

Huhne C.,German Aerospace Center | Huhne C.,Leibniz University of Hanover | Zerbst A.-K.,Leibniz University of Hanover | Kuhlmann G.,Airbus | And 2 more authors.
Composite Structures | Year: 2010

The structural behaviour of a single-lap, single-bolt composite joint is investigated using a three-dimensional finite element model. In contrast to previous investigations the influence of a liquid shim layer, added between the two laminates, on strength and structural behaviour of the joints is investigated by virtual testing. The finite element model is validated with experimental data. The experiments point out that the structural behaviour of these joints is dominated by progressive damage. Therefore, as a first approach, progressive damage is considered using Hashin's three-dimensional failure criterion and a constant degradation model. It is shown that this combination yields very conservative results. As a second approach the model is improved by a continuous degradation model. Considering continuous degradation, the numerical results show very good correlation with the experimental data. © 2009. Source

Mittelstedt C.,ELAN GmbH | Schroder K.-U.,Johannes Kepler University
Composite Structures | Year: 2010

In this paper, a closed-form method for the analysis of the local postbuckling behaviour of aircraft panels that are braced by hat-stringers is presented. The stiffened panels are loaded by transverse compression which is a load case that has been treated only scarcely in the open literature, and the corresponding buckling and postbuckling behaviour that eventually leads to failure of the panel is quite different to what is observed when a panel under longitudinal compression is considered. This contribution clarifies that the ultimate load bearing capacity of a stiffened panel with closed-profile stringers under transverse compression is governed by several consecutive stability cases. Firstly a closed-form approximate analysis method for the linear buckling analysis of the skin between two stringers taking the torsional stiffness of the hat-stringers into account is derived (stability case 1). Secondly, a simple Marguerre-type postbuckling analysis method is presented that accounts for the geometrically nonlinear behaviour of the panel skin after buckling (stability case 2) and enables a closed-form analysis of its effective width. Thirdly, the linear buckling analysis is adapted to the analysis of the panel skin under a stringer (stability case 3). It will be shown that stability cases 2 and 3 cannot be treated independently, but have to be considered interactively which necessitates an iterative procedure. The accuracy of the proposed analysis method, relying on the simplifying assumption of a perfectly flat plate rather than considering a cylindrically curved panel is established by comparison with results of accompanying geometrically nonlinear finite element calculations. © 2010 Elsevier Ltd. Source

The invention relates to a method and a system for detecting, transmitting, and analyzing at least one safety-related signal (S

Agency: Cordis | Branch: H2020 | Program: MSCA-ITN-ETN | Phase: MSCA-ITN-2014-ETN | Award Amount: 3.10M | Year: 2015

Composite structures are massively exploited in many engineering fields. For instance, the state-of-the-art civil aircraft (B787 and A350) are mostly made of composite materials. The design of composites leads to challenging tasks since those competencies that stemmed from the adoption of metallic materials are often inadequate for composites. Insights on many different disciplines and tight academic/industrial cooperation are required to fully exploit composite structure capabilities. The skills and the employability of young researchers increase to a great extent through an interdisciplinary and intersectoral training. The existing training schemes are often based on specific themes and disciplines rather than on a broad interdisciplinary and academic-industrial integrated approach. The main aim and novelty of this project is the creation of a multidisciplinary, intersectoral and international research training network based on a strong academic basis and industrial partnerships for a new generation of top talented young researchers that will work in the European academic and industrial scenarios. The multidisciplinary features are guaranteed by the presence of 7 universities, 1 research centre and 1 industry. The intersectoral approach will be pursued by including secondments and specific industrial training requirements in each individual project. The consortium is composed by partners from 8 countries. OTC partners were included for secondment and training opportunities; they were chosen on the basis of their expertise and to enhance the internationality features of the training. Their presence is seen as an opportunity for the European partners and researchers to strengthen competencies. The full spectrum of the design of composite structures will be dealt with - manufacturing, health-monitoring, failure, modelling, multiscale approaches, testing, prognosis and prognostic - to develop integrated analysis tools to improve the design of composites.

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