Efficient design and verification of composite structures

Projektinformationen

EDAVCOS

ID Finanzhilfevereinbarung: BRPR980611

Projekt abgeschlossen

Startdatum 1 März 1998

Enddatum 28 Februar 2001

Finanziert unter

• Specific research and technological development programme in the field of industrial and materials technologies, 1994-1998

Gesamtkosten Keine Daten

EU-Beitrag Keine Daten

Koordiniert durch

SAAB AB
Schweden

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Verwertbare Ergebnisse

Efficient design and verification of composite structures; EDAVCOS

The EDAVCOS programme has been focused on methods necessary for the development of a cost efficient route to certification of composite aircraft structures. The objective was to propose and partly validate an analysis based procedure for structural verification from design to final certification. The targets for the new verification procedure were a 50% reduction of the total cost for verification and a 60% reduction of the time scale. The work in EDAVCOS was concentrated on development of design and analysis methods with the purpose to reduce the huge amount of testing and to optimise testing still required and thereby save costs and shorten the time spent in testing. The method development has been focused on five different structural types: sandwich panels, stiffened panels for fuselage applications, stiffened panels for wing applications, shear webs and bolted joints. The methods have been validated with well instrumented structural tests. To further increase the degree of validation, fractography has been used extensively to characterise the growth process and sequence of failure from initiation to total failure. A large number of both global and local analysis methods with varied sophistication and complexity have been developed. The cheap and fast methods which are suitable for the every day design work have the potential to directly save time and cost if they are implemented in appropriate design tools. The high precision methods can be used to reduce the need for testing and thereby save time and cost. A set of high quality test results has been created within the project. Extensive use of fractography gives failure mode evidence which increases the degree of validation of the methods and the value of the test results for future analysis method development. For sandwich panels the methods developed comprised of: FE based methods to predict growth of a skin delamination and a semi-analytical method for design of land-ramp regions. The methods have been validated with compression, bending and shear tests and tests with land-ramp regions. The methods developed for stiffened panels include: methods to predict buckling and post buckling behaviour including interaction with defects and damage (local delamination buckling); methods to predict failure at the skin-stiffener interfaces and ply drop-offs, damage due to impact, growth of impact damage and delaminations, and residual strength and life of free field delaminations containing impact damage. A large number of tests with stiffened panels have been carried out to validate the analysis methods developed. These tests include: flat and curved panels, compression and shear loading, fatigue loading, different stiffener configurations (blade, hat, Z, I), stiffened box skins, stringer run-outs, single impact damages and embedded disbonds at different locations (bay, foot), multiple impact damages and embedded disbonds and stringer disbonds. For shear webs, design and analysis methods for different hole configurations have been developed. These methods include buckling, stress concentrations and free edge effects. To validate the methods, shear tests with panels including four different hole configurations have been carried out. For bolted joints a special joint element, 2-D and 3-D FE based analysis methods and failure prediction methods including both progressive failure criteria and a characteristic distance approach have been developed. The methods were validated with tests including a well instrumented special multi fastener joint specimen and stiffened panels with a splice joint. The review of current airworthiness approaches has resulted in a known state-of-the-art for structural evaluation within the European Aircraft industry and among the European research institutes which has created good foundation for improvement of the certification procedure. A new verification procedure with a strong cost and time saving potential has been proposed but the demanding targets for cost and time scale reduction are only partly reached. The work carried out in EDAVCOS is, however, only a first step towards a new certification procedure and more research and development are needed before the indicated potentials can be fully utilised.