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FP7

CRASHING Report Summary

Project ID: 632438
Funded under: FP7-JTI
Country: Spain

Final Report Summary - CRASHING (Characterization of Structural Behaviour for High Frequency Phenomena)

Executive Summary:
In the project CRASHING an enhanced analysis strategy for composite structures suitable for accurate simulations of high frequency dynamic load events was developed and implement in the Topic Manager (TM) engineering environment. Towards this end, the state-of-the-art in techniques of modelling and simulation of composite materials was transferred to the TM, and implemented in the current numerical tools used by the relevant industry sector in general in the simulation of the mechanical behaviour of composite structures for aerospace applications (i.e. ESI – PAMCRASH). Overall, a multiscale analysis and simulation approach, rooted in solid material characterization experiments, to take into account the physical mechanisms of damage in composites at the different length scales from ply, laminate to component levels, was developed, implemented and validated using industry use cases. The approach was focused in composite materials currently used in aircraft innovative designs as well as new materials with potential application in the future. Overall, in the CRASHING project five different composite materials were addressed at their three length scales. It was demonstrated that the implemented simulation approach for these materials and structures will be suitable for simulations of aircraft crash-landing, ditching, bird strike, ice impacts and, in general, situations where the aircraft is subject to high frequency dynamic loading phenomena.

Project Context and Objectives:
The use of composite materials as principal structural elements in an aircraft requires the complete understanding of their mechanical properties. In particular, when the structure is subjected to high frequency loading conditions (i.e. low and high energy impacts) phenomena related to stress wave propagation, strain rate dependences, delamination and rupture need to be fully understood. Such cases are more and more important in fuselage designs, with the massive use of composite materials, as these materials are less ductile than metallic ones and are also prone to large invisible damages (delamination) after impact. This is crucial to obtain certification of aeronautical structures like those proposed within the “Clean Sky - Green Regional Aircraft” initiative.

Current numerical models are based on tests and technologies developed during the nineties in European R&T Programs. Since then, significant progress has been achieved in the development of physically-based models and multiscale modelling strategies, which provide more accurate results and can be applied to different materials. In the CRASHING project, the state-of-the-art in multiscale simulation of composites was transferred to the current numerical tools used by the industry in the simulation of the mechanical behaviour of composite structures for aerospace applications. The project was focused in composite materials currently used in aircraft innovative designs. In addition, new materials with potential application in the future were assessed as well.

The CRASHING project implemented a systematic strategy to determine the mechanical behaviour of composite materials under impact using numerical and experimental approaches in parallel. The objective was to develop and validate a multi-scale virtual design/testing strategy to take into account the physical mechanisms of damage at the different length scales, so the influence of the microstructure and loading conditions are taken into account rigorously. The multiscale approach describes systematically the material behaviour at different length scales from ply to laminate to component level. One additional advantage of this bottom-up multiscale approach is that changes in the properties of the constituents (fibre, matrices), the fibre architecture or laminate lay-up can be easily incorporated to provide new predictions of the macroscopic behaviour of the composite under static and dynamic behaviour.

It was demonstrated in CRASHING that the multi-scale approach is suitable for simulations of aircraft crash-landing, ditching, bird strike, ice impacts and, in general, situations where the aircraft is subject to high frequency dynamic loads, commonly described as the ‘vulnerability’ topic. Innovative damage models were developed and implemented in commercially-available numerical analysis tools typically used by the aeronautical industry for crashworthiness including the effect of various damage modes at ply level as well as delamination. Such models are fed by specific material properties as inputs that were experimentally measured during the project. Also, specific tests were carried to validate the numerical simulation methodologies. These new simulation tools provide better predictive capabilities but also a wider range of validity when compared with past approaches.

The coupled experimental-numerical strategy was specifically developed for two material architectures (unidirectional and woven) and two composite panel concepts (laminated monolithic and sandwich) representative of current applications within the Topic Manager engineering environment. In addition, the approach was extended to address new materials with potential application in the future.

Project Results:
In general lines, within the first 12 months of the project CRASHING, the bottom level of the multiscale approach was addressed with success: the prediction of the composite ply properties by means of computational micromechanics having as inputs their constituent properties (fibre, resin, interface, fibre architecture) which were characterized with advanced experimental micromechanic techniques. Within the last 18 months of the project the next two material scales were tackled. First, the prediction of laminate properties by means of computational mesomechanics having as inputs the properties of the plies. Then, high-fidelity computational simulation of the behaviour of structural composites under impact and crashing situations in aeronautics.

In specific, the following results were achieved:

- Five different types of composite materials defined according to the agreement with the topic manager during the negotiations phase, were procured in enough quantities to produce small specimens for material property characterization and larger specimens for experimental characterization of impact response.
-Coupons for the characterization of the properties of the five different materials were manufactured. This included manufacturing of composite panels (layup and curing/consolidation), quality checking and specimen cutting.
-Material characterization test campaigns were carried out, after the definition of respective test matrices, to determine the mechanical properties of the five different materials: quasi-static ply properties, dynamic ply properties and fracture properties including analysis of failure mechanisms.
-Specimens were produced for the experimental evaluation of the (low- and high-velocity) impact response of the five different materials studied in the project, as agreed with the TM. This includes manufacturing of composite panels (layup and curing/consolidation), quality checking and specimen cutting.
- Experimental characterization of the response of the five materials to (low- and high-velocity) impact was carried out.
- An exhaustive literature review was performed on numerical modelling of composite materials for impact and crashing analysis and implementation of modelling strategies in the numerical software selected with the topic manager in the negotiations phase i.e. PAMCRASH provided by ESI.
- Numerical models were developed and implemented in ESI – PAMCRASH to simulate the five different materials under impact and crashing loads.
- The implemented multiscale simulation approach was validated using the experimental impact results obtained in the project and other experimental results provided by the Topic Manager.

Potential Impact:
The final objective of the project CRASHING was to develop and validate a multiscale modelling strategy to carry out high fidelity simulations of the mechanical performance of composite structures under impact. There are two main innovations provided by the new toolset. Firstly, the bottom-up, multiscale modelling strategy includes the actual physical deformation and damage mechanisms at different length scales (ply, laminate and component) so the influence of the microstructure and loading conditions in the material deformation is rigorously taken into account. Secondly, the models were implemented and optimized (GUI, coarse meshes, etc.) in commercial software to be used in an industrial environment for the analysis of impact and crashworthiness of aircraft structures.

The new multiscale modelling and simulation approach transferred to the Topic Manager engineering environment, and available for exploitation within a wider market, will lead to a substantial improvement in the understanding of the mechanical behaviour of the structural composites subjected to high frequency loading conditions and will lead to better designs in the components developed within the Clean Sky - Green Regional Aircraft (GRA) programme. Although this is an important achievement, the industrial implementation on the new multiscale strategy is expected to have a very large impact on the design and certification of composite structures in aerospace because it will open the door to the industrial implementation of the virtual design and virtual testing strategies. The multiscale approach will allow the introduction of the materials at the constituent level (fibre, resin, interface, fibre architecture) in the design process of new components because the influence of these parameters on the mechanical performance can be easily and rapidly assessed by means of high-fidelity, multiscale simulations. This will lead to faster and better designs, accelerate materials development, transform the engineering design optimization process and unify design and manufacturing. In addition, high fidelity simulations will reduce the number of costly experimental tests to certify safety and, eventually, virtual mechanical testing by means of these advanced simulations is expected to play a very important role on the certification process of aircraft structures. Thus, the industrial implementation of the new analysis capabilities will provide a strategic technological leadership in structural design with composite materials for the European aerospace industry.

Overall, CRASHING will contribute to the successful development of the GRA demonstrator that aims at developing a low-weight regional aircraft to reduce the fuel consumption and therefore reducing CO2 emissions in order to fulfil the European aviation environmental objectives for 2020 (a decrease of 50% in CO2 emissions). In addition, the project contributes to some of the objectives identified in the ACARE’s report European Aeronautics: A Vision for 2020, the most relevant being ”securing global leadership responding to society’s needs”.

In result of its success, the project CRASHING is foreseen to have a strong technological impact (with significant improvements in design flow, reductions in development cost and on weigh reduction), will contribute to the environmental H2020 strategy, and will provide socio-economic benefits within the next five to ten years by means of:

- Enhancing the technological leadership of the topic manager and ITD members in the field
- Enhancing the competitiveness and leadership of European aerospace industry
- Supporting employment of highly skilled professionals
- Meeting society needs for environmentally friendly, safe and efficient air transport.

List of Websites:
For more information about the CRASHING project, please contact:

Dr. Claudio Lopes – CRASHING Project Technical Coordinator and Senior Researcher at IMDEA Materials Institute
claudiosaul.lopes@imdea.org

Miguel Ángel Rodiel – CRASHING Project Manager and Technology Manager of IMDEA Materials Institute
miguel.angel.rodiel@imdea.org

Project CRASHING website: http://www.crashing-project.eu/

Contact

Claudio Saul Lopes, (Researcher)
Tel.: +34 915493422
E-mail
Record Number: 195797 / Last updated on: 2017-03-10
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