Impact Analysis of an Oxygen Mask Locking Panel of Aircraft using Finite Element Modelling

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1 Applied Mechanics and Materials Online: ISSN: , Vol. 657, pp doi: / Trans Tech Publications, Switzerland Impact Analysis of an Oxygen Mask Locking Panel of Aircraft using Finite Element Modelling CROITORU Emilian-Ionut a and OANCEA Gheorghe b Transilvania University of Brasov, Eroilor Street, no. 29, , Brasov, Romania Department of Manufacturing Engineering a emil.ca2651@yahoo.ro, b gh.oancea@unitbv.ro Keywords: composite materials, composite panels, finite element modelling, impact analysis, oxygen mask panel, mesh, Patran, Nastran. Abstract. This paper presents a method of finite element modelling used for the impact analysis of a composite panel. In this research, the composite panel consists of an oxygen mask locking panel of an aircraft. This panel is loaded with one concentrated abuse loading and three uniform distributed abuse loading cases and the stress variation within the composite panel for each load case is determined. In order to assess the impact analysis on the oxygen mask panel of the aircraft, a finite element model is created using Patran as the main application for pre/post-processing and Nastran as the main processor. The paper also presents a comparison between results obtained using the same finite element modelling of the composite panel CAD model of the panel with four load cases with different material types. The results are used to determine the most capable material stresswise. Introduction The drivers to produce light-weight structures were provided by the price of oil, the change in attitude towards environmental issues and predicted increase in airline traffic and security. Also, the cost of development and introduction of these new structures is now offset by the gains. Hence, the increase in the usage of composites in aerostructures is a target for industrial companies. Composite structures are extensively employed in the aerospace industry. The understanding of their behaviour under impact conditions is extremely important for the design and manufacturing of these engineering structures since impact problems are directly related to structural integrity and safety requirements. This paper investigates the damage behaviour of composite sandwich panels with NOMEX flame-resistant meta-aramid material and glass or carbon fibre composition. A method for performing this investigation is a local stress analysis. Such an analysis is described and its capabilities are demonstrated. The local model is analyzed independently of the global model of the structure. This approach can be used to determine local, detailed stress states for specific structural regions using independent refined local models. This approach also reduces the computational effort necessary to obtain the detailed stress state in comparison to a global stress analysis. This local stress analysis is performed using finite element modelling, which is a numerical technique for finding approximate, solutions to boundary value problems for differential equations. Finite element model encompasses all the methods for assessing many simple element equations over many small subdomains, named finite elements, to approximate a more complex equation over a large domain [1]. The method presented is not restricted to having a priori knowledge of the location of the regions requiring local detailed stress analysis. Whoever, it does require knowledge regarding composite panels and their complete mechanics such as mechanical properties, strength, fracture, damage and fatigue mechanics, effect of environment, ageing, nondestructive testing and mechanical aspects of technology. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-04/03/16,21:47:10)

2 736 Engineering Solutions and Technologies in Manufacturing The complete mechanical behaviour and mechanics analyses of composite panels are presented literature [2], [3], including many concepts explanations, theory vs. experiment issues, description of fibers, deformations, properties, laminated plate failure criteria, deflection, buckling, and vibration problems. The current state of impact analysis on a sandwich composite panel of NOMEX and PEI is described[4], where the global/local stress analysis of composite panels using the finite element analysis program PAM-CRASH reproduces physical behaviour observed experimentally [5]. The recent increase in the use of composites has involved the development of new and improved manufacturing methods. These manufacturing methods are now allowing to develop parts that are testing the limitations of the materials used. For the future applications that will require developments in material properties, tests are required and finite element analysis is proving again to be the key to this issues. Finite Element Analysis of the Oxygen Mask Locking Panel of Aircraft The finite element analysis of impact analysis of the panel in question in Patran [6] and Nastran [7] involves the following steps: 3D modelling of the part presented in the Fig. 1 and the adequate materials from Table 1; finite element model generated using basic constraints and additional boundary conditions required (see Fig. 2); finite element analysis of the behaviour of the composite panel under the proposed loadings of 685 N, which is the equivalent of a 70 kg person weight impact in different critical areas (see Fig. 3). Table 1. Material properties used in FE modelling Property / Type of Material Aluminium Carbon Fibre Glass Fibre Nomex Elastic modulus [MPa] Poisson s ratio [-] Shear Modulus [MPa] Density [t/mm 3 ] 2.70E E E E-11 Thickness [mm] Fig. 1. 3D CAD model of the oxygen mask panel view from interior

3 Applied Mechanics and Materials Vol Fig. 2. Finite element model constraints and boundary conditions Fig. 3. Finite element model - loadings In order to complete the necessary analysis data, the following conditions and requirements have to be used: General: o units [1000 mm] used; Geometry: o unnecessary holes and uncritical radiuses removed from model; FE-model: o parts connected appropriately; o no open edges in the model; o normal vector of the elements justified; o no double elements in model; o node equivalence; Elements: o not more than 5% CTRIAs used; o no bad elements jacobian ratio less than 2.00; Properties: o correct properties for all element types; o correct material and orientation for all elements; o correct layup and orientation for composites global ply ID used; o weight of the panel correct;

4 738 Engineering Solutions and Technologies in Manufacturing Boundary conditions: o correct boundary conditions on correct nodes; o renumbering of nodes with boundary conditions; o correct loads and forces (force [N], pressure [MPa], acceleration [m/s]); Load cases: o load cases correct loads and boundary conditions; o scale factor 1.00; Jobs: o correct solver; o correct output file format (*.op2 / *.xdb); o additional results defined in the load case; o non-linear analysis with correct convergence criteria; Calculations: o no fatal message in *.f06 file; o no bad elements in *.f06 file; o non-linear convergence 100%; o job finished successfully; Results: o displacements look natural; o correct reaction forces; In the finite element analysis of panels metallic or composite otherwise is usually used the finite element type of linear quadrilater CQUAD4 which is the element that defines an isoparametric membrane-bending or plane strain quadrilateral plate. According to the size of RAM and computer processor CPU performance, the calculations are an intensive hardware consumer and also time in the order of tens of minutes. After the calculation phase, the result files are obtained which include the displacement and tension obtained for each loading investigated. The results of the finite elements analysis are influenced by the input parameters, the simulated phenomenon s accuracy, the establishment of the restrictions, and by the conditions of interaction between surfaces in contact if there are any. Obtained Results The complete results of this finite element analysis are presented in the Table 2. The results considering Aluminium as the material from which the panel is composed will be ignored for the following reasons: overweight 10 times more weight in the Aluminium model compared to the Carbon or Glass model; thickness is very high which requires milling of the parts that leads to expensive costs for a non-structural part of the aircraft; Table 2. Finite element analysis results Aluminium Carbon Fiber Glass Fiber Weight kg kg kg Load Case Displacement [mm] Stress [MPa] Displacement [mm] Stress [MPa] Displacement [mm] Stress [MPa] LC LC LC

5 Applied Mechanics and Materials Vol Thus, for this research, the results obtained for Carbon Fiber and Glass Fiber are adequate. A comparison between the maximum stresses for the critical load case is presented in Fig. 4. Fig. 4. Critical load case Carbon Fiber vs. Glass Fiber Conclusion The study of impact analysis of the oxygen mask locking panel of aircraft using finite element modelling proves the advantages of composite materials being used in the aerospace industry in general and in the aircraft interiors in particular. Thus, these materials are: light-weight materials reduction in weight for the considered panel of 90%; high strength related to weight tensions related to mechanical properties are similar; good resistance to corrosion; high-impact strength proven also in this article; good flexibility low deformations according to the detailed FEM; dimensional stability no change in the shape of the materials; part consolidation lower number of parts; durable many composites have been in service for half a century; others: low thermal conductivity, radio translucent, non-conductive and non-magnetic properties. Acknowledgement This paper is supported by the Sectoral Operational Programme Human Resources Development (SOP HRD), ID financed from the European Social Fund and by the Romanian Government References [1] O.C. Zienkiewicz, R.L. Taylor, J.Z. Zhu, The Finite Element Method: Its Basis and Fundamentals, sixth ed., Butterworth-Heinemann, [2] Jones, Robert M, Mechanics of Composite Panels, second ed., Taylor Francis, [3] Gibson, Ronald F, Principles of Composite Material Mechanics, first ed., McGraw-Hill Higher Education, [4] Aktay, Levent, Johnson, Alastair F, Holzapfel, Martin, Prediction of impact damage on sandwich composite panels, Institute of Structures and Design, German Aerospace Center, Elsevier B.V., [5] J.B. Ransom, F. Knight Jr, Global/local stress analysis of composite panels, Structural Mechanics Division, NASA Langley Research Center, Hampton, VA, U.S.A., [6] *** MSC Patran 2010 Quick Reference Guide Non-Linear Static Analysis User s Guide, Revision 1, VOL-1, [7] *** MSC Nastran 2010 Quick Reference Guide Non-Linear Static Analysis User's Guide, Revision 1, VOL-1, 2010.

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