Study and design of a monocoque wing structure with composite materials BACHELOR'S DEGREE THESIS Bachelor's degree in Aerospace Vehicles Engineering Miguel Alejandro Pareja Mu~noz Director: Llu´ısGil Espert June 2016 DOCUMENT 1.- REPORT Universitat Polit`ecnicade Catalunya Escola Superior d'Enginyeries Industrial, Aeroespacial i Audiovisual de Terrassa "Inspiration unlocks the future." The Wind Rises (2013) i Acknowledgements Firstly, I would like to express my sincere gratitude to my advisor Prof. Llu´ısGil for the continuous support during the making of my Bachelor's degree thesis, for his patience, motivation, and immense knowledge. His guidance has helped me in all the time of research and design, and also in the writing of this thesis. My most sincere thanks also goes to my team mate and friend, Roger Serra. He has selflessly dedicated his precious time to help me so many times, not only allowing me to reach the solution of my problems, but also making me have a great time with him. I also want to acknowledge my team mate Oriol Chandre for his great company at the Trencal`osTeam workshop, in which we both have spent several hours working on our thesis. He always being in a great mood and his energy have always motivated me and influenced me very positively. Lastly, my highest appreciation goes to my family and friends, without whom I would not be who I am today. Special thanks goes to my mom, as she has supported me wholeheartedly throughout the making of this thesis - both in the good and bad moments I have experienced. ii Abstract Trencal`osTeam - an aeromodelling research team, is looking to enlarge its know-how about composite-made structures. For their own experience, the best option to win the competitions they attend is with a monocoque wing structure made with composite materials. Me, as a member of Trencalos Team, I have taken this oportunity to help in the study of that matter. The thesis covers the study of the main the knowledge necessary to approach a design of such a structre in depth. This type of structure is more complex to characterize than a classical truss structure - its structural behaviour is influenced by several parameters, i.e. is multi-parametric. This parameters/features have been studied, as well as the governing laws that describe the structural beeahviour of tgis structures. Additionally, the design of a structure of this kind has been performed following a design methodology that is based in optimisation of two objectives. The design of such a structure represents a problem with multiple possible objectives, and for the sake of simplicity, just two of them have been addressed. The design methodology has been implemented in the following way: making a set of initial cases, analyse them and then apply an optimisation procedure to discard cases and find the best ones. After doing that, more cases have been made from the best cases of the last iteration. The modelling of the geometry in this thesis has been done with CATIA V5R20. The structural analysis has been performed with AbaqusTM. From the methodology premises that have been set in order to delimit such a multi-parametric study, results have been obtained. These mainly have been useful to observe the trends/effects of each of these design parameters in the final structure behaviour. Besides, an optimal solution has been found following an optimisation procedure, which is interesting from the perpspective of familiarising with this kind of tool, as any complex engineering problem depends on a lot of parameters and they are required to solve it. With all this accomplished, conclusions have been extracted about which are the best parameters combinations to include in a monocoque wing structure made with composite materials. iii Summary The thesis is divided in 8 chapters: Introduction, State of the Art, Methodology, Results, Conclusions, Future Work, Environmental Impact, Budget and Annxes. In the Introdcution chapter, a brief and concise summary of the aim, scope and objectives of the thesis is delivered. Also, the justification and a planning of the same is attached. In the State of the Art chapter, all the bibliographical research is done. All the infomation necessary to build a base on how monocoque wing structures made of composite materials behave is given there. Also, basic information about the design tools used for the design process is given here. In the Methodology chapter, the premises on which the design is based on are detailed. Then, the design procedure - set of steps - followed to obtain an optimal solution is explained. And finally, the process to prepare, execute and post-process an structural analysis is explained. In the Results chapter, the results obtained are thoroughly explained with all kinds of details and different supports - i.e. tables, plots, figures, etc. In the Conclusions chapter, all the information collected in the thesis is analysed from a general point of view and some conclusions are extracted. In the Future Work chapter, a suggestion of how the work perfomed in this thesis could be continued¸c,and in what direction, is explained. In the Environmental Impact, an insight of the impact of what has been done to accomplish this thesis on the environment is explained. In the Budget chapter, a budget of how much a project like this one would cost if it was undertaknen professionally is given. The budget is done separately in a different document. And for last, Annexes are attached providing complementary information that is of interest. The annexes are done separately in a different document. iv Contents Acknowledgements ii Abstract iii Summary iv List of Figures vii List of Tables xi List of Abbreviations and Symbols xiii 1 Introduction1 1.1 Aim........................................1 1.2 Scope.......................................1 1.3 Requirements...................................2 1.4 Objectives.....................................3 1.5 Justification....................................3 1.5.1 Identification of the Need........................3 1.5.2 Usefulness of the Study.........................4 1.6 Study's Approach.................................6 1.7 Planning......................................6 1.7.1 Brief Description of Tasks........................6 1.7.2 Detailed Relation Between Tasks....................8 1.7.3 Scheduling................................8 2 State of the Art 10 2.1 Historical Preamble................................ 10 2.2 Structural Concepts............................... 15 2.3 Composite Materials............................... 18 2.3.1 Main Properties of Composites..................... 20 2.3.2 Classification of Composites....................... 22 2.3.3 Laminae and Laminates......................... 24 2.3.3.1 Laminae............................ 26 2.3.3.2 Laminates........................... 28 2.4 Laminae Mechanical and Physical Properties................. 31 2.5 Classical Laminated Plate Theory....................... 35 2.5.1 Kinematics................................ 37 2.5.2 The Material Law............................ 38 2.5.3 Resultant Forces and Moments..................... 38 2.6 Buckling of Laminated Plates.......................... 40 2.7 Finite Element Analysis of Laminates..................... 43 v 2.7.1 Basic FEM Procedure.......................... 43 2.7.2 General FEM Procedure......................... 47 2.7.3 AbaqusTM ................................. 48 2.7.4 Shell Elements.............................. 49 2.8 Failure Criteria.................................. 50 2.8.1 Hashin Criterion............................. 50 2.8.2 Tsai-Hill Criterion............................ 51 2.9 Pareto Optimality................................ 51 3 Methodology 54 3.1 Premises of the Design.............................. 54 3.1.1 Type of Structural Testing....................... 54 3.1.2 Structural Requirements......................... 55 3.1.3 Geometrical Features of the Wing................... 55 3.1.4 Load-bearing Elements Employed.................... 56 3.1.5 Materials Employed and its Properties................. 57 3.1.6 Maximum Weight of the Structure................... 59 3.1.7 Minimum Buckling Constant...................... 59 3.1.8 Variation of Parameters Criterion.................... 60 3.1.9 Parameters of the Design........................ 61 3.2 Design Process Description........................... 62 3.2.1 Initial Tests................................ 62 3.2.1.1 Mesh Convergence....................... 62 3.2.1.2 Boundary Conditions..................... 63 3.2.1.3 Load Definition........................ 64 3.2.1.4 Buckling Modes Check.................... 67 3.2.1.5 First Tendencies Observed.................. 67 3.2.2 Starting Point.............................. 68 3.2.2.1 Decision Making........................ 68 3.2.3 Improvements............................... 69 3.2.4 Final Decision.............................. 70 3.2.5 Flowchart of the Design Process.................... 70 3.3 Analysis Process Description.......................... 72 3.3.1 Pre-processing.............................. 72 3.3.1.1 Geometry Preparation..................... 72 3.3.1.2 AbaqusTM Model Making................... 73 3.3.2 Simulation of the Analysis........................ 76 3.3.3 Post-processing.............................. 77 3.3.4 Flowchart of the Analysis Process................... 78 4 Results 80 4.1 Initial Tests Results............................... 80 4.1.1 Converged Mesh............................. 80 4.1.2 Final Encastre.............................. 82 4.1.3 Final Load Distribution........................