Introduction to the course
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AEROSPACE STRUCTURES Prof. Alessandro Airoldi INTRODUCTION TO THE COURSE Introduction to the course Objectives of the course Stressed skin constructions in aircraft structures Peculiar aspects of helicopter structures Examples of space structures Contents and organisation of the course Space Structures - Prof. Alessandro Airoldi 2 Introduction to the course Objectives of the course Approaches to the analysis of structures in aerospace constructions Space Structures - Prof. Alessandro Airoldi 3 Introduction to the course Objectives of the course Aerospace constructions INERTIAL LOAD AERODYNAMIC LOADS AERODYNAMIC LOADS INERTIAL LOAD Aerospace structures Structure works to transfer the applied loads Force equilibrium (D’Alembert principle) Such considerations apply to all type of structures (not only aerospace structure) THRUST Space Structures - Prof. Alessandro Airoldi 4 Introduction to the course Objectives of the course Aerospace constructions THRUST AERODYNAMIC LOADS ROTOR THRUST Aerospace structures Structure works to transfer the applied loads Force equilibrium (D’Alembert principle) INERTIAL LOAD Such considerations apply to all type of structures (not only aerospace structure) Space Structures - Prof. Alessandro Airoldi 5 Introduction to the course Objectives of the course Requirements: Stiffness AERODYNAMIC LOADS AERODYNAMIC LOADS Limitation to the relative displacements due to functional requirements (e.g. aerodynamics) Avoid frequency coupling (resonance) Strength INERTIAL LOAD Avoid permanent deformation and the collapse of the structures under operative load INERTIAL LOAD Shape Constraints AERODYNAMICS, INTERNAL VOLUMES FOR PAYLOADS THRUST OBJECTIVE: perform structural functions, fullfilling requirements, respect constraints with MINIMUM WEIGHT Space Structures - Prof. Alessandro Airoldi 6 Introduction to the course Objectives of the course Why analysis ? 1 Analysis of existing structures helps understanding the functions of structural elements, critical issues in design, the available solution for design (synthesis) Space Structures - Prof. Alessandro Airoldi 2 Design is an iterative process, which involve analysis of design hypothesis at different level of detail 7 Introduction to the course Objectives of the course Enhance the capability to apply the approaches of structural mechanics to the structural types that are employed in aerospace structure. Given the applied loads: -methods for the evaluation of internal stress and strain states -methods for the evaluation of stiffness, displacements, natural frequencies Learn the main features of aerospace structures: comprehension of structural roles, capability to critically analyse a structure Achieve the bases for a proper use of structural calculation software (Finite Element Method): knowledge of principles, technologies, limitations Space Structures - Prof. Alessandro Airoldi 8 Introduction to the course Objectives of the course Stressed skin constructions in aircraft structures Peculiar aspects of helicopter structures Examples of space structures Contents and organisation of the course Space Structures - Prof. Alessandro Airoldi 9 Introduction to the course Stressed skin constructions in aircraft structures Vickers Wellington (1943) Truss Structures were used at the beginning of flight history They consist of slender members connected at the ends They are a very efficient structural concept, which is still widely used in aerospace engineering PA-18 welded tubes structure Space Structures - Prof. Alessandro Airoldi Engine Mounts Integrated Truss Structure Section in ISS 10 Introduction to the course Stressed skin constructions in aircraft structures However, the peculiar and severe requirements for aircraft structures led to the development of another very effective structural typology: Thin load bearing skin (stressed skin), reinforced by longitudinal stringers and internal frames SEMI-MONOCOQUE STRUCTURES They still represent the basic structural concept in all aerospace structures (toghether with truss structures) Space Structures - Prof. Alessandro Airoldi 11 Introduction to the course Stressed skin constructions in aircraft structures STRESS SKIN STRUCTURES Longitudinal stringers Airbus A340 Thin load bearing skin Transverse Frames Space Structures - Prof. Alessandro Airoldi 12 Introduction to the course Stressed skin constructions in aircraft structures FABRIC COVER TRUSS STRUCTURE Biplane (1916) INTERNAL FRAMES (RIBS) AND LONGITUDINAL REINFORCEMENT (SPARS) Motivations for the development of stressed skin constructions can be traced to the beginning of flight Space Structures - Prof. Alessandro Airoldi 13 Introduction to the course Stressed skin constructions in aircraft structures Q 1 C p V 2 S 2 Torsional stiffness: critical issue in wing design High pitch angle Low pitch angle WING TORSION Space Structures - Prof. Alessandro Airoldi 14 Introduction to the course Stressed skin constructions in aircraft structures Torsional stiffness of biplane wings Space Structures - Prof. Alessandro Airoldi 15 Introduction to the course Stressed skin constructions in aircraft structures Hurricane had originally a fabric cover (1935) All metal stressed skin provided in 1939 Load bearing skin provides a closed highstiffness path for shear stress, contribute to bending stress and stiffness Space Structures - Prof. Alessandro Airoldi 16 Introduction to the course Stressed skin constructions in aircraft structures Thin load bearing skin (stressed skin), reinforced by longitudinal stringers and internal frames Semi-monocoque structure (1943) Space Structures - Prof. Alessandro Airoldi 17 Introduction to the course Stressed skin constructions in aircraft structures Modern airliner structure COMPOSITE VERTICAL TAIL WITH SEMIMONOCOQUE MORPHOLOGY Space Structures - Prof. Alessandro Airoldi CLOSELY SPACED FRAME AND RIBS (internal diaphragm in fuselage and wing 18 Introduction to the course Stressed skin constructions in aircraft structures Wing box and ribs REAR SPAR FWD SPAR Integrally stiffened composite skin Space Structures - Prof. Alessandro Airoldi 19 Introduction to the course Stressed skin constructions in aircraft structures TRUSS STRUCTURES Type of diaphragms and instability C – SHAPED BEAMS WITH VARIABLE SECTION AND CUTOUTS CLOSED LOOP OF BEAMS WITH L, C, Z or other shape SECTIONS Space Structures - Prof. Alessandro Airoldi 20 Introduction to the course Stressed skin constructions in aircraft structures Tail structure and bulkheads AIRBUS A 300 TAIL BULKHEAD WORKING UNDER PRESSURE LOADS A380 COMPOSITE BULKHEAD Space Structures - Prof. Alessandro Airoldi 21 Introduction to the course Stressed skin constructions in aircraft structures Supersonic fighters FUSELAGE FRAMES ARE MORE SPACED DUE TO NEED OF LARGE CUT-OUTS (Cockpit, cut-out inspections of engines, air inlets) WINGS BECOME VERY THIN AND STRINGERS ARE MERGED IN A SERIES OF SPARS Space Structures - Prof. Alessandro Airoldi 22 Introduction to the course Objectives of the course Stressed skin constructions in aircraft structures Peculiar aspects of helicopter structures Examples of space structures Contents and organisation of the course Space Structures - Prof. Alessandro Airoldi 23 Introduction to the course Helicopter anatomy Different structural parts can be distinguished for the static design: fuselage; tail boom; tail planes; rotor blades. Space Structures - Prof. Alessandro Airoldi 24 Introduction to the course Stressed-skin and helicopter structure -FEW SPACED FUSELAGE FRAMES - LARGE CUT-OUTS -TAIL BOOM AND PLANES FOLLOW A MORE CONVENTIONAL STRESSEDSKIN CONSTRUCTION SCHEME EH 101 structure Space Structures - Prof. Alessandro Airoldi 25 Introduction to the course Fuselage and tail boom Apache structure Space Structures - Prof. Alessandro Airoldi 26 Introduction to the course Application of beam schemes BEAM AXES A 109 structure Space Structures - Prof. Alessandro Airoldi 27 Introduction to the course FUSELAGE STRUCTURE WITH LARGE CUTOUTS Fuselage, floor and subfloor REAR FRAME ROTOR THRUST CUTOUT FOR DOORS FORWARD FRAME INERTIAL LOAD Space Structures - Prof. Alessandro Airoldi FLOOR AND SUBFLOOR 28 Introduction to the course Importance of crashworthiness Landing Gear Fuselage SOIL Subfloor Energy Absrober Seats OCCUPANTS Structural part the influences occupant survivability Controlled failure of the tail boom to reduce the mass to be decelerated Roof response Landing gears Fuel tank response Crashworthy seats Space Structures - Prof. Alessandro Airoldi Subfloor Crashworthy seats Fuselage structure must withstand to avoid occupants injuries 29 Introduction to the course Rotor Blades VERY LARGE CENTRIFUGAL LOADS -ORIGINAL DESIGN FOLLOWED THE PRINCIPLES OF STRESSED SKIN CONSTRUCTION APPLICATION OF COMPOSITES: D SPAR (UD FIBRE REINFORCEMENT) TORSIONAL STIFFNESS PROVIDED BY +/-45 BOXES FOAM AND HONEYCOMB FILLERS Space Structures - Prof. Alessandro Airoldi 30 Damage tolerance and helicopter composite components Rotor Blades: section D-spar: 0° UD bulk core wrapped by +/- 45° anti-torsion box Metallic wear strap Space Structures - Prof. Alessandro Airoldi Carbon +/-45° trailing edge skin Nomex honeycomb 31 Damage tolerance and helicopter composite components Rotor Blades: root Centrifugal load is reacted at two lugs connecting the blade to the hub Blade root Space Structures - Prof. Alessandro Airoldi UD material of D-spar arranged in ribbons wrapped around lug bushes 32 Introduction to the course Objectives of the course Stressed skin constructions in aircraft structures Peculiar aspects of helicopter structures Examples of space structures Contents and organisation of the course Space Structures - Prof. Alessandro Airoldi 33 Introduction to the course Examples of space structures: SPACE SHUTTLE Unique combination of semimonocoque, pressure vessels, truss structures structural concepts Orbiter SRB External tank Space Structures - Prof. Alessandro Airoldi Many different materials used: -Aluminium alloy - high strength steel -Titanium -Boron/aluminium composite -Carbon/epoxy composites -Fibreglass -Ceramics 34 Introduction to the course Examples of space structures: SPACE SHUTTLE Solid busters MAIN STRUCTURE: SEGMENTED STRUCTURE (11 SEGMENT) HIGH STRENGTH STEEL 13 mm THICK JOINED BY STEEL PINS JUNCTIONS WRAPPED BY FIBERGLASS SEALED WITH RUBBER BANDS SUCH MAIN STRUCTURE IS CLOSED BY THE FWD AND AFT SEGMENT DOMES IT IS THE EXTERNAL STRUCTURE BETWEEN THE FORWARD AND THE AFT SKIRT EXTERNAL COVER, SUCH AS NOSE CAP AND SKIRTS ARE MADE OF WELDED ALUMINUN Space Structures - Prof. Alessandro Airoldi 35 Introduction to the course Examples of space structures: SPACE SHUTTLE External Tank TWO TANKS: OXYGEN AND HYDROGEN PRE-FORMED ALUMINUM ELEMENTS (PANELS, MACHINED THICK ELEMENTS) PRESENCE OF INTEGRALLY MACHINED STRINGERS AND RING FRAMES RING FRAMES STABILIZE THE TANK AT HIGH COMPRESSIVE LOADS INTERTANK STRUCTURE IS A MORE CONVENTIONAL SEMIMONOCOQUE STRUCTURE (PANELS-SKIN-FRAMES MECHANICALLY JOINTED) Space Structures - Prof. Alessandro Airoldi 36 Introduction to the course Examples of space structures: SPACE SHUTTLE Orbiter BASED ON SEMIMONOCOQUE PRINCIPLES LARGE PARTS MADE OF ALUMINUM ALLOY PECULIAR ASPECTS CONVENTIONAL FORWARD FUSELAGE STRUCTURE HOSTS WELDED PRESSURISED CREW MODULE CENTRAL SECTION FRAMES MADE OF BORON/ALUMINUM TRUSS STRUCTURE THRUST BEARING TRUSS STRUCTURE WITH BORON/EPOXY REINFORCEMENTS WINGS WITH HONEYCOMB SKIN COVER Space Structures - Prof. Alessandro Airoldi 37 Introduction to the course Examples of space structures: SPACE SHUTTLE Orbiter FORWARD FUSELAGE: EXTERNAL SHELL STRUCTURE (SEMIMONOCOQUE CONCEPT) INTERNAL PRESSURIZED VESSEL Space Structures - Prof. Alessandro Airoldi 38 Introduction to the course Examples of space structures: SPACE SHUTTLE Orbiter CENTRAL SECTION LONGHERON CARRY BENDING LOADS HIGH STIFFNESSSTRENGTH REQUIRMENT FOR FRAMES: TRUSS WITH BORON/ALUMINUM TUBES CONCEPTS OF STRESSED SKIN CONSTRUCTION LARGELY EMPLOYED Space Structures - Prof. Alessandro Airoldi 39 Introduction to the course Examples of space structures: SPACE SHUTTLE Orbiter GRAPHITE\EPOXY PAYLOAD BAY DOORS REINFORCED BY FRAMES AND END TORQUE BOXES HIGH STRENGTH 3D TRUSS STRUCTURE TO SUSTAIN THE THRUST LOAD OF MAIN ENGINES Space Structures - Prof. Alessandro Airoldi 40 Introduction to the course Examples of space structures: SPACE SHUTTLE Orbiter CONVENTIONAL ALUMINUM STRUCTURE WITH MULTI SPAR AND RIB ARRANGEMENT HONEYCOMB SKIN REINFORCED BY ALUMINUM HAT-SHAPED STRINGERS Space Structures - Prof. Alessandro Airoldi 41 Introduction to the course Examples of space structures: SATURN V First Stage Separate serial tanks within semimonocque structure SEMI-MONOCOQUE AL 7075 INTERTANKS AND SKIRTS AL 2219 – T87 TANK WITH ANTI-SLOSH BAFFLES (diaphragms that reduces fuel movements) Space Structures - Prof. Alessandro Airoldi 42 Introduction to the course Examples of space structures: SATURN V Second Stage Integral serial tanks with common bulkhead INTEGRALLY STIFFENED TANKS MADE OF DIFFUSIONWELDED AL 2014 PARTS COMMON BULKHEAD: AL 2014 SHEET + FIBERGLASS/ PHENOLIC HONEYCOMB CORE SKIRTS, INTERSTAGES, THRUST STRUCTURE: AL7075 SEMIMONOCOQUE Space Structures - Prof. Alessandro Airoldi 43 Introduction to the course Examples of space structures: SATURN V Third Stage Serial tanks with common bulkhead VERY SIMILAR TO 2° STAGE STRUCTURE INTEGRALLY STIFFENED TANKS AND SEMIMONOCOQUE STRUCTURES Space Structures - Prof. Alessandro Airoldi 44 Introduction to the course Examples of space structures: SPACECRAFTS Experimental spacecraft designed at John Hopkins University: multisensor platform including a Spatial Infrared Telescope IN SPACECRAFTS THE DISTINCTION BETWEEN PRIMARY AND SECONDARY STRUCTURES IS IMPORTANT: PRIMARY STRUCTURES TRANSMIT LOADS TO THE BASE OF THE SATELLITE THROUGH SPECIFICALLY DESIGN COMPONENTS (CENTRAL TUBE, HONEYCOMB PLATFORM, BAR TRUSS, ETC.). PROVIDE THE ATTACHEMENT POINTS FOR THE PAYLOAD AND THE ASSOCIATED EQUIPMENTS. FAILURE OF THE PRIMARY STRUCTURE LEADS TO COLLAPSE OF SATELLITE SECONDARY STRUCTURES BAFFLE, THERMAL BLANKET SUPPORT AND SOLAR PANELS MUST ONLY SUPPORT THEMSELVES AND ARE ATTACHED TO THE PRIMARY STRUCTURE WHICH GUARANTEE THE OVERALL STRUCTURAL INTEGRITY. Space Structures - Prof. Alessandro Airoldi 45 Introduction to the course Examples of space structures: SPACECRAFTS SEVERAL DIFFERENT STRUCTURAL TYPES: -TRUSS (ALSO IN HIGH STIFFNESS/STRENGTH COMPOSITE MATERIAL) - HONEYCOMB PANELS (OFTEN USED FOR ELECTRONIC SUPPORT AND SOLAR CELL SUPPORT) -MACHINED BEAMS AND PLATES Space Structures - Prof. Alessandro Airoldi 46 Introduction to the course Examples of space structures: SPACECRAFTS MANNED SPACECRAF INCLUDES -TRUSS STRUCTURES -SEMI-MONOCOQUE CONCEPTS (THIN WALLED STRUCTURES WITH STIFFENERS AND FRAMES) -STIFFENED PRESSURE VESSELS Space Structures - Prof. Alessandro Airoldi 47 Introduction to the course What have we learned ? Structural concepts: truss and semi-monocoque • Central role of two different but very effective structural types: semimonocoque and truss structures Basic structural elements: beams and plates Beam models can be applied at level of the vehicle structure, for the analyses of truss systems, for the analyses of ribs and frames Plate theory is required to understand the behavior of panels and covers Different materials: metals, fiber reinforced composites, sandwich plates Composite materials are used to increase structural efficiency: lower weight, higher stiffness (and strength ?) Composite structures requires additional tools for analysis and design Space Structures - Prof. Alessandro Airoldi 48 Introductory lessons Course Content and Organisation: Lectures (theory) 1. CONTINUUM MECHANICS 2. BEAM MODELS AND BEAM SYSTEMS 3. SEMI-MONOCOQUE STRUCTURES 4. DISPLACEMENT BASED APPROACHES 5. PLATES AND COMPOSITES 6. INSTABILITY 7. FE METHOD Space Structures - Prof. Alessandro Airoldi 49 Introductory lessons Course Content and Organisation: Course Material & Textbooks Slides of the lectures will be provided during the course MALVERN, MECHANICS OF CONTINUOUS MEDIUM Continuum mechanics, general principles T.H. MEGSON, AIRCRAFT STRUCTURES FOR ENGINEERING STUDENTS, BUTTERWORTHHEINEMANN, 1972 Semi-monocoque structures, force and displacement approach to beam systems J.N. REDDY, ENERGY PRINCIPLES AND VARIATIONAL METHODS IN APPLIED MECHANICS, WILEY 2002 Energy methods, Ritz Method, Plate Theory K.J. BATHE, FINITE ELEMENT PROCEDURES, PRENTICE HALL 1982 Finite elements V. GIAVOTTO, STRUTTURE AERONATICHE CITTA’ STUDI Covers several parts of the course Space Structures - Prof. Alessandro Airoldi 50 Introductory lessons Course Content and Organisation: Exercise Classes (for written test) 1. CONTINUUM MECHANICS 2. BEAM MODELS AND BEAM SYSTEMS 3. SEMI-MONOCOQUE STRUCTURES 4. DISPLACEMENT BASED APPROACHES 5. PLATES AND COMPOSITES 6. INSTABILITY 7. FE METHOD Space Structures - Prof. Alessandro Airoldi 51 Introductory lessons Course Content and Organisation: Computer Labs 1. CONTINUUM MECHANICS 2. BEAM MODELS AND BEAM SYSTEMS 3. SEMI-MONOCOQUE STRUCTURES 4. DISPLACEMENT BASED APPROACHES 5. PLATES AND COMPOSITES 6. INSTABILITY 7. FE METHOD Space Structures - Prof. Alessandro Airoldi 52 Introductory lessons Course Content and Organisation: Written Examination Based on the same type of exercises that have been presented, solved and discussed during classes Capability to critically apply concepts as well as to organize and carry out calculations Admission to oral examination is possible only if the written text will obtain a positive mark Oral Examination Comprehension of structural concepts, analytical and numerical approach Will include proofs of main theorems and formulation development Space Structures - Prof. Alessandro Airoldi 53
