AE321_ch0_2008 - AE 321 Aerospace Structures I John Lambros...

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Unformatted text preview: AE 321 Aerospace Structures I John Lambros Department of Aerospace Engineering University of Illinois at Urbana-Champaign Fall 2008 AE 321 0. 1 Evolution of Aircraft Structures • • 1890s : Octave Chanute (Civil Engineer) 1904 : Wright brothers • 1909 : Louis Bleriot - monoplane and fuselage AE 321 0. 2 Evolution of Aircraft Structures • 1914-1918 - WWI: Metallic structures and thicker wings • 1930s : Civil Aviation - (semi)monocoque Douglas DC-3 AE 321 0. 3 Evolution of Aircraft Structures • 1940-1945 - WWII: First jets • 1950s to now: Advanced materials Titanium for hypersonic flight (X-15) AE 321 0. 4 Key Issues •Aircraft design involves multidiscplinary and competing requirements – Payload – Power-plant – Structure – Maintainability – Electronics –… •But key underlying issue: performance vs. weight – Search for materials with high specific property (i.e., property/density) – Low safety factors •Key questions Weight required for performance equivalent to – What is the optimum structure to sustain 100 lb of Aluminum aerodynamic loads? – What materials to select for various components? Material Carbon fiber / Epoxy Boron fiber / Epoxy Glass fiber / Epoxy Titanium Steel Stiffness 30 25 85 110 120 Strength 30 20 15 70 120 AE 321 0. 5 What Structure? Aircraft (and spacecraft…) are among the most complex man-made structures AE 321 0. 6 What Material? AE 321 0. 7 Trend: Increasing Use of Composites Basic idea: combine two or more materials to make a better one Key advantage: anisotropy offers more flexibility in design Example: fiber-reinforced composites Composite layer Microstructure Composite laminate AE 321 0. 8 What Material? • Boeing 787 – Composite: 50% – Aluminum: 20% – Titanium: 15% – Steel: 10% Composites in other airliners (weight %) – Boeing 777: 12% – Airbus A380: 25% – F18 E/F Hornet: 18% – F22: 20% – F35 Joint Strike Fighter: 35% Advantages for Boeing 787 – Less corrosion (allows for more humidity) – Lighter (allows for better range and/or fuel efficiency) – Less parts (19:1 ratio compared to Al sheets with fasteners) – Less maintenance 0. 9 • • AE 321 Aircraft Accidents: “Design Failures” Comet aircraft (1952) Old design New design AE 321 0.10 Aircraft Accidents: “Material Failures” Fatigue: Aloha Airlines 243 (April 1988) Ductile vs. brittle: Challenger (Jan. 1986) Internal cracks in composite AE 321 0.11 Other Accident Scenarios Explosions: TWA flight 800 (1996) American Airlines Flight 587 (2001): Delamination of the composite vertical tail Bird impact test on F-16 canopy AE 321 0.12 Course Objectives • Key objectives • To understand how structures/materials fail • To predict when a structure/material will fail • To prevent a structure/material from failing (catastrophically) • Analytical tool: theory of elasticity • Kinetics: analysis of stress • Kinematics: analysis of strains • Conservation laws: equilibrium P A P L before L after L • “1-D prelude” stress = P = A L Lbefore = >0 <0 Lafter tension compression Lbefore <0 >0 Failure point stress strength strain = = Lbefore shrinks expands • Question: How to expand to 3-D? strain AE 321 0.13 The Big Picture… • Rigid body motion – Theory • TAM210: Statics • AE252/352: Aerospace Dynamics – Applications • AE201: Principles of aerospace systems • AE302: Flight mechanics • Deformable solids – Theory • AE321: Theory of elasticity: Stress, strain, equilibrium, 3-D problems, 2-D (plane stress/plane strain/antiplane shear) problems • AE322: Strength of materials: 1-D: Extension, bending, twisting and buckling of beams, closed- and open-cell thin-walled structures, 2-D: plates, energy methods – Lab: AE360 – Numerics: AE470: Computational methods in aerospace engineering: Finite difference and finite element methods – Applications: AE420: Finite element method, AE427: Mechanics of polymers, AE428: Composites, AE451: Aeroelasticity, … AE 321 0.14 Course Outline 1. Mathematical preliminaries (1*) 1.1 Review of vector theory 1.2 Indicial notation 1.3 Tensor theory 2. Kinetics: Theory of stresses (3) 2.1 Stress tensor 2.2 Equilibrium equations 2.3 Principal stresses 3. Kinematics: Theory of strain (2) 3.1 Definition of strain 3.2 Physical interpretation 3.3 Compatibility 3.4 Summary of stress and strain 4. Material behavior (4) 4.1 Uniaxial response - Tensile test 4.2 Generalized Hooke’s law 4.3 Isotropic solids 4.4 Viscoelastic materials 5. Formulations and solution strategies (5) 5.1 Formulations 5.2 Solution strategies 6. Extension, bending and torsion of cylindrical components (9) 6.1 Extension 6.2 Bending 6.3 Torsion 7. Failure and fatigue 7.1 Failure criteria 7.2 Yield surfaces 7.3 Fatigue 8. 2-D plane stress/plane strain problems 8.1 Plane strain (7) 8.2 Plane stress (7) 8.3 Solutions (8) * Numbers in parentheses refer to chapters in “Elasticity: Theory, Applications and Numerics” by M. H. Sadd AE 321 0.15 ...
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