Lecture 12- Structures 2

Lecture 12- Structures 2 - AOE 2104-Aerospace and Ocean...

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AOE 2104--Aerospace and Ocean Engineering Fall 2010 Virginia Tech October 19, 2010 Aircraft Structures 2 Click to edit Master subtitle style AOE 2104 Introduction to Aerospace Engineering Aircraft Structures 2
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AOE 2104--Aerospace and Ocean Engineering Fall 2010 Virginia Tech October 19, 2010 Aircraft Structures 2 Had an overview of the history of aircraft structures Named major structural components of the fuselage and wing Any questions? Last time…
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AOE 2104--Aerospace and Ocean Engineering Fall 2010 Virginia Tech October 19, 2010 Aircraft Structures 2 To answer this, we need to understand a little about solid mechanics Stress – what is it? A measure of intensity of forces over a particular surface in a body Stress is 3-Dimensional and has 9 components in it’s matrix! Essentially it is how hard the atoms at a point in a material are being pulled apart or pushed together. For now, we will consider 1-D only What happens when an external force is applied to a material? Solid tends to deform Material attempts to resist change by an internal force The force per unit area is called stress! (1-D) How does the structure cope with ground and in flight loads? A F area force = = σ
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AOE 2104--Aerospace and Ocean Engineering Fall 2010 Virginia Tech October 19, 2010 Aircraft Structures 2 Compressive – acts perpendicular to cross-sectional area (pushing) Tensile – acts perpendicular to cross-sectional area (pulling) Shear – acts tangentially to cross-sectional area A look at the three forms of stress A F area force = = τ F F F F F F
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AOE 2104--Aerospace and Ocean Engineering Fall 2010 Virginia Tech October 19, 2010 Aircraft Structures 2 When stress acts on a material it tends to change shape and size For the rods, the length looks like it should change, right? Say the original length is L then we can write Stress and strain can be related! How? Hooke’s Law E is the modulus of elasticity or Young’s modulus What are the units of E? A look at the strain L L length originial length in change = = ε ε σ E =
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AOE 2104--Aerospace and Ocean Engineering Fall 2010 Virginia Tech October 19, 2010 Aircraft Structures 2 Shear strain is just a little different Here the material is undergoing what looks like an angular deformation of θ . Can we use E here? No! G is the modulus of rigidity or shear modulus Materials tend to be about half as strong in shear as compared to tensile forcing A look at the strain θ τ G = τ
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AOE 2104--Aerospace and Ocean Engineering Fall 2010 Virginia Tech October 19, 2010 Aircraft Structures 2 Consider an aircraft wing experiencing a lift force Think again about the same wing and lift force generating an aerodynamic moment – causes tangential shear stress What about temperature? Will this have an effect?
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