User:Eas4200c.f08.ZYX.reger/Week1,2

September 9th, 2008

The goal of aerospace design is to build aircraft that are light and strong so we try to use materials with:



$$\displaystyle E = \sigma / \epsilon $$ Yield Stress = $$\displaystyle \sigma_Y$$ Ultimate Stress = $$\displaystyle \sigma_u$$ (Yield stress is the stress at the point of transition from Elastic to Plastic deformation). Stress in Plastic Response: Increasing = Hardening / Decreasing = Softening
 * High Stiffness: Where stiffness is defined by Young's Modulus, $$\displaystyle E$$, which is defined by a linear relationship between stress and strain:
 * High Strength: Where strength is defined by yield stress and ultimate stress

$$\displaystyle \rho = m / V$$
 * Low Density: We simply attempt to use less dense, $$\displaystyle \rho$$ materials than more dense ones.

$$ \frac \mbox{energy} \mbox{volume} = \int_{0}^{\epsilon_f} \sigma\, d\epsilon $$
 * High Toughness: Where toughness is the ability to resist fracture and damage.


 * High Durability: Where durability defines the ability to endure.

Examples of Materials:
 * High stiffness and high strength: Steel Alloys
 * High stiffness and low toughness: Glass
 * Low stiffness and high toughness: Nylon, Plastics
 * High stiffness and high toughness: Composite Materials



Most aircraft structures use a Monocoque or Semi-Monocoque structure. However, design is also limited by aerodynamic considerations, i.e. drag and lift.

Aircraft are made of many different materials for various purposes, for example, the F?A-18 Hornet:


 * Aluminum is used for the skin
 * Steel for the landing gears
 * Titanium for engine encasing and structural portions
 * Carbon/Epoxy for the fuselage and aileron.

The Boeing 787 is made of 50% composite material in order to save weight.

Introduction