User:Eas4200c.f08.gator.edwards/Chapter One Notes

Emphasis of the course includes: the understanding of mechanics, the ability to formulate problems, to be able to judge correctness of solutions, and to avoid the old ad hoc methods of structural analysis.

There are two basic aircraft design goals: we want the aircraft to be both light and strong.

The desired aircraft material properties include: high stiffness, high strength, and lightweight.



Stiffness is the Young's Modulus  $$\displaystyle E$$ (slope) in linear relation between stress  $$\displaystyle \sigma$$ and strain  $$\displaystyle \epsilon$$, i.e.,   $$\displaystyle \sigma$$ =  $$\displaystyle E$$  $$\displaystyle \epsilon$$

Strength includes yield stess  $$\displaystyle \sigma$$ Y, and ultimate stress (rupture stress)  $$\displaystyle \sigma$$ u.

Toughness is the material's ability to resist fracture and damage. This is also called fracture toughness.

Some high stiffness and high strength materials include: steel alloys, titanium alloys (which have lower stiffness and strength than steel alloys), and aluminum alloys (which have lower stiffness and strength than titanium alloys).

A high stiffness and low toughness material is glass.

Some low stiffness and high toughness materials include: plastic and nylon. An example of a material with good fracture toughness is aluminum (which has lower stiffness, strength, and fracture toughness than steel alloys) and it is used in aircraft skin.

Some high stiffness and high toughness materials include: composite materials.
 * composite materials- fiber reinforced composites where the material used as the base material (called the matrix) is reinforced with many fibers (which increases strength and stiffness).

There are two aspects of an aircraft structure we will consider: its geometry and the material that it is made out of. Two styles of the geometry of the aircraft is monocoque and semi-monocoque.

Some other considerations that need to be made for aircraft construction include the fact that the geometry is limited by aerodynamic considerations such as lift and drag of the airfoil. Also the fact that we want the aircraft to be used to its full potential and for there not to be any wasted weight. Optimizing the aircraft materials used is also important. This can be done by replacing aluminum and titanium with fiber reinforced composites, which saves up to 30 to 40 percent in weight.

 References 

Boeing 787 in Wikipedia

Metal Matrix Composite

Carbon Fiber Reinforced Plastic

Monocoque