User:Eas4200c.f08.blue.a/Lecture 4

 Introduction to Aerospace structures 

The goals of aerospace structures is to design aircraft that are very light yet also strong. this is accomplished through the use of materials that have a high stiffness, high strength, and lightweight.

The stiffness of a material is determined by  $$E$$  The young's modulus of the material which is relates the stress and strain on the material through hooke's law  $$\sigma=E*\epsilon$$  hooke's law is a linear equation and the Young's modulus is the slope of the equation. This means for the higher the Young's modulus the faster the stress will increase meaning little deformation will be able to occur in the material before the yield stress is reached.

The strength of a material is determined by  $$\sigma_y $$, $$ \sigma_u$$  which are the yield stress and the ultimate stress respectively.

The higher the stresses that the material is able to handle before yielding the stronger the material.

Toughness is also considered in materials because it is the ability of the material to resist fracturing. Which means that a material with a high toughness would be able to resist fracturing very well. An example of a very stiff material but has a very low toughness would be glass.

Two aspects of aircraft design are the geometry and materials used. The geometry for the aircraft body is constructed by a thin wall shell design instead of an internal truss design. Aerodynamics also play a larger role in the geometry of the aircraft. Materials that are used need to be used to their full capacity to avoid more weight than necessary in the design. Also when able replace aluminum and titanium with fiber reinforced composites which will reduce weight by approximately thirty to forty percent.

Book pg 1-3