User:Eas4200c.f08.team12.hepsworth/HW1

=EAS4200c: Aerospace Structures - Class Notes=

Lectures 1, 2, and 3 - 8/25/08 through 8/31/08
Course Information

Website - VQ Wikipage → "teaching" → "my course website" → "EAS 4200c Aerospace Structures" EAS 4200c Course website Password: fall08.wiki

MWF Period 4 (10:40-11:30PM), MAE 303 Office: NEB135

Lectures in week 1 centered around introductions and orientation. This course is focused around collaborative learning, in which students utilize interpersonal relationships to learn, teach, and retain course content. Groups of 5-6 members were organized, and the software (Wikiversity) was introduced.

The purpose of using a domain like Wikiversity is to promote collaboration between students teams, the entire class, and between the professor and the class. In addition the Wikiversity server is more reliable than that of E-learning, which tends to lock up at "peak times". This software also allows students in a group to complete homework assignments and exchange class notes without having to be in the same room, city, or state.

Syllabus[]

Lecture 4 - 9/3/08
Structural Goals for Aircraft: Aerospace structure materials differ from civil engineering materials based on one main characteristic: weight. Desirable aircraft structural goals are for the aircraft to be lightweight, yet have high strength and high stiffness. Stiffness is determined by examining the linear relationship between stress and strain. This relationship follows Hooke's Law, and is as follows: $$\displaystyle \sigma = E \epsilon$$ (where the factor E is known as Young's Modulus or the Modulus of Elasticity, $$\displaystyle \sigma$$ is the stress, and $$\displaystyle \epsilon $$ is the strain). The concepts of Yield Stress ,and  Ultimate Stress both designate the Strength of a material. Another important material property is known as Toughness, which refers to a material's ability to be firm but not brittle in nature, and strong but not flexible (See ).

Structural Materials: Many different materials are used in the construction of any aircraft, with each materials having their pros and cons to usage. Glass is a material with high stiffness, but low toughness. Plastic, Nylon, and Aluminum all have low stiffness, yet high Toughness. Compared to steel alloys, aluminum has low strength and lower fracture toughness. In addition to aluminum and titanium, recently composite materials have made up a significant percent of aircraft. Composite materials exhibit both high stiffness and high toughness. Composite materials can also be reinforced with fibers to increase its overall stiffness and strength. This material is called Composite reinforced plastic.

Structural Design: Changing the aircraft structure from aluminum and titanium to new fiber reinforced composites can save up to 30 to 40% in weight. Aircraft structural designs are always limited by aerodynamic considerations. The new Boeing 787 is made up of more than 50% composite materials.



The shape of structures also affects aircraft weight. Common constructions to maximize usage of components include monocoque (shell-like structures)and semimonocoque(stiffened shells).

Aircraft Loading: Loading on aircraft generally fits into three main categories: axial, bending moment, and torsional loading. It is important to prevent concentrated loads on the main frame, which can lead to deflections. Manufacturers make use of stringers, ribs, and subframes to locally "collect" and distribute the loading along the frame. The wings and fuselage carry torsional and axial loads.

Lecture 5 - 9/5/08
Problem 1.1 - A rectangular thin-walled beam section is designed to carry both torque T and bending moment M. A fixed total wall contour length of L = 2(a+b) is given.

Find the optimum ration of (b/a) to achieve the most efficient M = T, and σ = 2τ. Shear stress due to torsion for a closed thin-walled section is τ = T / (2abt).

Note: t is very small for a rectangular thin-walled section. Since the cross section wall are very thin, we can assume shear stress distribution to be uniform along the wall



Assumptions:


 * 1) L = 2(a+b) = Constant
 * 2) The moment is equal to the torque, M = T
 * 3) σ = 2τ

T = TAB + TBC + TCD + TDA

Case 1: Assume σ reaches σ allowable


 * $$\displaystyle \sigma = \frac{M z}{I}$$

The shear flow in the thin walls can be represented by an equivalent force system or resultant. In this case the resultant, V, is:

V = T²/(2abt)


 * $$\displaystyle \tau = \frac{V}{T}$$

Therefore:


 * $$\displaystyle \tau = \frac{T}{2 a b t}$$

=Contributing Team Members HW 1= The following students contributed to this report:

Victoria Watlington EAS4200C.Fall08.Team12.Watlington.VGEAS4200C.Fall08.Team12.Watlington.VG 18:57, 17 September 2008 (UTC)

Steven Hepsworth Eas4200c.f08.team12.hepsworth 17:37, 17 September 2008 (UTC)

Brian Taylor Eas4200c.f08.team12.taylor 12:01, 19 September 2008 (UTC)

Melisa Gaar Eml4500.f08.group.gaar 00:25, 19 September 2008 (UTC)