User:EAS4200C.F08.WIKI.A/HW

=MediaWiki=

MediaWiki is a web-based wiki software application originally written for Wikipedia by Lee Daniel Crocker. Wiki software refers to collaborative software the manages, creates, and edits web pages through common web browser applications as the user interface. The information in wiki software is stored in a file system, while the edits are stored using a relational database management system. The main features of MediaWiki is the rich core feature set and the ability to add extensions, allowing additional functionality. Also, this software is distributed under the terms of the GNU General Public License with some documentation in the public domain; thus, it is a free and open source software, which allows anyone to use and edit the stored content.

The overall idea behind MediaWiki is that by having anyone add information on topics they thoroughly understand, everyone can benefit from the collective knowledge. The let down is that since there is no credibility check before editing a page, people with less than adequate knowledge of a subject or people who's intentions aren't to improve the content can "vandalize" the stored information, whether it be adding incorrect segments or even deleting previous contributions. In order to control this problem, the history of different versions of each web-page is saved, and editors, or custodians, assess each contribution in order to determine the validity. In the case of vandalism, the web-page is simply returned to the last acceptable version.

= Reasons for Using Wikiversity for Homework Submission =

The Aerospace Structures class will be using Wikiversity in order to submit homework due to the versatility of the mediawiki software. Instead of having to meet in one place to collaborate, the group will be able to just post their part in their user web space and everyone else in the group will be able to view and edit in any additional information they have on the subject. Also, any other group will be able to see the other groups pages and share information.

The structure will be even better if it is carried out in future years as any subsequent classes will have the previous years work to look at.

Also, since the student is already on Wikiversity, it will be easier for him or her to investigate the subject further by looking at any related Wikipedia pages.

= Dangers of Using Wikiversity =

A downside to using Wikiversity is that any one will be able to see your work and change it. This includes people who are not in the class, and the student is asked to keep an eye on their page at all times to make sure no vandalism has been done to their work. Also, any other group in the class could steal another groups work and post it as their own since it's freely available on line. One way around this is for TA's to cross check the work of one group against every other group, but this won't guard against a group rewording the work of another group and doing the same thing. The suggested way around this is to wait until right before the homework is due to post it on line.

=Basics of Aerospace Structures=

The Finite Element method (FEM) can be used in a wide variety of fields, from various types of engineering, to applied math, and even geology. Aerospace structures is one of the fields where FEM can be used to solve the partial differential equations that govern this particular field.

The structure of an aircraft must be designed with two main goals in mind: it must be light, and it must be strong. More specifically, the structure of an aircraft should have a high stiffness, high strength, and be composed of light weight materials.

Stiffness refers to a Young’s modulus $$\displaystyle E$$, or the slope, in a linear relation between stress $$\displaystyle \sigma$$ and strain $$\displaystyle \epsilon$$, or $$\displaystyle \sigma = E \epsilon$$. Strength refers to a particular stress, such as the yield stress $$\displaystyle \sigma_Y$$, where a material begins to weaken, and the ultimate stress $$\displaystyle \sigma_U$$, where a material fails. Toughness is simply the capacity to endure fracture or damage.

Examples of materials with high stiffness and high strength include steel and titanium alloys, since they have a large Young’s modulus and large ultimate and yield strengths. Glass is an example of a material with high stiffness, but low toughness. It does not withstand much plastic deformation and does not resist fracture well. Plastics and nylon are materials with a low stiffness, and high toughness, as they are they behave oppositely to glass.

Aircraft structures typically have monocoque or semi-monocoque designs to them. The term monocoque refers to a “single shell” design, while semi-monocoque is a shell that is stiffened by a supporting structure. These designs allow aircraft to have low weight, while also remaining strong and resisting bending. The geometry of an aircraft is, of course, also restricted by aerodynamics such as lift and drag on an airfoil.

=Aircraft Example=

The following figure provides examples of materials used on the F/A-18E Hornet. All of the materials used in this aircraft are light, high in stiffness, and high in strength therefore allowing for optimal performance and long durability. It is desirable however to eliminate all aluminum and titanium and replace them with Fiber Reinforced Composites which would in turn decrease the weight of the aircraft by 30%-40%. In doing so the aircraft would be at its maximum performance. An example of the composites being used in aviation can be seen in the Boeing 787. Fifty percent of this vehicle is made up of these materials making it lighter and more efficient.

The table below gives some examples of parts made of the materials portrayed or not portrayed in the photo.

{| class="toccolours collapsible collapsed" style="width:100%" ! Metal Matrix Composite vs Fiber Metal Composite
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A metal matrix composite is material made up of at least two parts - one part is a metal and the other can be a different metal or some other type of material. A hybrid composite is composed of at least three materials. A metal matrix composite is formed by inserting a reinforcing material into a metal matrix. Sometimes the reinforcing material will have to be coated to prevent a chemical reaction that could cause the metal to break down. Usually the matrix is made up of a lighter metal, such as aluminum or titanium. The reinforcement material is not always added just to add structural strength, but also to change the properties of the composite material.1 Unlike metal matrix composites, fiber metal composites make use of organic materials and plastic. Natural fibers are refined, mixed, and merged to form high strength composite material in a polymer matrix. An advantage of this material is that it can be recycled up to 20 times.2