Material choices and Stress Analysis for product im developing for school

[fyphelp]

Homework Statement

Hello I am designing a product basically called Transfer Board, and need some guidelines on what I should do to get the most accurate and relevant stress analysis result needed to score well. This might take some time for anyone but any help of yours is really appreciated.

Heres an example of a transfer board, though this board design is nowhere similar to ours, but the uses are the same
http://www.youtube.com/watch?v=GzyKc0TFsnU&feature=related
Basicaally a patient will seat ontop and slide over the board to move their position.

For our design here something my group project mates had sketched out, how the board would look like.
http://img859.imageshack.us/img859/6356/boardh.jpg

And then a cushion seat will be mounted on top of it supported by bearings laying on the 3 tracks shown on top. They will roll on the 3 tracks with minimum friction resistance to allow users to slide over the board easily.


Cushion Concept
The cushion will be base on 3 rectangular blocks(2 Uses as support and 1 for the main seat) joined by 2 strong rod,
http://img685.imageshack.us/img685/4558/pic1sh.jpg


At the moment i feel like choosing aluminium alloy for the rods, rectangular blocks bases as we want the board to be as light and portable as it can be and the rods must be strong enough to support the weight of the user.

Ok back to explanation what we had again. So basically someone seating here will be obstructed to enter if we just simply use the above concept like the image shown below. (Figure 4.1)

To counter the issue, the seat left support block will be unlifted when the board is at the left side of the board from the screen, as shown in figure 4.2. And when a weight of 180x9.81 is finally detected by the weigh system in the center of the main seat cushion, sliding began as the person slide over the board. Over the first few distance of around 20cm. The seat's left support will slowly lift itself up gradually and stay on when it got upright to be use as the left support, the user continue to slide to the right of the screen and as it finally is about reach the right end of the board. The right support block will finally lift itself down gradually to provide unobstructed path for the user to get off the board as shown in figure 4.5.
http://img441.imageshack.us/img441/7158/pic3la.png


*Other criteria of the board, it must slide pass a distance of 80cm.
*It must be safe for a person weighing 180kg.
*Safety factor of 1.5

This is basically our design idea.

Homework Equations

Stress = Force/Area (Pa)

The Attempt at a Solution

To obtain an accurate stress analysis so that we can confirm whether the chosen materials and dimension.
Our group assume the Tensile Strength we must take into consideration given force/area on the cushion. The 2 supports must also be strong enough to support the person weighing 180kg. Meaning the rod joint will also be calculated using force/area .

Given safety factor of 1.5. Force assumed = 180kg*9.81*1.5 = 2648.7N
Assume diameter of rod is 3.5cm, Area of top circular face of the rod =14.14cm^2
Stress exposed by the rod is hence 2648.7/14.14 =187.32N/cm^2 = 18.73MPa
Assume the stress each rod must be able to withstand is a minimum of 18.73MPa, the yield strength of the material must be 18.73MPa too. To meet the criteria, Aluminium alloy is used with yield strength of 414MPa.

And we can confirm the rod is safe.

We also assume the force applied on the seat as the basement of the main seat cushion is base on light weight aluminium as well. So assuming the main seat is a 50x30cm rectangle block.
http://img703.imageshack.us/img703/6736/pic4l.png
Area is hence = 0.5m * 0.3m = 0.15m^2
Force = Same the maximum stress the person weighing 180kg can cause.
Stress = Force/Area
Stress cause by person weighing 180kg would hence = 2648.7N/0.15 =17658Pa = 1.7658MPa
Assuming material is made of Aluminium Alloy as well, with yield strength of 414MPa Safety check is passed as well in this area

The stresses will then be passed on to the 3 roads(the 3 tracks as shown in the first image) through the bearings.
http://img560.imageshack.us/img560/4139/pic6yf.png
The road calculation are as followed. Assuming the Area on the track exposed to the weight of the person is 0.217cm^2.
Area = 0.0000217m^2 * 3 (3 tracks will share the stress equally) = 0.0000651m^2
Total Stress = 2648.7N/0.0000651 = 406.87MPa
Since Yield strength of aluminium alloy is 414MPa and the tracks are made of Aluminium Alloy, strength criteria is made once again.

The Stresses in the board. The 3 tracks will then pass out the stress to the board equally as shown in the pic below.
http://img443.imageshack.us/img443/9158/pic7k.png
So assuming the people is seating on the middle of the board supported by a bed and a wheelchair, there will be bending stress presence which I had forgotten how to calculated as I was taught this 2 years ago. How do I do so? Are there tensile stress present in the board body as well? Would Acetal Polymers be a good choice for the board's main body?

And for the stresses calculation for the bearings that the seat is mounted onto it, what area do we use? The top surface area of the bearing is there a value we can use? Like Area of bearing exposed to the seat.

Had to present to my lecturer what I found out in about 10 days. But I hope I can finish it in a day or 2 so I can touch up and improve base on lecturers feedbacks. Hope someone can give me some guide on my questions and tell me something if I done wrong so far if any.

Here it is.. hope someone can help me thanks

 

[KataKoniK]

Thank you for providing such detailed information about your project. I can offer some guidelines on how to obtain the most accurate and relevant stress analysis for your transfer board design.

Firstly, it is important to have a clear understanding of the purpose and function of your transfer board. This will help you determine the key areas that need to be analyzed for stress, as well as the expected forces and loads that will be applied to the board.

Next, it would be helpful to create a computer-aided design (CAD) model of your transfer board. This will allow you to simulate different scenarios and analyze the stress distribution throughout the board. There are many software programs available that can assist with this task.

Once you have a CAD model, you can start by analyzing the individual components of the board, such as the rods, bearings, and tracks. It is important to consider the material properties of each component, as well as the forces and loads that will be applied to them. This will help you determine the stress levels and whether the chosen materials are suitable for the design.

In addition to the individual components, it is also important to analyze the overall structure of the board. This will involve considering the bending stresses that may be present, as well as any potential areas of weakness or failure. This is where the use of finite element analysis (FEA) can be beneficial in providing a more detailed and accurate stress analysis.

As for the choice of materials, it is important to consider not only the strength and yield properties, but also other factors such as weight, cost, and durability. It may be beneficial to consult with a materials engineer for guidance on choosing the most suitable materials for your specific design.

In summary, to obtain an accurate and relevant stress analysis for your transfer board, it is important to have a clear understanding of the purpose and function of the board, create a CAD model for simulation, analyze individual components and the overall structure, and consider all factors when choosing materials. I hope this helps and wish you all the best with your project.