User:Klcooper11/updates

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Project Preference
1. MakerBot PLA

2. Smart Shoe

3. Hallway Robot

Problem Statement
Our group aims to discover the material properties of the PLA product used with the makerbot. We are currently on the design phase of the project and intend to first discover which properties are important to users and second construct several test to quantify these properties.

Project Plan
This is a rough outline of weeks to come, subject to change.  Week 1- The main goal of week one is to research different material properties while keeping the user in mind. This will help the group decide which properties are the most important and they will have some background knowledge when the development of tests begin. Week 2- Team members will spend this week designing tests for the material properties chosen. Team members will also choose the shape of PLA needed for each test. Week 3- This week will be spent building prototype test apparatuses and collecting trial data. During this process the group will keep in mind ways to improve prototypes.  Week 4- The last week will be spent perfecting all prototypes into a polished, finished design to pass onto the implement phase of this project.

Week 1 Narrative
My objective for this week was to research the material property of hardness. I have learned that are several methods to test the hardness of the material we will be using in this project.


 * Brinell Hardness Test

The test is achieved by applying a known load to the surface of the tested material through a hardened steel ball of known diameter. The diameter of the resulting permanent impression in the tested metal is measured and the Brinell Hardness Number is calculated as

BHN = 2 P / (π D (D - (D2 - d2)1/2))        (1)

where

BHN = Brinell Hardness Number

P = load on the indenting tool (kg)

D = diameter of steel ball (mm)

d = measure diameter at the rim of the impression (mm)

https://www.youtube.com/watch?v=RJXJpeH78iU


 * Rockwell Hardness Test

The Rockwell Superficial Hardness Tester is used to test thin materials, lightly carburized steel surfaces, or parts that might bend or crush under the conditions of the regular test. This tester uses the same indenters as the standard Rockwell tester but the loads are reduced. A minor load of 3 kilograms is used and the major load is either 15 or 45 kilograms depending on the indenter used. Using the 1/16" diameter, steel ball indenter, a "T" is added (meaning thin sheet testing) to the superficial hardness designation. An example of a superficial Rockwell hardness is 23 HR15T, which indicates the superficial hardness as 23, with a load of 15 kilograms using the steel ball.


 * Durometer Hardness Test

A Durometer is an instrument that is commonly used for measuring the indentation hardness of rubbers/elastomers and soft plastics such as polyolefin, fluoropolymer, and vinyl. A Durometer simply uses a calibrated spring to apply a specific pressure to an indenter foot. The indenter foot can be either cone or sphere shaped. An indicating device measures the depth of indentation. Durometers are available in a variety of models and the most popular testers are the Model A used for measuring softer materials and the Model D for harder materials.

https://www.youtube.com/watch?v=9CWjcn5MbV4

I hope to gain more information by doing some more reseach on the material we will be using for the project.

Week 2 Narrative
In week one we each member had different properties to research. After some discuss we decided that strength and stiffness would be a more cost effect way to test in our project. The objective this week was to fine different way to test the material with these two properties. It would definitely be cost effective if we came up with simple ways to test strength and stiffness with PLA.

Ideal #1

Tensile Testing:

We could hang a material (example: weights) one end of some material from a solid point that does not move, then you can hang weights on the other end. Measure the change in length while adding weight until the part begins to stretch and finally breaks.

http://www.youtube.com/watch?v=o6RKK5B92AgTensile Test

Ideal #2

3 Point Bending Test

The bending characterizes the behavior of a slender structural of the plastic that will be subjected to an external load applied perpendicular to an axis of the plastic. This would be a ideal to see how we can make the 3 point test effective in getting the results we need. I

Three Point Flexural Test

[http://www.youtube.com/watch?v=-Jf0nERGxqY 3 Point Bending Testing

References:

Definition of Hooke's Law:

Hooke's law is a principle of physics that states that the force F needed to extend or compress a spring by some distance X is proportional to that distance. That is, F = k x, where k is a constant factor characteristic of the spring, its stiffness.

Week 3 Narrative
=

Clamps
This week I wanted to come up with a different way of test strength/stiffness. I chose to do some research on clamps and the different type of designs what we could build in class. These designs would be cost effective and easily build in class. By using clamps we could either pull with force or push with force. The only issue I see with this method would be finding correct calculation to test the method. The measure of the force would not be as accurate as I would like it to be.

Pending: Calculations

This would be a sample model:

Flexural Strength Testing w/ Plastics
Flexural Strenght is the same as tensile strength. When the material is bent only the extreme fibers are the largest street.Measuring flexural strength this way could give us more of a accurate calculations. The design of this will also be feasible in the classroom.

For a rectangular sample under a load in a three-point bending setup (Fig. 3):$$\sigma = \frac{3FL}{2bd^2}$$


 * F is the load (force) at the fracture point (N)
 * L is the length of the support span (mm)
 * b is width (mm)
 * d is thickness (mm)

For a rectangular sample under a load in a four-point bending setup where the loading span is one-third of the support span: $$\sigma = \frac{FL}{bd^2}$$


 * F is the load (force) at the fracture point
 * L is the length of the support (outer) span
 * b is width
 * d is thickness

For the 4 pt bend setup, if the loading span is 1/2 of the support span (i.e. Li = 1/2 L in Fig. 4): $$\sigma = \frac{3FL}{4bd^2}$$

If the loading span is neither 1/3 or 1/2 the support span for the 4 pt bend setup (Fig. 4): $$\sigma = \frac{3F(L-L_i)}{2bd^2}$$


 * Li is the length of the loading (inner) span

Week 4 Narrative
My goal this week was to gather information for the procedures to for the 2 Point Bending Test.

This was most cost effective way of measure the ultimate stress of the PLA.

Experimental Procedure 2 Point Bending Test that we have design to pass on to the next group to the implement phase. 2 Point Bending Test

Equations used in 2 point bending test:

σult = (FLc)/(12wh^3)

σult = Ultimate Stress F = Applies load, calculated as above L = Distance between the hanging mass and the clamp c = .5h w = width of the beam h = height of the beam