User:1eagbai/Project1

Project Preference
My top 5 choices


 * MakerBot PLA Material Characterization


 * Autonomous Power Wheel


 * Robot Hallway Navigation


 * Smart Shoe

Problem Statement
A-Team group project has set out two specific goals for this project
 * Testing the material properties of PLA, the primary material a MakerBot uses.
 * Run test to determine quantitative data relating to this properties with respect to its CTE, strength, stress, stiffness, strain and ductility

Project Plan
A-Team came up with a 4 week plan. We will be concentrating on the design phase of this projects; hence we have opted to understand the material properties of PLA.
 * Week 1: Research on the different material properties pertaining to a MakerBot PLA. Get a parts list done for materials we will need for the project
 * Week 2: This week will be used to run tests for 3 (or +1) specific materials properties on identified shapes of PLA, i.e. different shapes of bolts
 * Week 3: Quantitative data collection of different prototypes
 * Week 4:

Week 1 Narrative
During this week. I wanted to research the material property of stiffness. These properties are two of some of the different properties that my team will be researching about. We plan to understand these material properties and further runs test on the PLA to collect quantitative data. "Wikipedia" defined stiffness as the rigidity of an object — the extent to which it resists deformation in response to an applied force. I modelled my research based on the calculations of stiffness

Stifness, k, measures resistance offered by an elastic body to deformation. This information was from "Wkikipedia" and if explains that, for an elastic body with a single degree of freedom, the stiffness is defined as


 * $$k=\frac {F} {\delta} $$

where,


 * F is the force applied on the body
 * &delta; is the displacement produced by the force along the same degree of freedom

I also found two different test that measures stiffness


 * Taber Stiffness Tester
 * Crease and Board Stiffness Tester

During the course of my stiffness research, I found that measuring modulus of elasticity is also an important property when selecting a material.

Week 2 Narrative
In the first week, I research about the material property of stiffness (see week 1). My team came up with a range of material properties that can be tested but we decided that strength and stiffness is the most useful PLA material property to test. We identified strength and stiffness as the properties to test. This weeks task was identify method of testing of for strength and stiffness and since we don't have a prototype, I researched online to find existing tests that have already been done.

Stiffness is a measure of the materials ability to resist deformation under load as measured in stress. Stiffness is measured as the slope of the stress-strain curve. From my week 1 research, I found that the value of Young's Modulus is important property when selecting a material.

Hooke's Law: σ=Eε

Where, σ is stress

E is Modulus of elasticity (Young’s modulus)

ε is strain

Modulus of Elasticity (E) or Young’s Modulus is the ratio of stress to corresponding strain (within specified limits).

For plastic, I found that the limits are within (E= 0.2 to 0.7 million psi).

After a couple of days of fruitless research, I found something useful. Quantitative data of experiments carried out on PLA material property, which we can use to have more understanding of PLA since we don't have a prototype to test with yet. This data represents typical values that have been calculated from all products classified as: Generic PLA

3 Point Bending Test
I focused my research on because it seemed the most feasible and accurate quantitative data can be collected. Tensile testing would have been another method but it would prove difficult because the load needed to cause any type of deformation to a PLA would be on average 500 newtons.

Since we had no prototype to test, and i was having a hard time finding a test carried on a PLA that has quantitative data, I studied a 3 point bending test carried out on a plastic (similar properties of a PLA). The 3 point Bend test I found online, ends when the material has acheived 5% deflection or it breaks. The 5% deflection is determined by a calculation that takes into account the support span and depth of beam.

3 point bending test

The three point bending flexural test provides values for the modulus of elasticity in bending $$E_f$$, flexural stress $$\sigma_f$$, flexural strain $$\epsilon_f$$ and the flexural stress-strain response of the material.

The data at the bottom of the link, shows the quantitative values of 3 point bending test carried out by a ASTM D790 machine. The Modulus of elasticity in this test after is documented at 1569922.6 psi.

The data found already will give my team an idea of the properties of PLA and also help calculate the Young's modulus.

Week 3 Narrative
For this week, figuring a way to actually produce a 3-Point test was imperative. This week was, however frustrating and researching suitable ways that is suitable for testing for stress and stiffness was difficult due to the scarcity of information relating to PLA on the would wide web. However, after an extensive research and on databases of institutions like UMBC and UMCP, I was able to find something feasible.

After two weeks of researching and finding out different ways to test a PLA, it was time to find out what can work within our constraints and with the materials we have at our disposal. That bring me back to 3-Point bending, which we identified at the best way to simply measure the stiffness of a PLA. Bend or flexure testing is common in brittle materials whose failure behaviours are linear such as plastics.

Bend test is suitable in evaluating strength of brittle materials and PLA happens to fall under that category.

where M is the bending moment c is half of the specimen width as shown in figure 1 t is the thickness of the specimen as shown in figure 1

I is the moment of inertia of the cross-sectional area



For brittle materials having a liner stress-strain relation, the fracture stress (σf) can be determined from the fracture stress in bending according to a linear elastic beam analysis as shown below;

σ f = Mc/I=2M/2tc^2

I = 2tc^3/3

From researching this test, I was able to find equations that would help us calculate the ultimate stress when we start out test. My other team member has really good ideas on ways to test and for next week, we plan to look at what we currently have and decide if we think we can test tentatively or if we need to find other ways to test before we start designing and testing to find real quantitative values.

Week 4 Narrative
Leading up to this week, the team has researched on several material properties of a PLA and in the last two weeks, we have focused primarily on stiffness test and strength test. This week, I'll be focusing on analysing the project and where we are now and then develop a design procedure for the 2 point testing of a PLA material.

Firstly, looked into hardness test in a PLA, which is basically the material's ability to resist plastic deformation from a standard source like a load. We also researched about Thermal Expansion (CTE), and the goal was to have an idea about the melting point of a PLA. We also gathered some useful information on ductile test, which tests a materials ability to deform under tensile stress. After researching on all these different material properties in the first couple of week, we decided to narrow it down to the two most important one. After deliberating, we agreed that strength test and stiffness test were the two most relevant one. The rest were get aside.

The last couple of week, each group member has either had to work on finding ways to test for strength and stiffness or finding the limitation that could be encountered in the course of this test, test the accuracy of our two final material property testing (stiffness and strength). This week, our goal is to design a step by step procedure, outlining the process of experimentally determining the material properties of the PLA material through testing.

Firstly, i identified material needed to successfully carryout a 3-point bending test
 * PLA Material printed from the MakerBot printer
 * Load and a hang and rope to suspend the load
 * Measuring device (calliper or a ruler)

With those materials, you can then conduct the experiment and acquire values of your deflection $$\delta$$ and then solve to get E, Young's Modulus, I, moment of Inertia.

To accomplish this test and finding the Young's Modulus E (test of stiffness), these two equations can be employed to find E


 * $$\delta$$ = {F L^3 /48EI }
 * and, I = bh^3/12


 * where,
 * F is force applied
 * L is the length of the two supports apart
 * I is the polar moment of inertia (term used to define how the geometry of the specimen influences it's reaction to loads)
 * $$\delta$$ is the value of deformation (change in length of stretched PLA)

The values needed for this experiment are,
 * Length of L in mm
 * Mass of F in Newton
 * Deformation $$\delta$$ in mm
 * Specimen height (h)
 * Specimen width (w)