Week 8:

     This week, we created a housing to hold the load cell for testing.  Using this new housing, we tested the load cell using weights.  We did this to get a line of best fit for voltage outputs vs. force.  Below are the results of the testing.

Mass (grams)	Force	Volts (in mV)
0	0	-0.088
50	.49	-0.127
100	.94	-0.185
200	1.96	-0.29
500	4.9	-0.31
700	6.86	-0.81
900	8.82	-1.02

Using this graph, the line of best fit, y = -9.3906 x - 0.7689 was found, and can be used to find the force easily.  If you plug in a voltage value x and solve, the answer will be the force.

     Also this week, a scanning electron microscope was used to photograph the carbon black and polyethylene fibers.  The fibers will not be able to be tested using a kawabata evaluation system due to their size.  The mats did not come out thick enough, making it impossible for the machine to test it.  This most likely happened from in-optimal conditions for spinning the fibers.  There are a lot of variables when electrospinning, and without the correct conditions fibers will not spin correctly.  

Week 7:


     This week we had a large setback in our design of the table top tensile strength tester.  We found that after using weights from 50-500 grams that most of the voltage results were exactly the same.  This is because the load cell is meant for a minimum 130 grams and the voltmeter does not have a more accurate result other than one decimal place.  In order to create this strength tester we would need much more sophisticated equipment to get usable results because the electrospun fibers will not put up that much resistance.  So after that had been decided, our new task is to continue creating the tensile strength tester, but instead use it as a demo with string or some other type of material like string.  We are to show that we did create a system to do the job, and that with the proper equipment it can test the strength of fibers also.
     In the Materials Science lab, the polyethylene fiber compound has been spun.  The polyethylene and 1% carbon black compound and the polyethylene and 9% carbon black have also been spun.  Next week the mixtures containing 3% and 6% carbon black will also be electrospun.  Once the fibers are finished spinning, they will be tested using Kawabata machine due to the load cell and voltmeter being used for the table top tensile strength tester.

Week 6:


     This week, our designated group members doing the electrospinning went into the Materials Engineering Department lab and mixed the chemical compounds that will be used to do electrospin polyethylene and the polyethylene and carbon black compounds.  They also learned from experienced electrospinners some of the variables needed to be set to spin polyethylene.  After the compounds have set for a while they will electrospin the fiber next week.
     In the engineering lab this week, the we figured out how to use the load cell by calling the company who created it.  We borrowed a power supply to apply 5 volts and a volt meter to read the voltage for ensuring that the load cell worked properly which it did.  We also researched how the load cell actually works.  The way it is used is through a series of resistors.  As the resistors stretch due to pulling on the load cell, the output voltage changes due to the change in resistance.  Using this output voltage, the force applied to the load cell can then be determined.  Finding this will then allow for the calculation of the stress and strain on the fibers tested.  Below is an image of the circuit board that is normally used in a load cell.  It shows how the series of resistors work to give a voltage output based on the bending of the circuit board [5].

Figure 1:  Circuit Board of a Load Cell [5]

     Now that we have figured out how the get the load cell working, the next job is to find a way to attach it to the NXT model we created.  It has to be attached in a way that it will be immobile, so the voltage reading is as accurate as possible.

Week 5:


     This week, in lab a design has been created for a table top tensile strength tester.  It was made using the Lego NXT as planned.  We did run into an issue with the load cell though.  We found a way to attach it to our design, but we do not have a way to get a reading from it.  The wires are in okay condition, but we have no clue where to plug them in.  The plan is to find a way to get a reading from the load cell next week.
     As far as the electrospinning goes, two of our group members have taken their safety tests and are ready to spin, so at the end of week 5 they are planning on going into the materials science lab and mixing the polyethylene and its mixtures to be spun the next day.
     Below is a picture of our tensile strength tester design created in Lego Digital Designer:

Figure 1:  Isometric View of the Strength tester