Section G
CONSTRUCTION OF A TESTABLE PROTOTYPE
VII.1 Preliminary Prototype Development
Before the team started to build the prototype, templates needed to be created. The team chose to create them out of plastic drop cloth as a cheaper alternative to fabric. Our school SRO volunteered to wear the vest to test and give feedback on how comfortable prototype was. Because of this, it was decided to create a model for him to wear. The team took his measurements and compared them with measurements from several donated vests in order to decide the final dimensions. Once the templates were finished, the team made a mock-up of the carrier and fitted it to the SRO. Because comfort is one of the most important criterion, the team wanted to be certain that the measurements were as accurate as possible. Consequently, the measurements had to be revised after the first fitting of the templates. After the revisions, the group proceeded to create the first fabric model.
Before the team started to build the prototype, templates needed to be created. The team chose to create them out of plastic drop cloth as a cheaper alternative to fabric. Our school SRO volunteered to wear the vest to test and give feedback on how comfortable prototype was. Because of this, it was decided to create a model for him to wear. The team took his measurements and compared them with measurements from several donated vests in order to decide the final dimensions. Once the templates were finished, the team made a mock-up of the carrier and fitted it to the SRO. Because comfort is one of the most important criterion, the team wanted to be certain that the measurements were as accurate as possible. Consequently, the measurements had to be revised after the first fitting of the templates. After the revisions, the group proceeded to create the first fabric model.
VII.2 First Fabric Prototype
Using the drop cloth templates, the team cut and sewed fabric pieces together. Then the group took nylon and Velcro straps and attached them to each fabric segment. Since mobility and flexibility were criteria for the design, it was crucial to be certain that the sections would overlap properly. To test these things, the group took the prototype to our school's SRO for fitting.
The team learned several things when trying the vest on. First off, our school’s SRO liked how the segments layered on top of each other, didn't pinch him, didn’t ride up to his neck, and how there was no elastic belt in the vest, because it generates a lot of heat. However, there were issues with the design, such as the segments were too large to fit snugly, and the fabric that was used created too much friction for the sections to slide over each other. Also, the small "flaps" of fabric in the top segments (as seen in the image above) are supposed to fold around the user, but they stuck out, which is undesirable. The team retook certain measurements to solve the dimensional issues.
Using the drop cloth templates, the team cut and sewed fabric pieces together. Then the group took nylon and Velcro straps and attached them to each fabric segment. Since mobility and flexibility were criteria for the design, it was crucial to be certain that the sections would overlap properly. To test these things, the group took the prototype to our school's SRO for fitting.
The team learned several things when trying the vest on. First off, our school’s SRO liked how the segments layered on top of each other, didn't pinch him, didn’t ride up to his neck, and how there was no elastic belt in the vest, because it generates a lot of heat. However, there were issues with the design, such as the segments were too large to fit snugly, and the fabric that was used created too much friction for the sections to slide over each other. Also, the small "flaps" of fabric in the top segments (as seen in the image above) are supposed to fold around the user, but they stuck out, which is undesirable. The team retook certain measurements to solve the dimensional issues.
VII.3 Second Fabric Prototype
Although the first prototype provided the team with optimism about the design, there were a myriad of other issues with reusing the first design. The first design used twice as much fabric as necessary, it had sew lines that were either amateur or not strong enough, the fabric used was not suitable for a carrier, and the nylon straps and Velcro were nearly impossible to relocate without damaging the polyester fabric. A completely new carrier had to be made and it had to be professional looking and had to exactly fit our SRO. For this, it was necessary to consult some outside help for creating the carrier. This came in the form of an engineering teacher of ours, who is also an experienced seamstress. The team ordered high-strength navy CORDURA nylon fabric, reused the previous nylon straps and Velcro from the first carrier, and began to build the second carrier.
For the construction of the second carrier, our SRO consulted more often during the construction process to make sure that the vest would accurately fit him, making sure that the comfort, fit, and mobility criteria would be fulfilled. Various small issues popped up during the construction process, but the team could come up with an objective plan to fix them. For example, there was still the issue of the fabric "flaps" popping out, as seen below (Keep in mind the person wearing it is smaller than our SRO that the team designed it for).
Although the first prototype provided the team with optimism about the design, there were a myriad of other issues with reusing the first design. The first design used twice as much fabric as necessary, it had sew lines that were either amateur or not strong enough, the fabric used was not suitable for a carrier, and the nylon straps and Velcro were nearly impossible to relocate without damaging the polyester fabric. A completely new carrier had to be made and it had to be professional looking and had to exactly fit our SRO. For this, it was necessary to consult some outside help for creating the carrier. This came in the form of an engineering teacher of ours, who is also an experienced seamstress. The team ordered high-strength navy CORDURA nylon fabric, reused the previous nylon straps and Velcro from the first carrier, and began to build the second carrier.
For the construction of the second carrier, our SRO consulted more often during the construction process to make sure that the vest would accurately fit him, making sure that the comfort, fit, and mobility criteria would be fulfilled. Various small issues popped up during the construction process, but the team could come up with an objective plan to fix them. For example, there was still the issue of the fabric "flaps" popping out, as seen below (Keep in mind the person wearing it is smaller than our SRO that the team designed it for).
To fix this issue, the team put a strap around the front and back the pull those pieces together. By the time the first test was performed, the team had a fairly confident understanding of what small details would have to added or changed.
VII.4 Kevlar Panels
In order to make the vest bulletproof, the team had to create ballistic panels for it. In order to do this, the group took a donated vest, cut it open, and used the Kevlar in it. Since the vest is composed of three panels per side is shaped differently, the team had to cut the Kevlar in the shape of the vest. The team did not have the proper cutting equipment, the most effective tool was one pair of fabric scissors. This made the cutting process extraordinarily painful and time consuming. An Kevlar template was created using the outline of the carrier and that was used to draw the rest of the pieces. The Kevlar pieces were grouped by shape and the team then wrapped the groups in drop cloth, which simulates a plastic envelope that would hold the shear thickening fluid. When the finished panels were to be put into the carrier, the team ran into the problem that the panels were slightly too large. This meant that the team had to cut them all over again. Although one piece of Kevlar fit flawlessly into the carrier, the layers of them bunched up and caused the fit to be too tight. Once the pieces were cut some more, it was possible to fit them into the carrier, and then testing could begin.
VII.5 Final Modifications
One of the issues discovered when testing was that equipping the vest by using the Velcro straps was very hard to accomplish. Identifying which strap belongs to which Velcro strip is difficult from the user's perspective. In order to fix this without buying wider Velcro straps, the team needed to figure out how to combine the two separate Velcro straps that are on each piece and each side. To accomplish this, a piece of fabric was sewn to the straps to unite them.
One of the issues discovered when testing was that equipping the vest by using the Velcro straps was very hard to accomplish. Identifying which strap belongs to which Velcro strip is difficult from the user's perspective. In order to fix this without buying wider Velcro straps, the team needed to figure out how to combine the two separate Velcro straps that are on each piece and each side. To accomplish this, a piece of fabric was sewn to the straps to unite them.
VII.6 Development of the Shear Thickening Fluid
In order to make the design lighter, more comfortable, flexible, and mobile, the team was required to directly tackle the largest component of body armor weight. The amount of Kevlar that a vest needs can be reduced by coating the Kevlar with a silica nanoparticle shear thickening fluid, which thickens when a considerable force is acted upon the fluid. A combination of this fluid and Kevlar can reduce the amount of Kevlar needed while keeping the same ballistic protection. As the team did not have the necessary equipment and resources to produce the shear thickening fluid. Therefore, the team contacted the head of the chemistry department at MTSU and asked him if he could assist the team by providing our group with facilities, equipment, and mentoring. He granted the team these requests, which meant STF production could begin.
The STF the team was going to make consists of silica nanoparticles suspended in a fluid. As per his advice, the team started by testing the process of producing silica nanoparticles outlined in this paper (Sections 2.2 & 2.3) by making a small batch of the particles. The reason for this was because the instructions outlined were vague and the procedure might have required modification depending on the volume of silica nanoparticles produced. The first time the process was completed, about a gram of the particles were produced.
In order to make the design lighter, more comfortable, flexible, and mobile, the team was required to directly tackle the largest component of body armor weight. The amount of Kevlar that a vest needs can be reduced by coating the Kevlar with a silica nanoparticle shear thickening fluid, which thickens when a considerable force is acted upon the fluid. A combination of this fluid and Kevlar can reduce the amount of Kevlar needed while keeping the same ballistic protection. As the team did not have the necessary equipment and resources to produce the shear thickening fluid. Therefore, the team contacted the head of the chemistry department at MTSU and asked him if he could assist the team by providing our group with facilities, equipment, and mentoring. He granted the team these requests, which meant STF production could begin.
The STF the team was going to make consists of silica nanoparticles suspended in a fluid. As per his advice, the team started by testing the process of producing silica nanoparticles outlined in this paper (Sections 2.2 & 2.3) by making a small batch of the particles. The reason for this was because the instructions outlined were vague and the procedure might have required modification depending on the volume of silica nanoparticles produced. The first time the process was completed, about a gram of the particles were produced.
Now that the team had the nanoparticles, it was possible to mix them into the fluid. It was determined that the appropriate solution was ethylene glycol (although many other papers used polyethylene glycol) by using this paper and it was determined the mass volume ratio of silica to ethylene glycol by using this paper.
Although the production of the silica nanoparticles appeared successful, the fluid the team had did not appear to thicken, no matter what was done to it. It was determined that since the majority of STF papers used PEG, the team decided to used PEG and make a larger batch using the PEG. Around this time, additional research provided this thesis which was entirely about the synthesis of STFs and their usage and testing in body armor. This helped to confirm the team's hypothesis about the PEG, provided the team with a plethora of data about virtually every facet of STFs, and allowed the group to confidently order the right PEG, as there are multiple different types of PEG.
When the team started the upscaled production of the silica nanoparticles, previous experience and new equipment helped to upscale the process. This allowed the group to produce significantly larger amounts of nanoparticles in roughly the same amount of time. However, when a sample of the particles was taken and was combined them with PEG, there was still no sign of the fluid actually having shear thickening capabilities (other than one case which could have been a fluke). At this point, the team hypothesized that a very large force had to be applied for the fluid to thicken. This means a bullet or a knife could cause the fluid to thicken, but poking it with a stir rod couldn't. In order to determine if the fluid worked, one of the team members set up a stab test treated some panels with the fluid. and compared it to a control panel with no fluid. The group determined the process of impregnating the Kevlar with the STF by using the paper above in which it was used to determine the silica and PEG mass to volume ratio.
When the test was completed, the team was able to determine that the PEG solution was a shear thickening fluid. The Kevlar panels with the STF showed a significant stab reduction versus the non treated Kevlar. The group decided to test another type of silica, fumed silica. The fumed silica has different properties from the colloidal silica, as it is lighter and airier than the colloidal silica. Several papers have used fumed silica to make STFs for body armor. Panels treated with the fumed silica and PEG mixture were tested in the stab test. Although the solution was thicker than the colloidal silica STF under normal conditions, it did not undergo shear thickening. Because it didn't shear thicken, there wasn't any stab resistance associated with the fumed silica. The reason for this was most likely because the wrong fumed silica was purchased, as there are multiple versions. The only detail that the team had to reference to was the company that the author of the STF thesis purchased it from, not a model number.
After this, the team made one more batch of silica nanoparticles and then finally used all of our silica and combined it with PEG and ethanol, which the ethanol allowed the group to impregnate the fabrics of the ballistic test panel easier.