Analysis Overview

 

The Green sheets and all the calculations for this project that are stated down below can be found in the link in the proposal section of the site.

 

            A1- Horizontal Impact Testing of the Base

 

            The base plastic is ABS and the force needed to withstand through the bumper impact is around 20 N of force. This base helps guide the bumper and adds a reinforced back to the bumper to help with any contact. As seen in A1 the base went under various force and weight calculations to come up with a force of 20 N. a picture of the base can be seen in drawing B1.

 

            A2- Vertical Impact Testing on the Insert

           

             This was used to calculate how much force the whole insert could take when the insert is being dropped or “stepped” on from a two-foot height. In the A2 analysis, the calculations used are shown to give the force it can withstand to be around 107 N. This may not seem like a lot but with proper testing the insert could come out to be higher.

 

            A3- K Factor for Leg and Foot

 

            This value was calculated in order to find the “K” factor for a foot or leg. The value will be used for later calculations if need be regarding deformation in the insert material. The difficulty was trying to find the equation that worked best for a foot since the leg was all that could be found. After using an equation online, the value came out to be 71.3 as seen in A3.
 

            A4- Weight of the base

 

            The whole insert needs to be accounted for being lightweight, so it does not weigh down the foot or person wearing it. In A4 below, the equations shown calculated the mass of the base part of the insert through means of simple volume and density equations. The base was calculated to be around .295 pounds which is exactly what the weight needed to be for just the base.

 

            A5- Weight of the bumper

 

            Just as previously stated the insert needs to be optimized and accounted for with the weight. In A5, the same calculation methods used in A4 to calculate the weight of the bumper were used. Through the calculation it was found that the weight of the bumper to be about .335 pounds. This makes the weight of the insert to be around half a pound which is exactly where it needs to be for the person to not feel uncomfortable.

 

            A6-Frictional Force on the inside of the insert

 

            The inside of the insert is the piece that connects the whole part to the foot. There will be a frictional force associated with the skin to the ABS plastic in this case. According to the simple calculations in A6, the frictional force on the inside of the insert is 9.8 Newtons. Which, in this case of the insert, seems pretty reasonable. 

 

            A7- Endurance Limit

 

            The endurance limit shown in A7 is around where the limit was thought to be. Through the calculations shown and using an Sn of 300, the limit was fond to be 209.29 psi. Which, for a piece that goes towards the front of a foot is not that bad. This value could change as the project changes and changing the value of Sn to something closer to 400 would increase the value as well.

 

            A8- Deflection of bumper

 

            The front bumper of the insert is made up of a different plastic than the rest of the insert. The reason being is the n-Gen flex material is more flexible than ABS and would allow for more issues to occur. Through the calculations in A8, it was found that the front bumper could deflect just over half an inch without failure. After that, there will be mechanical and other issues associated with the piece. This seems like a good deflection for a bumper because it’s high enough not to worry about and will need a good amount of force to break past.

 

            A9- Normal Stress

 

            In appendix A under A9 there are calculations for the normal stress of the cylinder. Using the diameter of 4 inches and using the sample of 300 pounds the calculations were simple. Using the diameter, the area was found to be 4 pi or around 12.56 in squared. After finding the area it can be used to calculate the stress by dividing the sample of 300 pounds by it to get a simple normal stress of 23.87 psi.

 

            A10- Hoop Stress

 

            In A10 the hoop stress was calculated using the diameter of 4 inches, wall thickness of .5 inches and a 300lb force. The 300-pound force was used to fit a required size and weight for the insert. By multiplying the 300-pound force and dimeter it was found to be 1200-pound inches and was divided by 2 times the wall thickness which just happened to be 1. So, the final answer came to be 1200 psi with the equation found online.

 

            A11- Longitudinal Stress

 

            In A11 the longitudinal stress was found using the same given materials in A10. The equations were roughly the same except the thickness of the wall was multiplied by 4 not 2. Which makes the final answer to be 600 psi. This answer seems to fit the right requirements of the part and is used for the insert not just the one piece or other.

 

            A12- Modulus of Elasticity

 

            The modulus of Elasticity was found in A12 in appendix A. Using the E value of .33 x 10^6 psi which was found online and the poisons of .35 which was found online the value could be found. By simply using the equation in A12 the modulus was found to be 1.22 x 10^5 psi which sounds really high for ABS plastic. This is for the base not the bumper of the insert since the bumper is made of a different plastic.

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