Sam Hunt is a Manufacturing Engineer from Santa Rosa, CA. His main roles were CAD Modeling potential solutions, design analysis, manufacturing, and testing. Sam reported data directly to the team to analyze, and documented testing results through caliper measurements, pictures, and video recordings. This was crucial for finalizing and concluding the recommendation report.
Design Analysis Lead
Ronel Ordona is a fourth-year Manufacturing Engineering student at California Polytechnic State University, San Luis Obispo. His main roles were design analysis, manufacturing, and testing. Ronel researched mechanical properties in potential materials, assisting the team with prototype design and testing methods. He will continue on with the project in Fall 2021 to support scaling and manufacturing.
Austin Warren is a fourth year Industrial Engineering major from Berkeley, CA. His main roles were design analysis, testing, researching material properties, prototyping, brainstorming potential solutions. This was all beneficial for the finalization and overall product as a whole.
We would like to thank our sponsor Fabian Araujo for allowing us to work on this project, and guiding us through the current state. We would also like to thank Jill Speece for guiding our team on a weekly basis to the final report, and Trian Georgeou of the IME Department for his industry insights and material recommendations.
Our Project's Videos
Our Project's Digital Poster
Armadillo Design has a demand from a local retailer for 10 shells a month that they cannot fulfill due to product defects. This calculates to $168,000 in annual lost revenue. The shell is not completely water resistant and is only able to fit the Ford F150 standard bed. The company would like their truck shell to fit multiple truck make and models. This would increase customer demand and versatility of their product. The current retractable roof system is outsourced from a Peragon® truck bed covers. This increases cost and constrains the company’s truck shell design to fit only truck beds with specific dimensions. Armadillo Designs is seeking to design their own roof system that is capable of accommodating multiple truck bed dimensions and will reduce manufacturing costs. The truck shell is marketed towards construction workers and tradesmen alike. These men and women travel from worksite to worksite with expensive tools and equipment that they need to secure in their truck bed. The truck shell must be sturdy, secure, and be able to withstand all environmental conditions. Armadillo Designs would also like their truck shell to be modular and easily assembled. This will reduce shipping cost and allow the shell to be shipped and assembled at the customers home.
- Armadillo Designs current design is catered to the Ford F150 standard bed. The truck shell uses a water resistant retractable roof system that is outsourced from Peragon® truck bed covers. The back door of the shell uses a hinge mechanism that is not water resistant. The shell walls are made with fiberglass panelling and the frame is made with plain carbon steel. The frame is outsourced from Austin Waterjet; a metal fabrication shop located in Austin, Texas.
The main goal of the team when finding key metrics was improving the original prototype brought to them by Armadillo Designs. The first was to minimize cost and keep it below a total of $2,500 per unit. The next was to have the shell have less than 5 leak spots throughout the entire structure. We found that with water tests in the automotive industry, 5 leak spots were considered within specification to be considered “watertight”. The next was to keep the total number of parts under 60. This was to decrease the amount of difficulty when constructing and manufacturing the product. And the final metric was the overall weight of the shell which the team aimed to keep under 250 pounds for ease of shipping and maneuverability.
To evaluate the different designs and materials for our project, we used priority matrix diagrams to come up with the highest benefit and easiest to implement solutions. We initially researched HDPE sliding roof panel designs with four HDPE panels sliding along G-channels. To test the HDPE, we subjected it to a water test and then direct sunlight for a week. After this time, there was considerable warpage and distortion in the panels. We tried to nullify the warpage and decrease weight by routing grooves into the HDPE, but this only created bowing in the opposite direction. The team then tested fiberglass for the roof material, as well as a series of G-channels each designated for one of the panels. After creating the prototype, this design allowed the panels to slide very well – being able to be opened or closed within 5 seconds. However, there was still visible warpage in the middle of the fiberglass panels.
This project is sponsored by Armadillo Designs
Due to its vibration resistance, machinability, and low coefficient of static friction, High Density Polyethylene (HDPE) was considered as a roofing material. HDPE Stress/Strain Graph received from (Amjadi & Fatemi, 2020)
Due to being industry standard for truck shells, and having a high strength to weight ratio, Fiberglass Reinforced Plastic (FRP) was considered as a roofing material. Graph received from (Haery et al., 2012).
Stress/strain analyses were key in understanding the elastic modulus and ultimate tensile strength of each material. Elastic modulus measures how stiff a material is and ultimate tensile strength measures how much stress a material can withstand before it fails. HDPE was a top contender amongst other materials as it is very cost-effective. A 4mm thick sample had an ultimate tensile strength of about 20 MPa and an elastic modulus of about 800 MPa. HDPE is also a very slick material and will provide less sliding friction in the retractable roof mechanism. Fiberglass material is the industry standard in truck shells because it is lightweight and durable. It has excellent material properties, a 5 mm sample demonstrated an ultimate tensile strength of about 100 MPa. The downside of fiberglass is it is more expensive and brittle. If a failure event were to happen, fiberglass would break into pieces instead of deforming.
Verification & Validation
The shell was subjected to water-tightness tests, shock and vibration tests, construction site testing, as well as others.
Video cameras were used to document the testing, and allow the team to analyze and observe results more closely post-testing
Verification and Validation Results
We focused on 7 criteria for our verification and validation of the convertible truck shell. We implemented a HogWash and Drive-Through CarWash test, to test for leakage of the truck shell and to test durability in simulated rough environmental conditions. The truck shell did not meet the metric for under 5 leak-spots during both these tests, however it allowed the team to reach a valuable conclusion. Sun Exposure was tested by leaving the roof panels out in broad daylight for over a week and measuring warpage. From our testing, the fiberglass panel and the routed HDPE panel passed this test with < 1” of deflection. Functionality was tested for by being able to open/close the shell in under 10 seconds. The shell completed this test in under 5 seconds. Shock and Vibration was tested for by driving around town, on the highway, and up Cuesta Ridge. The shell passed this test and the team utilized video cameras to document the process. Lastly, the shell underwent a Construction Site Test. The team loaded tools on and in the shell and had other construction workers interact with the shell to test for durability and ergonomics. The shell passed this test when accounting for panel warpage following the sun exposure test.
Weight ~200 lbs
Overall Cost – $2,147.52
# of Components – 55
- Plywood Toolboxes
- Frame Rails
- Weatherproofing Strips
- Roof panels
- G-channel Rails
- Screws, Nuts, Bolts
- Black Paint
- Toolbox Locks
The team’s design was able to meet 3 out of 4 of the key metrics. The prototype cost a total of $2,023.12, well under the maximum of $2,500. The total number of parts came out to be 55 parts, and the weight of the shell ended up at 200 lbs overall. The one key metric the team was unable to meet was the total number of leak spots throughout the shell being under 5. The team concluded that this was because of the slight warpage of the fiberglass panels, and overall, concluded that any warpage in the panels would be detrimental to the water-tightness of the shell. Moving forward, the team recommends that Armadillo Designs keep the structure and G-channel design, but instead use an aluminum honeycomb panel. Based on research and literature review, this material only had a .7 inch deflection when undergoing a load of 200 pounds, meaning it will warp considerably less than HDPE and fiberglass even under load.
Amjadi, M., & Fatemi, A. (2020). Tensile Behavior of High-Density Polyethylene Including the Effects of Processing Technique, Thickness, Temperature, and Strain Rate. Polymers, 12(9), 1857. https://doi.org/10.3390/polym12091857
Haery, H., Zahari, R., Kuntjoro, W., & Taib, Y. (2012). Tensile strength of notched woven fabric hybrid glass, carbon/epoxy composite laminates. Journal Of Industrial Textiles, 43(3), 383-395. https://doi.org/10.1177/1528083712456055