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Things to look for when selecting adhesives
When deciding on what adhesive to use, one of the first things that should come to mind is identifying what substrates need to be bonded together. Most adhesives are engineered for a certain application or a limited set of materials, e.g. only wood or only steels.
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Afterwards, there are many other adhesive factors such as working time, curing time, etc. that will be factored into the final adhesive choice. The primary focus for this project was to find an adhesive that was appropriately specified based on its adhesive strength.
How the adhesive strength required was calculated
The adhesive must sustain all appropriate loading that individual components of the car are expected to withstand. For example, aerobody panels are not expected to be structural as per regulation therefore it only needs to withstand its own weight. The bonding between the chassis and the bottom panel is expected to be structural as per our design requirements for the car to function safely therefore it needs to withstand a 2G bump and vehicle collisions (based on regulation).
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The bonding between the Chassis and the Bottom Panel must be structural.
This structure contributes to the foundation of the car.
The bonding between the bulkheads and the Chassis.
Bulkheads A and C cover the front and back of the Chassis.
They are used for cover and may be used for mounting.
They are not designed to be structural; the Chassis is primarily responsible for withstanding vehicle impacts
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Figure 3: Shows the bonding area and force diagram for the bonding between the Chassis and Bottom Panel. Bulkhead A can be seen at the front (to the left) and Bulkhead C can be seen at the back (to the right). | Figure 4: Bonding areas for Bulkhead A | Figure 5: Bonding areas for Bulkhead C |
Table #1: Shows the bonding scenarios to be analyzed and the related design and stress elements associated with each bonding scenario.
Bonding Scenario | Design Requirement | Loading Scenario | Expected Stress | Notes |
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Chassis and Bottom Panel | Structural | 2G Bump | Tensile | This analysis laid the foundation for adhesive selection |
Vehicle Crash Scenarios | Shear | |||
Bulkheads to Chassis | Strong enough to allow mounting of potential dynamic assembly parts | 2G Bump | Shear | Later in the analysis, bulkheads were concluded to not be structural which led to ceasing its analysis. Documentation is still written for educational purposes. |
Vehicle Crash Scenarios | Tensile |
Tips for Creating a Simplified Model or Worst Case Scenario
The importance of creating a simplified model is to create a more feasible way of understanding the problem so that basic hand calculations can be performed. It is strongly preferred that the physics model is modified in a way that makes it weaker meaning it will result in larger stresses hence the name worst case scenario. It is better to design towards an approximated higher standard than an approximated lower standard for safety reasons.
In terms of the analysis of the adhesives, creating a worst case scenario involves assuming all stresses in tensile (since adhesives are weaker in tensile and stronger in shear) and reducing bonding area (decreasing area increases stress).
Hand calculations are required to compare with simulation results. If the simulation results are far from your hand calculations, it strongly suggests that a miscalculation or a misinterpretation of the physics model has occurred. It is important to revisit the assumptions made.
Hand Calculations and Simulations for Finding Adhesive Strength Requirement for Bonding the Chassis and the Bottom Panel
Loading Scenario: 2G Bump
Finding Sum of Forces:
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Finding Bonding Area:
Bonding Area was found by reviewing the SolidWorks Assembly and using the measuring tool. The bonding area is where two parts are expected to interface with each other and have adhesives applied.
Initial bonding area was determined to be all flat tubes at that touch the bottom flaps of the Bottom Panel. After multiple analysis reviews, the bonding area has been reduced to create a new worst case scenario.
The analysis consisted of finding the force reactions in the Chassis tubes that interfaced with the Bottom Panel. If all tubes were selected, then an average value of the forces would be given. This is easily calculated by hand. Simulations allow for more in-depth analysis by allowing probes to measure specific tubes. This means we can know the approximate force reaction of each tube. Contact probes were used to remove the need to add unnecessary fixed boundaries that may invalidate the physics model.
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Figure 6: The final bonding areas between the Chassis and Bottom Panel
Debrief of Results:
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Figure 7: Hand Calculations and Simulation Results
Hand Calculations and Simulations for Finding Adhesive Strength Requirement for Bonding the Bulkheads A and C to the Chassis
Safety Factor of Adhesives can be found on this page:
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