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This page will document the work and progress involved in selecting and validating an adhesive option for aero-chassis integration.
Final Adhesive Selected is: EA E-120HP (TDS attached to page)
Document used to compile all the work is here:
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Figure 1: Images to show complex bonding in MS XIV compared to more basic bonding scenarios
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scenarios
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go from hand calc approach to simulation set up (features used)
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display hand calc results and sim results in an organized table + should show formulas used as equations
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lastly talk about design safety factor for adhesives -
There are two main loading scenarios that the vehicle should be designed towards:
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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 |
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Hand Calculations and Simulations for Finding Adhesive Strength Requirement for Bonding the Chassis and the Bottom Panel
Loading Scenario: 2G Bump
A 2G Bump is a frequent loading condition that a car will undergo. By selecting an adhesive to withstand this load, it can be certain that the bonded adhesive joints will remain intact during regular travel.
Finding Sum of Forces:
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Finding Bonding Area:
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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
Loading Scenario: Vehicle Collisions
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Vehicle Collisions include the absolute worst case scenarios that a vehicle is designed to withstand in the case of emergency. In terms of selecting an adhesive, only vehicle components that are required to be structural will need to have sufficient adhesive strength. In MS XIV, there are many bonded joints between carbon fibre parts and steel tubes, but not all joints are designed to be structural. For example, the purpose of an aerobody is to enhance our vehicle’s aerodynamics; it is not meant to sustain a load as large as a vehicle collision. On the contrary, the purpose of the Chassis is to withstand large impacts and large loads, i.e. vehicle collisions, therefore it is very much a structural part.
When analyzing MS XIV, the most concerning structural joint being bonded by adhesives is between the Chassis and the Bottom Panel. This connection revolves around very frequent loads and large range of loads during vehicle use. Other potential areas of concern include the Bulkheads A, B, and C. Research and analysis has been done on the stresses in the Bulkheads, but it was concluded that the Bulkheads did not serve a structural role. The largest area of debate was whether the Bulkheads served a role in distributing the force during a vehicle collision as they spanned the entire width of the car. As the Chassis has already been designed to independently withstand vehicle collisions, the analysis of the Bulkheads was no longer significant to selecting a sufficient adhesive.
In face of the vehicle collisions, the main stress induced in the adhesive joint between the Chassis and the Bottom Panel is a shear stress.
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Figure 8: Hand Calculations and Simulation Results
Safety Factor of Adhesives can be found on this page:
Adhesive Research (Types of Adhesives, Adhesive Behaviour, Adhesive Design Tips)
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In conclusion, our minimum safety should be 6.
Summary of Results
From extracting the information from the hand calculations and simulation results, the peak stresses are as outlined in the table below.
Table #2: Strength Requirements Derived from Simulations and Hand Calculations
Loading | Hand Calc Stress (MPa) | Simulated Stress (MPa) | Types of Stress |
2G Bump | 0.17 | 0.47 | Mostly Tensile |
B Pillar Impact (5G) | 0.93 | 2 | 1.5 MPa in Tensile and 1.3 MPa in Shear |
Minimum Safety Factor Required: 6
Final Decision on Adhesive and Quantity
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The process of making a final decision on an adhesive involves finding suppliers and adhesive options for your application. As mentioned before, this process can be shortened through asking companies for their recommendations for our application. They might even provide free samples. Once adhesive options have been gathered, it is valuable to collect information from each adhesive’s technical data sheets to compare critical factors such as tensile strength, working time, curing time, curing temperature, and any other factor relevant to your application.
In the case of MS XIV, many discussions have been had with Henkel and they were generous enough to already provide us samples. They have also given a list of their recommendations for our specific application. From their list of recommendations, there were a few that met the design requirements. Here is a list of things that should be considered:
Adhesive Strength
Components
If it’s two component then it requires mixing
Cure Temperature
If the curing process requires high temperatures then it would increase the difficulty and inconvenience
Working Life
After the adhesive is applied, the adhesive joint must be held with pressure for a duration up to 24 hours. The process to put the bonding parts into a jig may be difficult or time-consuming depending on the complexity of the adhesive joint
Bond line thickness
This is the thickness of the adhesive layer that will produce the adhesive’s maximum strength. It is better to have one that is slightly larger because in-house manufacturing of carbon fibre parts can result in gaps up to 3 mm.
Although, it was found that adhesives generally have similar bond line thickness of between 0.2-0.3 mm.
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Figure 9: Example of a Comparison Table
The final adhesive decision was E-120HP because it had a significantly longer working life. It has a tensile strength of 41 MPa therefore it will have a safety factor of 20.5. It is reassuring to have a larger than necessary safety factor because as of right now it is uncertain whether the manufacturing of carbon fibre parts and the process of applying adhesives will yield a bond line thickness within the adhesive’s ideal range. This larger adhesive strength will hopefully compensate for any causes for concern.