Carabiner Failure Model
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In this project, I focused on understanding the failure of climbing carabiners. These small, metallic devices are commonly used in rock climbing and other activities to connect ropes and other equipment, and it's important for them to be able to withstand high loads without breaking. It’s also important for the carabiners to be reliable so that people are able to trust that they won’t break, as people rely on them as life-saving devices. To analyze the strength of carabiners, I used finite element analysis (FEA) to model the carabiners in both open and closed positions. This was necessary because the position of the carabiner significantly affects its overall strength. I then validated our FEA model by conducting tension tests on two carabiners using the Instron machine, one in the open position and one in the closed position. Finally, I took scanning electron microscope (SEM) photos of the fracture surfaces of the two carabiners that broke during the tension tests. This allowed me to examine the microstructures of the materials and better understand what caused them to break. By combining the results of the FEA modeling, tension tests, and SEM analysis, I was able to gain a more comprehensive understanding of the failure of climbing carabiners.
FEA: Closed Carabiner
Von Mises Stress
Strain
Displacement
Deformation
Factor of Safety
FEA: Open Carabiner
Von Mises Stress
Strain
Displacement
Deformation
Factor of Safety
Testing
For the tension test, I initially wanted to use rope rated to 100 kN looped through the top and bottom of my carabiner to mostly closely simulate a real-life loading scenario. Unfortunately, the rope I used broke at 18 kN, which was before our carabiner broke. I then decided to just use metal pieces on the inside face of the carabiner and grip directly to those. I set up our carabiners on the Instron and gripped a round metal piece in the two groove where rope would normally lie. I then preloaded them to 10 kN at 50 mm/min, a force well below their written rating. After that, I lowered the rate down to 10 mm/min to get a more accurate reading of their failure load. The test ran until the carabiners both broke completely.
Closed Carabiner
Open Carabiner
Results
Comparison of broken shapes. The closed carabiner retained its curves more than the open one, which stretched into a straight shape.
Load vs. Extension data for the closed carabiner. Final load was 28 kN, which is above the carabiner’s rating of 24 kN for this configuration. The closed carabiner failed first at the point where the hook meets the main body of the carabiner, then the instron pulled the main body apart by continuing to move. This data stops where the carabiner broke the first time. The data shows us that the material is in between ductile and brittle, as it plastically deforms before breaking, but ultimately fails without any.
Load vs. Extension data for the open carabiner. Final load was 12 kN, which is above the carabiner’s rating of 8 kN for this configuration. The dip in the data represents where the carabiner transitions from bending into an “E” shape to pulling apart vertically along the axis.
Scanning Electron Microscope Results
The fracture surface shows a transgranular fracture, which is a common pattern to see in brittle materials and represents a higher energy break than an intergranular fracture.
Conclusion
In conclusion, my testing of the carabiners revealed that the final load for each configuration was higher than the load it was rated for. However, it's important to note that my testing involved applying a static load to the carabiners, while in real life the load would be applied dynamically. Dynamic loads can be more unpredictable and potentially more destructive than static loads, so it's possible that the carabiners may not be able to withstand as high of a load when subjected to dynamic forces. Despite this, it's worth noting that the manufacturers of the carabiners likely built in a factor of safety to account for real-world conditions and ensure that the carabiners will not break and potentially cause harm to users. Without the ability to test the carabiners with dynamic loads, we have to rely on this factor of safety to ensure their safety and reliability. It's important for users of the carabiners to be aware of this and to use them responsibly, following all instructions and guidelines for their proper use.
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