Carabiner Design
The final project for my first design/stress analysis class focused on creating a carabiner with a maximum strength to weight ratio. This class introduced me to finite element analysis (FEA) software and truly sparked my interest in failure modes and design.
A group mate and I created a CAD model in SolidWorks® that featured a functional gate. Note that experimental testing only focused on "open gate" configuration so less emphasis was placed on gate design and refinement. This model was then moved to Fusion for FEA simulation.
Using Fusion, I conducted a mesh convergence study and concluded that a 3% mesh with no localized mesh maintained the highest resolution without using unnecessary computing power. The FEA predicted failure at the inner radius of the lower bend, close to the spine.
This plot shows the Von Mises stress at a probed location of max stress, highlighting the importance of choosing an adequate mesh size as reported values fluctuate greatly.
This plot shows the percent change in stress at the probed location of maximum stress compared to the previous run. It clearly shows the 2% and 1% meshes provide insignificant added resolution, and therefore do not justify the additional simulation time and computing power.
Next, a PLA plastic model was 3D printed. We chose to print with 4 outer shell layers and 60% infill to compromise between additional strength of higher infill values and minimizing weight.
After testing (uniaxial tensile) our PLA plastic carabiner, we summarized our results in the table seen above. For a second iteration, I would make the lower member of the carabiner more asymmetric such that the rope and associated load oriented closer to the spine to reduce the bending moment seen at the point of failure.
This project taught me rapid prototyping and introduced me to finite element analysis. It highlighted how obtaining early experimental results can provide invaluable insights that can help shape and drive a design.