For the final lab in MIE320 (Mechanics of Solids II), we worked in pairs to construct an optimized link for a class competition. The goal is to create the link with the largest load to weight ratio. We started with a 1/4 in thick 6″ x 6″ piece of PMMA plastic and machined the link with the requirement that both the width and length of the link must remain at 6″.
Our design strategy was to test the load on iterative designs in Solidworks to reduce any unstressed material. We polished the machined surfaces with a nail buffer to take out any small cracks and stress concentrations that come with those cracks which can induce early failure. Our link failed at the loading hole for what we expect to be two reasons: 1) this is a region of high concentration not sufficiently resolved by the link design and 2) we enlarged the hole at the last minute with a coarse file because the pin was not the correct size and didn’t fit into the hole – which induced cracks and heightened the stress concentration. Our link placed 4/70 in the class and we were really happy with the results. You can see the report here: