The different cup designs were subjected to Finite Element Analysis (FEA). The FEA revealed that the flared rim has an area that leads to stress concentration when force is locally applied to the rim of the cup to seat the lid. The results of FEA for rim displacement for the three cup designs are shown in Figure 10. The FEA clearly reveals a stress concentration effect caused by the flared rim design. When a force is applied to the top of the rim of the flared rim cup, the principle tensile stress is concentrated right on the top of the rim to the left and right of the applied stress. If the localized concentrated stresses exceed the tensile strength of the material, a crack may be initiated. Cups without a flared rim offer much better distribution of the stresses across the rim of the cup. The stresses on the top of the thick rim cup are very evenly distributed.