CASE STUDY: THE ROOT CAUSE OF FAILURE OF AN EPS FOAM COFFEE CUP

摘要

This study was carried out to determine the root cause of failure of a coffee cup resulting in serious personal injury. Billions of disposable coffee cups are used annually around the world. Most of the cups are molded using expandable polystyrene (EPS). EPS is a very complex material with many structural variables that affect the strength of molded parts including the cup design, bead microstructure, bead size, and bead fusion. We have tested EPS coffee cups having the most common designs as to their robustness against failure during human contact; i.e., lidding and holding/squeezing. The study revealed that cup design has a huge effect on the cup strength and rigidity. Cups having a flared rim design (Figure 1) are least robust and are thus most likely to fail during (e.g., lidding and holding/squeezing) compared with cups having a straight rim design.