Abstract
This paper presents an effort to minimise the mass of a threaded plastic cap of a plastic bottle while the load carrying capacity is kept on the same level or it is also reduced. Finite Element Analysis with axisymmetric and contact element is used to evaluate the weak points of the plastic bottle and plastic cap connection. To obtain more realistic results non-linear elastic material law, the friction coefficient and the loosening torque were determined through tests. By theoretical investigation the number of mated threads was reduced and the related outer geometric shape was also modified producing all together about 39% reduction in mass and parallel to it about 10% increase in the load carrying capacity. Results of this theoretical investigation are in close correlation with everyday experiences as the attached photo of a typically damaged cap testifies it.
