Report to Curver Packaging Ltd.

S F Bush

Summary

An earlier report (January 1985) examined the failure mechanism of a wide range of Curver containers and established approximate formulae for the limiting loads which could be carried either directly on the lid membrane (stack loading – L₁) or on the lid rim (pallet loading – L₂). The main source of failure was unclipping of the lid from the container.

The present report is concerned with estimating the limiting loads on the new T design whose lid clip design avoids the failure mechanism of the earlier types. The main failure mode is now found to be by buckling of the container walls, though it is shown (and found experimentally) that unclipping can still occur befoe buckling, for some values of the container and lid dimensions.

The theory now broadly explains the buckling limits and the character of the buckling observed, although it must be emphasised that the results are based on a heavily simplified approach and cannot be pushed too far.

Report to Curver Packaging Ltd

S F Bush

Summary

Short-term failure tests have earlier been carried out on a wide range of lidded containers, 1-30 litres, by C Grigg of Curver Packaging Ltd. The primary objective of the present report is to investigate how far the failure test results may be explained analytically in ways which will give guidance to practical lid and container design.

A second objective is to explain quantitatively time dependent stack failures. This objective is relevant to designing against long-term creep failure. To supplement the earlier (Grigg) experiments, some small-scale experiments have been done on 0.25 litre containers to observe lid and buckle failures in slow motion.