Vibration does the damage, drops get the budget

Ask anyone what breaks packaging in transit and they will describe a drop. Drops are visible, easy to reproduce and satisfying to test. They are also a minority of the damage we find in returned goods.

The bigger cause is hours of low-amplitude vibration, which does not break anything suddenly and instead wears through it.

What vibration actually does

Abrasion. Two surfaces in light contact for six hours remove print, then coating, then board. Packs arrive intact and unsellable.

Fatigue at the crease. A corrugated case flexes a few tenths of a millimetre per cycle at a fold. Over a long run that crease loses a substantial fraction of its stiffness, and the stack settles rather than collapses.

Migration. Contents move within the pack until they find the one orientation where a corner presses on a seal. Then they stay there for four hundred miles.

Why it is under-tested

A drop test takes minutes. A representative vibration profile takes hours of machine time, and the result is a pack that looks slightly worse rather than a pack that is obviously broken. It is difficult to put in a slide.

What we run instead

A random vibration profile taken from logger data on the client's actual route, run for the duration of their actual longest leg, with the pack loaded as it actually ships. Then we look at the crease, the print and the seal, in that order.

The first time we did this for a client we found the failure in ninety minutes, after they had passed every drop test for three years and been returning about 2% of shipments the whole time.