The original goal was to test a fuel additive designed to reduce catastrophic fuel fires. That didn't go so well, but some of the other experiments added on yielded safety improvements including fire retardant materials, cabin lighting, and flight data recording.

All those poor, peacefully napping test dummies got a much rougher ride than they bargained for.

Link to Wikipedia article has much more technical detail: https://en.m.wikipedia.org/wiki/Controlled_Impact_Demonstration