A company that makes shock absorbing wheelchair casters needed to insure minimum strength levels in the product. Some aluminum extrusions used for this purpose came from a particular supplier and showed markedly weaker strength, as evidenced by a low resistance to bending. This material had supposedly been heat treated properly to provide adequate strength requirements.
It is known that aluminum will exhibit various electrical conductivities during different stages of the heat treating process. The frames that bent easily had a higher conductivity than the more resilient pieces. This was conclusive proof that the heat treatment process needed better control and monitoring. The quality of the extruded material could now be verified prior to extensive machining.