In boats , some of the tooling shops use a syntactic foam to develop a machineable surface. The foam is a mixture of glass or plastic spheres in polyester resin.This is applied and machined prior to application of tooling primers and topcoats. Spraycore is one brand.
There is a testing device called the Hydromat, Developed by Gougeon Brothers (Proset Epoxy). This is probably the most real world fatigue tester. It uses an inflatable bladder ,I believe, to simulate hull bottom pressures.The bladder keeps you from killing yourself if the panel fails...
