Experimental study of the effect of cryogenic cycling and metal surface treatment on flexural properties of aluminum- epoxy/basalt fibers laminate composite

In this article, the effect of cryogenic cycling on flexural properties of fiber metal laminate (FML) has been investigated. This laminates were composed by two aluminum 2024-T3 plates and an epoxy matrix composite ply formed by four layers of basalt fibers by hand lay- up technique. Various surface treatments include mechanical (grinding), chemical (etching) and electrochemical (anodizing) were used for improving the adhesion between polymer composite layer and aluminum sheet. Each cryogenic cycle was carried out in 4 min and temperature range was between -40 °C and 25 °C. Flexural properties were evaluated on samples after 15 and 30 cycles and compared to non-exposed samples. While the cryogenic cycling decreased the flexural strength of the FML with etched aluminum, increasing at first, and then decreasing after a while was observed in the FML with anodized aluminum. About samples that the FML with grinded aluminum, both of flexural modulus and fracture energy increased at first and then decreased; while the flexural strength decreased continuously. Evaluation of optical microscope showed that the reason of decreasing in flexural properties about samples with etched aluminum and also decreasing in flexural strength for samples with grinded aluminum after cycles is changing in mechanism of failure from failure of composite to separation between layers of FML; while about FMLs with anodized aluminum, the only observed mechanism was failure of composite and it has not changed.