Influence of lamination direction on fracture behaviour and mechanical properties of TiNi SMA wire embedded CFRP smart composites

TiNi/CFRP composites were fabricated by hot-pressing in the temperature range of 130∼180°C, by controlling the applied pressure. The TiNi wires were embedded as an 1mm interval into the center of CFRP layers and CFRP host materials were stacked as 0, 30, 60 and 90 degrees configuration on tensile direction, respectively. The stress-strain curve and tensile strength of composites strongly depends on stacking direction of carbon fibers. The tensile strength of TiNi/CFRP composites with stacking direction of 0 and 90 degrees configuration are about 1.2GPa and 50MPa, respectively. The microstructural properties of TiNi/CFRP composites were observed by SEM. Pore and/or voids were found to congregate near the embedded TiNi wire and they increased in proportion to stacking direction of carbon fibers. Larger pores and interfacial crack were also observed at interface between TiNi wires and epoxy resin. Furthermore, the fracture behaviour was studied by an AE technique during tensile test, to analyze the fracture process. The effects of surface treatment of TiNi wire by acid etching to improve the interracial bonding strength between TiNi wire and epoxy matrix are also investigated. The average interfacial bonding strength of the TiNi wire embedded in CFRP matrix was evaluated by pull out test. It was confirmed that surface treatment of TiNi wire by acid etching improved the interracial bonding strength. Acid etching by HF+HNO₃ mixed solution significantly increased the interfacial bonding strength. The damage recovery effect of SMA in specimen was successfully confirmed by heating above 70°C.