Optimal design of a bio-inspired self-healing metal matrix composite reinforced with NiTi shape memory alloy strips

Utilizing smart materials such as shape memory alloys as reinforcement in metal matrix composites is a novel method to bio-mimic self-healing. This study aims to investigate the influence of design factors of a self-healing metal matrix composite by employing the Taguchi method for designing of the experimental procedure. Three design factors, each in three levels, was studied simultaneously according to L9 standard Taguchi orthogonal array to determine the optimal level of each factor in mechanical properties enhancement with a reduced number of experiments. Composite specimens were fabricated from Sn-13 wt.% Bi alloy as matrix and nickel-titanium shape memory alloy (SMA) strips as reinforcement with gravity casting process. Matrix alloy was melted and casted in a preheated metallic mold in which SMA strips were installed in various quantities (1, 2 or 3 strips) and different pre-strains (0, 2 or 6 percent). After fabrication of the specimens, a tensile test was conducted until fracture to specify mechanical properties. Then specimens were placed in a furnace in three different temperatures (170, 180 and 190 °C) to activate the shape memory effect of strips and achieve crack closure and healing. Specimens were tensile tested again after healing to calculate the amount of healed properties and healing efficiency. Results show that using three strips with 6% of pre-strain and applying 190 °C healing temperature can maximize the ultimate tensile strength efficiency. Also, the existence of 1 strip, 0% pre-strain and 190 °C healing temperature creates the best circumstances for healing ductility.