EFFECT OF FIBRE INCLINATION ANGLES ON THE SUPERELASTIC BEHAVIOUR OF ANNEALED NiTi FIBRES

Metallic networks are promising candidates for new age porous materials wherein porosity is induced by manoeuvring network architecture. Their properties are thus highly dependent on architectural parameters like fibre segment length, orientation of fibres, porosity etc., apart from being dependent on the nature of material and processing conditions. As such, varied networks having diverse properties can be constructed depending on the choice of architectural or structural parameters and fibre material. Shape memory alloys (SMAs), when used to make the network, can bring about additional properties like superelasticity and shape memory effect in network that can be beneficial for increasing the recoverable strain of SMAs. In the current study, the as-received cold worked Nitinol wire of 0.125 mm diameter has been considered. In order to achieve the required SMA properties for manifesting the characteristic behaviour of Nitinol, an annealing treatment is needed. The specimens were subjected to heat treatment at 400°C for 5, 15 and 30 minutes and evolution of transformation temperatures was measured by differential scanning calorimetry (DSC). Further, the effect of fibre orientation– a critical structural parameter of the networks – on the shape memory properties of SMAs in the porous network form has been considered. For this, SMA fibre specimens annealed at 400 °C for 30 min were inclined at different orientations and loaded in tension till fracture. It was observed that with the increase in inclination angle from the loading axis, the plateau and fracture load decreases, whereas the superelastic strain range increases. The SMA deformation characteristics were then modelled in ANSYS software to determine the effect of inclination angles and further validated.