Nitinol, a shape-memory alloy (SMA), is gaining popularity for use in various applications. Machining of these SMAs poses a challenge during conventional machining. Henceforth, in the current study, the wire-electric discharge process has been attempted to machine nickel-titanium (Ni55.8Ti) super-elastic SMA. Furthermore, to render the process viable for industry, a systematic approach comprising response surface methodology (RSM) and a heat-transfer search (HTS) algorithm has been strategized for optimization of process parameters. Pulse-on time, pulse-off time and current were considered as input process parameters, whereas material removal rate (MRR), surface roughness, and micro-hardness were considered as output responses. Residual plots were generated to check the robustness of analysis of variance (ANOVA) results and generated mathematical models. A multi-objective HTS algorithm was executed for generating 2-D and 3-D Pareto optimal points indicating the non-dominant feasible solutions. The proposed combined approach proved to be highly effective in predicting and optimizing the wire electrical discharge machining (WEDM) process parameters. Validation trials were carried out and the error between measured and predicted values was negligible. To ensure the existence of a shape-memory effect even after machining, a differential scanning calorimetry (DSC) test was carried out. The optimized parameters were found to machine the alloy appropriately with the intact shape memory effect.

Wire arc additive manufacturing is a metal additive manufacturing technique that allows the fabrication of large size components at a high deposition rate. During wire arc additive manufacturing, multi-layer deposition results in heat accumulation, which raises the preheat temperature of the previously built layer. This causes process instabilities, resulting in deviations from the desired dimensions and variations in material properties. In the present study, a systematic investigation is carried out by varying the interlayer delay from 20 to 80 s during wire arc additive manufacturing deposition of the wall structure. The effect of the interlayer delay on the density, geometry, microstructure and mechanical properties is investigated. An improvement in density, reduction in wall width and wall height and grain refinement are observed with an increase in the interlayer delay. The grain refinement results in an improvement in the micro-hardness and compression strength of the wall structure. In order to understand the effect of interlayer delay on the temperature distribution, numerical simulation is carried out and it is observed that the preheat temperature reduced with an increase in interlayer delay resulting in variation in geometry, microstructure and mechanical properties. The study paves the direction for tailoring the properties of wire arc additive manufacturing-built wall structures by controlling the interlayer delay period.

Zinc oxide nanorods synthesized via a wet chemical approach were used to fabricate an ultra-flexible flutter-piezoelectric nanogenerator (UF-PENG). The UF-PENG has demonstrated good capabilities to act as not only an energy generator but also a wind velocity/direction sensor. Using the same procedure, the ZnO nanorods have been doped with lanthanum, and the doped device was found to exhibit three times the output of intrinsic PENG. Furthermore, through the process of annealing, the output of the PENG was enhanced. Peak power density calculations, capacitance charging, and stability analysis (1500 cycles) were performed. We have implemented this approach to make an ultralightweight/sensitive and wind modulated device which can flutter in low wind speed and can operate under a light breeze (2.8–3.8 m s⁻¹). The device was able to harvest a voltage of over 1.6 V at 3.8 m s⁻¹. The observed results indicate that the developed device could work as a self-powered wind velocity sensor. It can also function as a wind direction sensor (0–90°). Finite element simulation was performed to investigate the underlying mechanism. Additionally, the stability analysis of the sensor for more than 4500 cycles was conducted, and the obtained results showed the high stability of the device.

In this paper, a shape memory alloy (SMA) actuated subcarangiform robotic fish has been demonstrated using a spring based propulsion mechanism. The bionic robotic fish developed using SMA spring actuators and light weight 3D printed components can be employed for under water applications. The proposed SMA spring-based design without conventional motor and other rotary actuators was able to achieve two-way shape memory effect and has reproduced the subcarangiform locomotion pattern. The positional kinematic model has been developed and the dynamics of the proposed mechanism were analysed and simulated using Automated Dynamic Analysis of Mechanical Systems (ADAMS). An open loop Arduino-relay based switching control has been adopted to control the periodic actuation of the SMA spring mechanism. The undulation of caudal fin in air and water medium has been analysed. The caudal fin and posterior body of the developed fish prototype have taken part in undulation resembling subcarangiform locomotion pattern and steady swimming was achieved in water with a forward velocity of 24.5 mm/s. The proposed design is scalable, light weight and cost effective which may be suitable for underwater surveillance application.

Zinc oxide (ZnO) is a remarkable inorganic semiconductor with exceptional piezoelectric properties compared to other semiconductors. However, in comparison to lead-based hazardous piezoelectric materials, its properties have undesired limitations. Here we report a 5∼6 fold enhancement in piezoelectric features via chemical doping of copper matched to intrinsic ZnO. A flexible piezoelectric nanogenerator (F-PENG) device was fabricated using an unpretentious solution process of spin coating, with other advantages such as robustness, low-weight, improved adhesion, and low cost. The device was used to demonstrate energy harvesting from a standard weight as low as 4 gm and can work as a self-powered mass sensor in a broad range of 4 to 100 gm. The device exhibited a novel energy harvesting technique from a wind source due to its inherent flexibility. At three different velocities (10∼30 m s-1) and five different angles of attack (0∼180 degrees), the device validated the ability to discern different velocities and directions of flow. The device will be useful for mapping the flow of air apart from harvesting the energy. The simulation was done to verify the underlining mechanism of aerodynamics involved.