Nano-impact (fatigue) characterization of as-deposited amorphous nitinol thin film.

This paper presents nano-impact (low cycle fatigue) behavior of as-deposited amorphous nitinol (TiNi) thin film deposited on Si wafer. The nitinol film was 3.5 µm thick and was deposited by the sputtering process. Nano-impact tests were conducted to comprehend the localized fatigue performance and failure modes of thin film using a calibrated nano-indenter NanoTest(TM), equipped with standard diamond Berkovich and conical indenter in the load range of 0.5 mN to 100 mN. Each nano-impact test was conducted for a total of 1000 fatigue cycles. Depth sensing approach was adapted to understand the mechanisms of film failure. Based on the depth-time data and surface observations of films using atomic force microscope, it is concluded that the shape of the indenter test probe is critical in inducing the localized indentation stress and film failure. The measurement technique proposed in this paper can be used to optimize the design of nitinol thin films

Numerical and experimental studies of acoustic streaming effects on microparticles/droplets in microchannel flow

Exploiting acoustic streaming effects for microfluidic devices has been proven to be important for cell, microparticle and fluid manipulation in many fields such as, biomedical engineering, medical diagnostic devices, cell studies and chemistry. Acoustic streaming is used in acoustofluidic systems for directing and sorting microparticles as well as mixing and pumping fluids. To understand the underlying physics of such acoustofluidic systems and thus use them more efficiently in practical setups, computational modelling is critically needed. Although some work has been done to numerically model acoustofluidic systems, there are few studies to evaluate the capability and accuracy of different numerical schemes for analysing this complex multi-physics problem and to be directly validated by experiments. This paper aims to investigate the acoustic streaming effects caused by surface acoustic waves in a microchannel flow by using two different computational approaches to model the acoustic effects in three dimensions. In the first approach, we model the whole acoustic field caused by the oscillating lower wall. Here, the acoustic streaming effects were directly calculated from the density and velocity fields caused by the acoustic field. In the second approach, a low fidelity model is employed to capture the effects of acoustic streaming without modelling the acoustic field itself. In this approach, we substituted the velocity of a one-dimensional attenuating wave in the acoustic streaming force formula, and calculated the acoustic streaming force without using the density and velocity caused by the acoustic field. Both the computational methods are then validated by the results obtained from microflow experiments. The results from the second approach are in reasonable agreement with experiments while being more efficient in terms of computational cost. On the contrary, the first approach, while being computationally more expensive, allows to estimate the pressure field resulting from acoustic waves and thus predicts the dynamic behaviour of microparticles more accurately. Results suggest that the first approach is best to use for analysing the mechanism of microparticle and fluid manipulation in microfluidic devices

Simultaneously enhancing the strength and ductility in titanium matrix composites via discontinuous network structure

In this study, titanium matrix composites reinforced with graphene nanoplates (GNPs) were successfully prepared via an in-situ processing strategy. Both TiC nanoparticles and TiC@GNPs strips are in-situ formed at the grain boundaries, and enhance interfacial bonding strength between GNPs and Ti matrix by acting as rivets in the microstructure. The GNPs can be retained in the center of TiC layer, which provides a shielding protection effect for the GNPs. These in-situ formed TiC nanoparticles are linked together to form a discontinuous and three-dimensional (3D) network structure. Due to the formation of 3D network architecture and improved interfacial bonding, the composites show both high strength and good ductility. The significant strengthening effect reinforced by the GNPs can be attributed to a homogeneous distribution of in-situ formed TiC nanoparticles and TiC@GNPs strips, resulting in TiC interface/particle strengthening and excellent interfacial load transfer capability

Influence of αs precipitates on electrochemical performance and mechanical degradation of Ti-1300 alloy

The influence of αs precipitates on electrochemical behavior and mechanical degradation of Ti-1300 alloy in artificial seawater have been studied. The results show that corrosion resistance and mechanical degradation have been significantly affected by the formation of acicular αs precipitates. The precipitated αs phase with an acicular shape around 40–60 nm in width are uniformly distributed inside β grain. Many αs precipitates are intersected each other and keep a well-defined Burgers orientation relationship with β matrix, which restricts the growth of other αs phases due to pinning effect. Within the electrolyte, the αs phases can form “microgalvanic cells” with their adjacent intergranular β phases, which dramatically deteriorate its corrosion resistance. The mechanical properties of the alloy are also degraded with the increase of immersion time due to the pitting reaction. The precipitated microstructure exhibits an inferior mechanical degradation behavior, and this is mainly because a lot of corrosion cavities are nucleate d and propagated at the interface between αs precipitates and prior β grains

Piezoelectric Smart Patch Operated with Machine Learning Algorithms for Effective Detection and Elimination of Condensation

Timely detection and elimination of surface condensation is crucial for diverse applications in agriculture, automotive, oil and gas industries, and respiratory monitoring. In this paper, a smart patch based on a ZnO/aluminum (~5 μm/50 μm thick) flexible Lamb wave device has been proposed to detect, prevent and eliminate condensation, which can be realized using both of its surfaces. The patch is operated using a machine learning algorithm which consists of data preprocessing (feature selection and optimization) and model training by a random forest algorithm. It has been tested in six cases, and the results show good detection performance with average Precision = 94.40 and average F1 score = 93.23. Principle of accelerating evaporation is investigated in order to understand the elimination and prevention functions for surface condensation. Results show that both dielectric heating and acoustothermal effect have their contributions, whereas the former is found more dominant. Furthermore, the functional relationship between the evaporation rate and the input power is calibrated, showing a high linearity (R2 = 97.64) with a slope of ~3.6×10-5 1/(s·mW). With an input power of ~0.6 W, the flexible device has been proven effective in the prevention of condensation

Coupling mechanism of kinetic and thermal impacts of Rayleigh surface acoustic waves on the microdroplet

An experimental study has been conducted to investigate the coupling mechanism between thermal and kinetic impacts of surface acoustic waves (SAW) using a water droplet (25 µl) on the zinc oxide (ZnO) thin-film piezoelectric substrate fabricated on an aluminium plate. The temperature is measured by an infrared (IR) thermal camera, and fluid streaming was detected by particles image velocimetry (PIV). The input power ranges from 0.096 W to 3.2 W resulting in a temperature rise and streaming velocity in the droplet up to 55 °C and 24.6 mm/s, respectively. It is found that the thermal impact is insignificant at lower input power (2.0 W. The study also found that heat inside the droplet is distributed via streaming from the heat source. The heat is distributed from the heat source where SAW power penetrates to the droplet. Another key finding of this investigation revealed that when the input power is>0.50 W, inverse heat transfer from the droplet to the substrate is observed due to the increase in fluid temperatures

A rapid and controllable acoustothermal microheater using thin film surface acoustic waves

Temperature control within a microreactor is critical for biochemical and biomedical applications. Recently acoustothermal heating using surface acoustic wave (SAW) devices made of bulk LiNbO3 substrates have been demonstrated. However, these are generally fragile and difficult to be integrated into a single lab-on-a-chip. In this paper, we propose a rapid and controllable acoustothermal microheater using AlN/Si thin film SAWs. The device's acoustothermal heating characteristics have been investigated and are superior to other types of thin film SAW devices (e.g., ZnO/Al and ZnO/Si). The dynamic heating processes of the AlN/Si SAW device for both the sessile droplet and liquid within a polydimethylsiloxane (PDMS) microchamber were characterized. Results show that for the sessile droplet heating, the temperature at a high RF power is unstable due to significant droplet deformation and vibration, whereas for the liquid within the microchamber, the temperature can be precisely controlled by the input power with good stability and repeatability. In addition, an improved temperature uniformity using the standing SAW heating was demonstrated as compared to that of the travelling SAWs. Our work shows that the AlN/Si thin film SAWs have a great potential for applications in microfluidic heating such as accelerating biochemical reactions and DNA amplification

Acoustofluidic patterning in glass capillaries using travelling acoustic waves based on thin film flexible platform

Surface acoustic wave (SAW) technology has been widely used to manipulate microparticles and biological species, based on acoustic radiation force (ARF) and drag force induced by acoustic streaming, either by standing SAWs (SSAWs) or travelling SAWs (TSAWs). These acoustofluidic patterning functions can be achieved within a polymer chamber or a glass capillary with various cross-sections positioned along the wave propagating paths. In this paper, we demonstrated that microparticles can be aligned, patterned, and concentrated within both circular and rectangular glass capillaries using TSAWs based on a piezoelectric thin film acoustic wave platform. The glass capillary was placed at different angles along with the interdigital transducer directions. We systematically investigated effects of tilting angles and wave characteristics using numerical simulations in both circular and square shaped capillaries, and the patterning mechanisms were discussed and compared with those agitated under the SSAWs. We then experimentally verified the particle patterns within different glass capillaries using thin film ZnO SAW devices on aluminum (Al) sheets. Results show that the propagating SAWs can generate acoustic pressures and patterns in the fluid due to the diffractive effects, drag forces and ARF, as functions of the SAW device’s resonant frequency and tilting angle. We demonstrated potential applications using this multiplexing, integrated, and flexible thin film-based platform, including patterning particles (1) inside multiple and successively positioned circular tubes; (2) inside a solidified hydrogel in the glass capillary; and (3) by wrapping a flexible ZnO/Al SAW device around the glass capillary

Test structures for characterizing the integration of EWOD and SAW technologies for microfluidics

This paper presents details of the design and fabrication of test structures specifically designed for the characterization of two distinct digital microfluidic technologies: electro-wetting on dielectric (EWOD) and surface acoustic wave (SAW). A test chip has been fabricated that includes structures with a wide range of dimensions and provides the capability to characterize enhanced droplet manipulation, as well as other integrated functions. The EWOD and SAW devices have been separately characterized first of all to determine whether integration of the technologies affects their individual performance, including device lifetime evaluation. Microfluidic functions have then been demonstrated, including combined EWOD/SAW functions. In particular, this paper details the use of EWOD to anchor droplets, while SAW excitation is applied to perform mixing. The relationship between test structure designs and the droplets anchoring performance has been studied.</p