Three-dimensional VOF simulation of droplet impacting on a superhydrophobic surface

It is very important to analyze and study the motion process of droplets impacting superhydrophobic surface, which is of great significanee to understand the mechanism of superhydrophobic surface and guide the design and manufacture of superhydrophobic surface. Taking by three-dimensional volume of fluid (VOF) simulation coupling coupled level set (CLS) algorithm, on the one hand, we simulate the morphological changes in the process of droplet impingement, as well as the internal velocity and the pressure distribution;on the other hand,we focus on the effects of droplet impact velocity, surface wettability, surface tension on the dynamics of the droplets. The CLSVOF model inherits the advantages of the VOF model for accurately constructing the phase interface and inherits the advantage that the level set can accurately calculate the surface tension, which improves the accuracy of the calculation of the droplet impact on the superhydrophobic surface. The computed results distinctly demonstrated there were four stages: falling, spreading, shrinking and rebounding. The time history of each stage agreed well with the pictures captured by high-speed camera, which indicated the computational fluid dynamics scheme was effective. Moreover, the motion mechanism of the droplets impacting on the solid surface is elaborated, which was helpful to control the solid-liquid interface to achieve a variety of solid interface characteristics.

3D printed aluminum matrix composites with well-defined ordered structures of shear-induced aligned carbon fibers

Carbon fiber reinforced aluminum composites with ordered architectures of shear-induced aligned carbon fibers were fabricated by 3D printing.The microstructures of the printed and sintered samples and mechanical properties of the composites were investigated.Carbon fibers and aluminum powder were bonded together with resin.The spatial arrangement of the carbon fibers was fixed in the aluminum matrix by shear-induced alignment in the3D printing process.As a result,the elongation of the composites with a parallel arrangement of aligned fibers and the impact toughness of the composites with an orthogonal arrangement were 0.82%and 0.41 J/cm^(2),respectively,about 0.4 and 0.8 times higher than that of the random arrangement.

The Novel Variable Stiffness Composite Systems with Characteristics of Repeatable High Load Bearing and Response Rate

On the base of controllable variable stiffness property,variable stiffness composites were the main components of functional materials in aerospace.However,the relatively low mechanical strength,stiffness range,and response rate restricted the application of variable stiffness composite.In this work,the novel variable stiffness composite system with characteristics of repeatable high load bearing and response rate was successfully prepared via the double-layer anisotropic structure to solve the bottlenecks of variable stiffness composites.The novel variable stiffness composite systems were composed of variable stiffness layer of polycaprolactone(PCL)and the driven layer of silicone elastomer with alcohol,which continuously changed Young’s modulus from 0.1 to 7.263 MPa(72.63 times variation)in 200 s and maintained maximum weight of 11.52 times its own weight(8.5 g).Attributed to the relatively high variable stiffness range and load bearing value of variable stiffness composite system,the repeatable response process led to the efficient high load driven as“muscle”and diversified precise grab of objects with different shapes as“gripper”,owning widespread application prospects in the field of bionics.

A Stiffness-Tunable Composite with Wide Versatility and Applicability Based on Low-Melting-Point Alloys

Flexible materials are essential in bionic fields such as soft robots.However,the lack of stiffness limits the mechanical performance of soft robots and makes them difficult to develop in many extreme working conditions,such as lifting and excavation operations.To address this issue,we prepared a stiffness-tunable composite by dispersing low-melting-point alloy into thermosetting epoxy resin.A dramatic and rapid change in stiffness was achieved by changing the state of matter at lower temperatures,and accurate control of the composite modulus was achieved by controlling the temperature.When the alloy content is at 30vol%,the tensile modulus changes 41.6 times,while the compressive modulus changes 58.9 times.By applying the composite to a flexible actuator,the initial stiffness of the actuator was improved by 124 times,reaching 332 mN/mm.In addition,the use of stiffness-tunable materials in the wheel allowed for timely changes in the grounding area to improve friction.These flexible materials with manageable mechanical properties have wide applicability in fields including bionics,robotics,and sensing.Our findings provide a new approach to designing and developing flexible materials with improved stiffness and controllability.

PEEK modified PLA shape memory blends:towards enhanced mechanical and deformation properties

Polylactic acid(PLA)is one of the most promising shape memory polymers with outstanding biocompatibility,while poly(ether ether ketone)(PEEK)is a special engineering plastic with excellent mechanical performance.In this work,PEEK was selected to modify PLA,and a series of PLA blended with different PEEK contents(PLA/PEEK blends)were obtained.The effects of PEEK on thermodynamic,mechanical and shape memory properties of PLA/PEEK blends were investigated.The results showed that the thermal stabillity of the PL A/PEEK blend was improved with the PEEK content increase.The tensile strength reached the highest value of 20.6 MPa when the PEEK content was 10%.While the best shape memory performance occurred with the PEEK content of 15%,the shape recovery time was less than 2 s,and the shape fixation/recovery ratio was more than 99%.Furthermore,the programmable mimetic flower opening process was achieved by using PLA/PEEK blends with different PEEK content ratios.The above results indicated that the blend of an appropriate proportion of PEEK had positive effects on mechanical and deformation performances of PLA.

High-performance Multilayer Flexible Piezoresistive Pressure Sensor with Bionic Hierarchical and Anisotropic Structure

Flexible pressure sensor that enables detection of multimodal signals has greater advantages in human–computer interaction,medical/health care,and other applications.To make a versatile flexible pressure sensor,hierarchical and anisotropy structure are key features to improve sensing performance and realize multi-signal detection.However,traditional flexible sensors usually have narrow linear range and single signal detection capability.Herein,a highly sensitive flexible piezoresistive pressure sensor which has broad linear range of pressure is developed by replicating one dimensional microstructures from reed leaf and using multilayer superposition of micropatterned polydimethylsiloxane(m-PDMS).Through superposing 4 layers of parallel micropatterned constructive substrates,the multilayer piezoresistive pressure sensor exhibits a high sensitivity of 2.54 kPa?1,a fast response time of 30 ms,and a broad linear range of 107 kPa.The flexible piezoresistive pressure sensor is also highly robust:there is no fatigue after testing for at least 1000 cycles.Due to the specific anisotropy of the micro-structure,the sensor can measure the tangential force in different directions.It permits multimode signal detection,including pressure,tangential force,and deformation.The versatile flexible pressure sensor enables effective monitoring of multisignals,it reveals great potential for medical and health care,flexible human–computer interaction,and intelligent robot.