A novel thermo-mechanical anti-icing/de-icing system using bi-stable laminate composite structures with superhydrophobic surface

A novel anti-icing/de-icing system composed of bi-stable laminate composite structures with superhydrophobic surface and soft electrothermal patch is investigated in this paper. In this system, the superhydrophobic surface has superior performance in anti-icing and de-icing by reducing the adhesion of the ice-skin interface; meanwhile, a thermo-mechanical way to remove ice is conducted by deforming the bi-stable structures using heating actuation method. The superhydrophobic layer is fabricated by decreasing the free energy of copper oxide on the copper surface. The water contact angle of the superhydrophobic surface is tested by an optical contact angle measuring device, which reaches above 155° and the sliding angle is less than 10°. In addition, the microstructure of superhydrophobic layer is characterized by using a scanning electron microscope (SEM) to illustrate the superhydrophobic mechanism. Moreover, outstanding self-cleaning properties and UV-durability are obtained on the prepared surface. Experimental results indicate that the system has good performances in both anti-icing and de-icing processes when working at the subzero temperature. Meanwhile, there is no liquid water left on the surface after the snap-through process of bi-stable structures. Besides, the factors that affect the anti-icing and de-icing performance of system are discussed, including the superhydrophobic property, morphing characteristic of bi-stable laminate composite structures and actuating method. Finally, the finite element method is used to simulate the factors that affect the deformation of bi-stable structures independently, including the single layer thickness, stacking sequence of the laminate and the embedment of the electrothermal alloy

Study on the Properties of Vertical Carbon Nanotube Films Grown on Stainless Steel Bipolar Plates

Research on the conductivity and corrosion resistance of stainless steel bipolar plates in a proton exchange membrane fuel cell (PEMFC) is commonly performed in a normal-temperature environment (about 20 °C). However, these fuel cells must function in low-temperature environments (lower than 0 °C) in some conditions, such as in vehicle fuel cells and in portable power supplies that operate during the winter in northern China. Stainless steel bipolar plates have higher requirements in terms of their hydrophobic and anti-icing properties, in addition to needing high conductivity and corrosion resistance. In this study, carbon nanotubes (CNTs) are grown on the surface of 304 stainless steel (304 SS) without a catalyst coating by plasma-enhanced chemical vapor deposition (PECVD), which is a simple and cheap method that allows stainless steel to be used as bipolar plates in low-temperature environments. The Raman spectroscopy and scanning electron microscopy (SEM) results show that the CNTs grown on the surface of 304 SS have different morphologies. The stainless steel samples with different CNT morphologies are tested by hydrophobicity and in situ icing experiments to prove that vertical CNTs can achieve a superhydrophobic state and have good anti-icing properties. The interfacial contact resistance (ICR) of the bare 304 SS and the 304 SS with vertical CNTs is compared by voltammetry, and then the corrosion resistances of both types is compared in a simulated PEMFC environment via a three-electrode system. Consequently, the ICR of the 304 SS with vertical CNTs was lower than the bare 304 SS. The corrosion potential was positive, and the corrosion current density was greatly reduced for the stainless steel with vertical CNTs grown directly on its surface when compared with the bare 304 SS. The experimental results show that vertical CNTs have good application prospects as bipolar plates for PEMFCs in low-temperature environments

Unveiling the growth mode and structure relaxation of Polytetrafluoroethylene film by radio-frequency magnetron sputtering

Relying on radio-frequency (RF) magnetron sputtering, Polytetrafluoroethylene (PTFE) films with a series of thicknesses in the range from 80 to 2000 nm were prepared on silicon substrates. The surface morphology and roughness of the PTFE films were measured by atomic force microscope (AFM) technology at microscale. Results indicated that the PTFE film grew in an island pattern during sputtering, while the surface roughness of PTFE films was almost invariable throughout the sputtering process. Then the structure relaxation of PTFE film annealed at 100 °C for 15–480 min was investigated. Annealing treatment induced columnar protrusions on the PTFE surface, which was due to the flow and rearrangement of molecules. During annealing duration, the columnar structures could continuously rearrange and decompose, and therefore lowering film thickness from 2000 to 1110 nm with increasing annealing time. Due to molecule flow and redistribution of the annealed film, the columnar structures were formed on the surface, which resulted in the higher roughness. Finally, the effects of film thickness and annealing time on the hydrophobicity were also studied

Effect of Compressive Strain of Brake Pads on Brake Noise

Brake noise, a principal component of vehicle noise, is among the most critical measures of vehicle quality. The perceived quality of cars can be improved by reducing brake noise; therefore, vehicle manufacturers are extensively investigating the influencing factors, generating mechanism, and solutions of brake noise. Compressive strain is one of the most influential performance parameters of a brake pad and can be adjusted by regulating the material elastic modulus and by modifying the shape of the brake lining. In this study, the compressive strain of a brake pad was adjusted through four methods, and the noise characteristics of brake pads with different elastic modulus, section outlines, lining widths, and chamfers were studied through finite element analysis and the complex-eigenvalue method. The effects of compressive strain of a brake pad on brake noise were examined, and an optimized brake-pad scheme was developed. A dynamometer test conducted to validate the effectiveness of the optimized scheme confirmed a clear alleviation in brake noise

Effects of adjustment devices on the fore-and-aft mode of an automobile seat system: headrest, height adjuster, recliner and track slide

The automobile seat is an important and unique device in the automobile system, which directly contacts the human body. The dynamic characteristics of the automobile seat are the key parameters for its vibration security and dynamic performance. Both experiments and finite element simulations are conducted to analyse the fore-and-aft operating modes of a new type of automobile seat system in this paper. The results and their correlation analysis between the experimental data and the computational models are given. By using finite element simulations, the computational results of the modes with the first 12 orders for the automobile seat are in the range 0-100 Hz, including the integral modes and the local modes of the automobile seat. An experimental method was designed to measure the seat frame mode using an impact hammer, a triaxial accelerometer, uniaxial accelerometers and a 24-channel LMS vibration test system. The experimental data were analysed by estimating the frequency response function and the modal parameters and validated using LMS Test.Lab software. The experimental results for five integral modal parameters of the automobile seat between 0 Hz and 100 Hz are given. The orthogonal experimental method is used to design nine different working states of the automobile seat with variations in the positions of different adjustable devices (the headrest, the height adjuster, the recliner and the track slide). Finally, the influences of the above-mentioned adjustable devices on the fore-and-aft operating mode are analysed by the single-factor analysis method using finite element simulations

Electric Conductivity and Corrosion Resistance of Amorphous Carbon Films Prepared by Direct Current Magnetron Sputtering on304 Stainless Steel

The conductive amorphous carbon films were deposited on the 304SS by conventional direct current magnetron sputtering. The effect of substrate bias on the microstructure and property of amorphous carbon films were mainly investigated. The results show that the electrical conductivity and corrosion resistance are improved significantly for the carbon films coated stainless steel in comparison to the untreated ones. Specifically, when the substrate bias was -200 V the contact resistance was about 16.65 mOmega·cm~2, which may be ascribed to the highest fraction of sp~2 bonds under the normal compacting force of the fuel cells at 1.5 MPa. The corrosion potential of the carbon films coated stainless steel significantly increased in the simulated PEM fuel cells environment, while the corrosion current density obviously decreased, especially when the bias was - 200 V the carbon film performs the best corrosion resistance, which may be attributed to its best compactness, for this case the corrosion current density is 1.22*10~(-8) A/cm~2 and the corrosion potential is 0.25 V

Revealing the Plastic Mode of Time-Dependent Deformation of a LiTaO3 Single Crystal by Nanoindentation

Recently, instrumental nanoindentation has been widely applied to detect time-dependent plastic deformation or creep behavior in numerous materials, particularly thin films and heterogeneous materials. However, deformation mechanism at nanoindentation holding stage has not been well revealed hitherto. In the current work, nanoindentation holding tests with high loads were performed on a brittle LiTaO3 single crystal. The surface morphologies of residual impressions with various holding times were investigated. It was indicated that generation of secondary cracks and propagation of both main and secondary cracks were the dominating mechanism for time-dependent plastic deformation at the initial holding stage, and the density and length of cracks were invariable at the steady-state holding stage, which suggested a nonlocalized plastic deformation beneath the indenter. It could be concluded that time-dependent plastic deformation of brittle ceramic under nanoindentation is composed of instant cracking as the continuation of loading sequence and homogeneous creep flow by high shear-compression stress at room temperature