基于FPGA的超声环形探头性能检测系统初探

超声环形探头的性能检测可以为改善超声计算机断层成像质量提供重要的参考依据此外,环形探头老化和损伤也需要进行定期检测与维护。目前,超声探头声学性能检测主要基于现有设备进行系统搭建,集成度低,成本高,也不适用于超声环形探头。为提高集成度、降低成本,本文设计了一种基于FPGA的超声环形探头性能检测系统,可以检测超声环形探头各个阵元的性能指标,包括中心频率,带宽和回波灵敏度等参数。本文完成了性能检测的预研性实验:对一个256阵元的环形探头进行了8个阵元的手动选通检测。实验结果表明,该系统可以方便准确地进行阵元切换和检测,检测结果与探头指标吻合。

Impact of Sino-US Trade Friction on Import and Export Trade Pattern of Soybean in Heilongjiang

Under the background of Sino-US trade friction,soybean,as an important variety in the important and export trade of agricultural products,has become a key bargaining chip. After the Ministry of Commerce of China announced the counter list of agricultural products including soybean,the price fluctuations of domestic soybean and related agricultural products are rapidly expanding. Under the background of SinoUS trade friction,taking the soybean-producing areas in Heilongjiang as an example,the impact of Sino-US trade friction on the important and export pattern of soybean in Heilongjiang was explored to provide a certain theoretical basis for the development of soybean industry in Heilongjiang.

Complicated deformation simulating on temperature-driven 4D printed bilayer structures based on reduced bilayer plate model

The four-dimensional(4D) printing technology, as a combination of additive manufacturing and smart materials, has attracted increasing research interest in recent years. The bilayer structures printed with smart materials using this technology can realize complicated deformation under some special stimuli due to the material properties.The deformation prediction of bilayer structures can make the design process more rapid and thus is of great importance. However, the previous works on deformation prediction of bilayer structures rarely study the complicated deformations or the influence of the printing process on deformation. Thus, this paper proposes a new method to predict the complicated deformations of temperature-sensitive 4D printed bilayer structures,in particular to the bilayer structures based on temperature-driven shape-memory polymers(SMPs) and fabricated using the fused deposition modeling(FDM) technology. The programming process to the material during printing is revealed and considered in the simulation model. Simulation results are compared with experiments to verify the validity of the method. The advantages of this method are stable convergence and high efficiency,as the three-dimensional(3D) problem is converted to a two-dimensional(2D) problem.The simulation parameters in the model can be further associated with the printing parameters, which shows good application prospect in 4D printed bilayer structure design.

Modeling and prediction of tribological properties of copper/aluminum-graphite self-lubricating composites using machine learning algorithms

The tribological properties of self-lubricating composites are influenced by many variables and complex mechanisms.Data-driven methods,including machine learning(ML)algorithms,can yield a better comprehensive understanding of complex problems under the influence of multiple parameters,typically for how tribological performances and material properties correlate.Correlation of friction coefficients and wear rates of copper/aluminum-graphite(Cu/Al-graphite)self-lubricating composites with their inherent material properties(composition,lubricant content,particle size,processing process,and interfacial bonding strength)and the variables related to the testing method(normal load,sliding speed,and sliding distance)were analyzed using traditional approaches,followed by modeling and prediction of tribological properties through five different ML algorithms,namely support vector machine(SVM),K-Nearest neighbor(KNN),random forest(RF),eXtreme gradient boosting(XGBoost),and least-squares boosting(LSBoost),based on the tribology experimental data.Results demonstrated that ML models could satisfactorily predict friction coefficient and wear rate from the material properties and testing method variables data.Herein,the LSBoost model based on the integrated learning algorithm presented the best prediction performance for friction coefficients and wear rates,with R^(2) of 0.9219 and 0.9243,respectively.Feature importance analysis also revealed that the content of graphite and the hardness of the matrix have the greatest influence on the friction coefficients,and the normal load,the content of graphite,and the hardness of the matrix influence the wear rates the most.

Influence of binder systems on sintering characteristics, microstructures, and mechanical properties of PcBN composites fabricated by SPS

Cubic boron nitride(cBN)with high hardness,thermal conductivity,wear resistance,and chemical inertness has become the most promising abrasive and machining material.Due to the difficulty of fabricating pure cBN body,generally,some binders are incorporated among cBN particles to prepare polycrystalline cubic boron nitride(PcBN).Hence,the binders play a critical factor to the performances of PcBN composites.In this study,the PcBN composites with three binder systems containing ceramic and metal phases were fabricated by spark plasma sintering(SPS)from 1400 to 1700℃.The sintering behaviors and mechanical properties of the composites were investigated.Results show that the effect of binder formulas on mechanical properties mainly related to the compactness,mechanical performances,and thermal expansion coefficient of binder phases,which affect the carrying capacity of the composites and the bonding strength between binder phases and cBN particles.The PcBN composite with SiAlON phase as binder presented optimal flexural strength(465±29 MPa)and fracture toughness(5.62±0.37 MPa·m^(1/2)),attributing to the synergistic effect similar to transgranular and intergranular fractures.Meanwhile,the excellent mechanical properties can be maintained a comparable level when the temperature even rises to 800℃.Due to the weak bonding strength and high porosity,the PcBN composites with Al_(2)O_(3)–ZrO_(2)(3Y)and Al–Ti binder systems exhibited inferior mechanical properties.The possible mechanisms to explain these results were also analyzed.

Bioinspired PcBN/hBN fibrous monolithic ceramic:High-temperature crack resistance responses and self-lubricating performances

The high strength and toughness of natural materials are mainly determined by a combination of mechanisms operating at different length scales,which can be used as a strategy to reduce the intrinsic brittleness of ceramics.Inspired by the architectures of bamboo,the polycrystalline cubic boron nitride/hexagonal boron nitride(PcBN/hBN)fibrous monolithic ceramics with a long fiber arrangement structure was constructed with PcBN fiber cells and hBN cell boundaries,and its crack resistance responses and tribological performances were investigated.The composite ceramic failed in a non-brittle manner with the rising resistance curve(R-curve)behavior,which was attributed to multiscale crack effects in the hierarchical architecture.The maximum crack growth toughness was extremely high(approximately 21 MPa×m^(1/2)),corresponding to a 270%increase over the crack initiation toughness.Excellent fracture resistance could be retained even above 1000℃.Moreover,the composite ceramic exhibited low and stable friction coefficients(approximately 0.33)when paired with a Si_(3)N_(4)pin at high temperature(1000℃),owing to the lubrication function of hBN cell boundaries with weak van der Waals forces and a small amount of liquid B_(2)O_(3)produced.As a result,a synergistic improvement of mechanical and tribological properties at high temperature(1000℃)was realized by combining bionic structure and tribological design.It provides important theoretical and technical support for expanding the application of self-lubricating composite ceramics in harsh environments.

Low-temperature and flexible strategy to in-situ fabricate ZrSiO_(4)-based ceramic composites via doping and tuning solid-state reaction

Synthetic zircon(ZrSiO_(4))ceramics are typically fabricated at elevated temperatures(over 1500℃),which would lead to high manufacturing cost.Meanwhile,reports about preparing ZrSiO_(4)-based ceramic composites via controlling the solid-state reaction between zirconia(ZrO_(2))and silica(SiO_(2))are limited.In this work,we proposed a low-temperature strategy to flexibly design and fabricate ZrSiO_(4)-based ceramic composites via doping and tuning the solid-state reaction.Two ceramic composites and ZrSiO_(4) ceramics were in-situ prepared by reactive fast hot pressing(FHP)at approximately 1250℃ based on the proposed strategy,i.e.,a ZrSiO_(4)-SiO_(2) dual-phase composite with bicontinuous interpenetrating and hierarchical microstructures,a ZrSiO_(4)-ZrO_(2) dual-phase composite with a microstructure of ZrO_(2) submicron-and nano-particles embedded in a micron ZrSiO_(4) matrix,and ZrSiO_(4) ceramics with a small amount of residual ZrO_(2) nanoparticles.The results showed that the phase compositions,microstructure configurations,mechanical properties,and wear resistance of the materials can be flexibly regulated by the proposed strategy.Hence,ZrSiO_(4)-based ceramic composites with different properties can be easily fabricated based on different application scenarios.These findings would offer useful guidance for researchers to flexibly fabricate ZrSiO_(4)-based ceramic composites at low temperatures and tailor their microstructures and properties through doping and tuning the solid-state reaction.

Synthesis and mechanical and elevated temperature tribological properties of a novel high-entropy(TiVNbMoW)C_(4.375) with carbon stoichiometry deviation

High-entropy carbides are a nascent group of ceramics that are promising for high-temperature applications due to the combination of good stability,high hardness(H),high strength,and superior creep resistance that they display.Due to high melting points and low lattice diffusion coefficients,however,the high-entropy carbides are usually difficult to consolidate to a nearly full density.To cope with this challenge,herein,binary carbides including TiC,V_(8)C_(7),NbC,Mo_(2)C,and WC with different carbon stoichiometry were used to prepare dense high-entropy(TiVNbMoW)C_(4.375),and the influence of carbon vacancy on formation ability and mechanical properties of carbon-deficient high-entropy(TiVNbMoW)C_(4.375) were investigated.Intriguingly,although the starting binary carbides have different crystal structures and carbon stoichiometry,the as-prepared high-entropy material showed a rock-salt structure with a relatively high density(98.1%)and good mechanical properties with hardness of 19.4±0.4 GPa and fracture toughness(KIC)of 4.02 MPa·m^(1/2).More importantly,the high-entropy(TiVNbMoW)C_(4.375) exhibited low coefficient of friction(COF)at room temperature(RT)and 800℃.Wear rate(W)gradually increased with the temperature rising,which were attributed to the formation of low-hardness oxidation films at high temperatures to aggravate wear.At 800℃,lubricating films formed from sufficient oxidation products of V_(2)O_(5) and MoO_(3) effectively improved tribological behavior of the high-entropy(TiVNbMoW)C_(4.375).Wear mechanisms were mainly abrasive wear resulting from grain pullout and brittle fracture as well as oxidation wear generated from high-temperature reactions.These results are useful as valuable guidance and reference to the synthesis of high-entropy ceramics(HECs)for sliding parts under high-temperature serving conditions.