Predictive model for minimum chip thickness and size effect in single diamond grain grinding of zirconia ceramics under different lubricating conditions

To address the current bottleneck of debris formation mechanism in plastic removal for hard-brittle materials, a minimum chip thickness (h_min) model that considers lubrication conditions (represented by frictional angle β) is developed according to strain gradient, as well as geometry and kinematics analyses. Model results show that h_min decreases with increasing β. Furthermore, grinding experiments using single diamond grain under different lubricating conditions are carried out to verify the model. With increasing β, h_min values are 71.6, 57.8, 52.0, 50.7, 45.6, 39.7, and 32.4 nm, thereby verifying the trend of h_min decreasing with increasing β. Furthermore, the location of size effect occurs is determined according to the variation trend of single abrasive particle specific energy and unit grinding force curves. The size effect occurs in the border area of ploughing, the cutting region, and mainly, in the ploughing region. Theoretical analysis results are consistent with experimental results with a model error of 6.06%, thereby confirming the validity of the theoretical model.     

高光谱成像的红提总酸与硬度的预测及其分布可视化

利用高光谱成像技术实现对红提总酸和硬度无损检测和分布可视化。首先,利用高光谱采集生长期360个红提样本在波段450～1 000 nm的高光谱图像信息后用化学方法测定对应样本的总酸,用质构仪测定硬度。采用KS(Kennard-Stone)算法将总样本按照3∶1的比例划分为训练集（270个样本）和测试集（90个样本）。对红提原始光谱数据分别利用标准正态变量变换（standard normal variate transformation,SNV）、卷积平滑（Savitzky-Golay,SG）处理法、多元散射校正（multivariate scatter correction,MSC）、归一化等光谱预处理方法处理,确定最优光谱预处理方法。然后,分别采用一次降维（竞争性自适应重加权算法（competitive adaptive reweighted sampling,CARS）、连续投影算法（successive projections algorithm,SPA）、遗传算法（genetic algorithm,GA）、无信息变量消除法（uninformative variable elim...     

变分自编码器模型综述

变分自编码器（VAE）作为深度隐空间生成模型的一种，近年来其表现性能取得了极大的成功，尤其是在图像生成方面。变分自编码器模型作为无监督式特征学习的重要工具之一，可以通过学习隐编码空间与数据生成空间的特征映射，进而在输出端重构生成输入数据。梳理了传统变分自编码器模型及其衍生变体模型的发展与研究现状，并就此做了总结和对比，最后分析了变分自编码器模型存在的问题与挑战，并就可能的发展趋势做了展望。     

Graphene-Based Heterostructure Composite Sensing Materials for Detection of Nitrogen-Containing Harmful Gases

Graphene-based heterostructure composite is a new type of advanced sensing material that includes composites of graphene with noble metals/metal oxides/metal sulfides/polymers and organic ligands. Exerting the synergistic effect of graphene and noble metals/metal oxides/metal sulfides/polymers and organic ligands is a new way to design advanced gas sensors for nitrogen-containing gas species including NH₃ and NO₂ to solve the problems such as poor stability, high working temperature, poor recovery, and poor selectivity. Different fabrication methods of graphene-based heterostructure composite are extensively studied, enabling massive progress in developing chemiresistive-type sensors for detecting the nitrogen-containing gas species. With the components of noble metals/metal oxides/metal sulfides/polymers and organic ligands which are composited with graphene, each material has its attractive and unique electrical properties. Consequently, the corresponding composite formed with graphene has different sensing characteristics. Furthermore, working ambient gas and response type can affect gas-sensitive characteristic parameters of graphene-based heterostructure composite sensing materials. Moreover, it requires particular attention in studying gas sensing mechanism of graphene-based heterostructure composite sensing materials for nitrogen-containing gas species. This review focuses on related scientific issues such as material synthesis methods, sensing performance, and gas sensing mechanism to discuss the technical challenges and several perspectives.     

Effect of free stream angle on mixing performance of hydrogen multi-jets in supersonic combustion chamber

The fuel mixing process within the combustion chamber is a critical procedure for advance of scramjet engine. In current study, the influence of free stream angle on the fuel mixing process of multi jets was thoroughly investigated. This research attempts to applied computational technique to disclose the structure of multi-fuel jets when the supersonic air stream is not normal to the jet direction. The effect of both positive and negative supersonic free stream on the diffusion and penetration of multi-hydrogen jets is fully described. The attention of this research is the flow structure of the multi jets and their interaction in the presence of different free stream angle. Our results indicate that the positive free stream angle expands the mixing zone in the downstream while the negative angle of free stream limited jet distribution inside the combustor. Our results show that mixing efficiency increase approximately 50% when the angle of free stream augments from +20° to −20°. According to our findings, mixing efficiency surges up to 17% when the jet spaces are increased from 4Dj to 10 Dj.     

Multi-mode data augmentation and fault diagnosis of rotating machinery using modified ACGAN designed with new framework

As one of the representative unsupervised data augmentation methods, generative adversarial networks (GANs) have the potential to solve the problem of insufficient samples in fault diagnosis of rotating machinery. However, the existing unsupervised GANs are usually incapable of simultaneously generating multi-mode fault samples and have some shortcomings such as mode collapse and gradient vanishing. To overcome these deficiencies, a supervised model called modified auxiliary classifier GAN (MACGAN) designed with new framework is proposed in this paper. Firstly, a new ACGAN framework is developed by adding an independent classifier to improve the compatibility between the classification and discrimination. Secondly, the Wasserstein distance is introduced in the new loss functions to overcome mode collapse and gradient vanishing. Finally, to achieve stable training, a spectral normalization is used to replace the weight clipping to constrain the weight parameters of discriminator. The proposed method is applied to fault diagnosis of bearing and gear. Compared with the existing GANs, the proposed method can more efficiently generate multi-mode fault samples with higher qualities, which can be used to assist the training of deep learning-based fault diagnosis models with high accuracy and good stability.     

Energy aspects and workpiece surface characteristics in ultrasonic-assisted cylindrical grinding of alumina–zirconia ceramics

Ultrasonic assisted grinding is a novel method for improving the grinding process of difficult-to-cut materials. In the present research a novel setup has been designed and manufactured for utilizing ultrasonic vibrations in external cylindrical grinding. The designed ultrasonic head vibrates a rotating workpiece in axial direction. An alumina–zirconia ceramic (AZ90) has been selected as the workpiece material. Energy aspects and workpiece surface characteristics of ultrasonic assisted cylindrical grinding (UACG) and conventional cylindrical grinding (CG) processes have been analytically modeled and corresponding grinding experiments have been performed. The combined kinematics of the cylindrical plunge grinding process and axial ultrasonic vibrations provide a unique surface treatment conditions, which leads to reduced peak heights and increased valley depths of the surface topography. The main axial vibration mode provides the overlap of the adjacent cutting traces and consequently smoothens the surface topography in cylindrical plunge grinding. It has been analytically and experimentally shown that, applying ultrasonic vibrations, grinding energy can be reduced up to more than 35% depending on the process parameters. The surface characteristics of the ground workpieces have been investigated in terms of four surface roughness parameters and the roundness error.     

馈能悬架并联机构动力学分析

针对传统馈能悬架机械效率低、机构复杂等特点,设计一种简单且高效的少自由度并联机构馈能悬架系统。该系统可以将汽车悬架的垂直运动转化为机构的旋转运动,并带动电机发电。以少自由度并联机构为研究对象,首先采用旋量理论分析该机构实现空间一转一移运动的机构学原理,建立雅克比矩阵,对该机构的正逆位置进行分析,并定义支载力评价指标。然后利用拉格朗日法建立该馈能系统的动力学模型,应用数值方法对该机构的可行性进行分析,最后利用ADAMS对该机构进行运动学和动力学进行仿真分析。数值计算与仿真结果的误差不超过3%,验证了该算法和所建模型的正确性,也为该机构应用到车辆馈能悬架提供了参考。     

基于中型水果的自动分级包装一体机设备的设计

目的 为解决现有分级包装设备存在劳动强度大、效率低、易损伤果皮等问题,设计一种基于自动化水果筛选分级包装一体机。方法 将水果通过上料装置输送到果杯中,通过齿轮齿条的配合实现水果的360°旋转,筛选后通过特制的冲模分流装置进行一次分流,进入包装机后利用45DF型凸轮分割器搭配电机带动棘轮实现水果的二次单个分流,利用发泡型塑料网的物理特性,通过凸轮的急回特性来实现单个水果包装自动化。结果 基于机械原理和机械设计,对关键部件进行计算设计和仿真设计,得到传送盘与地面的安装角度为3°,传送盘工作时最大变形量为0.503 69 mm,棘轮工作时最大变形为5.763 9×10⁻⁵ mm,最大应变为4.799×10⁻⁷,最大应力为9.56×10⁻⁴ N,满足使用要求。结论 通过实现分级包装一体机的自动化,减少了劳动力,降低了人工成本,提高了经济效益。     

硅烷偶联剂及氧化石墨烯二次改性对芳纶纤维界面性能的影响EI北大核心CSCD

为改善芳纶纤维(PPTA)与丁腈橡胶(NBR)复合材料之间的界面强度,采用硅烷偶联剂A172和氧化石墨烯(GO)对芳纶纤维表面进行接枝改性处理,并对处理前后的芳纶纤维进行化学结构、表面形貌及H抽出力分析。利用SEM对抽出纤维表面和橡胶基芳纶纤维复合材料截面进行微观结构分析。结果表明:硅烷偶联剂和氧化石墨烯对芳纶纤维进行二次表面改性后,纤维表面含氧基团增加,化学活性提高,处理后表面存在明显的表层附着物,纤维结构未发生明显损伤且表面粗糙度得到明显改善。每个处理阶段后H抽出力均有提高,且氧化石墨烯二次改性后的芳纶纤维H抽出力提高效果最佳,从18.192 MPa提高到48.748 MPa,芳纶纤维与丁腈橡胶的界面结合力得到了显著提升,从而证实了硅烷偶联剂和氧化石墨烯二次改性芳纶纤维的有效性,为橡胶基芳纶纤维复合材料性能的研究提供了参考。