Effect of drawing condition on mechanical properties and molecular orientation of self-reinforced poly(lactic acid) screws

Effects of extrusion ratio (ER) during extruding on mechanical properties of poly(lactic acid) (PLA) screws were investigated in terms of shear and twist strength. Shear strength increased by drawing, while twist strength decreased. This might be due to orientation of molecular chains during drawing. In order to evaluate orientation of molecular chains, orientation function in extruded billets was measured as a function of ER. Since orientation function increased with ER, drawing is effective method to improve shear strength of screw, where fibrous structure which was formed during extruding resisted shear stress in cross-section perpendicular to screw axis. Although orientation functions for billet extruded at ER 1.3–4 were equivalent, both strengths changed for the screw extruded at the range of this ER. Infrared spectra suggested transforming from α to β crystal for the billet extruded at the range of this ER. This result suggested that mechanical properties of screw also depended on the crystal forms.     

Tensile stress–crack width law for steel fibre reinforced self-compacting concrete obtained from indirect (splitting) tensile tests

In this work, mode I fracture parameters of steel fibre reinforced self-compacting concrete (SFRSCC) were derived from the numerical simulation of indirect splitting tensile tests. The combined experimental and numerical research allowed a comparison between the stress–crack width (σ–w) relationship acquired straightforwardly from direct tensile tests, and the σ–w response derived from inverse analysis of the splitting tensile tests results. For this purpose a comprehensive nonlinear 3D finite element (FE) modeling strategy was developed. A comparison between the experimental results obtained from splitting tensile tests and the corresponding FE simulations confirmed the good accuracy of the proposed strategy to derive the σ–w law for these composites. It is concluded that the post-cracking tensile laws obtained from inverse analysis provided a close relationship with the ones obtained from the experimental uniaxial tensile tests.     

表面活性剂对TiO_2纳米晶体生长动力学的影响

采用水热法,分别以丙二酸、正丁醇、乙二胺为表面活性剂,研究3种体系下TiO2纳米晶体的生长过程。XRD结果显示3种体系下主要产物为锐钛矿TiO2;TEM和HRTEM结果表明在不同的生长阶段,纳米晶体的生长结构特点明显不同。分别采用定向生长理论(Orientation attachment,OA)、弗兰克尔收缩理论(Frenkel shrinking,SH)、奥斯特瓦尔德熟化理论(Ostwald ripening,OR)对3种体系下的晶体生长进行理论模拟,结果发现在丙二酸、乙二胺体系下晶体生长分为3个阶段:定向聚集生长、颗粒收缩、奥斯特瓦尔德熟化,且乙二胺体系下颗粒明显增大;但是在正丁醇体系下晶体生长仅显示明显的OR特征,不存在OA生长。理论和实验分析说明不同体系下晶体生长方式不同的主要原因是由于3种表面活性剂以及溶液pH值的不同作用。     

夏热冬冷地区供暖基准温度的影响因素分析

为研究气象参数、窗墙比以及建筑朝向等因素对夏热冬冷地区供暖基准温度的影响,采用Energy Plus能耗模拟软件,选取成都等8个夏热冬冷地区典型城市,分别计算了室外干球温度、太阳辐射强度、窗墙比和建筑朝向等不同模拟工况下的供暖基准温度,确定了夏热冬冷地区供暖基准温度的大致范围。结果表明:窗墙比和建筑朝向对供暖基准温度影响较小,相同城市不同模拟工况下供暖基准温度的波动范围最大为0.5℃;太阳辐射强度对供暖基准温度的影响较大,重庆地区由于太阳辐射强度最弱,其供暖基准温度最大,成都次之,上海最小;若太阳辐射强度相差不大,而室外干球温度相差较大时,室外干球温度较低者供暖基准温度较小;不同城市的供暖基准温度波动范围为14.6~16.4℃。     

Strain‐induced deformation mechanisms of polylactide plasticized with acrylated poly(ethylene glycol) obtained by reactive extrusion

This work aimed at identifying the tensile deformation mechanisms of an original grade of plasticized polylactide (pPLA) obtained by reactive extrusion. This material had a glass transition temperature of 32.6 °C and consisted of a polylactide (PLA) matrix grafted with poly(acryl‐poly(ethylene glycol)) (poly(Acryl‐PEG)) inclusions. pPLA behaved like a rubber‐toughened amorphous polymer at 20 °C, and its tensile behavior evolved toward a rubbery semicrystalline polymer with increasing temperature. The drawing of pPLA involved orientation of amorphous and crystalline chains, crystallization, and destruction of crystals. It was found that crystal formation and crystal destruction were in competition below 50 °C, resulting in a constant or slightly decreasing crystallinity with strain. Increasing temperature enhanced crystal formation and limited crystal destruction, resulting in an increased crystallinity with the strain level. Drawing yielded a transformation of the initial spherical poly(Acryl‐PEG) inclusions into ellipsoids oriented in the tensile direction. This mechanism may engender the formation of nanovoids within the inclusions due to a decreased density, assumed to be responsible for the whitening of the specimen. © 2015 Society of Chemical Industry     

基于反馈Hough变换的管道点云检测和识别

管道是流程工厂的主体，其几何形状表现为圆柱体或圆台。针对现有管道检测识别方法对噪声较为敏感、检测精度不高、检测结果难以验证等问题，本文提出一种具有轴向反馈修正的三维霍夫变换方法。首先，根据八叉树划分点云空间，计算点云法向量并生成圆柱体或圆台高斯映射图，利用三维霍夫变换法估计初始轴向；然后，基于初始轴向计算圆柱体横截面或圆台投影轮廓，并建立轴向优化目标函数，通过迭代优化获得最终的轴向；最后通过霍夫变换法拟合圆柱体或圆台轴心位置并计算半径值。实验结果表明，该方法可有效提高管道轴向、半径等参数的估算准确度，同时，本文提出的优化目标函数也为检测结果提供了一种新的评价方法。     

基于双树复小波的无参考立体图像质量评价

随着3D技术的不断发展，立体图像的使用领域越来越广泛，同时人们对图像的清晰度要求越来越高，因此，立体图像的质量评价成为关注点，基于此，提出了一种基于双树复小波变换的立体图像质量评价算法。使用双树复小波变换对立体图像的左、右视图进行处理，生成纹理结构图像，且根据最小能量误差的原理，获取左右视图的视差图；对纹理结构图像和视差图提取非对称广义高斯分布模型的参数、梯度幅值、相对梯度方向方差和奇异值曲线与坐标轴的面积等特征；使用AdaBoosting BP神经网络，进行训练和预测立体图像的质量得分。在LIVE立体图像数据库上的实验结果表明，新方法预测得分与主观得分有较好的一致性，获得了比较好的实验结果。     

Electric-field-aligned functionalized-layered double hydroxide/polyphenyl ether composite membrane for ion transport

To address the insufficient ion conductivity of hydroxide exchange membranes (HEMs) used in alkali membrane fuel cells (AMFCs), we present a series of aligned layered double hydroxide (LDH)/polyphenyl ether (PPO) composite membranes based on the electrorheological effect. The hexagonal LDH was functionalized with N-spirocyclic ammonium (ASU-LDH) to enhance the electrorheological effect of the ASU-LDH as well as improve the ion conductivity of the ASU-LDH. The aligned ASU-LDH/triple-cation-functionalized PPO (ASU-LDH/TC-PPO) composite membranes were prepared by applied-electric field. The effective electric-induced ion channels (EICs) were constructed by aligned ASU-LDH nanosheets in HEMs, which are distinctly observed by scanning electron microscope (SEM). Notably, these EICs-contained ASU-LDH/TC-PPO composite membranes exhibit the higher ion conductivity and alkaline stability than those of normal TC-PPO and ASU-LDH/TC-PPO membranes. It is worth noticing that these EICs are different with the traditional phase-induced ion channels, the EICs show the shorter ion transport distances and broader water channels in HEMs. Attributing to EICs, the longitudinal ion conductivity of aligned ASU-LDH/TC-PPO membrane shows 32.2% and 18.7% improvement compared to pristine TC-PPO and normal ASU-LDH/TC-PPO membrane. The maximum ion conductivity of the aligned ASU-LDH/TC-PPO composite membrane reaches to 109.8 mS/cm at 80 °C. The long-term stability test shows that the aligned ASU-LDH/TC-PPO membranes still exhibit enhancing alkali resistance (83.2%) in 1 M KOH at 80 °C for 500 h. In brief, this work provides a novel and effective approach to prepare high-performance HEMs.     

Preparation of (110)-oriented SrTiO3 film on quartz glass by laser chemical vapor deposition

SrTiO₃ (STO) film was prepared on quartz glass by laser chemical vapor deposition at a deposition temperature (T_dep) ranged from 760 to 1104 K. Effect of the T_dep on the orientation, crystallinity, texture, and microstructure of the STO film was investigated. As the T_dep was increased, the preferred orientation of the STO film tended to be (110)-orientated with corresponding texture coefficient (TC) on the (110) reflection enhanced from 2.3 to 6; meanwhile, the full width at half maximum of the ω-scan on the (110) reflection decreased from 0.85° to 0.59°. The (110)-oriented grains were in wedge shape about 60 × 150 nm in size, which tended to be flat at an elevated T_dep of 1104 K.