生物可降解材料PLGA的应力松弛性能

针对基于生物可降解材料聚乳酸-羟基乙酸共聚物(PLGA)的热压成型工艺仿真研究中,粘弹性材料模型参数缺乏的问题,通过单轴拉伸应力松弛试验,研究了生物可降解材料PLGA在5种温度状态下的应力松弛性能。基于时间-温度等效原理,平移得到60℃的松弛模量主曲线,并采用广义Maxwell模型对此主曲线进行拟合。结果表明:随着温度的升高,PLGA材料的松弛时间明显缩短,且拟合曲线与原数据误差较小,说明广义Maxwell模型能较理想地模拟PLGA材料的应力松弛行为。这些数据的获得为后续仿真研究提供了参考。     

有机玻璃热压弹性回复实验与建模

首先通过热压缩实验研究热压工艺参数对有机玻璃(PMMA)热压后弹性回复的影响。从实验结果可知,温度和作用时间是影响热压后弹性回复率的重要因素。然后引入广义麦克斯韦方程作为热压应力松弛的控制方程,通过实验结果和模型计算结果对比,由该方程拟合的热压应力松弛曲线和实验测得的曲线具有较高的吻合度。最后由麦克斯韦方程导出弹性回复的数学模型,通过与实验结果对比可知,该数学模型对弹性回复的预测的误差小于10%。     

变频变温条件粘弹材料参数化数学模型

采用分数导数模型并结合温频等效原理,提出了粘弹性材料的复模量、损耗因子与温度、频率关系的参数化数学模型——五参数Zener模型;结合DMA测试实验数据对模型参数进行了拟合,结果表明：该模型能够很好地反映粘弹性材料在变频、变温条件下的动态力学特性。     

基于LM算法的粘弹性材料剪切松弛模量的拟合

在对粘弹性材料进行有限元计算时,需要材料的剪切松弛模量,必须对经验公式或实验数据进行转换。根据KWW经验公式与广义Maxwell剪切松弛函数的对应关系,列出了求解松弛时间与剪切松弛模量的超定非线性方程组,用LM优化算法得到了方程组的最优解。初步讨论了初值的选取方法。根据此方法得到的松弛时间与剪切松弛模量的拟合曲线的拟合度达到了0.99以上。所提出的方法也适用于用实验数据(随时间变化的应力应变)求解材料的剪切松弛模量。     

碳纤维增强形状记忆聚合物复合材料的热-力学行为建模与影响因素碳纤维增强形状记忆聚合物复合材料的热-力学行为建模与影响因素

采用变形梯度分解的方法,基于热力学内变量理论,构建了适用于描述碳纤维增强形状记忆聚合物（CF/SMP）复合材料热-力学行为的热黏弹性本构模型。模型中考虑了材料的结构松弛效应和应力松弛效应,且适用于有限变形条件。依据该模型研究了一种CF/SMP薄板在受到单向均布载荷作用且处于平面应力状态时的碳纤维有效应变影响因素。理论上证实了虽然碳纤维的容许应变很小,但合理取向的纤维分布形式能使其应用于有限变形条件下而不被破坏。此外,分析了该CF/SMP形状记忆热-力学循环过程中形状记忆效应（SME）的影响因素。结果表明,碳纤维含量的增大和纤维倾斜角的减小会导致CF/SMP刚度增大,从而降低其形状固定率。此外,碳纤维体积含量和温度变化率对升温回复阶段也存在一定影响。上述研究方法和结果能对单向连续CF/SMP的设计与应用提供一定理论指导。      

形状记忆纤维热粘弹性基体复合材料的力学行为

应用热粘弹性理论和Voigt混合律,在变温场中针对马氏体逆相变过程建立了NiTi形状记忆纤维热粘弹性基体复合材料的应力-应变关系,在逆相变过程和基体呈现热粘弹态阶段,由于基体松弛其模量减小,在跃阶拉应力的作用下,复合材料的压缩应变迅速增大,纤维回复应力先增大后减小;在跃阶拉应变的作用下,复合材料的应力增加先变缓然后加快直至稳定,较高的温度和材料参数对NiTi纤维热粘弹性基体复合材料的力学行为和纤维的作动性能有明显的影响.     

定频变温下粘弹材料动力学特性数据拟合分析

本文研究了粘弹性阻尼材料的耗能机理和动态阻尼特性,采用分数导数模型,并与温频等效原理相结合,得到了粘弹性阻尼材料的复模量、损耗因子与温度关系的参数化数学模型;并结合粘弹性阻尼材料的DMA测试实验数据对模型参量进行了拟合。实验结果和误差分析表明拟合的数学模型能够准确反映粘弹性材料在定频率变温度条件下的动力学特性的变化情况。     

一种新的聚合物基复合材料应力松弛经验模型

视黏弹性元件弹簧和粘壶的特性参数为时间的函数,建立双变参Maxwell模型,求解其本构方程及松弛函数,探讨了其松弛函数与经验KWW函数的关系,提出了一种新的应力松弛经验模型。运用最小二乘原理,建立该模型参数的确定方法。开展了玻璃纤维增强聚合物(GFRP)复合材料的长期应力松弛实验,并通过实验数据的分析验证了该模型的正确性。研究表明,新应力松弛经验模型拟合曲线与实测曲线吻合较好,相关系数达到96%以上,说明了该模型适合描述GFRP复合材料的黏弹性松弛特性。     

热变形中的动态回复过程

本文提出了动态回复型金属在热变形过程中应力—应变曲线的数学模型,并与实验数据进行了详细比较,结果证明理论曲线与实验曲线符合甚好。     

基于GA改进BP神经网络预测热变形流变应力模型的建立EI北大核心CSCD

应力-应变曲线对研究金属热变形过程中的加工硬化、动态再结晶和动态回复的变化具有重要的意义,而预测不同热变形参数下的应力-应变曲线有助于研究热加工过程中金属的可加工性和不稳定性。在应变速率为0.01~3 s^(-1)以及变形温度为1000~1200℃条件下,利用Gleeble-3500热模拟试验机对Nb-V-Ti微合金钢进行热压缩实验,研究了Nb-V-Ti微合金钢的热变形行为。建立BP神经网络模型和基于GA改进BP神经网络模型,分别预测在应变速率0.5 s^(-1)、变形温度1050℃和应变速率1 s^(-1)、变形温度1100℃条件下的流动应力行为并验证模型效果。研究结果表明:经GA改进后的BP神经网络模型对测试数据的应力-应变曲线与实验曲线具有很好的吻合,相关系数分别达0.99202和0.99734,误差仅为2.7816%和2.1703%,预测结果与实验结果相对误差在[-2,2]范围内,证明了模型的预测可靠性,且适用于较广的应变范围,为工业生产轧制工艺提供理论指导。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Synthesis of Alumina-Zirconia Nanocomposites by Solgel Process

Al₂O₃-ZrO₂ nanocomposites were developed starting with the solgel process. Composite alumina-zirconia nanopowders were synthesized from metallorganic precursors (Aluminium secondary butoxide and zirconium Iso propoxide) using the solgel process. The parameters affecting the synthesis—solvent, concentration of precursor, R/H ratio (i.e., dilution of water in solvent)—were varied as also the temperature and pH. BET and TEM were used to measure nanosize. Diffuse reflectance spectroscopy and also qualitative optical absorption led to identical particle size estimate. The variation of process parameters was used to study the effect and interdependence of process parameters. Artificial Neural Networks was used to rigorously analyze the process. Although this led to confirmation of interdependence of parameters, the presence of a single overwhelming solvent variable was also established. Then the optimal process was used to synthesize more nanopowder. To produce bulk nanocomposite the nanopowders were sintered by varying the temperature and time period. The sintered lithoids were probed with a vickers hardness tester to measure elastic modulus, hardness, and fracture toughness. The results showed high elastic modulus, modest hardness, and very high fracture toughness.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.