聚合物热黏弹塑性变形微热压成型机理的数值模拟研究

研究了聚甲基丙烯酸甲酯（PMMA）超疏性阵列圆柱微结构特征功能表面的微热压成型技术,通过模拟研究了成型工艺参数对成型过程的影响规律,揭示了其热黏弹塑性变形充填流动机理,明晰了关键调控参数。结果表明,基片材料的弹性模量、成型温度和压力是影响充填成型的关键调控参数,成型压力和变形应力与成型温度呈负关联关系,而充填高度与成型温度呈正关联关系;提高成型温度至高于基片材料的玻璃化转变温度（Tg）,使基片处于黏弹性高弹态,易使基片快速产生明显的热黏弹塑性变形,且可使成型压力和变形应力趋于最小值,这有利于基片避免断裂损伤并加速充模流动。     

PMMA滚压成型的数值模拟

建立了PMMA(聚甲基丙烯酸甲酯)的黏弹性材料模型,以微结构的复制率作为评判依据,利用Abaqus软件研究了滚压过程中滚筒微结构和基板的几何参数对滚压工艺的影响。仿真结果表明:在相同的压印温度、压印力和牵引速度下,随着微结构直径的增大,复制率增大;随着微结构间距的增大,复制率先减小后保持不变;随着基板厚度的减小,复制率增大。     

基于Pareto遗传算法的聚合物黏度模型参数拟合

针对传统聚合物黏度模型参数拟合方法中存在的初值选取问题及权重分配问题,采用基于Pareto多目标遗传算法的拟合方法.根据实验测得PP和PMMA材料流变数据对常用的Cross-WLF 7参量黏度模型进行了拟合,拟合结果的复相关系数分别达到了0.999929和0.999036.研究结果为聚合物注射成型仿真提供了必需的材料流变数据,为塑料制品的模具设计、工艺参数优化和质量预测提供了理论依据.     

PMMA双面滚压成型的数值模拟与验证实验

利用有限元软件ABAQUS,对聚甲基丙烯酸甲酯(PMMA)光扩散板双面滚压成型过程进行了数值模拟。通过建立PMMA的黏弹性模型,以微结构的复制率作为评价标准,利用数值模拟方法,分析了滚筒旋转速度、滚筒下压距离和PMMA基板温度对PMMA光扩散板两面不同形状微结构复制率的影响。结果表明,半圆形微结构复制率比等边三角形微结构复制率高;在一定范围内,复制率随着滚筒旋转速度的减小和滚筒下压距离的增大而增大,随PMMA基板温度升高而先增大后减小;当滚筒旋转速度为0.05rad/s,滚筒下压距离为0.45mm,PMMA基板温度为140℃时,半圆形和等边三角形微结构复制率均达到最大,分别为65.5%和51.2%。滚筒下压距离对复制率的影响最大,针对该参数进行实际滚压成型实验并将实验结果与仿真结果进行了对比验证,发现两者基本一致。     

基于动态蠕变试验的沥青混合料黏弹性分析

基于沥青混合料Burgers模型的黏弹性理论,通过动态蠕变试验进行AC-20黏弹性分析,得到不同温度及应力下的混合料变形特征曲线及Burgers模型4个参数的变化规律．结果表明：在同一温度下,随应力水平增加,永久变形随之增大,稳定期永久应变发展速率增大且破坏期提前到来,Burgers模型参数中E1、E2增大,η1、η2减小;在同一应力水平下,永久变形会随温度升高而增大,同时E1、E2减小,η1,η2增大．因此应力及温度对沥青混合料黏性及弹性影响程度不同,随着应力增加,弹性增强而黏性降低;随温度升高,则弹性降低而黏性增加,该结论与路面实际使用状况一致．     

聚碳酸酯的应力松弛实验及数据处理分析

以黏弹性力学理论为基础,选用广义Maxwell模型作为聚碳酸酯(PC)黏弹性的力学模型。在120℃温度场下以不同的初始应变进行应力松弛试验,得到应力松弛过程中作用力与时间的实验数据。利用ABAQUS软件拟合得出不同初始应变下的黏弹性模型的prony参数,再结合Origin软件优化得出广义Maxwell黏弹性模型在参考温度为120℃时的普适prony级数参数,来供ABAQUS调用分析,为有限元仿真分析奠定理论基础。     

模外装饰鼠标外壳贴膜工艺仿真分析

为了研究模外装饰鼠标外壳贴膜工艺,对PMMA塑料板材进行高温单向拉伸实验,计算出DSGZ黏弹性本构模型系数,并将DSGZ模型的预测曲线与其实验数据进行对比分析。采用弹性预测-径向回映算法设计编写了DSGZ黏弹性本构模型的ABAQUS用户材料子程序,然后基于OMD工艺原理,对鼠标外壳OMD贴膜的工艺成型过程进行仿真分析,得到了成型后薄膜的厚度分布及其在X、Y方向上的变形量。     

有机锆交联AM/DMAM/AMPS三元聚合物流变动力学

以乳酸/丙三醇有机锆为交联剂,聚合物[一种耐高温的丙烯酰胺(AM)/N,N-二甲基丙烯酰胺(DMAM)/2-丙烯酰胺基-2-甲基丙磺酸(AMPS)三元聚合物]为稠化剂,获得了耐高温聚合物凝胶.研究了聚合物凝胶的流变学特性(黏弹性、触变性)及其交联流变动力学,获得了聚合物交联过程中黏度、黏弹性模量随时间的变化关系,并考察了剪切速率和温度对凝胶形成的影响,建立了交联流变动力学模型.结果表明,交联聚合物凝胶具有明显的黏弹性和触变性;在180℃、170 s^-1下剪切120 min后,黏度达176.8 mPa·s,获得了耐高温达180℃的凝胶;一级交联流变动力学模型可拟合聚合物的交联流变动力学过程,拟合的模型参数物理意义明确合理.     

微流控芯片热压成型仿真研究

建立了聚甲基丙烯酸甲酯(PMMA)的黏弹性材料模型,利用有限元仿真软件Abaqus,以填充率为质量评价标准,对微流控芯片热压印的填充过程进行仿真。研究在等温条件(模具与芯片温度相同)下时间、温度和压力对微流控芯片沟槽填充效果的影响。仿真结果表明,压印温度和压印力对PMMA聚合物填充效果的影响较大,提高温度和压力都能达到加快聚合物填充速率和提高复制率的作用;时间参数的影响主要体现为增大PMMA的应力松弛现象,延长压印时间同样能达到提高复制率的作用。     

换能器结构参数对聚合物超声塑化黏弹生热的影响

为研究超声换能器结构参数对聚合物超声塑化过程黏弹性生热的影响，首先确定超声黏弹性生热系统的组成，进行纵振超声换能器结构设计；然后分析超声黏弹性生热过程及超声黏弹性生热原理；最后采用单一变量法分析超声换能器的主要结构参数对其纵振频率及工具头前端质点最大振幅的影响，将其实际输出的纵振激励加载于熔融聚合物，研究其结构参数对聚合物超声黏弹性生热过程及达到聚合物玻璃化转变温度所用时间的影响。结果表明，随纵振激励作用时间的增加，聚合物温度非线性升高；放大比对聚合物温度变化影响最大，前盖板厚度和工具头长度次之，影响最小的是变幅杆长度。     

Modeling and Stress Analysis During Drying of a Deformable and Saturated Porous Medium

This article addresses how to express the behaviors that develop stresses within a porous media during convective drying processes. The work is focused on the coupling of the thermal (temperature distribution), hygroscopic (moisture, humidity), and mechanical (strains and stresses) aspects shown during the drying process of a saturated porous medium. Natural clay plate samples were used as a model material. Using two different mechanical behaviors (elastic and viscoelastic), the strain–stress equations were studied and discussed through the simulation results. Obtaining almost the same parameters of the main modeling variables (temperature, liquid pressure, and moisture content), a significant difference was observed between the results obtained for the stresses assuming the two behaviors, particularly depending on the viscoelastic parameters deduced from an experimental study. The simulation highlights a response of the medium supposed viscoelastic different to that of elastic case in intensity and response time.     

GA-BP神经网络在钢铁加热炉建模中的应用

基于现场采集的大量的数据,采用BP神经网络建立现场加热炉炉温的非线性模型,并提出利用遗传算法优化BP神经网络的参数与阈值,有效避免了BP神经网络易陷入局部最小值、收敛速度慢的不足。仿真结果表明:在同样的数据集下,GA-BP神经网络的稳定性更好,预测精度更高。     

BP神经网络与GA算法相结合的空调风叶翘曲均匀性优化

以模具温度、熔体温度、注射时间、保压时间、保压压力5个因素为设计变量,空调风叶叶片尖部Z轴坐标最大差值为目标变量,采用田口方法进行实验设计并根据实验方案进行CAE模拟,根据模拟结果采用BP神经网络构建设计变量与目标变量之间的数学关系模型,并利用GA算法对数学模型进行全局最优求解。求得最优工艺参数为：模具温度45 ℃、熔体温度205 ℃、注射时间1.8 s、保压时间6 s、保压压力50 MPa。模拟验证得到优化工艺参数下的目标变量为0.08 mm,低于各个实验设计方案,且风叶各叶片翘曲均匀性得到提高。     

An experimental and theoretical study of creep of a graphite/epoxy woven composite

The creep behavior of woven fiber polymer composites has been investigated through both an experimental study and analytical modeling. In the modeling, the matrix is assumed to be a 4-parameter model (a Maxwell-Voigt combination) and the fibers to be elastic. The fiber undulation model developed by Ishikawa and Chou for elastic behavior of woven fiber composites has been extended to the viscoelastic system by the correspondence principle. This considers the longitudinal and transverse fibers separately. The weave geometry and dimensions are accounted for, thus bringing the model closer to the actual composite. While this model has been used previously to predict the composites elastic behavior, this is the first time it is considered as a viscoelastic solid, which helps determine its time dependent behavior. The resultant model takes into account the different parameters associated with the weave (the density of the fibers in the weave, the radius of the fibers and the profile of the fill and warp fibers), volume concentration of the fiber and matrix in the composite, and the elastic moduli of the fill and warp fibers and the viscoelastic properties of the polymer matrix. We have conducted creep tests on graphite fiber/epoxy composites to evaluate our model. Experiments have been conducted from room temperature (22°C) to 200°F (93°C). The results from experiments have been analyzed and an inverse simulation has been performed to obtain the unknown parameters of the matrix and fibers in the composite. The model is then used to predict the creep behavior of the woven fiber composite under other loading conditions and temperature levels, showing satisfactory agreement with the data.     

Creep and stress relaxation modeling of vinyl ester nanocomposites reinforced by nanoclay and graphite platelets

This article discusses the viscoelastic behavior of a vinyl ester (Derakane 411‐350) reinforced with 1.25 and 2.5 wt % nanoclay and exfoliated graphite nanoplatelets during short‐term creep and relaxation tests with a dynamic mechanical analyzer. Linear viscoelastic models are generally composed of one or more elements such as dashpots and springs that represent the viscous and elastic properties. Stress relaxation data from the dynamic mechanical analyzer have been used to obtain the elastic parameters based on model constitutive equations. The standard linear solid model, which is a physical model, has been used for predicting the creep deformation behavior of the vinyl ester nanocomposites over a wide temperature range. Some correlations have been made with the mechanical model, such as the effect of temperature on the deformation behavior, which is well explained by the dashpot mechanism. At lower temperatures, higher creep compliance has been observed for the vinyl ester versus the nanocomposites, whereas at temperatures near the glass‐transition temperature of the vinyl ester, creep compliance in the nanocomposites is closer in magnitude to that for the vinyl ester. The creep response of the pure vinyl ester and its nanocomposites appears to be modeled reasonably well at temperatures lower than their glass‐transition temperatures. A comparison of the predictions and experimental data from the creep tests has demonstrated that this model can represent the long‐term deformation behavior of these nanoreinforced materials reasonably well. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

逆向法测定酮洛芬对映体在Chiralpak AD柱上的吸附等温线

模拟移动床（SMB）色谱分离与纯化的操作过程复杂,对其进行设计与优化需要使用数值模拟方法,准确测定竞争型吸附等温线具有重要意义。采用逆向法确定了25℃下酮洛芬对映体在直链淀粉手性固定相（Chiralpak AD）上的竞争吸附等温线,先用高效液相色谱测得酮洛芬对映体在Chiralpak AD 柱上的过载流出曲线,再通过拟合实验测得的流出曲线确定吸附等温线模型及其参数。研究中采用平衡扩散模型描述酮洛芬对映体在色谱柱上流出的瞬态过程。参数拟合过程中,首先用非支配基因算法（NSGA-Ⅱ）在较广的参数空间内搜索吸附等温线模型参数,再以所得结果作为初值,使用Levenberg-Marquardt 算法（LMA）对参数进一步优化。比较了4种不同竞争吸附等温线模型对实验测得的流出曲线的拟合结果,其中五参数的Bi-Langmuir 模型拟合程度最好。测量了不同进料浓度和进料量条件下的流出曲线,并通过与模型预测结果的对照验证了所确定吸附等温线模型和参数。     

Measurement and simulation of low‐density polyethylene extrudate swell through a circular die

BACKGROUND: Extrudate swell is a common phenomenon in polymer processing. The investigation of its mechanism is of both scientific and industrial interest. RESULTS: The rheological parameters of a material described by the viscoelastic PTT (Phan‐Thien–Tanner) constitutive model are obtained by fitting the distributions of material functions detected with a strain‐controlled rheometer. The swelling ratios of low‐density polyethylene (LDPE) under different volume flow rates are indirectly obtained using a photographic technique. A mathematical model of extrudate swell is established and its finite element model is derived. A penalty method is employed to solve the extrudate swell problem with a decoupled algorithm. Computation stability is improved by using the discrete elastic‐viscous split stress algorithm incorporating the inconsistent streamline‐upwind scheme. CONCLUSION: The swell phenomenon of LDPE through a circular die is investigated using both experimental measurement and numerical simulation. The swelling ratios obtained from the simulation are compared with those measured: they agree well with each other. The essential flow characteristics of polymer melts are predicted and the mechanism of the swell phenomenon is further discussed. Copyright © 2009 Society of Chemical Industry     

A macromolecular deformation model to estimate viscoelastic flow effects in polymer melts

The elastic deformation of polymer macromolecules in a shear field is used as the basis for quantitative predictions of viscoelastic flow effects in a polymer melt. Non-Newtonian viscosity, capillary end correction factor, maximum die swell, and die swell profile of a polymer melt are predicted by the model. All these effects can be reduced to generic master curves, which are independent of polymer type. Macromolecular deformation also influences the brittle failure strength of a processed polymer glass. The model gives simple and accurate estimates of practically important processing effects, and uses fitting parameters with the clear physical identity of viscoelastic constants, which follow well established trends with respect to changes in polymer composition or processing conditions.     

Theoretical model of warping deformation during self-rotating grinding of YAG wafers

YAG wafers are the most host laser crystals used for high-power lasers, which are usually machined by grinding to meet the required accuracy for laser components. Warping deformation induced by the residual stress is one of the main damages for YAG wafers after the grinding process, which will seriously decrease the service accuracy and life of the lasers. Developing theoretical model of warping deformation is of great significance to achieving the ultra-precision machining of YAG wafers. The cutting depth of single abrasive and grinding force in self-rotating grinding were investigated by considering the kinematic trajectory of abrasives, brittle-to-ductile transition, elastic mechanics, elastic deformation of the grinding wheel and strain rate effect. A theoretical model of warping deformation in self-rotating grinding of YAG wafers was developed based on the cutting depth and grinding force. The influence of subsurface damage and residual stress on warping deformation was analyzed based on the theoretical model and finite element simulation. Self-rotating grinding tests of YAG wafers were performed, and the results showed that the warping deformation decreased as the wheel rotational speed increased, and increased as the abrasive size, workpiece rotational speed and feed speed increased. The experimental results agreed well with the simulated results of the theoretical model, indicating that the theoretical model can accurately predict the warping deformation induced by self-rotating grinding process. This work will not only enhance the understanding of the essence of the wafer warping induced by ultra-precision machining, but also provide a guide for optimizing the processing parameters in self-rotating grinding of YAG wafers.