外部气体辅助注射成型制品加强筋表面凹痕实验分析

通过外部气体辅助注射成型（EGAIM）工艺对不同加强筋所造成的平板表面凹痕深度进行实验研究。单因素实验揭示了模具温度、熔体温度、注气延迟时间、注气压力及注气保压时间对不同加强筋制品表面凹痕具有不同程度的影响;正交实验发现,注气延迟时间与注气压力是影响制品表面凹痕的主要因素;在工艺参数最佳化的EGAIM中,与制品厚度比高达1.5的加强筋造成的凹痕深度（1.3 μm）小于传统注塑成型中比值为0.6所造成的凹痕深度（2.3 μm）,表明EGAIM优化工艺能有效改善较大厚度加强筋所造成的表面凹痕、提高制品设计自由度。     

外部气体辅助注塑成型制品翘曲变形耦合有限元分析

将外部气体辅助注塑成型(EGAIM)的制件作为研究对象,基于耦合有限元分析方法(CFEA),模拟仿真了EGAIM制品翘曲变形。研究发现,EGAIM只采用较低的气压(4.5 MPa),就能够达到CIM相对高压(40 MPa)的保压效果,因此,实验结果与文献结论一致。单因素试验结果表明,注气工艺参数对EGAIM制品翘曲变形的影响规律,在研究的工艺参数范围内,随着气体保压压力增加,制件的翘曲变形量呈先减小,后增大的"U"形曲线变化;随着气体保压时间的增长,制件的翘曲变形量呈减小,并逐渐变化平稳的趋势;随着气体注射延迟时间的增长,制件翘曲变形量逐渐减小,但是影响相对较小。     

适于混合气体基于k分布的灰气体加权和模型

工业燃烧环境的复杂性,使得传统的灰气体加权和（WSGG）模型很难满足气体辐射特性计算的精度要求。基于HITEMP2010数据库,利用等级相关原理将k分布法引入WSGG模型,并假设各参与性气体之间是统计非关联的,采用叠加法建立了适用于任意浓度、温度分布的混合气体WSGG模型。对四种不同燃烧条件下的非等温、非均匀混合气体的辐射换热进行了计算,将新模型计算的辐射热流和辐射源项与逐线法（LBL）及其他模型计算结果进行比较来验证新模型的有效性。结果显示新模型参数能很好地预测任意工况下混合气体的辐射特性。     

后台阶气固流动的双流体大涡模拟和二阶矩两相湍流模型的验证

用基于气体Smagorinsky亚网格应力模型和颗粒动理学模型的双流体大涡模拟（LES）和统一二阶矩两相湍流模型的RANS模拟（USM-RANS）,对后台阶气固流动进行了数值模拟。瞬态模拟结果给出各向异性两相湍流结构和颗粒弥散的发展过程。LES经过统计平均得到的颗粒速度及颗粒均方根脉动速度和USM-RANS的模拟结果与实验结果的对照表明,两种模拟结果和实验结果在定量上吻合较好。因此USM模型基本上得到了LES的验证。但是在剪切流区域中,LES得到的颗粒-气体纵向脉动速度关联的峰值大于USM-RANS模拟的结果,这就表明LES和USM-RANS模拟还需要进一步验证和改进。     

高浓度水煤浆管道气膜减阻两相流模拟及代理辅助优化

为解决高浓度水煤浆管道输送阻力大的问题,提出在水煤浆管道中通入气体,采用气膜减阻以降低管道的阻力损失。针对宾汉非牛顿流体水煤浆,基于流体体积（VOF）多相流模型,通过数值模拟研究分析了加气管关键参数对管道阻力系数的影响,并结合遗传聚合响应面模型与二次拉格朗日非线性规划（NLPQL）算法进行代理辅助优化。结果表明：在水煤浆管道中通入气体能够有效降低壁面剪切应力,气体速度与加气管直径对管道阻力系数影响较为显著,并且提升气体速度与增大加气管直径能够降低阻力系数,而管道阻力系数基本不受加气管道角度影响。优化以阻力系数最小化为目标函数,得出一组加气管参数,优化后管道阻力系数降低了0.0207,减阻率增加了16.90%,研究结果为高浓度水煤浆管道加气减阻机理及结构优化提供了理论指导。     

外加声场微小流化床中A类与C类颗粒流化的数值模拟

文章基于多相流欧拉模型,应用计算流体动力学（CFD）软件Fluent 6.3,在有无外加声场的情况下,分别对A类与C类颗粒在微小流化床（内径10mm,床高60 mm）中的颗粒分布进行了数值模拟,得到了一系列的固含率云图.模拟结果发现,在通入气体的初始阶段,C类颗粒流化出现了活塞流现象;加上声场后,上述现象消失.无声场时A类颗粒床层有较大气泡;引入声场后气泡变小.引入声场使得C类颗粒与A类颗粒有相似的固含率云图.     

微型流化床内碱金属和碱土金属对稻壳热解动力学的影响特性

通过微型流化床反应分析仪（MFBRA）研究两种典型碱金属和碱土金属（AAEM）钠与镁对稻壳热解气体生成动力学的影响,并采用模型积分法求解出4种主要气体组分（H₂、CO、CH₄与CO₂）的生成动力学参数。结果表明：不同气体组分具有不同的开始与终止释放时间,说明4种气体对应不同的生成路径和机理,高温条件和添加钠、镁离子均会提高气体生成的反应速率。采用典型气固反应动力学模型对气体生成过程进行了拟合求解,获取了气体组分在不同条件下的最概然机理函数。通过最概然机理函数求得了4种气体生成动力学参数,对比发现钠离子与镁离子降低了H₂、CO、CH₄与CO₂生成反应的表观活化能,其中CO受钠离子和镁离子的影响最为显著,进而从活化能角度证实了两种金属离子对于生物质热解特性的影响。     

非灰系统当量灰吸收系数的反演

提出了一种由气体温度场反向分析计算气体当量灰吸收系数的方法.采用段法（区域法）求解正问题,反演中采用求目标函数极小值的共轭梯度法.以直通式实验炉的测量数据为求解条件,用该计算得到了炉内气体介质当量灰吸收系数的分布.数值模拟结果表明,段法与共轭梯度法结合可以较好地反演非灰系统的当量灰吸收系数.与指数宽带段法模型结果的比较表明,反演得到的当量灰吸收系数具有与指数宽带模型相当的精度,但计算量小于宽带模型的1/10.     

甘肃油页岩红外光谱分析及热解特性

基于热重分析仪（TG）、傅里叶变换红外光谱分析仪（FTIR）和质谱分析仪（MS）三机联用对甘肃油页岩进行光谱和热解实验。通过分析光谱谱图,得到了样品中的化学成分和化学结构的相关信息。结果表明,其化学结构的特征在于相对较高量的脂肪族基团。在TG/FTIR/MS三联机上研究了甘肃油页岩的热解特性,实验结果表明：整个热解过程主要有两个阶段,即低温段和高温段。大部分的热解行为发生在低温段（400～600℃）,此阶段里油页岩的失重量占总失重量的70%,可挥发物质迅速热解,热解产生的气体有H2、H2O、CO2、CH4、CO、轻质烃等。而在高温段（600～850℃）的热解气体产率很小,失重量只占总重量的2.167%。这个阶段主要是含碳酸盐的矿物质分解而产生一定量的气体。本文主要研究两个热解阶段产生的气体。对产生气体的种类、时间和产生机理进行了研究,并得出热解的化学反应动力学参数。     

基于多级混合单元模型的最小混相压力计算方法

最小混相压力（MMP）是混相气体注入工程设计的关键参数之一,在MMP下,驱替效率达到100%。在本研究中,提出了一个基于多级混合单元模型的新方法来识别关键结线,从而计算出最小混相压力。多级混合单元模型是细管实验中连续气体注入过程中的一个离散模型。在该方法中,对于nc组分的体系,研究发现有nc＋1个相同组成的区和nc-1个关键结线。随着注入气体批次数的增加,关键结线以反序的形式出现,如初始结线首先出现,注入结线最后出现。该研究结果有助于新方法识别所有的关键结线,因此特别适用于气体注入的研究。本方法所预测的结果与细管实验的结果和其他研究者的结果相对比是十分吻合。     

Study on the packing effects of external gas‐assisted injection molding on part shrinkage in comparison with conventional injection molding

Applying gas pressure on the reverse side of the part that called external gas‐assisted injection molding (EGAIM) has the potential to solve shrinkage‐related molding problems. We investigate the packing effects of EGAIM on part shrinkage and sink mark under various rib design and compare it to that of conventional injection molding (CIM). It was found that EGAIM has uniformly distributed packing pressure within the entire mold cavity. To achieve equivalent part shrinkage, CIM requires 100 MPa packing pressure from the molding machine, whereas EGAIM requires only 9 MPa. EGAIM can further reduce part shrinkage if the gas pressure and gas packing time are both increased. EGAIM can also eliminate sink marks for rib designs of an aspect ratio (rib width /part thickness) up to 1.2, whereas CIM can achieve the same sink mark level only at an aspect ratio of less than 0.5. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

碱液下GFRP筋力学性能劣化模型研究

为研究碱液下玻璃纤维增强复合材料（GFRP）筋力学性能劣化规律,对直径为20 mm和25 mm的GFRP筋进行碱溶液分别浸泡30、90 d和180 d后的拉伸试验,得到筋体在碱液不同腐蚀时间后筋体的极限拉伸强度及弹性模量等力学性能指标;对比研究了相同直径筋体在盐溶液浸泡180 d后的力学性能变化;建立了碱液下GFRP筋剩余强度衰减模型。结果表明,相同的腐蚀龄期,碱性环境对GFRP筋力学性能劣化影响高于盐环境;碱液下GFRP筋拉伸强度随浸泡时间的增长呈下降趋势,GFRP筋前期被腐蚀速率高于后期;分析修正后的碱液下筋体剩余强度衰减模型与试验结果吻合度较高。     

A comprehensive sintering mechanism for TBCs‐Part I: An overall evolution with two‐stage kinetics

A comprehensive sintering mechanism for lamellar thermal barrier coatings was reported experimentally and theoretically in this study. To begin with, an overall property evolution with two‐stage kinetics was presented during thermal exposure. The increase in mechanical property at initial thermal exposure duration (stage‐I) was much faster with respect to that in the following longer duration (stage‐II). At the stage‐I, the in situ pore healing behavior revealed that the significant faster sintering kinetics was attributed to the rapid healing induced by multipoint connection at the intersplat pore tips, as well as a small quantity of the narrow intrasplat cracks. At the following stage‐II, the residual wide intersplat pore parts and the wide intrasplat cracks decreased the possibility of multiconnection at their counter‐surfaces, resulting in a much lower sintering kinetic. Moreover, a structural model based on the microstructure of plasma sprayed YSZ coatings was developed to correlate the microstructural evolution with mechanical property. Consequently, the model predicted a two‐stage evolutionary trend of mechanical property, which is well consistent with experiments. In brief, by revealing the pore healing behavior, this comprehensive sintering mechanism shed light to the structure tailoring toward the advanced TBCs with both higher thermal‐insulating effect and longer life time.     

接触式机械密封端面磨合过程平均膜厚预测

为研究和掌握接触式机械密封端面磨合过程平均膜厚的变化规律,采用分形参数表征磨合过程中密封端面形貌的变化,基于机械密封端面接触分形模型,通过求解端面上微空穴的体积,建立接触式机械密封端面平均膜厚预测模型。对两套B104a-70型机械密封进行磨合试验,试验密封流体为20℃清水,压力为0.5 MPa,转速为2900 r·min^-1,弹簧比压分别为0.15 MPa和0.3 MPa。研究结果表明,随着磨合过程的进行,软质环端面迅速趋于光滑,端面平均膜厚迅速减小;当进入正常磨损阶段后,两套机械密封试件的平均膜厚均稳定在0.295 μm左右。这也表明,密封端面的形貌对平均膜厚的影响较大,而弹簧比压对平均膜厚的影响较小。掌握磨合过程中端面形貌及平均膜厚的变化规律,对接触式机械密封实际运行时端面间工作特性的预测和密封端面设计具有重要意义。     

Numerical modeling assessment of mechanical effect in bovine leather drying process

Leather manufacturing involves a crucial energy-intensive drying stage in the finishing process to remove its residual moisture and generates important heat gradients. The numerical model presented in this study has been developed to describe the drying process of porous medium: bovine leather that undergoes deformation due to shrinkage. The mathematical formulation of fundamental heat, mass and momentum transfers’ phenomena during drying summarizes a two-dimensional model considering elastic behavior of bovine leather. The evolution of moisture content, temperature, and mechanical stresses during drying was discussed. The model was validated with experimental results. Numerical simulations show good agreement with experimental results. The study shows that the elastic model keeps the stress sign at the final stage of drying. The deformations induce tensional stresses near the surface equilibrated by compressive stresses within the product. They reached their maximum for normal stresses equal to 5.97 and 3.52?MPa at around 2145 and 868?s, respectively, for normal stresses along x and y directions and then decrease.     

Analysis of Effect of Pressure and Heat on Mechanical Characteristics of Butt Fusion Welding of Polyethylene Pipes

The butt fusion process is one of the most effective processes in welding polyethylene pipes. The heating stage is the most important step in this process. In this investigation, while the main objective was to reduce the final bead's size of the weld, 9 different experiments with different heat and pressure conditions and equal timing for each heating stage were defined. Numerical modeling of Finite Element Method (FEM) of the heating process was carried out in the computer software considering governing physical conditions in the weld to determine heat distribution as well as primary bead geometry. Subsequently, the model was compared with results from experimentations. Cross-cut of the formed primary beads at the end of the heating process were prepared and compared with results from the model. To review final quality of the weld and its mechanical characteristics, all samples were welded under equal pressure conditions. Cross-sections of beads formed at the final stage as well as some samples for tension test and impact test from all welded areas were prepared according to standard for determination of mechanical characteristics and then compared with each other. From mechanical strength perspective, the weld formed in 210°C and 0.18 MPa pressure demonstrated higher values. However, impact strength in the weld formed in 180°C was higher. By reducing pressure in a specified heating process, value of impact energy required to break the piece was reduced. Mechanical strength in heating condition 240°C was lower than all other cases. As for geometry of the formed bead; its size in 180°C and 0.03 MPa pressure in the first stage of the heating process was smaller than other cases.     

剪弯梁宏细观多尺度非线性有限元分析

为深入研究细观粗骨料粒径对混凝土宏观构件非线性力学性能的影响,通过生成满足Fuller级配的骨料粒径,以放置区域像素的RGB(红绿蓝)值判断骨料重叠情况,实现骨料在混凝土内部的随机分布。在此基础上,运用均匀化方法求解二维细观随机多边形骨料模型的等效弹性模量及刚度矩阵,并引入混凝土材料损伤因子模拟剪弯梁裂缝展开,由此构建混凝土多尺度非线性力学模型。结果表明,当混凝土进入塑性阶段后,骨料最大粒径对拉、压状态下损伤因子的相关性不可忽略,并直接影响宏观剪弯梁的裂缝开展及最大塑性应变大小,且有可能改变剪弯梁的破坏模式。     

Characterization of the viscoelastic behavior of the pure bitumen grades 10/20 and 35/50 with macroindentation and finite element computation

In this article, we present an identification procedure that allows the determination of the viscoelasticity behavior of different grades of pure bitumen (bitumen 35/50 and bitumen 10/20). The procedure required in the first stage a mechanical response based on macroindentation experiments with a cylindrical indenter. A finite element simulation was performed in the second stage to compute the mechanical response corresponding to a viscoelasticity model described by three mechanical parameters. The comparison between the experimental and numerical responses showed a perfect matching. In addition, the identification procedure helped to discriminate between different bitumens characterized by different asphaltene and maltene contents. Finally, the developed procedure could be used as an efficient tool to characterize the mechanical behavior of the viscoelastic materials, thanks to the quantified relationship between the viscoleastic parameters and the force–penetration response. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3440–3450, 2013     

Strain rate influence on nonlinear response of polymer matrix composites

In this article, influence of strain rate on nonlinear response of unidirectional fiber‐reinforced composites is studied. The fibers are assumed to be periodic arrays in composite structures. By studying a representative volume element, a microscopic constitutive model for characterizing macro‐mechanical response of polymer matrix composites is developed. Viscoplastic material parameters of polymer matrix are acquired by axial tension and pure shear experiment, and the proposed method is validated by experimental data. The results showed that mechanical behavior of composites, which is affected by strain rate, can be ignored in the linear stage of loading. Furthermore, with the increase in strain rate, stiffness behavior of composites tends to be stiffer at the stage of nonlinear deformation. POLYM. COMPOS., 36:800–810, 2015. © 2014 Society of Plastics Engineers