Characteristics of hydrostatic bearing/seal parts for water hydraulic pumps and motors. Part 1: Experiment and theory

In this paper, the load-carrying capacity, power losses and stiffness of disk-type hydrostatic thrust bearings including the case of eccentric loading are discussed theoretically. The numerical analysis method is established based on a two-dimensional elastohydrostatic problem with an elastic deformation model, which is extended to adapt it for a non-axisymmetric load acting on the thrust bearing. The bearing is made of a combination of stainless steel/stainless steel and stainless steel/plastics. For the elastic materials, the maximum stiffness derived from, i.e., minimum film thickness is, larger than that of the rigid material in the range of a large ratio of pocket pressure and a hydrostatic balance ratio of over unity, which is defined as the ratio of the load to the maximum hydrostatic load-carrying capacity. The maximum load-carrying capacity and minimum power loss can exist in the domain of the hydrostatic balance ratio over unity for the case of the bearing consisting of elastic/rigid materials, in comparison with that composed of the same rigid materials. For the case of water, the power loss due to leakage flow is slightly larger but that due to frictional torque is much smaller than that in the case of hydraulic oil. Then, the total power loss is much smaller than that of hydraulic oil.     

1991年我国工程塑料进展

根据国内有关工程塑料的文献,报道1991年国内热塑性树脂及塑料、热固性树脂及塑料、成型加工技术的进展,以及工程塑料在国民经济各个领域中的研究开发和应用。     

操作参数对玻纤毡增强复合材料流动成型的影响

研究了玻纤毡增强热塑性复合材料(GMT)流动成型过程中模腔压力和材料流动方向对制品力学性能和纤维取向的影响。研究表明：随着压力提高，弯曲强度和模量同步增加；但压力超过18MPa后，性能变化不明显。随布料面积分数减小，单轴拉伸流动成型将导致沿流动方向和垂直流动方向强度及模量差异变大，纤维取向严重；但双轴拉伸流动成型得到的制品各方向性能较均匀，基本呈现各向同性。     

Investigation of the relationships of process parameters,molten pool geometry and shear strength in laser transmission welding of polyethylene terephthalate and polypropylene

This study concerns the laser transmission welding (LTW) of polyethylene terephthalate (PET) and polypropylene (PP) which are widely used in the automotive, aerospace and medical industries. The relationships of process parameters, molten pool geometry (both width and depth) and shear strength (SS) in LTW process are systematically investigated through finite element method (FEM), response surface methodology (RSM) and experiments. Thereinto, the relationships between the molten pool depths to width (D/W) ratio and SS are firstly investigated. Firstly, a three-dimensional thermal model is developed to simulate the temperature field and molten pool geometry of the LTW process. The simulation results are confirmed by experiments. Then RSM is utilized to design the experiments and establish the mathematical relationships between the process parameters and molten pool geometry based on the simulation results. The interaction effects of the process parameters on the molten pool geometry are analyzed. Finally, the simulation results are further used for searching the relationships between the molten pool D/W ratio and the SS (from tensile experiments). The maximum value of the SS and the corresponding molten pool D/W ratio is found. The result reveals that the molten pool D/W ratio has a significant influence on the SS. Moreover, this finite element model can also play a commendable guiding role in the LTW experiments with acceptable accuracy.     

汽车前端框架轻量化进展

简要回顾了汽车前端框架设计方案轻量化的演变历史,基于前端框架设计指标、虚拟仿真和材料方案三个方面轻量化现状的详细描述,论证了前端框架日趋精益轻量化的趋势。     

热塑性EVA半导电屏蔽料的研制

研究了基体树脂、导电材料、润滑剂、抗氧剂对热塑性乙烯-乙酸乙烯共聚物(EVA)半导电屏蔽料性能的影响,确立了EVA半导电屏蔽料配方:EVA100份,导电炭黑55份,润滑剂8.5份,抗氧剂0.80份。对产物性能的表征表明,该半导电屏蔽料20℃时的体积电阻率为48.3Ω·cm,拉伸强度为14.2MPa。     

Syntheses and characterization of novel biostable polyisobutylene based thermoplastic polyurethanes

The synthesis of polyisobutylene (PIB) based thermoplastic polyurethanes (TPU) with enhanced mechanical properties have been accomplished using poly(tetramethylene oxide) (PTMO) as a compatibilizer. PIB TPUs with Shore 60-100 A hardness were prepared by employing PIB diols (hydroxyallyl telechelic PIBs) for the soft segment and 4,4′-methylenebis(phenylisocyanate) (MDI) and 1,4-butanediol (BDO) for the hard segment. The TPUs exhibited number average molecular weight (M_n) in the range of 83,000-110,000 g/mol with polydispersity indices (PDIs) = 1.8-3.1. These TPUs, however, were inferior compared to commercial TPUs such as Pellethane™ (Dow Chemical Co.) as they exhibited low tensile strength (6-15 MPa) and/or ultimate elongation (30-400%). Processing of the harder compositions was also difficult and some could not be compression molded into flat sheets for testing. Differential Scanning Calorimetry (DSC) showed the presence of high melting (≥200 °C) crystalline hard segments suggesting longer - MDI-BDO - sequences than expected based on the stoichiometry. Easily processable TPUs with excellent mechanical properties (tensile strength up to 40 MPa, ultimate elongation up to 740%) were obtained by incorporating PTMO in the soft segment. Examination of PIB-PTMO TPUs with varying hard: soft compositions (20:80, 35:65 and 40:60 wt:wt) and Shore hardness (60 A, 80 A and 95 A) indicated that substituting 10-30 wt% of PIB diol with PTMO diol is sufficient to reach mechanical properties similar to Pellethanes.     

Experimental and numerical prediction of effect of frequency on bending fatigue performance of polyamide 66/hectorite nanocomposite

An increased use of thermoplastics in components and structures that are subjected to cyclic loads necessitates a specific attention to variables that affect the hysteretic heating. Hysteretic heating effect in polyamide 66/hectorite nanocomposite has been investigated under bending strain control mode using a custom-built bending fatigue test setup in a laboratory environment. Dynamic mechanical analysis (DMA) results revealed a considerable rise in loss modulus with a decrease in frequency from 1 to 0.1?Hz irrespective of the temperature of the specimen. Alternatively, a reduction in fatigue test frequency from 2 to 0.5?Hz resulted in a significant decrease in cyclic softening. Fatigue behaviour predicted from DMA results using coupled structural/thermal finite element analysis is fairly in agreement with the experimental one. An accelerated crack initiation at decreased specimen temperature and high cyclic steady state stress reduced the fatigue life at 0.5?Hz compared with 2?Hz.     

1997～1998年我国塑料工业进展

根据１９９７年７月～１９９８年６月国内有关合成树脂和塑料工业的文献资料,对通用热塑性树脂（聚乙烯、聚丙烯、聚氯乙烯、聚苯乙烯、ＡＢＳ）、热固性树脂（酚醛树脂、环氧树脂、聚氨酯、不饱和聚酯、双马来酰亚胺）、工程塑料（尼龙、聚碳酸酯、聚甲醛、热塑性聚酯、聚苯醚）、特种工程塑料（聚苯硫醚、液晶聚合物、聚醚醚酮、聚砜、聚醚砜等）、其它树脂（聚酰亚胺、有机氟树脂、丙烯酸树脂、降解塑料、功能树脂）等在合成工艺、树脂改进、性能研究、新产品开发方面的研究成果进行了全面系统的介绍。同时介绍了成型加工与设备、塑料助剂、应用开发等领域的研究热点和最新进展,充分展示了我国１９９７～１９９８年合成树脂和塑料工业的进展。     

Modeling Foam Growth in Thermoplastics

Foaming of thermoplastic polymers is a complex process. Here models are presented that address the viscoelastic character of the thermoplastic melt during the expansion phase of foam development. Each cell is described as consisting of a spherical gas bubble surrounded by a spherical shell of polymer containing dissolved gas (see Figure).