玻璃微珠增强超高分子量聚乙烯的耐磨耐热性能研究

采用热压成型工艺制备了偶联玻璃微珠填充的超高分子量聚乙烯(UHMWPE)复合材料,通过万能材料试验机、洛氏硬度计考察了玻璃微珠含量对复合材料力学性能、硬度的影响,对复合材料进行了X射线衍射分析(XRD)、差示扫描量热分析(DSC)和静态热机械分析(TMA),通过热变形、维卡温度测定仪考察了玻璃微珠含量对复合材料维卡软化温度的影响,通过高速环块磨损试验机和自制砂浆磨损水浴试验装置考察了玻璃微珠含量对复合材料耐摩擦磨损性能的影响,通过扫描电子显微镜观察复合材料磨损表面形貌并分析了其磨损机理.结果表明:偶联玻璃微珠在UHMWPE体系中起填充增强作用,能有效提高复合材料的硬度、维卡软化温度、熔点和玻璃化转变温度,从而降低材料的摩擦系数与磨耗.维卡软化温度最多能提高12.5%,而磨损质量最多能降低62%,玻璃微珠质量分数在5%~20%之间效果明显,材料的力学性能随玻璃微珠的含量增加而有所下降.     

Flow disturbance in polymer melt behind an obstacle

In polymer processing weld-lines occur when a polymer melt is separated and then reunited. The internal structure of a weld-line region is determined by the rheological state of the reunited melt streams. An experimental investigation of the region of interest within the mold is almost impossible. Thus, computer simulation is necessary to examine weld-lines. This paper presents a detailed analysis of the flow behavior at a weld-line interface which was caused by a flow obstacle. The results show a gradual increase of the velocity within a short distance behind the obstacle which coincides with a short weld-line determined by the advancement of the flow fronts obtained from conventional mold filling studies. However, based on the residence time history of the melt there is a weld-line over the full length of the part. Its formation mechanism was additionally described by experimental filling studies by the sandwich injection molding technique. In conclusion, the formation of the weld-line should be determined not only by the flow fronts, but also by the thermo-rheological history of the reunited melt streams. Received: 18 September 1997 Accepted: 3 March 1998     

聚合物注射成型流动残余应力的数值分析

建立了可压缩黏弹性聚合物熔体在薄壁型腔中充模/保压过程中非等温、非稳态流动 的数学模型,用数值方法实现了注射成型过程中流动应力和取向建立及松弛过程的模拟,研 究了熔体温度、模具温度和注射速率等工艺条件对分子冻结取向的影响,取得了与实验相符 的结果.     

The role of viscoelasticity in polymer sintering

An experimental study for polymer sintering has been carried out using pairs of powder particles. Although in many cases Newtonian sintering models successfully describe polymer sintering, they predict a faster coalescence rate than that observed with the polypropylene copolymer resins used in this study, indicating that factors other than the surface tension and the viscosity play a role in polymer sintering. Observations of coalescence under the microscope and rotational molding experiments suggest that melt elasticity slows down the process. Based on these findings, a mathematical model describing the complete polymer sintering process for viscoelastic fluids has been developed. The approach was similar to that of Frenkel (1945) and the convected Maxwell constitutive equations were used together with the quasi-steady state approximation. The proposed viscoelastic sintering model is capable of predicting the sintering rate slowdown observed in this study. Received: 18 August 1997 Accepted: 30 March 1998     

注塑模充模过程动态分析

注塑成型是利用型腔模制造理想制品主要的成型加工方式 ,塑料熔体的流动行为将直接影响着最终塑件的质量 ,塑料熔体在三维薄壁型腔内的流动属于带有运动边界的粘性不可压缩流体的流动 ,本文针对塑料注塑成型特点 ,经过量纲分析和引入合理而必要的假设 ,得到了适合于充模分析的数学模型。控制方程的求解主要包括三个阶段 :压力场、温度场和流动前沿位置的确定。数值求解采用有限元法求解压力场、有限差分法求解温度场、并利用控制体积法跟踪熔体前沿 ,实现了充模过程的动态模拟     

微沟槽结构注塑成形的充型过程计算方法

微注塑成形制造方法适合于热塑性材料微小型器件大批量加工,对微注塑关键步骤——充型进行分析计算,有助于微注塑工艺参数和模具结构优化。目前研究表明,微尺度聚合物熔体流动与常规流动存在显著差异,采用常规尺度流动计算分析工具会带来较大偏差。本文以开源计算代码OpenFOAM为基础,综合由实验获得的熔体表面特性规律和粘度变化规律等,采用面向对象编程方法构建了熔体填充微结构型腔流动过程的计算模块,以微流体器件中的典型微结构——微沟槽注塑充型过程为例进行数值模拟,分析了表面力和粘度作用对其注塑充型填充率的影响。     

气体辅助注射成型气体穿透界面计算模型研究

气体辅助注射成型由于其显著的优越性得到了迅速地推广应用，对气辅成型过程的计算机模拟成为当前研究的热点课题。针对气辅成型充填模拟的关键问题－气体穿透界面的求解，首次提出了采用匹配渐近展开法求解气体穿透厚度的计算模型，初步的模拟计算获得了与实验一致的结果。     

Analysis of Composite Molding Using the Homogenization Method

In this paper, we present an application of the homogenization method to the analysis of Resin Transfer Molding (RTM) and Structural Reaction Injection Molding (SRIM). RTM and SRIM are relatively new molding processes for manufacturing continuous fiber reinforced polymer composites. First, the mold flow is analyzed. In the molding process, the resin experiences significant temperature changes as it fills the mold and forms a free boundary with air as it pushes out the air. In addition, the flow domain is the mold cavity packed with fiber perform, which is a porous medium. Here, the homogenization method is used to model the non-isothermal flow through porous media with free boundaries. A computer program is developed which is capable of simulating a three-dimensional mold flow using the finite element approximation. An example is provided for a three-dimensional part. Then, an analysis of the residual stress developed in the curing stage is given. The curing stage starts when the mold is completely filled and it involves chemical reaction and large temperature variation. In curing, the resin part undergoes larger volume shrinkage than the fiber part, and the residual stresses are developed due to this volume mismatch. In some cases, these stresses are large enough to cause micro-cracking and to exhaust the strength of the material. Here, a brief discussion of the application of the homogenization method to a residual stress analysis is given and one example is provided.     

注塑模流道优化设计

在注塑成型过程中，浇注系统的设计合理与否对产品质量和效益都有决定性的影响，给出了基于流动模拟的流道平衡算法。该算法在流道、型腔布置及浇口尺寸确定后自动调整流道尺寸直到满足熔体流动平衡约束，通过一个三型腔家族式模具验证了该算法。     

Flowing simulation of injection molded parts with micro-channel简

In the micro-molding of component with a micro-sized channel, the ability for polymer melt to flowing into the micro-channel in a macro-sized part is a big challenge. The multidimensional flow behaviors are included in the injection molding the macro-component with a micro-channel. In this case, a simplified model is used to analyze the flow behaviors of the macro-sized part within a micro-channel. The flow behaviors in the macro-cavity are estimated by using the finite element and finite difference methods. The influence of the injection rate, micro-channel size, heat transfer coefficient, and mold temperature on the flowing distance is investigated based on the non-isothermal analytic method. The results show that an increase in the radius of the micro-channel and mold temperature can improve effectively the flowing distance in the micro-channel.     

Dynamic shearing resistance of molten metal films under high pressures and extremely high shearing rates

In the present study plate-impact pressureshear experiments have been conducted to study the dynamic shearing resistance of molten metal films at shearing rates of approximately 10⁷ s⁻¹. These molten films are generated by pressure-shear impact of relatively low melt-point metals such as 7075-T6 Al alloy with high hardness and high flow-strength tool-steel plates. By employing high impact speeds and relatively smooth impacting surfaces, normal interfacial pressures ranging from 1–3 GPa and slip speeds of over 100 m/s are generated during the pressure-shear loading. The resulting friction stress (∼100 to 400 MPa) combined with the high slip speeds generate conditions conductive to interfacial temperatures approaching the fully melt temperature regime of the lower melt-point metal (7075-T6 aluminum alloy) comprising the tribo-pair. During pressure-shear loading, laser interferometry is employed to measure normal and transverse motion at the rear surface of the target plate. The normal component of the particle velocity provides the interfacial normal traction while the transverse component provides the shearing resistance of the interface as it passes through melt. In order to extract the critical interfacial parameters, such as the interfacial slip-speed and interfacial temperatures, a Lagrangian finiteelement code is developed. The computational procedure accounts for dynamic effects, heat conduction, contact with friction, and full thermo-mechanical coupling. At temperatures below melt the flyer and target materials are described as an isotropic thermally softening elastic-viscoplastic solid. For material elements with temperatures in excess of the melt point, a purely Newtonian fluid constitutive model is employed. The results of this hybrid experimental-computational study provide insights into the dynamic shearing resistance of molten metal films at high pressures and extremely high shearing rates.     

Dynamics of solid-melt front migration from a reaction–diffusion model

Using physical experiments we investigated the evolution of thermally driven melt patterns in a semi-infinite solid crystalline phase subjected to uniform heating from one side, maintaining melting temperature. We treat the melt initiation phenomenon theoretically in the perspective of two-phase interactions on the microscopic level, and propose a new reaction–diffusion model based on the prey–predator dynamics. This model predicts the fractal behavior of melt fronts observed in the experiments.     

High-speed frictional slip at metal-on-metal interfaces

In this study plate-impact pressure-shear friction experiments are employed to investigate dynamic slip resistance and time-resolved growth of molten metal films during dry metal-on-metal slip under extreme interfacial conditions. By employing a tribo-pair comprising of a hard tool-steel against a relatively low melt-point metal (7075-T6 Al alloy), interfacial normal stress of up to 5 GPa and slip speeds of approximately 250 m/s have been achieved. These extreme interfacial conditions are conducive to the development of molten metal film at the tribo-pair interface. A Lagrangian finite element code is developed to understand the evolution of the thermo-mechanical fields and their relationship to the observed slip response. The code accounts for dynamic effects, heat conduction, contact with friction, and full thermo-mechanical coupling. At temperatures below the melting point of the tribo-pair materials are described as isotropic, thermally softening, elastic–viscoplastic solids. For material elements with temperatures in excess of the melt temperature a purely Newtonian fluid constitutive model is employed.     

罐内爆炸成型技术在修复结晶器中的实验研究

随着连铸生产的发展,易损件结晶器铜管的消耗越来越大,使用报废的铜管结晶器越积越多.为重复利用结晶器,采用罐内爆炸成型技术做修复实验.针对200×200规格的结晶器铜管修复选择参数为:导爆索间距t=20mm;导爆索距离铜管外表20mm;炸药筒长度依据铜管长度加100mm确定.依据方案给出具体实验案例,成型后的结晶器经过测量表明修复后的结晶器完全可以再次利用.尤其,为实现厂内、连续、方便的修复结晶器,提出在1kgTNT当量爆炸罐体内实现.实验表明结晶器可以实现厂内便捷修复.     

Mechanical response of a short fiber-reinforced thermoplastic: Experimental investigation and continuum mechanical modeling

The present work can be regarded as a first step toward an integrated modeling of mold filling during injection molding process of polymer composites and the resulting material behavior under service loading conditions. More precisely, the emphasis of the present paper is laid on how to account for local fiber orientation in the ground matrix on the prediction of the mechanical response of the composite at its final solid state. To this end, a set of experiments which captures the mechanical behavior of an injection molded short fiber-reinforced thermoplastic under different strain histories is described. It is shown that the material exhibits complex response mainly due to non-linearity, anisotropy, time/rate-dependence, hysteresis and permanent strain. Furthermore, the relaxed state of the material is characterized by the existence of an equilibrium hysteresis independently of the applied strain rate. A three-dimensional phenomenological model to represent experimentally observed response is developed. The microstructure configuration of the material is simplified and assumed to be entirely represented by a distributed fiber orientation in the ground matrix. In order to account for distributed short fiber orientations in a continuum sense, a concept of (symmetric) generalized structural tensor (tensor of orientation) of second order is adopted. The proposed model is based on assumption that the strain energy function of the composite is given by a linear mixture of the strain energy of each constituent: an isotropic part representing Phase 1 which is essentially related to the ground matrix and an anisotropic part describing Phase 2 which is mainly related to the fibers and the interphase as a whole. Hence, taking into account the fiber content and orientation, the efficiency of the model is assessed and perspectives are drawn.     

Co-continuity interval in immiscible polymer blends by dynamic mechanical spectroscopy in the molten and solid state

The work focuses on the detection of the co-continuity window in immiscible polymer blends. The purpose of the paper is to describe how rheological techniques can help to evaluate the composition range of the co-continuous morphology through the study of a particular system: PEO/PVDF-HFP. First, the blends were characterized by selective dissolution experiments and SEM observations. Then the ability of dynamic mechanical spectroscopy to detect the co-continuity was investigated in the melt and in the solid state. The evolution of the storage modulus of molten blends with their composition at a constant low frequency gives information about the co-continuity interval, especially as far as the onset of the continuity of the PEO phase is concerned. Then the immiscibility of the polymers and the continuity of PVDF-HFP as a function of blend composition have been highlighted by means of dynamic mechanical spectrometry below the melting point of PVDF-HFP. Comparison with results from classical methods shows fair agreement.This paper was presented at the first Annual European Rheology Conference (AERC) held in Guimarães, Portugal, September 11-13, 2003.     

Flow regimes of a high-viscosity polymer mass bounded by the free surface in the region of drastic expansion of a channel

Flow regimes of the polymer mass filling cylindrical variable-section molds are studied by means of the numerical solution of the problem of a nonlinear viscoplastic fluid flow with a free surface in cylindrical channels of geometrically complicated shapes. A mathematical formulation of the problem is given, and factors affecting the molding process are analyzed. Numerical experiments performed in a wide range of problem parameters make it possible not only to elucidate the specific features of the hydrodynamic behavior of the free surface of the moving polymer mass, but also to establish the existence of two flow regimes depending on the ratio of the generalized Reynolds number to the Froude number. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 1, pp. 81–88, January–February, 2008.     

Elastic behavior of saturated porous materials under undrained freezing

The elastic behavior of saturated porous materi- als under undrained freezing is investigated by using a poro- mechanical approach. Thermodynamic equilibria are used to describe the crystallization process of the partially frozen solution in bulk state and confined state in pores. By phase transition at freezing, fusion energy, thermal contraction of solid, solution and ice crystals, volume changes of crystallization build up remarkable pore pressure that induces expansion or shrinkage of solid matrix. Owing to the lower chemical potential when pore water mixes with salts, fewer ice forms in pores. Penetration of ice into the porous materials increases the capillary pressure, but limits effect on the pore liquid pressure and the strain of solid matrix. On the contrary, the pore pressure induced by solution density rises as salt concentration increases and causes significant shrinkage of solid matrix.     

Compression creep of molten poly (butylene terephthalate)

Viscoelastic parameters of poly(butylene terephthalate) melt in compression creep have been measured in an Instron Capillary Rheometer. Bulk compression creep complianceB(t) shows plateau regions in the molten state and in the melt crystallized state, both decreasing with increasing stress. Shifting ofB(t) curves provides master curves suitable for analyzing the total (superposed elastic and viscous) bulk compression behavior.Volume viscosity decreases with both increasing stresses and compression rates but seems to be independent of temperature. Its values are larger than those from constant compression rate experiments, possibly due to the presence of elastic effects.     

Non-isothermal transient flow and molecular orientation during injection mold filling

The properties of injection molded products are directly related to the microstructure which in turn strongly depends on the flow kinematics and thermal history of the polymer melt during the filling process. In this study the mold filling process has been analyzed by using an FEM-code (FIDAP) to solve the equation of continuity, momentum, and energy under transient and non-isothermal conditions. As constitutive relation for a purely viscous fluid, the Bird-Carreau and Arrhenius model was chosen. The phenomenon at the flow front, its flow kinematics, and its significant implication on the microstructure of the part have been investigated in detail. Computed particle tracking showed good agreement with experiments under real processing conditions. Furthermore, a rather simple but effective and useful method for predicting the orientation distribution in an injection molded part was proposed. It was found that the local deformation near the solid wall may be considered as the main source for a typical layer of high orientation on the surface of the part. Received: 1 December 1999 Accepted: 9 August 2000