树脂膜熔渗工艺充模过程的模拟与分析

树脂膜熔渗工艺(RFI)是一种新型的复合材料成型工艺.为了更深入了解树脂膜熔渗工艺过程中充模阶段的控制参数对制品质量的影响,避免制品出现空斑、充模不完全等问题,针对该工艺过程中树脂在复杂形状预制件中的流动行为进行了分析,在达西定律基础上建立了二维等温流动控制方程,利用有限元/控制体方法建立了数值分析模型,编制了FORTRAN程序进行模拟运算,并讨论了流动过程中施加的压力对充模时间的影响.由计算实例可见,所编制程序能够很好地预测树脂膜熔渗工艺过程中充模时间、各个时刻树脂的流动前沿位置及模腔中的压力分布.     

A numerical simulation of the resin film infusion process

A numerical analysis was conducted for the resin film infusion (RFI) process using semi-cured thermosetting resin films. Mathematical models were developed for the compression of fiber and the viscosity of resin. The force balance between the fiber preform and the resin was considered to account for the deformation of fiber preform and the swell of fiber during the infusion. In an effort to locate the optimal process conditions such as the mold temperature, the fiber volume fraction, and the infusion pressure, a parametric study was carried out for the progression of resin and the infusion time for different process conditions. The numerical code developed in this study was found to be useful in determining the maximum height of vertical sections that can be infused by squeezing the liquefied resin film from the base panel.     

Variation of part thickness and compaction pressure in vacuum infusion process

In vacuum infusion (VI), it is difficult to manufacture a composite part with small dimensional tolerances, since the thickness of the part changes during resin injection. This change of thickness is due to the effect of varying compaction pressure on the upper mold part, a vacuum bag. In this study, random fabric layers with an embedded core distribution medium is used. The thickness of the composite part and resin pressure are monitored using multiple dial gages and pressure transducers; the results are compared with the model developed by Correia et al. [Correia NC, Robitaille F, Long AC, Rudd CD, Simacek P, Advani SG. Analysis of the vacuum infusion molding process: I. Analytical formulation. Composites Part A: Applied Science and Manufacturing 26, 2005. p. 1645–1656]. To use this model, two material characteristics databases are constructed based on the process parameters: (i) the thickness of a dry/wet fabric preform at different compaction pressures, and (ii) the permeability of the preform at different thicknesses. The dry-compacted preform under vacuum is further compacted due to fiber settling in wet form after resin reaches there; the part thickens afterwards as the resin pressure increases locally. The realistic model solution can be achieved only if the compaction characterization experiments are performed in such a way that the fabric is dry during loading, and wet during unloading, as in the actual resin infusion process. The model results can be used to design the process parameters such as vacuum pressure and locations of injection and ventilation tubes so that the dimensional tolerances can be kept small.     

Sizing related kinetic and flow considerations in the resin infusion of composites

Fibres used in preforms of resin transfer moulded (RTM) composites are coated with sizings, binders, and/or finishes that serve multiple purposes, including facilitating handling, protection of the fibres from compaction and process induced damage (including notching), aiding in compatibility and wetting of the fibres by the resin, and overall enhancement of the behavioural response of the composites. In this investigation four different sizings applied to S2 glass fibres are shown to significantly affect two aspects of RTM processing - resin infusion, and cure. In both cases phenomena at the microscopic level are seen to affect response variables at the macroscopic level. On a microscopic level, the behaviour of a thermosetting resin based composite is affected by the formation of interphase regions that greatly affect the cure kinetics and hence the mechanical and physical properties of the composite, which are dependent on the inter-constituent variations in local properties such as modulus and glass transition temperature. Similarly fibre-sizing-resin interactions occurring during the infusion stage affect wet-out and local flow behaviour through the development of stoichiometric imbalances in local regions. It is shown that the molecular interactions between the constituents (as initiated by the sizing) are affected by processing conditions such as temperature and rate of resin flow, and that heat evolution and resin rheology may be affected by the stoichiometric imbalances resulting from interphasial level reactions. This revised version was published online in November 2006 with corrections to the Cover Date.     

Fiber optic sensors for monitoring flow in vacuum enhanced resin infusion technology (VERITy) process

Today, with cost becoming a very important factor, alternate processes for manufacturing composite structures, wherein the cost can be reduced but having similar properties to prepreg systems are being explored. National Aerospace Laboratories, India is developing the VERITy process, which is essentially a hybridization of the VARTM and the autoclave moulding process. One of the concerns in this process, especially when making large integrated co-cured structures with varying thickness, is the knowledge of the resin flow front location at all times. A network of flow-sensors, which could provide information on the flow front location, would be very useful. This paper discusses the experimental studies carried out towards the development of a flow-sensor in the optical domain to determine the presence of resin qualitatively. Three different approaches have been attempted to detect the arrival of the resin flow front and these results are presented.     

Dynamic saturation curve measurement for resin flow in glass fibre reinforcement

A methodology is presented to determine the saturation curve of a resin/glass fabric system, during infiltration in a transparent mould under constant flow rate. Video acquisitions are transformed by image analysis into saturation level versus position and time, and coupled to inlet pressure measurements. A numerical multiphase flow model is then used to simulate the infiltration for various combinations of drainage curve parameters. The numerical parameters to describe the saturation and relative permeability are determined by response surface optimization. The drainage curve and relative permeability equations determined at one time are shown to adequately describe the entire injection process, and to be flow-rate dependent.     

Analysis of pressure profile and flow progression in the vacuum infusion process

New experimental set-ups are presented for measuring the pressure profile and fill-times in the Vacuum Infusion (VI) process. In these set-ups, the injection can either be from one of the mould faces (resulting in a rectilinear flow) or from a central port (resulting in a radial flow). From these measurements, the validity of previously reported analytical formulations is investigated. At the start of injection, the experimental results show a marked difference from analytical predictions. However, with flow progression, they change to match with analytical predictions. This phenomenon has not been observed previously and its analysis enhances the current understanding of the process physics, mainly the impact of compliance on the reinforcement thickness and flow progression.     

Out-of-autoclave cure cycle study of a resin film infusion process using in situ process monitoring

Liquid resin infusion (LRI) of textile tailored reinforcements (TRs) is increasingly applied in new processing technologies for manufacturing carbon fibre composites. This work presents a cure cycle study of an out-of-autoclave toughened resin film infusion (RFI) process as part of the examination of an alternative manufacturing process for composites. To successfully produce laminates using resin film infusion in combination with a fast-curing process, the flow behaviour of the selected resin material under changed processing conditions was investigated. The effect of processing parameters, specifically heating rates and dwell times, on resin viscosity and laminate infiltration was evaluated through experimental work and supported by in situ process monitoring. A DC-resistance sensor system was applied to track the change in resin viscosity during cure. Results showed that cure cycles with a relatively short dwell time and higher heating rate compared to an autoclave cure led to enhanced flow properties of the toughened resin system. High quality laminates, comparable to autoclave panels, were manufactured with vacuum pressure only by modifying the original vacuum bagging arrangement.     

Monitoring of resin flow in the resin transfer molding (RTM) process using point-voltage sensors

Multiple point-voltage sensors were used to monitor the mold filling stage of the resin transfer molding (RTM) process. Both lineal- and point-voltage sensors are electrical circuits in which the two poles of the sensor are closed when liquid thermoset resin arrives at the sensor location in the mold cavity. The electrical conductance of the liquid resin causes an increase in the output voltage, V_sens of the circuit. Although the gradually varying in situ data of a lineal sensor is more informative than a point-voltage sensor, lineal-voltage sensors might mislead the user if the resin covers the wires at multiple sections, or if the resin covers the wires starting from an unexpected section. Two kinds of sensors were developed: a set of similar, wrapped and compact lineal-voltage sensors acting as point-voltage sensors; and a point-voltage sensor with voltage amplification. Without this amplification, the increase in V_sens might be difficult to detect if the resin system has a low electrical conductivity and there is noise in the DAQ system. The accuracy and reliability of the new sensor system was verified by comparing the in situ sensor data with the visually recorded resin flow.     

Study on the resin temperature developments during UV imprinting process

During the imprinting process, the temperature of the UV resin increases as the phase of the resin changes from fluid into solid. During UV curing, some amount of heat is released from inside the resin and transferred into contacting materials. The heat flow is measured with photo-DSC, and other related thermal and mechanical properties of the resin. With the measured material properties, the temperature developments both inside of the resin layer and along the interfaces of the contacting materials are computed. During the UV exposure period, the thermal deformation of the mold, which directly influences the pattern distortion are investigated. Under this condition, the developments of strain and temperature inside the mold structure including the UV resin of 3-D shape are computed with the transient time scale during UV curing according to the thickness of resin layer. These computational results are expected to provide useful information for better designs of the imprinting mold and the process condition.     

Macrokinetics of the process of SHS compaction

Dependences are considered for the characteristic times of the main stages of the SHS compaction process—synthesis, compaction, and cooling — on the geometric size of a charge billet and the composition of a synthesized hard alloy. The existence is shown of two critical sizes for a starting billet which limit the region of producing a nonporous material. The presence of the critical conditions depending on the liquid phase fraction formed in the synthesis of a hard alloy is established. A satisfactory qualitative and quantitative agreement of calculated and experimental results is obtained.Institute of Structural Macrokinetics, Russian Academy of Sciences, Chernogolovka. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 63, No. 5, pp. 583–592, November, 1992.     

爆炸压实工艺参数对钢管能量与变形的影响

为了指导研究爆炸压实工艺参数的选择,通过改变爆轰速度与装药厚度来改变爆炸冲击能,重点研究爆炸压实工艺参数对钢管能量与变形的影响.研究表明:当其他工艺因素相同、仅爆轰速度不同时,将导致爆轰压力、钢管壁速度、爆炸冲击能、粉末压实能等显著不同,但钢管的变形与能量却几乎不变;当采用爆轰速度极高的黑索今炸药时,由于爆轰压力与爆炸冲击能过高,导致钢管头部被切掉;对硝酸脲炸药而言,随着装药厚度与炸药/钢管质量比增加,钢管的能量与变形、爆炸冲击能与粉末压实能单调增加.     

Analysis and minimization of void formation during resin transfer molding process

In the resin transfer molding process, residual air in the pores of fiber preform results in dry spots and microvoids in the finished product. The dry spots are usually formed due to irregular permeability of fiber mat and improper injection locations. The microvoids result from non-uniform microarchitecture of the fiber preform, and they are transported through the gap between fiber tows during infiltration of the resin. In this study, a real-time simulation/control method was proposed to actively control the formation and the transport of air voids during the mold filling. The flow equations were solved in real time to predict the change of the flow front shape. The flow front was detected by optical sensors and the control actions were taken based on the sensor signals. Through this automated simulation/control scheme, a real-time control of resin flow could effectively avoid the dry spots and minimize the formation of microvoids by modulating the injection pressure.     

Modelling microscopic flow in woven fabric reinforcements and its application in dual-scale resin infusion modelling

A physical unit cell impregnation model is proposed for the micro-scale flow in plain woven reinforcements. The modelling results show a characteristic relationship between tow impregnation speed, the surrounding local macro-scale resin pressure and the tow saturation within the unit cell. This relationship has been formulated into a mathematical algorithm which can be directly incorporated into a continuum dual-scale model to predict the ‘sink’ term. The results using the dual-scale model show a sharp resin front in inter-tow-pore spaces and a partially saturated front region in intra-tow-pore spaces. This demonstrates that the impregnation of fibre tows lags behind the resin front in the macro pore spaces. The modelling results are in agreement with two reported experimental observations. It has been shown that the unsaturated region at the flow front could increase or have a fixed length under different circumstances. These differences are due to the variation in tow impregnation speed (or the time required for the tow to become fully impregnated), the weave architecture and the nesting and packing of plies. The modelling results have also demonstrated the drooping of the inlet pressure when flow is carried out under constant injection rates. The implementation of the algorithm into a dual-scale model shows coherence with a single-scale unsaturated model, but demonstrates an advantage in flexibility, precision and convenience in application.     

Mathematical modeling of the process compaction of wood

Within the framework of the mechanics of heterophase systems a mathematical model for the process of pressing wood has been offered; this model takes account of the influence of its complex rheological properties and surface phenomena in thin interlayers of water on the change in a porous structure. With numerical methods, a study has been made of the influence of the sample’s humidity and temperature fields on the strength and quality of the material obtained. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 5, pp. 62–69, September–October, 2005.     

碳纤维／改性双马来酰亚胺复合材料RFI成型工艺数值模拟

通过在改性双马来酰亚胺树脂中添加热塑性酚酞聚芳醚砜（PES）,制备了在室温下具有良好成膜性的改性双马来酰亚胺树脂膜。改性双马来酰亚胺树脂的差示扫描量热（DSC）、凝胶时间、动态和恒温黏度研究表明,该树脂膜在初始反应温度130℃时,改性双马来酰亚胺的黏度为139．3mPa·s,黏度≤1000mPa·s和黏度≤3000mP...     

Simulation of surface roughness on the flow pattern in the casting process

In this investigation a mathematical model has been developed for simulation of the incompressible flow with free surface during mould filling. The simulation 3D melt flow with free surface is based on the SOLA-VOF technique. In the model the effects of variations parameters including heat and mass transfer as well as influences of backpressure, and friction have been considered. The solid and free boundary conditions have been modified and a new algorithm has been developed to calculate the effect of wall–slip ratio, during mold filling. In this algorithm, the effect of wall–slip ratio on the filling pattern has been modeled with an experimental function. In order to verify the computational results, a thin Al–7.5 Si% alloy plate has been poured into a sand mould with a transparent face to take into account the effect of surface roughness on flow pattern, the amount of erosion, and impact of the molten metal on the sand mould, utilizing photography. The comparison between the experimental and the simulation results of sequence filling shows a good consistency that confirms the accuracy of the model for predicting the erosion phenomenon in the moulding materials.     

High-shear granulation of high-molecular weight hypromellose: effects of scale-up and process parameters on flow and compaction properties

Context: Knowledge of the effects of high-shear granulation process parameters and scale-up on the properties of the produced granules is essential for formulators who face challenges regarding poor flow and compaction during development of modified release tablets based on high-molecular weight hypromellose (hydroxypropylmethylcellulose (HPMC)) polymers. Almost none of the existing studies deal with realistic industrial formulation.

Objective: The aim was to investigate the effects of scale-up and critical process parameters (CPPs) of high-shear granulation on the quality attributes of the granules, particularly in terms of the flow and compaction, using a realistic industrial formulation based on HPMC K100M polymer.

Methods: The flow properties were determined using flow time, Carr index, tablet mass, and crushing strength variations. The compaction properties were quantified using the ‘out-of-die’ Heckel and modified Walker models, as well as the tensile strength profile and elastic recovery. High-shear granulation was performed at different scales: 4?L, 300?L, and 600?L.

Results and conclusion: The scale itself had larger effects on the granule properties than the CPPs, which demonstrated high robustness of formulation on the individual scale level. Nevertheless, to achieve the desired flow and compaction, the values of the CPPs need to be precisely selected to fine-tune the process conditions. The best flow was achieved at high volumes of water addition, where larger and more spherical granules were obtained. The CPPs showed negligible influence on the compaction with no practical implications, however, the volume of water addition volume was identified as having the largest effects on compaction.     

Modeling the impact of capillary pressure and air entrapment on fiber tow saturation during resin infusion in LCM

Traditionally, capillary effects have been neglected when modeling the filling stage of Liquid Composite Molding processes. This simplification is justified because the inlet resin pressures are much higher than the capillary pressure. This simplification is also acceptable when impregnating fabrics in which their fiber tows saturate at the same rate as the bulk preform. However, this assumption is questionable for fabrics that exhibit dual scale in which the fiber tows saturate at a much slower rate than the bulk preform. In such cases, the capillary pressure can influence the time to saturate a fiber tow significantly and impact the overall impregnation dynamics. Since the flow front velocity inside the fiber tows is significantly smaller than the flow around them, it is important to include the capillary pressure that may aid the saturation of the tow. In this paper, we modify our existing simulation that can predict the filling of the bulk preform and the saturation of the fiber tows to include the capillary forces at the fiber tow level. Important parameters are identified and grouped in non-dimensional form. A parametric study is conducted to examine the role of these dimensionless parameters on the overall tow saturation levels. The modeling is extended to include the effect of entrapped air inside the tows on the overall saturation of the preform. An experimental technique using the optical properties of vinyl ester and glass fiber was used to qualitatively validate the proposed model.