An experimental investigation of class A surface finish of composites made by the resin transfer molding process

Achievement of high class surface finish is important to the high volume automotive industry when using the resin transfer molding (RTM) process for exterior body panels. Chemical cure shrinkage of the polyester resins has a direct impact on the surface finish of RTM molded components. Therefore, resins with low profile additives (LPA) are used to reduce cure shrinkage and improve surface quality of the composite parts. However, little is known about the behaviour of low profile resins during RTM manufacturing and their ultimate effects on the surface quality of molded plaques. In this work, the effects of controlled material and processing parameters on the pressure variations, process cycle times and ultimately on the surface quality of RTM molded components were investigated. Taguchi experimental design techniques were employed to design test matrices and an optimization analysis was performed. Test panels were manufactured using a flat plate steel mold mounted on a press. Pressure sensors were inserted in the mold cavity to monitor pressure variations during different stages of cure and at various locations in the mold cavity. It was found that a critical amount of LPA (10%) was required to push the material against the mold cavity and to compensate for the resin cure shrinkage. A significant increase in pressure was observed during the later stages of resin cure due to the LPA expansion. The pressure increase had a significant effect on the surface roughness of the test samples with higher pressures resulting in better surface finish. A cure gradient was observed for low pressure injections which significantly reduced the maximum pressure levels.     

Experimental investigation of three-dimensional woven composites

This paper summarizes an extensive experimental study of composites reinforced with three-dimensional woven preforms subjected to tensile, compressive and in-plane shear loading. Three innovative three-dimensional woven architectures were examined that utilize large 12 K and 24 K IM7 carbon tows, including two ply to ply angle interlock architectures and one orthogonal architecture. Additionally, a two-dimensional quasi-isotropic woven material was evaluated for comparison. Loads were applied in both the warp and the weft directions for tensile and compressive loading. Digital image correlation was used to investigate full field strains leading up to quasi-static failure. Experimental results including ultimate strengths and moduli are analyzed alongside representative failure modes. The orthogonal woven material was found to have both greater strength and modulus in tension and compression, though a ply to ply woven architecture was found to outperform the remaining three-dimensional architectures. Recommendations are made for improving the manufacturing processes of certain three-dimensional woven architectures.     

Reactive extrusion: A useful process to manufacture structurally modified PLA/o-MMT composites

In the present work, poly(lactic acid) (PLA) sheets reinforced with organically modified montmorillonite (o-MMT) were manufactured through reactive extrusion-calendering using a masterbatch approach in a pilot plant. Reaction monitoring analysis suggests the occurrence of premature reactions between o-MMT and the reactive agent; lowering further structural changes in the polymeric matrix. While calendered sheets exhibited a homogenous and preferential distribution of clay particles in MD, the coexistence of mixed structures, involving tactoids of various sizes as well as intercalated clay layers was observed. However, a higher and finer dispersion of o-MMT particles was achieved through clay–polymer tethering via chain extender molecules. Under tensile loading, the aforementioned clay dispersion enhanced multiple cavitation processes, notably improving PLA shear flow.     

Dispersion of carbon nanofibres in a low viscosity resin by calendering process to manufacture multiscale composites by VARIM

The use of mechanical processes, such as calendering, is an interesting method to disperse carbon nanofibres because this technique avoids the use of organic solvents needed in chemical methods. Variations of the process are used by researchers, and further study of the effect of the calendering parameters is still needed. For this reason, the effectiveness of the dispersion of several percentages of carbon nanofibres (0.5–3 wt.%) in epoxy resin using different parameters of the calendering process has been studied in this work. Carbon nanofibres/epoxy nanocomposites and non-cured nanoreinforced mixtures have been characterised. This study showed that the dispersion was enhanced with a Sequential method. Density and thermomechanical properties of nanocomposites manufactured by the selected calendering method were evaluated. The viscosity of the CNF/epoxy mixtures at different percentages of nanoreinforcement was adequate to use them as a matrix in multiscale reinforced composites.     

复合式土壤源VRV系统的试验研究

介绍一种可以分别采用土壤源或冷却塔＋锅炉作为水源VRV机组冷热源的复合式土壤源VRV试验系统,并分别对该系统的夏季制冷和冬季制热进行测试,比较土壤源VRV工况和冷却塔＋锅炉VRV工况的主机COP,分析土壤源VRV系统的节能性。试验结果表明,土壤源工况时,水源VRV机组的夏季和冬季的主机平均COP分别为6.73和4.01;冷却塔＋锅炉工况时,水源VRV机组夏季和冬季的主机平均COP分别为4.94和4.71。同时分析系统的一次能源利用率,认为定频水泵和天然气耗能较高导致系统PER偏低,为进一步提高土壤源VRV系统的节能性提供指导。     

Dispersion of carbon nanofibres in a low viscosity resin by calendering process to manufacture multiscale composites by VARIM

The use of mechanical processes, such as calendering, is an interesting method to disperse carbon nanofibres because this technique avoids the use of organic solvents needed in chemical methods. Variations of the process are used by researchers, and further study of the effect of the calendering parameters is still needed. For this reason, the effectiveness of the dispersion of several percentages of carbon nanofibres (0.5–3 wt.%) in epoxy resin using different parameters of the calendering process has been studied in this work. Carbon nanofibres/epoxy nanocomposites and non-cured nanoreinforced mixtures have been characterised. This study showed that the dispersion was enhanced with a Sequential method. Density and thermomechanical properties of nanocomposites manufactured by the selected calendering method were evaluated. The viscosity of the CNF/epoxy mixtures at different percentages of nanoreinforcement was adequate to use them as a matrix in multiscale reinforced composites.     

Experimental and numerical study of a new hybrid process: multi-point incremental forming (MPIF)

Multi-Point Incremental Forming (MPIF) process is a new hybrid process that combines two common manufacturing methods. These are Multipoint Forming (MPF) and Incremental Sheet Forming (ISF) processes. In this study, an experimental set-up, based on a MP reconfigurable die, was designed and manufactured to explore the flexibility of this innovative process and its potentialities to produce complex parts using the same tools. The obtained results have indicated that this novel technique, that doesn’t require costly equipments, is an effective approach to manufacture multitude of parts with different shapes. Moreover, it has been shown that the parts geometrical accuracy as well as thickness distribution are enhanced compared to the conventional ISF process and that the geometrical defects, called ‘dimples’ and caused by the pins’ ends, are significantly reduced and almost eliminated after the insertion of a rubber piece between the reconfigurable die and the blank sheet. On the other hand, the effect of the size and geometry of the rectangular pins on the geometrical accuracy and the dimpling defect has been studied using a finite element analysis.     

Experimental investigation of a novel hybrid metal–composite joining technology

An integrative joining technology between steel and carbon fibre-reinforced plastics (CFRP) is presented for lightweight design applications in aviation industries. Small spikes are welded onto metal surfaces via “cold-metal transfer” which then build up a fibre-friendly fixation through form-closure with co-cured composites. Manufacture of such reinforced hybrid specimens and results of static tensile testings are discussed. Video-extensometry is applied to characterize the hybrid joints in terms of strength and failure history. Comparisons with epoxy bonded references show improvements in ultimate load, maximum deformation and energy absorption capacity.     

Thermomechanical investigation of unidirectional carbon fiber-polymer hybrid composites containing CNTs

In this research, the thermoelastic response of unidirectional carbon fiber (CF)-reinforced polymer hybrid composites containing carbon nanotubes (CNTs) are analyzed using a physics-based hierarchical micromechanical modeling approach. The developed model consists of a unit cell-based scheme along with the Eshelby method which can consider random orientation, random distribution, directional behavior, non-straight shape of CNTs and interphase region generated due to the non-bonded van der Waals interaction between a CNT and the polymer matrix. The predictions are compared with the experimental data available in the literature and a quite good agreement is pointed out for the fibrous polymer composite, CNT-polymer nanocomposite and fiber/CNT-polymer hybrid composite systems. The influences of several factors, including volume fraction, aspect ratio, off-axis angle and arrangement type of CFs as well as CNT volume fraction on the thermoelastic behavior of CF/CNT-polymer hybrid composites are examined in detail. The results indicate that the transverse CTE of a unidirectional CF-reinforced composite is significantly improved due to the addition of CNTs, while the hybrid composite CTE in the longitudinal direction is negligibly affected by the CNTs. Also, it is found that the role of CNT in the hybrid composite thermoelastic behavior becomes more prominent as the CF aspect ratio decreases.

     

短切碳纤维增强尼龙66复合材料注塑成型工艺模拟

采用毛细管流变仪和自制小型模具,对不同质量分数的短切碳纤维增强尼龙66(CF/PA66)复合材料颗粒进行了熔体流动性能分析和注塑成型工艺模拟,实现少量原料快速模拟CF/PA66的注塑成型工艺参数。研究表明:短切CF/PA66复合材料的熔体属于幂律流体,熔体黏度随温度、压力和CF质量分数变化显著,当温度和压力升高到临界值后熔体流变特性从假塑性区进入牛顿区;随着CF质量分数的增加,CF/PA66复合材料适宜成型温度提高。实验中PA66、CF质量分数为10wt%和20wt%的CF/PA66三种颗粒的适宜成型温度分别为278~285℃、280~287℃、290~298℃,通过对熔体进行Bagley压力校正,三种颗粒适宜成型的最小注塑压力分别为24.3MPa、29.4MPa、35.1MPa;将流变仪模拟所得参数应用于注塑成型工艺,所得样品的拉伸强度与流变仪制备的试样非常接近,进一步说明了毛细管流变仪模拟CF/PA66注塑成型过程的可行性和有效性,为其注塑成型工艺条件提供了理论依据。     

Experimental investigation of novel hybrid phase change materials

Clean Technologies and Environmental Policy - The novel potential of hybrid phase change materials (PCM) as a mix of animal fat, specifically pork fat (lard), with edible and waste oil from the...     

On experimental investigation of failure process of woven-fabric composites

In this paper an experimental investigation is performed to describe the fracture behavior and failure mechanisms of woven fabrics composites, under static loading, using a compact tension test (CT). We studied the development of the different damage phases using the digital image correlation and the compliance method. The crack length was estimated at in the front of the notch tip. The approach of the effective crack length via the compliance procedure was compared to the measures of the damage in the epoxy/glass fiber composite obtained by the digital image correlation (DIC).     

Experimental investigation of the working process in a vortex tube

The authors present the results of an experimental investigation of the temperature separation process in the chamber of an energy separation vortex tube.     

A hybrid solar air conditioner: Experimental investigation

The removal of moisture from the supply air using conventional air conditioners (A/C) represents a considerable portion of the air conditioning load in hot and humid regions. Desiccant assisted A/Cs are used to address this issue. In this work, the performance of a hybrid A/C, which consists of a desiccant wheel, an enthalpy wheel, and a vapor compression cycle (VCC), is investigated experimentally. The effect of the process air stream's temperature and humidity, and the effect of the ventilation rate on the hybrid A/C performance are investigated. The experimental results show that the hybrid A/C is more effective than the standalone VCC in maintaining the indoor conditions within the comfort zone. The simulation of the complete hybrid solar A/C that uses a concentrating photovoltaic/thermal collector shows that a system coefficient of performance higher than unity is possible.     

Experimental investigation on drilling of natural flax fiber-reinforced composites

Natural fiber composites (NFCs) have strong potential to replace glass fiber-reinforced plastics. An instrumental operation in machining composite structures is hole making which facilitates assembly of parts. Understanding the effects of drilling process parameters on feature properties of NFCs has great benefits. In this regard, to make a good quality and accurate hole in composite structures, appropriate selection of drill bit and cutting parameters is important. This paper investigates delamination behavior and hole quality of flax/epoxy composite laminates in response to feed, spindle speed, and three different types of drill bit. As indicated by analysis of variance results, drill bit type and feed have greater influences on the thrust force. It appeared that delamination factor and surface roughness were significantly influenced by drill bit, but not by feed and spindle speed. The choice of drill bit has great impact on the delamination factor (67.27%) and surface roughness (74.44%), respectively.     

AA5052板材准静态/动态平面应变成形极限试验研究

为建立磁脉冲辅助冲压成形(EMAS)工艺的有效性,采用准静态平面应变预拉伸和动态磁脉冲成形相结合的方法对5052-O铝合金板材的准静态/动态平面应变状态复合成形极限进行了试验研究.结果表明:准静态/动态复合加载过程能显著改善该铝合金板材的室温成形性;准静态/动态平面应变复合成形极限比准静态平面应变成形极限有显著提高,相似或者略高于完全磁脉冲平面应变成形性,且随着准静态预应变水平的增加,准静态/动态复合变形成形极限变化不大.预变形的存在不会削弱复合成形过程的极限变形能力.     

Application of calcium carbonate in resin transfer molding process: An experimental investigation

The resin transfer molding (RTM) process is used to manufacture advanced composite materials made of continuous glass or carbon fibers embedded in a thermoset polymer matrix. In this process, a fabric preform is prepared, and is then placed into a mold cavity. After the preform is compacted between the mold parts, thermoset polymer is transferred from an injection machine to the mold cavity through injection gate(s). Resin flows through the porous fabric, and eventually flows out through the ventilation port(s). After the resin cure process (cross‐linking of the polymer), the mold is opened and the part is removed. The objective of this study is to verify the application of calcium carbonate mixed in resin in the RTM process. Several rectilinear infiltration experiments were conducted using glass fiber mat molded in a RTM system with cavity dimensions of 320 × 150 × 3.6 mm, room temperature, maximum injection pressure 0.202 bar and different content of CaCO₃ (10 and 40%) and particle size (mesh opening 38 and 75 µm). The results show that the use of filled resin with CaCO₃ influences the preform impregnation during the RTM molding, changing the filling time and flow front position, however it is possible to make composite with a good quality and low cost.     

一种新型便携式制冷保温容器的试验研究

研制一种新型便携式制冷保温容器制冷系统，主要用于保存血液。确定半导体制冷核心部件的参数，如半导体制冷片的选择、容器内部结构及系统的匹配。通过性能试验进行优化，对影响半导体制冷的因素进行讨论。实验结果表明，将半导体制冷应用于保温容器是可行的，而且是有利的。该研究结果对半导体制冷技术在小型制冷保温容器中的进一步研究和应用具有一定的指导意义。     

Experimental investigation and flow visualisation of the resin transfer mould filling process for non-woven hemp reinforced phenolic composites

Resin transfer moulding (RTM) of glass fibre reinforced polymeric composites offers the advantages of automation, low cost and versatile design of fibre reinforcement. A replacement of glass fibres with natural plant fibres as reinforcement in polymeric composites provides additional technological, economical, ecological and environmental benefits. The resin transfer mould filling process has significant effects on different aspects, such as fibre wetting out and impregnation, injection gate design, “dry patch” and void formation. Flow visualisation experiments were carried out using a transparent RTM mould to develop a better understanding of the mould filling process for hemp mat reinforced phenolic composites. The mould filling of unreinforced phenolics was characterised by a “quasi-one-dimensional steady state” flow. In the case of hemp non-woven reinforced system, the mould filling process can be considered as the flow of fluids through porous media. “Fibre washing” was a typical problem encountered during the injection process, leading to poor property uniformity. In addition, a preferential flow path was usually created near the edges and corners of the mould. The path exhibited low flow resistance and caused the resin flow front to advance much faster in these regions. The edge flow disturbed the steady flow, leading to difficulties in venting arrangement and “dry patch” formation. The edge flow and fibre washing were alleviated by reinforcement manipulation so steady state flow could be achieved. The relationships between the filling time and injection pressure and between filling time and different fibre weight fractions have been established for certain specific injection strategies.     

Mechanical properties investigation of carbon/carbon composites fabricated by a fast densification process

Carbon/carbon (C/C) composites were prepared by thermal gradient chemical vapor infiltration with a fast densification rate. The fracture morphology and mechanical properties were examined by scanning electron microscopy and mechanical testing, respectively. The effects of preform type and heat treatment temperature (HTT) on the mechanical properties of C/C composites were analyzed. The results show that the average flexural strength drops from 47.8 MPa to 38.6 MPa as the HTT increases from 2100 °C to 2500 °C. C/C composites with felt as preform show brittle fracture and samples with needle-punched felt as reinforcement present obvious pseudoplastic property. The interlaminar shear strength of needle-punched felt reinforced composites is higher than that of sample with felt as preform by 44.26% owing to the needle-punched fiber in the thickness direction. The strength of interfacial bonding plays a key role to mechanical properties and failure behavior of C/C composites.