Determination of stiffness properties of braided composites for the design of a hip prosthesis

This paper describes an experimental procedure used to determine the stiffness properties of two different composites made of braided glass and hybrid carbon–glass fibre reinforced epoxy resin. Tubular specimens manufactured by reinforcing an epoxy resin system with commercial braided preforms were used to determine the elastic constants. All specimens were manufactured using compression moulding technique assisted with internal pressure. The stiffness properties were determined from axial and circumferential strains recorded from strain gauges using internal water pressure tests. Identical types of composite laminates were used to manufacture two prototypes of a composite femoral prosthesis with controlled stiffness.     

Surface quality and shrinkage of the composite bus housing panel manufactured by RTM

Resin transfer molding (RTM) process has been widely used in automobile industries, because products with large area can be manufactured easily with lower manufacturing cost than that of compression molding or hand lay up method. Although composite structures manufactured by RTM have light weight, good dynamic and impact characteristics, the low surface quality of composite structures made by RTM often hinders the adoption of composite automotive panels because parts made of glass fiber mat and unsaturated polyester often have shrinkage and warpage problems. To investigate the relationship between the shrinkage and the surface quality of composite part, in this work, the formation of surface contour line and the surface quality were measured experimentally with respect to stacking sequence and fiber volume fraction of glass fiber. Based on the results obtained, a real size composite bus housing panel was successfully manufactured.     

Manufacturing of composite sandwich robot structures using the co-cure bonding method

The conventional manufacturing of composite sandwich structures is completed by adhesive bonding separately prepared composite faces to cores. The joining process during sandwich fabrication is a most difficult process, which requires strict quality control. However, the joining process can be eliminated when the sandwich structures are manufactured by the co-cure method inside a mold using the large difference of coefficient of thermal expansion between foam cores and steel mold.

In this work, the robot hands and wrists for handling large LCD glass panel displays were designed and manufactured using the co-cure method. Considering the non-linear thermal expansion properties of the foam during co-cure manufacturing, the pressure generated inside a mold was analyzed and the required pre-compression strain of the foam for sandwich beams was determined for enough consolidation. Finally, the composite sandwich robot hands and wrists were co-cure manufactured and the deflections of hands were measured under the weight of large LCD glass panel.     

Minimum cost and weight design of fuselage frames: Part B: cost considerations,optimization, and results

An approach is presented to design fuselage frames for minimum weight, minimum cost, or a combination of the two. The approach combines structural requirements and manufacturing constraints into an optimization scheme that alters the geometry of the individual frame components until the objective function is minimized. In addition to the lowest weight and cost points, a near-optimal Pareto set of designs is found, out of which the design that minimizes both cost and weight is determined through a penalty function approach. Four different fabrication processes are considered: conventional sheet metal, high speed machined metal, hand laid-up composite, and resin transfer molded composite. For lightly loaded frames, an automated resin transfer molding process gives the lowest cost and weight designs. For highly loaded frames, high speed machining gives the lowest cost design but automated resin transfer molding gives the lowest weight design. The effects of fabrication process and some of the design and manufacturing constraints on cost and weight are examined.     

Optimization of Resin Infusion Processing for Composite Pipe Key-Part and K/T Type Joints Using Vacuum-Assisted Resin Transfer Molding

In present study, the optimization injection processes for manufacturing the composite pipe key-part and K/T type joints in vacuum-assisted resin transfer molding (VARTM) were determined by estimating the filling time and flow front shape of four kinds of injection methods. Validity of the determined process was proved with the results of a scaling-down composite pipe key-part containing of the carbon fiber four axial fabrics and a steel core with a complex surface. In addition, an expanded-size composite pipe part was also produced to further estimate the effective of the determined injection process. Moreover, the resin injection method for producing the K/T type joints via VARTM was also optimized with the simulation method, and then manufactured on a special integrated mould by the determined injection process. The flow front pattern and filling time of the experiments show good agreement with that from simulation. Cross-section images of the cured composite pipe and K/T type joints parts prove the validity of the optimized injection process, which verify the efficiency of simulation method in obtaining a suitable injection process of VARTM.     

Resin infusion under flexible tooling process and structural design optimization of the complex composite part

Employing optimum structural design strategies and accompanying optimal production processing while employing efficient and cost effective methods is a key for the expansion of composite structures in various industrial applications. Within this context, Resin Infusion under Flexible Tooling (RIFT) process has become a rapidly growing manufacturing approach for large scale and complex parts. In this study, replacement of automotive body parts with glass woven fabric/epoxy composite manufactured by RIFT Type I (RIFT I) process is investigated both experimentally and numerically to improve the mechanical characteristics with weight saving. The optimization of the laminate stacking sequence is the first step taken. Then the simulation of resin infusion for the optimum location of gates and vents in order to shorten the filling time, decrease dry spots and voids, and avoid costly and time consuming trial-and-error procedures. Numerical results of the filling time and fluid front position over time are assessed by comparison with the experimental data and good accuracy was obtained. Based on the results of the optimization, an automotive part with a complex geometry is fabricated with 50% weight saving relative to steel.     

热膨胀工艺硅橡胶芯模对复合材料圆管成型的影响

在建立硅橡胶芯模尺寸及工艺间隙设计公式的基础上,采用硅橡胶热膨胀工艺制备了碳纤维/双马树脂复合材料圆管,考察了不同厚度硅橡胶芯模对成型过程温度分布及预浸料铺层内部树脂压力的影响,并分析了圆管的成型质量。结果表明：硅橡胶芯模的厚度对温度分布影响较大,厚度为5mm时,温度分布比较均匀;铺层内的树脂压力能够达到设计压力,但不...     

Improving joints between composites and steel using perforations

The elastic mismatch between fiber reinforced composites and steel makes joining them difficult. One way to reduce this mismatch is to decrease the average stiffness of the steel by introducing perforations. Further, this has the possible advantage of mechanical interlocking. In the present study, stainless steel strips were perforated with circular or triangular holes. The hole sizes were smaller near the edge of the composite, and increased with increasing depth in the composite, thus creating a graded steel component. Various surface preparations, perforation fillers, and degrees of perforations were investigated. The steel strips were joined to the composite by inserting them between glass fiber fabrics before vacuum assisted resin transfer molding the composite. Tensile experiments were performed, and the quasi-static strength was used as the measure by which the different joints were compared.     

The Wear Behaviour of Composite Materials with Epoxy Matrix Filled with Hard Powder

The wear behaviour of composite materials, sliding under dry conditions against smooth steel counterface, has been investigated. The composite materials consisted of glass woven fabric reinforcing three different systems of matrix: epoxy resin, epoxy resin filled with powders of silica and epoxy resin filled with powders of tungsten carbide. The powders were mixed in a volumetric fraction of 6% with the epoxy resin. Three laminates were manufactured by hand lay up technology. The sliding tests have been conducted on the specimens, cut from the three laminates, with a pin on disk apparatus. The results put in evidence different wear behaviours of the composite materials observed at different values of sliding speed and pressure. The presence of different wear mechanisms has been appreciated by SEM-micrographic examinations.     

Characterization of polyurethane composites manufactured using vacuum assisted resin transfer molding

Glass fiber-reinforced polymer composites have promising applications in infrastructure, marine, and automotive industries due to their low cost, high specific stiffness/strength, durability, and corrosion resistance. Polyurethane (PU) resin system is widely used as matrix material in glass fiber-reinforced composites due to their superior mechanical behavior and higher impact strength. Glass fiber-reinforced PU composites are often manufactured using pultrusion process, due to shorter pot life of PU resin system. In this study, E-glass/PU composites are manufactured using a low-cost vacuum-assisted resin transfer molding process. A novel, one-part PU thermoset resin system with a longer pot life is adopted in this study. Tensile, flexure, and impact tests are conducted on both the thermoset PU neat resin system and E-glass/PU composites. A three-dimensional finite element model is developed in a commercial finite element code to simulate the impact behavior of E-glass/PU composite for three different energy levels. Finite element model is validated by comparing it with experimental results.     

低温固化双酚F型环氧树脂体系的化学流变模型

研究了用于真空辅助树脂传递模塑(VARTM)工艺的低温固化双酚F环氧树脂体系的化学流变特性,根据对等温黏度曲线的分析,建立了其工程黏度模型,并通过积分变换将模型推广到非恒温条件下使用。模型与实验结果具有良好的一致性。该体系固化产物玻璃化温度达111. 9℃,拉伸强度78.5 MPa,弯曲强度106 MPa。所建立的模型可有效地预测VARTM工艺的黏度变化和工艺窗口,为复合材料成型工艺模拟分析及工艺参数的确定奠定了基础。     

Reactive processing of textile fiber-reinforced thermoplastic composites – An overview

Thermoplastic composites offer some interesting advantages over their thermoset counterparts like a higher toughness, faster manufacturing and their recyclable nature. Traditional melt processing, however, limits thermoplastic composite parts in size and thickness. As an alternative, reactive processing of textile fiber-reinforced thermoplastics is discussed in this paper: a low viscosity mono- or oligomeric precursor is used to impregnate the fibers, followed by in situ polymerization. Processes that are currently associated to manufacturing of thermoset composites like resin transfer molding, vacuum infusion and resin film infusion, might be used for manufacturing of thermoplastic composite parts in near future. This paper gives an overview of engineering and high-performance plastic materials that are suitable for reactive processing and discusses fundamental differences between reactive processing of thermoplastic and thermoset resins.     

Architectural design in stretch-formed microtruss composites

Structural coatings of nanocrystalline metal can significantly enhance the mechanical properties of microtruss cellular materials, creating new types of cellular composites. This study investigated the optimal architectural design under a compressive load for stretch-formed low carbon steel cores reinforced with ～20 nm grain size nanocrystalline Ni–35 wt%Fe. During stretch-forming, the struts in the starting perforated low carbon steel sheet are elongated and thinned as higher internal truss angles are formed, leading to an optimal internal truss angle. While a nanocrystalline coating enhances the weight specific mechanical properties of an optimally designed conventional microtruss, the resulting composite microtruss becomes sub-optimal since the optimal internal truss angle changes with coating thickness. A strut design framework was therefore developed to determine the optimal truss angle for a given combination of starting material, reinforcing material, sheet geometry, and coating thickness.     

Composite wrist blocks for double arm type robots for handling large LCD glass panels

Recently, robot structures handling liquid crystal display (LCD) glass panels are increased in size as the size of LCD is increased. In order to handle large LCD panels, the robot structures should have high stiffness to reduce the deflection of robot end effector under the weights of LCD. The LCD manufacturing industries have a trend to employ double arm type robots rather than single arm type robots to increase productivity. Currently, two aluminum wrist blocks that have different configurations not to interfere with each other are mounted on the robot arms. The aluminum wrist block becomes one of the largest deflection sources as the size of the robot structures increases. Since the size of the wrist block can not be increased indefinitely to increase the stiffness due to the limitation of driving motor power, the best way to increase the stiffness of the wrist block is to employ carbon fiber epoxy composite material for structural material of the wrist block because the carbon fiber epoxy composite material has much higher specific stiffness and damping than aluminum. In this work, the two wrist blocks for the double arm type robot for handling large LCD glass panels were designed and manufactured using foam core sandwich structure. Finite element analysis was used along with an optimization routine to design the composite wrist blocks. Box type sandwich structures were employed to reduce shear effect arising from the low modulus of polyurethane foam core. The weight reduction of the composite wrist blocks was more than 50% compared to those of comparable aluminum wrist blocks and found that the composite wrist blocks had much improved performances compared to those of the aluminum wrist blocks from the static and dynamic tests.     

An integrated optimisation for the weight,the structural performance and the cost of composite structures

An integrated optimisation methodology is proposed to optimise the manufacturing cost as well as the structural performance and the weight of composite laminated plates manufactured by the resin transfer moulding (RTM) process. In the present approach, the fibre type, the number of fabrics, the layer stacking sequence and the fibre volume fraction are optimised to minimise the structural weight and the material cost of composite structure under the stiffness constraint and the mould filling time constraint which is a part of process cycle time. With the results obtained, it is investigated how the weight and the material cost are traded-off. The optimisation methodology suggests a guide to cost-effective material selection in the preliminary conceptual design stage.     

Composite robot end effector for manipulating large LCD glass panels

Recently, the design and the manufacture of light robot end effectors with high stiffness have become important in order to reduce the deflection due to the self-weight and weight of glass panel, a part of LCD, as the size of glass panels as well as robot end effectors increases. The best way to reduce the deflection and vibration of end effectors without sacrificing the stiffness of end effectors is to employ fiber reinforced composite materials for main structural materials because composite materials have high specific stiffness and high damping. In this work, the end effector for loading and unloading large glass panels were designed and manufactured using carbon fiber epoxy composite honeycomb sandwich structures. Finite element analysis was used along with an optimization routine to design the composite end effector. A box type sandwich structure was employed to reduce the shear effect arising from the low modulus of honeycomb structure. The carbon fiber epoxy prepreg was hand-laid up on the honeycomb structure and cured in an autoclave. A special process was used to reinforce the two sidewalls of the box type sandwich structure. The weight reduction of the composite end effector was more than 50% compared to the weight of a comparable aluminum end effector. From the experiments, it was also found that the static and dynamic characteristics of the composite end effector were much improved compared to those of the aluminum end effector.     

玻璃钢约束阻尼复合结构的阻尼特性

以玻璃纤维增强树脂作为约束层主要材料、丁腈橡胶为阻尼层、钢板为基板制备约束阻尼复合结构, 运用动态黏弹谱仪和悬臂梁共振法, 研究温度、约束层刚度和阻尼层结构对约束阻尼复合结构减振效果的影响。结果表明:自由阻尼复合板的最大阻尼范围落在阻尼层的玻璃化转变区;玻璃钢约束层能将复合结构的阻尼拓展至阻尼层的高弹态区域, 增加阻尼层厚度可以提高约束复合板的阻尼性能;提高孔隙率同样有利于约束复合板阻尼性能提升;铝板约束层提升作用尤为显著, 然而在海洋环境、干湿交替等强腐蚀场合中, 铝板极易腐蚀而丧失约束功能, 因此在这类特殊场合下耐腐蚀的玻璃钢具有优势。      

Mechanical properties of composite structures fabricated with the vacuum induced preform relaxation process

A new technique called vacuum induced preform relaxation (VIPR) can be used to improve the processing of composite parts manufactured using vacuum resin infusion methods. The VIPR process is a method for manipulating and guiding the resin filling pattern during a vacuum assisted resin transfer molding (VARTM) manufacturing process with a relatively small external vacuum chamber. This VIPR chamber can be sealed against the flexible molding surface of a VARTM mold and used to create vacuum above the preform. This causes the compressive forces compacting the fabric to decrease allowing the resin to flow faster in the effected region under the chamber. Thus the chamber can influence the resin flow pattern as well as avoid the formation of voids due to merging flow fronts. When the regulated vacuum in the chamber is applied it temporarily decreases the fiber volume fraction of the preform. It is important to investigate if this relaxation has a permanent adverse effect on the mechanical properties of the composite. The results of these tests strongly suggest that the use of the VIPR process does not compromise the mechanical properties of composite structures.     

热塑性玻璃纤维头盔服役性能分析与数值仿真

为了探究复合材料特别是碳纤维、玻璃纤维在头盔产品上的应用,本文基于模压成型工艺,对热塑性连续玻璃纤维材料增强头盔的成型过程进行实验。探究复合材料头盔所使用层合板最佳铺层方案,并通过实验获得层合板的应力应变曲线。对比不同头盔的穿透、碰撞和刚度服役性能数据,并使用有限元软件LS-DYNA进行数值仿真计算,得到不同材料对头盔性能及质量的影响。使用ABAQUS软件对头盔模型进行拓扑优化,在保持头盔刚度性能基本不变的情况下,优化得到头盔的加强筋结构,以此减轻头盔表层厚度并实现轻量化。结果表明,相比于普通ABS材料的头盔,热塑性连续玻璃纤维头盔的质量减轻了14.6%、刚度提升了10.6%;含有加强筋结构的玻璃纤维头盔质量减轻了14.2%,刚度与普通ABS头盔保持一致,但更节约材料、性价比更高。复合材料头盔的综合性能相比普通ABS塑料头盔有显著提升。     

Preparation and mechanical properties of carbon nanotube grafted glass fabric/epoxy multi-scale composites

In the present paper, carbon nanotubes (CNTs) were chemically grafted onto surfaces of the amino silane treated glass fabric by a novel chemical route for the first time to create 3D network on the glass fibers. The chemical bonding process was confirmed by Fourier transform infrared spectroscopy and scanning electron microscopy. The glass fabric/CNT/epoxy multi-scale composite laminates were fabricated with the CNT grafted fabrics using vacuum assisted resin infusion molding. Tensile tests were conducted on fabricated multi-scale composites, indicating the grafting CNTs on glass fabric resulted a decrease (11%) in ultimate tensile strength while toughness of the multi-scale composite laminates were increased up to 57%. Flexural tests revealed that the multi-scale composite laminates prepared with CNT grafted glass fabric represent recovering after first load fall. The interfacial reinforcing mechanisms were discussed based on fracture morphologies of the multi-scale composites.