模具对复合材料构件固化变形的影响分析

通过光纤光栅的方法实验研究了在热压罐成型工艺过程中, 复合材料构件由金属固化模具与复合材料构件热不匹配导致的沿厚度方向和面内的固化残余应力发展, 得到了固化后残余应力沿构件厚度方向和面内的分布情况, 并分析了该残余应力分布的产生机制以及对构件固化后变形的影响。结果表明: 复合材料与模具之间的热不匹配导致的固化残余应变沿构件厚度方向呈梯度分布, 靠近模具端大于远离模具端, 并且该应变会引起构件固化后的翘曲变形, 变形以沿纤维方向为主。     

模具对复合材料构件固化变形的影响分析

通过光纤光栅的方法实验研究了在热压罐成型工艺过程中,复合材料构件由金属固化模具与复合材料构件热不匹配导致的沿厚度方向和面内的固化残余应力发展,得到了固化后残余应力沿构件厚度方向和面内的分布情况,并分析了该残余应力分布的产生机制以及对构件固化后变形的影响.结果表明:复合材料与模具之间的热不匹配导致的固化残余应变沿构件厚度方向呈梯度分布,靠近模具端大于远离模具端,并且该应变会引起构件固化后的翘曲变形,变形以沿纤维方向为主.     

热固性树脂基复合材料构件固化变形数值模型

针对树脂基复合材料构件固化过程中的固化翘曲变形这一关键技术问题,通过引入剪切系数的方法来代替固化过程中模具与复合材料之间的相互作用,建立了预报树脂基复合材料构件固化变形的数值计算模型。通过少量实验数据来确定模具与复合材料之间的剪切系数,进而预测复合材料构件的固化变形。通过与文献中实验结果的比较证明了所建立的模型具有较高的可靠性。实验与计算结果表明,该模型能够在不考虑复杂的材料参数变化的情况下对不同结构尺寸及不同工艺参数下的复合材料构件的固化变形进行较为准确地预测。     

热固性树脂基复合材料固化变形和残余应力数值模拟研究综述

固化变形和残余应力给复合材料的应用带来威胁,准确的预测固化变形和残余应力可以为复合材料的结构和工艺设计提供调整依据,减小固化变形和残余应力。数值模拟方法因其简单、预测精度高而被广泛采用。本文主要介绍了复合材料固化变形和残余应力数值模拟流程中包含的热传导-固化模块、流动压实模块和应力变形模块。重点详述了应力变形模块中本构方程和模型-构件之间相互作用力研究的最新发展,为固化变形和残余应力预测提供方向和参考。简要讨论当前复合材料固化变形和残余应力预测的主要发展方向。     

模具对柱面复合材料构件固化变形影响的有限元分析

针对复合材料构件固化变形问题, 分析了复合材料热压罐成型固化过程的多场耦合关系, 考虑模具的作用, 建立了柱面复合材料构件固化过程的有限元分析模型。基于此模型, 研究了模具材料、 模具厚度和模具形式对柱面复合材料构件固化变形的影响。结果表明: 模具对柱面件固化变形的影响较大, 模具材料与构件材料热膨胀系数(CTE)不匹配程度影响构件回弹角的大小; 模具的厚度不同, 导致构件的不同回弹角; 采用阴模时, 构件回弹角小于阳模的, 且回弹方向相反。     

复合材料残余应力和固化变形数值模拟及本构模型评价

为了评价不同固化本构模型,建立了预测复合材料构件残余应力/应变和固化变形的三维数值模型。该模型由热化学分析模块和热力分析模块构成,考虑了热化学耦合、材料性能的各向异性、化学收缩及黏弹性等因素。基于线弹性、黏弹性和Path-dependent三种典型的本构模型,预测了构件的残余应力/应变及固化变形。通过与试验结果对比,验证了所建数值模型的有效性,并重点研究了不同本构模型的适用性。结果表明,黏弹性本构模型最佳,对构件的残余应力/应变及固化变形的预测结果均较好; Path-dependent本构模型次之,对构件的残余应变和固化变形的预测结果较好,但对构件的残余应力的预测结果稍差;线弹性本构模型最差,除了对构件的残余应变和较薄构件的固化变形的预测结果较好外,其他预测结果都较差。     

非热压罐工艺模具对复合材料加筋壁板固化变形影响的有限元分析

通过真空袋成型工艺,利用CYCOM 5320-1材料体系制备了碳纤维/树脂基复合材料T型加筋壁板,并应用激光跟踪仪测量了其固化变形量。针对考虑模具影响和不考虑模具影响两种情况,利用有限元方法模拟了该加筋壁板固化过程。结果表明：数值模拟固化变形趋势和实验结果趋势相同,在宽度方向上吻合较好。考虑模具因素比未考虑模具因素的模拟结果更接近真实变形值,这是由于复合材料在达到树脂凝胶点之前,模具受热挤压模腔,导致构件产生永久性变形造成的。     

复合材料结构固化变形预测

针对复合材料结构中广泛存在的固化变形现象,分析并讨论了其产生原因和可能的解决措施.并给出典型复合材料结构元件的固化变形预测规律.结合飞行器复合材料整体化结构的概念,以共固化复合材料加筋板为例,说明了整体化结构固化变形和几何设计参数之间的关系.     

基于模具-制件相互作用的复合材料制件固化变形数值模型

针对复合材料制件在成型过程中的固化变形这一关键技术问题,通过在模具与复合材料制件之间引入剪切层的方法,建立了预测复合材料制件固化变形的解析计算模型和有限元仿真模型。剪切层的剪切模量用来衡量固化过程中模具与复合材料制件之间的相互作用,其数值大小通过与实验数据进行比对而得到。基于建立的固化变形模型,与文献中已有的实验结果进行了比较。结果表明:所建立的模型具有较高的可靠性。同时针对L型复合材料制件建立了三维有限元仿真模型,模型中除考虑材料各向异性和化学收缩效应以外,还将成型过程中模具与复合材料制件间的相互作用考虑在内。模拟结果表明:引入模具作用后L型零件的固化变形预测结果更加准确。      

基于温度曲线优化的复合材料热压罐固化时间与固化质量协同控制

温度曲线是复合材料热压罐成型的重要工艺参数,对成型时间和构件的固化质量有着直接影响.对温度曲线进行合理的优化设计,可以实现对固化时间与固化质量的协同控制.本工作基于复合材料固化成型模拟计算方法,针对复合材料C形构件开展固化成型的数值预测,预测结果与实验测试结果吻合较好,验证了计算方法的合理性;在此基础上,考虑成型时间与固化质量的协同控制,采用实验设计(DOE)与粒子群算法集成的优化策略开展复合材料C形构件的固化温度曲线优化设计,并对优化结果进行实验验证.结果显示通过温度曲线优化设计,在满足固化均匀性、固化程度与固化变形约束的同时,可以有效减少成型时间,两个优化算例的成型时间分别减少了64％和45％.     

Tooling geometry optimization for compensation of cure-induced distortions of a curved carbon/epoxy C-spar

The respect of the manufacturing tolerances is a challenging issue due to the complex distortions caused by the curing process, being sometimes a major obstacle to an increasing use of composites in aeronautics. The cure-induced distortions are modeled and mitigated owing to the development of a computational mold compensation strategy. An in-house surrogate-based optimizer coupled to three-dimensional curing simulations, is used to iteratively alter the shape of the mold in order to minimize the discrepancy with respect to the nominal geometry. Two parametrization strategies are proposed and applied to a generic curved C-spar geometry. One strategy consists in the characterization of the major distortion modes caused by the curing process, and in the parametrization of the geometry to compensate for each mode. The other strategy is to select a number of control points which can move freely in space to find the optimal configuration. Each method performs well but in a different manner, and the optimal choice depends on the industrial specifications of the problem.     

Development of a carbonization-in-nitrogen method for measuring the fiber content of carbon fiber reinforced thermoset composites

Carbon fiber reinforced thermoset composites such as carbon fiber epoxy composites are widely used in aircraft and aerospace, and are being increasingly used in automotive applications because of their lightweight characteristics, high specific strength, and stiffness. The carbon fiber content in the composite plays a critical role in enhancing structural performance. The carbon fibers contribute to the strength and stiffness; therefore, the mechanical properties of the composite are greatly influenced by the carbon fiber content. Measurement of carbon fiber content is essential for product quality control and process optimization. In this work, a novel carbonization-in-nitrogen (CIN) method is developed to characterize the fiber content in carbon fiber thermoset composites. A carbon fiber composite sample is carbonized in a nitrogen environment at elevated temperatures, alongside a neat resin sample. The carbon fibers are protected from oxidization while the resin (the neat resin and the resin matrix in the composite sample) is carbonized under nitrogen environment. The neat resin sample is used to calibrate the resin carbonization rate and calculate the amount of the resin matrix in the composite sample. The new method has been validated on several thermoset resin systems, and found to yield accurate estimation of fiber content in carbon fiber thermoset composites.     

On avoiding thermal degradation during welding of high-performance thermoplastic composites to thermoset composites

One of the major constraints in welding thermoplastic and thermoset composites is thermal degradation of the thermoset resin under the high temperatures required to achieve fusion bonding of the thermoplastic resin. This paper presents a procedure to successfully prevent thermal degradation of the thermoset resin during high-temperature welding of thermoplastic to thermoset composites. The procedure is based on reducing the heating time to fractions of a second during the welding process. In order to achieve such short heating times, which are much too short for commercial welding techniques such as resistance or induction welding, ultrasonic welding is used in this work. A particularly challenging scenario is analysed by considering welding of carbon-fibre reinforced poly-ether-ether-ketone, with a melting temperature of 340 °C, to carbon-fibre reinforced epoxy with a glass transition temperature of 157 °C.     

Thermoplastic–epoxy interactions and their potential applications in joining composite structures – A review

This paper presents a literature survey on the theoretical backgrounds and the past research efforts in relation to the interactions between certain thermoplastics and epoxies, and their applications in polymer blending, epoxy toughening and composite joining. The main objectives are to understand the possible mechanisms of interfacial adhesion between thermoplastic and thermoset polymers, and also to explore the feasible approaches to improve interfacial adhesion for the purposes of joining fibre reinforced polymer (FRP) composite structures by fusion bonding. Further, it is expected that the review would provide some visions to the potential applications of the thermoplastic–thermoset interfacial interactions for the quick assembly of composite structures in cost-effective manufacturing of composite structures, through the uses of the technologies, such as thermoset composite fusion bonding, welding of thermoplastic composites with thermoset composites, and thermoplastic article attachment on thermoset composites.     

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.     

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.     

热固性环氧树脂形状记忆聚合物的研究进展

热固性环氧树脂形状记忆聚合物是目前形状记忆聚合物研究领域的热点之一,文中介绍了热固性环氧树脂形状记忆聚合物的最新研究进展,详细探讨了各种热固性环氧树脂形状记忆聚合物的特点与性能,以及温度、辐射、固化程度对环氧树脂形状记忆聚合物性能的影响,并对环氧树脂形状记忆复合材料的性能进行了讨论,最后分析了热固性环氧树脂形状记忆聚合物研究中存在的问题。     

The heating of polymer composites by electromagnetic induction – A review

Since the late 1980s a small number of research groups have been attracted with the idea of using induction heating technology for the processing of fibre reinforced polymer composites. Induction technology is suitable for the processing of thermoplastic and thermoset polymer materials but requires special susceptor additives (conductive materials) either in the form of structured fibres and fabric or particulate that can transform the electromagnetic energy into heat. This paper aims to summarize the principles of induction heating with respect to polymer composites processing taking a look first at material and equipment based process influences. State of the art applications and research activities are then reviewed, from thermoplastic composite welding, thermoset curing, selective material heating and fast mould heating technologies. Current simulation possibilities and available software tools have also been covered. Finally, some new ideas and possibilities for future developments in the field of polymer composites processing have been discussed.