基于神经网络遗传算法的GFRP拉挤双目标优化

为研究玻璃钢(GFRP)拉挤工艺参数对复合材料性能的影响,优化最佳拉挤工艺参数,建立了拉挤工艺过程数学模型,结合基于有限元/有限差分的间接解耦法进行求解,模拟得到了拉挤过程中GFRP内部的非稳态温度场和固化度变化情况.分别采用布拉格光栅光纤温度传感器和索氏萃取法检测拉挤GFRP内部的温度与固化度,实测温度和固化度均与模拟温度和固化度吻合,验证了数值模拟程序的正确性.以数值模拟结果为样本,建立反向传播神经网络,得到拉挤工艺参数(固化温度、拉挤速度)与GFRP固化度之间的非线性相关关系,再结合遗传算法解决拉挤过程中固化炉温度和拉挤速度双目标优化问题.优化得到的拉挤工艺参数可在保证复合材料固化度达标的情况下,提高拉挤速度降低固化炉温度,优化效果显著.神经网络遗传算法优化方法能有效解决此类具有复杂非线性关系的多目标优化问题.     

CFRP拉挤过程非稳态温度场数值模拟与FBG实时检测

碳纤维增强聚合物基复合材料的拉挤成型过程是动态的,其固化度与温度变化为强耦合关系。温度场是工艺过程控制关键之一。根据固化动力学和传热学理论,建立了非稳态温度场与固化动力学数学模型。通过差示扫描量热仪（DSC）分析计算出模型中固化动力学参数。采用有限元与有限差分相结合的方法,依据ANSYS求解耦合场的间接耦合法,编制了计算程序,对拉挤工艺不同工况CFRP内部非稳态温度场进行数值模拟。采用专门设计制作的铝毛细管封装的布拉格光栅光纤(FBG),排除了非温度应变的干扰。通过试验确定了FBG温度传感特性表征及FBG温度灵敏度系数值,保障了CFRP内部温度场实时动态检测的准确度。模拟与实验结果基本吻合,为取代传统试凑性实验,优化CFRP拉挤工艺提供了科学快捷的理论依据。      

预浸料先进拉挤成型的固化传热过程数值模拟

对M21C碳纤维/环氧树脂复合材料预浸料在先进拉挤成型过程中的温度与固化度曲线进行了研究。使用DSC测得M21C预浸料在升温与恒温状态下的固化反应动力学方程,用于树脂固化反应的计算。基于有限元软件,结合有限差分法与体积控制法编写脚本解决热传导与树脂固化反应的计算,从而得到温度与固化度曲线,并在先进拉挤生产中测得实际的温度与固化度曲线,结果表明计算与实测曲线基本吻合,因此验证了算法的可行性。改变先进拉挤的工艺参数（加热温度区间、拉挤速度）再进行模拟计算,通过计算结果优化工艺参数,得到帽形梁先进拉挤三区间加热的理想工艺参数:模具加热温度区间为160-180-200℃;拉挤速度为1 cm/60 s。      

A Dynamic Transient Model to Simulate the Time Dependent Pultrusion Process of Glass/Polyester Composites

The objective of this paper is to introduce a novel dynamic transient model to simulate the time dependent pultrusion process of glass/polyester composites. The model is able to simulate the resin curing process systematically. The resin curing process is divided in two liquid and gel-solid phases. Physical properties of the resin including resin specific heat, viscosity and thermal conductivity change by altering the resin temperature and the degree of cure. It is shown that in liquid and gel-solid phases, some of the resin physical properties have significant role in heat transfer phenomenon and affect simulation results. The physical and mechanical properties of fibers do not change during the curing process of composites; therefore, an equivalent material is introduced instead of the resin-fiber compound. The model simulates the heat generation during the resin curing process. The degree of cure of the resin, used for the resin viscosity calculation, is an important parameter indicating the final stage of simulation of resin curing process. The components of the model are integrated in a finite element method. As case studies, the process of pultrusion of circular, rectangular and I cross-sections are simulated by the model. The results show that the model is able to simulate the pultrusion process very well.     

Improved cure optimization in pultrusion with pre-heating and die-cooler temperature

Optimization studies are performed on the pultrusion of a thermosetting composite. The three-dimensional finite element/nodal control volume procedure developed for simulation and optimization of the process is employed for this purpose. The aim of optimization is to achieve the desired degree of cure with minimum local variations across the pultrudate cross-section. The die-heating environment is optimized for a few cases with different initial temperatures for a glass/epoxy wet preform and for the cooler installed within the pultrusion die near its entrance. The role of these temperature parameters in moderating the optimization constraints is examined. Simultaneous optimization of die-heater temperatures and pull-speed is also considered. It is observed that the temperature overshoot within the composite pultrudate can be reduced and better optimization results can be achieved by a proper choice of a pre-die temperature for the composite and the die-cooler temperature.     

连续玻璃纤维/聚丙烯热塑性复合材料拉挤成型中的工艺参数

采用复合纱拉挤方法制备连续玻璃纤维/聚丙烯(GF/PP)热塑性复合材料,研究了复合纱拉挤成型过程中模具温度及拉挤速度对GF/PP复合材料截面中心温度的影响。以傅里叶定律为理论基础,分析了拉挤过程中模腔内的瞬态传热过程;建立了工艺参数矩阵,通过有限元数值计算,预测了不同模具温度、拉挤速度下GF/PP复合材料截面中心的温度变化,优选了工艺参数组合。通过实验制备不同温度、不同拉挤速度的GF/PP复合材料,并进行弯曲模量测试及截面形貌观察。结果表明:在GF/PP复合纱拉挤过程中,拉挤速度不宜超过350 mm/min,模具熔融区温度设定应高于180℃;GF/PP复合材料在150℃-230℃-50℃成型温度、100 mm/min拉挤速度的工艺参数设定下获得最优的制品力学性能;在设定拉挤参数时,拉挤速度相较于熔融区温度更重要。      

Optimization of the Temperature-Time Curve for the Curing Process of Thermoset Matrix Composites

An intelligent optimization model aiming at off-line or pre-series optimization of the thermal curing cycle of polymer matrix composites is proposed and discussed. The computational procedure is based on the coupling of a finite element thermochemical process model, dynamic artificial neural networks and genetic algorithms. Objective of the optimization routine is the maximization of the composite degree of cure by the definition of the autoclave temperature. Obtained outcomes evidenced the capability of the method as well as its efficiency with respect to hard computing or experimental procedures.     

A hybrid of back propagation neural network and genetic algorithm for optimization of injection molding process parameters

This paper presents a hybrid optimization method for optimizing the process parameters during plastic injection molding (PIM). This proposed method combines a back propagation (BP) neural network method with an intelligence global optimization algorithm, i.e. genetic algorithm (GA). A multi-objective optimization model is established to optimize the process parameters during PIM on the basis of the finite element simulation software Moldflow, Orthogonal experiment method, BP neural network as well as Genetic algorithm. Optimization goals and design variables (process parameters during PIM) are specified by the requirement of manufacture. A BP artificial neural network model is developed to obtain the mathematical relationship between the optimization goals and process parameters. Genetic algorithm is applied to optimize the process parameters that would result in optimal solution of the optimization goals. A case study of a plastic article is presented. Warpage as well as clamp force during PIM are investigated as the optimization objectives. Mold temperature, melt temperature, packing pressure, packing time and cooling time are considered to be the design variables. The case study demonstrates that the proposed optimization method can adjust the process parameters accurately and effectively to satisfy the demand of real manufacture.     

雷击对碳纤维增强型航空复合材料损伤的影响

依据有限元仿真软件ABAQUS,建立碳纤维增强型复合材料(CFRP)层合板雷击损伤热-电耦合有限元仿真模型。利用叠加温度场的方法来近似表示内部受损状态,通过对比实验验证热-电耦合仿真方法的正确性与有效性。利用回归统计分析技术,定量分析雷电参数与CFRP雷击损伤的相关性,并绘制相关曲线。结果表明:雷电流比能是决定CFRP雷击损伤的关键因素,纤维破坏面积、分层面积与比能具有线性相关性,树脂破坏面积、分层厚度与比能具有对数相关性。     

CFRP感应加热线圈中心区域温度场

感应加热技术是实现碳纤维增强树脂复合材料(CFRP)低能耗高效固化成型的有效方法,提高CFRP感应加热温度场均匀性是保证成型质量的关键,而线圈中心区域温度场均匀性是保证材料整体温度均匀性的关键。根据电磁加热原理建立了CFRP有限元多场耦合的分析模型,通过对模拟计算和实验过程的温度场升温及分布情况的对比分析,证明了本仿真可以准确模拟CFRP感应加热温度场分布。根据图像的熵值理论将温度场均匀性通过熵值大小进行表示,实现了CFRP感应加热温度场均匀性的量化分析,并通过有限元模型计算研究了线圈直径及线圈与材料间距对线圈中心区域温度场均匀性的影响,得到了中心区域温度场均匀性与线圈直径及材料间距之间的关系曲线,为组合式线圈均匀加热CFRP提供了线圈直径及材料间距大小选择的理论依据。      

不同孔隙率CFRP层合板静态力学性能研究

为了研究孔隙率对织物碳纤维/环氧树脂复合材料层合板静态力学性能的影响规律,分别测量了孔隙率为0.33%至1.50%的CFRP层合板的弯曲强度和层间剪切强度,并进行有限元模拟.在适用于复合材料单向板的改进Hashin失效准则基础上,建立了适用于织物纤维增强复合材料静态力学强度的失效准则.通过引入复合材料基本强度参数预测不同孔隙率CFRP层合板的力学性能,结合刚度突然退化模型,采用ABAQUS软件建立了有限元模型.试验结果表明,随着孔隙率的增加,复合材料层合板的弯曲强度和层间剪切强度均呈下降趋势.有限元模型较为准确地预测了不同孔隙率织物碳纤维/环氧树脂复合材料层合板的弯曲强度和层间剪切强度.     

Cure simulation with resistively in situ heated CFRP molds: Implementation and validation

In composite processing of parts with varying cross-sections, homogeneous cure is sought but poses a significant challenge. Electrically heated molds for resin transfer molding (RTM) processes offer the potential to locally introduce heat and, thus, achieve more homogeneous cure and enhanced part quality. However, low conductivity of CFRP poses a risk of uncontrolled exothermic reactions. To target this potential, an appropriate and efficient numerical method is presented in this study to simulate part cure governed by resistive heated CFRP molds. A numerical control algorithm for 3D finite element cure simulations is developed, which uses the reaction flux of a temperature boundary condition to calculate the arising tool temperature field. The capability of this method to predict non-uniform tool temperatures of self-heated CFRP molds with close to thermocouple accuracy during the cure process is shown by means of numerical verification and experimental validation on a self-heated CFRP plate.     

基于Morris方法的纤维复合材料结构件固化均匀性的全局灵敏度分析

纤维增强树脂基复合材料结构件的残余应力问题是制约其在航空航天、汽车和建筑领域大规模应用的关键问题。复合材料固化过程中温度场和固化度场的非均匀性是引起残余热应力和固化收缩应力的重要因素。为了探讨纤维复合材料结构件在固化成型过程中固化工艺温度、热传导系数、对流换热系数及结构件厚度对固化均匀性的敏感程度,采用数值模拟分析了这4个关键参数对温度场和固化度场均匀性的影响规律。模拟结果表明:升高固化工艺温度,复合材料温度场的非均匀性增大,固化度场的非均匀性减小;增大对流换热系数和热传导系数,复合材料温度场和固化度场的非均匀性减小;增加复合材料结构件的厚度,复合材料温度场和固化度场的非均匀性增大。在此基础上,应用Morris全局灵敏度分析方法对4个关键参数对复合材料固化均匀性的影响程度进行定量分析,得到固化均匀性的影响因素按灵敏程度由大到小的顺序为:结构件厚度、热传导系数、固化工艺温度、对流换热系数。     

热固性树脂基复合材料固化过程的三维数值模拟

针对热固性树脂基复合材料成型工艺的固化过程建立了数学模型,并采用有限单元法进行了三维瞬态数值分析。编制了有限元模拟程序CURESIM,通过具体数值模拟算例,表明本文中所建立的分析模型及算法具有较高的可靠性。模拟的固化过程并不特指某一成型工艺,因而模拟的数值方法具有一定的普遍性。模拟程序可以计算得到任意时刻复合材料内温度及固化度分布,通过数值模拟可以有效地优化固化加热工艺参数,提高产品质量。      

Dielectric cure monitoring for glass/polyester prepreg composites

The on-line cure monitoring of fiber reinforced thermosetting resin matrix composite material has been performed for improving quality and productivity during manufacturing. Since the dissipation factor measured by dielectrometry method is dependent on the degree of cure and temperature of resin, in this study, a new method to obtain the degree of cure during on-line cure monitoring for S-glass/polyester composites without temperature effect was developed by employing a combination function of the temperature and the dissipation factor. The temperature signal was measured with a K-type thermocouple and the dissipation factor signal was measured with an interdigital dielectric sensor during curing process. Then the calculated degree of cure using the measured data from dielectrometry was compared to the measured value from differential scanning calorimetry. The developed on-line cure monitoring method was applied to a 2-step cure cycle for the verification of the developed procedure.     

基于涡流成像的碳纤维增强树脂基复合材料细观结构可视化

对碳纤维增强树脂基复合材料（CFRP）的细观结构成像方法进行了研究,利用涡流成像技术实现了CFRP层合板中纤维方向及纤维缺失、褶皱和空隙过大等缺陷的可视化。首先通过有限元仿真和电路理论分析了CFRP板中涡流的生成机制和分布特性,阐述了基于涡流法的CFRP细观结构成像机制。然后介绍了用于扫描成像的高频涡流检测（HF-ECT）实验系统并确定了涡流探头的形式及其参数。最后利用涡流成像技术分别对单层板、正交层合板和四方向斜交层合板进行了检测,绘制了涡流检测（ECT）信号的三维伪彩图并得到了清晰的纤维纹路分布。通过引入滤波去噪技术和二维快速傅里叶变换（2D-FFT）对图像进行进一步处理,提高了图像分辨率并完成了不同方向上纤维纹路的分离,从而实现对层合板每单向层中缺陷的精确定位。     

树脂基复合材料曲面结构件固化变形数值模拟

为了研究树脂基复合材料曲面结构件的固化变形过程,首先分析了碳纤维增强树脂基复合材料在固化过程中密度、模量、热膨胀系数、比热容及热传导系数等材料物性的变化,并将这些变化引入到数值模拟当中。接着,针对复合材料复杂曲面结构件,提出了利用定常流动的流线方程构建曲线坐标系的新方法。然后,根据建立的曲线坐标系,运用有限元法计算了某轻型飞机机翼上蒙皮板在固化过程中内部温度、固化度和内应力的分布情况以及材料物性随固化度的变化情况。最后,计算了由于内部温度场和固化度场的不均匀、热膨胀系数的各向异性和固化引起的树脂体积收缩而导致的结构变形。结果表明:引入材料物性变化使固化过程的数值模拟更加合理、模拟结果更加精确,利用定常流动的流线方程构建的曲线坐标系适用于复合材料曲面结构件的有限元分析。所得结论对研究树脂基复合材料的固化变形过程和各向异性复合材料复杂曲面构件的三维实体建模均具有指导意义。     

Finite element modeling of polymer curing in natural fiber reinforced composites

Plant-based fibers have been selected as suitable reinforcements for composites due to their good mechanical performances and environmental advantages. This paper describes the development of a simulation procedure to predict the temperature profile and the curing behavior of the hemp fiber/thermoset composite during the molding process. The governing equations for the non-linear transient heat transfer and the resin cure kinetics were presented. A general purpose multiphysics finite element package was employed. The procedure was applied to simulate one-dimensional and three-dimensional models. Experiments were carried out to verify the simulated results. Experimental data shows that the simulation procedure is numerically valid and stable, and it can provide reasonably accurate predictions. The numerical simulation was performed for a three-dimensional complex geometry of an automotive part to predict the temperature distribution and the curing behavior of the composite during the molding process.     

平纹编织碳纤维增强树脂复合材料离散电导率建模方法

编织碳纤维增强树脂复合材料(CFRP)的电阻抗分布具有各向异性、异质性、几何结构复杂等特点。建立电阻抗分布模型是利用电磁涡流无损检测技术获取编织CFRP缺陷及疲劳损伤信息的关键关节。基于电阻抗张量建模理论,采用多层编织结构CFRP二维平面的分块均化电学特性表征方法,建立编织结构CFRP的简化电阻抗分布模型,从而实现编织结构CFRP电磁特性的精确、快速有限元分析。在有限元仿真基础上,通过设计双空气旋转线圈电磁传感器对平纹编织CFRP进行电磁无损检测,选用阻抗的极坐标图描述被测材料沿不同方向的阻抗变化趋势,通过实验验证有限元建模的正确性。最后利用所提出的建模方法模拟了双空气旋转线圈传感器对平纹编织CFRP的结构缺陷及循环载荷疲劳的检测效果。