复合材料T型整体化结构固化翘曲变形模拟

针对复合材料T型整体化结构固化成型的工艺过程,分析了结构经固化而导致翘曲变形的原因;建立了整体化结构翘曲变形预测的理论模型及分析方法; 运用有限单元法计算了T型结构件的内部温度和固化度的分布,以及由于内部化学反应放热、固化引起的体积收缩和材料各个方向热膨胀系数的不一致而导致的结构翘曲变形量,同时考虑了树脂在固化过程中材料参数随着固化度的变化而变化;并研究了翘曲变形与T型结构件尺寸之间的关系。研究表明,选择合适的角材高度、宽度以及倒角半径可以有效地降低结构的翘曲变形。     

Thermo-viscoelastic analysis of the integrated T-shaped composite structures

A thermo-viscoelastic finite element analysis is used to investigate the residual stresses and the curing deformation of the integrated T-shaped composite structure. First, a three dimensional (3D) incremental viscoelastic constitutive equation is established and implemented into the finite element software ABAQUS to predict the full field warpage profiles of the integrated T-shaped structures. These results are validated based on the measured data obtained from digital speckle correlation technology. Second, the effects of the cooling rate on the warpage deformation and the residual stresses of the integrated T-shaped composite structure are studied. Finally, the relationships between the different curing strategies and the corresponding residual stresses are studied, and it shows that the Outside-to-Inside curing strategy will develop the smallest residual stresses for the integrated T-shaped composite structures.     

Curing Deformation Analysis for the Composite T-shaped Integrated Structures

Curing deformation of the T-shaped integrated structures is discussed in this paper. The mechanism of the deformation is analyzed for the T-shaped integrated structures, and a simple mathematical model for the deformation of the T-shaped integrated structures is established. Compare the mathematical model with the finite element analysis, the results show a good agreement. From the simple mathematical model, it can be seen that both cure shrinkage and thermal expansion are the major factors to produce the deformation of the typical T-shaped integrated structures and the tool-part contraction is the secondary factor. Therefore, it is important for the T-shaped integrated structures to select suitable fabrication process and the appropriate tool. The different geometry and material parameters of the T-shaped integrated structures are studied, and then a regression model is established.     

整体化复合材料结构分阶段固化变形预报方法及其实验验证

通过测试分析了T800/环氧预浸料固化过程中性能参数的变化规律; 针对热压罐工艺条件下复合材料整体化结构分阶段成型的特点,提出了一种基于应力传递的分阶段固化变形的有限元模拟方法; 对于不同成型工艺的工型加筋壁板结构,将分阶段模拟得出的变形结果与测试结果进行了对比,并分析了成型工艺与变形量之间的关系。结果表明,本文中提出的模拟方法能够准确预报整体化结构的固化变形,变形与成型工艺密切相关,针对特定的结构与铺层,采用合理的工艺过程能够有效减小构件的固化变形。     

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。     

Study on the Effect of Cure Cycle on the Process Induced Deformation of Cap Shaped Stiffened Composite Panels

Cap-shaped stiffened composite panels offer many excellent properties such as low density, high strength, high stiffness to weight ratio, and design flexibility. During their manufacturing processes, however, thermo-curing inherently produces the undesired residual stresses and cure deformations, which limits the applications of composite structures in a certain degree. In order to reduce the cure deformation, in this paper, the effect of cure cycle (curing temperature, curing pressure, cooling rate) on the process-induced deformation of cap-shaped stiffened composite panels was presented. A simple mathematical model based on the curing dynamics was established to predict the deformation of the cap-shaped stiffened composite panels. The deformation calculated by the mathematical model and experimental studies were compared, and an Error Correction Model was established. The Error Correction Model showed a good agreement with the experimental results.     

Reduction of residual stresses in thick-walled composite cylinders by smart cure cycle with cooling and reheating

The nozzle parts of solid rocket motors must endure both the internal pressure generated by high temperature exhaust gas and the mechanical load generated by steering operation. Therefore, the nozzle parts of solid rocket motors are fabricated with thick carbon fiber phenolic resin composites. When the thick-walled phenolic composite cylinder is cooled down from the curing temperature of about 155 °C to the room temperature, thermal residual stresses are created due to the anisotropic thermal deformation of the composite structure.

In this paper, a smart cure method with cooling and reheating was developed to reduce residual stresses in thick-wound composite cylinders made of carbon phenolic woven composite. The optimal cure cycle was obtained to reduce the residual stresses without increasing processing time and applied to fabrication of the thick-walled composite cylinder. From the residual stresses measured by the radial-cut-cylinder-bending method, it was found that the residual stresses were reduced 30% by using the smart cure method.     

Residual stress development during the composite patch bonding process: measurement and modeling

This paper presents an experimental technique for monitoring residual stress development throughout the composite patch repair curing process. Using this technique, process-induced strains and specimen warpage during a number of different cure cycles were measured for a simulated single-sided composite patch repair of an aluminum substrate. Models for adhesive cure rate and glass transition behavior of the patch adhesive resin (FM 300-1K) were combined with a simple bi-metallic strip model to predict specimen warpage and strain behavior during cure. Model predictions were compared with experimental measurements and were used to assist in the development of optimized cure cycles. Using these optimized cycles, it was found that it was possible to achieve significant (>20%) reductions in patch warpage and at the same time, minimize processing time and obtain a high final adhesive degree of cure. Experimental observations suggest that an improved patch model incorporating adhesive viscoelastic behavior during cure would assist in achieving additional process improvements.     

内加热固化环氧玻璃钢管制造系统

为提高环氧玻璃钢管生产的效率和质量,研制了仅用一台机床就能完成管道缠绕、固化和脱膜三道工序的集成制造系统.介绍了制造系统机床结构和工作原理,建立了缠绕运动控制和管道固化过程的数学模型.缠绕部分采用嵌入式多任务运动控制器实现主轴和小车的同步运动控制和缠绕逻辑控制.固化部分采用内加热固化工艺,由嵌入式工控机和PLC实现固化控制.利用有限元软件对管道固化过程的温度和固化度分布进行了数值模拟以优化固化工艺参数,并对该系统生产的管道进行了性能检测试验.实践应用表明采用内加热固化工艺可实现环氧玻璃钢管高效工业化制造.     

Consolidation and Warpage Deformation Finite Element Analysis of Filament Wound Tubes

This paper presents a process model for simulating the manufacturing process of prepreg filament wound composite tubes developed based on the finite element analysis. The model relates the process variables, such as degree of cure, viscosity, material property and temperature etc., to the parameters characterizing (residual stresses, warpage deformation) the composite tube and the mandrel. From the simulating results, several important trends in both the data and model are observed (1) Low temperature will go with low reaction rate and the reaction starts under low temperature will later compared with high temperature; (2) The results using CHILE model after demolding will smaller than the one using linear elasticity which assumes a stress-free prior to cool-down. After the mandrel (mold) is removed, some residual stresses, especially hoop stress will be released. (3) Remarkable stress concentration appeared in the transition zone between the boss and cylinder. In order to prevent the structural failure due to interlaminar shear or delamination, both the outer surface of the cylinder and the inner of the boss should have the same ply orientation angle.     

固化度与固化收缩对非对称复合材料层合板固化变形的影响

采用三维有限元方法研究复合材料非对称层合板在热载荷和固化收缩载荷下的固化变形情况, 建立了材料力学特性、 固化体积收缩量和温度与固化度之间的函数关系, 考察了层合板变形曲率与温度和固化度之间的关系。数值计算结果表明: 非对称层合板变形曲率与固化终止时固化度有密切关系; 固化变形主要发生在降温阶段; 固化收缩对层合板变形曲率影响很小, 主要发生在第二个保温平台的前半段。      

Neural-fuzzy optimization of thick composites curing process

This article addresses the optimization of curing process for thick composite laminates. The proposed methodology aims at the evaluation of the thermal cycle promoting a desired evolution of the degree of cure inside the material. At the same time, temperature overshooting as well as excessive temperature and cure degree gradient through the thickness of the material are prevented. The developed approach is based on the integrated application of artificial neural networks and a fuzzy logic controller. The neural networks promptly predict the behavior of composite material during curing process, while the fuzzy logic controller continuously and opportunely adjusts the proper variations on the imposed thermal cycle. The results highlighted the efficiency of the method in comparison with the cure profiles dictated by the material suppliers. For thick laminates, a reduction of 35% of cure time and improvements of approximately 10% of temperature overshooting was obtained compared to conventional curing cycles. The method was validated by experimental tests.     

Experimental study of tool–part interaction during autoclave processing of thermoset polymer composite structures

Autoclave manufacturing of thermoset polymer matrix composite structures with high dimensional fidelity requires a good understanding of various parameters affecting process-induced warpage and application of this knowledge to minimize the warpage through appropriate process control. One important contributor is the interaction between a composite part and the tool on which the part is laid and cured. This experimental study quantified the tool–part interaction by measuring the static and dynamic frictional coefficients as a function of process time, using a friction test fixture specially designed to simulate the autoclave environment. Temperature ramp rate was varied to understand the effect of autoclave cure cycle on the friction coefficients. Measured friction coefficients were maximum at the start of the cure cycle and varied as a function of degree of cure (α) and ramp rate owing to change in the tool–part interface, cure shrinkage, resin/composite properties, residual stress, and mode of interface failure.     

Role of tool-part interaction in process-induced warpage of autoclave-manufactured composite structures

The role of tool-part interaction in process-induces warpage of a large composite structure was studied using a three-dimensional process model, developed by integrating sub-models that describe the evolution of cure and properties of composite as well as various physical phenomena encountered, during autoclave processing. The process model was implemented through user sub-routines interfaced with the finite element software, ABAQUS. The tool-part interaction during processing was modeled using contact elements. The predicted temperature and warpage of an aircraft part, using a frictional tool-part interface and experimentally measured cure-dependent tool-part interfacial friction coefficients, compared very well with experimental temperature and warpage, validating the 3-D process model. A comparison of predictions using various models for the tool-part interface suggests that the two components of tool-part interaction that contribute to warpage are change in shape of the tool and part, and process-induced stress caused by constrained deformation of the tool and the part.     

Carbon fiber-reinforced cyanate ester/nano-ZrW2O8 composites with tailored thermal expansion

Fiber-reinforced composites are widely used in the design and fabrication of a variety of high performance aerospace components. The mismatch in coefficient of thermal expansion (CTE) between the high CTE polymer matrix and low CTE fiber reinforcements in such composite systems can lead to dimensional instability and deterioration of material lifetimes due to development of residual thermal stresses. The magnitude of thermally induced residual stresses in fiber-reinforced composite systems can be minimized by replacement of conventional polymer matrices with a low CTE, polymer nanocomposite matrix. Zirconium tungstate (ZrW(2)O(8)) is a unique ceramic material that exhibits isotropic negative thermal expansion and has excellent potential as a filler for development of low CTE polymer nanocomposites. In this paper, we report the fabrication and thermal characterization of novel, multiscale, macro-nano hybrid composite laminates comprising bisphenol E cyanate ester (BECy)/ZrW(2)O(8) nanocomposite matrices reinforced with unidirectional carbon fibers. The results reveal that incorporation of nanoparticles facilitates a reduction in CTE of the composite systems, which in turn results in a reduction in panel warpage and curvature after the cure because of mitigation of thermally induced residual stresses.     

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.     

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。     

Curing of Thick Thermoset Composite Laminates: Multiphysics Modeling and Experiments

Fiber reinforced polymer composites are used in high-performance aerospace applications as they are resistant to fatigue, corrosion free and possess high specific strength. The mechanical properties of these composite components depend on the degree of cure and residual stresses developed during the curing process. While these parameters are difficult to determine experimentally in large and complex parts, they can be simulated using numerical models in a cost-effective manner. These simulations can be used to develop cure cycles and change processing parameters to obtain high-quality parts. In the current work, a numerical model was built in Comsol MultiPhysics to simulate the cure behavior of a carbon/epoxy prepreg system (IM7/Cycom 5320–1). A thermal spike was observed in thick laminates when the recommended cure cycle was used. The cure cycle was modified to reduce the thermal spike and maintain the degree of cure at the laminate center. A parametric study was performed to evaluate the effect of air flow in the oven, post cure cycles and cure temperatures on the thermal spike and the resultant degree of cure in the laminate.     

基于代理模型和改进遗传算法的注塑翘曲优化

提出一种最小化制品翘曲的注塑工艺参数优化集成方法.以空调柜机顶盖注塑制品开发为例,该方法使用Moldflow软件分析制品的翘曲变形,运用田口方法确定与制品翘曲量密切相关的工艺因素,然后采用响应曲面法(RSM)和改进的精英保留自适应遗传算法(EAGA)相结合的方法,建立主要影响工艺参数与制品翘曲量之间的关系模型,通过对模型寻优以实现对制品翘曲的优化.该方法的适用性在制品的实际生产中得到了验证.     

热固性树脂基复合材料热隔膜成型过程数值仿真

为研究制件成型过程中的层间滑移情况及固化后的回弹变形,首先,利用自行开发的热隔膜成型装置制备了热固性树脂基复合材料C型制件。同时,针对热隔膜成型过程建立了三维数值仿真模型;该模型由3个复合材料固化过程子模型构成,包括热-化学模型、层间滑移模型和固化变形模型。然后,在此基础上将固化过程中复合材料性能的时变特性引入到仿真模型中,并将仿真结果与文献中的实验结果进行比较。最后,利用建立的仿真模型对热隔膜成型过程进行了数值模拟,并与实验进行比对,重点研究了成型过程中温度、固化度分布、层间滑移以及固化变形情况。所得结果证明所建立的数值模型对热隔膜成型过程的预测具有较高的可靠性及准确性,可以为后续热隔膜成型参数优化和模具修正提供参考。