基于材料物性参数时变特性的复合材料层合板固化残余应变应力数值模拟

热固性树脂基复合材料层合板成型过程形成的残余应力是影响材料质量的重要因素。针对复合材料固化过程建立了基于复合材料物性参数时变特性的复合材料固化过程的三维多场耦合计算模型。该模型包含经典的热-化学模型、树脂固化动力学模型、残余应力模型;在此基础上将材料物性参数时变特性引入多场耦合计算模型中,模型计算结果通过与文献中实验结果比较,验证所建立的固化模型的可靠性;在此基础上,对AS4/3501-6复合材料层合板的固化残余应变应力进行数值模拟,研究了固化过程中残余应变/应力的变化规律,分析工艺参数对应力应变的影响。通过与光纤光栅应变试验比较,验证其正确性。研究结果表明:模型可以很好地仿真复合材料固化过程;温度、树脂体积分数、铺层角度对层合板应力/应变都有较为显著的影响,为正相关关系,其中树脂的体积分数影响最为显著。     

固化环氧树脂中残余应力的研究

环氧树脂等热固性树脂中的残余应力是由固化时树脂的体积收缩,不同材质热膨胀系数的差异以及聚合物树脂本身的粘弹性本质所引起的。残余应力可以用应力松驰法、电阻应变丝法、逐步除层法和光弹技术来测定。针对其产生原因。在工艺上可通过降低官能团浓度,加入增韧剂和无机粉状填料,改进固化工艺等办法来消除残余应力。同时也探讨了利用膨胀性单体来根本消除残余应力的方法。     

厚截面复合材料结构固化残余应力研究进展

随着复合材料在飞机机架主承力构件的广泛应用,厚截面复合材料构件固化过程残余应力的预测和控制是必须解决的关键问题之一。厚截面复合材料的残余应力形成机制远较薄板复杂,更易发生温度过热、紧密压实不完全、非同步固化,固化残余应力大等问题。并且厚板在固化过程中形成的残余应力难以释放,降低复合材料结构的承载能力和使用寿命。采用数值模拟复合材料固化过程,优化固化工艺是是降低厚截面复合材料结构生产成本的有效方法。从热传导与化学反应、紧密压实和残余应力3个方面回顾了厚截面复合材料固化过程数值模拟的研究进展,对下一步的研究方向进行了展望。     

复合材料挖补修理固化过程残余应力的三维数值模拟

基于热化学和残余应力理论,采用顺序热-力耦合方法建立了复合材料固化过程的三维有限元模型,通过与文献中C形构件计算结果的对比,验证了该仿真模型具有较高的精度。采用该模型计算了AS4/3501复合材料层合板挖补修理固化过程中模量和残余应力的变化历程。结果表明,凝胶点之前,树脂模量和复合材料横向模量很小,而平行于纤维方向存在残余压应力;凝胶点之后,模量均随时间快速增大到一定值,残余应力先逐渐增大到一定值,再随降温过程快速增大。     

纤维增强热固性复合材料构件的固化变形研究进展

热固性复合材料的固化是一个热性能、化学性能和力学性能同时发生变化的复杂过程,也是固化变形和残余应力产生的过程。引起复合材料变形的因素主要包括构件的结构形式、树脂含量、铺层方式、基体树脂的特性、固化工艺参数及模具因素等。其中,复合材料固化过程中树脂的热收缩、化学收缩以及模具材料与复合材料间热膨胀系数的差异是引起复合材料发生固化变形的根本原因。     

纤维增强层合复合材料固化过程的研究

复合材料层板的制造是个复杂的过程，如何优化以操作温度和操作压力为主的工艺条件以提高产品质量，是许多科研工作者多年研究的课题，对此问题需从固化过程的四个方面的机理进行研究：热－ 化学机理、树脂流动－ 纤维作用机理、气泡活动机理、残余应力机理。本文分别介绍了这四方面的研究进展及有代表意义的理论模型。     

复合材料制品的固化变形研究

热固性树脂基复合材料在热压罐成型过程中,由于模具的约束作用,工件内部会产生残余应力,进而引起工件回弹变形和翘曲变形。本文以层合板为例,分析固化工艺、铺层方式等因素对固化变形的影响。     

热固性树脂微波固化研究进展

综述了近年来热固性树脂及其复合材料的微波固化研究进展,重点讨论了热固性树脂微波固化与加热固化的比较,热固性树脂微波固化工艺,颗粒、纤维增强树脂基复合材料的微波固化研究。研究发现微波固化和热固化在本质上是相同的,然而,微波极大地加速了固化进程,对体系性能无损害;加入无机、金属填料以及纤维可以改变体系介电性能,控制微波工艺对材料进行精加工。最后介绍了微波热效应原理,并展望了微波热固化技术发展与应用。     

环氧—酚醛体系固化过程及固化工艺

树脂固化不完全与开裂是浸渍制品的两个主要质量问题。 本文在探讨树脂固化机理的基础上,用红外光谱追踪不同温度、不同时间环氧基的吸收峰变化,得到了环氧基的转化率随温度、时间变化的曲线。以环氧基的转化率作为固化度,以此建立了红外光谱测环氧树脂固化程度的方法。由此,得到了树脂完全固化所需的温度和时间。对等当量配比与固化剂不足之配比在固化速度与固化程度上进行了对比。 我们又在分析开裂原因的基础上,用热分析配合红外光谱找出环氧—酚醛体系固化过程的反应温度区及反应速度最快的温度点。提出了能防止产生破坏性内应力的升温程序和固化工艺。     

VARTM工艺树脂固化过程温度场的模拟与实验

基于热传导和固化动力学理论,采用有限元法,建立了复合材料固化过程的物理模型和数学模型,采用fluent编制固化计算程序,模拟和分析了层合板固化过程中不同时刻的固化放热和温度分布情况,通过对比温度变化云图,获取相差最大部位的温差约为2.46℃。以R688型环氧树脂为基体、玻璃纤维布为增强材料使用真空辅助树脂传递模塑(VARTM)工艺固化成型中进行温度场的测量实验,通过温度记录仪采集预埋入纤维布中数点位置的热电偶的温度,记录复合材料在固化过程中不同位置和不同时刻的温度变化情况。研究表明:模拟和实验结果基本吻合,证明该方法的有效性和准确性。     

In situ monitoring of residual strain development during composite cure

Internal (residual) stresses build up in a thermosetting composite as the matrix shrinks during cure, and again as the composite is cooled to ambient from its elevated processing temperature. These stresses can be significant enough to distort the dimensions and shape of a cured part as well as initiate damage in off‐axis plies, either during fabrication or under the application of relatively low mechanical loads. The magnitude of these stresses depends on a number of factors including constituent anisotropy, volume fraction and thermal expansion, ply orientation, process cycle, and matrix cure chemistry. In this study, embedded strain gauges were employed to follow, in situ, the buildup of residual strains in carbon fiber‐reinforced laminates during cure. The data were compared to those from volumetric dilatometer studies to ascertain the fraction of resin shrinkage that contributed to residual stress buildup during cure. Based on earlier studies with single‐fiber model composites, the process cycle in each case was then varied to determine if the cycles optimized to minimize residual stresses for isolated fibers in an infinite matrix were applicable to the reduction of residual stresses in conventional multifiber composites. The results of these studies are reported here.     

Interferometric measurement of inhomogeneous swelling

Differential thermal contraction between matrix and fiber materials in composites and between adhesive and adherend materials in adhesive joints occurs during cooling from the resin cure temperature and gives rise to non-uniform internal stress fields. Resin swelling associated with water uptake during service gives rise to inhomogeneous stress, the magnitude and distribution of which is the subject of the present investigation. Thin layers of cured epoxy resin have been allowed to absorb water at their edges only, and the swelling normal to these layer planes has been measured by studying optical interference patterns. The stresses resulting from inhomogeneous swelling, a few tens of bars, are of similar magnitude to those resulting from inhomogeneous shrinkage during cooling from resin cure temperatures.     

模具对热固性树脂基复合材料固化变形的影响

热固性树脂基复合材料结构在热压罐成型过程中,由于模具的约束作用,导致构件内部产生残余应力,进而引起工件回弹变形和翘曲变形.综述和分析了影响残余应力和变形产生的各种模具因素,包括模具热传导性能、模具线膨胀系数、模具表面处理、模具角半径和模具的结构形式.     

碳纤维增强苯并噁嗪树脂基复合材料的研究进展

苯并噁嗪是近年来发展起来的一种新型的高性能复合材料基体树脂。本文较系统地综述了国内外碳纤维增强苯并噁嗪复合材料的研究进展,介绍了苯并噁嗪树脂及其复合材料的性能特点,指出了进一步的发展趋势。     

用于辐照改性的PBO纤维复合材料的树脂体系配方设计及其性能研究

结合γ-射线辐照改性PBO纤维表面技术,将辐照介质(接枝体化合物)作为树脂基体的一个成分设计出环氧树脂基体配方.通过浸润试验、树脂浇铸体力学试验、纤维湿法缠绕工艺试验和Microbond界面剪切试验等方法研究了树脂基体的各项性能.结果表明,与另外几种常用的树脂基体相比,本文设计的树脂基体与表面改性PBO纤维的浸润性能和界面粘接性能有明显的提高.树脂浇铸体力学性能满足高性能纤维复合材料的要求.     

Phase separation time/temperature dependence of thermoplastics-modified thermosetting systems

The cure-induced phase separation processes of various thermoplastics(TP)-modified thermosetting systems which show upper critical solution temperature (UCST) or lower critical solution temperature (LCST) were studied with emphasis on the temperature dependency of the phase separation time and its potential application in the cure time-temperature processing window. We found that the phase separation time/temperature relationship follows the simple Arrhenius equation. The cure-induced phase separation activation energy E_a(ps) generated from the linear fitting of the Arrhenius equation is irrelevant to the detection means of phase separation time. We also found that E_a(ps) is insensitive to TP content, TP molecular weight and curing rate, but it changes with the cure reaction kinetics and the chemical environment of the systems. With the established phase separation time-temperature dependence relation, we can easily establish the whole cure time-temperature transformation (TTT) diagram with morphology information which is a useful map for the TP/TS composites processing industry.     

玻璃钢拉挤工艺过程非稳态温度场与固化度数值模拟与试验

玻璃钢拉挤成型过程中其固化度和温度变化为强耦合关系。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。通过示差扫描量热实验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玻璃钢非稳态温度场和固化度进行数值模拟。采用特殊设计制作的铝毛细管封装的布拉格光栅光纤传感器,屏蔽了荷载效应应变干扰,对玻璃钢温度场进行实时捡测;采用索氏萃取实验测定玻璃钢制品固化度。实验表明,模拟与实验结果基本吻合。为避开繁多试凑性实验而进行工艺过程优化提供理论依据。     

快速固化环氧树脂/碳纤维复合材料的性能

利用差示扫描量热分析仪研究了一种快速固化环氧树脂体系的固化工艺参数,确定了以真空辅助树脂灌注工艺制备快速固化环氧树脂/碳纤维复合材料的成型方法,并与常规固化环氧树脂体系制备的碳纤维复合材料进行对比,采用傅里叶变换红外光谱仪对两种材料的树脂基体进行了分析,考察了两种复合材料的纤维含量、孔隙率及力学性能,最后通过扫描电子显微镜观察了快速固化树脂基体与碳纤维的界面结合性。结果表明,快速固化树脂在99℃下固化6 min后固化度可达96%,能够大幅缩减碳纤维复合材料的成型时间,以其制备的碳纤维复合材料拉伸强度比常规固化环氧树脂复合材料高11.20%,弯曲强度高16.92%,纵横剪切强度高7.44%,快速固化树脂与碳纤维界面结合性良好。     

Processing‐interphase‐property relationship in fiber‐reinforced thermosetting‐matrix composites

Fabrication of thermosetting‐matrix composites is based on a critical step of cure, which involves applying a predefined temperature cycle to a fiber‐resin mixture. Several temperature‐dependent mass transport processes occur in the vicinity of the reinforcement fiber, leading to the formation of an interphase region with different chemical and physical properties from the bulk resin. The cure cycles applied on the macroscopic boundaries of the composite govern the microscopic cure kinetics near the fiber surface, which in turn determines the interphase and composite properties. A predictive approach to directly linking the cure cycles and final composite properties is not presently available and is established for the first time in this paper. A multiscale thermochemical model is developed to predict the concentration profile evolution with time near fiber surfaces at various locations across the composite thickness. The concentration profiles at the gelation time are mapped to modulus profiles within the interphase region, and a finite element analysis is used to determine the overall composite modulus in terms of the constituent interphase, fiber, and matrix properties. Relevant numerical results are presented for the first time where the composite modulus is directly linked to the cure cycle and interphase formation parameters without assumed structures or properties of the interphase. The results provide useful information for selecting material components and cure cycles parameters to achieve desired interphase and composite properties. POLYM. COMPOS., 26:193–208, 2005. © 2005 Society of Plastics Engineers     

T700碳纤维/环氧树脂复合材料热降解实验研究

针对T700碳纤维增强环氧树脂复合材料的热降解行为以及回收所得碳纤维的力学性能进行了研究。研究结果表明,碳纤维的存在增加了环氧树脂降解时所需的活化能,热降解反应的温度、时间和气氛等因素对环氧树脂基体降解效果以及回收碳纤维力学性能均有影响。在空气条件下500℃处理30 min后碳纤维表面没有残留物,但其回收纤维的拉伸强度保留率仅为77.6%。通过首先在氮气气氛高温短时热处理,再在空气气氛下450℃进行30 min热降解的两步法处理后,碳纤维表面残炭得到去除,回收碳纤维的拉伸强度保留率达到了90.4%,由其制备单向复合材料的层间剪切强度保留率可达到75.8%。