碳纤维/环氧预浸料摩擦滑移特性测试及其变化规律

带曲率的复合材料层合结构在制备过程中,预浸料铺层之间、预浸料铺层与模具之间会发生摩擦滑移行为,其滑移程度影响复合材料的制造质量。本文采用自行建立的预浸料摩擦滑移特性测试装置,针对碳纤维/环氧树脂预浸料体系,测试分析了不同工艺条件下,预浸料铺层与铺层之间,以及预浸料铺层与钢模具、铝模具和橡胶模具材料之间的摩擦滑移特性。实验结果表明,温度变化会改变预浸料铺层间的摩擦机制,而外压变化不改变预浸料铺层间的摩擦机制;较高的温度或较小的外加压力会减小预浸料铺层的摩擦阻力,有利于预浸料铺层的滑移运动;预浸料铺层与模具材料之间的摩擦滑移特性与模具材料的表面粗糙度有关,其摩擦阻力受温度影响更明显,而受外压影响变化较小。     

单向碳纤维/环氧树脂预浸料热解特性

通过热重实验研究了单向碳纤维/环氧树脂预浸料的热解性能,利用FESEM测试分析了单向碳纤维/环氧树脂预浸料的热解残留物的形貌特征,得到其热解反应过程的物质参与。研究结果表明,单向碳纤维/环氧树脂预浸料的热解反应在空气中分为三个阶段,其中第一、二阶段是环氧树脂基体的热解,第三个阶段是碳纤维的热解。不同形态的单向碳纤维/环氧树脂预浸料在不同加热速率下的热解规律：随加热速率的增加,每个阶段的初始分解温度、反应最终温度及最大失重速率温度均向高温方向移动,热解温度范围逐渐扩大,质量损失明显增加。在相同的升温速率下,块状的单向碳纤维/环氧树脂预浸料相对于其粉末材料的热解时间较长,每个阶段的热解温度较高。     

碳纤维/环氧树脂预浸带铺放应力场及制品微观结构的模拟与实验

碳纤维/环氧树脂预浸带复合材料在铺放成型时,由于树脂基体与碳纤维之间的热膨胀系数存在差异以及成型时热-力参数作用下由于纤维的变形而导致纤维与基体接触处产生应力集中等原因,在制品材料中会产生热残余应力。针对碳纤维/环氧树脂预浸带复合材料的实际结构特点,利用ABAQUS有限元软件建立含有界面的碳纤维/环氧树脂预浸带复合材料的细观代表性体积单元(Representative volume element, RVE)有限元模型,采用实验研究和有限元仿真分析的方法,研究在温度-压力参数作用下预浸带铺放制品残余应力的分布规律及影响机理。首先,建立预浸带铺放时的温度和压力模型,研究不同温度和压力参数条件下碳纤维/环氧树脂预浸带铺放制品残余应力的分布情况。其次,采用耦合降温法模拟碳纤维/环氧树脂预浸带残余应力随纤维体积含量、铺放压力以及铺放温度的变化规律,并采用扫描电镜对不同工艺参数条件下预浸带铺放制品的微观结构进行分析。通过对模拟结果进行分析比较得到各因素对制品残余应力的基本影响规律;最后进行不同温度和压力等铺放参数对预浸带铺放成型时残余应力影响的实验测试研究。      

模拟雷电流作用下单向碳纤维/环氧树脂预浸料的电阻特性

为探究碳纤维/环氧树脂预浸料在雷电流作用下的电阻特性,采用10/350 μs波形的低峰值模拟雷电流对单向碳纤维/环氧树脂预浸料进行模拟雷击试验,并采用四电极法测量试验前后碳纤维/环氧树脂预浸料的直流（DC）电阻,利用SEM和拉曼光谱对雷击前后碳纤维/环氧树脂预浸料微观形态、物相结构进行表征,系统研究了受雷击后单向碳纤维/环氧树脂预浸料的DC电阻变化的原因。结果表明:单向碳纤维/环氧树脂预浸料DC电阻不随雷电流峰值的增加单调变化,而是呈先减小后增大的趋势,这是碳纤维石墨化、环氧树脂绝缘性能劣化、碳纤维断裂、隧道效应等因素综合作用的结果。      

预定型机织物剪切变形实验研究

在改进像框实验的基础上,对斜纹和缎纹预定型碳纤维织物的剪切性能进行了实验观察。研究发现,预定型机织物的剪切机制与织物剪切相似。根据实验结果,从定型剂的浓度和织物结构分析了预定型织物的剪切性能。随着定型剂浓度提高,织物的折皱角越大,织物剪切性能越差;与预定型斜纹织物相比,预定型缎纹织物相对较容易成型,剪切载荷较小。利用立式显微镜观察剪切过程中纱线宽度的变化,拟合得到了宽度变化方程,建立预定型机织物的折皱角模型,预测结果与实验结果误差在2°内,证明了该模型的有效性。     

单向碳纤维/环氧树脂预浸料叠层的面内变形行为

为了充分了解热隔膜成型过程中预浸料的变形行为，通过偏轴拉伸测试探索了热固性单向碳纤维/环氧树脂预浸料在高温条件下的面内变形机制。研究参数包括试验温度、拉伸速率、预热时间和铺层顺序等。利用数字图像相关技术，在测试过程中监测单向碳纤维/环氧树脂预浸料的变形和纤维的旋转情况。结果表明，提高试验温度或降低拉伸速率均有利于促进单向碳纤维/环氧树脂预浸料的变形。铺层顺序对单向碳纤维/环氧树脂预浸料铺层的变形行为有很大影响，[45/–45/90]_S铺层方式比 [45/90/–45]_S铺层方式更有利于纤维旋转，且[45/–45/90]_S铺层方式变形阻力更小。采用铰链连接网(Pin-joined net, PJN) 理论对单向碳纤维/环氧树脂预浸料铺层变形过程中纤维角度变化进行预测并与实验结果进行对比，结果表明，用PJN理论预测的纤维旋转角度值与测试值存在较大偏差，说明其并不适用于预测热固性单向碳纤维/环氧树脂预浸料变形过程中纤维角的变化。同时，80℃预加热可以提高单向碳纤维/环氧树脂预浸料的变形阻力。      

基于非正交本构模型的热塑性机织物预浸料宽温域赋形褶皱缺陷仿真方法

热塑性复合材料预制体的赋形质量直接影响结构件的制造质量。由于热塑性基体具有较高的熔融温度和黏度，赋形工艺温度设计不合理会导致褶皱等赋形缺陷，给热塑性复合材料结构高质量成型带来了挑战。现有的热塑性预浸料热成型研究主要基于连续介质力学、离散元、半离散元法，通过建立多机制耦合的本构模型分析热塑性预浸料的各向异性大变形行为，未充分考虑工艺调控对赋形宏观变形过程中褶皱缺陷的影响。发展了一种热塑性预浸料宽温域赋形褶皱缺陷仿真方法。通过表征热塑性机织物预浸料在不同温度、载荷下的力学性能，获取宽温域热塑性预浸料本构参数，基于非正交本构模型，提出了温度对热塑性预浸料赋形褶皱缺陷的作用规律，揭示了赋形过程中宽温域褶皱缺陷的变形机制，获得了赋形温度优化调控方案。研究结果表明：褶皱缺陷的萌生和演化过程由不同温度下的面内剪切和压缩变形行为共同影响，预浸料的褶皱缺陷变形程度随温度的增加而减弱，非正交本构模型的模拟结果与实验结果基本一致。     

预浸织物剪切变形时树脂细观分析模型

为了更好地研究在发生剪切变形时预浸织物材料的力学性能,建立了在像框剪切试验时未固化的树脂对织物发生剪切变形时的阻碍作用的细观分析模型.通过对材料的单胞进行分析,得到了织物单胞变形前、后各质点间的运动学关系,进而得到了树脂材料对整个织物单胞的阻力矩,即树脂的阻尼作用.此阻尼作用较好地说明了树脂在预浸织物材料中的作用.此外,通过树脂的流变试验得到其粘性系数,该粘度系数确定,即该材料的阻尼作用确定.     

热固性预浸料凝胶特性的固体扭转测试方法

采用固体扭转法研究了一种玻璃纤维织物/环氧预浸料和2种碳纤维织物/环氧预浸料的流变特性,为测定凝胶点和研究凝胶化过程提供了一种可行的表征方法。在此基础上考察了试样尺寸和纤维织物结构对预浸料凝胶特性的影响。结果表明：试样宽度对测试结果基本没有影响,而试样厚度增加会引起预浸料动态模量的降低,凝胶点不易判定;纤维织物结构对预浸料凝胶点有很大影响,说明预浸料流变特性反映的是树脂流变特性与纤维网络可变形性综合作用的结果。     

带有橡胶垫层的混凝土接触特性试验及其内聚力模型

针对带有橡胶垫层的混凝土试件,通过直剪试验研究了带有橡胶垫层的混凝土接触摩擦特性。采用PPR内聚力模型表征接触面的接触摩擦特性,对试验结果进行了模拟分析。试验结果表明:在带有橡胶垫层的混凝土接触面剪切过程中,剪切应力与剪切位移的变化过程可分为弹性、弹塑性硬化和应变软化变形阶段。当轴向应力在1.5 MPa~13 MPa范围内时,残余强度与剪切强度比在55%~65%,当轴向应力为17 MPa和21 MPa时,残余强度与剪切强度比大约分别为70%、80%。橡胶垫层在混凝土之间起到良好的缓冲作用。在轴向应力较大时,接触面的应力变形会伴有明显的软化变形阶段。利用Archard非线性幂次准则描绘了剪切峰值应力与轴向应力的关系,准则中常数k和m分别为0.97和0.33。PPR内聚力模型计算表明剪切应力随剪切位移变化关系曲线与试验结果基本吻合,为研究盾构管片块体间的接触摩擦作用研究提供借鉴。     

Research on the Shear Behaviour of Plain Weave Prepreg at Lateral Compaction Stage

Abstract:  An investigation of the shear behaviour of plain weave prepreg at lateral compaction stage was undertaken by the picture-frame test. A unit cell of weave prepreg was modelled and three moments were assumed in the unit cell: (i) the moment of shear force that picture frame applies on the unit cell; (ii) the friction moment at crossover of yarns; and (iii) the compaction moment between the yarns. Through moment balance, a relationship between the load and the shear rate was deduced. A plain sheet shearing film resin model was established to obtain the friction moment at crossover. To get the compaction moment, a constitutive equation of a single prepreged yarn was deduced and a transverse viscosity coefficient equation was given. Moreover, through an equivalent cross-sectional area model, the lateral contact thickness between the yarns was obtained. The comparison between the experimental and theoretical results shows that the presented model can describe the shear behaviour of weave prepreg at lateral compaction stage well.     

预定型平纹织物的剪切模型

预定型织物是一种用于纺织复合材料液态成型的新型材料, 可以提高复合材料构件的形状精度和尺寸精度。由于织物中存在定型剂, 使织物材料的性能发生改变。基于像框剪切试验, 建立预定型平纹织物剪切变形的理论模型。与干态织物相比, 重点分析了预定型织物中纱线的弯曲刚度和纱线摩擦系数的变化对剪切性能的影响; 同时模型中考虑了剪切过程中纱线轴向力的变化对剪切性能的影响。另外, 利用立式显微镜观察了在纱线挤压阶段纱线宽度变化的规律, 考虑了定型剂和织物结构对纱线宽度变化的影响。根据平衡方程得到预定型平纹织物的剪切模型, 通过与试验结果比较, 该模型可以较好地预测预定型平纹织物的剪切变形性能。      

Influence of prepreg conditions on the void occurrence and tensile properties of woven glass fiber-reinforced polyimide composites

The influence of prepreg solvent content on void occurrence in woven glass fiber-reinforced polyimide composites and their tensile properties was studied. A precursor solution of SKYBOND 703 was diluted in an additional solvent (n-methyl pyrrolidone) and the glass woven fabric was immersed in about 40 wt.% polyamic acid, in solvent. Prepregs were dried at 373 K for different time intervals, ranging from 2 to 24 h. Prepregs with varying residual solvent content under each condition were laid up, and their [(0/90)]₄ composite laminates were formed by autoclaving at a hydrostatic pressure of 0.7 MPa. The relationship of drying time with the amount of residual prepreg solvent, as well as with the volume fractions of fiber and voids was investigated. The void geography and content for each composite laminate, and the tensile strength and modulus at room temperature were also evaluated. The results clearly indicated that, depending on the altering residual solvent content in the prepreg, the void geometry and location influenced reduction of the tensile properties of woven fabric composite laminate. An appropriate prepreg resin viscosity during curing, which avoids reduction of the tensile properties, was revealed.     

A method for the direct measurement of the fibre bed compaction curve of composite prepregs

A method to measure the fibre bed compaction curve directly from composite prepreg is presented. The method was used to measure the compaction curve of unidirectional and quasi-isotropic AS4/3501-6 carbon–epoxy prepregs. Similar compaction curves were obtained in all cases. The compaction curve obtained was used by a finite element process model, COMPRO, to simulate the uniaxial compaction of 8 and 16 ply laminates at different temperatures. The force–displacement response predicted by the model closely matched the experimental results. The method which can be used on both tape and fabric prepregs, has the major advantages of being a direct measure of the prepreg behaviour, and requires no special preparation of the sample.     

经编间隔织物增强柔性复合材料冲击性能

针对传统个体防护材料刚硬、限制人体活动的缺点,设计了2种柔性复合材料: 剪切增稠液(STF)和硅橡胶填充经编间隔织物(WKSF)柔性复合材料,并对其冲击性能进行研究。WKSF具有上、下两个表层和间隔丝构成的间隔层,在其间隔层中加入STF和硅橡胶2种柔性材料。STF采用将纳米SiO₂分散于聚乙二醇(PEG)中制成,硅橡胶采用硅胶和固化剂混合而成。采用流变仪对STF的流变性能进行测试,采用Instron落锤冲击仪对WKSF及其复合材料的冲击性能进行测试。实验表明: STF在达到临界剪切速率后出现剪切增稠现象,纯织物的冲击过程可分为弹性、平台和压实3个阶段,且具有明显的平台阶段;经填充后所制成的2种复合材料的冲击过程与纯织物明显不同,其载荷-位移曲线呈线性;加入硅橡胶的复合材料刚度较大,没有应变率效应;加入STF的复合材料具有较好的能量吸收性能和明显的应变率效应。     

碟簧装置恢复力模型及其在自复位RC剪力墙中的应用

为了准确模拟碟簧装置和自复位RC剪力墙的力学性能,对碟簧装置的工作原理和力学特性进行了分析,提出并开发了碟簧装置恢复力模型,通过试验验证了恢复力模型的准确性。在低周往复荷载作用下,对内置碟簧装置的自复位RC剪力墙的滞回性能进行数值模拟,并与试验结果进行了对比。结果表明:应用碟簧装置恢复力模型的数值模型可有效模拟自复位RC剪力墙的滞回特性、自复位性能及耗能能力。自复位RC剪力墙的承载力随碟簧预压力、附加摩擦力及碟簧装置刚度的增大而增大;耗能能力随附加摩擦力的增大而增大;残余位移随附加摩擦力的增大而增大,随碟簧预压力和碟簧装置刚度的增大而减小。     

不同摩擦压力下TB2线性摩擦焊过程参量的变化规律研究

目的 深入分析钛合金线性摩擦焊接过程,掌握焊接参数变化时各摩擦阶段过程参量的变化规律及其与接头质量的关系。方法 采用不同摩擦压力进行TB2钛合金线性摩擦焊接试验,基于信号采集获得了焊接过程典型参量的变化曲线。结果 曲线特征分析表明,摩擦压力40 MPa时,在设定时间内未达到稳定摩擦阶段,曲线特征异常,接头明显未焊合。随摩擦压力增大至70和100 MPa,各曲线变化规律与线性摩擦焊接4个典型阶段相吻合,分别得到焊缝宽度不同的无缺陷接头。70 MPa下摩擦剪力过渡平缓,界面塑性金属的产生与挤出较为协调,焊接过程的稳定性及接头质量易于得到控制。结论 通过对比不同参数下焊接过程参量的变化规律,有助于认识不同线性摩擦焊接过程的内在差异,从而判断接头质量并选取合适的焊接参数。     

Influence of the shape of fiber cross section on fabric surface characteristics

Fiber cross sections for use in textiles and composites are becoming more and more complex. Shape impacts fiber or filaments properties and therefore the yarn and fabric characteristics. This paper presents the influence of the fiber cross section on the fabric surface characteristics. The material used was polyester staple fibers, of four different shapes: round, scalloped oval, cruciform and hexachannel. All fibers had the same cut length with different fineness. Yarns obtained from these fibers had nominally the same yarn count, torsion value and structure. Plain jersey fabrics were knitted from each of the yarns under identical conditions and then relaxed prior to testing. Friction behavior was evaluated and a roughness-friction criterion developed. An indirect measurement of the real area of contact was obtained in order to provide roughness and friction properties. The influence of fiber cross section on yarn bending rigidity and on the state of the knitted fabric surface was characterized.     

The experimental determination of prepreg tack and dynamic stiffness

A new peel test has been developed which quantifies the tack and dynamic stiffness of uncured prepreg. The test is designed to simulate the automated tape lay-up (ATL) and automated fibre placement (AFP) processes. It includes a pressure controlled application stage, where contact time is inversely proportional to peel rate. The use of a thin film allows stiffness to be isolated from peel resistance in a continuous two stage test. A repeatability study revealed consistent results with 16% standard deviation. Tack and stiffness variability has been observed across roll width and between faces in commercial hand lay-up prepregs. The overall tack and stiffness values for commercial hand lay-up prepregs were found to be inconsistent with the levels specified by manufacturers.A temperature increase revealed inconsistent effects on tack between materials. The contradictory results were rationalised by observing failure modes. The two failure modes observed appeared equivalent to those found in pressure sensitive adhesive (PSA) peel. The shear storage modulus of the prepreg resin was compared to the PSA Dahlquist criterion and found to support the principle of contact efficiency. However, the actual value for the criterion is expected to be a function of prepreg specific conditions such as resin content, fibre distribution and surface pattern.