基于宏微观分析的碳纤维增强高分子复合材料强度性能表征

微观力学强度理论(MMF)是一种新型的基于物理失效模式的复合材料强度理论。通过对碳纤维/树脂(UTS50/E51)复合材料单向层合板进行纵向、横向静载拉伸、压缩和弯曲试验, 得到层合板的基本力学性能和宏观强度指标。建立了碳纤维增强树脂基复合材料微观力学模型, 获取树脂基体和纤维不同位置的机械载荷应力放大系数和热载荷应力放大系数。结合获取的应力放大系数及试验测得的单向层合板宏观强度, 计算出层合板组分的MMF强度特征值。绘制了基于MMF强度理论的层合板破坏包络线, 并与Tsai-Wu失效准则预测结果进行对比。实现了对UTS50/E51层合板MMF强度特征值的表征。     

复合材料层合板机械连接结构累积损伤模型和挤压性能试验研究

建立了三维累积损伤有限元模型, 采用扩展拉格朗日乘子法对螺栓表面和复合材料层合板孔壁间的接触行为进行了模拟。对复合材料层合板中纤维断裂、基体开裂和纤维2基体剪切3 类基本损伤类型的产生、扩展以及它们之间的关联性进行了研究。计算得到了复合材料层合板单钉连接结构的载荷2位移曲线, 预测了它们的初始挤压破坏载荷。同时, 进行了T300 帘子布/ Q Y8911 双马来酰亚胺树脂层合板单钉单搭螺栓挤压强度试验,验证了不同铺层类型和结构尺寸对复合材料层合板机械连接挤压性能的影响。试验结果和计算结果吻合较好, 证明了该模型和算法的有效性。      

湿热环境下开孔复合材料层合板的强度

通过试验研究T300/5405复合材料层合板在6种湿热环境下开孔拉伸、开孔压缩的极限强度,分析了湿热环境对开孔复合材料层合板强度性能的影响,对比了不同湿热环境下材料的破坏模式。在有限元仿真方面,通过考虑湿热环境对材料刚度和强度的影响,建立了湿热条件下复合材料开孔层合板极限强度的预测方法,模拟了开孔复合材料层合板在不同湿热环境、不同载荷类型下的损伤演化全过程。有限元预测结果与试验结果的误差在20%以内,验证了该预测方法的有效性。     

聚酰亚胺树脂基MT300/KH420复合材料高温力学性能(Ⅱ)——弯曲性能

从宏、微观的角度研究了碳纤维增强聚酰亚胺树脂基MT300/KH420复合材料的高温力学性能,重点揭示了MT300/KH420复合材料[0°]14和[±45°/0°/90°/+45°/0°2]s层合板在常温~500℃的弯曲性能变化规律。研究表明:MT300/KH420复合材料高温力学性能优异,[0°]14层合板在420℃的弯曲强度保持在51%以上,弯曲模量在500℃以内变化很小。[0°]14层合板在常温下断口粗糙,且贯穿厚度,表现为脆性破坏;随温度升高,树脂流动性增强,呈现出黏弹效应,破坏逐渐集中在加载点处,在500℃,部分树脂热解,纤维束脱离基体并氧化。[±45°/0°/90°/+45°/0°2]s层合板高温弯曲性能较为稳定,主要破坏为上、下表面沿45°方向开裂,并伴有层间分离,在500℃出现严重分层破坏;相比于受基体控制的层合板弯曲性能,温度对受纤维控制的层合板弯曲性能影响较小。     

层合板极限强度判据及其最大承载能力的工程设计

在研究层合板在复杂载荷下的极限强度时,提出了基于层合板基本强度和最佳应力比实验强度所确定的层合板张量型强度准则和层合板联合强度理论.通过建立新的层合板铺层刚度退化理论并用实验测定“均衡型刚度退化系数”,实现了LPF包络线预测;进而提出了层合板退化张量型强度准则.该准则是一种由单向板基本刚度、强度性能,辅助以均衡型刚度退化系数,预测各种铺层序列的层合板在复杂载荷下最大承载能力的强度判据和工程方法.上述强度准则与[±θ]s,层合板的单向拉伸,[±45]s、[0/90]s层合板平板拉剪,以及[0/90]s、[0/±45]s和[0/45]s层合管状件的双向载荷强度实验结果相当吻合.所提出的层合板极限强度判据和最大承载能力的估算方法,对玻纤复合材料层合结构的工程强度设计,具有实际的指导意义和实用价值.     

表面带金属层的复合材料层合板低速冲击数值模拟

使用Abaqus/Explicit建立表面带金属层的复合材料层合板和复合材料裸板低速冲击有限元模型,与已有文献对比验证结果的可靠性,研究结果对复合抗弹结构有很好的借鉴和参考价值.采用Johnson-Cook本构关系模拟铝合金和钛合金层的力学行为,选用Hashin准则对复合材料层内损伤进行失效判断,用二次应力准则来模拟粘结层Cohesive单元的层间失效.结果表明,相同铺层与冲击能量下,表面带铝合金层合板对内部纤维的保护性能优于表面带钛合金层合板,表面带钛合金层合板的抗冲击性能优于复合材料裸板;[§/0°/90°/0°/90°/0°]s铺层层合板的抗冲击性能优于[§/-45°/90°/0°/45°/-45°]s铺层层合板的抗冲击性能;在子弹刚冲破层合板与子弹完全离开层合板阶段,表面带铝合金层合板对子弹动能吸收率最大.     

复合材料织物层合板挖补修理软件实现与试验验证

针对单向拉伸载荷作用下复合材料织物层合板胶接挖补修理结构,改进现有解析模型,建立适用于无附加层、附加1层和附加2层结构的阶梯型挖补修理结构和斜切型挖补修理结构的解析分析模型。给出求解算法,定义准确度用于评价数值计算精度,最终实现开发一套界面友好的复合材料胶接挖补修理设计与分析软件。该软件可以求解单向拉伸载荷作用下,复合材料胶接修理结构内部的剪应力场/剪应变场分布,评价搭接板受载情况,并预测结构失效载荷与失效模式。研究中采用T300/CYCOM-970织物作为母板与补片材料,METLBOND1515-4M作为胶层材料,设计进行了一系列阶梯型及斜切型挖补修理验证试验。试件失效载荷与软件计算结果吻合良好,阶梯型最大相差5.7%,斜切型最大相差14.0%。该软件可以对复合材料织物层合板胶接挖补修理进行高效、准确的初步辅助设计与分析。     

基于改进Hashin准则的复合材料低速冲击损伤研究

针对复合材料力学性能的分散性和传统模型中退化系数选取的随意性问题,将退化系数与复合材料强度的威布尔分布参数相结合,采用改进的三维Hashin准则建立了复合材料低速冲击渐进损伤模型。考虑复合材料非线性剪切行为改进了Hashin准则,将原始准则中的剪切项用应变能替代,并采用最大应变准则判断剪切失效,避免了应力准则导致的变形不连续。采用该模型对三种能量下的T300/3501复合材料层合板低速冲击过程进行了仿真分析,计算得到的冲击响应曲线、层内和层间分层损伤结果与实验结果吻合良好,表明建立的模型适用于复合材料层合板低速冲击损伤预测。     

复合材料层合板拉压和面内剪切性能的分散性实验研究

针对纤维增强T300/QY8911复合材料层合板进行大子样纵向拉伸、压缩实验和面内剪切实验,得到了材料拉伸、压缩、面内剪切的主要力学性能参数.研究纤维增强复合材料的刚度和强度特性,发现纵向拉压以及面内剪切应力-应变曲线都几乎为直线,具有脆性破坏的特点.并且利用统计学原理对实验结果进行统计分析,研究各力学性能参数的分布特性,结果表明:三参数威布尔分布、正态分布、对数正态分布能较好地描述各力学性能参数的分布规律,最后给出复合材料层合板拉、压、剪切性能的分散性参数.     

不同粒子改性环氧树脂基碳纤维复合材料低速冲击及冲击后压缩性能

使用单层纳米氧化石墨烯(GO)、纳米SiO2、陶瓷粉对环氧树脂进行改性处理,采用真空辅助树脂传递模塑成型(VARTM)工艺分别制备了[±45/0/90]S、[908]T、[08]T三种铺层角度下的碳纤维增强复合材料(CFRP)层合板.通过落锤冲击实验、超声C扫描检测、冲击后压缩实验等对不同粒子改性CFRP进行实验研究.结果表明:纳米粒子改性可以显著提升CFRP的抗冲击性能及冲击后压缩性能,与其他铺层角度相比,[±45/0/90]S铺层CFRP有效抑制了冲击裂纹的扩展,且单层纳米GO改性下的[±45/0/90]S铺层层合板最大冲击载荷及冲击后压缩强度分别达到3470 N、124.8 MPa,冲击损伤面积仅有580 mm2.与无粒子改性同种铺层层合板相比,最大冲击载荷及冲击后压缩强度相应提高了30％、47.3％,冲击损伤面积减小了15.5％.     

Quantification of flexural fatigue life and 3D damage in carbon fibre reinforced polymer laminates

Carbon fibre reinforced polymer (CFRP) laminated composites have become attractive in the application of wind turbine blade structures. The cyclic load in the blades necessitates the investigation on the flexural fatigue behaviour of CFRP laminates. In this study, the flexural fatigue life of the [+45/−45/0]_2s CFRP laminates was determined and then analysed statistically. X-ray microtomography was conducted to quantitatively characterise the 3D fatigue damage. It was found that the fatigue life data can be well represented by the two-parameter Weibull distribution; the life can be reliably predicted as a function of applied deflections by the combined Weibull and Sigmodal models. The delamination at the interfaces in the 1st ply group is the major failure mode for the flexural fatigue damage in the CFRP laminate. The calculated delamination area is larger at the interfaces adjacent to the 0 ply. The delamination propagation mechanism is primarily matrix/fibre debonding and secondarily matrix cracking.     

可收卷复合材料层板大变形弯曲性能研究

该文研究了玻璃纤维编织复合材料制成的可收卷层板在大变形条件下的弯曲静力性能和疲劳性能。通过弯曲静力试验得到了试验件在大变形条件下的应变和位移的关系;通过有限元模拟静力试验并与试验结果对照,确定了疲劳试验的载荷;研究了在大变形条件下不同铺层层板的弯曲疲劳寿命及失效模式和相同铺层层板的疲劳寿命曲线。结果表明:复合材料层板在大变形弯曲时具有明显的非线性行为,且(±45°)铺层层板弯曲疲劳性能明显优于(0°/90°)铺层层板;在最小应变和最大应变比不变的情况下,相同铺层层板的弯曲最大应变和对数疲劳寿命之间存在线性关系。     

复合材料可靠性设计的小子样系数法

对试验数据进行统计分析后,找到了T300/QY8911,T300/HD03和T300/QY8911-Ⅱ等几种常用复合材料强度性能的最大标准差,并发现:0°铺层或90°铺层的复合材料单层板强度性能分散性(变异系数或方差)要比多向铺层板大,这一性质对大多数复合材料都成立。通过对T300/QY8911,T300/HD03和T300/QY8911-Ⅱ等复合材料强度性能的分布检验,发现:复合材料强度性能遵循对数正态分布。提出复合材料强度性能可靠性设计的高精度小子样系数方法,与传统方法等进行了对比计算,发现:本文方法计算结果稳定,计算精度高,可以获得比其他方法更大的数值结果,使复合材料得到更加充分的利用,并节省试件。      

Fatigue performance of a bonded wavy composite lap joint

A novel wavy lap joint design was further studied. Our previous studies using cross‐ply composite adherends showed that the new design was indeed much stronger than the conventional flat joint. In order to fully demonstrate advantage of the new wavy lap joint over the conventional single lap joint, comparative fatigue tests were performed to determine the durability performance of the wavy joint. In this study, a comparative static strength test of the conventional flat joint and the wavy joint was first carried out using unidirectional composite adherends. Then fatigue tests at different load levels and load frequencies were conducted. The test results showed that the wavy lap joint had a much longer fatigue life than the conventional lap joint.     

Applicability of empirical models for evaluation of stress ratio effect on the durability of fiber-reinforced creep rupture–susceptible composites

Fiber-reinforced polymer–matrix composites are known to exhibit loading rate- and time-dependent mechanical response. Their fatigue strength is determined by a complex interaction of damage processes governed by loading duration and cycle number. Apart from mechanistic approaches, a number of empirical models of various sophistication have been proposed to predict the durability of composites, differing in the amount of experimental data needed for their application. The accuracy of several such models is evaluated by comparing the prediction to the experimentally determined stress ratio effect on fatigue life of glass fiber-reinforced polyester–matrix composite. It is found that the accuracy of prediction generally improves with increasing the amount of test data needed for model calibration. However, the most accurate method of fatigue life estimation, among the selected ones, is by the modified Goodman diagram.     

Creep of plain weave polymer matrix composites under on-axis and off-axis loading

Despite the increasing use of polymer woven composites in load-bearing structural applications, published research on their long-term durability is very limited. Hence, creep of plain weave polymer woven composites was investigated experimentally and analytically, using Hexcel Corporation’s F263/T300 2-harness (HS) composite material under on-axis (0°) and off-axis (45°) loading. Constant load creep experiments were conducted over a wide range of temperatures (80–240 °C) and stresses (1–70% of the ultimate tensile strength). Time–temperature-superposition-principle (TTSP) was used to obtain master creep curves at each stress level for a time period beyond the experimental time window. A modified equivalent laminate model (MELM) was developed to predict the creep compliance of plain weave composites for any load orientation with respect to fiber axis, using experimental creep compliance of unidirectional polymer composites. The model predictions were found to be in good agreement with the experimental results, within as well as beyond the experimental time window.     

Fatigue characterization of T300/924 polymer composites with voids under tension‐tension and compression‐compression cyclic loading

Fibrous polymer composites exhibit excellent properties such as high specific stiffness/strength and good fatigue performance. However, as inherent defects of polymer composites, voids have been reported to have an impact on their load‐bearing properties including fatigue resistance. In the interest of safety, the effect of voids on fatigue behaviours of composites should be understood and quantified. In this article, the effect of voids on the fatigue of T300/924 composites was evaluated in terms of their fatigue life, stiffness degradation, and cracks propagation under tension‐tension and compression‐compression loadings. The failure probability was assessed by Weibull distribution. Furthermore, crack measurement and fractographic analysis reveal that the effect of voids on the failure mechanisms of the material under various loading configurations could be different. Lastly, an analytical residual stiffness model was proposed, and a good correlation was obtained between the experimental data and the prediction results.     

铆钉分布形式对自冲铆接头力学性能的影响

该文采用Landmark试验机对5052铝合金自冲铆接头进行力学性能测试来研究铆钉分布形式对自冲铆接头力学性能的影响。获得了单铆钉自冲铆(简称SR)接头、横向分布双铆钉自冲铆(DRT)接头和纵向分布双铆钉自冲铆(DRL)接头的静力学和疲劳性能,采用正态分布和威布尔分布对试验数据进行分析检验其有效性。结果表明:DRT接头静强度约为SR接头的2倍;DRL接头静强度约为SR接头的1.9倍。DRL接头比DRT接头具有更好的能量吸收能力。双铆钉自冲铆接头的疲劳性能优于SR接头。铆钉分布形式对接头疲劳变形量影响较小,但是对寿命影响较大。当疲劳载荷较高时,DRL接头可提高疲劳寿命。随着疲劳载荷降低,DRT接头可显著增加疲劳寿命。     

An empirical model for fatigue behavior prediction of glass fibre-reinforced plastic composites for various stress ratios and test frequencies

Current models used to predict the fatigue life of glass fibre-reinforced plastic composites do not accurately consider the effects of load stress ratios and load frequencies. These models usually require significant amount of experimental data to establish a set of characteristic fatigue curves for a given composite. This paper proposes a fatigue model for glass fibre-reinforced plastic composites that includes the non-linear effect of stress ratio and load frequency on the fatigue life. The model can be used to predict the fatigue behavior of a composite material using a well-defined minimum number of tests. Fatigue data from the literature and selected research laboratories were used to test the model. Predictions were found to be in good agreement with all experimental data adequately accounting for the influence of test frequency and stress ratio on the fatigue life of composites.     

316L不锈钢的高温疲劳蠕变行为和寿命预测

进行316L不锈钢在单级和两级载荷作用下的高温疲劳蠕变试验,研究了载荷历程效应对材料行为的影响.在已有统一的疲劳蠕变损伤演化模型基础上,得到了316L高温单级载荷作用下非线性损伤演化曲线.同时,建立了一种耦合载荷历程效应的多级疲劳蠕变载荷作用下的材料破坏准则.基于该破坏准则,结合材料的非线性损伤模型对316L不锈钢高温两级载荷作用下的疲劳蠕变寿命进行了预测,预测结果与试验数据符合得比较好.