Study of damage behavior and repair effectiveness of patch repaired carbon fiber laminate under quasi-static indentation loading

Damage caused due to low-velocity impacts in composites leads to substantial deterioration in their residual strength and eventually provokes structural failure.This work presents an experimental investigation on the effects of different patch and parent laminate stacking sequences on the enhancement of impact strength of Carbon Fiber Reinforced Polymers(CFRP)composites by utilising the adhesively bonded external patch repair technique.Damage evolution study is also performed with the aid of Acoustic Emission(AE).Two different quasi-isotropic configurations were selected for the parent laminate,viz.,[45°/45°/0°/0°]s and[45°/0°/45°/0°]s.Quasi Static Indentation(QSI)test was performed on both the pristine laminates,and damage areas were detected by using the C-scan inspection technique.Damaged laminates were repaired by using a single-sided patch of two different configurations,viz.,[45°/45°/45°/45°]and[45°/0°/0°/45°],and employing a circular plug to fill the damaged hole.Four different combinations of repaired laminates with two configurations of each parent and patch laminate were produced,which were further subjected to the QSI test.The results reveal the effectiveness of the repair method,as all the repaired laminates show higher impact resistance compared to the respective pristine laminates.Patches of[45°/0°/0°/45°]configuration when repaired by taking[45°/45°/0°/0°]s and[45°/0°/45°/0°]s as parents exhibited 68%and 73%higher peak loads,respectively,than the respective pristine laminates.Furthermore,parent and patch of configuration[45°/0°/45°/0°]s and[45°/0°/0°/45°],respectively,attain the highest peak load,whereas[45°/45°/0°/0°]s and[45°/45°/45°/45°]combinations possess the most gradual decrease in the load.

Low-Velocity Impact and Compression after Impact(CAI)Behaviors of Carbon-Aramid/Epoxy Hybrid Braided Composite Laminates

Low-velocity impact and in-plane axial compression after impact(CAI)behaviors of carbon-aramid/epoxy hybrid braided composite laminates were investigated experimentally.The following three different types of carbon-aramid/epoxy hybrid braided composite laminates were produced and tested:(a)inter-hybrid laminates,(b)sandwich-like inter-hybrid laminates,and(c)unsymmetric-hybrid laminates.At the same time,carbon/epoxy braided composite laminates were used for comparisons.Impact properties and impact resistance were studied.Internal damages and damage mechanisms of laminates were detected by ultrasonic C-scan and B-scan methods.The results show that the ductility index(DI)values of three kinds of hybrid laminates aforementioned are 37%,4%and 120%higher than those of carbon/epoxy laminates,respectively.The peak load of inter-hybrid laminates is higher than that of sandwich-like inter-hybrid laminates and unsymmetric-hybrid laminates.The average damage area and dent depths of inter-hybrid laminates are 64%and 69%smaller than those of carbon/epoxy laminates.Those results show that carbon-aramid/epoxy hybrid braided composite laminates could significantly improve the impact properties and toughness of non-hybrid braided composite laminates.

Vibration characteristics of piezoelectric functionally graded carbon nanotube-reinforced composite doubly-curved shells

This paper presents an analytical solution for the free vibration behavior of functionally graded carbon nanotube-reinforced composite(FG-CNTRC) doubly curved shallow shells with integrated piezoelectric layers. Here, the linear distribution of electric potential across the thickness of the piezoelectric layer and five different types of carbon nanotube(CNT) distributions through the thickness direction are considered. Based on the four-variable shear deformation refined shell theory, governing equations are obtained by applying Hamilton's principle. Navier's solution for the shell panels with the simply supported boundary condition at all four edges is derived. Several numerical examples validate the accuracy of the presented solution. New parametric studies regarding the effects of different material properties, shell geometric parameters, and electrical boundary conditions on the free vibration responses of the hybrid panels are investigated and discussed in detail.

The effect of initial geometric imperfection on the nonlinear resonance of functionally graded carbon nanotube-reinforced composite rectangular plates

The purpose of the present study is to examine the impact of initial geometric imperfection on the nonlinear dynamical characteristics of functionally graded carbon nanotube-reinforced composite(FG-CNTRC) rectangular plates under a harmonic excitation transverse load. The considered plate is assumed to be made of matrix and single-walled carbon nanotubes(SWCNTs). The rule of mixture is employed to calculate the effective material properties of the plate. Within the framework of the parabolic shear deformation plate theory with taking the influence of transverse shear deformation and rotary inertia into account, Hamilton’s principle is utilized to derive the geometrically nonlinear mathematical formulation including the governing equations and corresponding boundary conditions of initially imperfect FG-CNTRC plates. Afterwards, with the aid of an efficient multistep numerical solution methodology, the frequency-amplitude and forcing-amplitude curves of initially imperfect FG-CNTRC rectangular plates with various edge conditions are provided, demonstrating the influence of initial imperfection,geometrical parameters, and edge conditions. It is displayed that an increase in the initial geometric imperfection intensifies the softening-type behavior of system, while no softening behavior can be found in the frequency-amplitude curve of a perfect plate.

Analysis of vibration attenuation characteristics of large thickness carbon fiber composite laminates

The vibration attenuation and damping characteristics of carbon fiber reinforced composite laminates with different thicknesses were investigated by hammering experiments under free boundary constraints in different directions.The dynamic signal testing and analysis system is applied to collect and analyze the vibration signals of the composite specimens,and combine the self-spectrum analysis and logarithmic decay method to identify the fundamental frequencies of different specimens and calculate the damping ratios of different directions of the specimens.The results showed that the overall stiffness of the specimen increased with the increase of the specimen thickness,and when the thickness of the sample increases from 24mm to 32mm,the fundamental frequency increases by 35.1%,the vibration showed the same vibration attenuation and energy dissipation characteristics in the 0°and 90°directions of the specimen,compared with the specimen in the 45°direction,which was less likely to be excited and had poorer vibration attenuation ability,while the upper and lower surfaces of the same specimen showed slightly different attenuation characteristics to the vibration,the maximum difference of damping capacity between top and bottom surfaces of CFRP plates is about 70%.

DELAMINATION FORMATION AND DELAMINATION PROPAGATION OF COMPOSITE LAMINATES UNDER COMPRESSIVE FATIGUE LOADING

Fatigue tests of the smooth composite laminates and the notched composite laminates under compressive cyclic loading have been carried out. The damage mechanism is discussed and analyzed. Damage evolution is monitored using stiffness decay. From these tests, it is found that the initial delamination occurs at the free boundary of smooth specimens, or the notch boundary of notched specimens, subjected to the compression-compression cyclic load. A point of view in relation to two-phases of compression fatigue delamination of composites is proposed, namely, compression-compression delamination consists of the delamination formation phase and the delamination propagation, and there is a 'damage transition point' to separate this two-phases. Furthermore, an empirical modulus degradation formula and its parameters fitting method are presented. According to the test data handling results, it is shown that this formula is univocal and can fit the test data conveniently. In addition, two kinds of new anti-buckling devices are designed for these tests. At last, the E-N curves, the D-N curves and the S-N curve of the smooth carbon fiber reinforced composite laminates of T300/648C are determined to predict the fatigue life of the notched composite laminate. And the E-N curve of the notched specimens at the given load ratio R = 10 and minimum load Pmin = -0.45 kN is also measured to verify the estimated result of fatigue life.

Microstructure and mechanical properties of bio-inspired Cf/Ti/Mg laminated composites

Inspired by an old fish skin structure,the Cf/Ti/Mg laminated composites were fabricated by squeeze casting technology.No porous or voids were found in final composite,and carbon fiber was uniformly dispersed in Mg matrix.Furthermore,the addition of net-shaped Ti adsorbed Al element and facilitated the nucleation of Mg_(17)Al_(12)nearby Ti.The reaction product Al_(4)C_(3)was found at the Cf and AZ91 interface.Mechanical tests indicate that the introduction of Ti could greatly improve the toughness of Cf/Mg composites.

Detection of stacking orientation error of CFRP composite laminates using ultrasound waves

A jig was developed for generating a shear wave. A pyramid with an isosceles triangle with two 45o was made of aluminum to generate shear waves using two longitudinal transducers based on ultrasonic-polarized mechanism. Also, the signal splitter was connected to the pulser jack on the pulser/receiver and to the longitudinal transducers. Therefore, an experimental way was performed in order to make shear wave on the bottom of aluminum alloyed pyramid. Also, a jig was manufactured and developed for generating a shear wave based on the computer numerical simulation. It is found that the experimentally shear wave variation of newly-designed jig is consistent with computer numerical simulation results and shear wave ultrasonic application can be very useful to detect the defects in CFRP composites.

Self-Sensing Curved Micro-Strip Line Method for Damage Detection of CFRP Composites

A self-sensing Time Domain Reflectometry (TDR) method for Carbon Fibre Reinforced Polymer (CFRP) laminates has been propped in the present study: carbon fibres are used as sensors using a transmission line. Authors have published research articles of the self-sensing TDR method. The self-sensing TDR method reduces number of required electrodes for damage detections although the sensitivity of detection is sacrificed. A micro-strip line (MSL) method is adopted to obtain impedance matching with a coaxial cable and successfully detected damage in a CFRP laminate in the previous study. In the present study, a long curved MSL is experimentally investigated as an impedance-matched transmission line for detection of damage of a CFRP laminate in wider area. Fibre breakage is simulated as a hole made by drilling. As a CFRP laminate has strongly orthotropic electric conductance and the electric properties of a CFRP laminate at the high frequency are not clarified, the effect of the orthotropic conductance at the curved transmission line is experimentally investigated. As a result, the effect of orthotropic conductance at the curved strip line is shown to be negligible, and fiber breakage that locates closed to the copper strip line can be detected by the self-sensing curved MSL method. It is, however, difficult to detect damage far from the copper strip line.

牛庄洼陷沙四上—沙三下亚段细粒沉积岩成分与纹层结构的关系

湖相细粒沉积岩的纹层发育,但纹层的厚度、密度、连续度等结构特征变化很大,这些变化与细粒沉积岩的沉积环境密切相关。利用图像分析的手段,对牛庄洼陷沙四上—沙三下亚段细粒沉积岩纹层的厚度、密度、侧向连续性进行定量表征,并与细粒沉积岩的各种物质成分对比研究。结果表明:牛庄洼陷沙四上—沙三下亚段细粒沉积岩的纹层厚度、密度、侧向连续性与长英质、黏土、碳酸盐等矿物质量分数基本没有相关性,纹层密度与有机碳含量具有一定的正相关性,长英质矿物与黏土矿物质量分数具有明显的正相关性;牛庄洼陷沙四上—沙三下亚段细粒沉积岩的沉积速率越低,越有利于有机碳含量的提高;长英质矿物与黏土矿物主要是洪水以表层流、层间流的形式一起搬运到深湖环境沉积下来的;湖泊表层碳酸盐矿物的产生与沉淀,与水体深度、沉积速率没有关系,也不存在湖相碳酸盐补偿界面(CCD)。

A deep feed-forward neural network for damage detection in functionally graded carbon nanotube-reinforced composite plates using modal kinetic energy

This paper proposes a new Deep Feed-forward Neural Network(DFNN)approach for damage detection in functionally graded carbon nanotube-reinforced composite(FG-CNTRC)plates.In the proposed approach,the DFNN model is developed based on a data set containing 20000 samples of damage scenarios,obtained via finite element(FE)simulation,of the FG-CNTRC plates.The elemental modal kinetic energy(MKE)values,calculated from natural frequencies and translational nodal displacements of the structures,are utilized as input of the DFNN model while the damage locations and corresponding severities are considered as output.The state-of-the art Exponential Linear Units(ELU)activation function and the Adamax algorithm are employed to train the DFNN model.Additionally,in order to enhance the performance of the DFNN model,the mini-batch and early-stopping techniques are applied to the training process.A trial-and-error procedure is implemented to determine suitable parameters of the network such as the number of hidden layers and the number of neurons in each layer.The accuracy and capability of the proposed DFNN model are illustrated through two distinct configurations of the CNT-fibers constituting the FG-CNTRC plates including uniform distribution(UD)and functionally graded-V distribution(FG-VD).Furthermore,the performance and stability of the DFNN model with the consideration of noise effects on the input data are also investigated.Obtained results indicate that the proposed DFNN model is able to give sufficiently accurate damage detection outcomes for the FG-CNTRC plates for both cases of noise-free and noise-influenced data.

Carbon nanotube protected composite laminate subjected to lightning strike:Interlaminar film distribution investigation

A kind of interlaminar film with carbon nanotubes inserted into polyether ketone with cardo was used for lightning strike protection of composite laminates. The distribution of the interlaminar film was investigated by experimental and numerical methods. Artificial lightning strike tests were conducted for 12-film carbon nanotube and traditional surface silver coating protected specimens. Then corresponding finite element models(FEMs) were established to analyze the lightning strike effect and validated by the experimental results. Based on the FEMs, the number, distribution and thickness of interlaminar film were investigated in order to obtain equivalent protection effect with the traditional surface silver coating. The results show that only the first two layers were damaged for the surface silver coating protected specimen, while 5 layers were ablated for the 12-film protected specimen. Lightning strike damage area of the laminate protected with 5-film carbon nanotube is almost the same as that of the laminate protected with 12-film carbon nanotube. Compared with traditional surface silver coating protection, one film protection with thickness of 360 lm can make the laminate to obtain equivalent damage depth, 54.8% smaller damage area and 58% less additional weight. And reparability of the laminate is better than that of the laminate protected with 5 interlaminar films.

铝板水热碳吸附工艺制备APC/Al层状复合材料的显微组织、力学性能和摩擦学性能

采用铝板水热碳吸附工艺(HTCAP)和真空热压烧结工艺(VHPS)制备无定形碳(APC)/Al层状复合材料,研究葡萄糖溶液浓度对其显微组织、力学性能和摩擦学性能的影响。结果表明,APC在层间分布均匀,并且通过Al的扩散与基体形成良好的界面结合。随着葡萄糖溶液浓度的增加,层间硬度、极限抗拉强度(UTS)和伸长率先增大后减小,而磨损率则呈现相反的趋势,摩擦因数(COF)逐渐减小。当葡萄糖溶液浓度为0.3 mol/L时,伸长率最大,为16.4%,磨损率最小,为0.344×10^(-5)mm^(3)/(N·m)。粘着磨损是APC/Al层状复合材料的主要磨损机制。耐磨性的提高是由于在磨损表面形成均匀的APC润滑膜。

纤维增强复合材料层压板的疲劳寿命预测方法

针对纤维增强复合材料层压板的疲劳寿命预测问题,提出了一种将理论与仿真、单向板与多向层压板紧密结合预测疲劳寿命的方法.基于几组碳纤维/树脂基T300/QY8911单向板在循环应力加载下的疲劳试验数据,通过灰色系统GM(1, 1)模型,建立单向板的疲劳寿命模型和损伤函数.与传统的最小二乘法拟合相比,该方法提高了预测精度.通过有限元方法对层压板进行应力分析、失效分析和材料性质退化.将失效分析的结果与建立的单向板疲劳寿命模型和损伤函数结合,从而来计算多向层压板的疲劳寿命和损伤.通过与实验数据及其他预测方法的结果对比,该预测方法降低了疲劳寿命预测相对误差,且与实验结果吻合较好.

碳/玻混杂纤维铺层顺序对其复合材料力学性能的影响

混杂纤维增强复合材料可通过混杂纤维的协调匹配产生协同混杂效应,从而提高复合材料在强度、刚度、性价比等方面的优势。为了研究碳纤维与玻璃纤维铺层顺序对复合材料力学性能的影响,制备5种不同铺层顺序的碳/玻混杂纤维增强复合材料,结合显微组织与拉伸断口分析了纤维铺层顺序对其强度、刚度、应力-应变曲线的影响规律。结果表明:铺层顺序对复合材料的力学性能影响显著,铺层间隔越均匀其增强效果越好,碳纤维或玻璃纤维集中分布于试样中间时均不利于复合材料性能的提升,碳纤维、玻璃纤维单层间隔时其抗拉强度比纯玻璃纤维增强复合材料提高了约60%,3层间隔时其强度略低于纯玻璃纤维增强复合材料;铺层间隔越均匀其层间开裂越集中且断口处纤维单丝拔出长度越大;碳纤维加入后复合材料的刚度大幅度提升,其应力-应曲线出现不同程度的波动,但铺层顺序对复合材料刚度影响甚微。

A novel domain decomposition-based model for efficient dynamic predictions of large composite machine tools

We propose a large combined moving component composed of carbon fiber reinforced polymer(CFRP)laminates for making lightweight machine tools with high dynamic performance.The accurate dynamic prediction of composite machine tools is essential for the new generation machine tool.This paper aims to address two challenges in numerical dynamic modeling and the design of composite machine tools to enhance development efficiency.(1)Anisotropic composite laminates,which form the composite machine tool,exhibit coupling in various directions.We propose the generalized continuity condition of the boundary to tackle this dynamic modeling challenge.(2)Composite machine tools feature numerous composite-metal coupled structures.The mechanical model correction of isotropic metals is performed to address their dynamics.We take the example of a five-axis gantry machine tool with composite moving parts,establish a dynamic model for efficient prediction,and verify it through simulation and experimentation.The proposed method yields remarkable results,with an average relative error of only 3.85%in modal frequency prediction and a staggering 99.7%reduction in solution time compared to finite element analysis.We further discuss the dynamic performance of the machine tool under varied stacking angles and layer numbers of the composite machine tool.We propose general design criteria for composite machine tools to consider the modal frequency and manufacturing cost of machine tools.

碳纤维开孔层合板拉伸载荷下的失效分析

【目的】研究开孔碳纤维复合材料层合板在拉伸载荷下的失效行为,并确定铺层顺序、铺层角度对极限载荷的影响。【方法】通过Abaqus有限元软件和Hashin失效准则,建立壳单元在拉伸载荷下的失效模型,利用该失效模型进行数值模拟分析。【结果】0°层失效首先发生在孔边,随着孔边失效区域的不断扩大,呈现由X形向沙漏形转变的趋势;在达到极限载荷前,承载力与位移成正比,之后承载力迅速下降,层合板将迅速失效;铺层顺序对层合板的强度影响不大,铺层角度对层合板的极限载荷影响较大。在一定范围内增加±45°铺层的数量,不仅可以延缓层合板的失效,而且可以提高极限载荷值。【结论】研究结果对开孔碳纤维复合材料层合板的实际应用具有指导作用。

磷酸铁锂电池碳纳米管膜加热结构设计及验证

针对磷酸铁锂电池低温环境下的性能衰减问题,设计开发了一种轻质高强、低压安全、高效节能的磷酸铁锂电池抗低温纤维碳纳米管膜加热功能结构并开展了实验验证。采用热压工艺实现了碳纳米管薄膜与复合材料层合结构的一体化成形。实验验证了FCL(fiber carbon-nanotube film laminated composite)加热器良好的温度均匀性、稳定性以及抗热疲劳性能。开展了低温环境下磷酸铁锂电池加热实验,并与传统的PTC(positive temperature coefficient)加热器进行了对比分析,结果表明:相较于传统的PTC加热器,FCL加热器质量减轻了59%,能量消耗降低了3.5%,温升效率提高了26%,功率质量比提升了195%。

碳纤维麦弗逊悬架控制臂铺层优化

根据3种极限工况的悬架硬点载荷,结合复合材料经典层合板理论和对称平衡的铺层设计方法,开展复合材料控制臂的纤维铺层角度设计,并使用OptiStruct软件以1个超级层关联4个单层铺层的方法进行铺层优化设计。进而通过拓扑分析的方法获得需要加强的区域,利用铺层尺寸优化方法对控制臂进行形貌优化设计,在满足使用要求的前提下实现较原金属结构减重64%。提出一种非均匀截面结构的铺层优化方法,对复杂截面复合材料结构铺层优化具有一定的指导意义。

热塑性复合材料防撞梁模压成型工艺研究

通过对某型号不锈钢防撞梁结构进行热塑性碳纤维/聚苯硫醚(CF/PPS)复合材料铺层和受力分析,利用热压罐成型工艺制备热塑性复合材料层合板,最后采用机械臂自动化转移和热模压成型工艺,研究了CF/PPS料片加热软化制备防撞梁零件的可行性。另外,对热塑性复合材料防撞梁零件进行了测试,结果表明:热塑性复合材料防撞梁外观质量良好,无明显缺陷以及纤维紊乱等现象;平均厚度为2.867 mm;单件防撞梁零件平均质量为462.4 g,比原来不锈钢零件质量减轻约51.3%;孔隙率平均值为1.20%;热塑性复合材料防撞梁零件耐环境性能良好;三点弯力学性能试验与仿真结果偏差为4%;热塑性复合材料防撞梁产品生产效率为10件/h。