孔隙对碳/环氧层压板层间剪切强度影响的神经网络预测(英文)

采用一种新的方法研究了孔隙(孔隙率、孔隙形状和尺寸)对复合材料层压板[(±45)4/(0,90)/(±45)2]S,[(±45)/(0,90)2/(±45)]S和[(±45)/04/(0,90)/02]S的层间剪切强度影响的非线性关系。建立了了一个四层前馈型BP网络神经网络。采用真空袋和热压罐技术制备了含不同孔隙率的复合材料层压板。神经网络的算法为Levenberg-Marquardt算法。研究结果表明:Levenberg-Marquardt算法的预测能力较高,即,92%的B(决定系数)值大于0.9。而且,神经网络的结构会影响不同孔隙率的环氧树脂基复合材料的层间剪切强度的预测结果。     

Effects of Cure Pressure Induced Voids on the Mechanical Strength of Carbon/Epoxy Laminates

This work aims at designing a set of curing pressure routes to produce laminates with various void contents. The effects of various consolidation pressures resulting in different void contents on mechanical strength of carbon/epoxy laminates have been examined. Characterization of the voids, in terms of void volume fraction, void distribution, size, and shape, was performed by standard test, ultrasonic inspection and metallographic analysis. The interlaminar shear strength was measured by the short-beam method. An empirical model was used to predict the strength vs porosity. The predicted strengths conform well with the experimental data and voids were found to be uniformly distributed throughout the laminate.     

复合材料胶接修理层合板拉伸性能及影响参数

胶接修理是效率较高、应用较广的复合材料结构修补技术。对采用不同参数进行挖补和贴补修理的复合材料层合板的拉伸性能进行实验研究。结果表明:挖补修理实验件的强度恢复率约为66%~91%,贴补修理实验件的强度恢复率约为44%~61%。在挖补修理实验件中,减小挖补斜度、采用双面挖补、使用热压罐固化,在贴补修理实验件中,采用双面贴补、增大补片尺寸,均可得到更高的强度恢复率。在实验基础上建立的有限元模型,能够有效预测实验件的失效载荷、破坏模式,并可分析实验件的应力分布和渐进损伤过程,为设计修理方案提供参考。     

Influence of Hygrothermal Conditioning on the Elastic Properties of Carall Laminates

The influence of hygrothermal conditioning on mechanical properties of Carall laminates have been investigated by tensile and compression tests. The environmental factors can limit the applications of composites by deteriorating the mechanical properties during service. The importance of temperature at the time of conditioning plays an important role in environmental degradation of such composite materials. In this work, the results show that for carbon fiber/epoxy composites tensile and compression values decrease after hygrothermal conditioning. However, the changes on mechanical properties of Carall are negligible, regardless the hygrothermal conditioning.     

Tensile fracture and thermal conductivity characterization of toughened epoxy/CNT nanocomposites

Rubber toughened epoxy/CNT nanocomposites were manufactured at different weight percents between 0 and 1% of multiwall carbon nanotube (MWNT) using a high intensity ultrasonic liquid processor with a titanium probe. Mechanical properties of manufactured dog bone samples were measured in tension and the results indicated a maximum of 23% increase in the elastic modulus at 0.6% by weight of MWNT. However, the fracture strength showed a maximum decrease of about 11% as a function of increasing MWNT loading. Scanning Electron Microscopy (SEM) images from the neat samples revealed a distinct circular pit at the top left edge of the specimen with an overall tearing deformation causing the fracture paths. Comparatively, all nanocomposite samples on an average seemed to show a prominent brittle fracture with little or no evidence of circular pit formation. The amount of tearing deformation seemed to be enhanced in the nanocomposite specimens as compare to the neat ones. Finally, Transmission Electron Microscopy images indicated that different states of dispersion exist in all of the nanocomposite samples. The data showed that agglomeration of nanotubes increases as a function of weight percent. In addition to mechanical property characterization, thermal conductivity of all the samples was determined as a function of temperature between 30 °C and 100 °C using the 3ω method. The tested samples showed an almost 16% increase in thermal conductivity. The minimal enhancement in thermal conductivity has been analyzed from the standpoint of the Effective Medium Theory. Interfacial thermal resistances exhibit no order of magnitude changes explaining the conductivity results.     

凝固条件对PBO初生纤维孔结构及拉伸强度的影响

研究了凝固浴条件对PBO初生纤维孔结构及拉伸强度的影响。结果表明：在考察范围内,随凝固浴温度的降低、凝固浴浓度的增大,初生纤维的孔体积总量减小,孔径分布范围变窄,优势孔的孔径分布峰数量减少,初生纤维的强度增大。随着凝固牵伸倍率（2～10）的增加,孔体积减小、优势孔的孔径分布峰数量减少;但当牵伸倍率大于10倍时,总孔体积和优势孔的孔径分布峰数量开始增加;初生纤维的强度则随牵伸倍率的增大而增长。     

缝合复合材料层板的面内拉伸强度预报

建立了缝合复合材料层板的面内拉伸强度模型,该模型考虑了缝合线对缝合层板拉伸强度的影响,将缝合线等效为椭圆形夹杂,应用含椭圆形夹杂的杂交应力单元建立了该模型的细节应力分析方法,通过引入特征长度的概念,采用点应力准则和最大应力判据实现了缝合层板的拉伸强度预报.试验数据和预报结果吻合较好,证明了该模型的有效性.同时系统讨论缝合参数对拉伸强度的影响规律,得到了一些重要结论.     

莫来石／环氧树脂纳米复合材料制备及其拉伸力学性能研究

用机械搅拌和超声波分散相结合的实验方法制备了莫来石／环氧树脂纳米复合材料,通过透射电镜照片分析得出纳米莫来石的最佳填充量,拉伸实验数据表明,最佳填充的莫来石／环氧树脂纳米复合材料的拉伸强度有显著提高。     

Effect of bubble based degradation on the physical properties of Single Wall Carbon Nanotube/Epoxy Resin composite and new approach in bubbles reduction

In this study the effect of bubble based degradation on the physical and structural properties of Single Wall Carbon Nanotube (SWCNT)/epoxy resin composite samples were investigated and new method based on vacuum shock was presented. For this purpose, with two different methods samples with and without bubble based degradation were fabricated and effect of degradation on the value of electrical conductivity and the amount of Electromagnetic (EM) waves absorption were investigated. Which vacuum shock technique can improve above mentioned properties about 58319.594 and 63.921 percentage for sample without degradation in comparison with destroyed sample due to the bubbles based voids effect. Moreover, the main factors in the bubbles formation and migration during the manufacturing process and their behavior in the matrix with the help of optical and SEM images were examined and their effect on structural properties of composite samples with Micro Raman Spectroscopy was evaluated.     

Tensile and Fracture Behavior of DZ68 Ni-base Superalloy

The tensile and fracture behavior of DZ68 directionally solidified Ni-base superalloy was studied in the temperature range of room temperature (RT) to 1000°C. The fracture mode was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show the tensile strength and yield strength of DZ68 alloy increase slightly with increasing temperature, so that at 760°C its reach maxima value: 1214 and 1019 MPa, respectively. When the experimental temperature is higher than...     

Tensile behaviour of early age concrete: New methods of investigation

The assessment of the tensile properties of early-age concrete is essential for reducing the risk of cracking due to restrained shrinkage. The tensile strain capacity of concrete, which was defined as a measure of the ability of the material to withstand deformation without cracking, is useful but few data can be found in available literature and the measure of the displacements of concrete is sometimes questionable. New direct tensile testing apparatus and experimental procedure were designed to provide reliable data on concrete specimens. The measure of displacements was deduced from digital image correlation. They enabled determining a stress–strain relationship of concrete before cracking. The results showed a very rapid increase of strength from the end of setting. The evolution of the tensile strain capacity showed a minimum corresponding to the period that includes the setting time and early hardening, thus this is a critical stage for plastic shrinkage cracking. Even if the values are closely linked to the boundary conditions and experimental procedure, the effect of aggregate type could be investigated.     

Tensile, thermal and dynamic mechanical properties of hollow polymer particle-filled epoxy syntactic foam

Four types of hollow polymer particles have been employed as fillers in UV-heat-cured epoxy resin. The effects of filler volume fraction and types on tensile properties of syntactic foams are investigated. All hollow particle types have exhibited approximately the same size, but with different groups on particle surface. Volume fraction of hollow particles for the syntactic foams varies up to 0.25. Thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and tensile tests have been performed. According to TGA and DMA test results, the addition of polymer particle leads to stronger interfacial particles-matrix interaction and high loss factor. Tensile tests have also shown that tensile strength and specific properties of all foams decrease with the increasing of particle content. In terms of tensile properties, the particles-matrix compatibility is more significant than that of the surface functional groups of particles.     

Influence of the Geometric Parameters on the Mechanical Behaviour of Fabric Reinforced Composite Laminates

A polymer fabric reinforced composite is a high performance material, which combines strength of the fibres with the flexibility and ductility of the matrix. For a better drapeability, the tows of fibres are interleaved, resulting the woven fabric, used as reinforcement. The complex geometric shape of the fabric is of paramount importance in establishing the deformability of the textile reinforced composite laminates. In this paper, an approach based on Classical Lamination Theory (CLT), combined with Finite Element Methods (FEM), using Failure Analysis and Internal Load Redistribution, is utilised, in order to compare the behaviour of the material under specific loads. The main goal is to analyse the deformability of certain types of textile reinforced composite laminates, using carbon fibre satin as reinforcement and epoxy resin as matrix. This is accomplished by studying the variation of the in-plane strains, given the fluctuation of several geometric parameters, namely the width of the reinforcing tow, the gap between two consecutive tows, the angle of laminae in a multi-layered configuration and the tows fibre volume fraction.     

碳纤维织物/环氧复合材料销钉连接实验研究

针对1K缎纹碳纤维织物/环氧复合材料层板销钉连接,实验研究了几何参数对连接性能的影响.选取了不同的端距和边距,测试了碳纤维织物复合材料层板W/D(试样宽度/孔直径)及E/D(孔端距/孔直径)对销钉连接强度的影响,并分析了销钉连接的破坏模式.实验结果表明:1K缎纹织物/环氧复合材料层板销钉连接承载能力随着边距E和端距W的增加而增加,当E/D=2,W/D=3时,销钉连接强度达到稳定值,此后增加边距E和端距W值连接强度不会有明显的增加.     

Ultimate Strength Prediction of Carbon/Epoxy Tensile Specimens from Acoustic Emission Data

The objective of this paper was to predict the residual strength of post impacted carbon/epoxy composite laminates using an online acoustic emission (AE) monitoring and artificial neural networks (ANN). The laminates were made from eight-layered carbon (in woven mat form) with epoxy as the binding medium by hand lay-up technique and cured at a pressure of 100 kg/cm2 under room temperature using a 30 ton capacity compression molding machine for 24 h. 21 tensile specimens (ASTM D3039 standard) were cut from t...     

Effect of Reactive Graphitic Nanofibers (r-GNFs) on Tensile Behavior of UHMWPE Fiber/Nano-Epoxy Bundle Composites

Ultra-high molecular weight polyethylene (UHMWPE) fibers have good mechanical and physical properties and effective radiation shielding functions, which are significant for aerospace structures. In our previous work, nano-epoxy matrices were developed based on addition of reactive graphitic nanofibers (r-GNFs) in a diluent to form a blend. It is found that improved wettability and enhanced adhesion of the matrices to UHMWPE fibers can be obtained. In this study, a series of nano-epoxy matrices with different concentrations of r-GNFs (up to 0.8 wt%) and different weight ratios of r-GNFs to a reactive diluent (1:4, 1:6, 1:7, and 1:9) were prepared. Composite bundle specimens of UHMWPE fiber/nano-epoxy were fabricated and their tensile behavior was investigated. All load-displacement curves of the UHMWPE/nano-matrix bundle composites under tensile loading showed three regions corresponding to the three deformation and failure stages of the materials: 1) elastic deformation stage, 2) plateau stage, and 3) UHMWPE fiber failure stage. The nano-epoxy with 0.3 wt% of r-GNFs and with 1:6 ratio of r-GNFs to the diluent proved to be the best matrix for UHMWPE fiber composites with enhanced tensile properties. For the resulting composite, the load level and consumed energy in the plateau stage were increased by 8% and 30% over the UHMWPE fiber/pure-epoxy specimens, respectively. This UHMWPE fiber composite with the optimized nano-epoxy matrix also possesses the highest initial stiffness and ultimate tensile strength among all the resulting UHMWPE fiber composites. These results laid a foundation for us to fabricate UHMWPE fiber reinforced composite laminates in the near future.     

Study on the Forming Limit Nomogram of Tensile Stamping Operations

Based on plasticity theory and physical experiments, the quantitative relationships between elongation δ obtained byuniaxial tensile test and forming limits of tensile stamping operations are given, which mainly resolves the problem thatforming limits can be derived from simple tensile test. The forming limit nomogram of tensile stamping operationsis also established to apply to engineering.     

Effect of Precipitating Phases on Tensile Strength and Microstructural Stability of a Spray-Deposited Al-Si-Fe-Mn-Cu-Mg Alloy

Spray deposition is a novel process which is used to manufacture rapidly solidified bulk and near-net-shape preforms. In this study, AI-20Si-5Fe-3Mn-3Cu-1Mg alloy was synthesized by spray deposition technique. The aging process of the alloy was investigated by differential scanning calorimetry (DSC) analysis and transmission electron microscopy (TEM). The results show that two kinds of phases, i.e. S(Al2CuMg) and σ(Al5Cu6Mg2), precipitate from matrix and improve the tensile strength of the alloy efficiently at both the ambient and elevated temperatures (300℃). In addition, the σ-Al5Cu6Mg2 is a relatively stable phase which improves microstructural stability of the alloy.     

起圈织物增强层合板层间力学性能有限元分析与实验研究

建立了一种起圈织物增强层合板的平拉单胞模型,通过有限元计算预测其平拉强度。研究起圈织物增强层合板的复合成型工艺,制作了符合要求的实验件。对该种材料的短梁剪切、平拉、双面剪切性能进行了实验研究,获得了该材料主要层间力学性能参数,并与传统复合材料层合板的力学性能进行了对比,得出了一些有益的结论,为该材料的性能分析和结构优化奠定了基础。