碳纤维-铝合金电磁铆接工艺及性能研究

目的 研究不同工艺参数下碳纤维-铝合金电磁铆接接头的力学性能.方法 利用电磁铆接技术对直径为Ф5 mm的2A10铝合金铆钉、厚度为2.0 mm的T300碳纤维复合材料和1.8 mm的5182铝合金板料进行铆接,借助金相显微镜和万能试验机对接头的微观形貌和力学性能进行观察和测试.结果 随着电磁铆接放电能量的增加,铆钉镦头...     

刚体碰撞约束柔性体局部撞击载荷特征分析

目的 掌握碰撞局部撞击载荷及其特征,为产品安全防护设计、碰撞响应分析与评估提供理论基础。方法 抽象刚体碰撞柔性体的共性特征,分别将被撞击柔性体的碰撞局部刚度特性和整体结构效应表征为弹簧力-位移关系,建立系统的二自由度刚-柔碰撞动力学模型,应用数值方法系统分析刚柔碰撞局部撞击载荷的特征及不同因素的影响。结果 获得了刚体初始碰撞速度、柔性体碰撞局部刚度特性与整体结构效应等主要因素对局部撞击载荷时程、冲量、峰值和脉宽等撞击载荷特征的影响规律。结论 深化了刚-柔碰撞局部撞击载荷的认知,为防护结构设计提供了理论基础。     

碳纤维复合材料构件加工缺陷与高效加工对策

碳纤维复合材料钻削加工时易产生分层、毛刺、撕裂等缺陷,是典型的难加工材料。本文以碳纤维增强/树脂基复合材料为研究对象,观察钻孔缺陷形成过程,建立单丝切削模型分析缺陷形成原因;讨论了轴向力对缺陷的影响规律。结论如下:纤维方向对缺陷形成有重要的影响,轴向力增大分层与撕裂缺陷相应增大;以磨代钻加工工艺、新型PCD刀具和螺旋面钻头对于提高碳纤维复合材料钻孔质量都有很大提高。     

物料冲击破碎过程的一种非线性力模型

针对冲击破碎过程，在初步准静压破碎实验的基础上，提出了物料层的分段线性接触力模型，并引入恢复系数来表示膨胀阶段和压缩阶段之间的参数关系。应用该模型进行了单球冲击破碎的计算机模拟，证明恢复系数能宏观反映冲击破碎过程的能量损失。与线性弹簧阻尼模型相比，不但在微观过程中接触力保持正压，物料破碎会产生不可恢复的变形，更符合实验观察的实际情况，而且计算精度更高。     

Impact Response of Stiffened Cylindrical Shells With/without Holes Based on Equivalent Model of Isogrid Structures

An equivalent continuum model of an isogrid structure is utilized to analyze the impact response of isogrid structures and stiffened structures. The parameters of the equivalent model are determined, and the comparison between the equivalent continuous structure and the real grid structure are examined to validate the reliability of the equivalent model. Then, the impact responses of stiffened cylindrical shells with and without an elliptical hole are investigated by using the equivalent model of grid structures. For a different location and geometry of the elliptical hole, the deformation and load-bearing capacity of the grid-stiffened cylindrical shells are studied. The numerical results indicate that the present equivalent model can be applied effectively in simulation for the impact behavior of the grid and stiffened structures. This work provides a comprehensive understanding for the impact performance of the complicated stiffened cylindrical shells.     

A comparison between wet and cryogenic drilling of CFRP/Ti stacks

This paper compares conventional and cryogenic cooling in the deep hole drilling of carbon fiber reinforced polymer (CFRP)/Ti stacks. Various parameters are taken into account to find if the use of cryogenic coolant is justified by the improvement of the final results. Both the thrust and the torque were acquired continuously during the machining operations and compared both in average and distribution. The use of a cryogenic coolant brings a reduction in thrust force and torque without any sensible drawback. Overall the results prove that cryogenic drilling is a suitable technology for CFRP/Ti stack drill.     

CFRP筋的疲劳性能

进行了不同循环应力下CFRP筋的常温疲劳试验,选取CFRP筋70％的极限拉伸应力作为最大循环应力,在R=0．5（最小循环应力与最大循环应力的比）和R=0的应力率下,测量了CFRP筋的疲劳寿命曲线,研究了CFRP筋的疲劳性能．结果表明：CFRP筋的最大循环应力应控制在70％极限拉伸应力以下;在R=0．5应力率下,最大循环应力下降5％的极限拉伸应力时,CFRP筋的疲劳寿命增长10倍左右;最大循环应力分别为60％和50％极限拉伸应力时,R=0应力率下CFRP筋的疲劳寿命分别为R=0．5应力率下疲劳寿命的百分之一和十分之一．这说明CFRP筋具有很大的脆性,需要有足够的强度安全系数,才能发挥作用;根据试验拟合的疲劳寿命曲线,CFRP筋的疲劳性能远高于Q235光圆钢筋．     

基于神经网络技术的南京长江大桥桥墩船舶撞击力识别

主要研究基于神经网络技术的南京长江大桥桥墩船撞力识别。在建立了南京桥4#桥墩的空间有限元分析模型后,对4#桥墩进行了动力特性分析;基于MATLAB平台建立了“船撞力-响应”神经网络,由沃辛试验船撞力曲线计算得到了船对桥墩的撞击响应并作为神经网络训练的样本。仿真计算结果表明,由桥墩墩顶的响应可有效识别船舶撞击力的大小、方向和撞击位置,该神经网络可用于有、无噪声干扰的船撞力识别,并且具有良好的容错性和鲁棒性。     

Impact Force Magnitude and Location Recognition of Composite Materials

In order to identify the location and magnitude of the impact force accurately, determine the damage range of the structure and accelerate the health monitoring of key components of the composite, this paper studies the location and magnitude of the impact force of composite plates by an inverse method. Firstly, a PZT sensor mounted on the material plate is used to collect the response signal generated by the impact force, which is from several impact locations, and establish transfer functions between the impact location and the PZT sensor. Secondly, this paper applies several forces to any location on the material plate, and collects the corresponding response signals, and reconstructs the impact force of several locations in turn. Finally, according to the reconstruction result of each location, the correct impact location is identified. Then, an improved regularization method is used to optimize the reconstructed impact force and accurate the magnitude of the impact force. The comparison experiments prove that the recognition error of this method is smaller.     

Experimental investigation of salt fog effect on the CFRP laminates

To investigate the effect of an ocean environmental condition to Carbon Fiber Reinforced Plastics (CFRP) specimen, salt fog tests were conducted on long immersion hours. After salt fog tests, tensile test was performed to examine the durability of specimens under salt fog condition. Fabric types, fiber orientations, and different manufacturing methods were also investigated to look into effects of salt fog and tensile strength. Diverse fabric types, resin types, and manufacturing methods exhibited different experimental results. Finally, the experimental results showed the salt fog reduced the tensile strength of CFRP laminates.     

Strengthening of thin-webbed castellated beam using CFRP

Abstract

The utilisation of fibre reinforced polymers (FRP) in the rehabilitation of steel structures increased in recent years. This article presents the advantages of using carbon fibre reinforced polymers (CFRP) in strengthening of the thin-webbed castellated beam (TCB). The performances of CFRP strengthened TCBs were analysed using finite element (FE) tool ABAQUS^®. Nonlinear FE analysis was carried out to find the optimum geometrical. Nine different designations of TCBs were arrived based on weld lengths, perforation sizes and strengthening technique (three each). Though all three techniques increased the strength considerably, the third one had much greater efficiency and was more suitable.     

On the response of two commercially-important CFRP structures to multiple ice impacts

Carbon-fibre reinforced composites (CFRPs) are likely to feature heavily as structural elements of future aerospace vehicles due to their high stiffness and low densities. However, such components are likely to be subjected to a variety of impact-related events during their in-service lives. One area which has only received limited attention in the literature is that of ice impact on CFRP structures; e.g. hail stone impacts on aerospace components. In this study the response of two aerospace-grade CFRP structures (one woven and one uni-directional lay-up) to multiple ice impacts with cumulative impact energies in the range 72–1215 J was investigated. Six empirical damage categories were identified, ranging from no apparent surface damage (Type 1) to penetration accompanied by complete lay-up disruption (Type 6). Surface damage was found to correlate with changes in recovered panel properties; determined by ultrasonic C-Scan and compression-after-impact strength tests. With both CFRP structures sub-surface disruption and residual compressive strength varied linearly with total impact energy; suggesting that damage in such structures is cumulative in nature. Further, in line with previous studies, the woven structure consistently exhibited lower levels of damage at a given impact energy, even when damage extent was normalised by areal density.     

Using thin-plies to improve the damage resistance and tolerance of aeronautical CFRP composites

Thin-ply composites are currently receiving specific attention from researchers due to their capabilities to delay matrix cracking. In this paper, the aim is to design a hybrid laminate that contains both thin- and normal plies. The objective is to improve the tolerance of normal plies by adding thin-plies to the composite in different configurations. Two alternatives were designed, tested, and compared to the specimens made of traditional plies. Impact and compression after impact tests were conducted on each configuration at different impact energies. After being impacted, the specimens were c-scanned to define the delamination pattern. Results showed that surrounding each normal ply with two thin-plies improved the delamination threshold by 15% as compared to the specimens made all of normal plies. Under compression, 15% improvements in the compression after impact strength were obtained. By using thin-plies, the size of each individual delamination was reduced, resulting in small threads instead of peanut delaminations.     

埋入CFRP的FBG光纤传感器界面传递特性实验研究

埋入碳纤维复合材料（CFRP）的光纤布拉格光栅（FBG）传感器应变测量值与基体实际应变存在误差,用光纤、保护层、粘贴层和基体材料的界面传递特性来表征应变测量值可提高精度．根据弹性力学和边界条件,得出FBG应变测量值与基体材料实际应变值的关系方程,通过裸光栅直埋基体材料界面传递的特征系数,可表征和计算FBG检测应变与测点实际应变的误差及修正系数．试验结果表明：对埋入裸光栅的碳纤维复合材料同时进行电阻应变与FBG—IS波长解调试验对比,试验测量FBG应变传感灵敏系数与理论值十分接近;对埋入CFRP的FBG裸光栅,由于不存在粘贴层界面传递的影响,其应变测量值可无需修正．     

Experimental Behaviour of RC Beams Shear Strengthened with NSM CFRP Laminates

Abstract: The near‐surface mounted (NSM) is one of the most recent techniques applied for the increase of the shear resistance of reinforced concrete (RC) beams. This technique involves the installation of carbon fibre reinforcement polymers (CFRP) laminates into thin slits open on the concrete cover of the elements to strengthen. The effectiveness of this technique for the shear strengthening of T cross‐section RC beams was assessed by experimental research. For this purpose, three inclinations of laminates were tested (45º, 60º and 90º) and, for each inclination, three percentages of CFRP were applied in RC beams with a percentage of steel stirrups of 0.10% (ρ_sw). The highest percentage of laminates was designed to provide a maximum load similar to the reference RC beam, which was reinforced with a reinforcement ratio of steel stirrups of 0.28% (ρ_sw = 0.28%). For each percentage of laminates, a homologous RC beam strengthened with unidirectional U‐shaped CFRP wet lay‐up sheets (discrete strips) applied according to the externally bonded reinforcement technique was also tested, with the purpose of comparing the effectiveness of these two CFRP‐strengthening techniques. To evaluate the influence of the percentage of steel stirrups in the effectiveness of the NSM technique, some of the abovementioned CFRP configurations were also applied in beams with ρ_sw = 0.17%.     

Experimental characterization of damage behavior in polycyanate CFRP laminates under high temperature atmospheric exposure

This study focuses on the experimental characterization of damage behavior due to thermo-oxidative-induced matrix shrinkage in carbon fiber reinforced plastics (CFRP) with polycyanate ester. To investigate the effects of laminate configuration on matrix shrinkage behavior, [90]₈ and [0]₈ unidirectional laminates, [±45]_2S angle ply laminates, and [45/0/–45/90]_3S quasi-isotropic laminates were exposed to high temperature atmospheric environment at 180 °C to analyze matrix shrinkage up to 2000 h. These samples were removed from convection oven to observe sample side surface changes. The thermo-oxidative-induced matrix shrinkage was measured on the side surface of CFRP sample by confocal laser microscopy. The results suggested thermo-oxidative-induced matrix shrinkage depended on aged hours, fiber-to-fiber distance, and fiber orientation angle. The matrix shrinkage coefficient could be calculated with a tensorial transformation and empirical formula. The model can predict matrix shrinkage tendency of the 45° intra-lamina layer in quasi-isotropic laminate using the data of 0° and 90° matrix shrinkage in the quasi-isotropic laminates.     

Identification of Chaos Representations of Elastic Properties of Random Media Using Experimental Vibration Tests

This paper deals with the experimental identification of the probabilistic representation of a random field modelling the Young modulus of a nonhomogeneous isotropic elastic medium by experimental vibration tests. Experimental data are constituted of frequency response functions on a given frequency band and for a set of observed degrees of freedom on the boundary of specimens. The random field representation is based on the polynomial chaos decomposition. The coefficients of the polynomial chaos are identified setting an inverse problem and then in solving an optimization problem related to the maximum likelihood principle.     

多齿铣刀侧铣加工多层CFRP铣削力的建模与仿真

由于碳纤维增强树脂基复合材料(CFRP)的层间结合强度较低,进行切削加工时在切削力的作用下容易出现分层和毛刺等质量缺陷。因此,通过对切削力的预测与控制可以有效提高加工质量。采用瞬时刚性力模型对多齿铣刀侧铣多层CFRP材料的加工过程进行铣削力建模与仿真,分析了多齿铣刀特有的几何结构对切削力的影响。试验中保持切削速度恒定,以不同进给速度分别对45°、0°、-45°和90°这4种典型纤维方向的单向CFRP进行侧铣加工,通过测得的切削力数据计算各自的铣削力系数。根据力学矢量叠加原理得到了多向CFRP铣削力系数的简化计算表达式,最后将计算结果代入铣削力模型得到了各时刻的铣削力仿真值。在同样的试验条件下对该多向CFRP进行侧铣加工验证试验,试验结果表明: 该模型能较好地预测铣削力,最大相对误差小于9%,平均相对误差小于5%,可为铣削参数优化和刀具结构优化提供理论基础。     

Experimental analysis of historic masonry walls reinforced by CFRP under in-plane cyclic loading

External bonding of Fiber Reinforced Polymers (FRPs) has become a popular technique for strengthening historic masonry wall buildings in seismic area. Although FRPs seem to improve response of historic masonry walls under in-plane shear loading, further investigations must specify a number of aspects for both researchers and practitioners. This paper presents an experimental analysis pertaining to the response of unreinforced and reinforced historic masonry walls built using full clay bricks in scale 1/3rd. On the basis of previous experimental research carried out by shear tests on triplets and unreinforced walls, a shear criterion for historic unreinforced masonry (HURM) has been assumed. In this experimental analysis two HURM walls, characterized by double T shape, were subjected to in-plane cyclic loading to shear cracking. The damaged walls were reinforced using horizontal–vertical and diagonal Carbon FRP strips. An anchorage system was also put into place to improve the adhesion of the strips used; the historic reinforced masonry (HRM) walls were tested by cyclic loading until failure. The experimental results are illustrated and discussed taking into account the delamination failure of the CFRP strips. Finally, the increase obtained in walls’ shear capacity is analysed considering theoretical bilinear diagrams and the coefficient of ductility.     

Experimental study of moment redistribution in RC frames strengthened with CFRP sheets

The present paper describes an experimental investigation of moment redistribution of continuous beams in 6 two-span RC frames strengthened with CFRP laminates. Design variables were the number of CFRP layers, and the configuration of the laminates. To prevent debonding of the CFRP laminates at the end region and at the beam-column connection, U-shaped CFRP anchorages were provided for all of the frame specimens. Furthermore, mechanical anchorages of steel plate strips and bolts were added to the laminates in one frame of these specimens. Test results showed that a maximum moment redistribution of 56% occurred in the strengthened frames. Furthermore, the load carrying capacities of the strengthened frames increased from 20% to 38%, while the flexural capacities had an increase of 9% to 20% and 35% to 55% at the negative and positive moment regions, respectively.