High-sensitivity phase imaging eddy current magneto-optical system for carbon fiber reinforced polymers detection

This paper proposed a high-sensitivity phase imaging eddy current magneto-optical (PI-ECMO) system for carbon fiber reinforced polymer (CFRP) defect detection. In contrast to other eddy current-based detection systems, the proposed system employs a fixed position excitation coil while enabling the detection point to move within the detection region. This configuration effectively mitigates the interference caused by the lift-off effect, which is commonly observed in systems with moving excitation coils. Correspondingly, the relationship between the defect characteristics (orientation and position) and the surface vertical magnetic field distribution (amplitude and phase) is studied in detail by theoretical analysis and numerical simulations. Experiments conducted on woven CFRP plates demonstrate that the designed PI-ECMO system is capable of effectively detecting both surface and internal cracks, as well as impact defects. The excitation current is significantly reduced compared with traditional eddy current magneto-optical (ECMO) systems.

A review on machinability of carbon fiber reinforced polymer(CFRP)and glass fiber reinforced polymer(GFRP)composite materials

Fiber reinforced polymer(FRP) composite materials are heterogeneous and anisotropic materials that do not exhibit plastic deformation. They have been used in a wide range of contemporary applications particularly in space and aviation,automotive,maritime and manufacturing of sports equipment. Carbon fiber reinforced polymer(CFRP) and glass fiber reinforced polymer(GFRP) composite materials,among other fiber reinforced materials,have been increasingly replacing conventional materials with their excellent strength and low specific weight properties. Their manufacturability in varying combinations with customized strength properties,also their high fatigue,toughness and high temperature wear and oxidation resistance capabilities render these materials an excellent choice in engineering applications.In the present review study,a literature survey was conducted on the machinability properties and related approaches for CFRP and GFRP composite materials. As in the machining of all anisotropic and heterogeneous materials,failure mechanisms were also reported in the machining of CFRP and GFRP materials with both conventional and modern manufacturing methods and the results of these studies were obtained by use of variance analysis(ANOVA),artificial neural networks(ANN) model,fuzzy inference system(FIS),harmony search(HS) algorithm,genetic algorithm(GA),Taguchi's optimization technique,multi-criteria optimization,analytical modeling,stress analysis,finite elements method(FEM),data analysis,and linear regression technique. Failure mechanisms and surface quality is discussed with the help of optical and scanning electron microscopy,and profilometry. ANOVA,GA,FEM,etc. are used to analyze and generate predictive models.

Parameters of static response of carbon fiber reinforced polymer(CFRP) suspension cables

The feasibility of longer spans relies on the successful implementation of new high-strength light weight materials such as carbon fiber reinforced polymer(CFRP). First, a dimensionless equilibrium equation and the corresponding compatibility equation are established to develop the cable force equation and cable displacement governing equation for suspension cables, respectively. Subsequently, the inextensible cable case is introduced. The formula of the Irvine parameter is considered and its physical interpretation as well as its relationship with the chord gravity stiffness is presented. The influences on the increment of cable force and displacement by λ2 and load ratio p′ are analyzed, respectively. Based on these assumptions and the analytical formulations, a 2000 m span suspension cable is utilized as an example to verify the proposed formulation and the responses of the relative increment of cable force and cable displacement under symmetrical and asymmetrical loads are studied and presented. In each case, the deflections resulting from elastic elongation or solely due to geometrical displacement are analyzed for the lower elastic modulus CFRP. Finally, in comparison with steel cables, the influences on the cable force equation and the governing displacement equation by span and rise span ratio are analyzed. Moreover, the influences on the static performance of suspension bridge by span and sag ratios are also analyzed. The substantive characteristics of the static performance of super span CFRP suspension bridges are clarified and the superiority and the characteristics of CFRP cable structure are demonstrated analytically.

Shear strengthening of pre-damaged reinforced concrete beams with carbon fiber reinforced polymer sheet strips

This paper presents the results of an experimental investigation on the response of pre-damaged reinforced concrete （RC） beam strengthened in shear using applied-epoxy unidirectional carbon fiber reinforced polymer （CFRP） sheet. The reasearch included four test rectangular simply supported RC beams in shear capacity. One is the control beam, two RC beams are damaged to a predetermined degree from ultimate shear capacity of the control beam, and the last beam is left without pre-damaged and then strengthened with using externally bonded carbon fiber reinforced polymer to upgrade their shear capacity. We focused on the damage degree to beams during strengthening, therefore, only the beams with sidebonded CFRPs strips and horizontal anchored strips were used. The results show the feasibility of using CFRPs to restore or increase the load-carrying capacity in the shear of damaged RC beams. The failure mode of all the CFRP-strengthened beams is debonding of CFRP vertical strips. Two prediction available models in AC1-440 and fib European code were compared with the experimental results.

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.

Strengthening reinforced concrete beams using prestressed glass fiber-reinforced polymer-Part I: Experimental study

This work is aimed at studying the strengthening of reinforced concrete (R. C.) beams using prestressed glass fi- ber-reinforced polymer (PGFRP). Carbon fiber-reinforced polymer (CFRP) has recently become popular for use as repair or rehabilitation material for deteriorated R. C. structures, but because CFRP material is very stiff, the difference in CFRP sheet and concrete material properties is not favorable for transferring the prestress from CFRP sheets to R. C. members. Glass fi- ber-reinforced polymer (GFRP) sheets with Modulus of Elasticity quite close to that of concrete was chosen in this study. The load-carrying capacities (ultimate loads) and the deflections of strengthened R. C. beams using GFRP and PGFRP sheets were tested and compared. T- and ⊥-shaped beams were used as the under-strengthened and over-strengthened beams. The GFRP sheets were prestressed to one-half their tensile capacities before being bonded to the T- and ⊥-shaped R. C. beams. The prestressed tension in the PGFRP sheets caused cambers in the R. C. beams without cracks on the tensile faces. The PGFRP sheets also enhanced the load-carrying capacity. The test results indicated that T-shaped beams with GFRP sheets increased in load-carrying capacity by 55% while the same beams with PGFRP sheets could increase load-carrying capacity by 100%. The ⊥-shaped beams with GFRP sheets could increase load-carrying capacity by 97% while the same beams with PGFRP sheets could increase the loading-carrying capacity by 117%. Under the same external loads, beams with GFRP sheets underwent larger deflections than beams with PGFRP sheets. While GFRP sheets strengthen R. C. beams, PGFRP sheets decrease the beams’ ductility, especially for the over-strengthened beams (⊥-shaped beams).

Study of galvanic corrosion and mechanical joint properties of AZ31B and carbon-fiber–reinforced polymer joined by friction self-piercing riveting

A new testing methodology was developed to quantitively study galvanic corrosion of AZ31B and thermoset carbon-fiber–reinforced polymer spot-joined by a friction self-piercing riveting process.Pre-defined areas of AZ31B in the joint were exposed in 0.1 M NaCl solution over time.Massive galvanic corrosion of AZ31B was observed as exposure time increased.The measured volume loss was converted into corrosion current that was at least 48 times greater than the corrosion current of AZ31B without galvanic coupling.Ninety percent of the mechanical joint integrity was retained for corroded F-SPR joints to 200 h and then decreased because of the massive volume loss of AZ31B。

Mechanical joint performances of friction self-piercing riveted carbon fiber reinforced polymer and AZ31B Mg alloy

Carbon fiber reinforced polymer(CFRP) and AZ31B Mg alloy were joined by the friction self-piercing riveting(F-SPR) with different steel rivet shank sizes. With the increase of rivet shank size, lap shear fracture load and mechanical interlock distance increased. Ultrafine grains were formed at the joint in AZ31B as a result of dynamic recrystallization, which contributed to the higher hardness. Fatigue life of the CFRP-AZ31B joint was studied at various peak loads of 0.5, 1, 2, and 3 kN and compared with the resistance spot welded AZ31B-AZ31B from the open literature. The fatigue performance was better at higher peak load(>2 kN) and comparable to that of resistance spot welding of AZ31B to AZ31B at lower peak loads(<1 kN). From fractography, the crack initiation for lower peak load(<1 kN) case was observed at the fretting positions on the top and bottom surfaces of AZ31B sheet. When peak load was increased, fretting between the rivet and the top of AZ31B became more dominant to initiate a crack during fatigue testing.

Investigating Some Parameters Affecting Flexural Behavior of Reinforced Concrete Beams Strengthened with Carbon Fiber Reinforced Polymer Laminate

In this paper,the influence of some important parameters affecting the flexural behavior of reinforced concrete beams strengthened with one layer of carbon fiber reinforced polymer(CFRP)laminate has been studied.For this purpose,six reinforced concrete beams were cast and tested in the laboratory.Based on the obtained data,when CFRP laminate is applied to the tension face,too close to the steel rebar,the flexural strength of the strengthened beam is reduced.In general,the performance of the beam strengthened with one wide CFRP strip is better than that strengthened with two equivalent narrow strips.Ultimate load capacity of each strengthened beam was calculated based on the method given by the ACI 440.2R and compared with the test one.It is concluded that,to avoid the steel rebar-CFRP laminate interaction effect,the CFRP laminate depth-to-the effective depth ratio(df/d)should not be smaller than about 1.17.

STUDY ON ULTRASONIC VIBRATION DRILLING IN CARBON FIBER REINFORCED POLYMERS

This paper researches ultrasonic vibration drilling of carbon fiber reinforced polymers composites that are hard, brittle, and have low shear strength between layers. An experiment plan has been developed to reduce the axial force. Experimental studies have been done on the influence of process parameters, tool structures on the drilling axial force. The drilling mechanism is specially investigated. Thus an effective method is presented to reduce the drilling axial force. The authors suppose that ultrasonic vibration drilling is feasible for carbon fiber reinforced polymers composites.

CFRP及EWSS复合加固震损双层高架桥框架式桥墩恢复力模型研究

为研究碳纤维布(Carbon Fiber Reinforced Polymer,CFRP)及外包型钢(Externally Wrapped Steel Section,EWSS)复合加固震损双层高架桥框架式桥墩的恢复力模型,对1榀原型对比试件、1榀无预损加固试件和2榀遭受不同地震损伤加固试件进行了低周往复加载破坏试验,获取了滞回曲线并提取骨架曲线,分析其滞回特性,提出一种弹性段和强化段为双折线、下降段为指数函数且考虑初始损伤的骨架曲线模型;采用试验数据回归拟合方法,定量描述了试件滞回曲线卸载刚度的退化规律,考虑了同级加载承载力退化和定点指向特征,建立了恢复力模型。研究结果表明:复合加固试件滞回曲线捏缩现象明显,呈倒S型,各滞回环分别相交于骨架曲线上正向、负向荷载为屈服荷载0.25倍的点,峰值荷载后EWSS产生包辛格效应;所提出的骨架曲线模型对中度震损和重度震损加固试件下降段指数函数的参数k建议取值分别为3.6和3.4;所建立的骨架曲线模型和恢复力模型计算结果与试验实测结果吻合较好,可为该类结构弹塑性地震反应分析提供依据。

Impact Responses of the Carbon Fiber Fabric Reinforced Composites

To study the response characteristics of the carbon fiber fabric reinforced composites under impact loading, one dimensional strain impact test, multi gauge technique and Lagrange analysis method are used. The decaying rule of the stress σ , strain ε , strain rate ε · and density ρ with time and space is obtained. By the theory of dynamics, the impact response characteristics of the material is analyzed and discussed.

侧向冲击荷载作用下CFRP型材-方钢管混凝土柱的动力响应

为了研究CFRP型材-方钢管混凝土固简柱的抗侧向冲击性能,采用水平撞击装置对3个CFRP型材-方钢管混凝土柱进行侧向冲击试验.根据柱的破坏模式、局部变形、整体变形及冲击力分析柱的动力响应,研究了CFRP型材、边界条件、冲击能量与冲击冲量对试件动力响应的影响规律.结果表明,CFRP型材-方钢管混凝土固简柱呈现弯曲破坏,具有良好的抗冲击性能,且随着支座约束能力的增大,抗侧向冲击性能增大.增加单位冲击冲量可使悬臂试件的峰值位移下降7%,而两端固支试件峰值位移仅变化1%.随着支座约束能力的下降,冲击冲量对试件变形的影响程度增大.在钢管混凝土固简试件中内置CFRP型材可使冲击位置处峰值位移下降9%,且降低程度随着支座约束能力的下降而增加.

弯-剪-扭复合受力CFRP布加固RC梁抗扭性能细观数值分析

为了研究弯-剪-扭复合受力条件下碳纤维增强复合材料(carbon fiber reinforced polymer, CFRP)布加固钢筋混凝土(reinforced concrete, RC)梁的抗扭性能,建立体现混凝土材料非均质性、钢筋-混凝土黏结滑移关系和CFRP布-混凝土相互作用关系的细观数值分析模型。由于缺乏CFRP布加固RC梁在弯-剪-扭复合受力作用下失效破坏的典型物理试验,采用复合对比验证法对数值模型的合理性进行验证,即分别与单独受剪、单独受扭以及受弯-扭复合作用下RC梁和CFRP布加固RC梁的试验结果进行对比验证。进而,基于建立的细观数值分析模型探究了配纤率和扭弯比对CFRP布加固RC梁在弯-剪-扭复合受力作用下抗扭力学性能的影响。结果表明:1)采用CFRP布加固能够显著提高RC梁的峰值扭矩;2)随配纤率增加,RC梁损伤分布范围逐渐变大,CFRP布应变逐渐减小,梁整体峰值扭矩增大,但其增大幅度减小;3)随扭弯比增加,RC梁裂缝分布愈加集中,裂缝与水平方向夹角逐渐减小,梁整体峰值扭矩增大,CFRP布应变减小。建立的考虑弯-剪-扭复合受力作用的数值模拟方法可为后续研究复杂应力状态下CFRP布加固RC梁尺寸效应行为等奠定基础。

CFRP板纵向加固RC柱在水平低周循环荷载下的力学性能研究与应用

开发了一种纵向粘贴CFRP(Carbon Fiber Reinforced Polymer,碳纤维增强复合材料)板的RC(Reinforced Concrete,钢筋混凝土)柱抗弯加固系统,该加固系统由纵向粘贴在柱表面的预制CFRP板和防止柱底CFRP板脱粘的混凝土加厚层组成.为研究纵向粘贴CFRP板对RC柱的抗弯性能影响,设计并开展了5根足尺矩形RC柱的水平低周循环加载试验.研究结果表明:粘贴CFRP板加固能有效延缓柱的开裂;柱的破坏模式得到明显改善;相较于未加固柱子,粘贴1层CFRP板和2层CFRP板加固的RC柱极限承载力分别提高了15.1%和17.4%;加固后柱的抗弯承载力和刚度得到提高,但增加CFRP板的层数对极限强度和刚度没有显著影响,反而会降低柱的延性,相较于仅采用增大柱底截面的方式加固的对照柱,粘贴1层CFRP板和2层CFRP板加固的试验柱的延性系数分别降低16.2%和35.1%;试验过程中,由于柱与基础节点承载力的限制,CFRP的最大应变仅达到极限应变的24%,抗拉强度未得到充分发挥.该加固方法已在某医院加固工程中得到应用,跟踪研究表明,加固后柱子的抗弯承载力有明显提升,加固方法得到工程业界的认可.

极地低温下CFRP筋与混凝土黏结性能数值分析

为进一步了解极地低温下碳纤维增强复合材料(CFRP)筋与混凝土的黏结性能,在现有试验的基础上,采用ABAQUS软件建立考虑CFRP筋表面特征的数值模型,分析64种工况,研究低温下CFRP筋直径、肋高、肋宽与混凝土保护层厚度等参数对黏结性能的影响。结果表明:考虑CFRP筋表面特征的数值模型可以较好地表征CFRP筋与混凝土之间的应力传递,能够反映低温下CFRP筋与混凝土的损伤情况与黏结破坏机制;低温可显著提高CFRP筋-混凝土的黏结强度;在低温下,随着CFRP筋直径的增加,CFRP筋与混凝土的黏结强度降低,同时弱化了低温对黏结强度的增强效应;随着CFRP筋肋高的增加,CFRP筋-混凝土的低温黏结强度呈现先提高后降低的趋势,肋高为筋材直径8%时黏结强度达到最大值;CFRP筋肋宽的变化主要影响黏结滑移曲线的形状;相比常温试件,在低温下试件发生拔出破坏时的混凝土保护层厚度更大。

超声振动辅助磨削CFRP复合材料薄管撕裂损伤研究

针对碳纤维增强复合材料(CFRP)薄管超声振动辅助磨削过程中存在撕裂损伤且形成原因不明确的问题,通过对M55J和T300复合材料薄管开展超声振动辅助磨削试验,探究了超声振幅、进给量及主轴转速对磨削力和撕裂尺寸的影响规律,通过对磨削过程的受力分析和对最大未变形切屑厚度的计算,分析了撕裂位置的形成原因和撕裂尺寸的变化规律。结果表明:磨削力随超声振幅的增大而减小,随进给量的增大而增大,与主轴转速的关联性较小;撕裂易出现于CFRP薄管内壁,其长度与高度随超声振幅的增大而减小,随进给量的增大而增大,随主轴转速的增大而减小。

新型CFRP网格-重组竹复合板力学试验研究

为提高重组竹的力学性能并减轻其各向异性缺陷,设计了一种新型CFRP网格-重组竹复合板(CBCP).分别对8组CBCP拉伸试样和18组CBCP拉拔试样进行单轴拉伸试验和拉拔试验,以分析其力学行为并评估复合方法的影响.选择3个相似的构成模型对拉拔试样的黏结应力-滑移曲线进行拟合,根据试验结果确定CFRP网格和重组竹的临界锚固长度及计算方法,并分析讨论了CFRP层数、横向CFRP束特性和锚固长度对CFRP网格与重组竹黏结性能的影响.结果表明,复合CFRP网格可使重组竹的顺纹和横纹抗拉强度分别提高35.77%和135.20%,从而改善了重组竹的各向异性缺陷.增加网格层数和间距可提高CBCP的拉伸性能.随着锚固长度的增加,平均界面黏结强度呈幂函数递减,而峰值载荷滑移则线性递减.

氯盐干湿循环作用下表面开槽CFRP-混凝土界面抗剪性能试验

为探究氯盐干湿循环作用下表面开槽CFRP-混凝土界面抗剪性能,开展干湿循环(0 d、60 d和120 d)不同沟槽形状(矩形、正梯形和倒梯形)的单搭接拉伸剪切试验,研究失效模式和断裂能的变化及影响最大剪应力的因素,结合试验结果推导了考虑干湿循环的界面黏结滑移本构方程,并通过数值模拟验证其有效性。结果表明:随干湿循环进行,表面开槽法失效模式由CFRP断裂破坏转变为剥离破坏;120 d界面断裂能下降量较未开槽法减少60.04%~69.42%;正梯形组120 d最大剪应力相比其他表面开槽形状提升7.18%~9.48%。表面开槽法在氯盐干湿循环作用下具有较好的抗剪性能,建立的界面本构劣化方程适用于氯盐干湿循环作用下表面开槽CFRP-混凝土界面黏结性能的分析和模拟。

CFRP-不锈钢夹层管混凝土柱轴压试验及承载力计算方法

为了提升薄壁不锈钢结构的承载性能和耐久性,在不锈钢管内外壁粘贴碳纤维增强复合材料(Carbon Fiber-Reinforced Polymer,CFRP)复合约束海水海砂混凝土,制得一种CFRP-不锈钢夹层管海水海砂混凝土结构。以CFRP粘贴层数和方式为变化参数,对18个短柱试件进行了单调轴心受压试验,观察了试件的受力破坏过程及形态,获取了荷载-位移曲线和材料应变分布数据,分析了试件轴压力学性能的变化规律。结果表明:内外贴CFRP能有效地提高结构的承载能力和变形能力;无CFRP和内贴CFRP试件的破坏形态均为剪切破坏,但破坏形态会随着外贴CFRP层数的增加向腰鼓破坏转变;在相同粘贴方式下,试件的承载能力、变形能力和耗能能力随着CFRP层数的增加呈非线性提高;在相同粘贴层数下,内贴CFRP的力学性能提升效果优于外贴CFRP,粘贴1层和2层CFRP时,内贴试件的极限承载力相较于外贴试件能再提高5.6%和6.7%,同时内贴1层CFRP的试件的耗能能力与外贴2层CFRP的相当;应变分析显示,在试件破坏前,CFRP与不锈钢协同工作良好。文中最后基于极限平衡法,考虑不锈钢的应变硬化效应,提出了CFRP-不锈钢夹层管混凝土柱极限轴压承载力的计算公式,并收集了73个样本的数据进行验证,发现计算值与试验值较为吻合。