Fracture detection in concrete by glass fiber cloth reinforced plastics

Two types of carbon (carbon fiber and carbon powder) and a glass cloth were used as conductive phases and a reinforcing fiber, respectively, in polymer rods. The carbon powder was used for fabricating electrically conductive carbon powder-glass fiber reinforced plastic (CP-GFRP) rods. The carbon fiber tows and the CP-GFRP rods were adhered to mortar specimens using epoxy resin and glass fiber cloth. On bending, the electrical resistance of the carbon fiber tow attached to the mortar specimen increased greatly after crack generation, and that of the CP-GFRP rod increased after the early stages of deflection in the mortar. Therefore, the CP-GFRP rod is superior to the carbon fiber tow in detecting fractures. Also, by reinforcing with a glass fiber cloth reinforced plastic, the strength of the mortar specimens became more than twice as strong as that of the unreinforced mortar.     

ARMT在长玻纤PU发泡成型中的应用研究

通过试验验证了金属电弧喷涂快速模具(ARMT)应用于长玻纤PU发泡成型的优良性。测得ZnAl15材料的ARMT可连续承受217℃热冲击,导热性比树脂模具高15%,硬度为90 HV,模具变形量在1 mm内为2‰左右。试验表明,ARMT在热物理性能和力学性能上均比树脂模具更适合于长玻纤PU发泡成型,成本和周期远低于传统金属模具。     

长玻璃纤维增强聚丙烯复合材料拉伸试样纤维取向模拟研究

介绍采用Moldflow软件对长玻璃纤维增强聚丙烯复合材料拉伸件的纤维取向及拉伸性能进行模拟研究,对模拟后的纤维取向、拉伸模量、泊松比进行了分析,结果表明:沿流动方向,靠近浇口部位的平均纤维取向不佳,远离浇口部位的标距尾部和过渡部位的平均纤维取向较好,垂直流动方向上平均纤维取向存在分层;纤维取向整体呈现明显的皮芯结构;试样的拉伸模量和泊松比随纤维取向的变化呈现出与其相一致的趋势。     

Fatigue crack growth behavior and fiber orientation of glass fiber reinforced polycarbonate polymer composites

The use of polymer-based composites has become increasingly common in the aeronautical and automotive industries. In this study, the fiber orientation of polymer composites was observed using microtoming techniques and the fatigue behavior of these composites was experimentally studied under mechanical loading. This involved the mechanical properties for parent and weld parts of polycarbonate (PC) composites in a tensile test and SEM. It was found that the tensile and hardness properties depended on the fiber orientation in the parent and weld parts of PC composites. Fatigue crack growth behavior depending on the fiber orientation was different in the parent and weld parts, according to a low cyclic-loading test.     

Aging characteristics of short glass fiber reinforced ZA-27 alloy composite materials

Aging characteristics of short glass fiber reinforced ZA-27 alloy composite materials have been evaluated in the present study. The liquid metallurgy technique was used to fabricate the composites, in which preheated short glass fibers were introduced into the ZA-27 alloy melt above its liquidus temperature. The aging temperature employed was 125 °C for 6, 12,18, and 24 h. The aged alloy (no fibers) reached the peak hardness after 18 h, while the composites (regardless of filler content) reached the same hardness in 12 h. It is hypothesized that the aging treatment of a composite improves the strength of the interface between the short fibers and the matrix. This is confirmed by the tensile fractograph analysis, which indicates that at a given aging temperature, the composites aged for 18 h exhibit short fibers that remain attached to the metal matrix, while those aged for 6 h undergo debonding.     

短炭纤维增强C/C-SiC制动材料的摩擦磨损性能

采用温压？原位反应法制备C/C-SiC复合材料,利用QDM150型摩擦试验机研究短炭纤维（SCF）长度和纤维体积分数对C/C-SiC制动材料摩擦磨损性能的影响。结果表明：C/C-SiC制动材料能够保持较高且稳定的摩擦因数;SCF的体积分数将影响C/C-SiC制动材料的摩擦磨损性能,纤维体积分数为10%时,材料具有适中的摩擦因数和较低的磨损率;SCF长度对C/C-SiC制动材料的摩擦磨损性能有显著影响,炭纤维长度为12 mm时,材料具有最佳的摩擦磨损性能。     

Laser-based repair of carbon fiber reinforced plastics

The recent progress in laser system technology enables innovative techniques for machining of carbon fiber reinforced plastics (CFRPs). A representative application is the layer-by-layer removal of damaged composite material to provide a cavity for refilling with repair plies. Results show that it is possible to achieve a reliable and automatable removal rate to perform arbitrary repair cavity geometries, obtaining a relevant time-reduction with respect to the conventional manual grinding process. The combination of modern UV-laser sources with a scanning technology enabling deflection speeds up to 2 m/s, suppresses heat affected zones (HAZs) and detachment of fibers from the polymer matrix. A method for the selective removal of surface matrix without damaging the fibers beneath is also presented.     

Design of eddy current-based dielectric constant meter for defect detection in glass fiber reinforced plastics

This paper presents the design of an eddy current testing probe for inspection of non-conductive glass fiber reinforced plastics. Because the magnetic field contains information pertaining to the permittivity of materials under test, eddy current testing offers the possibility of flaw detection in non-conductive materials through detection of the difference in permittivity between the intact part and the defective part of each material. We analytically investigated the design of a probe suitable for dielectric constant measurements. Experimental studies proved that the proposed probe can detect slit defects and flat-bottomed holes located 2 mm away from the surface of the glass fiber reinforced plastic samples.     

Aging behavior of Al2O3 short fiber reinforced Al-Cu alloy composites

Al2O3 short fiber reinforced AI-Cu composites containing 1%, 3%, 5% and 7% Cu were fabricated by a squeeze casting technique. The as-cast Al2O3/Al-Cu composites were solution treated at 535 ℃ and then aged at 170, 190 and 210 ℃, respectively. Age hardening behavior of the Al2O3/Al-Cu composites was analyzed by measuring the hardness of the samples at different aging temperatures and aging time. Microstructures of the composites were observed by transmission electron microscope（TEM）. The results indicate that the hardness of the Al2O3/Al-Cu composites containing 7% Cu is much higher than that containing 1%-5% Cu because of the large amount of CuAl2 precipitant in the Al2O3/Al-Cu composite. With the increase of Cu content from 1% to 7%, the time needed for the appearance of peak hardness shortened, indicating that the addition of Cu can accelerate the kinetic of CuAl2 precipitation in the Al2O3/Al-Cu composites. The Al2O3/Al-Cu composite containing 7% Cu shows the highest increment of hardness by aging treatment. Therefore, in order to get a higher peak hardness, the Al2O3/Al-Cu composites need more Cu addition as compared with the un-reinforced Al-Cu alloys.     

Optimization of the injection molding process of short glass fiber reinforced polycarbonate composites using grey relational analysis

This paper presents a fast and effective methodology for the optimization of the injection molding process parameters of short glass fiber reinforced polycarbonate composites. Various injection molding parameters, such as filling time, melt temperature, mold temperature and ram speed were considered. The methodology combines the use of the GRA (grey relational analysis) method and a CAE flow simulation software, to simulate the injection molding process and to predict the fiber orientation. This method can replace the traditional “change-one-parameter-at-a-time” approach, which is very inefficient, costly, time consuming and almost impracticable to yield an optimum solution. At the same time, the fiber orientation was examined by CAE simulation to forecast the shear layer thickness, and simultaneously to check the accuracy of the GRA. The results indicated that three distinct layers (a frozen layer, a shear layer and a core layer) are observed from the surface to the core for various injection molding conditions. The fiber orientation is perpendicular to the melt flow direction in the frozen layer and the core layer, but it has the opposite direction in the shear layer. From the CAE analysis, the optimum process parameters to obtain the thickest shear layer are found, which is the target of the present research.     

Feasibility study of the rotary ultrasonic elliptical machining of carbon fiber reinforced plastics (CFRP)

Carbon fiber reinforced plastics (CFRP) are used for various aircraft structural components because of their superior mechanical and physical properties such as high specific strength, high specific stiffness, etc. However, when CFRP are machined, rapid tool wear and delamination are troublesome. Therefore, cost effective and excellent quality machining of CFRP remains a challenge. In this paper, the rotary ultrasonic elliptical machining (RUEM) using core drill is proposed for drilling of holes on CFRP panels. This method combines advantages of core-drill and elliptical tool vibration towards achieving better quality, delamination free holes. The cutting force model and chip-removal phenomenon in ultrasonic elliptical vibration cutting are introduced and analyzed. The feasibility to machine CFRP for RUEM is verified experimentally. The results demonstrate that compared to conventional drilling (CD), the chip-removal rate has been improved, tool wear is reduced, precision and surface quality around holes is enhanced, delamination at hole exits has been prevented and significant reduction in cutting force has been achieved.     

Maximum cutting speed in laser cutting of fiber reinforced plastics

A simple one-parameter thermal model, predicting the maximum feed rate still resulting in a through cut as a function of beam power, focal spot diameter and thickness of worked material is presented and discussed for CO₂ laser cutting of composites. An extensive experimental program, including glass, carbon and aramide fabric reinforced polyester resin was carried out by varying all the parameters involved in the model. An excellent agreement is shown between experimental data and theoretical predictions. In addition, a criterion for cut quality classification, based on kerf geometry and heat affected zone size is formulated to help in selecting the optimum cutting conditions in order to obtain the best cut quality.     

Application of alumina fiber reinforced plastics as a grinding material

This work deals with the evaluation of ceramic fiber reinforced plastics as a grinding or polishing material. The plastics were manufactured by mixing continuous alumina fiber of definite diameters and thermosetting resin as a bond material. Composites containing fibers of three different diameters ranging from 10 to 22 μm were used in the study. The performance of these composites was evaluated for surface finishing of hardened steel. Bars of the composite were pressed against the rotating workpiece material S55C on a lathe. Wear of the work and the composite and the surface finish of the work materials were investigated. The self-sharpening characteristic was confirmed and the chip removal process is explained. The most important factor affecting the rate of metal removal to tool wear loss is the average pressure. The fine surface is obtained with the fine fiber. The advantages of the alumina fiber reinforced plastics as a grinding tool are their toughness and flexural strength. They assure a practically fracture-free grinding operation. Resin matrix composites reinforced with ceramic fibers are proposed as efficient tool materials for small stock removal. Paper presented at the First International Conference of New Manufacturing Technology, Chiba, Japan, March 1990.     

Sheet forming process of carbon fiber reinforced plastics for lightweight parts

The use of carbon fiber reinforced plastics is increasing markedly, particularly in aircraft bodies, but the time required to manufacture CFRP parts should be shortened to realize mass production. The stamping of solidified CFRP sheets can reduce the production time and may increase the flexibility of the manufacturing process. A new sheet forming process for solidified CFRP, in which a CFRP sheet is sandwiched by dummy metallic sheets during stamping, is proposed. The dummy metallic sheets act as protective materials as well as media for heating the CFRP sheet. The results of applying the proposed process are presented.     

Rapid 3D microwave printing of continuous carbon fiber reinforced plastics

Using microwave heating in 3D printing of continuous carbon fiber reinforced plastic (CCFRP) instead of the traditional resistive heating constitutes a new approach for the additive production of high performance composite components. Without the intrinsic slow speed and contact-needed heat transfer disadvantages, the instantaneous and volumetric heating benefits of microwave allows the fabrication of composites at higher speed. This paper presents the 3D microwave printing technology for CCFRP and investigates the mechanical properties of the tensile specimens that have been printed with different speeds. The printing process and mechanical properties of printed specimens are investigated and discussed.     

Quantification of metallic coating failure on carbon fiber reinforced plastics using acoustic emission

Carbon fiber reinforced plastic substrates were subsequently coated with an electrochemically applied nickel and an electroplated copper layer. The coating-substrate system was loaded in four-point bending and the acoustic emission from coating failure was recorded during loading. The acoustic emission signals were analyzed using pattern recognition and frequency analysis techniques. This approach yields three distinguishable types of acoustic emission signals, which are correlated to three different failure mechanisms: i) nickel cracking ii) copper cracking and iii) delamination between the two coating layers. To confirm the correlation between the types of acoustic emission signals and the respective failure mechanisms and to assess the validity of the acoustic emission method to describe mechanical failure, the micro-mechanical fracture energies released during mechanical loading were calculated based on microscopic measurements of the crack progress utilizing scanning electron microscopy and scanning acoustic microscopy. These energies were compared to the associated acoustic emission signals energy for each failure mechanism. We found the calculated micro-mechanical energy values to be proportional to the measured accumulated acoustic emission energy of the associated acoustic emission signal type. We conclude that the reported failure classification method offers the possibility to compare fracture toughness values in multilayered coatings with multiple failure types, derived solely from acoustic emission energies.     

W纤维/ZrTiCuNiBeNb基金属玻璃复合材料的断裂机制

研究了W纤维/ZrTiCuNiBeNb金属玻璃基复合材料的断裂机制。结果表明:宏观上,随着复合材料中纤维体积分数的增加,复合材料的压缩断裂方式从基体控制的"自锐性"断裂向"增强体撕裂"方式转变;微观上,复合材料的断裂方式实际上只受到增强体W纤维的控制。在压缩过程中,W纤维除了受到外加应力外,还受到由于扭转弯曲、基体剪切带塞积引起的应力集中等,纤维处于一个复杂的综合应力场,当纤维内部的纤维间介变形足以抵抗这个综合应力场时,纤维处于稳定状态,复合材料中基体的变形切过纤维,复合材料表现出自锐性特征;当纤维内部的纤维间介变形不足以抵抗综合应力场时,纤维失稳,沿间介劈裂,复合材料表现出沿纤维纵向撕裂的特征。     

内生枝晶增韧非晶基复合材料的摩擦磨损性能

采用电弧熔炼、铜模吸铸法分别制备Ti42Zr22V14Cu5Be17、Ti46Zr20V12Cu5Be17、Ti48Zr18V12Cu5Be17的Ti基内生枝晶增韧非晶基复合材料,利用球-盘式摩擦磨损试验机进行干摩擦磨损试验,研究了枝晶的体积分数对其耐磨性的影响,利用X射线衍射仪分析了样品的结构,利用扫描电子显微镜观察合金的显微组织和磨损表面形貌,分析了不同成分Ti基内生枝晶增韧非晶基复合材料的磨损机理。结果表明：在相同的试验条件下,不同体积分数晶体相的非晶复合材料的磨损机理不同。枝晶相体积分数较低时,磨损机理主要体现为轻微的磨粒磨损,随枝晶相体积分数的增加,粘着磨损成为主要的磨损机理,同时伴随有硬质颗粒压入软化相构成三体摩擦。材料耐磨性随着晶体相体积分数的增加而逐渐降低。     

Effect of thermal residual stresses on yielding behavior under tensile or compressive loading of short fiber reinforced metal matrix composite

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Precipitation behavior of Mg17Al12 in monolithic and Al2O3 short fiber reinforced Mg-Al-Zn alloys

The precipitation behavior of Mg₁₇Al₁₂ in monolithic and Al₂O₃ short fiber reinforced Mg-Al-Zn alloys was investigated by optical and transmission electron microscopies and hardness measurements. The maximum hardness was obtained when the long and short axes of the platelet type continuous Mg₁₇Al₁₂ precipitates were about 0.3 μm and 0.04 μm, respectively. The area fraction of the discontinuous Mg₁₇Al₁₂ precipitate nodule reached about 0.23. The coarsening behavior of the discontinuous Mg₁₇Al₁₂ precipitate nodule was found to obey the relationship suggested by the Johnson-Mehl-Avrami model. The slope of the Johnson-Mehl-Avrami plot for the Al₂O₃ short fiber reinforced Mg-Al-Zn alloy was four times larger than that for the monolithic alloy due to the increased number of nucleation sites, i.e. nucleation at the interface between the reinforcing material and the α-Mg matrix as well as at the α-Mg grain boundaries.