桥梁加固用碳纤维预浸带的制备与应用研究

结合桥梁加固工程实际,选择了合适的树脂体系,应用湿法成型预浸料制造技术,在外场制备了半固化状态的碳纤维预浸带,此预浸带有一定的柔韧性,在施工过程中能与待加固界面充分的接触,达到了良好的工艺性。并对固化后的碳纤维复合材料板进行了性能测试:抗拉强度>2875MPa,弹性模量>158.5GPa,断后伸长率1.7%。     

Microstructure and flexural properties of multilayered fiber-reinforced oxide composites fabricated by a novel lamination route

All-oxide ceramic matrix composites produced by a novel route based on the lamination of thermoplastic prepregs are investigated. This route allows for the production of composites with very homogeneous microstructures and a reduced amount of matrix cracks. Nextel^TM 610 alumina woven fabric is used here to reinforce a porous oxide matrix composed of 80 vol% Al₂O₃ and 20 vol% ZrO₂. The mechanical behavior of composites submitted to different heat treatments is investigated under 4-point bending and short beam shear. Results show that composites with low interlaminar shear strength present a graceful failure under 4-point bending, characterized by a stepwise stress reduction upon straining beyond the peak stress. The fracture of such composites is accompanied by a series of interfacial delamination events, which enhance energy dissipation during failure. An increase of the interlaminar shear strength due to matrix densification causes a loss of the stepped stress–strain behavior. Nevertheless, fiber-related toughening mechanisms such as crack deflection and bridging still ensure inelastic deformation up to failure of these composites.     

Blends of a thermotropic LCP and a thermoplastic elastomer. II: Formation and stability of LCP fibers

The formation of fibers during blending of a thermotropic liquid crystalline polymer (LCP) with a thermoplastic elastomer (TPE) using shear flow, and the stability of the fibers and the blend morphologies at elevated temperatures were studied. The polymers used were Vectra A900 (LCP) and Kraton G1650 (TPE). Fiber formation in (predominantly) shear flow was studied using a single screw extruder of which the die was removed. Fibers were obtained in blends with 5 vol% LCP at shear rates as low as 6.3 s^?1. Conventional extrusion through a die was used for preparing materials for the studies of the thermal stability of blends and isolated fibers–isolated LCP-fibers surrounded by a TPE-matrix disintegrate when held above the melting point of the LCP. Annealing of the blends at this melting temperature results in changes of the morphology and in a fairly rapid decrease of the modulus of elasticity.     

热塑性预浸带模压成型工艺研究

本文针对热塑性预浸带的模压成型工艺进行了探索研究，为成型连续纤维增强热塑性复合材料模压制品提供了简单，实用的工艺方法。     

Ceramic laminates with improved mechanical reliability by tailoring the porosity of the constituting layers

Two different ceramic laminates composed of porous alumina and alumina/zirconia layers were designed and produced in the present work. The two symmetrical architectures were selected whose fundamental difference is the presence on the surface of a porous layer in the first and a compact alumina/zirconia composite layer in the second. The residual stress profile and corresponding fracture toughness were tailored to promote the stable growth of surface defects prior to final failure to increase the mechanical reliability of the material. The laminates were realized by stacking together different green laminae (containing specific pore former content) in a specific order, thermo-compression and co-sintering. The results point out an important reduction of the strength scatter and a clear insensitivity to surface damage. It is also shown that the mechanical performances are strictly related to the specific architecture of the laminate, this allowing to tailor a priori the mechanical performances of the composite.     

Relationship between processing,microstructure, and mechanical properties of injection molded thermotropic LCP

A commercial thermotropic liquid crystalline polymer (LCP), Vectra A950, was injection molded into rectangular sheets of thickness ranging from 1 to 4 mm. By changing the thickness of the mold, the shear rate experienced by the TLCP melt in the mold could be varied. The 1‐mm test sample was highly anisotropic while that with larger thickness (4 mm) was less anisotropic. X‐ray diffraction profile at various depths for each of the test sample corresponded to the degree in the fiber orientation present in the test samples. The anisotropy can be described macroscopically by measuring the tensile strength and modulus in the longitudinal and transverse direction. The ratio between the longitudinal and transverse property decreases proportionally to the thickness of the test sample. This reduction corresponded to the reduction in the shear field as the thickness of the mold was increased. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1713–1718, 2003     

Microstructure and mechanical behavior of TiO2-MnO-doped alumina/alumina laminates

Tapes of TiO₂-MnO-doped alumina (d-Al₂O₃) and pure alumina (Al₂O₃) were shaped via tape casting. Laminates with three different layer numbers and respective thicknesses were produced and sintered at 1200°C. The microstructure and mechanical behavior of laminates were investigated and compared to the respective monolithic references (d-Al₂O₃ and Al₂O₃). The use of dopants in alumina decreased the initial sintering temperature, leading to higher densification at 1200°C (~98% theoretical density (TD)) when compared to Al₂O₃ (~73% TD). The higher density was reflected in a higher Young's modulus and hardness for doped alumina. A region of diffusion of dopants in pure alumina layers was observed along the interface with doped layers. The mechanical strength of d-Al₂O₃ samples sintered at 1200°C was not statistically different from Al₂O₃ samples sintered at 1350°C. The strength of laminates composed of doped layers with undoped, porous interlayers did not change. Nevertheless, as the thickness of these porous interlayers increases, a loss of strength was observed. Monolithic references showed constant values of fracture toughness (K_IC), ~2 MPa·m^1/2, and linear crack path. On the other hand, K_IC of laminates increases when the crack propagates from weak Al₂O₃ layers to dense d-Al₂O₃ layers.     

Scratch and wear resistance of transparent topcoats on carbon laminates

The present investigation deals with the application of low-curable powder paints on epoxy–carbon laminates. Carbon laminates were first peened to corrugate their surface, hence increasing the wettability and allowing a better adhesion of the overlying coatings. Powder coatings were then electrostatically sprayed onto peened and unpeened substrates and baked into a convection oven. Their aesthetic and tribological performance was comparatively evaluated. Powder coated peened carbon laminates exhibited good adhesion and visual appearance as well as noteworthy scratch resistance and tribological performance.     

Joining of carbon fiber reinforced polymer laminates by a novel partial cross‐linking process

Direct joining of partially cross‐linked and freshly infiltrated carbon fiber reinforced epoxy resin plates made from HTA/RTM6 is investigated as function of the partial curing degree. Partial cross‐linking maintains a certain chemical reactivity of the thermosetting resin which can be used for bonding to a second, freshly infiltrated resin part. A final curing cycle guarantees complete cross‐linking of the joined component. The bonding behavior and the interface morphology of the joined plates are analyzed by mechanical testing, acoustic emission analysis and microscopy. A significant dependence of the bonding and interfacial properties on the partial curing degree is found. Very low and very high partial curing degrees (below 70% and above 80%) result in low fracture toughness and discontinuous crack propagation. Intermediate curing degrees between 70% and 80% mainly show high fracture toughness, stable crack propagation and a ripple like interface morphology. The latter is created by the surface morphology of the partially cross‐linked plate with the typical peel‐ply imprint and results in a high contact surface and mechanical interlocking. The combination of chemical reactivity and high contact surface seems to be advantageous for the enhanced fracture toughness and the improved failure mode of samples with intermediate partial curing degree. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42159.     

穿透裂纹对层合板拉伸性能的影响

对含3种不同方向穿透裂纹的层合板进行了拉伸试验研究,通过观测试验过程与断口分析,研究了含穿透裂纹层合板的失效行为。在此基础上,采用ABAQUS软件建立了含穿透裂纹层合板渐进损伤有限元分析模型,对其拉伸性能进行了分析,并对初始损伤与裂纹扩展路径进行了研究,讨论了裂纹形式对复合材料层合板剩余拉伸强度的影响。结果表明,初始损伤发生在裂纹尖端,损伤有沿垂直于载荷方向扩展的趋势。裂纹方向的变化对层合板的剩余强度有明显影响。     

Delamination Cracking in a Laminated Ceramic-Matrix Composite

Delamination crack propagation has been investigated in a laminated fiber-reinforced ceramic-matrix composite. The crack growth initiation resistance has been shown to be dominated by the critical strain energy release rate for the matrix. However, the resistance increases with crack extension because of bridging effects associated with intact fibers and, in some cases, intact segments of matrix. The delamination cracks also assume a steady-state trajectory within a 0° layer close to the 0°/90° interface.     

Effects of applying a combination of surface treatments on the mechanical behavior of basalt fiber metal laminates

The surface treatment of metals has a great role on the adhesion of the metals to the polymers. There are various surface treatment methods for adhesive joint applications. However, the effect of the combination of surface treatment methods on the mechanical behavior of adhesive joints has not been extensively studied. In this study, the effects of applying a combination of surface treatments on the flexural and Charpy impact behavior of fiber metal laminates (FMLs) were investigated. The surface treatments included forest product laboratory etching (FPL), sulfuric acid anodizing (SAA), sandblasting, sandblasting + FPL and sandblasting + SAA. The FMLs were made from Al2024-T3, basalt fibers and epoxy. Scanning electron microscopy (SEM) was used to study the surface morphology of the Al2024-T3 laminates and fracture surface of the samples. Furthermore, the surface roughness of the Al2024-T3 sheets after different surface treatments were evaluated using profilometry. Results showed that the adhesion of Al2024-T3 to polymeric layers was significantly affected by various surface treatments. Results of bending tests indicated that the highest bending strength and strain to failure values were respectively achieved for the SAA and sandblast treated samples. On the other hand, although there was a slight improvement in the bending strength, the application of SAA or FPL etching after sandblasting caused a negative effect on the strain to failure value of the samples. However, impact test findings showed that the combination of FPL or SAA treatments after sandblasting rendered positive effects on the low-velocity impact behavior of the FMLs.     

Progressive failure analysis of bolted joints in composite laminates

Abstract

A three-dimensional progressive failure analysis methodology was developed to predict the strength of double lap bolted joints in [0°/90°/±45°]_2s carbon fibre reinforced plastic laminates. An experimental programme was conducted to verify and validate the proposed computational model. Good agreement was obtained between the experimental data and predictive model. A parametric study was conducted for varied clamping torque and friction coefficient values. The well known effect of those variables on the joint strength was captured. Although the in-plane mode of failure of each individual layer around the fastener hole was predicted, X-ray radiographs have shown that delamination failure is particularly dominant around the washer’s outer edge. At present, the proposed model does not account for delamination onset and propagation. Future work will involve implementing cohesive zone elements in regions of interest to capture this interlaminar cracking, a work in which the authors are currently engaged in.     

Lipase‐mediated preparation of epoxy lecithin and its evaluation as plasticizer in polyester laminates

A simple chemoenzymatic method was developed for the preparation of epoxy lecithin that contains epoxy oils and phospholipids. The parameters such as lipase concentration, hydrogen peroxide concentration, and time of the reaction were studied. The product was evaluated as a plasticizer in polyester laminates and compared with virgin polyester laminates. The laminates were prepared using various amounts of epoxy lecithin and evaluated for different properties. The epoxy lecithin modified laminates showed good impact strength, tensile, and chemical resistance properties. These laminates were also evaluated for vicat softening point and water absorption. The epoxy lecithin can be used as a plasticizer in polyester laminates. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Experimental Observations of High Fracture Resistance in Silicon Carbide/Alumina Laminated Composites

Model laminated composites were fabricated with porous-Al₂O₃ interfaces between SiC bars. The porous Al₂O₃ was deposited using an aerosol spray deposition technique, and the sandwich specimen was fabricated by hot pressing. Residual thermal stresses were present in the interface because of the difference in the coefficients of thermal expansion of SiC and Al₂O₃. Crack deflection was observed with measured interfacial fracture resistances that were considerably higher than the deflection threshold predicted by the He–Hutchinson criterion. Examination of the fracture surface revealed a tortuous crack path and significant crack–flaw interaction.     

Effect of BN or B4C content on physical and tribological properties of copper-clad laminates reinforced with carbon fiber and epoxy resin

Plasma treatment was used to improve the surface roughness of copper foil. The copper-clad laminates reinforced with carbon fiber, boron nitride (BN), or boron carbide (B₄C), and epoxy resin were prepared by hot pressing. The effect of BN or B₄C content on the physical properties and tribological properties of copper-clad laminates reinforced with carbon fiber and epoxy resin were studied. The resulting copper-clad laminate exhibited desirable properties, such as dielectric constant, peel strength, oxygen index, and arc resistance, which were influenced by the concentration of BN or B₄C particles. Additionally, the wear and friction properties of the laminate were evaluated, revealing the effects of load, sliding speed, and particle content on weight loss, specific wear rate, and coefficient of friction. SEM analysis of worn surfaces provided insight into the stages of wear, highlighting the importance of an oxide layer in reducing wear and protecting the copper surface.     

Unique Opportunities for Microstructural Engineering with Duplex and Laminar Ceramic Composites

Duplex (two-phase) microstructures and laminar composites offer some unique opportunities for improving the room-temperature mechanical reliability (e.g., flaw tolerance) and the high-temperature microstructural stability (e.g., resistance to grain growth and creep damage) of structural ceramic materials. Examples illustrating the approach to designing novel multiphase microstructures and laminar composites with enhanced structural reliability are given. These are based on current work on various alumina-based ceramics as well as zirconia-, silicon nitride-, and silicon carbide-containing ceramics. Critical issues and areas for future work are discussed.     

Processing of thermotropic liquid crystalline polymers and their blends—analysis of an in-situ LCP composite system

Thermotropic LCP/LCP fiber blends were prepared by a combination of meltblending and hot-drawing, using a wholly aromatic copolyester KU-9211 (also called K161 from Bayer A.G.) and an aliphatic containing LCP (liquid crystalline polymer) PET/PHB60 (from Kodak Tennessee Eastman). Morphological evidence, including scanning electron (SEM) and transmission electron microscopy (TEM), showed that the dispersed phase consisted primarily of highly oriented, 0.5 to 2 μm diameter rigid-rods of aromatic fibers imbedded in a matrix of predominantly aliphatic LCP fibrils with diameters in the range of 20 to 50 nm. An interphase of approximately 50 nm strongly bonded the two phases together. The fiber blends were characterized using dynamic mechanical thermal analysis (DMTA), thermogravimetric analysis (TGA), gas chromotography/mass spectroscopy (GC/MS), and rheological measurements. It appears that the processing conditions employed for melt blending had caused PET/PHB60 to undergo chain scission, thereby creating chemical interactions between the two LCP components during the melt blending process. Differential scanning calorimetry (DSC) thermograms as well as nuclear magnetic resonance (NMR) spectra of the extracted fraction from the mixture of 30 wt% K161/70 wt% PET(PHB60) confirmed the chemical interaction between the two thermotropic liquid crystalline polymers.