Bond strength of steel deformed rebars embedded in artificial lightweight aggregate concrete

The recycling of industrial waste such as bottom ash from furnaces is an important issue in construction industry, since it enables reduction in construction cost and has beneficial effect on the environment. In this study, we have investigated the bond characteristics of steel deformed bars embedded in artificial lightweight aggregate concrete which is manufactured from bottom ash. A pullout test was performed on 144 lightweight aggregate concrete specimens to measure the bond strengths. In this test, the parameters included the compressive strength of the concrete and embedment length of rebar. The pullout load vs. slip responses and modes of failure of the specimens were identified during the test. A bond strength equation for lightweight concrete is formulated by performing a regression analysis on the test results and compared with the predictions by the existing equations such as ACI 408, Orangun’s, and Darwin’s. The comparison shows that the existing bond strength equations cannot be directly applied to the design of lightweight concrete structures and the proposed equation is able to provide a more accurate estimation of the bond strength of lightweight concrete than the existing equations.     

Experimental study on bond strength of fiber reinforced polymer rebars in normal strength concrete

The bond behavior of reinforcing bars is an important issue in the design of reinforced concrete structures and the use of fiber reinforced polymer (FRP) rebars is a promising solution to handle the problems of steel reinforcement corrosion. This study investigates the bond characteristics of carbon and aramid FRP (CFRP and AFRP) bars embedded in normal strength concrete. A pullout test was performed on 63 normal strength concrete specimens reinforced with FRP and steel rebars with different embedment lengths and bar diameters. The average bond stress versus slip curve is plotted for all specimens and their failure modes are identified. The effects of the embedment length and diameter of an FRP rebar on its bond strength are examined in this work. The bond strengths obtained from the test results are compared with the predictions by the bond strength equation proposed by Okelo and Yuan (2005), and its validity is evaluated.     

Synthesis,Characterization and Material Application of Poly(Urea-Imide)s,Part 1

Poly(urea-imide)s (PUIs) were prepared by Diels-Alder (DA) intermolecular polymerization of hexamethylenebis(2-furanmethylurea) (BFU) (1) with various bismaleimides (2a-f). The DA reaction was carried out using 1,4-dioxane as solvent, as well as in bulk, followed by aromatization (dehydration) of poly(tetrahydro phthalimide) intermediates (3a-f) in the presence of acetic anhydride. All the PUIs (3a-f, 4a-f and 5a-f) were characterized by elemental analysis, IR spectral studies and thermogravimetrically. BFU (1) and bismaleimides (2a-f) were polymerized (at 145 ± 10°C) by in situ DA intermolecular reaction into moderately thermally stable PUIs (5a-f), glass fiber and carbon fiber composites without evolution of any byproducts. The prepared composites were characterized by chemical resistance and mechanical properties.     

不同种类碳纤维上浆剂的研究

实验并讨论了几种不同类型上浆剂对碳纤维复合材料的影响。分别从乳液稳定性、复合材料力学性能、表面形貌和冲击断面形貌进行考察,结果表明：聚丙烯醇乳液上浆剂稳定性好,经其处理后的碳纤维复合材料力学性能优异,其界面结合能力强。     

On the interfacial adhesion of fiber metal laminates using surface modified aluminum 7475 alloy for aviation industries – a study

Abstract

Aluminum-based hybrid laminates are used extensively during the fabrication process of structural components in aviation industries due to its light weight and mechanical properties. A majority of airframe components are usually fitted with adhesion joints and, hence, surface adhesion has a great deal with surface and subsurface properties. To promote adhesion between substrates, various surface activating techniques could be followed. The main objective of this work is to enhance the interfacial adhesion strength between the thin aluminum alloy (AA 7475) and glass fiber. Experimentation was carried out to monitor the increase in the interfacial adhesion, by investigating the change in surface free energy which is influenced by the effect of surface etching. Aluminum sheets were treated using alkali (NaOH), iron (III) sulfate (Fe₂(SO₄)₃) and potassium dichromate (K₂Cr₂O₇). Etching effects were analyzed using water contact angle (W_CA), profilometry, scanning electron microscope (SEM images), X-ray diffractometer (XRD) and Fourier transformed infrared spectroscopy (FTIR-ATR). Tensile strength testing was done to evaluate the interfacial adhesion strength. The outcome of experimentation proves that, iron (III) sulfate treated condition laminates have higher tensile strength and it has also increased the interfacial adhesion.     

整体式碳纤维复合材料纯电动汽车上车体结构件研制

依托某全新开发的纯电动车型,开展碳纤维复合材料上车体结构设计及验证;根据原上车体设计的性能要求及碳纤维复合材料的材料和成型工艺特性进行结构设计,CAE分析验证,零部件及整车验证,成功试制碳纤维复合材料上车体并应用于整车。研究结果表明,碳纤维复合材料经合理的结构设计更适合作为结构件在汽车领域中予以应用,并具有显著轻量化效果,在汽车尤其是纯电动轿车领域具有发展前景。     

聚苯乙烯泡沫球在新型墙体材料中的应用研究

以聚苯乙烯泡沫球作为轻集料,研制新型墙体材料,可以使有机材料与无机材料的特性相互补偿,发挥复合材料的特有优势,综合改善了墙体材料的各项性能。     

Synthesis,Characterization and Glass/Carbon Reinforcement of Acetone-Formaldehyde-1,5-Dihydroxynaphthalene-Epoxy Resin System

Acetone-formaldehyde (AF) resin containing the methylol group (–CH₂OH) has been prepared and condensed with 1,5-dihydroxynaphthalene (DN) in the presence of an alcoholic alkali catalyst at varying ratios of AF:DN: 1:1, 1:1.5 and 1:2, respectively. The resultant AFDN resins were characterized by elemental analyses, IR spectral studies, and number average molecular weight determined by the nonaqueous conductometric titration method. Further reaction of the AFDN resins was carried out with different epoxy resins (i.e., DGEBA, DGEBC and DGEBF). The curing of these resins was monitored by differential scanning calorimeter (DSC) and their kinetic parameters have been evaluated. Based on DSC thermograms both glass and carbon fiber-reinforced composites have been laminated and characterized for chemical, mechanical and electrical properties. The unreinforced cured resins were subjected to thermogravimetric analysis (TGA).     

Relationship Between Some Mechanical Strengths of CFRP and Interfacial Properties

The relationships between microscopic properties such as interfacial shear strength (IFSS) and macroscopic properties such as flexural strength were investigated for CFRP prepared from carbon fiber and epoxy resin. Flexural, tensile and impact strengths all went through maximum values when plotted against the surface treatment time of the carbon fiber. The flexural strength of CFRP as a function of the treatment time of the carbon fiber behaved similarly to the adhesive strength of the resin and carbon fiber. Also, the results indicated that the bahavior of tensile and impact strengths varied with the treatment time in much the same way as the interfacial shear strength did. The occurrence of these two types of macroscopic and microscopic property effects can be understood by taking into account the chemical activity and roughness of the carbon fiber surface.     

增强PA6／PP合金的研究

研究了影响玻璃纤维增强尼龙6(增强PA6)/聚丙烯接枝马来酸酐(PP-g-MAH)二元合金和增强PA6/PP/PP-g-MAH三元合金的吸水性、流动性、机械和热性能的诸因素。结果表明,当增强合金中的PP-g-MAH或PP/PP-g-MAH含量为10％～20％(质量含量)时,材料的拉伸强度和弯曲强度、热变形温度(HDT)基本保持增强PA6的水平,其冲击强度、吸水性和流动性得到改善,增强合金的界面化学键数量在3×10~(-9)mol/m~2以上;当PP-g-MAH或PP/PP-g-MAH含量增至30％时,增强合金的干湿态机械性能趋于一致。     

超高分子质量聚乙烯纤维黏结强度增强方法研究

为提高超高分子质量聚乙烯(UHMWPE)纤维复合材料中纤维与树脂基体之间的界面黏结强度,提出通过不同质量分数的硅烷偶联剂KH-570处理纳米SiO_2对UHMWPE纤维进行表面改性。对改性处理后的纤维与乙烯基酯树脂进行黏结强度试验,发现硅烷偶联剂处理纳米SiO_2能有效提高纤维的界面黏结强度,同时使纤维保持一定的断裂强度。