连续SiC纤维增强钛基复合材料横向强度分析

连续SiC纤维增强钛基复合材料(SiCf/Ti)具有良好的综合性能,但其横向性能低于钛合金基体,为了准确地预测SiCf/Ti复合材料的横向强度,提出一种基于界面脱粘强度的计算模型。采用SiCf/Ti复合材料十字拉伸试件来测试复合材料的纤维/基体界面脱粘强度,并分析了热处理工艺对界面脱粘强度影响规律,以及不同纤维之间界面脱粘强度的差别。复合材料横向拉伸试件采用箔-纤维-箔方法制备,每个试件的纤维层数为10层,纤维百分数为30%左右。在不同温度条件下测试复合材料的横向拉伸强度,拉伸温度分别为室温、300,400,550℃,通过对比实验结果和模型预测结果,模型预测的结果与实验结果的误差不超过5%。     

陶瓷基复合材料及其界面问题

概述了作者及其合作者们在陶瓷基复合材料领域的研究成果,包括陶瓷纤维的结构及性能,玻璃陶瓷粉的制备,复合材料的制备和性能,界面强度的测定方法和影响界面强度的因素,复合材料热暴露破坏机制和界面微观结构等问题。     

锈蚀植筋下新老混凝土黏结面压剪试验研究

为研究锈蚀植筋下新老混凝土的黏结性能,采用某工程锈蚀钢筋作为植筋,制备了不同植筋率（0、0.223%、0.446%、0.502%、0.893%、1.004%、1.396%、1.786%和2.792%）的新老混凝土试件.在RYL-600微机控制岩石伺服剪切流变仪上进行了不同初始静压力（0、1、2、3和4 MPa）下混凝土试件的剪切试验.对试件的剪应力-位移曲线进行了归纳总结,得到了锈蚀植筋下新老混凝土试件在外力作用下产生变形乃至破坏的演化规律;分析了锈蚀植筋下新老混凝土黏结面的抗剪强度,得到了抗剪强度随植筋率及初始静压力变化的规律.同时根据试件试验破坏结果,着重分析了不同植筋率和不同初始静压力对其破坏模式的影响.试验结论为新老混凝土力学性能的研究提供了理论依据.      

感应加热温度对冷?热轧制成形钛/钢复合板界面的影响

对钛/钢组坯进行冷轧预复合成形,将钛/钢预复合板感应加热至热轧温度后单道次热轧成形制备了钛/钢复合板,研究了感应加热温度对钛/钢复合板的界面组织和界面结合性能的影响。结果表明,冷?热轧制复合法制备的钛/钢复合板的界面结合紧密,没有孔洞和间隙。钛/钢复合板由于感应加热和热轧的时间较短（<5 s）,钛/钢界面仅有少量硬化层碎块,没有金属间化合物析出。钛/钢复合板的界面Ti和Fe元素扩散层宽度随感应加热温度增大而增大,950 ℃时界面扩散层宽度达到8 μm。在感应加热温度为750 ~ 950 ℃的条件下,钛/钢复合板的界面结合良好。      

重熔时间对WCP/Fe复合材料微观界面组织及压缩断裂机制的影响

本研究中,用真空烧结法制得WCP/Fe复合材料并在某一温度下保温一定时间,完成界面重熔工艺,研究重熔时间对物相转化,微观形貌和压缩性能的影响。结果表明,碳化钨颗粒与钢铁基体的界面区域出现新的物相,并对材料性质和性能造成了影响。具体为:随着重熔时间的延长,界面区域从简单的机械结合转变为冶金结合,界面层宽度也在平稳增加。在这一过程中,界面层中发生了Fe3W3C的形核与长大。压缩实验表明,材料的压缩强度随着重熔时间的延长,呈现出先上升后下降的规律。在重熔时间40 min时达到最大值,为379.673 MPa。     

碳纤维加固技术在铁路桥梁加固补强中的应用

利用碳纤维片高强和可粘贴的性能,把碳纤维片用环氧树脂粘贴在被补强的混凝土结构表面,有效封闭了混凝土裂缝,并与原混凝土结构形成一体共同承受荷载,使混凝土结构得到了有效的加固补强.     

高炉水渣用作混凝土细骨料的可行性研究

研究了高炉水渣和天然黄砂的区别,水渣代砂配制混凝土的新拌混凝土性能,混凝土强度及抗渗、抗碳化和抗氯离子渗透等耐久性能。研究发现水渣符合2级配区砂,水渣具有一定的胶凝活性,但不会对混凝土结构产生危害。随着水渣代砂率的增大,水泥砂浆干缩性减小,混凝土坍落度逐渐降低;混凝土达到相同坍落度所需减水剂掺量逐渐增大;混凝土抗压强度和抗折强度均缓慢增大;混凝土的抗渗性能、抗氯离子渗透性能、抗碳化性能均得到了改善。     

连续SiC纤维增强钛基复合材料横向强度分析

连续SiC纤维增强钛基复合材料（SiCf／Ti）具有良好的综合性能,但其横向性能低于钛合金基体。为了准确地预测SiCf／Ti复合材料的横向强度,北京航空制造工程研究所赵冰等人提出一种基于界面脱粘强度的计算模型。采用SiCf／Ti复合材料十字拉伸试件来测试复合材料的纤维／基体界面脱粘强度,并分析了热处理时间对界面脱粘强度影响规律,以及不同纤维之间界面脱粘强度的差别。     

烧结返矿分布及形成机理研究

烧结料层不同位置、反应条件不同造成烧结矿质量差异,通过对烧结台车不同位置烧结矿进行取样,测试不同位置烧结矿的冶金性能及返矿率,并对不同位置烧结矿微观结构进行分析,探究烧结饼内返矿的分布状况及产生机理.结果表明:沿料层高度方向由上至下烧结矿最终还原度逐渐降低,低温还原粉化指数降低.烧结返矿大部分在烧结料层上部和靠近挡板的边缘产生,只有少部分在中部和下部形成.料层上部烧结矿黏结相主要为铁橄榄石和少量粒状铁酸钙,强度差,返矿率较高,料层中下部黏结相主要以针状铁酸钙和板条状铁酸钙为主,整体矿化较好,返矿率较低.     

复合板轧制界面处理方法综述

金属基复合材料因具有较高的比刚度、比强度、耐磨性和高温性能,而具有可设计性,是一种高性能先进材料,在航空、航天、汽车等领域具有良好的应用前景。而其复合界面的结合机理对其性能是最为关键的因素。本文介绍了有关复合板轧制界面处理常用的几种方法如机械处理法、化学处理法、电化学处理法、其他处理法,以及其优缺点和使用条件。采用这些方法可以有效改善复合板界面的性能。     

Hybrid Bonding of FRP to Reinforced Concrete Structures

The adhesive attachment of fiber-reinforced polymers (FRP) laminate to the external face of reinforced concrete structures is currently one of the most popular and effective methods for retrofitting and strengthening concrete structures. With this method, the additional strength of the attached reinforcement is transmitted into the concrete members through adhesion. However, the relatively weak adhesive interface fundamentally limits the efficacy of the method. Much effort has been made in the research community to improve the bond strength and develop bond models, but a satisfactory solution has yet to be found. Mechanical fastening is another more traditional technology that is used to bond one material to another. This paper introduces a new hybrid bonding technique that combines adhesive bonding and a new type of mechanical fastening. The new mechanical fastening technique does not rely on bearing to transmit the interfacial shear, but instead increases the interfacial bond by resisting the separation of the FRP laminate from the concrete substrate. Experimental tests demonstrated that the bond strength with this new hybrid bonding technology was 7.5 times that of conventional adhesive bonding. Furthermore, the new bonding technique is applicable to all types of commercially available FRP laminate (fabric, sheet, plate, and strip), and in principle is also applicable to materials other than FRP.     

Load Transfer in Rammed Aggregate Piers

Predicting the load–settlement and load–transfer behaviors of rammed aggregate piers are important aspects of design. Use of advanced engineering models, however, can be complex involving uncertainty in selection of nonlinear constitutive model parameters for the aggregate and surrounding matrix soils and in selection of in situ stress fields. For purposes of simpler design calculations, this paper uses the closed-form approximate solution and the boundary-element method using both elastic (i.e., neglecting interface slip) and elastic–plastic soil–pier interface (i.e., considering interface slip) to predict load–settlement and load–transfer for rammed aggregate piers. Unlike previous studies that evaluate load–settlement and load–transfer for stiff, slender piles (e.g., concrete and steel piles) or fully penetrating granular piles, this paper focuses on floating rammed aggregate piers having slenderness ratios (L/D) of 3–10 and pier–soil stiffness ratios (Ep/Es) of 5–80. Predictions of load–settlement and load–transfer as a function of depth are compared to three full-scale instrumented load tests. Based on the calibrated models, equations for predicting load–settlement response and load–transfer as functions of Ep/Es, and L/D are presented with example calculations.     

延性相增韧的陶瓷材料中相界面对韧性的作用

论述了相界面结合与延性相的几何形态之间的匹配关系对延性相增韧的陶瓷基复合材料韧性的影响。对于连续延性相,例如网状、纤维或片状的延性相,界面结合较弱对增韧非常有益,因为裂纹扩展过程中相界面可发生部分分离,使桥接裂纹的延性相发生很大的塑性变形,消耗大量能量。而对于颗粒状的延性相,由于其球形形状及小的连续程度,经常导致断裂时断口上的延性相被完全拔出,几乎没有发生塑性变形,增韧效果较差,因此强的相界面结合强度是非常重要的。     

Nonlinear Deterioration Model for Bond Interfacial Fracture Energy of FRP-Concrete Joints in Moist Environments

This study proposed a bond mechanism based deterioration model of bond interfacial fracture energy for fiber-reinforced polymer (FRP)-concrete joints in moist environments. The bond interface region relative humidity (IRRH) in a moist environment was correlated to the bond fracture energy in this deterioration model. The IRRH-dependent interface separation tractions were derived in the frame of a cohesive zone model. Such an IRRH-dependent interface separation-traction law was simulated by a series of nonlinear interface elements attached to the bond interface to calculate the macroscopic load-displacement curves for the modified double cantilever beam (MDCB) specimens. Through moisture diffusion analysis, IRRH was determined as a function of the moisture exposure time for given specimen dimension and environmental RH. Using IRRH as the bridge, the time-dependent load-displacement curves of the MDCB specimens were obtained. The good agreement with the experimental data indicated that the model worked well. The approach developed in this study can be used to simulate and predict the durability of the bond between the FRP and concrete in moist environments.     

A Robust Macroelement Model for Soil–Pile Interaction under Cyclic Loads

The principal focus of this study is the development of a robust macroelement model for soil–pile interaction under cyclic loads. The model incorporates frictional forces and formation of gaps at the soil–pile interface as well as hysteretic behavior of the soil. The plastic envelope of the soil behavior is modeled via the so-called p–y approach, outlined in American Petroleum Institute’s guidelines for design of foundation piles for offshore platforms. The macroelement is an intuitive assembly of various basic elements, each of which incorporating a particular aspect of the soil–pile interaction. The modular structure of this macroelement allows straightforward adaptation of improved constitutive models for its building blocks. Herein, we focus on large-diameter, cast-in-drilled-hole reinforced concrete piles (piers) that are partially or fully embedded in soil. These types of piles are frequently used as support structures in highway construction. Consequently, the numerical robustness of the interaction model is assessed with parametric studies on pile systems and soil types relevant to this type of construction. Both elastic and inelastic pile behaviors are considered in the parametric studies. The results indicate that the proposed interaction element is numerically robust, and thus, amenable to routine structural analysis.     

Experimental Investigation of the Influence of Moisture on the Bond Behavior of FRP to Concrete Interfaces

The effects of moisture on the initial and long-term bonding behavior of fiber reinforced polymer (FRP) sheets to concrete interfaces have been investigated by means of a two-year experimental exposure program. The research is focused on the effects of (1) moisture at the time of FRP installation, in this paper termed “construction moisture,” consisting of concrete substratum surface moisture and external air moisture; and (2) moisture, in this paper termed “service moisture,” which normally varies throughout the service life of concrete. Concrete beams with FRP bonded to their soffits were prepared. Before bonding, concrete substrates were preconditioned with different moisture contents and treated with different primers. The FRP bonded concrete beams were then cured under different humidity conditions before being subjected to combined wet/dry (WD) and thermal cycling regimes to accelerate the exposure effects. Adhesives with different elastic moduli were used to investigate the long-term durability of each adhesive when subjected to accelerated WD cycling. Pull-off tests and bending tests were conducted at the beginning of the cycling and then again after 8 months, 14 months, and 2 years of exposure so as to evaluate the tensile and shear performance of the FRP-to-concrete interfaces. It was found that the effect of the concrete substrate moisture content on short-term interfacial bond performance could be eliminated if an appropriate primer was used. All FRP-to-concrete bonded joints failed at the interface between the primer and concrete after exposure while those not exposed usually failed within the concrete substrate. After exposure to an environment of accelerated WD cycles, it was also found that the interfacial tensile bond strength degraded asymptotically with the exposure time while the flexural capacity of the FRP sheet bonded plain concrete beams even increased. The mechanism behind the above, which is an apparently contradictory phenomenon, is discussed.     

Energy-Based Modeling Approach for Debonding of FRP Plate from Concrete Substrate

For concrete beams and slabs strengthened with bonded fiber reinforced plastic (FRP) plates, plate debonding from the concrete substrate is a common failure mode. In this paper, the debonding process is modeled as the propagation of a crack along the concrete/adhesive interface, with frictional shear stress acting behind the crack tip. Crack propagation is taken to occur when the net energy release of the system equals the interfacial fracture energy. The analysis is first performed for the special case with constant shear stress along the debonded interface, and then for the general case with slip softening in the debonded zone. From the results, a direct correspondence between energy-based and strength-based analyses can be established for arbitrary softening behavior along the interface. Specifically, through the proper definition of an effective interfacial shear strength, the conventional strength-based approach can be employed to give the same results as the much more complicated energy-based analysis. Also, based on the relation between the effective shear strength and other material parameters, it is possible to explain the very high interfacial shear stresses observed in experimental measurements. As an application example, distribution of plate stress and interfacial shear stress for the linear softening case is derived. The model results are found to be in good agreement with experimental measurements, showing that the simple linear softening model can describe the debonding process in real material systems.     

Strength Evaluation of Deteriorated RC Bridge Columns

Condition-rating methods followed by load rating calculations are used for evaluating existing bridges in the United States. Ratings are assessed visually based on engineering expertise and experience, and in some cases supplemented by nondestructive tests. Good understanding of the effects of deterioration on the structural performance leads to better inspection procedures, planning, and cost-effective rehabilitation methods. This paper presents a bridge pier column strength evaluation method that can be adapted into a currently used bridge condition evaluation method. This method uses damaged material properties, and accounts for amount of corrosion and exposed bar length for each reinforcement, concrete loss, bond failure, and type of stresses in the corroding reinforcement. The proposed evaluation method provides a good estimate of the condition and load-carrying capacity of bridge piers that currently cannot be obtained by normal visual surveys. In addition, the proposed evaluation approach will help reduce repair costs, avoid overconservative condition ratings, and result in a more uniform level of safety of concrete bridge substructure in the United States.     

Experimental Investigation and Fracture Analysis of Debonding between Concrete and FRP Sheets

The last few years have witnessed a wide use of externally bonded fiber reinforced polymer (FRP) sheets for strengthening existing reinforced and prestressed concrete structures. The success of this strengthening method relies on the effectiveness of the load-transfer between the concrete and the FRP. Understanding the stress transfer and the failure of the concrete–FRP interface is essential for assessing the structural performance of strengthened beams and for evaluating the strength gain. This paper describes an experimental investigation of the interfacial bond behavior between concrete and FRP. The strain distributions in concrete and FRP are determined using an optical technique known as digital image correlation. The results confirm that the debonding process can be described in terms of crack propagation through the interface between concrete and FRP. The data obtained from the analysis of digital images was used to determine the interfacial material behavior for the concrete–FRP interface (stress versus relative displacement response) and the fracture parameter GF (fracture energy). The instability in the test response at failure is shown to be the result of snapback, which corresponds with the elastic unloading of the FRP as the load carrying ability of the interface decreases with increasing slip.     

Development of the Nonlinear Bond Stress–Slip Model of Fiber Reinforced Plastics Sheet–Concrete Interfaces with a Simple Method

A new analytical method for defining the nonlinear bond stress–slip models of fiber reinforced plastics (FRP) sheet–concrete interfaces through pullout bond test is proposed. With this method, it is not necessary to attach many strain gauges on the FRP sheets for obtaining the strain distributions in FRP as well as the local bond stresses and slips. Instead, the local interfacial bond stress-slip models can be simply derived from the relationships between the pullout forces and loaded end slips. Based on a series of pullout tests, the bond stress–slip models of FRP sheet–concrete interfaces, in which different FRP stiffness, FRP materials (carbon FRP, aramid FRP, and glass FRP), and adhesives are used, have been derived. Only two parameters, the interfacial fracture energy and interfacial ductility index, which can take into account the effects of all interfacial components, are necessary in these models. Comparisons between analytical results and experimental ones show good accordance, indicating the reliability of the proposed method and the proposed bond stress–slip models.