考虑纤维端头脱粘的金属基复合材料轴向弹塑性拉伸性能的研究*

本文建立在广义自洽有限元迭代平均化方法的基础上,分析了纤维端头脱粘对SiC晶须增强铝基复合材料的轴向弹塑性拉伸性能的影响.分别计算了不同纤维长径比与体分比下有纤维端头脱粘情况的金属基复合材料的轴向拉伸性能.并与界面完好的情况相对比,得出了纤维端头脱粘的影响随纤维长径比增大而减小,和随纤维体分比增大而增大的结论.     

The study of applicability for PLK method

This paper researches the applicability of the PLK method. We give the general formulae of the asymptotic solution and strained coordinates, and we establish necessary conditions for the applicability PLK method. Besides, the applicability of the approach is also exemplified by means of examples in this paper.     

Interfacial debonding of two-phase composite with periodic structure

A mixed analytical-numerical (boundary element method) procedure is presented for estimating the effective elastic moduli of a two-phase periodic composite by application of a unit cell. The two-phase composite consists of a metal/polymer matrix and one/three circular ceramic inclusions with adhesive and partial debonding of the interface. The results are displayed numerically with special attention given to development of plastic zones as debonding occurs. Dependence of load-time history is exhibited.     

Crack paths formed by multiple debonds in LFRP composites

Onset and growth of debonds at fibre-matrix interfaces in a bundle of fibres subjected to transverse loads are studied numerically. In particular, the crack path formed by debonded neighbour fibres is analysed. The Linear Elastic–Brittle Interface Model (LEBIM) is used to model the fibre-matrix interface behaviour. This simple model of a Long Fibre Reinfoced Polymer (LFRP) composite includes ten parallel fibres embedded in a matrix cell whose external dimensions are much larger than the fibre radius. The advantage of the present LEBIM formulation of the so-called matrix cracking lies in its ability to make quantitative predictions about the concurrent fibre-matrix debond onset and mixed-mode interface crack growth in a fibre bundle. The numerical analysis predicts failure loads producing the first and subsequent debond onsets, leading to a crack path. A discussion on the position where debond occurs is also included. Finally, the effect of the load biaxiality on the crack path is studied in detail.     

FRP加固梁的FRP-混凝土界面脱胶分析

为了研究纤维增强聚合物(fiber reinforced polymer, FRP) 加固梁的FRP-混凝土界面脱胶破坏过程,本文将混凝土梁和FRP 板均视为线弹性的欧拉-伯努利梁(Euler-Bernoulli beams), 且两者通过粘结层胶结在一起. 对于FRP-混凝土结构,有两种形式的脱胶破坏：板端脱胶破坏和跨中裂缝导致的脱胶破坏.对于FRP-混凝土梁,利用合理的粘结模型按第2 种脱胶失效形式,详细讨论了FRP-混凝土界面的脱胶过程,得到了不同阶段的胶结滑移、界面剪应力和FRP 轴向力的解析解. 实验研究验证了理论分析的结果,参数研究进一步探讨了胶结长度和粘结层厚度对于FRP-混凝土界面脱胶行为的影响.     

INVESTIGATION ON FATIGUE HYSTERESIS LOOPS MODELS OF FIBRE-REINFORCED CERAMIC-MATRIX COMPOSITES

纤维增强陶瓷基复合材料初始加载到疲劳峰值应力时, 基体出现裂纹, 纤维/基体界面发生脱粘. 在疲劳载荷作用下, 纤维相对基体在界面脱粘区往复滑移使得陶瓷基复合材料出现疲劳迟滞现象. 建立了纤维陶瓷基复合材料疲劳迟滞回线细观力学模型, 采用断裂力学方法确定了初始加载纤维/基体界面脱粘长度、卸载界面反向滑移长度与重新加载新界面滑移长度, 分析了4种不同界面滑移情况的疲劳迟滞回线. 假设正交铺设与编织陶瓷基复合材料疲劳迟滞回线主要受0°铺层、轴向纱线内纤维/基体界面滑移的影响, 预测了单向、正交铺设与编织陶瓷基复合材料在不同峰值应力与不同循环的疲劳迟滞回线, 与试验结果吻合.     

An analytical study on the bond behaviour between an externally bonded FRP and concrete in the case of continuous beams

One of the greatest challenges in structural engineering nowadays is the strengthening, upgrading, and retrofitting of existing structures. The use of fibre-reinforced polymers (FRPs) bonded to the tension face of a structural member is an attractive technique in this field of application. The strengthening of reinforced concrete structures by means of an externally bonded reinforcement (EBR) is achieved by gluing a FRP laminate to the concrete substrate. For an efficient utilization of the FRP EBR systems, an effective stress transfer is required between the FRP and concrete. The paper discusses the bond behaviour between a FRP and concrete in the case of flexural strengthening of continuous beams. With respect to this type of beams, only a few studies have been reported, though continuous members often occur in concrete constructions. The structural behaviour of statically indeterminate elements is typically characterized by redistributions of the internal forces. These distributions are related to the nonlinear deformations of the beams and has also a distinct influence on the bond behaviour between the FRP and concrete. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 3, pp. 389–402, May–June, 2008.     

Volume changes under strain resulting from the incorporation of rubber granulates into a rubber matrix

The strength of an elastomer is in part determined by the size of the intrinsic flaws that are present. It has been observed that the incorporation of rubber granulates into a virgin matrix results in a reduction in strength and this has previously been attributed to an increase in the intrinsic flaw size. The precise nature of this intrinsic flaw is the subject of this investigation. Fundamental questions concerning the change in flaw size with strain and the reduction in strength resulting from a weaker interface have been investigated using volume change experiments. Initial experiments on carbon black filled rubber with no granulates incorporated have shown no significant volume change under strain. This contrasts with granulate filled materials whose experimentally measured volume changes with strain were seen to be substantially greater. Microstructural finite element analysis has revealed how this change in volume might result from a net increase in the flaw size with increasing strain. This work suggests that flaw size increases in a characteristic way with strain for materials where the matrix and granulates have a similar modulus, whereas a modulus mismatch between the matrix and the recycled granulate results in much larger volume changes and hence greater flaw size which also appears to increase with strain. This work emphasizes the importance in practical applications of matching the modulus of recycled granulate materials to that of the new virgin material in the matrix. This article introduces a novel technique for examining small changes in the interfacial bonding mechanisms under strain such as that caused by surface modification techniques. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3169–3180, 2007     

Theoretical analysis on the local critical stress and size effect for interfacial debonding in particle reinforced rheological materials

The mechanisms of interfacial debonding of particle reinforced rheological materials are studied. Based on an energy criterion, a simple formula of local critical stress for interfacial debonding is derived and expressed in terms of the interfacial energy. The particle size effect on interface debonding can then be analyzed easily owing to the fact that critical stress is inversely proportional to the square root of particle radius. By taking PP/CaCO₃ system as an example, the present energy criterion is compared with the mechanical debonding criterion, and it is found that under the condition that bond strength is equal to matrix strength and particle radius not over 0.2μm, the mechanical debonding criterion can be automatically satisfied if the energy criterion is satisfied. A relation between critical time and interface energy is calculated by using the energy criterion. The influences of the particle volume fraction and the parlicle size, the loading rate and the relaxation time of the matrix on the critical time of interfacial debonding are also discussed. Supported by the National Natural Science Foundation of China (19632030 and 19872007) and Natural Science Foundation of Jiangsu Province.     

考虑疲劳累积损伤的FRP-混凝土界面剥离模拟

鉴于疲劳累积损伤对FRP-混凝土界面黏结性能有重要影响, 通过统计分析既有FRP-混凝土界面疲劳剪切试验数据, 基于界面黏结疲劳退化双线性模型获得界面残余滑移量、峰值剪应力和初始刚度的疲劳退化规律, 发现随着荷载循环次数的增加, 界面残余滑移量增加, 而峰值剪应力与初始刚度均减小. 并采用基于内聚力模型的有限元法对典型界面疲劳剪切试验进行模拟, 得到了不同荷载循环次数下的界面黏结滑移关系. 模拟所得峰值剪应力、界面断裂能和界面剪切刚度与理论模型接近, 但极限滑移量大于理论模型, 黏结滑移曲线符合典型试验曲线特征. 从有限元模拟结果可知, 疲劳荷载作用会显著降低界面承载力, 但界面破坏特征并未发生显著变化.