双向耦合地震作用下含软弱层岩质边坡锚固界面剪切作用

为研究地震作用下锚固岩质边坡锚杆-砂浆界面和砂浆-岩体界面上的剪切作用,利用FLAC~(3D)软件构建锚固含软弱层岩质边坡数值模型,对水平向和竖向地震波耦合作用下的全长黏结锚杆锚固边坡两锚固界面上的剪切作用进行了深入研究。研究结果表明:两锚固界面上的剪应力分布很不均匀,界面处于弹性变形阶段时,两峰值剪应力紧邻中性点,随锚固界面脱黏破坏的发展,两峰值剪应力不断地向锚杆两端转移;双向耦合地震波较单向和双向未耦合地震波对锚固界面剪应力影响更为显著。考虑双向地震波耦合作用的锚固边坡抗震设计更为合理。研究结果可为边坡锚固抗震设计提供参考。     

地震作用下岩体边坡锚固界面剪应力分布及其影响因素分析

基于FLAC3D软件,尝试采用修正的cable单元建立全长粘结锚杆锚固顺倾层状岩体边坡数值分析模型,改进剪应力提取方法,分别模拟分析了锚杆杆体-砂浆界面上和砂浆-岩体界面上的剪应力分布及其影响因素。研究发现:砂浆-岩体界面上的剪应力比杆体-砂浆界面上小得多,且均以中性点为界方向相反,分布很不均匀,中性点附近大,锚杆两端小;不仅地震波幅值和频率对边坡锚固界面剪应力分布有很大影响,而且随地震波持时的增加锚固界面剪应力增大;锚杆长度也对锚固界面剪应力分布有很大影响,锚杆安设角度的影响则较小。获得了地震作用下锚固界面上剪应力分布,并揭示了地震动参数和锚固方式对剪应力分布的影响,为边坡锚固设计施工提供了重要参考。     

胶结式锚固段有效传力长度研究

胶结式锚固段在坚硬岩体中，其破坏主要发生在锚杆与胶结体材料结合面体。本文研究了结合面上剪应力的分布规律，同时给出了锚固段的有效传力长度与极限张拉荷载的关系曲线，并对数值解与解析解的结果进行了比较。为锚固体系的设计提供了理论依据。     

界面相多重开裂对纤维强度的影响

当纤维表面的界面相(如涂层)较脆时,纤维发生断裂之前界面相一般会发生多重开裂的损伤,这种损伤裂纹垂直于纤维轴向,故能导致纤维强度下降.本文以四相(纤维,界面相,基体,复合材料)圆柱体模型为基础,并假设界面脱粘后不再传递剪应力.首先用剪切滞后理论求得了界面相发生多重开裂后,纤维、界面相中的应力集中系数,以及界面上的剪应力,并同时考虑了纤维与界面相间界面部分脱粘的影响;然后,假设纤维强度统计特性用Weibull分布函数表示,从而根据界面相多重开裂在纤维中引起的应力集中系数K_f得到广纤维破坏概率的变化.最后利用界面脱粘区的大小,定性研究了界面剪切强度τ0对纤维强度的影响,结果表明:存在一个最佳的界面剪切强度τ0,使界面相多重开裂对纤维强度的影响最小.     

地震作用下软弱夹层参数对岩质边坡锚固界面剪切作用影响

利用FLAC~(3D)软件建立了含软弱夹层的锚固岩质边坡数值模型,研究了软弱夹层参数对边坡位移响应和锚固界面剪切作用的影响,并通过正交试验对软弱夹层参数进行了敏感性分析。研究结果表明:锚固界面上的剪应力随时间呈阶梯式变化,且与地震动能量密切相关;随着软弱夹层厚度增加,边坡永久位移和峰值剪应力都增大,随着黏聚力和内摩擦角增大,二者减小,随着倾角增大,二者则先增大后减小;软弱夹层参数对界面剪应力的敏感性由大到小依次是软弱夹层倾角、黏聚力、内摩擦角和厚度。     

两级载荷作用下复合材料界面的脱粘

研究了两级拉伸疲劳载荷作用下,纤维增强复合材料界面的脱粘。首先基于剪切筒模型,建立了求解纤维与基体应力的控制微分方程,并求得了相关解答。然后借助断裂力学中描述疲劳裂纹扩展的公式和能量耗散率理论,给出了界面脱粘长度、加载次数以及脱粘应力之间的关系式。最后通过实例模拟了两级拉伸疲劳载荷作用下的界面裂纹扩展,分析了界面疲劳裂纹扩展速率、脱粘长度在不同加载方式下的变化规律,以及材料泊松比的变化对界面脱粘的影响。从而为进一步研究工程结构的疲劳破坏和材料的最优设计提供一定的理论依据。      

重组竹-混凝土界面粘结-滑移本构模型

为研究胶粘剂连接的重组竹-混凝土界面粘结性能及构建粘结-滑移本构模型,对44个重组竹-混凝土粘结试件进行单剪试验,并考虑了粘结长度、重组竹粘结宽度与厚度、混凝土强度及胶层厚度等因素对粘结性能的影响。研究结果表明：在不同影响因素下,试件破坏模式基本相同,均为混凝土表面发生剥离破坏,粘结界面间裂缝从加载端产生并向自由端发展,破坏过程分为弹性阶段、软化阶段和脱粘平台阶段;界面峰值剪应力随重组竹厚度、混凝土强度、胶层厚度增加而增大,随粘结宽度增加而减小。根据试验粘结-滑移曲线,建立了重组竹-混凝土界面粘结-滑移本构模型,与实验结果进行对比,该模型能较好地反映重组竹-混凝土界面剪应力与滑移量间的关系。     

热残余应力对C/SiC复合材料界面剪切强度影响的有限元分析

根据C/SiC复合材料的属性,建立单纤维顶出的二维轴对称模型,采用有限元法对C/SiC复合材料的界面剪切强度进行数值研究,分析中考虑材料制备过程中的残余应力对界面剪切强度的影响,在细观力学层面上系统分析纤维顶出过程的界面剪应力及其相关影响因素。分析得出,残余应力会对界面造成损伤,降低界面脱粘载荷。材料的界面承受能力与热膨胀系数呈正相关,与固化温度呈负相关。     

纤维—基体脱粘的界面应力分析

本文建立了单纤维拔出时考虑纤维与基体间径向压应力及界面剪应力的简单模型，分析了纤维的轴向脱粘应力与界面剪应力纤维包埋长度的分布规律。     

界面脱粘对正交铺设SiC/CAS复合材料基体开裂的影响

采用细观力学方法研究了正交铺设SiC/CAS复合材料在单轴拉伸载荷作用下界面脱粘对基体开裂的影响。采用断裂力学界面脱粘准则确定了0°铺层纤维/基体界面脱粘长度, 结合能量平衡法得到了主裂纹且纤维/基体界面发生脱粘(即模式3)和次裂纹且纤维/基体界面发生脱粘(即模式5)的临界开裂应力, 讨论了纤维/基体界面剪应力、 界面脱粘能对基体开裂应力的影响。结果表明, 模式3和模式5的基体开裂应力随纤维/基体界面剪应力、 界面脱粘能的增加而增加。将这一结果与Chiang考虑界面脱粘对单向纤维增强陶瓷基复合材料初始基体开裂影响的试验研究结果进行对比表明, 该变化趋势与单向SiC增强玻璃陶瓷基复合材料的试验研究结果一致。     

三维锚杆单元理论及其应用

本文建立了一种考虑锚芯与灌浆间剪切破坏作用的三维锚杆计算模型．在这种模型中，假设锚芯的轴向位移沿锚杆方向成线性分布；沿径线方向位移为常数；假设灌浆的轴向位移沿锚杆方向成线性分布、沿径线方向则取空间轴对称问题的解析解．错芯中的轴向应力、灌浆中的切向剪应力以及由于侧向位移引起的横向剪应力是锚杆中的主要应力。锚芯与灌浆间的剪切破坏通过计算残余力来模拟，在数值计算时采用Ｎｅｗｔｏｎ－Ｒａｐｈｓｏｎ迭代法。作为实际应用的例子，该模型被用于分析岩体拉拔试验和路堤加固，并与解析解和无锚杆作用的弹性分析进行了对比．计算结果显示了模型的可靠性和实用性．     

力、热载荷作用下纤维在复合材料中的界面应力传递行为

采用三维光弹性实验应力分析和有限元计算两种方法,在拉拔载荷和热残余应力联合作用下,对单丝拔出树脂基复合材料三维冻结切片界面剪应力进行了研究。实验结果和计算表明,在单纤维与基体界面的埋入端及埋入末端附近出现界面残余剪应力的极值;力、热载荷作用下纤维界面剪应力呈抛物线分布,单丝埋入端附近是应力的主要传递区域,最先达到危险应力,出现界面脱胶破坏,然后剪应力沿纤维埋入长度由纤维埋入端附近向埋入末端逐渐传递;界面热残余应力对界面剪应力的影响是使纤维埋入末端应力集中程度降低,使界面剪应力最大值增大。      

Effects of higher-order interface stresses on the elastic states of two-dimensional composites

We propose a simple model to simulate higher-order interface stresses along the interface between two neighboring media in two dimensions. The interface behavior is modeled from a thin interphase of constant thickness by taking a proper limit process. In the formulation the deformation of the thin interphase is approximated by the Kirchhoff-Love assumption of thin shell. To incorporate the higher-order interface stresses, we consider the bending effects resulting from the non-uniform surface stress across the layer thickness. The stress equilibrium conditions is fulfilled by consideration of balance for forces as well as stress couples. Depending on the difference in stiffness and length scales of the interphase, we show that the interfaces can be classified into four different types. This findings, upon suitable definitions of material parameters, agree with a rigorous asymptotic analysis proposed by Benveniste and Miloh [Benveniste, Y., Miloh, T., 2001. Imperfect soft and stiff interfaces in two-dimensional elasticity. Mech. Mater. 33 309-323]. To illustrate the higher-order effects, we derive analytically the stress concentration factor of an infinite plate containing a circular cavity with interface stresses of different orders subjected to a remote transverse shear loading. The closed-form expressions show how the orders of interface stresses influence the concentration factor in a successive manner. In addition, we examine the effective shear modulus of composites with circular inclusions with higher-order interface effects. The effective transverse shear modulus is derived based on the generalized self-consistent method.     

碳纤维布加固RC梁中粘结性能的非线性有限元分析

碳纤维布加固钢筋混凝土(RC)梁中,碳纤维布与梁底混凝土的剥离破坏使碳纤维布的强度不能得到充分发挥。分析碳纤维布与梁底混凝土的粘结应力,是研究碳纤维布加固剥离破坏承载力的基础问题。根据4根碳纤维布加固RC梁的试验研究结果,采用商业有限元程序MSC.Marc建立有限元模型,进行了非线性计算分析。通过分离总粘结应力中的局部粘结应力,得到粘结延伸长度范围内的锚固粘结应力分布,并结合试验数据对其分布规律进行了研究。根据分析和试验结果,引入了“有效锚固粘结长度”和“锚固粘结应力”的概念,给出了极限荷载下锚固粘结应力的计算建议。     

Stress field of a disclination dipole in hcp bicrystal with imperfect interface

In this paper, exact stress field solutions are derived for an interfacial disclination dipole in an hcp bicrystal with an imperfect interface described by the traction discontinuity, displacement discontinuity and slipping models. The solutions show that the stress variation is not necessarily monotonic with worsening imperfection and can exceed 100% of the stresses in bicrystals with perfect interfaces. A strong bias exists between the influence of the normal and shear traction jump parameters, and between the influence of the normal and tangential displacement jump parameters, on the interfacial stresses. The traction and displacement discontinuity models also predict very different dependence of the interfacial stresses on the jump parameters. These results suggest that imperfect interfaces may significantly raise the internal stresses and thus drastically alter the damage mechanisms (nucleation and propagation of dislocations/cracks, fatigue, etc.) as well as the mechanical properties (effective properties, failure modes, strength, etc.) of polycrystalline materials.     

Bond-slip model for FRP-to-concrete bonded joints under external compression

The influence of compressive stresses exerted on FRP-concrete joints created by external strengthening of structural members on the performance of the system requires better understanding especially when mechanical devices are used to anchor the externally bonded reinforcement (EBR). The numerical modelling of those systems is a tool that permits insight into the performance of the corresponding interfaces and was used in the present study, essentially directed to analyse the effectiveness of EBR systems under compressive stresses normal to the composite surface applied to GFRP-to-concrete interfaces. The compressive stresses imposed on the GFRP-to-concrete interface model the effect produced by a mechanical anchorage system applied to the EBR system. An experimental program is described on which double-lap shear tests were performed that created normal stresses externally applied on the GFRP plates. A corresponding bond-slip model is proposed and the results of its introduction in the numerical analysis based in an available 3D finite element code are displayed, showing satisfactory agreement with the experimental data. The results also showed that lateral compressive stresses tend to increase the maximum bond stress of the interface and also originate a residual bond stress which has significant influence on the interface strength. Also, the strength of the interface increases with the increase of the bonded length which have consequences on the definition of the effective bond length.     

Micromechanical modeling of interface damage of metal matrix composites subjected to transverse loading

A three-dimensional finite element micromechanical model was developed to study effects of thermal residual stress, fiber coating and interface bonding on the transverse behavior of a unidirectional SiC/Ti–6Al–4V metal matrix composite (MMC). The presented model includes three phases, i.e. the fiber, coating and matrix, and two distinct interfaces, one between the fiber and coating and the other between coating and matrix. The model can be employed to investigate effects of various bonding levels of the interfaces on the initiation of damage during transverse loading of the composite system. Two different failure criteria, which are combinations of normal and shear stresses across the interfaces, were used to predict the failure of the fiber/coating (f/c) and coating/matrix (c/m) interfaces. Any interface fails as soon as the stress level reaches the interfacial strength. It was shown that in comparison with other interface models the predicted stress–strain curve for damaged interface demonstrates good agreement with experimental results.     

基于裸光纤光栅传感技术GFRP抗浮锚杆荷载传递机制的原位试验研究

基于3根全螺纹GFRP抗浮锚杆现场拉拔破坏性试验,成功地将植入式裸光纤光栅传感技术应用于抗浮锚杆拉拔试验中,研究了全长黏结GFRP抗浮锚杆在各级荷载作用下的承载特性、荷载传递特征及破坏机制。研究表明:植入式裸光纤光栅传感技术有其独特的优越性,不会对锚杆自身造成损伤;GFRP抗浮锚杆破坏以杆体基体材料剪切破坏为主,锚固长度为5.0 m,ϕ28 mm锚杆极限抗拔承载力为400 kN,能够满足工程需求;锚杆的轴向应力主要集中在距孔口约3.0 m的区域,且随着锚固深度的增加迅速衰减;剪应力峰值出现在距离孔口以下约0.8 m的位置,随着荷载的增加,剪应力曲线的峰值逐渐增大并向深部移动。在此基础上,进一步分析论证了GFRP抗浮锚杆的破坏机制,为GFRP抗浮锚杆的工程应用提供了理论依据。     

Fatigue behaviour related to interface modification during load cycling in ceramic-matrix fibre composites

Ceramics reinforced with continuous fibres exhibit delayed failure under pulsating load. A micromechanical model describing the fatigue effects is proposed. It is based on a decrease in shear stress at the fibre/matrix interfaces, as a result of interfacial wear caused by see-saw sliding. The main features of this model are as follows. During the first load cycle, the material exhibits multiple matrix cracking and some fibre breaks. The system is then a serial set of matrix cracks, each of them bridged by a parallel set of intact or broken fibres. During subsequent cycles the interfacial shear stress decreases, leading to an increase in the failure probability of the bridging fibres. These changes give both a reduction of stiffness and a widening of the hysteresis loops. For a critical fraction of broken bridging fibres, instability occurs and the specimen fails, thus defining the lifetime. The higher the applied load, the higher is the initial damage on the first cycle and the faster the instability condition is reached. For peak stresses that are lower, but still higher than the proportionality limit, the material also changes but no failure occurs (up to 10⁶ cycles), indicating that the interfacial shear stress decreases to a non-zero value; this limiting value controls the fatigue limit in the lifetime diagram.