Bonded Joints with Nonhomogeneous Adhesives

The problem is considered of two semi-infinite elastic plane regions bonded by a non-homogeneous adhesive along their common linear boundary and subject to constant applied stresses at infinity. The complex variable method has been employed to achieve the closed-form solution for generic interface stiffness distributions. Two particular cases of practical interest have been treated in detail as particular applications of the proposed general solution. This revised version was published online in August 2006 with corrections to the Cover Date.     

On the Elastic Field of a Shpherical Inhomogeneity with an Imperfectly Bonded Interface

This study is devoted to the development of a unified and explicit elastic solution to the problem of a spherical inhomogeneity with an imperfectly bonded interface. Both tangential and normal displacement discontinuities at the interface are considered and a linear interfacial condition, which assumes that the tangential and the normal displacement jumps are proportional to the associated tractions, is adopted. The elastic disturbance due to the presence of an imperfectly bonded inhomogeneity is decomposed into two parts: the first is formulated in terms of an equivalent nonuniform eigenstrain distributed over a perfectly bonded spherical inclusion, while the second is formulated in terms of an imaginary Somigliana dislocation field which models the interfacial sliding and normal separation. The exact form of the equivalent nonuniform eigenstrain and the imaginary Somigliana dislocation are fully determined in this paper.     

剪胶接结构的混合模式断裂分析

给出了Ｇｏｌａｎｄ－Ｒｅｉｓｓｅｎｅｒ型剪接结构的Ｊ积分表达在被粘物体小转角和胶层很薄的假设下与路径无关。Ｊ积分代表胶层厚度与胶层内最大能量密度的乘积。对单剪接接头，本文计算了裂纹在胶层内和界面上两种情况下的局部Ｉ型和Ⅱ型应力强度因子之比，即局部载荷相角，从而给出了单剪接接头的断裂判据。     

Glass Fracture in the Region of Its Contact with Steel Balls

Results of experiments on indentation of steel balls of various diameters into glass specimens shaped as rectangular parallelepipeds are reported. The limiting load of formation of an annular crack near the contact area and the radius of this crack are experimentally determined. The field of the contact stress in the fracture region is found by using the Huber solution of the Hertz problem of ball indentation into an elastic half-space. Modeling fracture caused by contact interaction is based on using the local criterion of the maximum stress and several nonlocal criteria: average stress criterion, Nuismer criterion, and gradient criterion. For calculating the parameter that has the length dimension and is included into the nonlocal fracture criteria, the ultimate tensile stress and the critical stress intensity factor of glass are experimentally determined for beams without and with a notch. It is demonstrated that the experimental data on the annular crack radius are most adequately predicted by the gradient criterion among all criteria considered in the study. However, this criterion overpredicts the ultimate tensile stress in the course of beam bending, which is caused by the scale factor.     

直角结合异材界面端应力强度系数的经验公式

由不同材料结合而成的材料(简称异材或双材料)的力学性能及其可靠性评价是工程中亟待解决的问题。表征界面端奇异应力场大小的应力强度系数是结合异材强度评价的依据，本文针对工程中最常见的直角结合异材，通过对大量不同材料组合的异材的边界元数值分析，提出了界面端应力强度系数的近似计算公式，无量纲化后的应力强度系数的值只与异材Dundurs参数a，卢有关，该公式具有较高的精度，可以作为一般工程上的应力强度系数的计算以及异材结构设计的依据。     

Experimental and Numerical Study of Shear Fracture in Brittle Materials with Interference of Initial Double Cracks

A simultaneous experimental and numerical study of shear fracture of concrete-like materials is carried out using Brazilian disc specimens with initial double edge cracks and fourpoint bending beam specimens with double edge-notches.The interference effects of two cracks/notches are investigated through varied ligament angles and crack lengths.It is shown that shear fracturing paths change remarkably with the initial ligament angles and crack lengths.The cracked specimens are numerically simulated by an indirect boundary element method.A comparison between the numerical results and the experimental ones shows good agreement.     

Phase-Field Modeling of Thermal Fracture and Shear Heating in Rocks with Degraded Thermal Conductivity Across Crack

By incorporating two different fracture mechanisms and salient unilateral effects in rock materials,we propose a thermo-mechanical phase-field model to capture thermally induced fracture and shear heating in the process of rock failure.The heat conduction equation is derived,from which the plastic dissipation is treated as a heat source.We then ascertain the effect of the non-associated plastic flow on frictional dissipation and show how it improves the predictive capability of the proposed model.Taking advantage of the multiscale analysis,we propose a phase-field-dependent thermal conductivity with considering the unilateral effect of fracture.After proposing a robust algorithm for solving involved three-field coupling and damage-plasticity coupling problems,we present three numerical examples to illustrate the abilities of our proposed model in capturing various thermo-mechanically coupled behaviors.     

界面端应力奇异性与复合材料界面剪切强度细观实验分散性分析

复合材料细观实验方法主要有纤维拔出、纤维压力、纤维段裂和微球脱粘实验等四种；但这四种试验得到的界面剪切强度结果存在很大的分散性。虽经三十余年的研究和改进，仍未能消除。为研究分散性产生的原因，本文以轴对称界面端应力奇异性分析为基础，推导出求解四种试件界面端的特征值的特征方程，并给出了特征值随Dundurs常数的变化情况，由此发现用相同的纤维和基体制作的四种试件在界面端存在奇异性不同的应力场，从而阐明了四种界面剪切强度试验结果巨大分散性的产生原因在于纤维和基体间界面处的应力奇异性。     

Electroelastic Analysis of an Internal Interface Crack in a Half-Plane Consisting of Two Bonded Dissimilar Piezoelectric Quarter-Planes

The problem of an interface crack in a half-plane consisting of two bonded dissimilar piezoelectric quarters is considered under antiplane shear and inplane electric loading. The problem is solved under the electrically permeable assumption for a crack. The integral transform technique is employed to reduce the problem to triple integral equations, which is further converted to a hypersingular integral equation for the crack sliding displacement. By solving the resulting equation analytically, the electroelastic field along the interface and the energy release rate are obtained in explicit form, respectively. Several examples are given to illustrate the influence of the material properties and the crack position on the energy release rate.     

Analysis of Two Collinear Cracks in a Piezoelectric Layer Bonded to Two Half Spaces Subjected to Anti-plane Shear

In this paper, the behavior of two collinear anti-plane shear cracks in a piezoelectric layer bonded to two half spaces is investigated by a new method for the impermeable crack face conditions. The cracks are parallel to the interfaces in the mid-plane of the piezoelectric layer. By using the Fourier transform, the problem can be solved with two pairs of triple integral equations. These equations are solved using the Schmidt method. This process is quite different from that adopted previously. Numerical examples are provided to show the effect of the geometry of the interacting cracks and the piezoelectric constants of the material upon the stress intensity factor of the cracks.     

On the Use of Ultrasound Waves to Monitor the Local Dynamics of Friction Joints

Experimental Mechanics - Friction joints are one of the fundamental means used for the assembly of structural components in engineering applications. The structural dynamics of these components...     

Effect of Shear Displacement and Stress Changes on Fracture Hydraulic Aperture and Flow Anisotropy

Transport in Porous Media - Fluid flow in fractures has the potential to drastically change the economic, environmental, and safety risks associated with a subsurface operation. This work focuses...     

Experimental and Numerical Analysis of an In-Plane Shear Specimen Designed for Ductile Fracture Studies

An in-plane shear specimen made of dual phase steel designed for ductile fracture studies is presented and then analyzed experimentally and numerically. In the experiment, digital image correlation (DIC) technique is utilized to measure the deformation of the specimen. Based on the implicit nonlinear FE solver Abaqus/Standard, numerical analysis of the specimen is performed by using plane stress and solid elements respectively. The elongation of the specimen’s gauge length and the shear strain distribution within the shear zone are compared between the experimental and numerical results and a general good agreement is obtained. Thereafter, based on calculated results, the stress state of the shear zone is investigated in detail. It is shown that the shear stress is dominant within the shear zone despite of the emergence of normal stresses. The deformation is concentrated in the shear zone, where the incipient fracture is most likely to occur. The stress triaxiality and the Lode parameter at the fracture initiation are found to be maintained at a relatively low level, which implies that the stress state achieved by the specimen is close to pure shear. The present study demonstrates that the proposed in-plane shear specimen is suitable for investigation of the fracture behavior of high strength materials under shear stress states.     

Total Internal Reflection(TIR)Behavior of Heterogeneous Interface Shear Waves in Layered Soft Structure

The total internal reflection(TIR)behavior of interface shear waves is crucial for ensuring the reliability of dielectric elastomer(DE)devices.However,due to the complex force-electric coupling and large deformation of DEs,the TIR behavior of shear waves in heterogeneous force-electric interface models is still unclear.This study modeled an elastic/DE bi-material interface to analyze the trajectory of out-of-plane shear waves.Employing Dorfmann and Ogden's nonlinear electroelastic framework and the related linear small incremental motion theory,a method has been developed to control the TIR behavior of interface shear waves.It has been found that the TIR behavior is significantly influenced by the strain-stiffening effect induced by biasing fields.Consequently,a biasing field principle involving preset electric displacement and pre-stretch has been proposed for TIR occurrence.By controlling the pre-stretch and preset electric displacement,active regulation of TIR behavior can be achieved.These results suggest a potential method for achieving autonomous energy shielding to improve the reliability of DE devices.     

The Analysis of Structures with Conditional Joints

ABSTRACT

The elements of a structure whose forces and/or displacements are limited by prescribed conditions are called “conditional joints.” This paper deals with mechanical and mathematical models of conditional joints and shows that their behavior can be characterized by relationships similar to the constitutive equations of ideal plastic and ideal locking materials. It is shown that the analysis of limit states and state changes of structures with conditional joints may also be carried out by means of theorems which are known in the theory of structures of ideal plastic and ideal locking materials.     

On the Role of the Interface Mechanical Interaction in a Gravity-Driven Shear Flow of an Ice-Till Mixture

The ice-till mixtures at the base of glaciers and ice sheets play a very important role in the movement of the glaciers and ice sheets. This mixture is modelled as an isothermal flow which is overlain by a layer of pure ice. In this model, ice is treated as usual as a very viscous fluid with a constant true density, while till, which is assumed to consist of sediment and bound (that is, moving with the sediment) interstitial water and/or ice, is also assumed in a first approximation to behave such as a fluid. For an isothermal flow below the melting point the water component can be neglected. Therefore, only the mass and momentum balances for till and ice are needed. To complete the model, no-slip and stress-free boundary conditions are assumed at the base and free-surface, respectively. The transition from the till-ice mixture layer to the overlying pure ice layer is idealized in the model as a moving interface representing in the simplest case the till material boundary, at which jump balance relations for till and ice apply. The mechanical interactions are considered in the mixture basel layer, as well as at the interface via the surface production. The interface mechanical interaction is supposed to be only a function of the volume fraction jump across the interface. In the context of the thin-layer approximation, numerical solutions of the lowest-order form of the model show a till distribution which is reminiscent to the ice-till layer in geophysical environment.     

Local Mechanical Behavior of Steel Exposed to Nonlinear Harmonic Oscillation

The local mechanical behavior of fatigued steel specimens was probed using nanoindentation. High-carbon steel cantilevers were exposed to nonlinear harmonic oscillation. The indentation modulus on the beam surface and plastic work during indentation decreased as a function of cycles, which was attributed to grain fragmentation and reorientation as well as the continuous reduction in inherent energy dissipation capacity of the material. X-ray diffraction, electron backscatter diffraction, and atomic force microscopy were used to characterize this microstructural evolution during early stages of the beam fatigue life, which altered 1) the local mechanical properties and 2) the global structural dynamic response. The results provide insight into fatigue damage precursors and provides a framework for connecting materials evolution with nonlinear structural dynamics.