Mode III fracture of a magnetoelectroelastic layer: exact solution and discussion of the crack face electromagnetic boundary conditions

This paper develops a closed-form solution for anti-plane mechanical and in plane electric and magnetic fields in a magnetoelectroelastic layer of finite thickness. Explicit expressions for the stresses, electric fields, and magnetic fields, together with their intensity factors are obtained for the extreme cases for impermeable and permeable cracks. Solutions for some special cases, such as a magnetoelectroelastic layer with infinite thickness, are also obtained. Applicability of the crack face electromagnetic boundary conditions is discussed. It is found that the crack profile is important in obtaining the correct electromagnetic fields and their intensity factors. The stress intensity factor, however, does not depend on the crack face electromagnetic boundary condition assumptions.     

Transverse shear and pressurization effects in the bending of plates with reinforced cracks

The authors develop an eigth-order model for bending of transversally isotropic plates and use integral transforms and a collocation method to form a line-spring model for a cracked plate. The eigth-order model allows satisfaction of the three standard plate bending boundary conditions; the normal moment, twisting moment, and transverse shear force, and an additional shear stress resultant that allows analysis of transverse normal stresses near the crack tip. The line-spring model is used to develop geometry correction factors for bending of finite-thickness plates, accounting for transverse shear deformation and pressurization of the plate near the crack tip. The line-spring model is then applied to the problem of a plate with a reinforced crack, and the results are used to validate an interpolation solution based on an energy method. While not explicitly analysed, the models are applicable to many problems, including bending of bonded repairs, fracture and fatigue of composite and layered materials, surface cracks, crack tip plasticity and crack closure or crack face interaction.     

Explosions and impacts

This paper was prepared in response to being awarded the Hypervelocity Impact Society's Distinguished Scientist Award at HVIS 2003 held in Noordwijk, The Netherlands. It is traditional that the paper associated with the HVIS Distinguished Scientist Award is a retrospective on the recipient's career. This paper is in that tradition.     

Influence of surface condition on the fatigue behaviour of specimens made of a SAE 5115 case-hardened steel

The effect of different surface conditions on the fatigue properties of cyclically loaded bending specimens of the case‐hardened steel SAE 5115 (Material Number 1.7131) was investigated. The aim of the investigations was to achieve further knowledge of the processes that finally lead to the failure of case‐hardened and cyclically loaded bending specimens. Surface roughness, microstructure and residual stress distribution were regarded as parameters that govern the fatigue process. On the basis of a well‐defined adjustment of different surface conditions the effect of internal oxidation, surface roughness and residual stresses on fatigue crack initiation and growth were assessed. The effect of different parameters on the endurance limit has been quantified by the application of a fracture mechanics and a weakest‐link approach. The calculations contributed to a deeper insight into the complex interaction between the parameters governing the fatigue process.     

The perturbation method and the extended finite element method. An application to fracture mechanics problems

The extended finite element method has been successful in the numerical simulation of fracture mechanics problems. With this methodology, different to the conventional finite element method, discretization of the domain with a mesh adapted to the geometry of the discontinuity is not required. On the other hand, in traditional fracture mechanics all variables have been considered to be deterministic (uniquely defined by a given numerical value). However, the uncertainty associated with these variables (external loads, geometry and material properties, among others) it is well known. This paper presents a novel application of the perturbation method along with the extended finite element method to treat these uncertainties. The methodology has been implemented in a commercial software and results are compared with those obtained by means of a Monte Carlo simulation.     

Identification of ductile damage and fracture parameters from the small punch test using neural networks

This paper presents a method for the identification of deformation, damage and fracture properties of ductile materials. The small punch test is used to obtain the material response under loading. The resulting load displacement curve contains information about the deformation and failure behavior of the tested material. The finite element method is used to compute the load displacement curve depending on the parameters of the Gurson-Tvergaard-Needleman damage law. Via a systematic variation of the material parameters a data base is built up, which is used to train neural networks. This neural network can be used to predict the load displacement curve of the SPT for a given material parameter set. The identification of the material parameters is done by using a conjugate directions algorithm, which minimizes the error between an experimental load displacement curve and one predicted by the network function. The identified material parameters are validated by independent tests on notched tensile specimens. Furthermore, these parameters can be used to compute the crack growth in fracture specimens, which finally leads to a prediction of classical fracture toughness parameters.     

Fully plastic J-integral solutions for surface cracked plates under biaxial loading

In this paper, surface cracked plates under biaxial tension are studied. Three-dimensional elastic-plastic finite element analyses have been carried out to calculate the J-integral for surface cracked plate for a wide range of geometry, biaxiality and material properties. Fully plastic J-integral solutions along the front of the surface cracks are presented for Ramberg-Osgood power law hardening material of n = 3, 5, 10 and 15. Geometries considered are a/c = 0.2, 1.0 and a/t = 0.2, 0.4, 0.6 and 0.8 and the biaxial ratios of 0, 0.5 and 1. Based on these results, the J-integral along the crack front for general elastic-plastic loading conditions can be estimated using the EPRI scheme. These solutions are suitable for fracture analyses for surface cracked plates under biaxial loading.     

Fracture mechanics of air-entrained concrete subjected to compression

Air voids are entrained in concrete for protection of constructed elements, especially highway pavements, against freeze-thaw damage. Entrained air void systems inadvertently reduce the compressive strength of the concrete. The present study describes development of an analytical model for evaluation of the effects of entrained air void system on the compressive strength of concrete. The model developed here will assist in predicting the compressive strength of concrete for specified mix designs. The constitutive relationships for air-entrained concrete were established by considering a micro cracked porous material with randomly distributed circular air voids and uniformly oriented cracks from the air voids. Linear elastic fracture mechanics was employed to explain the evolution of damage due to the individual voids and cracks that emanate from such voids. The damage model considers the interactions among the voids and cracks during various stages of loading. The analytical results from this study were evaluated through an experimental program for comparison of the computed and measured compressive strengths. A wide range of samples were examined that included concretes with air contents ranging from 2% to 13% air by volume of concrete. The experiments involved microscopic determination of air content and spacing factors as well as compressive strength tests for all the concrete samples.     

升温氧化过程煤表面介观特征和分形参数研究

将原子力显微镜（AFM）用于煤表面结构研究,提出介观尺度下煤表面结构研究方法. 得出基于分形理论和AFM观测结果计算分形维数D的方法.实验分析证明,煤表面有明显的分形特征,在煤样的升温氧化过程中,分形维数随温度的升高趋于增大.     

SOI基光学电流传感器的设计与仿真

将光纤与微电子机械系统(MEMS)技术相结合,设计了一种新颖的检测50Hz高压交流电的光学电流传感器(OCS)。用ANSYS软件分析了器件的模态、动态响应与热膨胀特性,并通过Matlab软件模拟了器件的工作性能。模拟计算表明:ANSYS与理论公式得到的结果基本一致;传感器的量程为100~3600A,对于大电流下的灵敏度可达到0.02dB/A,温度变化±50K时传感器相应的测试误差为0.2%。