Ali Sangghaleh

Circular loadings on the surface of an anisotropic and magnetoelectroelastic half-space

In this paper, we derive the analytical solutions for two types of surface loadings over an anisotropic magnetoelectroelastic half-space: a uniform and an indentation-type load. Our solutions in terms of the simple line integral over [0,π] contain various decoupled materials and materials with high symmetry as special cases. Furthermore, the surface results of the solutions of the half-space are also provided. It is shown that on the surface: (1) for the uniform loading, the integrands for the extended displacements are continuous whilst those for the extended stresses have two weak singularities of order 1/r1/2 along the integral interval [0,π], which are integrable in the sense of Cauchy principal value and (2) for the indentation-type loading, the order of the singularity in the extended stress is exactly Cauchy type of 1/r, which can also be integrated via the Cauchy principal value. For a general anisotropic magnetoelectroelastic half-space, numerical examples in the vertical plane are presented for a uniform horizontal/vertical load and a vertical indentation-type load. The physical quantities presented are the magnitude of the elastic displacement vector, the electric and magnetic potentials, the hydrostatic and effective stresses, and the magnitudes of the electric and magnetic field vectors. These numerical results not only show some distinguished features associated with the loadings, but also can serve as benchmarks for future numerical endeavors in this field.

Fields induced by three-dimensional dislocation loops in anisotropic magneto-electro-elastic bimaterials

The coupled elastic, electric and magnetic fields produced by an arbitrarily shaped three-dimensional dislocation loop in general anisotropic magneto-electro-elastic (MEE) bimaterials are derived. First, we develop line-integral expressions for the fields induced by a general dislocation loop. Then, we obtain analytical solutions for the fields, including the extended Peach–Koehler force, due to some useful dislocation segments such as straight line and elliptic arc. The present solutions contain the piezoelectric, piezomagnetic and purely elastic solutions as special cases. As numerical examples, the fields induced by a square and an elliptic dislocation loop in MEE bimaterials are studied. Our numerical results show the coupling effects among different fields, along with various interesting features associated with the dislocation and interface.

Backcalculation of pavement layer elastic modulus and thickness with measurement errors

This paper presents a backcalculation method for pavement layer elastic modulus and thickness. The effect of deflection measurement errors on the backcalculated results is also considered. The falling weight deflectometer (FWD) data are generated by applying a load to the pavement while calculating deflection at various fixed distances from the load centre. The measurement errors in FWD data are simulated by perturbing the theoretical deflections. Using these data, a backcalculation technique based on the improved genetic algorithm is proposed. In order to deal with the measurement errors, besides the common root mean square, a new objective function called area value with correction factor is introduced to the backcalculation algorithm. Numerical examples for two- and four-layer pavement structures are presented, which show the capability of the proposed method in backcalculation of pavement layer modulus and thickness.

Inverse calculation of elastic moduli in cross-anisotropic and layered pavements by system identification method

Material properties of cross-anisotropic (or transversely isotropic) elastic and layered systems including pavement structures are essential for the analysis of mechanical responses. Besides laboratory determination of these material properties, direct inversion using in situ input data is fundamental and more useful. In this paper, the system identification (SID) method with constraints is proposed to invert the elastic moduli in an anisotropic layered half space in general and in a layered pavement in particular. Since in the inverse calculation, the forward calculation is required, we have also presented briefly the forward calculation approach based on the cylindrical system of vector functions and the propagating matrix method. Our SID algorithm is then applied to three-layer and four-layer pavements with different numbers of cross-anisotropic layers, with the deflections at the surface of the layered pavement as inputs. Our numerical results demonstrate clearly that the proposed SID-based inverse method is accurate and efficient for a broad range of seed moduli.

Near-interface charged dislocations in AlGaN/GaN bilayer heterostructures

Understanding the behavior of semiconductor dislocation defects in AlGaN/GaN heterostructures is necessary in order to produce powerful and efficient transistors. This letter presents a straightforward technique to characterize dislocation defects with charges along their loops in a bilayer system. This is important regarding the behavior of near-interface dislocations in order to obtain an insight of the mechanical and physical responses. We characterize piezoelectric polarization and emphasize on the importance of dislocation-core electric charge. The results elaborate the variations of the dislocation force by the accumulation of charge and provide an explanation for the dominant dislocation types in nitride semiconductors.

Stress perturbation around a fault by hydraulic fracturing

In this paper we present an exact closed-form solution for the stress perturbation around a fault in a half plane induced by nearby multiple hydraulic cracks. First, we apply the complex potential function method to find the stress field induced by a concentrated displacement discontinuity in a two-dimensional half plane. Then we integrate the fundamental stress field along the crack to find the corresponding field due to a crack with finite length. Method of superposition is simply applied to obtain the corresponding solution due to multiple cracks. Finally, as numerical examples, we apply our exact closed-form solution to a couple of cases to investigate the effect of hydraulic fracturing on the stress field around the fault under different in-situ stress conditions. Particularly, the normal and shear stresses along the fault line are calculated. By applying the Mohr-Coulomb failure criterion to the fault, the critical distances between cracks and fault are estimated with and without the in-situ stress ...