Teerapong Senjuntichai

Analysis of planar cracks in 3D elastic media with consideration of surface elasticity

This paper presents an efficient numerical procedure for analysis of arbitrary shaped, planar cracks in a three-dimensional, linear elastic infinite medium by taking the surface elasticity into account. The concept of surface stresses via Gurtin–Murdoch surface theory is integrated with the classical theory of linear elasticity to form a mathematical model capable of simulating cracks under general loading conditions and nano-scale influences. The key governing equations for the bulk material are established in terms of weakly singular displacement and traction boundary integral equations involving only unknowns on the crack face, whereas that for a zero-thickness material layer on each crack face is established in a weak form following the weighted residual technique. The final governing equations for the bulk material and the two crack-face layers are fully coupled via the continuity condition along the interface. The solution of the resulting coupled system is determined numerically by the coupling of a standard finite element procedure and a symmetric Galerkin boundary element method. Owing to the weakly singular feature of all involved boundary integrals, C

Fatigue Damage Evaluation of Railway Truss Bridges from Field Strain Measurement

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Analysis of Indentation on Layered Elastic Medium with Surface Energy Effects

0 basis functions are adopted everywhere in the approximation of crack-face data and only the special quadrature for evaluating nearly singular and weakly singular double surface integrals is required. Once the implemented numerical scheme is fully tested with existing reference solutions, it is then applied to investigate the role and influence of surface parameters such as the residual surface tension and the in-plane modulus on the near-front field and the size dependency of predicted solutions. Results of several examples under various scenarios are reported not only to demonstrate the capability and robustness of the proposed method but also to indicate the significance of the surface stresses in enhancing the near-surface stiffness and reducing stresses in a local region ahead of the crack front.

Effective Properties of Piezoelectric Fiber-Reinforced Composites with Imperfect Interface

This paper presents the analysis of a layered elastic half space under the action of axisymmetric surface loading and the influence of the surface energy effects. The boundary value problems for the bulk and the surface are formulated based on classical linear elasticity and a complete Gurtin-Murdoch constitutive relation. An analytical technique using Love’s representation and the Hankel integral transform is employed to derive an integral-form solution for both displacement and stress fields. An efficient numerical quadrature is then applied to accurately evaluate all involved integrals. Selected numerical results are presented to portray the influence of various parameters on elastic fields. Numerical results indicate that the surface stress displays a significant influence on both displacement and stress fields. It is also found that the layered half space becomes stiffer with the presence of surface stresses. In addition, unlike the classical elasticity solution, size-dependent behavior of elastic fields is noted. The present analytical solutions provide fundamental understanding of the influence of surface energy on layered elastic materials. It can also be used as a benchmark solution for the development of numerical techniques such as FEM and BEM, for analysis of more complex problems involving a layered medium under the influence of surface energy effects.

Thermo-Electro-Mechanical Behavior of Finite Piezocomposites Cylinder

This paper is concerned with fatigue damage evaluation of railway truss bridges in Thailand, which have been in service for more than 60 years by using the deterministic approach. The dynamic strain measuring system was installed on selected bridge members to record the actual strain histories induced by the passing trains. The fatigue damages of all bridge members are evaluated based on Palmgren-Miner damage rule and the S-N curves of the stress ranges from field strain measurement of daily train traffic. For the members that their field strains were directly not monitored, the finite element analysis has been employed to estimate their stress ranges. The finite element models of the bridges are verified with the stress data obtained from the field load test of a locomotive. It is found that the vertical and diagonal members of the railway bridges appear to have the most fatigue damage risk whereas the lower chord and floor beams have the lowest estimated fatigue damage potential.

Field Investigation on Slab-on-Girder Steel Bridges over Intersections in Thailand

ABSTRACT The dynamic response of a multilayered poroelastic medium under 3D time-harmonic loading is studied using an exact stiffness method. The poroelastic medium under consideration consists of N layers of different thicknesses and properties and an underlying poroelastic half-space. The exact stiffness matrices for each layer and the underlying half-space are derived explicitly using Biot’s poroelastodynamic theory and double-dimensional Fourier transforms. Selected numerical results are presented to demonstrate the influence of various parameters on dynamic response of multilayered poroelastic media under traction and fluid loading. The application of proposed solution scheme to soil–structure interaction problems is also presented.

Singularity-Reduced Integral Representations for Discontinuity in Smart Materials

This paper presents the analysis of an axisymmetric frictionless rigid punch on a layered elastic medium with the consideration of surface energy effects by adopting Gurtin-Murdoch continuum theory of surface elasticity. The indentation problem is formulated as a mixed-boundary value problem with the displacement boundary condition being imposed at the contact area. The unknown contact pressure under the indenter is then determined by employing a discretization technique with use of the displacement Green’s functions. The required Green’s functions are expressed in the form of the Hankel integral transform. The accuracy of the proposed solution scheme is verified by comparing with existing solutions. Selected numerical results on displacement and stress profiles in a layered elastic half-space are presented to demonstrate the influence of various parameters on elastic fields. It is found that the layered medium becomes stiffer and shows size-dependent behavior due to the presence of surface stresses.

Modeling of Crack Front Singularity in 3D Piezoelectromagnetic Media by Weakly Singular SGBEM

AbstractComposites of piezoelectric materials are widely used in practical applications such as medical devices, nondestructive testing devices, and intelligent or smart structures. The study of mechanics and effective properties of piezocomposites is crucial to the design and development of this class of materials. In this paper, a micromechanics model is developed to determine the effective properties of piezoelectric fiber-reinforced composite materials with imperfect fiber-matrix interface bonding conditions. The micromechanics analysis is based on the periodic microfield micromechanics theory and the boundary element method (BEM). The imperfect bonding between the piezoelectric fibers and matrix is taken into account and represented by a spring-factor parameter. Selected numerical results are presented to show the influence of fiber-volume fraction, material properties of fiber and matrix, and interface bonding conditions on the effective properties of piezoelectric fiber-reinforced composites.