Raju Sethuraman

Semi-elliptical surface cracks subjected to cyclic bending loads are of importance to nuclear industry. In this study, the results of experimental studies on a SS316L(N) plate subjected to bending loads, at room temperature are presented. Plates with semi-elliptical surface cracks were experimentally subjected to cyclic bending loads. The crack profiles were monitored at regular intervals using a crack depth gauge. The crack profiles were used to characterize crack propagation laws along both surface and depth direction. The crack propagation profiles were simulated using available empirical equations and compared with the experimental results. The validity of the empirical equations for prediction of crack propagation was established. The experimental observations and empirical simulations indicate that the cracks tend to propagate more in the surface direction as compared to the depth direction, for the chosen loading and geometric conditions. The observed nature of crack propagation is significant for the design of the components for Leak Before Break (LBB).

Composite circular discs with polar orthotropic and rectangular orthotropic fibers of different composite materials are modeled and their vibration response due to harmonic point load was computed by finite element method (FEM) using ANSYS. Acoustic response of composite circular disc was computed by coupling the vibration data from FEM to the boundary element method using LMS SYSNOISE. © 2009 IMACS.

Modelling of plates with internal defects or cut outs is often an issue in the traditional isogeometric methods and hence extended isogeometric methods are developed. In order to reduce the computational cost involved in extended isogeometric methods based on weak form, a new extended isogeometric hybrid collocation–Galerkin method is proposed in the present paper. The natural frequencies of a homogeneous and functionally graded material plate with internal defects of varying gradient index, sizes and shapes are obtained using the proposed method. The obtained results are compared and found to be in good agreement with the reference results.

The study of vibration behaviour of cracked system is an important area of research. In the present work we present a mathematical model to study the effect of inclination, location and size of the crack on the vibrational behavior of beam with different boundary conditions. The model is based on the assumption that the equivalent flexible rigidity of the cracked beam can be written in terms of the flexible rigidity of the uncracked beam, based on the energy approach as proposed by earlier researchers. In the present work the Differential Quadrature Method (DQM) is used to solve equation of motion derived by using Euler's beam theory. The primary interest of the paper is to study the effect of inclined crack on natural frequency. We have also studied the beam vibration with and without vertical edge crack as a special case to validate the model. The DQM results for the natural frequencies of cracked beams agree well with other literature values and ANSYS solutions.

Interaction effects of two coplanar self-same shallow and deep semi-elliptical surface cracks in finite thickness plates subjected to remote tension have been previously investigated by Sethuraman et al. Using the finite element based force method. In the present study, the effect of remote bending load on interacting semi-elliptical surface cracks in a finite thickness plate is analyzed. Stress intensity factors are evaluated along the entire crack front using a modified force method based on the three-dimensional finite element solution. The line spring model has also been used to evaluate stress intensity factors at the deepest point of a crack using shell finite element analysis. Parametric studies involving a wide ranges of geometric dimensions and crack configurations viz. crack shape aspect ratio (0.2≤a/c≤1.0), crack depth ratio (0.2≤a/t≤0.9), relative crack location (0.2≤2c/d ≤0.9) and normalized location on the crack front (0≤2φ/π ≤2) are carried out for numerical estimation of crack interaction factors. Due to the crack interaction, the stress intensity factor distribution is observed to be asymmetric along the crack front. The interaction is also observed to cease when the distance between two cracks is more than five times the crack width (i.e. 2c/d less than 0.2) irrespective of crack shape aspect ratio. Finally, an empirical relation is proposed for the evaluation of crack interaction crack interaction factors for the range of parameters considered. For the ranges considered, the proposed empirical relation predicts the crack interaction factors at the inner and outer surface points of the crack within ±4% of the three-dimensional finite element solutions. © 2005 Elsevier Ltd. All rights reserved.

Numerical issues like dispersion error and the demand of high degrees of freedom at higher wave numbers, limit the use of conventional low order polynomial based numerical methods in wave problems. As a remedy, enriched techniques based on non-polynomial bases like Partition of Unity method, Discontinuous enrichment method and Ultra-weak variational methods are proposed in the literature. When material inhomogeneity is present, where the wave number is smoothly varying in the medium, the conventional enriched techniques are limited to the use of homogeneous ansatz solutions like plane waves with constant wave number. A new enrichment based on plane wave expansion which accounts for the variation of wave number in the medium, is proposed within the framework of Partition of Unity Isogeometric Analysis for solving Helmholtz equation in a heterogeneous medium. The performance of the proposed enriched basis is illustrated numerically using two case studies.

Purpose - The purpose of this paper is to present numerical studies on thermally induced vibrations of piezo-thermo-viscoelastic composite beam subjected to a transient thermal load using coupled finite element method. Design/methodology/approach - The thermal relaxation and viscoelastic relaxations are taken into consideration to obtain the system response. The concept of "memory load" along with the thermal relaxation is accounted for viscoelastic core material. The influence of type of core material on the response of the system also analyzed. Findings - The findings show viscoelastic behavior with relaxation times in composite sandwich structures. Originality/value - The paper shows accounting relaxation times as a memory load in composite sandwich structures. © Emerald Group Publishing Limited.

Parametric studies are carried out on the prediction of vibro-acoustic response from an elliptic disc made up of Functionally Graded Material with several cases of FGM index n, varying minor axis a and for different ceramic combinations with steel. Displacement, velocity, acceleration, radiated sound pressure, radiated sound power level and radiation efficiency of the elliptic disc are examined over a range of varying frequencies. Vibration response due to harmonic point load under thermal environment was computed by finite element method using a macro developed in Ansys Parametric Design Language by the authors, using available physics in ANSYS. Acoustic response of the FGM elliptic disc was computed by coupling the vibration data from the finite element method to the boundary element method using LMS SYSNOISE.

This paper presents a methodology based on Partition of Unity Finite Element Method (PUFEM) and Pseudo Elastic Analysis for solving material non-linear fracture problems within the scope of total deformation theory of plasticity. Local enrichment base functions are used to represent the asymptotic field near the crack tip and discontinuous field across the crack faces. An iterative linear elastic analysis using PUFEM is carried out for the determination of elasticplastic crack tip stress fields by treating effective material properties as spatial field variables. The effective material parameters are defined using deformation theory and are updated in an iterative manner based on strain controlled projection method using experimental uniaxial tensile test curve. Discrete system of linear equations for the elastic-plastic analysis is obtained from the weak form of the equilibrium equation using the enriched trial function. Application of the present methodology has been illustrated considering non-linear fracture problems for the evaluation of elastic-plastic crack-tip parameters using boundary layer analysis. Ramberg-Osgood model with different hardening exponents is used to characterize the material behavior. Results of the present study for J-dominant HRR field and K dominant elastic field are compared with both the analytical and non-linear finite element solutions and found to be in very good agreement. Copyright © 2009 Tech Science Press.

In general, numerical concerns in simulation of time harmonic acoustic waves are mainly due to the dispersion errors and the demands in modeling the problems with higher number of degrees of freedom per wavelength to obtain acceptable results. As a remedy, plane wave enriched Partition of Unity Finite Element Method (PUFEM) was earlier proposed by Melenk and Babuška (1996). Even though, PUFEM gives accurate results with lesser degrees of freedom and shows exponential convergence, it suffers from the approximate representation of geometry and leads to the boundary representation induced errors. In this regard, plane wave enriched PUFEM under Isogeometric framework named Partition of Unity Isogeometric Analysis (PUIGA) is proposed for accurate geometry representation and smooth solution approximation which can lead to a better solution. Several benchmark problems are considered in the present study, to illustrate the computational effectiveness of PUIGA.