Katsutoshi Yamada

Quantitative nondestructive evaluation with ultrasonic method using neural networks and computational mechanics

This paper describes an inverse analysis method using hierarchical neural networks and computational mechanics, and its application to the quantitative nondestructive evaluation with the ultrasonic method. The present method consists of three subprocesses. First, by parametrically changing the location and size of a defect hidden in solid, elastic wave propagation in the solid is calculated with the dynamic finite element method. Second, the back-propagation neural network is trained using the calculated relationships between the defect parameters and the dynamic responses of solid surface. Finally, the trained network is utilized to determine appropriate defect parameters from some measured dynamic responses of solid surface. The accuracy and efficiency of the present method are discussed in detail through the identification of size and location of a defect hidden in solid.

Transient thermal stresses in an infinite plate with two elliptic holes

A method of solving uncoupled quasi-static thermoelastic problems in perforated plates is presented. As an illustrative example, a transient thermal stress problem is solved for an infinite plate containing two elliptic holes with prescribed temperatures. The following hole temperatures are considered in detail: (1) Both holes are at the same constant temperature T0; ()2) one hole is at T0, the other at −T0. Numerical results are given for minor diameter/major diameter ratios of 1 (circular hole), ½, and ⅓, and for major diameter/pitch ratios of 0 (one hole)−0.9. The results show the power and flexibility of the method.

THERMAL STRESSES IN AN INFINITE PLATE WITH TWO ROWS OF HOLES

Abstract A theoretical method is presented for a two-dimensional, steady thermoelastic problem of perforated plates with two rows of holes. The analysis is developed by the complex variable approach. The numerical results for stress concentration factors are given in the form of curves for a wide range of diameter/pitch. The extension of the present method to holes of arbitrary shape, number, and array is quite straightforward.

Thermal flexure of an infinite plate with a doubly periodic array of holes

Abstract A theoretical method is presented for bending problems of perforated plates. The method is illustrated by giving the solution for an infinite plate with a doubly periodic set of circular holes having a square or triangular pattern under a uniform temperature difference between upper and lower faces of the plate within the framework of the Poisson-Kirchhoff theory of thin plates. Numerical results are given for the bending moment around holes and curves of stress concentration factors. The results show the power and flexibility of the technique. The solution obtained here can be used, just as it is, for a plate with holes of arbitrary shape and array. Also the extension of the method to a plate under a class of loads other than thermal load, e.g. uniform bending or twisting moment, is quite straightforward.

Nondestructive Evaluation of Residual Stresses by Heating Method (Simultaneous Estimation of Rate of Heat Release and Residual Stresses)

In the heating method which can be available for nondestructive and in situ measurements of residual stresses, a new method is proposed for simultaneous estimation of the heat flux and residual stresses. The approach is formulated as an inverse problem by using the surface displacements relieved by local heating and the resulting nonlinear least square problem is solved by Levenberg-Marquardt method. In this procedure, the displacements of the direct problem are computed by FEM. The approach is applied to estimation of uniaxial and biaxial stresses in a plate. The numerical results show the effectiveness of the proposed method.

Defect Identification with Ultrasonics Using Neural Networks and Computational Mechanics. Verification of Accuracy through Laser Ultrasonics Experiment.

This paper describes an application of the neural networks to defect identification with laser ultrasonics. The present method consists of three subprocesses. First, sample data of identification parameters vs. dynamic responses of displacements at several monitoring points on surface are calculated using the dynamic finite element method. Second, the back-propagation neural network is trained using the sample data. Finally, the well trained network is utilized for defect identification. This method is applied to the identification of a surface defect hidden in solid with laser ultrasonics. Its performance in accuracy and robustness is quantitatively verified in detail through both numerical simulations and experiments.

Thermal Stresses and Their Singularities in Coated Half-Space due to Point Heat Source. 3D Analysis.

This paper is concerned with the exact solution of a coated half-space subjected to a point heat source which acts in the interior of the layer. The problem is formulated by Mukis method using Hankel transforms. We perform the inverse integrals involved analytically, and thus obtain a closed form solution, which is represented by the associated Legendre function of the first kind. Some considerations are given for stress singularities when the point heat source is located at the interface, and it is found that the shear stress becomes singular at the heat source point. From the present solution, some existing solutions of special cases can be derived.

Quantitative Nondestructive Evaluation with Laser Ultrasonics Using Neural Network and Computational Mechanics

Nondestructive Evaluation (NDE) techniques to detect cracks and defects hidden in solid are very important to assure the structural integrity of operating plants and structures, and to evaluate their residual life time. Various NDE techniques using ultrasonic wave, X-ray, magnetic powder, eddy current and so on have been studied so far. In most cases, they detect only the existence of cracks and defects. Then, quantitative nondestructive evaluation (QNDE) techniques to determine sizes, shapes and locations of cracks and defects are strongly desired.

Thermal stresses in an infinite plate containing a double infinite row of circular holes with arbitrary stagger.

A steady-state thermal stress problem is solved for an infinite plate containing two infinite rows of circular holes which are heated by prescribed temperatures T0 and T0, respectively. The plates are considered in detail having one row of pairs of circular holes, and holes of triangular, square and rectangular configurations. For each configuration, numerical computations are carried out for holes having diameter-to-pitch ratios of 0.1-0.95, and the results are given in the form of figures. From the comparison of the present results with those of two holes in an infinite plate, the thermal stress concentration or relaxation mechanism for the complex hole configurations considered here has been clarified.

Transient Thermal Stresses in a Semi-Infinite Plate Containing a U-Shaped Edge Notch

A transient thermal stress problem is solved analytically for a U-shaped edge notch in a semi-infinite plate in which the straight and notch edges have a prescribed temperature. The transient thermal stress concentration factors are computed numerically for the U-shaped notches having a notch-depth/notch-radius of up to 20, and the results are shown in the form of tables and figures. The stress concentration factors of steady state, which correspond to those under compression, are compared with other results available and very good agreements are found between them.