Shizuo Mawatari

A New Computer-Aided System for Photoelastic Stress Analysis with Structure-Driven Type Image Processing

Two major difficulties in the currfent computer-aided photoelastic analysis, namely automatic determination of principal stress direction and of fringe order over the whole area of specimen, were successfully overcome with single-valued representative functions for principal stress direction with the diagonal summation theorem and for fringe order with the concept of trans-versality of intersection in Catastrophe Theory. Utilizing a structure-driven type image processing, not only the stress trajectories but also the stress distribution on an arbitrarily designated axis are successfully calculated on the basis of theories of differential geometry and ordinary differential equations, respectively. A new system developed in this study is useful for two dimensional analysis as well as for the stress-frozen technique in three dimensional analysis, in which the isochromatics and the isoclinics are inevitably superimposed.

New Method for Automatic Construction of Boundary Contour in Photoelastic Image Data.

When performing computer-aided stress analysis using photoelastic image data, difficulty in accuate extraction of the boundary contour of the specimen and the image data near the boundary is often experienced since there exist many kinds of unavoidable noise due to the fluctuation of the source light intensity, the resolution of optical equipments and the characteristics of interference phenomena. It is, however, essential to determine the boundary contour of the specimen and the image data on and near the boundaries, because of the requirement for solving boundary value problems regarding the equilibrium equations of stresses. Accordingly, it is desirable to develop an efficient method for construction of approximate contour and boundary values preserving the feature of the specimen boundary. In thi paper, the authors discuss a new plane-spline function method for automatic construction of the specimen boundary, where an algebraic plane curve is fitted to each set of measured points which corresponds to respective ramification, after considering the boundary as a simple arc and dividing it into finite ramifications.

Application of Function Approximation Method to Photoelastic Image around Mode I Crack.

When performing a photoelastic stress analysis around a stress singularity, such as a concentrated loading point or a crack tip, accurate results of stress analysis usually cannot be expected because of a collapsed image of the fringe due to a steep variation of stress and the insufficient resolving power of ordinary equipments. The function approximation method is a successful and convenient method for compensation of collapsed photoelastic isochromatic data in an extremely condensed area, which has been developed based on a concept of hybrid theoretical and experimental stress analysis. In this study, we determined the opening mode stress intensity factor using the function approximation method in a photoelastic experiment within 3 percent relative error against the theoretical value. The isochromatic image data around a stress singular point were reconstructed.

NUMERICAL ANALYSIS ON DIFFERENTIABLE STRUCTURE AND NOISE REDUCTION IN PHOTOELASTIC DIGITAL DATA

ABSTRACT The investigations so far made on the computer-aided numerical differentiation technique for experimental data involving noise is not always successful. The authors propose new algorithms not only for analysis of the differentiable structure in experimental data but also for reduction of the effect of noise. The numerical differentiation formulae are derived from the concept of differentiation of smoothed polynomials.