The experimental mechanics became popular to evaluate the stresses and the principal stress direction in structures in the twentieth-century. The optimun design of structures will be popular in the twenty-first-century, and stress distribution will become homogeneous. Even if the structures would not be broken, it will be necessary to destroy them for recycling of materials. Especially full-field methods will become more important to detect the maximum stress and the principal direction. The present situation and the prospect of experimental mechanics including the societies, trends, methods, standardization and soundness evaluation systems in the twenty-first century are anticipated in this paper.

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To obtain accurate values and directions of stresses in photoelasticity, phase analysis of a fringe pattern has been introduced. The algorithm proposed by Patterson and Wang can analyze isochromatics and isoclinics at the same time, and has no ambiguous of sign on phase calculation of isoclinics. These phase analysis methods for isochromatics and isoclinics are, however, for static stress analysis. To analyze photoelastic phase maps under dynamic loading, a new high speed phase analysis algorithm is requested. In this paper, a high speed phase analysis algorithm for isochromatics and isoclinics is proposed. In this algorithm, a quarter wave plate and an analyzer are rotated at every π/4 and π/8 respectively. Then shifted photoelastic fringe patterns are obtained continuously. Therefore the optical instruments in this method are able to rotate at high speed easily, and only a short time is required to take images for phase analysis. Since the proposed algorithm can provide the phase maps of isochromatics and isoclinics so quickly, it will be able to apply to slowly varying time-dependent stress analysis.

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Thermographic NDT technique using an active thermal stimulation method was applied for the detection of delamination defects in concrete structures. An oil heater, which can apply heat flux to the objective body by radiation and convection heat transfer, was employed for active heating. Evaporation cooling by water spray was used for active cooling. Preliminary experimental investigations were carried out for concrete specimens with artificial delamination defects. It was found that delamination defects can be detected from the thermal images, in which localized high or low temperature regions appeared above the delamination defects. Proposed technique was applied for the inspection of actual delamination defects in the concrete railway bridges. It was found that the defect shape was clearly estimated from the localized temperature region appeared in thermal images under active thermal stimulation.

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This paper discusses the interference effects of stress intensity factor K_I in the case of a strip plate with three edged cracks under a uniform tension by the caustic method. The material of specimens used is the epoxy resin and DAP resin, which have already been used for the stress analysis by photoelastic method, caustic method and so on. Next, the validity of the experimental result is estimated by simulation of J-integral. Two kinds of simulation model shape are prepared: one is the same model shape as experimental model and the other is for simulation. Though the values by simulation are a little larger than the ones obtained by experiments, both values do not show so much difference; rather comparatively both values are close. And, from the above result, our experiments have led interference effects of K_I.

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