Satoru Yoneyama

Deformation measurement by phase-shifting digital holography

The out-of-plane displacement of a cantilever is measured by phase-shifting digital holography. From four phase-shifted holograms of a cantilever recorded by a CCD image sensor, a complex amplitude at each pixel of the CCD plane is obtained using the conventional phase-shifting method. The complex amplitude of a cantilever is reconstructed from the complex amplitude of the CCD plane using the Fresnel diffraction integral. The phase difference distribution on the cantilever before and after deformation, i.e., the out-of-plane displacement distribution, is calculated. In order to decrease the effect of speckle noise, a new method using divided holograms is proposed. The theory and experimental results are shown.

Two-dimensional stress separation using phase-stepping interferometric photoelasticity

A phase-measuring method is proposed for stress separation in two-dimensional interferometric photoelasticity. A Mach–Zehnder-type interferometer combined with a circular polariscope is used for the observation of isochromatics and isoclinics as well as isopachics. Phase-stepping is performed for the determination of the phase values of isochromatics and isoclinics by rotating both a quarter-wave plate and an analyser. On the other hand, the phase of the isopachics is analysed from images obtained by shifting a mirror in the interferometer. Then, the phases of isochromatics and isoclinics without ambiguity are obtained by introducing a load-stepping technique. The phases obtained by the load-stepping are also used for unwrapping the phases of isochromatics and isopachics. In the present paper, light intensity equations for the proposed optical set-up are derived using Jones calculus. Then, the effectiveness is demonstrated by applying the proposed method to a simple problem.

Photoelastic Analysis with a Single Tricolor Image

A new approach to simultaneous measurement of isochromatics and isoclinics from a single image using a tricolor light, called as the tricolor photoelastic technique, is proposed in order to enable and facilitate the analysis of time varying phenomena. Not only an apparatus of experiment but the whole analysis system and procedure are developed. Using a color digital camera and a tricolor light source under linear polarization, fringe order and the principal direction of birefringence are obtained from a piece of color image data by a single shot using the method proposed. It is emphasized that this method can be applicable to time varying phenomena in which good repeatability and reproducibility of experiments are not expected, since multiple exposures are not necessary for sufficient data acquisition in the completion of stress analysis.

Phase-measuring profilometry of moving object without phase-shifting device

A new phase-measuring surface profiling technique of a moving object is proposed in the present paper. An interference fringe pattern is projected onto the object that moves at a constant speed. Multiple linear sensors are used for recording the deformed fringe pattern on the object. The phase distribution along the recording line can be calculated using a phase-shifting algorithm without any phase-shifting devices. The length of a target is not limited and a long object can be measured by the proposed method. It is expected that the proposed method can be used for the profile inspection of products moving on a conveyor system in a factory.

Simultaneous observation of phase-stepped photoelastic fringes using a pixelated microretarder array

An instantaneous phase stepping and subsequent phase analysis method, using a charge-coupled device (CCD) camera with a pixelated form-birefringent microretarder array, is proposed for 2-D birefringence distribution measurement. A birefringent sample placed behind a polarizer and a quarter-wave plate is analyzed by the proposed method. Light emerging from the sample is recorded using a CCD camera that has a pixelated microretarder array on the CCD plane. This microretarder array has four different principal directions. That is, an image obtained by the CCD camera contains four data corresponding to four different optical axes of the retarder. The four images separated from the image recorded by the CCD camera are reconstructed using gray-level interpolation. Then, the distributions of the Stokes parameters that represent the state of polarization are calculated from the four images. The birefringence parameters, that is, the angle of the principal axis and the phase retardation, are then obtained from these Stokes parameters. This method is applicable to real-time inspection of optical elements as well as the study of the mechanics of time-dependent materials, because multiple exposures are unnecessary for sufficient data acquisition in the completion of data analysis.

Instantaneous Phase-stepping Interferometry Using Polarization Imaging with a Micro-retarder Array

An instantaneous phase-stepping and subsequent phase analysis method, using a CCD camera with a form-birefringent micro-retarder array, is proposed for interferometry. An optical setup of a polarization interferometry using a Twyman-Green interferometer with two polarizers is constructed to analyze the distribution of out-of-plane displacement. Light emerging from the interferometer is recorded using a CCD camera that has micro-retarder array on the CCD plane. This micro-retarder array has four different principal directions. That is, an image obtained by the CCD camera contains four types of data corresponding to four different optical axes of the retarder. The four images separated from the image recorded by the CCD camera are reconstructed using gray-level interpolation. Then, the distributions of the Stokes parameters that represent the state of polarization are calculated from the four images. The phase distribution of the interference fringe pattern produced by the Twyman-Green interferometer is then obtained from these Stokes parameters. This method is applicable to time-dependent phenomena because multiple exposures are unnecessary for sufficient data acquisition in the completion of phase analysis.

A new method for photoelastic fringe analysis from a single image using elliptically polarized white light

Abstract A new two-dimensional photoelastic method for the analysis of fringe order and the principal direction of birefringence from a single image combining an elliptically polarized white light and color image processing is demonstrated. To determine fringe order, a database-search approach based on the primary color analysis is employed. After determining fringe order, the principal direction of birefringence is obtained by solving a non-linear equation. The equation of emerging light intensity is derived and the theory of the proposed method is described. Then, the successful application of the method to photoelastic analysis is shown. It is emphasized that the proposed method can be applicable to time-varying phenomena since multiple exposures are not necessary for sufficient data acquisition for the completion of stress analysis.

Nucleation, bifurcation and propagation of local deformation arising in NiTi shape memory alloy

The main purpose of this paper is to investigate the local deformation arising in NiTi plate subjected to stress concentration during tensile loading. First, a test system is constructed on the basis of digital image correlation (DIC) in order to measure the local strain distribution over the surface of the specimen. Second, we measure the local deformation (local strain distributions) arising in a 50.5Ni49.5Ti plate with a double notch under tensile loading. The results are as follows. (1) NiTi shows local deformation, such as nucleation and propagation of local strain bands, and its bands have a fixed angle (about 54°–55°) relative to the loading direction. On the other hand, the distribution of local shear strain is almost uniform when the local longitudinal strain bands propagate during tensile loading. (2) NiTi with stress concentration shows that the local longitudinal and lateral strain bands initiate at the stress concentration part, and propagate with a symmetrical shape. Later, the local strain band shows bifurcation and propagates toward both ends of the specimen with a fixed angle relative to the loading direction. The distribution of local shear strain is almost uniform when the local longitudinal strain bands propagate, but it is not uniform when the phase transformation initiates. NiTi with stress concentration shows local deformation, such as nucleation, bifurcation and propagation of phase transformation, and its bands have a fixed angle relative to the loading direction. The transition of the local deformation mode has an effect on the macroscopic stress–strain curve. When predicting the macroscopic deformation behavior of NiTi structures, these local deformation modes arising in NiTi should be considered.

Instantaneous phase-stepping photoelasticity for the study of crack growth behaviour in a quenched thin glass plate

A new approach to simultaneous acquisition of phase-stepped photoelastic fringes using a CCD camera equipped with a pixelated micro-retarder array is described for the investigation of time-variant problems. This method is applied to the study of quasi-static crack growth in a quenched thin glass plate. The distributions of the principal direction as well as the principal stress difference around a growing crack tip are obtained by the proposed method. Then, not only the mixed-mode stress intensity factors but also the T-stress are evaluated from the distribution of the principal stress difference, and they are validated using the reconstructed phase maps. The results show that the proposed instantaneous phase-stepping technique is effective for the study of the crack growth behaviour in a thin glass plate.

Photoelastic fringe pattern analysis by real-time phase-shifting method

This paper describes high-speed phase-shifting method for the real-time analysis of isochromatic and isoclinic parameters in photoelasticity. By rotating an analyzer at a constant rate and an output quarter-wave plate at a double rate of the analyzer and recording images by a CCD camera continuously, sequential phase-shifted images whose brightness is integrated by sensors are obtained. Then, the distributions of the isochromatic and isoclinic parameters are obtained at a video rate using the proposed phase-shifting algorithm. The phase distributions of the isochromatic and isoclinic parameters of a disk under the static and increasing loadings are simulated. Then, an application of the proposed method to a problem under increasing load is demonstrated and the time variation of the isochromatic parameter is evaluated.