Key Engineering Materials Vols. 326-328

Abstract: Two different types of experimental methods have beeen developed for measuring lateral interaction forces between two solid surfaces for nano- and micro-meter scale contacts. One is the type of direct measurement methods which typically utilize AFM instrumentations. In the direct lateral force measurements some size-scale effects are commonly observed due to the effects of adhesion and surface roughness. A recent development of a fine AFM lateral force calibration method, a diamagnetic lateral force calibrator, has made it possible to study such size-scale effects systematically. The other type is the field projection method which requires a high resolution measurement of a deformation field near the edge of a contact. For such measurements a comprehensive map of deformation measurement techniques is introduced in a domain of spatial and strain resolutions. This technique provides a way of assessing the non-uniform distribution of the surface interaction forces for nano and micro-meter scale contacts.

Abstract: New experiment systems that can offer electromechanical and electromagnetic coupling loads were established. Measurement skills and technologies under coupling loads have been developed. The experimental difficulties and technical problems, such as insulation, discharge, compressive testing of brittle ferroelectrics and so on, were well resolved. The constitutive experiments of piezo/ferroelectrics or ferromagnetic materials were carried out. Moiré Interferometry was applied to the measurement of transformation of the crack tip in ferroelectric ceramics under coupling loads. The deformation concentration near the internal electrode tip caused by non-uniform electric field was investigated by means of Digital Speckle Correlation Method (DSCM). With an aim to accomplish both measurements of constitutive response of the magnetostrictive materials and the fracture experiments of general soft ferromagnetic materials, a magnetomechanical-coupling testing setup was established, which is controlled by an industrial PC. The software was programmed to monitor the testing process and to deal with the acquired data. The characteristic curves of ferromagnetic materials, such as TbxDy1-xFe2 alloys, were measured, including the hysteresis loops, the magnetostriction curve and stress-strain curve.

Abstract: The authors have been developing some novel methods to measure shape, deformation, stress and strain of structures using optical methods and image processing as follows: (1) Phase analysis methods using Fourier, wavelet or Gabor transforms, etc., (2) Real-time 2-D strain measurement using moiré interferometry, (3) Scanning moiré method using thinning-out of scanning lines and a DMD camera (4) Strain rate distribution measurement by a high-speed video camera, (5) Real-time integrated phase-shifting method, (6) Shape measurement methods using multi-reference planes, a linear image sensor, or a frequency modulated grating, and (7) Windowed phase-shifting digital holographic interferometry (WPSDHI). Theories of these methods and some applications are introduced. The most accurate result is 88 picometer standard deviation of errors using the WPSDHI.

Abstract: Phase-shifting digital holography can be used for displacement measurement instead of strain gauge. Our research group is developing the measurement equipment for phase-shifting digital holography. Generally, in the measurement equipment, piezo stages are used as phaseshifting devices. But the piezo stage is expensive. Cheaper and smaller phase-shifting device is required in order to put the measurement equipment into practical use. In this paper, we, therefore, propose a phase-shifting device using the deflection of a cantilever and we verify whether this phase-shifting device can be used
for digital holography.

Abstract: In this paper, in-line digital holography is combined with time average method and applied for vibration analysis of an aluminum membrane. The numerically reconstructed wave from time average holograms contains information of mode shape and mean deformation of the vibrating objects. At lower amplitudes of vibration only the deformation fringes are observed and as the amplitude is increases, the Bessel fringes representing the time average vibration amplitude also become visible. Experimental results for a 10mm size membrane are presented.

Abstract: Phase-shifting technique is an effect way to suppress the zero order diffraction and the conjugate term in digital holography. However the phase-shifting error will influence inevitably the evaluation precision in practice operation. In this paper, the deformation evaluation errors by means of two kinds of four-step phase-shifting algorithms, which are in common use in digital holography, are analyzed and compared by computer simulation. In addition, the phase-shifting errors may cumulate or not according to different phase-shifting techniques, and both cases are considered in this paper. The results based on the digital in-line holography show that the two four-step phase-shifting algorithms possess different sensitivity to the phase-shifting errors, and the preferable one, which is more immune to the phase-shifting errors, is educed in conclusion.

Abstract: We previously proposed a real-time shape measurement method using two-component synthesis grating projection. In the method, phase unwrapping of the projected grating is performed by using aliasing of the Fourier spectrum of the grating images. It requires only 5 images obtained for one-cycle phase-shifting. Each phase in the two-component can be extracted from only 5 phase-shifted grating images. In this paper, we propose a real-time shape measurement system. The theory, the algorithm for the analysis and the experimental results are shown.

Abstract: Photoelasticity is one of the most widely used techniques for experimental stress and strain analysis. With the availability of low cost digital image processing systems, a separate branch of photoelasticity known as digital photoelasticity came into existence providing whole-field values of the isoclinics (θ) and isochromatics (N) in a true sense. Among the several methods available for data acquisition, phase shifting / polarization stepping techniques are most widely used for their simplicity and accuracy. In this paper a new digital photoelastic method based on phase shifting using monochromatic light source is presented. It provides full field values of θ and N. The arrangement is carefully chosen with the intention of reducing the influence of quarter wave mismatch error in the evaluation of θ and N. The methodology is validated for the benchmark problem of a disk under diametral compression.