Determination of residual stresses by an optical correlative hole-drilling method

In conjunction with the incremental hole-drilling method, a new evaluation procedure is presented for determining the residual stress state in components. In contrast to the classical method, the whole displacement field around the drilled hole is measured using the electronic speckle pattern interferometry technique. The displacement patterns, measured without contact to the surface, are then correlated with those obtained by finite-element simulations using statistical methods. The simulated displacement patterns, used for calibration purposes, result from the application of properly defined basic loads. In this way, the values and the orientation of the residual stresses can be determined by superposition of these properly scaled and shifted basic loads. Even complex states of stress can be evaluated. The theoretical background and experimental results are presented.     

Theoretical analysis for surface tilt and translation detection based on speckle photography in the Fresnel domain

The theoretical and numerical analysis in this work show that both surface tilting and translational motion can be simultaneously calculated using the speckle photographic technique by recording consecutive speckle pattern images in two different Fresnel diffraction distances. A simulation example based on the proposed scheme is given to verify the method’s validity and high accuracy of the calculated motion detection. Compared with other previous works the results show that this method is efficient and easy to implement.     

Nanometer-scale displacement sensing using self-mixing interferometry with a correlation-based signal processing technique

A self-mixing interferometer is proposed to measure nanometre-scale optical path length changes in the interferometer’s external cavity. As light source, the developed technique uses a blue emitting GaN laser diode. An external reflector, a silicon mirror, driven by a piezo nanopositioner is used to produce an interference signal which is detected with the monitor photodiode of the laser diode. Changing the optical path length of the external cavity introduces a phase difference to the interference signal. This phase difference is detected using a signal processing algorithm based on Pearson’s correlation coefficient and cubic spline interpolation techniques. The results show that the average deviation between the measured and actual displacements of the silicon mirror is 3.1 nm in the 0–110 nm displacement range. Moreover, the measured displacements follow linearly the actual displacement of the silicon mirror. Finally, the paper considers the effects produced by the temperature and current stability of the laser diode as well as dispersion effects in the external cavity of the interferometer. These reduce the sensor’s measurement accuracy especially in long-term measurements.     

Investigation on spectral-domain optical coherence tomography using a tungsten halogen lamp as light source

The objective of this research was to investigate a new detection method using a thermal light source in a spectral domain optical coherence tomography (SDOCT) operation to improve both image acquisition rate and axial resolution economically. A tungsten halogen lamp was chosen as the illumination source and a Michelson fiber interferometer was employed to generate the interference pattern of an object collected by a spectrometer; the inner structure of the object was obtained from the interference pattern by a Fourier transform. An experiment was performed by measuring a thin film coated on a glass base with the system, and the experimental results indicated that the structure of the thin film could be clearly observed as expected. It was theoretically stated and experimentally verified that the technique was feasible and enables imaging to realize the reconstructions of internal structure of engineering and biological object.     

刚体运动对云纹干涉法的影响

本文详细讨论了试件在空间六个自由度中产生刚体运动时所形成的云纹图特性，定量地分析了各种刚体运动形式对云纹干涉法的影响。经分析表明：在用云纹干涉法测量变形位移场时，只有当试件绕坐标轴刚体转动时才会影响所测变形位移场。     

Adaptive filter for unwrapping noisy phase image in phase-stepping interferometry

An adaptive filter for preprocessing wrapped phase image with high noise content has been developed. The window size of this median filter is adjustable according to its location in the noisy phase image. This size-adjustable median filter has not only high noise-rejection ability, but also both good phase-jump identification and image-detail preservation properties. Phase unwrapping can then be done to recover the real phase image without the hampering influence of noise, especially the noise near the phase jumps. Both numerical simulation and experimental results used to examine the effectiveness of this adaptive filter are presented.     

Strain solitary waves in inhomogeneous wave guides

The paper presents recent results of the research on strain solitary wave (soliton) evolution in elastic wave guides with different types of inhomogeneities. We analyze in calculations, numerical simulations and in experiments how physical or geometrical inhomogeneities affect the parameters of a density soliton propagating in it. In our experiments strain solitons are produced in a wave guide from an initial shock wave generated in the surrounding water by laser evaporation of a metallic target immersed into it nearby the input edge of the wave guide. Strain solitons are recorded in a desired part of the wave guide by means of holographic interferometry that allows to visualize the whole process and to obtain the complete set of data at different stages of the wave evolution.     

Coherence Spectrotomography: Optical Spectroscopic Tomography with Low-Coherence Interferometry

In low-coherence reflectometry, light scattered back from a medium is expected to contain spectral properties as well as range information on the reflective boundaries and backscattering sites. Low-coherence interferometric systems with particular signal-processing techniques have been proposed that can extract both the range and spectral properties inside the medium simultaneously. This class of systems is called coherence spectrotomography. In this paper, basic principles of coherence spectrotomography are reviewed referring to the experimental results on multi-layered media.     

Evaluation of the curvature of an object by Talbot interferometry

In this study a modified method of Talbot interferometry is developed to evaluate the curvature of an object. The tilt angle of moiré fringe formed by two gratings is related to the wavelength, the grating periods, the angle between these two gratings, and the object curvature. Therefore, substituting the known experimental parameters into a special derived equation the object curvature can be evaluated. In order to show the validity of this method, stainless steel balls with curvatures of 1.326 and 1.261 mm⁻¹ were measured. The measurement resolution of curvature was about 3.729 × 10⁻³ mm⁻¹. It is shown that this method is suitable for both transmission and opaque objects with high accuracy.