Key Engineering Materials Vols. 326-328

Abstract: This paper demonstrates instantaneous phase-stepping and subsequent phase analysis methods for interferometry and two-dimensional photoelasticity. The camera that has a pixelated form-birefringent micro-retarder array acquires phase-stepped fringes in a single camera frame. Then, the distributions of Stokes parameters that represent the state of polarization are calculated from a single image. In the case of the polarization interferometer, the phase difference of the two orthogonally polarized light beam can be easily determined from the Stokes parameters. On the other hand, the phase distributions of the isochromatics and the isoclinics are obtained in the case of the photoelasticity. It is emphasized that 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.

Abstract: The two-dimensional deformation of wood with different grains under shearing loads was measured using an electronic speckle pattern interferometry (ESPI) technique. The radical, tangential and end sections of Douglas firs (Pseudotsuga menziesii) were used as specimens. Results revealed that the deformation values significantly vary for every part of the specimens, and the ring directions of earlywood and latewood, which compose the annual rings, have an effect on the two-dimensional deformation of wood.

Abstract: In this paper, we describe an optical interferometer applied to 3D inspection of microcomponents. The resulting interference fringes that are related to the deformation and surface contour of MEMS-components are analyzed by the fast Fourier transform (FFT) and 3-step phaseshifting algorithms. Experimental results show the feasibility of the proposed method for 3D deformation and surface contour measurement of micro-components.

Abstract:
The reconstruction of instantaneous contour is a common method to analyze the kinetic characteristic of a continual deformation object. In this paper a continuous wavelet transform method (CWT) is applied to analyze the instantaneous contour of a continual deformation object based on shadow moiré technique. The modulated moiré fringe patterns are captured by use of a high-speed CCD camera and the temporal intensity variation of each pixel related to the object deformations is recorded. The intensity variation of each pixel is analyzed along the time axis by CWT. From the extraction of the ridges and from the value of the CWT along the ridges, the information of modulated phase relative to the contour of object can be obtained. In this application, a cantilever beam with a motion in the Z direction is tested by use of the method and the high-quality instantaneous contour of the continual deformation object can be retrieved. Experimental results prove that the CWT can successfully be applied to the instantaneous contour analysis of continual deformation object and these results demonstrate the advantages of the CWT with respect to the applicable simplicity and the resistance of noise pollution.

Abstract: Velocity and density distributions of a high-speed and initial CO2 jet flow have been analyzed simultaneously by a developed three-dimensional digital speckle tomography and a particle image velocimetry (PIV). Three high-speed cameras have been used for the tomography and the PIV since a shape of a nozzle for the jet flow is asymmetric and the initial flow is fast and unsteady. The speckle movements between no flow and CO2 jet flow have been obtained by a cross-correlation tracking method so that those distances can be transferred to deflection angles of laser rays for density gradients. The three-dimensional density fields for the high-speed CO2 jet flow have been reconstructed from the deflection angles by the real-time tomography method, and the two-dimensional velocity fields have been calculated by the PIV method simultaneously.

Abstract: Fiber optic sensor with small size, light weight and immunity to electromagnetic interference can be embedded and integrated into the host material to form a smart structure system. One must recognize that optical fibers are foreign entities to the host structure, therefore will alter the stress state in the vicinity of the embedded sensor irrespective of the small size of the fiber. This is a result of the material and geometric discontinuity introduced by the embedded optical fiber. In this study, the local stress fields in the vicinity of the embedded fiber are examined. The host material is considered to be a composite with reinforced fiber parallel to the optical fiber. The geometry in the vicinity of the embedded fiber is modeled by four concentric cylinders which represent the optical fiber, protective coating, resin and host material, respectively. In this investigation, the host structure is subjected to longitudinal normal stress and transverse hydro-static stress. The effects of the coating and host material on the stress distribution in the vicinity of the embedded optical fiber are presented through a parametric study.

Abstract: In this paper, the residual deformation induced in laser welding processing was studied by using the moiré interferometry and a novel high-temperature specimen grating technology. The experimental results indicate that the heat-affected zone of laser welding is a narrow strip. There exists great residual strain gradient in the heat-affected zone, especially great residual shear strain gradient. It implies that great residual stress and stress gradient exist near the welded seam. The relationship between the size of the heat-affected zone and the changes of the technology parameters were discussed in the experiments, which can supply some reliable experimental data for optimizing processing technology.

Abstract: Phase unwrapping is an important and challenging process in optical interferometry. Difficulties in phase unwrapping are usually caused by either noise (“bad” pixels) or invalid areas (“bad” regions). If the “bad” pixels can be removed, the problems due to the noise are solved. Further, if the “bad” regions can be identified, they can be avoided in phase unwrapping. In our previous work the noise can be successfully removed using a windowed Fourier transform [Optics and Lasers Technology, 37:458-462 (2005)]. In this paper we will show that the invalid areas can be identified by the same windowed Fourier transform. Thus a single windowed Fourier transform is able to process both “bad” pixels and “bad” regions simultaneously, which makes the phase unwrapping simple and effective.

Abstract: Three-dimensional density distributions of an impinging and eccentric flame have been analyzed numerically and experimentally by a combined optical system with a digital speckle tomography. The flame has been ignited by premixed butane/air from air holes and impinged vertically against a plate located at the upper side of the burner nozzle. In order to compare with experimental data, computer synthesized phantoms of impinging and eccentric flames have been derived and reconstructed by a developed three-dimensional multiplicative algebraic reconstruction technique (MART). A new scanning technique has been developed for the analysis of speckle displacements to investigate wall jet regions of the impinging flame including sharp variation of the flow direction and pressure gradient. The reconstructed temperatures by the digital speckle tomography have been compared with a temperature photography by an infrared camera and results of a numerical analysis using a finite element method.

Abstract: This paper presents an application of a new point-wise technique for unwrapping the isoclinic parameter determined by a four-step color phase shifting. The unwrapping technique is based on a largest region in a binary image that corresponds to a largest visible-wrapped period of the computed isoclinic parameter. The largest region is obtained using an intersection operation between the extended ranges of the computed isoclinic parameter. The method uses four raw photoelastic fringe images. The technique is applied to a circular ring containing isotropic points subjected to diametral compression. Results show the method provides the correct isoclinic parameter in the true interval over the entire domain.