Shang Huai Min
Email Address
mpeshm@nus.edu.sg
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150 results
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Now showing 1 - 10 of 150
Publication Scanning moiré and phase shifting with time delay and integration imaging(1997-09-01) Sajan, M.R.; Tay, C.J.; Shang, H.M.; Asundi, A.; MECHANICAL & PRODUCTION ENGINEERINGScanning moiré is generated by undersampling of a phase-modulated grating pattern. In projection profilometry the scanning moiré pattern represents equal height and depth contours on a test object. By use of time delay and integration (TDI) imaging, it is possible to generate an on-line scanning moiré pattern from the complete periphery of a rotating cylindrical object. For automated phase and profile unwrapping from scanning moiré fringes, phase-shifting interferometry techniques are most desirable. However, lack of spatial information in the undersampled scanning moiré fringes introduces serious errors in phase unwrapping. We report a method that uses oversupply of data to balance the effect of undersampling. This oversupply is achieved with a TDI feature that permits programmable image magnification in the scanning direction. © 1997 Optical Society of America.Publication Measurements of surface coordinates and slopes by shearography(1992-08) Tay, C.J.; Shang, H.M.; Poo, A.N.; Luo, M.; MECHANICAL & PRODUCTION ENGINEERINGThis paper represents an optical method which is based on speckle-shearing interferometry for the measurement of surface coordinates and slopes. The technique enables generation of carrier fringes which measure surface coordinates, or displacement derivative fringes which measure surface slope. The theory of the method as well as some experimental results are presented. © 1992.Publication The use of carrier fringes and FFT in holographic nondestructive testing(2001-07) Quan, C.; Tay, C.J.; Shang, H.M.; MECHANICAL ENGINEERINGThe carrier fringe technique for holographic interferometry was discussed. The use of fast Fourier transforms (FFT) in the method enabled phase measurement from fringe patterns caused due to interference of tilted wavefronts. The FFT approach was used to extract deformation information automatically from complex interferograms and was shown to have considerable potential for solving images in its ability to extract data in the presence of pixel noise.Publication Holographic inspection of plates with regions of local thinning as defects(1992-06) Shang, H.M.; Tay, T.E.; Lwin, M.; MECHANICAL & PRODUCTION ENGINEERINGThis paper describes the use of double-exposure holography on the detection and assessment of plates containing locally thinned regions as artificial defects. The artificial defect is programmed by thinning locally a plate to various depths with a milling cutter. During testing, the plate, illuminated by an expanded laser beam, is clamped along its periphery and an incremental uniform pressure applied between two exposures on the holographic plate. Local thinning is revealed from anomaly in the reconstructed fringe pattern-the boundary of the anomalous fringes is larger than the boundary of the actual artificial defect, and the amount of thinning is deduced from the number of fringes within the boundary. Artificial defects with eccentric local thinning are more readily revealed from the reconstructed fringe pattern than the artificial centric defects. A simple theoretical model is developed so that when the experimental fringe-counts are compared with the theoretical ones, any discrepancy between them reveals not only the presence of centric and eccentric artificial flaws but also their sizes and depths. © 1992 Plenum Publishing Corporation.Publication Design of an optical probe for testing surface roughness and micro-displacement(2001-10) Wang, S.H.; Jin, C.J.; Tay, C.J.; Quan, C.; Shang, H.M.; MECHANICAL ENGINEERINGThis paper presents a practical monitoring tool for measurements of surface roughness and micro-displacement. An optical probe of the methods based on light scattering for measuring surface roughness and optical triangulation for measuring micro-displacement is described. The proposed technique allows evaluation of surface roughness and micro-displacement of specimen by using just one device. The theoretical models of surface roughness and micro-displacement measurements have been established for the probe. The measuring principles applied in the design are described in detail and the validity of the design is demonstrated by experimental evaluations. The experimental results show that, for specimens with surface roughnesses Ra in the range from 0.005μm to 0.1 μm, micro-displacement measurements in the linear range of ± 300μm can be obtained. © 2001 Elsevier Science Inc. All rights reserved.Publication Flaw detection in composites using time-average shearography(1991-02) Toh, S.L.; Shang, H.M.; Chau, F.S.; Tay, C.J.; MECHANICAL & PRODUCTION ENGINEERINGResults on flaw detection of glass fibre reinforced plastic beams using time- average shearography are presented here. Detection and sizing of flaws such as debonds or delaminations are successfully carried out using this technique. For easy detection of flaws, the component has to be excited at the resonance frequencies of the flaws. As the flaw gets smaller, a higher frequency is required. For flaws of the same exterior size, a deeper one will also require a higher frequency. © 1991.Publication Shape measurement by use of liquid-crystal display fringe projection with two-step phase shifting(2003-05-01) Quan, C.; Tay, C.J.; Kang, X.; He, X.Y.; Shang, H.M.; MECHANICAL ENGINEERINGThe use of an optical fringe projection method with two-step phase shifting for three-dimensional (3-D) shape measurement of small objects is described. In this method, sinusoidal linear fringes are projected onto an object's surface by a programmable liquid-crystal display (LCD) projector and a long-working-distance microscope (LWDM). The image of the fringe pattern is captured by another LWDM and a CCD camera and processed by a phase-shifting technique. Usually a minimum of three phase-shifted fringe patterns is necessary for extraction of the object shape. In this method, a new algorithm based on a two-step phase-shifting technique produces the 3-D object shape. Unlike in the conventional method, phase unwrapping is performed directly by use of an arccosine function without the need for a wrapped phase map. Hence, shape measurement can be speeded up greatly with this approach. A small coin is evaluated to demonstrate the validity of the proposed measurement method, and the experimental results are compared with those of the four-step phase-shifting method and the conventional mechanical stylus method. © 2003 Optical Society of America.Publication Stretching during axisymmetrical forming of sheet metal(1997-01) Qin, S.; Shang, H.M.; Tay, C.J.; Mo, J.; MECHANICAL & PRODUCTION ENGINEERINGIn sheet metal forming, the surface area of the blank normally is increased simultaneously with the reduction in the overall blank thickness. The distribution of and overall change in the thickness and, consequently, the efficacy of the forming process are influenced by forming parameters such as the blank size, blank holding load, lubrication and tool geometries. In most forming processes, drawing-in of the flange is unavoidable, unless this is deliberately prevented using a serrated die set and a very large blank holding load. This paper demonstrates that forming processes may be viewed as mixtures of two basic processes, namely, ideal stretch forming and ideal deep drawing. The ideal stretch forming process is typified by extensive thinning, due to bi-axial stretching, of the blank within the die throat, with drawing-in of the flange being absent. Ideal deep drawing contrarily requires the complete drawing-in of the flange into the die throat, with negligible change in the overall thickness of the blank. In the light of this, a parameter χ, describing the extent of stretching relative to drawing, is proposed. The contributing factors on sheet formability are subsequently discussed with reference to χ; this approach should assist die designers in selecting the appropriate parameters for successful forming operations.Publication Application of the holographic carrier fringe and FFT technique for deformation measurement(1996-02-01) Quan, C.; Shang, H.M.; Bryanston-Cross, P.J.; MECHANICAL & PRODUCTION ENGINEERINGThis paper describes a holographic system based on the use of fibre optics and automatic spatial carrier fringe pattern analysis. Carrier fringes are generated by simply translating the object beam between two exposures. Single-mode optical fibres are used to transfer both the object and reference beams. The fast Fourier transform method is used to process the interferograms: it extracts phase from fringe patterns resulting from the interference of tilted wavefronts. The method is illustrated by measuring the deformation of an arbitrarily clamped, uniformly loaded circular plate. The results are given for the perspective plot of the out-of-plane deformation field, the maps of wrapped and unwrapped phase, and a contour map of the unwrapped phase.Publication Determination of stress-strain relationship of sheet metal under biaxial tension(1993-03) Tay, C.J.; Shang, H.M.; Shit, S.K.; MECHANICAL & PRODUCTION ENGINEERINGThis paper demonstrates that the biaxial stress-strain relationship of sheet metal may be determined from the hydraulic bulge test with values for stress and strain being calculated from local curvature measurements. It is also shown that the workhardening characteristics may be derived for stress ratios other than those in equibiaxial tension. This need arises from the fact that the critical section of a sheet metal product is frequently subjected to stress and strain paths other than uniaxial or equibiaxial tension.