Key Engineering Materials Vols. 326-328

Abstract: In this paper, a new technique for fabricating grating on the surface of porous TiNi SMA is proposed. The grating is directly written onto the surface of the specimen using the FIB milling. No photoresist is required during the lithography process. From the experimental results, it can be obviously seen that the grating fabricated by FIB milling has a better quality than that by electron beam lithography. Using the self-made FIB grating, the in-plane deformation of the porous TiNi SMA in microscale is studied by SEM moiré method. Moiré and the microscopical structures are synchronously observed, including microcracks, martensites and grain boundaries.

Abstract: In the field of experimental mechanics, there exist some circumstances when only data at the boundary can be obtained while the internal data are unavailable, or when some data are missed due to shadow, illumination saturation and other reasons. Thus it would be helpful if a reasonable estimation of the unavailable or missed data can be obtained. In this study, an algorithm is developed to reconstruct the missed data from the existing ones by generating a series of equations about the missed data and solving for an optimal solution using least-squares approach. Results based on both simulation data and real incomplete experimental data obtained by shearography and fringe projection show the usefulness and potential of the algorithm for experimental mechanics applications.

Abstract: A Multipoint Diffraction Strain Sensor (MISS) with the novel feature of simultaneous strain measurement at multiple points is characterized. Unlike conventional interferometry based systems, this patented sensor uses principles of diffraction to directly measure strain at large number of points. In this sensor, a high-frequency diffraction grating is illuminated by two symmetric laser beams and the diffracted beams are sampled on a CCD camera via a micro-lens array into an array of dots. The shift of the individual dots is sensed and strains or rigid body tilt are calculated directly. This novel technique is expected to be very valuable in numerous industrial applications.

Abstract: In the present study, a real-time calibration method for micro displacement sensors is introduced, and a calibration system is developed. SPCM, the sequence pulse counting method previously proposed by us, is capable of automatically determining both the larger range displacement and the performance of a sensor, such as the nonlinear error and the displacement sensitivity within a quarter of the light source wavelength. The new calibration system consists of a programmable motor driven platform, an out-of-plane sensitive electronic speckle pattern interferometry (ESPI), and a sequence image acquisition system. The platform is used to provide displacement changes of a moving component and its displacement is measured by the ESPI and calibrated sensor synchronously. The calibration accuracy of the proposed method is in the submicrometer level and the displacement range can be from sub-micrometer to millimeters depending on the storage capacity of the computer and the correlation property of the interferometer. Three capacitance-type displacement sensors have been calibrated successfully, whose displacement ranges are –300μm to 300μm, –30μm to 30μm, and –3μm to 3μm, respectively.

Abstract: In Dynamic Electronic Speckle Pattern Interferometry (DESPI), deformation analysis could be done for successively acquired frame data of interfering speckle patterns with no additional frames like phase shifting speckle patterns. Our final goal is to obtain a temporally varying process of two-dimensional strain field. Two normal strains and shearing strain are derived by numerical derivatives of two components of in-plane deformation. Analyzed results of tensile experiments of an Al-alloy sample will be shown. In the experiments, propagation of a strain localization band accompanied by serration of a stress curve was clearly observed quantitatively analyzed.

Abstract: Digital image correlation method (DICM) is described as a robust in-plane deformation measuring method due to its simple optical setup and the insensitivity against ambient noise. Based on DICM, digital speckle projection has been developed for shape measurement. This paper explores the possibilities for vibration analysis using digital speckle projection together with DICM. A digital speckle pattern, generated by computer, is projected on an object surface using an LCD projector. Then the dynamic deformation modulated speckle images are captured by a high-speed CCD camera and saved in the computer. By using the self-developed temporal sequence digital images correlation algorithm, the deformation and vibration mode can be analyzed quantitatively. The proposed method avoids using stroboscopic or laser illumination and simplifies the experimental setup for vibration measurement, while it is time-consuming thanks to calculating a large amount of correlation coefficients. The experimental performance on a harmonic-vibrating cantilever beam well demonstrates the validity of the new method.

Abstract: The curing characteristics of a photocurable resin are critical factors that often decide the ultimate resolution and structural sharpness of a final product fabricated by microstereolithography (μ-STL). In this study, we investigated the curing characteristics of the FA1260T photopolymer under a visible laser light of 442nm wavelength. Modification of the curing property of the FA1260T is attempted to reduce the cure depth (Dc) by adding a radical quencher to the resin. Also, an organic solvent was used to reduce the resin viscosity for an improvement of the flatness of the liquid surface during layer-by-layer curing. As a result, the minimum Dc has been reduced over a factor of 3 with no abrupt increase. Samples of three dimensional microstructures fabricated using the modified FA1260T are presented.

Abstract: The electron moiré method uses a high frequency grating to measure microscopic deformation. Finer and finer gratings are being pursued to meet higher and higher resolution requirements in microscopic stress analysis. In this study, the techniques of fabricating electron grid by means of a scanning electron microscope are improved. The use of a low accelerating voltage shows a better effect than the high accelerating voltage in fabricating a superfine grid. A new group of parameters is suggested based on this consideration. A cross-line grid with a frequency of 10,000 lines/mm and a parallel grating with a frequency of 13,000 lines /mm have been successfully fabricated.

Abstract: Pulsed UV laser beams, which are widely used in the processing of polymers, offer many advantages in the field of polymer production, primarily because their photon energy is higher than the binding energy of the polymer. In particular, the fabrication of polymers with an excimer laser process is faster and more convenient than with other processes. Nevertheless, some problems occur in the precision microprocessing of polymers, including the formation and deposition of surface debris, which is produced from the breakdown of either polymer chains or radical bonds. In the present work, a process for eliminating carbonized surface debris contamination generated by the laser ablation of a polymer was developed. The proposed approach for removing surface debris utilizes an erasable ink pasted on the polymer. The surface debris ejected from the polymer is then combined with the ink layer on the polymer. Finally, both the surface debris and the ink layer can be removed using adhesive tape.