Papers by Keyword: Moiré Interferometry

Abstract: Residual stress is one of the important factors in thermally sprayed deposits which affects both processing and performances. In the present study, the hole-drilling method and moire interferometry were used to determine the residual stress of thermally sprayed coatings to overcome certain limitations of the strain rosette version of hole drilling. The methodology was established based on the elastic theory and finite element method. The residual displacement was measured by moire interferometry and the residual stress of the thermally sprayed coating was calculated. The results have demonstrated that moire interferometry for surface displacement caused by hole-drilling is high sensitive, reliable and stable.

Abstract: Experimental investigation is conducted to examine, evaluate, and characterize the fundamental elastic-plastic stress/strain response of friction stir-welded butt joints in thin-sheet, fine grain Ti-6Al-4V titanium alloy under normal tensile loading using traditional global stress-strain tensile testing and the full-field displacement measurement techniques of Digital Image Correlation (DIC). It was found that overall strength of friction stir-welded Ti-6Al-4V is comparable to the accepted values for mill-annealed Ti-6Al-4Valloy. Overall strain performance of friction stir-welded Ti-6Al-4V is roughly half that of the accepted values for pure mill-annealed Ti-6Al-4V. In addition, friction stir-welded Ti-6Al-4V demonstrates a consistent pattern of strain localization between the onset of yielding and ultimate failure.

Abstract: In this paper,Fracture Toughness of TC11 alloy material at normal temperature is found out by Finite Element Simulation and Moire Interferometry. The feasibility and veracity of Finite Element Simulation is shown by comparing numerical and experimental results.

Abstract: Moiré interferometry is a very sensitive optical method to measure the in-plane displacement of a solid specimen, and is useful to measure small deformation of solids. But, there often appears measurement error caused by the residual strain of the grating that is pasted on a specimen in Moiré interferometry. The present paper applies a method to eliminate the error brought by the residual strain of the grating. The method measures the change of the order of Moiré interference fringes with varying the tensile force applied to the specimen, and obtain the true opening displacement of the notch. The present paper uses the method mentioned above to measure the opening displacement of a bifurcated notch in a plate specimen

Abstract: A three-dimensional finite element model of CMOS image sensor QFN packaging using ANSYS codes is developed to investigate the solder joint reliability under thermal cycle test. The predicted thermal-induced displacements were found to be very good agreement with the Moiré interferometer experimental in-plane deformations. The developed finite element model is then applied to predict fatigue life of Sn4.0Ag0.5Cu, Sn3.5Ag0.5Cu and Sn3.9Ag0.6Cu alloys based on JEDEC standard JESD22-A104. In order to save computational time and produce satisfactory results in the region of interest, an independent more finely meshed so-called submodel scheme based on cut-boundary displacement method is generated. The mesh density for different area ratio of refinery/coarse model was verified and the results were found to be good agreement with previous researches. The modified Coffin-Manson equation and strain energy density based equation are applied to evaluate the reliability of SnAgCu alloys. A series of comprehensive parametric studies were conducted in this paper.

Abstract: Creep properties of polymer bonded explosives (PBXs), a particulate composite, was studied by using the method of moiré interferometry in this paper. The specimens fabricated by different heat pressing technology were used. Extensive creep deformation of PBXs material was indirectly measured by the aid of compressive circular disk test. The obtained results shown that creep properties are greatly influenced by pressing pressures and temperature of heat pressing technology. The results indicated that the higher the temperature and the pressing pressure are in the heat pressing technology to some degree, the better the PBXs material creep resistance is. The creep fracture surfaces of PBXs were also observed using Scanning Electronic Microscopy (SEM). It was shown that most of the fracture crack was initiated and propagated along the explosives crystal surface during creep.

Abstract: Martensitic phase transformation can greatly affect the mechanical behaviors and the stress-strain response of shape memory alloys (SMAs). In this study, the effect of martensitic phase transformation on the deformation of a single-crystal TiNi SMA specimen with a triangle crack was investigated experimentally by means of moiré interferometry method. A typical displacement field and the corresponding strain field in areas both around and far from the tip of the crack were measured in a certain time during the loading process in which the tensile load is coupled with the stress-induced martensitic phase transformation. Some characteristics of the deformation and the martensitic phase transformation of the specimen are revealed. These results may provide a reliable support for revealing the fracture mechanism of single crystal TiNi SMAs, and may enable further development in putting forward the failure criterion of SMAs.

Abstract: The characteristic of overall structure for CMOS image sensor has been studied in this research. A three-dimensional solid model of CMOS image sensor based on finite element ANSYS software is developed to predict the thermo-induced strain and the stress induced by moisture absorption. The predicted thermal-induced displacements were found to be very good agreement with the Moiré interferometer experimental in-plane deformation. The developed finite element 3D model, therefore, is applied to simulate the mechanism of thermal and hygroscopic stresses based on JEDEC pre-condition standard JESD22-A120. A series of comprehensive parametric studies were conducted in this research. The design rules for thermal optimization of CMOS image senor are summarized.

Abstract: Fatigue crack closure is an important phenomenon which needs to be taken into account in the development of models for crack propagation. This paper presents an overview of techniques for measuring crack closure. The moiré interferometry approach is described in more detail and some experimental results are presented and compared with the predictions of closure models.

Abstract: A micro mechanical study of Carbon/Epoxy composites with internally dropped plies has been made using micro-moiré interferometry. The experimental results show that there is a stress concentration region before the dropped ply. Micro cracks were initiated and propagated in this region. Two failure mechanisms in the dropped ply region were observed.