Mechanical Engineering
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Item ADVANCEMENT OF MOIRÉ INTERFEROMETRY FOR RATE-DEPENDENT MATERIAL BEHAVIOR AND MICROMECHANICAL DEFORMATIONS(2018) Wu, Bulong; Han, Bongtae; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Moiré interferometry is an optical technique to map full field in-plane deformations with extremely high resolution and signal to noise ratio. The technique is advanced and implemented to study the rate-dependent thermo-mechanical behavior of Sn-based Pb-free solder alloys and micromechanical deformations. In Part I, the mechanical/optical configuration of moiré interferometry for real-time observation of thermal deformations is enhanced to provide measurement capabilities required for the analyses. Two most notable advancements are (1) development of a conduction-based thermal chamber for a wide range of ramp rates with accurate temperature control, and (2) implementation of microscope objectives in the imaging system to observe a microscopic field of view. The advanced system is implemented to analyze the anisotropic behavior of Sn-based Pb-free solder alloys. A novel copper-steel specimen frame is developed to apply a controlled loading to single-grain solder joints. After measuring the grain orientation by electron backscatter diffraction (EBSD), detailed in-situ deformation evolutions and accumulated deformations of solder alloys are documented during a thermal cycle of -40 °C to 125 °C. The results quantify grain orientation-dependent deformations that can lead more accurate anisotropic constitutive properties of Sn-based Pb-free solder alloys. In Part II, an advanced immersion microscopic moiré interferometry system based on an achromatic configuration is developed and implemented for higher displacement sensitivity and spatial resolution. In order to achieve the desired displacement resolution, a high frequency grating (2500 lines/mm) is fabricated on a silicon substrate using lithography first. The square profile is subsequently modified by reactive-ion etching so that it can be used to produce a specimen grating by replication. Secondly, the algorithm of the optical/digital fringe multiplication method is improved to further enhance the measurement resolution of the immersion microscopic moiré interferometry. The system and the noise-free grating are used to analyze thermal deformations of micro-solder bumps. With the basic contour interval of 200 nm, the displacement resolution of 25 nm is achieved with the multiplication factor of 8.Item DEVELOPMENT OF MOIRÉ INTERFEROMETRY FOR REAL-TIME OBSERVATION OF NONLINEAR THERMAL DEFORMATIONS OF SOLDER AND SOLDER ASSEMBLY(2005-04-20) Cho, Seungmin; Han, Bongtae; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An experimental apparatus using moiré interferometry is developed to characterize the thermo-mechanical behavior of solder joints. A compact moiré interferometer is combined with an environmental chamber to allow real-time observation of non-linear and time-dependent solder and solder assemblies. The first apparatus is based on convection heating and cooling to simulate an accelerated thermal cycling (ATC) condition. Vibrations caused by an environmental chamber are circumvented by unique rigid links that connect the specimen to the moiré interferometer. Displacement fields are documented while the chamber is being operated. The system is utilized to analyze thermo-mechanical behavior of a ceramic ball grid array package assembly and a plastic ball grid array package assembly. The effect of thermal cycling on the accumulated permanent deformation is documented, which reveals the temperature-dependent non-linearity of solder joints. The second apparatus is based on conduction heating and cooling to achieve a high ramp rate. A special chamber is designed and fabricated using a high power thermoelectric cooler to achieve the desired ramp rate. The system is utilized to investigate the time-dependent behavior of solder joints. A new solder joint configuration is designed and fabricated to be tested with the conduction based apparatus. The specimen is an extension of the conventional bi-material joint configuration but the unique design offers two important features; it negates the inherent shortcoming from cross sectioning required in moiré interferometry and produces a virtually uniform shear strain field at the solder joint. The deformation of solder joint is documented at a controlled ramp rate over several thermal cycles. The experimental results are analyzed and compared with those of Finite Element analysis to investigate the validity of solder constitutive models available in the literatures.