Publications

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As the specimen gets smaller and thinner, traditional strain measurement method using the strain gage is impossible. In this paper, the strain is measured using non-contact laser interferometry method. Two markers are placed on the LIGA specimens along the loading direction to reflect the laser beams to generate the interferometric fringe patterns. The markers are generated using micro-hardness indentation for the LIGA specimens. A pair of CCD cameras is used to capture the interferometric fringes during each step of the loading along the longitudinal direction. Fast Fourier Transform (FFT) is then applied to calculate the frequency and phase shift of the fringes. The displacement and strain can be obtained from the phase shift of the fringe pattern. This ISDG strain measurement technique is further developed by using multi markers to obtain fringes during the whole loading when the specimen undergoes larger motion. Biaxial strain measurement using ISDG is also developed to obtain both Young's modulus and Poisson's ratio simultaneously. A third marker is located orthogonal to the first pair of markers along the loading direction. Two pairs of CCD cameras are used to acquire the digital images of the interferometric fringes patterns along both longitudinal and transverse directions. The stress-strain curves as well as the material properties are very consistent from the different tests using ISDG. Copyright © 2006 by ASME.

A new constitutive model for large deformation of aluminum honeycomb has been developed. This model has 6 yield surfaces that are coupled to account for the orthotropic behavior of the cellular honeycomb being crushed on-axis and off-axis. Model parameters have been identified to fit uniaxial and biaxial crush test data for high density (38 1b/ft3) aluminum honeycomb. The honeycomb crush model has been implemented in the transient dynamic Presto finite element code for impact simulations. Simulations of calibration and validation experiments will be shown with model predictions compared with test data. Also, the honeycomb model's predictions will be compared with the older Orthotropic Rate Model predictions. Copyright © 2006 by ASME.

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Resist substrates used in the LIGA process must provide high initial bond strength between the substrate and resist, little degradation of the bond strength during x-ray exposure, acceptable undercut rates during development, and a surface enabling good electrodeposition of metals. Additionally, they should produce little fluorescence radiation and give small secondary doses in bright regions of the resist at the substrate interface. To develop a new substrate satisfying all these requirements, we have investigated secondary resist doses due to electrons and fluorescence, resist adhesion before exposure, loss of fine features during extended development, and the nucleation and adhesion of electrodeposits for various substrate materials. The result of these studies is a new anodized aluminum substrate and accompanying methods for resist bonding and electrodeposition. We demonstrate successful use of this substrate through all process steps and establish its capabilities via the fabrication of isolated resist features down to 6 {micro}m, feature aspect ratios up to 280 and electroformed nickel structures at heights of 190 to 1400 {micro}m. The minimum mask absorber thickness required for this new substrate ranges from 7 to 15 {micro}m depending on the resist thickness.

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This paper describes the analyses and the experimental mechanics program to support the National Aeronautics and Space Administration (NASA) investigation of the Shuttle Columbia accident. A synergism of the analysis and experimental effort is required to insure that the final analysis is valid - the experimental program provides both the material behavior and a basis for validation, while the analysis is required to insure the experimental effort provides behavior in the correct loading regime. Preliminary scoping calculations of foam impact onto the Shuttle Columbia's wing leading edge determined if enough energy was available to damage the leading edge panel. These analyses also determined the strain-rate regimes for various materials to provide the material test conditions. Experimental testing of the reinforced carbon-carbon wing panels then proceeded to provide the material behavior in a variety of configurations and strain-rates for flown or conditioned samples of the material. After determination of the important failure mechanisms of the material, validation experiments were designed to provide a basis of comparison for the analytical effort. Using this basis, the final analyses were used for test configuration, instrumentation location, and calibration definition in support of full-scale testing of the panels in June 2003. These tests subsequently confirmed the accident cause.

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The effects of chemical aging on the behavior of carbon black filled rubber were investigated by two types of tests, aging under no strain and aging under a constant strain. A slight modification of the damage-based theory of Segalman, used previously on unaged samples, was found to be consistent with the experimental data.

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