Ryan Dale Jamison

Indentation and overall compression behavior of multilayered thin-film composites. Effect of undulating layer geometry

Two finite element models are used to investigate the behavior of aluminum/silicon carbide thin-film layered composites with imperfect internal geometry when subjected to various loadings. In both models, undulating layers are represented by regular waveforms with various amplitudes, wavelengths, and phase offsets. First, uniaxial compressive loading of the composite is considered. The modulus and stress/strain response of the composite is sensitive to both loading direction and frequency of the undulation. Second, the nanoindentation response of the composite is investigated. The derived hardness and modulus are shown to be sensitive to the presence of undulating layers and the relative size of the indenter to the undulation. Undulating layers create bands of tensile and compressive stress in the indentation direction that are significantly different from the flat layers. The amount of equivalent plastic strain in the Al layers is increased by the presence of undulating layers. The correlations between the two forms of loading, and the implications to composite property measurement are carefully examined in this study.

Analysis of Laser Weld Induced Stress in a Hermetic Seal

Laser welding of glass-to-metal electrical connectors is a common manufacturing method for creating a hermetically sealed device. The materials in these connectors, in particular the organic glass, are sensitive to thermal induced residual stress and localized heating. An analytical laser weld model is developed that provides simulation and analysis of both thermal and mechanical effects of the welding process. Experimental studies were conducted to measure the temperature at various locations on the connector. The laser weld is modeled using both surface and volumetric heating directed along the weld path to capture the thermal and mechanical response. The weld region is modeled using an elastic-plastic weld material model, which allows for compliance before welding and stiffening after the weld cools. Results from a finite element model of the glass-to-metal seal are presented and compared with experimental results. The residual compressive stress in the glass is reduced due to the welding process but hermeticity is maintained.

Computational Assessment of Brittle Fracture in Glass-to-Metal Seals

Glass-to-metal seals are widely used in engineering applications, but are often plagued by cracking and loss of hermeticity despite design efforts to avoid these problems. Standard computational approaches typically rely on under-refined meshes and rule-of-thumb approaches that are not always effective. This paper investigates improvements to current practice in glass-to-metal seal design. First, material models with more extensive temperature dependence are used to enhance the accuracy of residual stress prediction. Second, a Weibull-statistics approach is adopted for the prediction of the likelihood of failure. These approaches are then applied to a simplified seal geometry. The paper demonstrates that the application of these methods, especially the Weibull-statistics approach, have difficulties that need to be addressed before this proposed set of approaches can be effectively used for seal design. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.© 2010 ASME