Browsing by Subject "Strain energy"

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    Improved seal design based on minimizing strain energy
    (2010-06) Matus, Daniel Alexander.
    Minimizing the strain energy in an oring seal has been identified as a mode of improving its useful lifetime. The intent of this research was to manipulate the strain energy content in oring seals by varying material properties and material behavior over the crosssection of the oring. Oring designs were developed that contained regions of modified material properties referred to as insets. These oring designs incorporating insets were evaluated numerically to determine the effects that the inset’s stiffness, size, and placement, had on the strain energy content and maximum sealing pressure of the oring design. Achievements included the development of oring designs that demonstrated lower strain energy content than a baseline design made of a single homogeneous material. Experimental orings were created using commercially available materials. Compression set and compression stress relaxation experiments were conducted. Performance of new oring designs including insets made of a softer material than the main oring was compared to baseline single material orings. Improved sealing performance was demonstrated by a decreased rate of sealing force decay over time, and by decreased compression set, for the new oring designs proposed.
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    Structural analysis of implantable biomedical heart assist device fixation
    (2013-12) Conway, Thomas James
    This thesis presents how experimentation, numerical simulation, optimization, and mathematical analysis, can be applied to study and improve the fixation of left-ventricle leads within a cardiac vein. Left-ventricle cardiac leads for implantable pacemakers can lose fixation within a cardiac vein and dislodge. A common lead-fixation mechanism for left-ventricle leads was investigated that used a two- or three-dimensional shape at the distal end. The lead and the distal end are constructed from a metal coil that is pre-formed into a two- or three-dimensional shape. Analytical beam approximations of a coil were developed to determine how coil stiffness is affected by coil geometry and material. In-vitro experimentation with a radial force tester was used to measure the overall force between a two- or three-dimensional distal shape within a straight cylindrical tube. Data processing techniques using a moving average were applied to interpret the force data. Numerical simulation using a beam approximation for the coil determined the overall force between a distal shape and a straight cylindrical tube. The distribution of force along the distal shape, including tip force was also obtained from the simulation. The simulation models were validated with experimental data. Using numerical simulation, the model of the distal shape was changed to a spiral shape and then optimized. Since actual cardiac veins are curved, the simulation model was updated with a curved tube to determine how the distal shapes would perform. A mathematical analysis using engineering principles was also applied to obtain a simple analytical equation relating a deformed distal shape to force.