h n g k y -center https://ntrs.nasa.gov/search.jsp? R=19870011944 2018-05-09T17:43 energy release rates for the 'bare' interface laminate, i.e. one without the resin layer, and for the laminate with the resin showed that the 'bare' interface models are a very good approximation for the resin case if the delamination tip elements were one-quarter to one-half of the ply thickness.

A mixed-mode delamination test procedure was developed combining double cantilever beam (DCB) mode I loading and end-notch fixture (ENF) mode II loading on a split unidirectional laminate. By loading with a lever, a single applied load simultaneously produces mode I and mode II bending loads on the specimen. This mixed-mode bending (MMB) test was analyzed using both finite-element procedures and beam theory to calculate the mode I and mode II components of strain-energy release rate G I and G II , respectively. A wide range of G I /G II ratios can be produced by varying the load position on the lever. As the delamination extended, the G I /G II ratios varied by less than 5%. Beam theory equations agreed closely with the finite-element results and provide a basis for selection of G I /G II test ratios and a basis for computing the mode I and mode II components of measured delamination toughness. The MMB test was demonstrated using AS4/PEEK (APC2) unidirectional laminates. The MMB test introduced in this paper is rather simple and is believed to offer several advantages over most current mixed-mode test.

In this article, we present a method for optimizing the design of a shape memory alloy–actuated robotic catheter. Highly maneuverable robotic catheters have the potential to revolutionize the treatment of cardiac diseases such as atrial fibrillation. To operate effectively, the catheter must navigate within the confined spaces of the heart, motivating the need for a tight bending radius. The design process is complicated by the shape memory alloy’s hysteretic relationships between strain, stress, and temperature. This article addresses the modeling and optimization of both a single-tendon and antagonistic tendon robotic catheter using COMSOL Multiphysics Modeling and Simulation software. Several design variables that affect the actuator behavior are considered; these include the shape memory alloy tendon radius and its prestrain, the shape memory alloy tendon offset from the neutral axis of the flexible beam, the flexible beam radius and elastic modulus, and the thermal boundary condition between the shape memory alloy tendon and the beam. A genetic algorithm is used to optimize the radius of curvature of the two catheter designs. Both a single-crystal and polycrystalline models are implemented in COMSOL and are experimentally validated.

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