Interference fit

Abstract: A collapsible electrode body is assembled to an end of a catheter tube. A generally rigid stem element having an exterior diameter is connected to the catheter tube. A flexible tube, which has an initial interior diameter smaller than the exterior diameter of the stem element, is deformed into a desired geometry for the electrode body, including a neck region with an enlarged interior diameter greater than the exterior diameter of the stem element. The neck region is slipped about the stem element. Heat is applied to shrink the neck region about the stem element and form a first interference fit junction therebetween. A sleeve is fitted about the first interference fit junction, and heat is applied to shrink the sleeve about the interference fit junction and form a second interference fit junction therebetween. Preferably, after the first interference fit junction is formed, additional heat is applied to thermally fuse the neck region to the stem region.

Abstract: A device and a method for stabilizing cervical vertebrae in a human spine for the purpose of fixing one vertebra with respect to other vertebrae and with respect to other parts of the spinal column. This device comprises a plate and bone screws fabricated from non-metals. The bone screws maintain the plate in contact with the vertebrae. An interference fit screw head is pulled into a hole in the plate and into a machined hole in the vertebral bone, locking the screw to the plate and locking the screw to the bone. This locking reduces the screw bending within the plate and within the bone. The screw thread runout is threaded below the screw/bone interference fit area, protecting the runout stress raisers from bending and shear stresses. The interference fit is configured to create sufficient friction to eliminate the screw from backing out.

Abstract: A stress intensity factor solution is developed for a large plate containing radial hole cracks loaded with arbitrary crack face pressure. When the pressure is defined as the unflawed hoop stress surrounding a mechanical fastener, stress intensity factor calibrations are readily computed by the linear superposition principle. Results obtained in this manner agree well with previous solutions determined for open holes loaded in remote tension. The potential usefulness of the present analysis is further demonstrated with application to specific fastener configurations, including interference fit fasteners, pin-loaded plates, and cold-worked holes.

Abstract: Crack initiation and crack growth behavior were determined experimentally for aluminum and titanium specimens with fastener holes that were either cold worked or were propped by interference fit fasteners. The specimens were subjected to a randomized flight-by-flight spectrum. Analytical procedures were evaluated, based on correlation with the test data. These procedures included elastic-plastic analysis which was utilized to determine the stress-strain distributions surrounding the fastener holes. Estimates of elastic proportional limits in tension and compression were based on material cyclic stress-strain characteristics. Purely elastic analysis was used to determine the K T and stress gradient for the propped fastener holes with various ratios of plate-to-fastener modulus of elasticity. Finite-element model elastic-plastic computer results provided the stress-strain distributions for the cases of superimposed cold working and external loading, and superimposed interference fit fasteners and external loading. Approximate analytic equations were developed to fit the finite-element model computations. These equations were used to calculate the stress-strain excursions that would occur during flight-by-flight spectrum fatigue loading. The stress-strain excursions were then used to enter strain-life curves to compute crack initiation. They were also used to determine stress intensities to enter da / dn versus ΔK curves to compute crack growth. The delay in crack initiation due to beneficial compressive residual stresses that would be induced during spectrum loading was accounted for by using a stress ratio correction factor based on strain-life data generated at different stress ratios. Crack growth retardation due to periodically applied high loads was accounted for, using the Wheeler plastic zone model. The comparison of the crack initiation life calculations to the test data was favorable if initiation was defined as the development of a 0.25-mm crack. Good agreement between the crack growth calculations and the test data was also obtained for growth from a 0.25-mm crack.