Fixture for mechanical analysis of a hollow tube

An apparatus for determining the mechanical properties of a material, comprising:

• a base platform including a programmable drive configured to move relative to a stationary post;
• a test specimen including a hollow cylindrical tube substantially formed from the material and having a first end and a second end;
• and
• a test fixture, including:
• a first mount coupled to the drive and extending upwards therefrom, the first mount including at an upper end thereof a first member applying pressure about the circumference of the hollow tube first end, and
• a second mount coupled to the post and disposed over the drive, the second mount including at an upper end thereof a second member applying pressure about the circumference of the hollow tube second end;
• wherein the first mount comprises a clamp capable of restraining an extruded polymer hollow cylindrical tube during a mechanical analysis without imparting a net torque on the tube sufficient to change the mechanical properties of the tube to affect a measurement of a mechanical property of the material, the clamp including
• a ring connecting two arms, and
• a plurality of fingers defining a bearing surface, the plurality of fingers forming an approximately circular bearing surface when the arms are brought adjacent to each other, wherein the stiffness of the ring is varied between one or more fingers to produce the desired boundary condition during testing.

An apparatus for determining the mechanical properties of a material, comprising:

• a base platform including a programmable drive configured to move relative to a stationary post;
• a test specimen including a hollow cylindrical tube substantially formed from the material and having a first end and a second end;
• and
• a test fixture, including:
• a first mount coupled to the drive and extending upwards therefrom, the first mount including at an upper end thereof a first member applying pressure about the circumference of the hollow tube first end, and
• a second mount coupled to the post and disposed over the drive, the second mount including at an upper end thereof a second member applying pressure about the circumference of the hollow tube second end;
• the first mount further including means for applying a uniform pressure to the outer circumference of the tube without preloading the tube including a ring member having a plurality of radial bearing surfaces and a plurality of T-shaped sections separating the bearing surfaces.

An apparatus for testing properties of a material, comprising:

• a DMA;
• a hollow cylindrical tube made from the material and suited for forming a medical prosthesis;
• a fixture mounted within the DMA, the fixture including a clamp holding the tube, the clamp being capable of restraining without imparting a torque preload on the tube or otherwise changing the mechanical properties of the unloaded tube when restrained by the clamp, the clamp including
• two arms,
• a plurality of radial extending fingers having surfaces defining an inner diameter and adapted for gripping the tube outer surface,
• a connector extending between the arms and configured for selectively reducing/enlarging the inner diameter by changing the distance between the arms,
• a flexible coupling extending between the fingers and adapted for producing a load distribution among the fingers that produces a desired boundary condition, and
• a post disposed within the inner diameter and received within the bore of the tube.