Rotary Beam Fatigue Tests of Wire Used for Medical Devices

Solid, round, fine wire is often used by the medical industry in devices such as catheter guide wires and as stents for the repair of arteries and containment vessels such as vena cava filters. A new ASTM International standard, E2948, Test Method for Conducting Rotary Beam Fatigue Tests of Wire, will be used to determine the fatigue life characteristics of such wire, in order to assess its reliability.

"Fatigue strain strength values at specific cyclic lives are of interest to both the wire manufacturer and consumer for production control, design and material acceptance," say ASTM members K.L. Jerina, D.Sc., and M.R. Mitchell, Ph.D.. "E2948 will be useful in assessing the effects of internal material structure, such as inclusions, in melt technique and cold work processing studies."

The test method describes a procedure for the performance of rotating beam fatigue tests of small diameter wire to obtain the fatigue strength of metallic materials at a specified life in the fatigue regime where the strains are predominantly and nominally elastic. Material suppliers and device manufacturers have used various methods to assess fatigue life, but E2948 is the first standardized method for such testing of fine wires.

"The standard can be useful, for example, in assessing the effects of internal material microstructure in melt technique, surface modifications and cold work processing studies," say Jerina and Mitchell. "The current procedure used in industry was incorporated into E2948 and consists of a test method that requires a simple loading device and simple data reduction."

E2948 was developed by Subcommittee E08.05 on Cyclic Deformation and Fatigue Crack Formation, part of ASTM International Committee E08 on Fatigue and Fracture.

The task group that developed E2948 is seeking material suppliers and laboratories with E2948 testing capability to participate in an interlaboratory study in order to develop data for a precision and bias statement.

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CONTACT Technical Information: K.L. Jerina, D.Sc., Washington University • St. Louis, Mo. • Phone: 314-935-4960 | M.R. Mitchell, Ph.D., Mechanics and Materials Consulting LLC • Flagstaff, Ariz. • Phone: 928-814-8622 | ASTM Staff: Jeffrey Adkins • Phone: 610-832-9738 | Upcoming Meeting: Nov. 10-13 • November Committee Week • New Orleans, La.

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