tungsten cable failure analysis brad james ph.d. p.e
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Tungsten Cable Failure Analysis
Brad James Ph.D. P.E.
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Tungsten Cable Failure Analysis
Background• Medical device company uses tungsten cables as
part of a surgical apparatus• Non-sterilized cables withstand hundreds of
durability test cycles (consists of cyclic and static loading)
• Sterilized cables fail after a few durability test cycles
• Tensile testing shows no real difference between sterilized and non-sterilized cables
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Tungsten Cable Failure Analysis
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Tungsten Cable Failure Analysis
Sterilized Non-Sterilized
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Tungsten Cable Failure Analysis
Sterilized Cable After Durability Testing
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Tungsten Cable Failure Analysis
Sterilized Cable After Durability Testing
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Tungsten Cable Failure Analysis
Cables After Tensile Testing:Sterilized Non-Sterilized
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Tungsten Cable Failure Analysis
Hydrogen content tests (Leco Interstitial)
Non-sterilized cable: ~20 ppm hydrogenSterilized cable: ~ 60 ppm hydrogen
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Tungsten Cable Failure Analysis
Conclusions• Classic case of hydrogen embrittlement! (tungsten is
known to be susceptible)• Corrosion during sterilization is the source of hydrogen• Embrittlement is stress/time dependent• Tensile testing not long enough to allow diffusion of
hydrogen to high stress locations• Static loads during durability allowed hydrogen to
diffuse to higher stress locations – resulting in fracture