tungsten cable failure analysis brad james ph.d. p.e
TRANSCRIPT
Tungsten Cable Failure Analysis
Brad James Ph.D. P.E.
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
Tungsten Cable Failure Analysis
Tungsten Cable Failure Analysis
Sterilized Non-Sterilized
Tungsten Cable Failure Analysis
Sterilized Cable After Durability Testing
Tungsten Cable Failure Analysis
Sterilized Cable After Durability Testing
Tungsten Cable Failure Analysis
Cables After Tensile Testing:Sterilized Non-Sterilized
Tungsten Cable Failure Analysis
Hydrogen content tests (Leco Interstitial)
Non-sterilized cable: ~20 ppm hydrogenSterilized cable: ~ 60 ppm hydrogen
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