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