1. Tungsten Cable Failure Analysis Brad James Ph.D. P.E.

2. 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

3. Tungsten Cable Failure Analysis

4. SterilizedNon-Sterilized

5. Tungsten Cable Failure Analysis Sterilized Cable After Durability Testing

6. Tungsten Cable Failure Analysis Sterilized Cable After Durability Testing

7. Tungsten Cable Failure Analysis Cables After Tensile Testing: Sterilized Non-Sterilized

8. Tungsten Cable Failure Analysis Hydrogen content tests (Leco Interstitial) Non-sterilized cable: ~20 ppm hydrogen Sterilized cable: ~ 60 ppm hydrogen

9. 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