The purpose of this investigation was to evaluate whether irradiation causes significant embrittlement of the devices so as to create a risk of fracture during use.  This is done by measuring the change in mechanical properties of the two materials following an irradiation treatment.

Results

The key mechanical properties identified for investigation are the tensile strength at yield, the elongation at yield and the total elongation to failure.  Ten samples were machined for each of the materials. Five from each set of samples were sent for irradiation, at approximately three times the dosage typically used. Consequently the tensile properties in terms of strength at yield, elongation and yield and total elongation to failure were measured before and after irradiation, and then statistically analysed.
During tensile testing, pulling of the HIP normal and irradiated samples was carried out until specimen failure occurred. The PP normal samples elongated beyond the system’s capacity to pull and calculations were done accordingly. Failure did occur in the PP irradiated samples; however the elongation was localised to a specific region on the gauge length of the specimen.

Conclusion

Statistical analysis shows that sufficient evidence has been provided to conclude that:

• Irradiation of the HIPS and PP resulted in a statistically significant change in the yield strength of the material. 
• Irradiation of the HIPS resulted in a statistically significant increase in elongation at yield of the material.  Irradiation did result in a statistically significant decrease in the total elongation to failure of the material, however the elongation to failure post irradiation is still high enough so as to conclude that the material has not become brittle.  Hence Irradiation has not caused the material to become brittle. 
• Irradiation of the PP did not result in a statistically significant change in elongation at yield, but did cause a statistically significant decrease in the total elongation to failure.  The elongation to failure following irradiation is high enough so as to not cause the material to become brittle.