Slow strain rate testing of welded copper

Abstract: In Sweden spent nuclear fuel is planned to be placed 500 m down in the bedrock. The spent nuclear fuel will be contained in copper canisters. The reason behind the selection of copper is its thermodynamic stability against corrosion in the depository. The copper will be exposed to mechanical loading and will be plastically deformed due to creep. The canisters will be sealed by friction stir welding. Since the canisters have to survive intact for many thousands of years, the properties of the welds are critical. Oxygen free P-doped copper (Cu-OFP) is selected for its excellent creep ductility properties and corrosion resistance. In this thesis work creep ductility behavior of friction stir welded copper chosen at different areas of the weld is evaluated by using the test slow strain rate tensile test. Samples are chosen at different weld areas namely weld, cross weld and HAZ. A sum of 21 specimens is tested. These tests are achieved at three various strain rates and each rate are carried out at three different temperatures. The strain rates used for tests are 1e-4, 3e-6 and 1e-7 [1/s]. The samples are strained until rupture, 20% and 5% of the gauge length. Yield strength and tensile strength are usually decreasing with increasing temperature and at higher temperature the material can be easily deformed. Few strange behaviors are also observed for the samples from HAZ areas at strain rate 1e-7[1/s]. The experimental results are justified by using the Knock-Mecking model. The parametersand ω were evaluated by curve fitting method.