A few weeks ago the testing in our corrosion-fatigue rig did not go well. The machine somehow went into position control instead of load control, which resulted in the stroke moving upwards. This put a lot of load on the test specimen and the chamber, which then both broke. We had to repair the induction coil. Luckliy, only a small hole was formed so Teknoheat repaired it very fast using silver solder. New ceramic plates for the chamber was also manufactured. This time I have prepared an extra set in case a chamber breakage happens again. Before starting my experiment there were two important things I had to do.
1. Alignment: Looking at the test specimen we can clearly see the high force it has been exposed to. This means that the alignment of the machine might have been affected. It is therefore very important to check this before we start our expriments again. We perform the alignment by mounting a test specimen containing 8 strain gauges in the grips and then change the alingment by tighten or loosen different positions of the alignment cell. The resulting strain in the test specimen is monitored and we are satisfied when we have an aligmment resulting in zero strain of the test specimen. After calibration we reached alignment class 10. It is not perfect but it is okay. This class means that we have below 1% deviation in strain. The last time we did the alignment we got class 5, which means below 0.5% deviation.
2. Adjustment of the induction coil: To make sure we have an homogeneous temperature on the test specimen, I attached thermo couples on different positions and modified the distance between the coil wires until I reached a temperature gradient of +/- 5 to 10 degrees over the gauge length.