Non-Destructive Lifetime Prediction in Material Testing with the Bonn Positron Microprobe

For the construction of heavy duty mechanical components it is essential to know the lifetime of the sample under dynamical load conditions. Material fatigue tests in rail vehicle axles were first made in the year 1858 by August Wohler. Up to now the measurement of a Wohler diagram remains extraordinarily time and money consuming. Since iron based materials fail at a critical defect density independent of cycle number and load, we are able to extrapolate the remaining lifetime of the sample from a few cycles. With positron annihilation measurements employing the Bonn Positron Microprobe different stress states in standard samples can be observed as a function of position. This leads to a novel non-destructive way to determine a complete Wohler diagram (SN-diagram) with just one sample. (Materials: austenitic stainless steel, ferritic stainless steel.)