The presence of hydrogen is known to accelerate the growth of fatigue cracks in steels. Prior work has suggested that hydrogen disrupts the formation of dislocations at the microscale and causes a localisation of plastic flow ahead of the crack tip at the mesoscale. However, this hypothesis has not tested in experiments because it is difficult to track dislocation movement or to measure the morphology of the plastic zone ahead of the crack.
Professor Patterson’s group has developed techniques for measuring the density of dislocations using electron back-scattering and for measuring the size and shape of plastic zones in growing fatigue cracks using thermoelastic stress analysis.
As a first step, it is proposed to use these techniques to elucidate the mechanisms underpinning the effect of hydrogen on fatigue crack growth in steels; and in a second step, to extend current work to explore the combined effect of hydrogen and irradiation damage on fatigue crack growth in steels. The work will exploit state-of-art facilities at the University of Liverpool for experimental fracture mechanics and the Pelletron ion accelerator at the Dalton Cumbria Facility.
The programme is funded by EPSRC, industrial partners and participating institutions.