In situ Neutron Transmission Bragg Edge Measurements of Strain Fields near Fatigue Cracks Grown in Air and in Hydrogen

In situ transmission Bragg edge measurements of the strain fields in an X70 steel were performed near fatigue cracks grown in air and in hydrogen. Through the use of a novel test chamber which is capable of pressurization with hydrogen gas, and amenable to neutron-scattering measurements, fatigue cracks were grown in X70 steel specimens at the NG-6 neutron-imaging beam line at the NIST Center for Neutron Research. The measured strain fields are presented and discussed in the context of proposed mechanisms of hydrogen-assisted fatigue crack growth.