Neutron diffraction measurements of residual stress have been carried out for the past decade in North America and Europe. The particular advantage of neutron diffraction stems from the fact that thermal neutrons are highly penetrating particles, permitting measurements to be made throughout the thickness for example, of 40 mm of steel. Testing has been done on a wide variety of components, ranging from large, 90 cm diameter, steel linepipe welds, through 6 mm thick zirconium alloy pressure tubes, to regions in the neighbourhood of small stationary welds. Where comparisons have been made between finite element calculations of stress and neutron measurements the agreement has been good. In addition to measuring Type 1 stresses, or macrostress fields, much effort has recently been made in measuring phase-interaction stresses in composite materials such as AlSiC, and intergranular stresses in anisotropic alloys.
A number of case studies will be reviewed discussing both macro- and microstresses.
Designing a neutron stress experiment requires much discussion between the scientist and the engineer/customer to resolve uncertainties and misconceptions at an early stage, e.g. what is the best reference lattice spacing. The design often requires ancillary measurements to be made of the crystallographic texture which enables the scientist to choose the diffraction lines which best characterize the sample. The approach we have adopted in our laboratory to these problems to satisfy our industrial customers will be outlined.