Determination of residual stresses at ILL: present and future

The ILL is constructing, in collaboration with the Manchester Materials Science Centre, a neutron strain imager for the non-destructive determination of residual stresses. The project is funded by ILL and the EPSRC (Engineering and Physical Science Research Council) on a fifty–fifty basis. A special feature of the instrument is the sample table, which will be a Stewart platform or hexapod. It allows most flexible sample movement, having a load capacity of more than 500 kg and allowing sample sizes of up to 2-m length. A new supermirror neutron guide and a specially developed two-dimensional focusing monochromator will provide more than 2.6 times the neutron flux of the present instrument. A limitation of the neutron strain scanning technique is the surface effect, which introduces huge errors when scanning through interfaces or surfaces. Experiments have shown that the use of radial collimators for beam-defining optics reduces the surface error drastically. Such a configuration is one option of the present strain scanner and will as well be part of the future instrument, which will be commissioned to ILL in 2004.