LENS Webinar #6, New Directions in Instrumentation
Dr. Thilo PIRLING:
Neutron Diffraction Instrumentation for stress determination
22 October 2020, 11:00am CEST
Chair: Markus Strobl, Paul Scherrer Institute
Join via Zoom: https://ill.zoom.us/j/99877481390
A record of the webinar will also be available here soon
Abstract: The first diffractometers for the determination of stress were modified (high resolution) powder diffractometers. Simple slit diaphragms were used to achieve spatial resolution and with additional xyz-tables it was possible to map a strain field within a sample. The success of this technique and its applications in engineering science led to the need of dedicated instrumentation. This move started in the 90’s and today a dedicated stress diffractometer takes part of practically all neutron facilities. And not only this, their performance has continuously increased and we can perform measurements that were not possible 20 years ago. An important trend is towards in-situ experiments.
The development of a dedicated instrument requires a thorough selection and optimization of the different mechanical and optical components, based on detailed analysis of their function. In this presentation I would like to describe these components, present existing equipment and give detailed reasons for their specific selection.
An important part of the presentation will be committed to uncertainties and errors, introduced by beam optics and how to avoid or correct them. This concerns especially measurements near surfaces or interfaces. Here the spatial resolution can be increased by diving the gauge volume into the sample, but which results in a peak shift not related to strain variations, the so called pseudo peak-shift, or pseudo strain. A method for the correction of these errors will be presented, allowing measurements as close as several 10 micrometers from the interface.
Dr. Thilo PIRLING studied physics at the Johann Wolfgang Goethe Universität in Frankfurt and obtained his PhD in Materials Science in 1995 at the Technische Hochschule Darmstadt (Germany). Already during his physics studies he was very much interested in measuring techniques and electronics. After his thesis, he started as post-doc at the ILL (Institut Laue Langevin, Grenoble, France) where he developed a technique for precise neutron stress determination, in particular for measurements near surfaces or interfaces. This was the basis for the development of SALSA a monochromatic diffractometer for stress analysis (Stress Analyzer for Large Scaled engineering Applications) at the ILL. A project he led in collaboration with the University of Manchester (Prof. Philip Withers).
Since then he is responsible for the operation and further development of the instrument and user support. He took active part in the VAMAS- and RESTAND-projects for developing a standard for stress determination using neutron diffraction, which has now become ISO 21432:2019 and takes part in ongoing projects on this subject.
He collaborates with international research groups and industrial partners on the determination of stress with special interest in surface treatment and coatings and since recent times in metal printing.
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