Volumetric measurement of residual stress using high energy x-ray diffraction

Abstract

We present results and recent developments from our laboratory, bench-top high energy x-ray diffraction system (HEXRD), between diffraction energies 50 and 150 KeV, to measure internal strain of moderately sized objects. Traditional x-ray strain measurements are limited to a few microns depth due to the use of Cu Kα1 Mo Kα1 radiation. The use of high energy x-rays for volumetric measurements of strain is typically the domain of synchrotron sources. We discuss the use of industrial 320kVp tube sources to generate a brighter x-ray beam along with a method using the intrinsic 43 eV width of the Kα1 characteristic peak of tungsten to measure volumetric strains in a number of industrially relevant materials. We will present volumetric strain measurements from two examples, first, additive manufacturing (AM) parts with various build configurations and, secondly, residual strain depth profiles from shot peened surface treatments. The spatial resolution of these depth profiles is ∼75 microns. The development of a faster method as compared to energy dispersive or θ-2θ scans is based on the intensity variation measurement of the strain using the aforementioned 43 eV characteristic tungsten kα line. We will present recent results on the development of this new tool and on x-ray diffraction measurements at high energy.