Investigation of wrinkle artifacts along metallic fatigue cracks in phase contrast synchrotron tomography via simulations and experiments

Abstract

• X ray imaging simulations are used to study the formation of artifacts (wrinkle artifact) in phase contrast tomographic images. • Practical solutions to reduce those wrinkle artifacts are predicted and their efficiency is demonstrated in the case of fatigue cracks in metals. • The physical origin of wrinkle artifacts is discussed. Due to higher lateral coherence length of beams available at high brilliance synchrotron sources, the presence of diffraction fringes on crack edges and at crack tips can improve crack detectability in the reconstructed Synchrotron Radiation Computed Tomography (SRCT) images. However, when the crack shape is less planar and more disturbed, strong artifacts (named here wrinkle artifacts) in SRCT images are found all along crack edges leading to difficulties in quantitative analysis of cracks. To investigate the origin of these artifacts and to find some ways to reduce them, phase contrast tomography simulations (using GATE software) associated with experiments (conducted at ESRF) were performed. We show that these artifacts come from Fresnel interference patterns on the detector which are especially strong when the crack orientation is normal to the rotation axis, and they can be reduced by minimizing the phase contrast intensity (smaller sample-to-detector distance or higher X-ray energy) or simply by inclining cracks with respect to the plane defined by the beam trajectory.