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Abstract: Polycrystalline diffraction is a robust methodology employed to assess elastic strain within crystalline components. The Extended Caking (exCaking) method represents a progression of this methodology beyond the conventional azimuthal segmentation (Caking) method for the quantification of elastic strains using Debye–Scherrer 2D X-ray diffraction rings. The proposed method is based on the premise that each complete diffraction ring contains comprehensive information about the complete elastic strain variation in the plane normal to the incident beam, which allows for the introduction of a novel algorithm that analyses Debye–Scherrer rings with complete angular variation using ellipse geometry, ensuring accuracy even for small eccentricity values and offering greater accuracy overall. The console application of the exCaking method allows for the accurate analysis of polycrystalline X-ray diffraction data according to the up-to-date rules presented in the project repository. This study presents both numerical and empirical examinations and error analysis to substantiate the method’s reliability and accuracy. A specific validation case study is also presented to analyze the distribution of residual elastic strains in terms of force balance in a Ti-6Al-4V titanium alloy bar plastically deformed by four-point bending.

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Abstract: The Dual Imaging and Diffraction (DIAD) beamline at Diamond Light Source (Didcot, U.K.) implements a correlative approach to the dynamic study of materials based on concurrent analysis of identical sample locations using complementary X-ray modalities to reveal structural detail at various length scales. Namely, the underlying beamline principle and its practical implementation allow the collocation of chosen regions within the sample and their interrogation using real-space imaging (radiography and tomography) and reciprocal space scattering (diffraction). The switching between the two principal modes is made smooth and rapid by design, so that the data collected is interlaced to obtain near-simultaneous multimodal characterization. Different specific photon energies are used for each mode, and the interlacing of acquisition steps allows conducting static and dynamic experiments. Building on the demonstrated realization of this state-of-the-art approach requires further refining of the experimental practice, namely, the methods for gauge volume collocation under different modes of beam–sample interaction. To address this challenge, experiments were conducted at DIAD devoted to the study of human dental enamel, a hierarchical structure composed of hydroxyapatite mineral nanocrystals, as a static sample previously affected by dental caries (tooth decay) as well as under dynamic conditions simulating the process of acid demineralization. Collocation and correlation were achieved between WAXS (wide-angle X-ray scattering), 2D (radiographic), and 3D (tomographic) imaging. While X-ray imaging in 2D or 3D modes reveals real-space details of the sample microstructure, X-ray scattering data for each gauge volume provided statistical nanoscale and ultrastructural polycrystal reciprocal-space information such as phase and preferred orientation (texture). Careful registration of the gauge volume positions recorded during the scans allowed direct covisualization of the data from two modalities. Diffraction gauge volumes were identified and visualized within the tomographic data sets, revealing the underlying local information to support the interpretation of the diffraction patterns. The present implementation of the 4D microscopy paradigm allowed following the progression of demineralization and its correlation with time-dependent WAXS pattern evolution in an approach that is transferable to other material systems.

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Abstract: Current experimental and numerical quantification methods are limited in their ability to full-field mapping of the unpredictable distribution of all residual stress and permanent plastic strain components in additive manufacturing parts with discontinuous processing properties. To address this limitation, a tomographic eigenstrain (inherent strain) reconstruction method, that merges eigenstrain reconstruction with diffraction strain tomography for mapping volumetric distribution of all components of eigenstrains and corresponding elastic deformations like residual stresses non-destructively using minimum amount of tomographic scans is presented through numerical experiments, and then applied to the analysis of a CM 247 LC superalloy additive manufacturing part using diffraction strain tomography data. The method reconstructs all eigenstrain and corresponding residual stress components, parallel to the build direction, aligned with the experimental data component accurately, demonstrating its potential in optimizing the performance and reliability of parts designed for high-tech industries such as aerospace. Subsequent validations using the X-ray diffraction and neutron diffraction strain scanning techniques confirm the method's reliability in reconstructing residual stress components parallel to the plane of powder bed that are different from the experimental data component. Furthermore, the novel findings of this study reveal a characteristic residual stress distribution pattern within additive manufacturing parts particularly those featuring rectangular shapes. Microstructural analysis also validates eigenstrain distribution in accordance with the findings on the characteristic distribution of residual stresses, highlighting the significance of this method in advancing materials research and development.

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Abstract: Hydrodynamic cavitation is useful in many processing applications, for example, in chemical reactors, water treatment and biochemical engineering. An important type of hydrodynamic cavitation that occurs in a Venturi tube is vortex cavitation known to cause luminescence whose intensity is closely related to the size and number of cavitation events. However, the mechanistic origins of bubbles constituting vortex cavitation remains unclear, although it has been concluded that the pressure fields generated by the cavitation collapse strongly depends on the bubble geometry. The common view is that vortex cavitation consists of numerous small spherical bubbles. In the present paper, aspects of vortex cavitation arising in a Venturi tube were visualized using high-speed X-ray imaging at SPring-8 and European XFEL. It was discovered that vortex cavitation in a Venturi tube consisted of angulated rather than spherical bubbles. The tangential velocity of the surface of vortex cavitation was assessed considering the Rankine vortex model.

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Abstract: The formation of residual stresses is inevitable during the additive manufacturing of metallic parts due to thermo-mechanicals effects, but the chaotic nature of printing processes makes it impossible to have a comprehensive understanding about the magnitude and distribution of these residuals. The voxel-based eigenstrain (inherent strain) reconstruction method is capable of the full-field reconstruction of residual stresses in discontinuous processing bodies at a scale that depends on the resolution of experimental data without using simplifying assumptions and regularisation functions. This advanced method firstly maps the distribution of eigenstrains and then quantifies corresponding residual stresses, residual elastic strains, and displacements by a cost-effective linear elastic computational framework. The reliability of this process solely depends on the quality of experimental data and the availability of computational power. The motivation behind this study is the use of the voxel-based eigenstrain reconstruction method for the full-field mapping of complex residual stress fields, that cannot be predicted by regularizing assumptions, in discontinuous processing additive manufacturing parts. The height Digital Image Correlation (hDIC) technique satisfied the need for high-quality experimental data by calculating triaxial displacements, corresponding to the elastic response of CM 247 LC powder bed fusion (PBF) additive manufacturing part after changes in the boundary conditions due to separation from the base, using optical profilometry measurements at a resolution adjusted in a way to reconstruct Type I residual stresses. Three components of displacements calculated by the hDIC were used to map the distribution of three components of eigenstrains for the reconstruction of six residual stress, six residual elastic strain and three displacement components that belong to the before and after separating from the base states. The reliability of calculations has been validated by monochromatic synchrotron X-ray beams in powder diffraction mode from the same surface of optical profilometry measurements and in transmission mode from the sampling volumes.