[en] Determination of the strains in a polycrystalline material using 4-D XRD reveals sub-grain and grain-to-grain behavior as a function of stress. Here 4-D XRD involves an experimental procedure using polychromatic micro-beam X-radiation (micro-Laue) to characterize polycrystalline materials in spatial location as well as with increasing stress. The in-situ tensile loading experiment measured strain in a model aluminum-sapphire metal matrix composite using the Advanced Light Source, Beam-line 7.3.3. Micro-Laue resolves individual grains in the polycrystalline matrix. Results obtained from a list of grains sorted by crystallographic orientation depict the strain states within and among individual grains. Locating the grain positions in the plane perpendicular to the incident beam is trivial. However, determining the exact location of grains within a 3-D space is challenging. Determining the depth of the grains within the matrix (along the beam direction) involved a triangulation method tracing individual rays that produce spots on the CCD back to the point of origin. Triangulation was experimentally implemented by simulating a 3-D detector capturing multiple diffraction images while increasing the camera to sample distance. Hence by observing the intersection of rays from multiple spots belonging to the corresponding grain, depth is calculated. Depth resolution is a function of the number of images collected, grain to beam size ratio, and the pixel resolution of the CCD. The 4DXRD method provides grain morphologies, strain behavior of each grain, and interactions of the matrix grains with each other and the centrally located single crystal fiber

[en] Local damage evolution in a composite is the primary micromechanical process determining its fracture toughness, strength, and lifetime. In this study, high energy X-ray microdiffraction was used to measure the lattice strains of both phases in a Ti-SiC fiber composite laminate. The data provided in situ load transfer information under applied tensile stress at the scale of the microstructure. To better understand damage evolution, predictions of a modified shear lag model were compared to the strain data. This comparison (1) demonstrated the importance of accounting for the matrix axial and shear stiffness, (2) optimized the stiffness ratio for load transfer, and (3) improved the interpretation of the ideal planar geometry commonly used in micromechanical composite models. In addition, the results proved the matrix within and around the damage zone sustained substantial axial load and locally yielded. It was also shown that an area detector is essential in such a diffraction study as it provides multi-axial strain data and helps eliminate the ''graininess'' problem

[en] A new method of sensing and analyzing three-dimensional (3D) x-ray diffraction (XRD) cones was introduced. Using a two-dimensional area detector, a sequence of frames was collected while moving the detector away from the sample with small equally spaced steps and keeping all other parameters constant. A 3D dataset was created from the subsequent frames. The 3D x-ray diffraction (XRD"3) pattern contains far more information than a one-dimensional profile collected with the conventional diffractometer and 2D x-ray diffraction (XRD"2). The present work discusses some fundamentals about XRD"3, such as the data collection method, 3D visualization, diffraction data interpretation and potential applications of XRD"3. (paper)

[en] A new method was developed using AFM images of a fiber surface to regenerate the surface roughness in 3D geometry, such as the cylindrical shape of a 'model' fiber. The Langevin equation was used to derive the fluctuations of a carbon fiber surface image. The equation contains two quantities, D⁽¹⁾ (h) and D⁽²⁾ (h) which in physics represent drift and diffusion coefficients. Knowing this coefficient and adding a proper noise function, a similar surface of larger dimension with the same statistical properties of the initial data was created. The generated surface was mapped into cylindrical coordinates, then a mesh generated. The resulting reconstructed surface, input over the geometry of a cylindrical shape, can be implemented for finite element analysis of a single fiber surrounded by matrix and generalized to a many fiber model.

[en] Highlights: • A novel in-situ technique is used for direct observation of air-filled space formation in cement paste microstructure. • Air-filled voids are observed to increase in volume and then decrease and stay constant. • The void size distribution changes from a few coarse voids to a large number of small and uniformly distributed voids. • It is suggested that the air-filled void changes are caused by exsolution. This paper follows the hydration of both portland cement and tricalcium silicate pastes between 30 min and 16 h of hydration. In-situ fast X-ray computed tomography (fCT) was used to make direct observations of the air-filled void formation in w/s of 0.40 to 0.70 with a micron resolution. The results show that over the first hour of the acceleration period the volume of air-filled voids reaches a maximum value and then decreases during the acceleration period and stays constant. The void distribution changes from a few coarse voids to a large number of smaller and more uniformly distributed voids. This behavior is suggested to be controlled by changes in the ionic strength that cause exsolution of dissolved air from the pore solution.

[en] While there is great interest in characterizing and modifying materials at the nanoscale, progress has been slow because few techniques allow for critical observations at this length scale. This work presents a data fusion technique that combines synchrotron-based X-ray nano computed tomography and nano X-ray fluorescence to non-destructively investigate complex nanoscale materials and provide combined three-dimensional (3-D) renderings of microstructure and chemistry. The technique has been named nano tomography-assisted chemical correlation (nTACCo) and is demonstrated on fly ash particles with nanoscale chemical inhomogeneities. Our findings show that nTACCo is capable of providing the concentration and location of seven different nano-inclusions within a particle. This work also provides direct observations of reactivity and chemical distribution of fly ash. This ability to combine 3-D structure and chemistry at the nanoscale will provide unprecedented tools for nanoscience in material science, biology, chemistry and medical science

[en] Disagreements about the mechanisms of cement hydration remain despite the fact that portland cement has been studied extensively for over 100 years. One reason for this is that direct observation of the change in microstructure and chemistry are challenging for many experimental techniques. This paper presents results from synchrotron nano X-ray tomography and fluorescence imaging. The data show unprecedented direct observations of small collections of C₃S particles before and after different periods of hydration in 15 mmol/L lime solution. X-ray absorption contrast is used to make three dimensional maps of the changes of these materials with time. The chemical compositions of hydration products are then identified with X-ray fluorescence mapping and scanning electron microscopy. These experiments are used to provide insight into the rate and morphology of the microstructure formation.

[en] The reasons for the start and end of the induction period of cement hydration remain a topic of controversy. One long-standing hypothesis is that a thin metastable hydrate forming on the surface of cement grains significantly reduces the particle dissolution rate; the eventual disappearance of this layer re-establishes higher dissolution rates at the beginning of the acceleration period. However, the importance, or even the existence, of this metastable layer has been questioned because it cannot be directly detected in most experiments. In this work, a combined analysis using nano-tomography and nano-X-ray fluorescence makes the direct imaging of early hydration products possible. These novel X-ray imaging techniques provide quantitative measurements of 3D structure, chemical composition, and mass density of the hydration products during the induction period. This work does not observe a low density product on the surface of the particle, but does provide insights into the formation of etch pits and the subsequent hydration products that fill them.

[en] The evolution of in situ elastic strain with cyclic tensile loading in each phase of a single Al₂O₃-fiber/aluminum-matrix composite was studied using neutron diffraction (ND). An analytical model appropriate for metal matrix composites (MMCs) was developed to connect the measured axial strain evolution in each phase with the possible micromechanical events that could occur during loading at room temperature: fiber fracture, interfacial slipping, and matrix plastic deformation. Model interpretation showed that the elastic strain evolution in the fiber and matrix was governed by fiber fracture and interface slipping and not by plastic deformation of the matrix, whereas the macroscopic stress-strain response of the composite was influenced by all three. The combined single-fiber composite model and ND experiment introduces a new and quick engineering approach for qualifying the micromechanical response in MMCs due to cyclic loading and fiber fracture