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I rapporten analyseres bestandsdata for rådyr baseret på vildtudbyttestatistikken (1955-2020) og påkørsler i trafikken (2003-2010, 2017-2019) med henblik på at beskrive bestandens sammensætning og status samt variation i tid og rum. Analyserne har særlig fokus på at tilvejebringe viden, som kan forklare nedgangen i det nationale vildtudbytte siden 2011. Tætheden (dyr per km2 landzone uden for hovedstadsområdet) af nedlagte og påkørte rådyr i perioden 2003-2020 var tæt positivt korreleret mellem kommuner (r = 0,82) og var højest i kommuner med mere end 25 % skovdække og 40-60 % dyrkningsareal samt øst for israndslinjen. Siden 1955 har de nationale vildtudbytter udvist fem forskellige vækstfaser: 1955-1980 (+1,8 % per år), 1980-1995 (+6 % per år), 1995-2000 (stabil), 2000-2011 (+2,7 % per år) og 2011-2020 (-4,3 % per år). Den nuværende nedgangsperiode indtraf først på Fyn (1996) og senest i Nordjylland (2013). Markante regionale fald i enkelte år (op til -23 % på Fyn) tyder på drastiske demografiske hændelser, såsom dødelige sygdomsudbrud. Gennemsnitsvægtene på lam og råer i vildtudbyttet var negativt korreleret med bestandstæthed på kommuneniveau. Fra 2013-2020 øgedes gennemsnitvægten for lam med 3 % og var stabil for ældre dyr. Når der blev korrigeret for bestandstæthed (som faldt i perioden), faldt den tæthedskorrigerede vægt dog gennem perioden for både lam og ældre dyr, hvilket tyder på at den økologiske bæreevne har været faldende. Antal lam per rå (udtryk for bestandens reproduktionsevne) var positivt korreleret med andelen af 2+-årige råer > 14 kg (brækket vægt), men ikke med bestandenes vækstrate. Dette kan indikere, at bestandenes vækstrater (som var negativ i undersøgelsesperioden) i højere grad har været drevet af dødelighed end af tæthedsafhængige reproduktionsrater. Modsat Danmark, hvor det nationale vildtudbytte er faldet med 42 % siden 2011, har vildtudbytterne i Sydnorge, Sydsverige og Nordtyskland været stabile. Det konkluderes, at de seneste to årtiers tilbagegang næppe skyldes øget prædation (ræv), konkurrence med andre hjortearter eller vejrforhold, men muligvis en kombination af en epidemisk sygdom i kombination med eller afledt af faldende økologisk bæreevne. Hvis de bestandsbiologiske årsager til den fortsatte bestandsmæssige tilbagegang, som er et unikt dansk fænomen, skal findes, forudsætter det formentlig målrettende bestandsbiologiske undersøgelser af mærkede dyrs overlevelse, reproduktion og adfærd i nutidens danske landskaber.

Grain boundary velocity has been believed to be correlated to curvature, and this is an important relationship for modeling how polycrystalline materials coarsen during annealing. We determined the velocities and curvatures of approximately 52,000 grain boundaries in a nickel polycrystal using three-dimensional orientation maps measured by high-energy diffraction microscopy before and after annealing at 800°C. Unexpectedly, the grain boundary velocities and curvatures were uncorrelated. Instead, we found strong correlations between the boundary velocity and the five macroscopic parameters that specify grain boundary crystallography. The sensitivity of the velocity to grain boundary crystallography might be the result of defect-mediated grain boundary migration or the anisotropy of the grain boundary energy. The absence of a correlation between velocity and curvature likely results from the constraints imposed by the grain boundary network and implies the need for a new model for grain boundary migration.

In situ x-ray diffraction was performed on shock-generated microjets composed of Sn and Sn–4Ag. Under low pressure drives (∼21 GPa), a significant fraction of the jet volume was found to be in the [Formula: see text] phase, and these crystallites were much smaller than the initial grain size of the material. Significant quantities of amorphous (molten) material were observed for higher drive pressures (∼25–35 GPa). The extent of melting at these pressures was greater than would be predicted for uniaxial shock loading. Diffraction patterns from the Sn–4Ag alloy showed a peak that is consistent with the expected Ag3Sn intermetallic phase. This peak remained evident under drive conditions where the sample was otherwise fully amorphous. This indicates a slushy or a mixed phase of liquid Sn and solid Ag3Sn. Given the eutectic character of this alloy, this observation is attributed to a kinetic limitation on the dissolution of Ag3Sn. This implies that a much broader range of drive conditions will lead to mixed phase jets and ejecta than would be predicted from the equilibrium melt boundary of such alloys.

The science and engineering communities have significant interest in experimental platforms to evaluate and improve models for dynamic material deformation. While well-developed platforms exist, there are still gaps to fill for strain and strain rate conditions accessed during impact and other high-rate loading scenarios. To fill one such gap for strength measurements, a platform was recently developed that accesses high strain rate ([Formula: see text]) and large strain ([Formula: see text]) conditions by measuring the transient closure of a cylindrical hole using in situ x-ray imaging. In the work reported here, further refinement of the platform is performed to reduce the potential effects of porosity and anelasticity on the measurement. This helps us to isolate the strength effects that are the focus of the experiment. The updated experimental configuration employs a two-layer flyer design and elongated target to reduce the magnitude of the tensile excursions associated with rarefaction wave interactions. This allows for a more direct assessment of strength models commonly used for dynamic simulations of metals. We apply the new technique to well-characterized tantalum material, allowing for a robust connection to other experimental techniques. Deformation localization can be a concern in large strain experiments, and to help inform future use of the experimental platform, we use simulations with a sub-zone treatment of shear banding to explore potential localization behavior. Overall, we develop and utilize an experimental configuration with improved isolation of strength effects that can be applied to an expanded range of materials.

Performance-based managed entry agreements (PB-MEAs) might allow patient access to new medicines, but practical hurdles make competent authorities for pricing and reimbursement (CAPR) reluctant to implement PB-MEAs. We explored if the feasibility of PB-MEAs might improve by better aligning regulatory postauthorization requirements with the data generation of PB-MEAs and by active collaboration and data sharing. Reviewers from seven CAPRs provided structured assessments of the information available at the European Medicines Agency (EMA) Web site on regulatory postauthorization requirements for fifteen recently authorized products. The reviewers judged to what extent regulatory postauthorization studies could help implement PB-MEAs by addressing uncertainty gaps. Study domains assessed were: patient population, intervention, comparators, outcomes, time horizon, anticipated data quality, and anticipated robustness of analysis. Reviewers shared general comments about PB-MEAs for each product and on cooperation with other CAPRs. Reviewers rated regulatory postauthorization requirements at least partly helpful for most products and across domains except the comparator domain. One quarter of responses indicated that public information provided by the EMA was insufficient to support the implementation of PB-MEAs. Few PB-MEAs were in place for these products, but the potential for implementation of PB-MEAs or collaboration across CAPRs was seen as more favorable. Responses helped delineate a set of conditions where PB-MEAs may help reduce uncertainty. In conclusion, PB-MEAs are not a preferred option for CAPRs, but we identified conditions where PB-MEAs might be worth considering. The complexities of implementing PB-MEAs remain a hurdle, but collaboration across silos and more transparency on postauthorization studies could help overcome some barriers. ispartof: International Journal Of Technology Assessment In Health Care vol:37 issue:e83 pages:1-11 ispartof: location:England status: Published online

In this work we demonstrate a method for leveraging high-fidelity, multi-physics simulations of high-speed impacts in a particular manufactured material to encode prior information regarding the impactor material's strength properties. Our simulations involve a material composed of stacked cylindrical ligaments impacted by a high-velocity aluminum plate. We show that deep neural networks of relatively simple architecture can be trained on the simulations to make highly-accurate inferences of the strength properties of the impactor material. We detail our neural architectures and the considerations that went into their design. In addition, we discuss the simplicity of our network architecture which lends itself to interpretability of learned features in radiographic observations.

The orientations, locations, and sizes of approximately 2500 grains in a Ni polycrystal were measured at six points in time during an interrupted annealing experiment by synchrotron x-ray based, near field high-energy diffraction microscopy. The volume changes were compared to the geometric characteristics of the grains in both the original microstructures and microstructures in which adjacent twin related domains were merged. Neither the size of a grain nor the number of its nearest neighbors correlates strongly to a grain's volume change over the time scale of this experiment. However, the difference between the number of neighbors a grain has, F, and the average number of neighbors of the neighboring grains have, " open=" F N N , is correlated to the volume change. A grain with more (fewer) neighbors than " open=" F N N usually grows (shrinks). The correlation between the volume change and F - " open=" F N N is obvious only if adjacent twin related domains are merged. The correct sign of the volume change is predicted by F - " open=" F N N about two thirds of the time. The results show that the volume change for a given grain is better predicted by comparing a grain's characteristics to its neighbor's characteristics than to the characteristics of the entire ensemble of grains.

Pressure–density relationships derived from the experimentally obtained shock and particle velocities are critical to define a material’s equation of state (EOS). Typically, impact experiments coupled with velocimetry are used to map a material’s Hugoniot. Limitations such as sample geometry and varying indices of refraction may prevent proper characterization using traditional techniques such as photon doppler velocimetry (PDV) or velocity interferometer system for any reflector (VISAR). Here, traditional Hugoniot measurements using PDV are compared to dynamic x-ray imaging encompassing two different sample geometries on the gas gun platform. Through each of these methods an experimentally derived Hugoniot is determined for a previously uncharacterized polymeric material, Somos Watershed XC11122, that is used 3D printed stereolithography parts. A Us–up relationship was determined to be Us = 2.93 us + 1.73 mm/μs through traditional PDV. Slope and sound speed values determined from x-ray imaging methods varied 11% from PDV measurements. Each method yielded a Hugoniot with densities similar to poly(methyl methacrylate) (PMMA). The similarity shows the viability of such analyses for dynamic properties and Hugoniot data. The performance and analysis of both PDV and dynamic x-ray measurements are laid out in this work. Comparing PDV and x-ray imaging highlights distinct advantages and disadvantages among each method. PDV provides less uncertainty for velocity measurements, however x-ray imaging is more spatially resolved allowing for shock steadiness observations of value when studying heterogeneous materials. Additionally, x-ray imaging provides greater insight into the shape and heterogeneity of the shock front as well as uniaxial strain state (1D zone) assumptions.

The flow stress in a metal is dependent on a variety of factors such as strain, strain rate, microstructure, and temperature. Experiments (i.e. quasi-static tensile testing or Kolsky bar testing) with well characterized stress states have been used to determine the relation between flow stress and these many factors. However, for higher strain rates (>105/s) there is a dearth of high-fidelity data at high plastic strains. Here, we present results of a recent in-situ gas-gun experimental technique that can probe strength effects at strain rates of >105/s. By measuring the diameter of a long cylindrical hole using x-ray imaging in conjunction with back surface velocimetry while the sample is subjected to controlled dynamic loading, the factors affecting flow stress can be inferred. Materials with higher dynamic flow stresses tend to exhibit less diameter reduction than materials with lower flow stresses all else being equal. Typically, the hole size is measured through imaging, but if the hole is blocked, it becomes necessary to infer the amount of closure from another diagnostic like velocimetry. We present preliminary analysis and results on the velocimetry traces from a suite of hole closure experiments that indicates hole size information may be embedded in velocimetry traces.

The dynamic response of structured materials, such as regular lattices, is nontrivial partly due to the interaction of mechanical waves throughout the structure and free surfaces as the material is dynamically compressed. The existence of an elastic precursor wave in additively manufactured lattices was recently shown to match theoretical predictions and simulation results. Following up on this work, we have investigated the behavior of the elastic precursor with propagation distance, impact speed, and impact material. Through a series of gas gun experiments coupled to X-ray phase contrast imaging measurements and complementary simulations, the elastic precursor wavespeed appears to be nearly independent of impact speed and impact material. We observed evidence for the sustained elastic wave propagation through many unit cells at four significantly different impact conditions. We compared these results with direct numerical simulations of the experiments and found good agreement.

The complex mechanical response of open-cell foams depends strongly on the hierarchy of length scales inherent in them, from engineering-part scale to the ligament scale through the grain scale down to the crystal-lattice scale. A first step toward understanding and predicting the coordinated mechanical response across length scales requires characterizing the open-cell foam structure in three dimensions at relevant scales. Here, we present an initial attempt to digitally represent a physically-realized aluminum alloy foam in terms of both its geometry/topology as well as its underlying crystallographic orientations by integrating several advanced techniques. Specifically, we use a combination of X-ray computed tomography and X-ray diffraction microscopy in conjunction with synthetic grain mapping. Experimental investigation of the foam shows relatively large grain sizes with respect to the ligament length scale, implying that competing mechanics at different length scales (i.e. grain scale vs. ligament scale) will need to be fully incorporated to understand the mechanical behavior of the foam. The integration of non-destructive measurement techniques with synthetic-data generation provides a path toward realistic modeling of bulk samples of open-cell metal foam resolved at the scale of individual grains.

Shockwave data on mineral‐forming compounds such as Mg2SiO4 are essential for understanding the interiors of Earth and other planets, but correct interpretation of these data depend on knowing the phase assemblage being probed at high pressure. Hence direct observations of the phase or phases making up the measured states along the forsterite Hugoniot are essential to assess whether kinetic factors inhibit the achievement of the expected equilibrium, phase‐separated assemblage. Previous shock recovery experiments on forsterite, which has orthorhombic space group Pbnm, show discrepant results as to whether forsterite undergoes segregation into its equilibrium phase assemblage of compositionally distinct structures upon shock compression. Here, we present the results of plate impact experiments on polycrystalline forsterite conducted at the Dynamic Compression Sector of the Advanced Photon Source. In situ x‐ray diffraction measurements were used to probe the crystal structure(s) in the shock state and to investigate potential decomposition into periclase and bridgmanite. In contrast to previous interpretations of the forsterite shock Hugoniot, we find that forsterite does not decompose, but instead reaches the forsterite III structure, which is a metastable structure of Mg_2SiO_4 with orthorhombic space group Cmc2_1.

Hydrogen embrittlement (HE) causes sudden, costly failures of metal components across a wide range of industries. Yet, despite over a century of research, the physical mechanisms of HE are too poorly understood to predict HE-induced failures with confidence. We use non-destructive, synchrotron-based techniques to investigate the relationship between the crystallographic character of grain boundaries and their susceptibility to hydrogen-assisted fracture in a nickel superalloy. Our data lead us to identify a class of grain boundaries with striking resistance to hydrogen-assisted crack propagation: boundaries with low-index planes (BLIPs). BLIPs are boundaries where at least one of the neighboring grains has a low Miller index facet—{001}, {011}, or {111}—along the grain boundary plane. These boundaries deflect propagating cracks, toughening the material and improving its HE resistance. Our finding paves the way to improved predictions of HE based on the density and distribution of BLIPs in metal microstructures., Exactly how hydrogen renders metals brittle is still unclear, and it remains a challenge to predict component failure due to hydrogen embrittlement. Here, the authors identify a class of grain boundaries in a nickel superalloy that deflects propagating cracks and improves alloy resistance to hydrogen.

Grain fracture and crushing are known to influence the macroscopic mechanical behavior of granular materials and be influenced by factors such as grain composition, morphology, and microstructure. In this paper, we investigate grain fracture and crushing by combining synchrotron x-ray computed tomography and three-dimensional x-ray diffraction to study two granular samples undergoing uniaxial compaction. Our measurements provide details of grain kinematics, contacts, average intra-granular stresses, inter-particle forces, and intra-grain crystal and fracture plane orientations. Our analyses elucidate the complex nature of fracture and crushing, showing that: (1) the average stress states of grains prior to fracture vary widely in their relation to global and local trends; (2) fractured grains experience inter-particle forces and stored energies that are statistically higher than intact grains prior to fracture; (3) fracture plane orientations are primarily controlled by average intra-granular stress and contact fabric rather than the orientation of the crystal lattice; (4) the creation of new surfaces during fracture accounts for a very small portion of the energy dissipated during compaction; (5) mixing brittle and ductile grain materials alters the grain-scale fracture response. The results highlight an application of combined x-ray measurements for non-destructive in situ analysis of granular solids and provide details about grain fracture that have important implications for theory and modeling.

Knowledge of the critical resolved shear stress (CRSS) values of different slip modes is important for accurately modeling plastic deformation of hexagonal materials. Here, we demonstrate that CRSS can be directly measured with an in-situ high energy X-ray diffraction microscopy (HEDM) experiment. A commercially pure Ti tensile specimen was deformed up to 2.6% strain. In-situ far-field HEDM experiments were carried out to track the evolution of crystallographic orientations, centers of masses, and stress states of 1153 grains in a material volume of 1.1 mm × 1 mm × 1 mm. Predominant prismatic slip was identified in 18 grains, where the orientation change occurred primarily by rotation around the c-axis during specimen deformation. By analyzing the resolved shear stress on individual slip systems, the estimated CRSS for prismatic slip is 96 ± 18 MPa. Predominant basal slip was identified in 22 other grains, where the orientation change occurred primarily by tilting the c-axis about an axis in the basal plane. The estimated CRSS for basal slip is 127 ± 33 MPa. The ratio of CRSSbasal/CRSSprismatic is in the range of 1.7–2.1. From indirect assessment, the CRSS for pyramidal 〈c+a〉 slip is likely greater than 240 MPa. Grain size and free surface effects on the CRSS value in different grains are also examined.

The enhanced properties of grain boundary engineered metals are a result of their unique microstructures, which contain large clusters of twinned grains, called twin related domains. These large twin related domains in grain boundary engineered Ni were found to form through recrystallization. Orientation mapping showed that sparse nucleation and multiple twinning resulted in twin related domains containing hundreds of grains connected together in complex morphologies. A correlation was found between the size of the twin related domains and the overall twin boundary fraction. The same correlation was also observed in Cu and a Ni superalloy, showing that this is a general observation for grain boundary engineered microstructures. This finding can be understood through the topology of the twin related domains and an accompanying scaling relation is provided. The crystal orientations contained within each twin related domain were observed to depend on both the spatial correlation of twinning variants and the degree of branching in the twin boundary network. The results suggest a natural way of quantifying grain boundary engineered microstructures and provide a step toward making a closer connection between processing, microstructure, and performance.

For understanding material performance under dynamic loading, there is significant interest in the strain rate dependence of material response and in the degree to which high-rate response depends on initial material state. Experimental tests at high strain rates (> 10 3 / s ) often use measurement of shape change to infer flow strength behavior. Given stress and strain heterogeneities, inferences about flow strength behavior from those observations are facilitated by comparisons with advanced simulations. A new plate impact-based experimental test is described, consisting of in situ X-ray imaging to observe the closure of a cylindrical hole during the passage of a pressure pulse of controlled amplitude and duration. With the goal of providing unique data regarding plastic response at high strain rates, the closure of the hole is measured through time using multi-frame imaging. A first set of experiments on copper examines the role of starting microstructure on material flow behavior. The experimental observations are compared with predictions from direct numerical simulations using the Preston-Tonks-Wallace (PTW) and the Mechanical Threshold Stress (MTS) flow strength models. The quantitative utility of the overall approach is demonstrated in that the results provide information about MTS model parameters associated with high-rate hardening behavior, with the parameters having been unconstrained by quasi-static experimental data.

We use high-energy X-ray diffraction microscopy (HEDM) to characterize the microstructure of Ni-base alloy 725. HEDM is a non-destructive technique capable of providing three-dimensional reconstructions of grain shapes and orientations in polycrystals. The present analysis yields the grain size distribution in alloy 725 as well as the grain boundary character distribution (GBCD) as a function of lattice misorientation and boundary plane normal orientation. We find that the GBCD of Ni-base alloy 725 is similar to that previously determined in pure Ni and other fcc-base metals. We find an elevated density of Σ9 and Σ3 grain boundaries. We also observe a preponderance of grain boundaries along low-index planes, with those along (1 1 1) planes being the most common, even after Σ3 twins have been excluded from the analysis.

Combined application of a near-field High Energy Diffraction Microscopy measurement of crystal lattice orientation fields and a tomographic measurement of pore distributions in a sintered nickel-based superalloy sample allows pore locations to be correlated with microstructural features. Measurements were carried out at the Advanced Photon Source beamline 1-ID using an X-ray energy of 65 keV for each of the measurement modes. The nickel superalloy sample was prepared in such a way as to generate significant thermally induced porosity. A three-dimensionally resolved orientation map is directly overlaid with the tomographically determined pore map through a careful registration procedure. The data are shown to reliably reproduce the expected correlations between specific microstructural features (triple lines and quadruple nodes) and pore positions. With the statistics afforded by the 3D data set, we conclude that within statistical limits, pore formation does not depend on the relative orientations of the grains. The experimental procedures and analysis tools illustrated are being applied to a variety of materials problems in which local heterogeneities can affect materials properties.

The concept of twin-limited microstructures has been explored in the literature as a crystallographically constrained grain boundary network connected via only coincident site lattice (CSL) boundaries. The advent of orientation imaging has made classification of twin-related domains (TRD) or any other orientation cluster experimentally accessible in 2D using EBSD. With the emergence of 3D orientation mapping, a comparison of TRDs in measured 3D microstructures is performed and compared against their 2D counterparts. The TRD analysis is performed on a conventionally processed (CP) and a grain boundary engineered (EM) high purity copper sample that have been subjected to successive anneal procedures to promote grain growth. The EM sample shows extremely large TRDs which begin to approach that of a twin-limited microstructure, while the TRDs in the CP sample remain relatively small and remote.

In an effort to reproduce computationally the observed evolution of microstructurally small fatigue cracks (MSFCs), a method is presented for generating conformal, finite-element (FE), volume meshes from 3D measurements of MSFC propagation. The resulting volume meshes contain traction-free surfaces that conform to incrementally measured 3D crack shapes. Grain morphologies measured using near-field high-energy X-ray diffraction microscopy are also represented within the FE volume meshes. Proof-of-concept simulations are performed to demonstrate the utility of the mesh-generation method. The proof-of-concept simulations employ a crystal-plasticity constitutive model and are performed using the conformal FE meshes corresponding to successive crack-growth increments. Although the simulations for each crack increment are currently independent of one another, they need not be, and transfer of material-state information among successive crack-increment meshes is discussed. The mesh-generation method was developed using post-mortem measurements, yet it is general enough that it can be applied to in-situ measurements of 3D MSFC propagation.

Architected lattices are gaining prominence for structural applications as additive manufacturing technologies mature. Emergent behavior, such as material jetting and wave propagation, arising from the open architecture has been observed under dynamic loading conditions. The origin of the observed jetting and how it might come about across a broad spectrum of lattice types, material compositions, length scales, and dynamic loading conditions is still an open question. The jetting behavior due to lattice structures was studied through a series of dynamic compression plate impact experiments with in situ x-ray imaging. The role of the impact conditions, the lattice spacing, the lattice architecture, and the lattice base material is explored in the context of promoting or suppressing jet formation. A transition from lattice-led to impactor-led jetting is observed above a certain impact threshold. Complementary direct numerical simulations were also performed to compare with the experiments, to study the underlying stress state giving rise to jetting, and to provide insight into conditions not accessed experimentally. We present a geometric argument on the competitive process leading to lattice and/or impactor jetting which incorporates base material properties, the periodicity of the lattice, and basic tunable length scales of the lattice. Using two-dimensional calculations, we further look at how tuning of a single parameter of the studied systems changes the observed jetting transition.

Accurately describing the dynamic compaction of granular materials is a persistent challenge in computational mechanics. Using a synchrotron x-ray source we have obtained detailed imaging of the ev...

The response of particulate materials to impulsive loading includes complex interactions between grains due to fracture and comminution and the presence of interstitial material. The quasi-static strength of saturated powders is related to the concept of “effective stress” in which the fluid stiffens the material response and reduces the shear strength. However, detailed information regarding the effects of saturation under dynamic loading is lacking since static equilibrium between phases cannot be assumed and the interaction becomes more complex. Recent experiments on the IMPULSE (IMPact System for ULtrafast Synchrotron Experiments) capability at the Dynamic Compression Sector (DCS) of the Advanced Photon Source (APS) have captured in-situ X-ray phase-contrast images of shock loaded soda lime glass spheres in dry and saturated conditions. Previous investigations have observed reduction of fragmentation attributed to “cushioning” of an interstitial fluid in impact recovery experiments. The differences between the modes of deformation and compaction are compared with direct numerical simulations showing that the cause of fracture is different. In drained (dry) impact experiments at 300 m/s, the fractures initiate near the contact point between grains. In fully saturated experiments with identical impact conditions, spallation is observed during the incident stress-wave passage in the glass before the H2O has equilibrated.

The study of dynamic compression of materials requires high precision spatial and temporal resolution to infer the material state at any given time. In ultra-fast imaging experiments such as those performed at the Dynamic Compression Sector at the Advanced Photon Source, the current CCD frame rate is less than the X-ray pulse rate necessitating that 4 CCDs be used to image a single scintillator screen to obtain the same projection of transmitted or diffracted beam at time intervals synchronized with the X-ray beam. The use of multiple-camera setups is often employed for a variety of reasons including enhancing the temporal resolution through interleaving frames or increasing the number of viewpoints, for example. Physical corrections are made to have each CCD approximately viewing the same field of view, however we present corrections that can be made after the data collection to further refine and be able to compare movements and changes in the sample between independent CCDs. These software corrections enable higher precision and higher fidelity comparison of position changes due to sample deformation. We present a method to correct images (or frames) as a demonstration toward high fidelity displacement measurements in these types of ultra-fast multi-camera setup experiments.

An important advance in understanding the mechanics of solids over the last 50 years has been development of a suite of models that describe the performance of engineering materials while accounting for internal fluctuations and anisotropies (ex., anisotropic response of grains) over a hierarchy of length scales. Only limited engineering adoption of these tools has occurred, however, because of the lack of measured material responses at the length scales where the models are cast. Here, we demonstrate an integrated experimental capability utilizing high energy X-rays that provides an in situ , micrometer-scale probe for tracking evolving microstructure and intergranular stresses during quasi-static mechanical testing. We present first-of-a-kind results that show an unexpected evolution of the intergranular stresses in a titanium alloy undergoing creep deformation. We also discuss the expectation of new discoveries regarding the underlying mechanisms of strength and damage resistance afforded by this rapidly developing X-ray microscopy technique.

We present a non-destructive in-situ measurement of three-dimensional (3D) microstructure evolution of 99.995 % pure polycrystalline copper during tensile loading using synchrotron radiation. Spatially resolved three-dimensional crystallographic orientation fields are reconstructed from the measured diffraction data obtained from a near-field high-energy X-ray diffraction microscopy (nf-HEDM), and the evolution of about 5000 3D bulk grains is tracked through multiple stages of deformation. Spatially resolved observation of macroscopic texture change, anisotropic deformation development, and the correspondence of different crystallographic parameters to defect accumulation are illustrated. Moreover, correlations between different crystallographic parameters, such as crystal rotation evolution, short- and long-range orientation gradient development, microstructural features, and grain size effects are investigated. The current state of data mining tools available to analyze large and complicated diffraction data is presented and challenges associated with extracting meaningful information from these datasets are discussed.

The Monte Carlo model is one of the most frequently used approaches to simulate grain growth, and retains a number of features that derive from the closely related Ising and Potts models. The suitability of these features for the simulation of grain growth is examined, and several modifications to the Hamiltonian and transition probability function are proposed. The resulting model is shown to not only reproduce the usual behaviors of grain growth simulations, but to substantially reduce the effect of the underlying pixel lattice on the microstructure as compared to contemporary simulations.

Far-field high-energy X-ray diffraction microscopy (HEDM) was used to study {1 0 1 ‾ 2}〈 1 ‾ 0 1 1〉 twinning in Ti. Twin nucleation within a bulk parent grain is observed at a resolved shear stress (RSS) of 225 MPa. During unloading, the RSS on the twin plane reversed sign, providing a driving force for detwinning. Formation of the twin, however, prevented the parent grain from returning to its original stress state even after complete unloading. The twin morphology and surrounding environment were examined using near-field HEDM.

© 2017 Acta Materialia Inc. The deformation behavior of metal lattice structures is extremely complex and challenging to predict, especially since strain is not uniformly distributed throughout the structure. Understanding and predicting the failure behavior for these types of light-weighting structures is of great interest due to the excellent scaling of stiffness- and strength-to weight ratios they display. Therefore, there is a need to perform simplified experiments that probe unit cell mechanisms. This study reports on high resolution mapping of the heterogeneous structural response of single unit cells to the macro-scale loading condition. Two types of structures, known to show different stress-strain responses, were evaluated using synchrotron radiation micro-tomography while performing in-situ uniaxial compression tests to capture the local micro-strain deformation. These structures included the octet-truss, a stretch-dominated lattice, and the rhombic-dodecahedron, a bend-dominated lattice. The tomographic analysis showed that the stretch- and bend-dominated lattices exhibit different failure mechanisms and that the defects built into the structure cause a heterogeneous localized deformation response. Also shown here is a change in failure mode for stretch-dominated lattices, where there appears to be a transition from buckling to plastic yielding for samples with a relative density between 10 and 20%. The experimental results were also used to inform computational studies designed to predict the mesoscale deformation behavior of lattice structures. Here an equivalent continuum model and a finite element model were used to predict both local strain fields and mechanical behavior of lattices with different topologies.

We performed experiments combining three-dimensional x-ray diffraction and x-ray computed tomography to explore the relationship between microstructure and local force and strain during quasistatic granular compaction. We found that initial void space around a grain and contact coordination number before compaction can be used to predict regions vulnerable to above-average local force and strain at later stages of compaction. We also found correlations between void space around a grain and coordination number, and between grain stress and maximum interparticle force, at all stages of compaction. Finally, we observed grains that fracture to have an above-average initial local void space and a below-average initial coordination number. Our findings provide (1) a detailed description of microstructure evolution during quasistatic granular compaction, (2) an approach for identifying regions vulnerable to large values of strain and interparticle force, and (3) methods for identifying regions of a material with large interparticle forces and coordination numbers from measurements of grain stress and local porosity.

Low-symmetry crystals and polycrystals have anisotropic mechanical properties which, given better understanding of their deformation modes, could lead to development of next generation materials. Understanding how grains in a bulk polycrystal interact will guide and improve material modeling. Here, we show that tensile twins, in hexagonal close-packed metals, form where the macroscopic stress does not generate appropriate shear stress and vice versa. We use non-destructive high-energy X-ray diffraction microscopy to map local crystal orientations in three dimensions in a series of tensile strain states in a zirconium polycrystal. Twins and intragranular orientation variations are observed and it is found that deformation-induced rotations in neighboring grains are spatially correlated with many twins. We conclude that deformation twinning involves complex multigrain interactions which must be included in polycrystal plasticity models.

An experimental methodology based on post-mortem measurements is proposed to quantify rates of propagation and crack-surface crystallography of a 3-D, naturally nucleated, microstructurally small fatigue crack (MSFC) in a polycrystalline aluminum alloy (Al–Mg–Si). The post-mortem characterization involves: scanning electron microscopy-based fractography to measure crack-front projections (marker bands) at known cycle counts during the load history, X-ray computed tomography to provide high-resolution reconstructions of the 3-D crack-surface morphology, and near-field high-energy X-ray diffraction microscopy to provide 3-D grain geometries and orientations adjacent to fatigue-crack surfaces. Local MSFC-propagation rates are measured by accounting for the 3-D crack-surface morphology and varied by two orders of magnitude in the Al–Mg–Si specimen. Both intergranular and transgranular MSFC evolution were observed, with the latter occurring along a wide range of crystallographic planes. The findings demonstrate: (i) the complexity and variability of 3-D MSFC evolution in the Al–Mg–Si alloy; and (ii) the viability of the post-mortem characterization approach for quantifying 3-D MSFC evolution in polycrystalline alloys.

The study of fatigue in metals, and fatigue initiation specifically, lends itself to analysis via an emerging set of characterization and modeling tools that describe polycrystals on the meso- or microstructural length scale. These include three-dimensional characterization techniques, elastic anisotropic and visco-plastic stress models, new approaches to the statistical description of stress and strain distributions, synthetic microstructure modeling, and improved tools for manipulating the large datasets generated. A specific example of analysis in both 2D and 3D of fatigue cracks in a nickel-based superalloy is given where all the cracks are effectively coincident with coherent twin boundaries. A spectral method is used to analyze the stress state based on a fully anisotropic elastic calculation. The results indicate that, although a high resolved shear stress is associated with the locations of the observed cracks, the length of the trace of the twin boundary is more strongly correlated with crack formation.

The response of polycrystals to plastic deformation is studied at the level of variations within individual grains, and comparisons are made to theoretical calculations using crystal plasticity (CP) . We provide a brief overview of CP and a review of the literature, which is dominated by surface observations. The motivating question asks how well does CP represent the mesoscale behavior of large populations of dislocations (as carriers of plastic strain). The literature shows consistently that only moderate agreement is found between experiment and calculation. We supplement this with a current example of microstructure evolution in the interior of a copper sample subjected to tensile deformation. Nondestructive measurements of orientation fields were performed using the near-field high-energy X-ray diffraction microscopy (nf-HEDM) technique at the Advanced Photon Source (APS). Starting at highly ordered grains, a single two-dimensional slice of microstructure containing ∼150 grains was followed through multiple strain states, where it tracked lattice rotations and defect accumulation of up to 14% elongation. In accord with the literature, at the scale of individual grains, comparison of observations with CP models indicates reasonable qualitative agreement but significant variations between simulation and experiment are apparent. The conclusion is that in order to be able to quantify the effects of microstructure on the distributions of slip, orientation change, and damage accumulation, the empirically derived constitutive relations used in continuum-scale simulations need to be improved. Equally important will be the development of large-scale simulations of polycrystals that directly model dislocations.