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Summary Compressive loading of granular materials causes inter-particle forces to develop and evolve into force chains that propagate through the granular body. At high-applied compressive stresses, inter-particle forces will be large enough to cause particle fracture, affecting the constitutive behavior of granular materials. The first step to modeling particle fracture within force chains in granular mass is to understand and model the fracture of a single particle using actual three-dimensional (3D) particle shape. In this paper, the fracture mode of individual silica sand particles was captured using 3D x-ray radiography and Synchrotron Micro-computed Tomography (SMT) during in situ compression experiments. The SMT images were used to reconstruct particle surfaces through image processing techniques. Particle surface was then imported into Abaqus finite element (FE) software where the experimental loading setup was modeled using the extended finite element method (XFEM) where particle fracture was compared to experimental fracture mode viewed in radiograph images that were acquired during experimental loading. Load-displacement relationships of the FE analysis were also compared with experimental measurements. 3D FE modeling of particle fracture offers an excellent tool to map stress distribution and monitors crack initiation and propagation within individual sand particles. Copyright © 2015 John Wiley & Sons, Ltd.

The constitutive behavior of sheared sand is highly influenced by particle morphology, gradation, mineralogy, specimen density, loading condition, stress path, and boundary conditions. The current literature lacks a three-dimensional (3D) systematic experimental study that investigates the influence of particle morphology, confining pressure, and specimen density on the failure mode of sheared sand. In this paper, surface texture, roundness, and sphericity of three uniform sands and glass beads with similar grain size were quantified by using 3D images of particles. In situ nondestructive 3D synchrotron microcomputed tomography (SMT) was used to monitor the deformation of medium-dense and very dense dry sand specimens that were tested under axisymmetric triaxial loading condition at 15 and 400 kPa confining pressures. The particles were identified and tracked in 3D as shearing progressed within the specimens, and maps of incremental particle translation and rotation were developed and used to uncover the relationship between particle morphology, specimen density, and confining pressure on the deformation and failure mode of sheared sand. This paper discusses the relationship between the failure mode and particle morphology, specimen density, and confining pressure. Scopus

High strain rate loading conditions such as blast, impact, or projectile penetration cause major damages to infrastructure and soils. Sand particles will likely fracture if they are exposed to such loading conditions. Modeling the constitutive behavior of sand deposits when they are subjected to dynamic loading requires a high-fidelity particle-scale analysis, calibration, and validation using experimental measurements. In this paper, natural sand particles with complex morphology, mineralogy, and grain size were randomly selected from the bulk material and were separated based on particle size and mineralogy. Intact particles were first imaged using a desktop X-ray computed tomography (CT) scanner to calculate morphology and provide further input to the mineralogy and internal structure. Each particle was placed between incident and transmitter bars of a Kolsky bar setup, and two optical images (side and top views) were collected to visualize the loading geometry and direction. Each particle was then dynamically loaded to failure, at which load and compressive displacement were measured. Some of recovered particle fragments were imaged using synchrotron microcomputed tomography (SMT) to determine the fracture mode and fracture surface. Weibull statistical analyses were performed and multivariable nonlinear regression was implemented, using particle characteristics as predictors. The paper discusses the influence of morphology, mineralogy, internal structure, and size of particles on dynamic particle failure strength.

Particle morphology plays a significant role in influencing engineering behavior of granular materials. Surface texture, roundness, and sphericity represent distinct multiscale measures needed to fully describe particle morphology. Most studies reported in the literature rely on two-dimensional (2D) projected images of particles with a few three-dimensional (3D) images that mostly focused on relatively large-size aggregate samples. In this paper, 3D synchrotron microcomputed tomography (SMT) was used to acquire high-resolution images of glass beads, F-35 Ottawa sand, #1 dry glass sand, GS#40 Columbia sand, Toyoura sand, and Hostun RF sand. New roundness and sphericity indexes are proposed and calculated for the samples based on 3D measurements of surface area, volume, and three orthogonal diameters of particles. In addition, the surface texture of particles were measured using optical interferometry technique. The measurements reported in this paper can serve as a good source for other researchers working on sands to build on these intrinsic particle properties to link engineering behavior of sands to their morphology. 2014 American Society of Civil Engineers. National Science Foundation Scopus

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Objective. Headache is a common reason for consulting the general practitioner. The goal of the investigation was to characterize the headache consultation rates, the associated symptoms, the frequency of diagnostic and therapeutic procedures, and the results of the encounter of patients with headache. Methods. Cross-sectional data were collected from randomly selected patients during the German SESAM 2 study and compared with unpublished but publicly available data from the Dutch Transition Project. Results. Headache accounts for up to five percent of all general practice consultations. Women consult the general practitioner for headache twice as often as men. Physical examination and drug prescription are the most frequent procedures. Most of the patients suffer from primary headache; secondary headache is due to upper respiratory tract infections or problems of the spinal column. Dangerous courses occur in very rare cases. Conclusion. This work confirms the findings of earlier studies regarding the management of patients that consult the general practitioner for headache. It broadens the preexisting database since cross-sectional data regarding headache in general practice was rarely published.

Granular materials are composed of discrete particles in contact with each other. At the micro scale, each particle is in contact with neighboring particles where individual particle properties and contact mechanics govern particle interaction. At the meso scale, multiparticle assemblies interact through contact networks at particle contact. In this paper, synchrotron X-ray micro-tomography (SMT) is used to study particle kinematic behavior during in situ axisymmetric triaxial testing. High-resolution SMT images are used to discretize and track individual particles at multiple SMT-imaging stages of axisymmetric triaxial experiment. A particle-tracking algorithm, similar to digital image correlation, was developed by the authors to track individual particles throughout the entire test, and particle kinematics are quantified at each imaging stage. The algorithm allows tracking of individual particles and quantifies the relative (between images) and absolute (total) translation and rotation of particles as the test progresses.

Field and laboratory tests were conducted on 10 projects during base course layer construction to evaluate the quality of the constructed base layers. Base aggregates were also collected from these sites for laboratory testing. The field testing program consisted of the in place density by the sand cone method, the dynamic cone penetration (DCP) test, the light weight deflectometer (LWD) test, and the GeoGauge test. Laboratory tests conducted are the particle size analysis, the standard compaction test (AASHTO T 99), and the repeated load triaxial test (AASHTO T 307) for determining the resilient modulus. Analyses were conducted on field and laboratory test results. High spatial variability in field density and moisture content exists in base course layers under construction, as demonstrated by the relative compaction test results. High variability exists along the depth of base course layers, as demonstrated by the dynamic cone penetrometer test results and the estimated profile of California Bearing Ratio (CBR) along the depth of the investigated base layers. Spatial variability and non-uniformity were also demonstrated by the results of the light weight deflectometer and GeoGauge, in which the layer modulus varies within a large range of values.