Volumetric Plasticity Research Articles

Development of a Multimode Field Deployable Lidar Instrument for Topographic Measurements of Unsaturated Soil Properties: Instrument Description

The hydrological and mechanical behavior of soil is determined by the moisture content, soil water (matric) potential, fines content, and plasticity. However, these parameters are often difficult or impractical to determine in the field. Remote characterization of soil parameters is a non-destructive data collection process well suited to large or otherwise inaccessible areas. A ground-based, field-deployable remote sensor, called the soil observation laser absorption spectrometer (SOLAS), was developed to collect measurements from the surface of bare soils and to assess the in-situ condition and essential parameters of the soil. The SOLAS instrument transmits coherent light at two wavelengths using two, continuous-wave, near-infrared diode lasers and the instrument receives backscattered light through a co-axial 203-mm diameter telescope aperture. The received light is split into a hyperspectral sensing channel and a laser absorption spectrometry (LAS) channel via a multi-channel optical receiver. The hyperspectral channel detects light in the visible to shortwave infrared wavelengths, while the LAS channel filters and directs near-infrared light into a pair of photodetectors. Atmospheric water vapor is inferred using the differential absorption of the on- and off-line laser wavelengths (823.20 nm and 847.00 nm, respectively). Range measurement is determined using a frequency-modulated, self-chirped, coherent, homodyne detection scheme. The development of the instrument (transmitter, receiver, data acquisition components) is described herein. The potential for rapid characterization of physical and hydro-mechanical soil properties, including volumetric water content, matric potential, fines content, and plasticity, using the SOLAS remote sensor is discussed. The envisioned applications for the instrument include assessing soils on unstable slopes, such as wildfire burn sites, or stacked mine tailings. Through the combination of spectroradiometry, differential absorption, and range altimetry methodologies, the SOLAS instrument is a novel approach to ground-based remote sensing of the natural environment.

Astrocytic water channel aquaporin-4 modulates brain plasticity in both mice and humans: a potential gliogenetic mechanism underlying language-associated learning.

The role of astrocytes in brain plasticity has not been extensively studied compared with that of neurons. Here we adopted integrative translational and reverse-translational approaches to explore the role of an astrocyte-specific major water channel in the brain, aquaporin-4 (AQP4), in brain plasticity and learning. We initially identified the most prevalent genetic variant of AQP4 (single nucleotide polymorphism of rs162008 with C or T variation, which has a minor allele frequency of 0.21) from a human database (n=60 706) and examined its functionality in modulating the expression level of AQP4 in an in vitro luciferase reporter assay. In the following experiments, AQP4 knock-down in mice not only impaired hippocampal volumetric plasticity after exposure to enriched environment but also caused loss of long-term potentiation after theta-burst stimulation. In humans, there was a cross-sectional association of rs162008 with gray matter (GM) volume variation in cortices, including the vicinity of the Perisylvian heteromodal language area (Sample 1, n=650). GM volume variation in these brain regions was positively associated with the semantic verbal fluency. In a prospective follow-up study (Sample 2, n=45), the effects of an intensive 5-week foreign language (English) learning experience on regional GM volume increase were modulated by this AQP4 variant, which was also associated with verbal learning capacity change. We then delineated in mice mechanisms that included AQP4-dependent transient astrocytic volume changes and astrocytic structural elaboration. We believe our study provides the first integrative evidence for a gliogenetic basis that involves AQP4, underlying language-associated brain plasticity.

Quasi-static crush behavior of hollow microtruss filled with NMF liquid

Nanoporous materials functionalized (NMF) liquid has high energy absorption efficiency which holds great promise in advanced protective and damping devices. In this work we incorporate the NMF liquid into hollow microtruss structures to construct a superior energy absorption system. The compressive deformation map of hollow microtruss is given, and then the yielding criterion of NMF liquid filled microtruss is proposed. The quasi-static crush behavior is systematically studied through FEM simulation, then the plastic deformation of the microtruss and NMF liquid are analyzed in detail. By filling NMF liquid into the microtruss the plastic buckling of the microtruss is effectively suppressed, so as to improve the load capacity as well as energy absorption efficiency more than two times for relative thin microtruss (t/R<0.02). The origin of the energy absorption enhancement comes from two parts: one is the volumetric plasticity of NMF liquid and the other part is plastic deformation enhancement of the microtruss. Furthermore, the strain hardening effect of the materials of microtruss can further improve the energy absorption of NMF liquid filled microtruss as the microtruss can hold larger infiltration pressure and reduce the plastic strain localization in the wrinkles of the microtruss to avoid the leaking of NMF liquid.

Cardiac volume regulation: transition among two phenotypes in heart failure (1073.2)

Background. Guidelines for heart failure (HF) with preserved ejection fraction (pEF) dictate that left ventricular (LV) end‐diastolic pressure &gt; 16 mmHg, EF &gt; 50% and end‐diastolic volume index (EDVI) &lt; 97 mL/m2. Only half of HF patients (pts) present with a classical pattern of reduced EF (rEF). Prevalence of transition from HFpEF to HFrEF reportedly constitutes (either way) as much as 39%. The volume regulation graph (VRG) is explored to theoretically elucidate this occurrence.Methods. LV EDVI and end‐systolic volume index (ESVI) by angiography are analyzed in 48 pts receiving betablockers, with HFpEF (n=35) and HFrEF (n=13) subgroups. Regression analysis for ESVI to EDVI yields VRG. The 2SE ranges and 98% CI limits show potential transition to the complementary territory.Results. For pEF: ESVI = 0.31 EDVI ‐ 2.55, r=0.51 and for rEF: ESVI = 0.66 EDVI ‐ 5.45, r=0.95. The 2SE zones show overlap, suggesting occurrence of transition, especially for 50 &lt; ESVI &lt; 100 mL/m2. An additional group of 44 pts with follow‐up (ranging from 27 to 2385 days) reveals that over time ESVI may decrease by 50% or increase by up to 250%, thus demonstrating LV volumetric plasticity. Notably, about 25% of HFpEF pts can transit to HFrEF territory with a 10% increase in ESVI, while some 40% would convert to HFpEF with a 10% reduction in ESVI.Conclusions. The VRG explains considerable transition from HFrEF to HFpEF and v.v., requiring only a 10% change of ESVI, or roughly a 10% alteration in EF. The novel VRG construct confirms observations from other longitudinal studies.

A phenomenological variational multiscale constitutive model for intergranular failure in nanocrystalline materials

We present a variational multiscale constitutive model that accounts for intergranular failure in nanocrystalline fcc metals due to void growth and coalescence in the grain boundary region. Following previous work by the authors, a nanocrystalline material is modeled as a two-phase material consisting of a grain interior phase and a grain boundary affected zone (GBAZ). A crystal plasticity model that accounts for the transition from partial dislocation to full dislocation mediated plasticity is used for the grain interior. Isotropic porous plasticity model with further extension to account for failure due to the void coalescence was used for the GBAZ. The extended model contains all the deformation phases, i.e. elastic deformation, plastic deformation including deviatoric and volumetric plasticity (void growth) followed by damage initiation and evolution due to void coalescence. Parametric studies have been performed to assess the model's dependence on the different input parameters. The model is then validated against uniaxial loading experiments for different materials. Lastly we show the model's ability to predict the damage and fracture of a dog-bone shaped specimen as observed experimentally.

Scanning Laser Optical Tomography Resolves Structural Plasticity during Regeneration in an Insect Brain

BackgroundOptical Projection Tomography (OPT) is a microscopic technique that generates three dimensional images from whole mount samples the size of which exceeds the maximum focal depth of confocal laser scanning microscopes. As an advancement of conventional emission-OPT, Scanning Laser Optical Tomography (SLOTy) allows simultaneous detection of fluorescence and absorbance with high sensitivity. In the present study, we employ SLOTy in a paradigm of brain plasticity in an insect model system.MethodologyWe visualize and quantify volumetric changes in sensory information procession centers in the adult locust, Locusta migratoria. Olfactory receptor neurons, which project from the antenna into the brain, are axotomized by crushing the antennal nerve or ablating the entire antenna. We follow the resulting degeneration and regeneration in the olfactory centers (antennal lobes and mushroom bodies) by measuring their size in reconstructed SLOTy images with respect to the untreated control side. Within three weeks post treatment antennal lobes with ablated antennae lose as much as 60% of their initial volume. In contrast, antennal lobes with crushed antennal nerves initially shrink as well, but regain size back to normal within three weeks. The combined application of transmission-and fluorescence projections of Neurobiotin labeled axotomized fibers confirms that recovery of normal size is restored by regenerated afferents. Remarkably, SLOTy images reveal that degeneration of olfactory receptor axons has a trans-synaptic effect on second order brain centers and leads to size reduction of the mushroom body calyx.ConclusionsThis study demonstrates that SLOTy is a suitable method for rapid screening of volumetric plasticity in insect brains and suggests its application also to vertebrate preparations.

A variational void coalescence model for ductile metals

We present a variational void coalescence model that includes all the essential ingredients of failure in ductile porous metals. The model is an extension of the variational void growth model by Weinberg et al. (Comput Mech 37:142---152, 2006). The extended model contains all the deformation phases in ductile porous materials, i.e. elastic deformation, plastic deformation including deviatoric and volumetric (void growth) plasticity followed by damage initiation and evolution due to void coalescence. Parametric studies have been performed to assess the model's dependence on the different input parameters. The model is then validated against uniaxial loading experiments for different materials. We finally show the model's ability to predict the damage mechanisms and fracture surface profile of a notched round bar under tension as observed in experiments.

Computational assessment of ballistic impact on a high strength structural steel/polyurea composite plate

Ballistic impact on a polyurea retrofitted high strength structural steel plate is simulated and validated. A soft material model for polyurea, which is capable of capturing complex mechanical behavior characterized by large strains, hysteresis, rate sensitivity, stress softening (Mullins effect), and deviatoric and volumetric plasticity, is calibrated against several uniaxial tension experiments and a three-dimensional release wave experiment to capture both the material point and bulk behaviors. A porous plasticity model is employed to model the high strength structural steel and localization elements are included to capture adiabatic shear bands and strain localization. The computational capabilities of these models are demonstrated by the prediction of the target plate displacement, which shows excellent agreement with experiments.

A variational constitutive model for soft biological tissues

In this paper, a fully variational constitutive model of soft biological tissues is formulated in the finite strain regime. The model includes Ogden-type hyperelasticity, finite viscosity, deviatoric and volumetric plasticity, rate and microinertia effects. Variational updates are obtained via time discretization and pre-minimization of a suitable objective function with respect to internal variables. Genetic algorithms are used for model parameter identification due to their suitability for non-convex, high dimensional optimization problems. The material behavior predicted by the model is compared to available tests on swine and human brain tissue. The ability of the model to predict a wide range of experimentally observed behavior, including hysteresis, cyclic softening, rate effects, and plastic deformation is demonstrated.

Modification of godunov's numerical scheme for solving problems of pulsed loading of soft soils

This paper considers a modification of the “predictor” stage of Godunov's discontinuity decay method for problems of nonlinear deformation of soft soils. Soil behavior is described by the Grigoryan's taking into account nonlinear diagrams of volumetric deformation, shear strength, and plasticity. Assumptions are formulated that reduce the auxiliary problem of the decay of a discontinuity in soils to the well‐known problem that has a unique solution. Examples of numerical calculations are given.

Load-Factor Stability Analysis of Embankments on Saturated Soil Deposits

A continuum-based finite-element methodology is established for quantifying the stability of earthen embankments built on saturated soil deposits. Within the methodology the soil is treated as a fluid-solid porous medium, in which the soil skeleton's constitutive behavior is modeled using a smooth elastoplastic cap model that features continuous coupling between deviatoric and volumetric plasticity. In the stability analysis procedure, self-weight of the embankment soils is monotonically increased at rates characteristic of the em- bankment construction time, until instability mechanisms develop. The transient effects of excess pore pressures and their impact on soil strength are explicitly modeled, allowing for computation of embankment safety factors against instability as a function of construction rate. Details on the proposed method are presented and discussed, including (1) how the construction rate of an embankment can be modeled; (2) how load-based safety factors can differ from resistance-based safety factors; and (3) solved example problems corresponding to a case history of an embankment failure. INTRODUCTION AND MOTIVATION The objective of this work is to develop methods for sta- bility analysis of earthen embankments constructed on satu- rated soil deposits. Using classical methods and assumptions, stability analysis of such systems typically proceeds using Mohr-Coulomb soil models and various slice-type methods (Nash 1987) and by assuming that the saturated soil has a response behavior that is either fully undrained (short-term response) or fully drained (long-term response). Because the computed factors of safety against instability associated with the fully drained and fully undrained soil assumptions are gen- erally not close in value, with undrained stabilities being sig- nificantly less than drained stabilities, the classical methods can leave considerable uncertainty directly attributable to time- dependent pore-pressure diffusion effects. Methods of slope stability analysis are thus needed that take into account the rate at which the embankment is constructed together with the spatially/temporally evolving pore-pressure field it generates in the underlying soil deposit. Such stability information is often needed by engineers planning safe yet timely rates of construction for embankment systems. When analyzing geotechnical systems, both load and resis- tance factors, analogous to those used in structural engineer- ing, can be used to quantify the stability of the system. Load factors of safety against instability are simply the ratio of the load magnitude that first generates instability of the system to the magnitude of the expected load, while the strength or re- sistance of the system is held constant. Resistance factors of safety against instability are the ratio of actual system strength (or resistance) to reduced system strength at which system in- stability first occurs, while holding the loading on the system fixed. Although classical slope stability methods (such as slice methods) typically produce resistance-type safety factors, both factors are valid, although not necessarily the same. In Swan and Seo (1999), where continuum/FEM models for computing both resistance and load factors of safety against instability were presented for soil slopes, it was shown that neither method is consistently more or less conservative than the other. In this work, load-based stability analysis is investigated for sand embankments constructed on soft, saturated clay soil deposits. Load-based stability analysis techniques are poten- tially attractive, because they quite naturally permit stability analysis of embankments as a function of construction time. Geotechnical analysts who utilize load-based safety factors and load-based stability analysis should be well aware of the differences between such methods and the more traditional re-

Isothermal Stress Relaxation in Passivated Alsicu- and Al- Lines with Different Aspect Ratios

ABSTRACTMechanical stress relaxation in passivateci metal lines generally has two components, shear relaxation at constant volume, changing the stress distribution, and volumetric relaxation changing the hydrostatic stress. In order to contribute to the understanding of the underlying mechanisms we have collected detailed data on relaxation of passivated Al- and AlSiCu-lines with different aspect ratios a (0.2 ≤ a ≤ 1) and different thicknesses. A bending beam technique was used to measure the stress of these lines during thermal cycling from RT to 450°C and isothermal relaxation at different temperatures between RT and 350°C. Main results are: i) During thermal cycling the stress at RT and the total stress amplitude increase with increasing aspect ratio a, while stress hysteresis formation increases with decreasing a. ii) During isothermal relaxation the relaxed stress is strongly dependent on temperature with maxima between 150 and 250°C. The maximum shifts to lower temperatures with decreasing aspect ratio. From the temperature dependence the effective activation energy of 0.6±0.3eV for AlSiCu can be determined, iii) Finite element calculation and the method of “eigenstrains” are used to estimate seperately volumetric (voiding) and shear plasticity in these lines. Clearly voiding dominates the isothermal stress relaxation in all measured samples.

A finite element model for the analysis of tailored pulse stimulation of boreholes

AbstractA constitutive model is described for the prediction of dynamic crack formation in geological media. The model includes a simple tensile failure criterion for crack formation and a soil plasticity model for both deviatoric and volumetric plasticity. Numerical results are presented which show that the model reproduces the observed dependence of fracture formation on loding rate for dynamic pressure loading of boreholes. The use of the model as a numerical tool for design is demonstrated through two example parameter studies.