Experimental Deformation Data Research Articles

Moving Particle Semi-Implicit and Finite Element Method Coupled Analysis for Brain Shift Estimation

Neuronavigation is a computer-assisted technique for presenting three-dimensional images of a patient’s brain to facilitate immediate and precise lesion localization by surgeons. Neuronavigation systems use preoperative medical images of patients. In neurosurgery, when the dura mater and arachnoid membrane are incised and the cerebrospinal fluid (CSF) drains out, the brain loses the CSF buoyancy and deforms in the direction of gravity, which is referred to as brain shift. This brain shift yields inaccurate neuronavigation. To reduce this inaccuracy, an intraoperative brain shift should be estimated. This paper proposes a dynamic simulation method for brain-shift estimation combining the moving-particle semi-implicit (MPS) method and the finite element method (FEM). The CSF was modeled using fluid particles, whereas the brain parenchyma was modeled using finite elements (FEs). Node particles were attached to the surface nodes of the brain parenchyma in the FE model. The interaction between the CSF and brain parenchyma was simulated using the repulsive force between the fluid particles and node particles. Validation experiments were performed using a gelatin block. The gelatin block was dipped into silicone oil, which was then gradually removed; the block deformation owing to the buoyancy loss was measured. The experimental deformation data were compared with the results of the MPS-FEM coupled analysis. The mean absolute error (MAE) between the simulated deformation and the average across the four experiments was 0.26 mm, while the mean absolute percentage error (MAPE) was 27.7%. Brain-shift simulations were performed using the MPS-FEM coupled analysis, and the computational cost was evaluated.

Extensive CGMD Simulations of Atactic PS Providing Pseudo Experimental Data to Calibrate Nonlinear Inelastic Continuum Mechanical Constitutive Laws.

In this contribution, we present a characterization methodology to obtain pseudo experimental deformation data from CG MD simulations of polymers as an inevitable prerequisite to choose and calibrate continuum mechanical constitutive laws. Without restriction of generality, we employ a well established CG model of atactic polystyrene as exemplary model system and simulate its mechanical behavior under various uniaxial tension and compression load cases. To demonstrate the applicability of the obtained data, we exemplarily calibrate a viscoelastic continuum mechanical constitutive law. We conclude our contribution by a thorough discussion of the findings obtained in the numerical pseudo experiments and give an outline of subsequent research activities. Thus, this work contributes to the field of multiscale simulation methods and adds a specific application to the body of knowledge of CG MD simulations.

Semantic modeling of plastic deformation of polycrystalline rock

We have developed the first iteration of the Plastic Rock Deformation (PRD) ontology by modeling the semantics of a selected set of deformational processes and mechanisms that produce, reconfigure, displace, and/or consume the material components of inhomogeneous polycrystalline rocks. The PRD knowledge model also classifies and formalizes the properties (relations) that hold between instances of the dynamic physical and chemical processes and the rock components, the complex physio-chemical, mathematical, and informational concepts of the plastic rock deformation system, the measured or calculated laboratory testing conditions, experimental procedures and protocols, the state and system variables, and the empirical flow laws that define the inter-relationships among the variables.The ontology reuses classes and properties from several existing ontologies that are built for physics, chemistry, biology, and mathematics. With its flexible design, the PRD ontology is well positioned to incrementally develop into a model that more fully represents the knowledge of plastic deformation of polycrystalline rocks in the future. The domain ontology will be used to consistently annotate varied data and information related to the microstructures and the physical and chemical processes that produce them at different spatial and temporal scales in the laboratory and in the solid Earth. The PRDKB knowledge base, when built based on the ontology, will help the community of experimental structural geologists and metamorphic petrologists to coherently and uniformly distribute, discover, access, share, and use their data through automated reasoning and integration and query of heterogeneous experimental deformation data that originate from autonomous rock testing laboratories.

Twisted and coiled polymer (TCP) muscles embedded in silicone elastomer for use in soft robot

Researchers are seeking to create robots that could conform to non-uniform objects during handling and manipulation. High performance artificial muscles are the key factors that determine the capabilities of a robot. Twisted and coiled polymeric (TCP) muscle embedded in soft silicone skin solves some of the problems of soft robots in attaining morphed structure using low voltages, contrary to other technologies such as dielectric elastomer and piezoelectric. Furthermore, the TCP actuation system does not generate noise like pneumatic systems. The TCP embedded skin shows great promise for robotics to mimic the flexible appendages of certain animals. In this paper, we present experimental results on the effect of muscle placement and the thickness of the artificial skin on the actuation behavior, which can be used as a benchmark for modeling. We demonstrate the effect of three different skin thicknesses and three different muscle locations within the skin, by taking experimental deformation data from stereo camera. In general, two modes of actuations (undulatory and bending) were observed depending on the muscle placement, skin thickness, applied voltage, and actuation time. The thinner skin showed two-wave undulatory actuation in most cases, whereas the 4 mm skins showed mixed actuation and the 5 mm skins exhibited one-wave undulatory actuation. In all cases, the increase in voltage resulted in higher magnitudes of actuation. In addition, we showed consistent strain of the TCP muscles from 18 samples from two batches that produced an average strain of 22% (batch 1) to 20% (batch 2) with standard deviation of 2.5–1.8% respectively.

고강도강 차체 박판부품 프레스성형 CAE의 예측 정확도 고찰

In the current study finite element forming analysis is performed to understand the final geometric accuracy limitations for the stamping of an automotive S-rail from four different steel sheets having tensile strengths of 340MPa, 440MPa, 590MPa and 780MPa. Comparisons between the analysis and the experiments for both springback and formability as measured by the amount of edge draw-in and the thickness distribution were conducted. The springback modes were classified according to a scheme proposed in the current investigation and the error was calculated using the normalized root mean square error method. While the analysis results show fairly good agreement with the experimental data for deformation and formability, the simulation accuracy is lower for predicting wall curl, camber and section twist as the UTS of steel sheet increases.

Magnetite deformation mechanism maps for better prediction of strain partitioning

AbstractA meta‐analysis of existing experimental deformation data for magnetite and other spinel‐structured ferrites reveals that previously published flow laws are inadequate to describe the general deformation behavior of magnetite. Using updated rate equations for oxygen diffusion in magnetite, we present new flow laws that closely predict creep rates similar to those found in deformation experiments and that can be used to predict strain partitioning between cubic Fe oxides and other phases in the Earth's crust. New deformation mechanism maps for magnetite have been constructed as functions of temperature and grain size. Using the revised creep parameters, estimates of strain partitioning between magnetite, ilmenite, and plagioclase indicate that concentrated zones of Fe‐Ti oxides in oceanic crust near slow‐spreading ridges could accommodate significant amounts of strain at moderate temperatures and may contribute to aseismic creep along spreading‐segment faults.

Stiffness of the Extrafibrillar Phase in Staggered Biological Arrays

A number of important biological tissues such as nacre, tendon, and bone consist of staggered structural arrays as universal motifs. Such arrays usually include stiff fibril-like (or plateletlike, or needlelike) elements embedded in an extrafibrillar (XF) phase. This work discusses the effect of the stiffness of such an XF matrix on the elastic properties of the resulting staggered composite. In the case of most biological composites, this XF stiffness is hardly accessible and very little data are available. We develop an analysis based on previous analytical formulation that results in a relation between the XF modulus and the deformations of the staggered particles. This analysis is then used to back-calculate the yet unmeasured modulus of the XF phase from experimental deformation data, thereby providing a simple alternative to potentially complex direct measurements. This is demonstrated and validated for parallel-fiber bone tissue.

Characterization of High Temperature Mechanical Properties for Lithium Metatitanate Pebble Beds

Lithium metatitanate (Li2TiO3) is a candidate tritium breeding material for fusion reactor blankets. In an actual blanket the pebbles are geometrically confined in a containing structure subjected to displacement and stress constraints under operating conditions. For an accurate description of pebble behavior during operations, existing data of pebble deformation under compressive loads is inadequate. In this study a uniaxial compression experimental apparatus was built to investigate time dependent creep on a single pebble as a function of applied force and temperature relevant to blanket conditions. Experimental results shows that at a temperature range of 700-800 °C, the crush load of Li2TiO3 pebbles is reduced by about half of its room temperature crush load. The experimental results allow for the establishment of a pebble creep failure map as a function of force and temperature, which provides guidance to the blanket designs. The study also introduces an FEA model based on experimental deformation data to obtain the constitutive equation needed for Discrete Element Model simulation of the pebble bed.

Determination of stress–strain relationship of tubular material with hydraulic bulge test

Based on the plastic membrane theory and force equilibrium equations, etc., a unique approach is proposed with the curve fitting of experimental data to determine the stress–strain relationship of a thin-walled tube in hydroforming process (THF). A simple and practical hydraulic bulge test tooling was developed and free-bulged tests were performed on stainless steel and low carbon steel tubes to obtain required experimental deformation data. Finite element (FE) simulations of the free bulges were carried out to verify the approach indirectly. The results indicate that the present approach is accurate and acceptable to define the stress–strain behavior of tubular material, and furthermore, an extended flow stress curve with large strain can be obtained by the approach.

Finite Element Analysis of Cable Products for High Impaction and Fatigue Resistance with Nonlinear Material Models

This paper presents experimental and numerical simulation for deformation and fatigue life prediction of various cables, such as electrical, optical and network cables. The cable damage is produced by the tensile, bending and torsional action under moving and fixing condition, and by direct external impact. To obtain material responses of the cable, uniaxial tensile tests and drop-weight impact tests were adopted, and the nonlinear constitutive equations based on various strain energy potentials or material models were employed to analyze deformation of polymer sheath and metallic armor layer of the cable. Finite element results were compared with experimental data for deformation and impact absorption energy of the cable during direct external impact. Also, fatigue strength of the cable was predicted from variation of calculated stress level under tensile conditions. Fractured surface of the cable were analyzed by scanning electron microscopy (SEM).

Calculation of spherical red blood cell deformation in a dual-beam optical stretcher

We present a numerical method based on the linear elastic membrane theory to compute the morphological deformation of a spherical cell from the photonics stress distribution over the cellular membrane. The method is applied to fit the experimental data for deformation of a spherical human red blood cell trapped and stretched in a fiber-optical dual-beam trap with a single fitting parameter Eh where E is the Young's modulus of elasticity and h is the thickness of the cell membrane. We obtained Eh = (20+/-2)muNm(-1) which is comparable to results reported earlier. This numerical method can be applied in general experimental conditions.

Microstructures, textures and deformation mechanisms in hematite

Deformation and recrystallization of hematite in iron formations and high-grade ore bodies of the Cauê Formation from the Quadrilátero Ferrı́fero District, Minas Gerais, Brazil, resulted in several types of fabrics, depending on the tectonic and metamorphic imprint. The fabrics vary from randomly oriented granoblastic to strongly oriented lepidoblastic/mylonitic with local development of cataclastic features.Complete pole figures of the crystallographic planes (003)-basal plane; {110}-prism and {104}-rhombohedron were measured on several samples from different areas by means of neutron diffraction revealing a typical crystallographic preferred orientation for the different fabric types. The configuration and intensity of the maxima are directly related to the magnitude of the deformation and the type of response of the ore.The analysis of the textures and microstructures of the iron ores and comparison with experimental deformation data lead us to the conclusion that three main mechanisms are active: basal slip, diffusion processes and anisotropic grain growth. Post-tectonic recrystallization and secondary grain growth did not affect the textures developed during deformation.

Densification Behavior of Ti-6Al-4V Power Compacts by Hot Isostatic Pressing

Densification behavior of titanium alloy powder was investigated under hot isostatic pressing at various pressures and temperatures. Uniaxial creep responses of a dense specimen were also obtained at high temperatures. The densification model of Abouaf and co-workers was implemented into a Finite element program (ABAQUS) to compare with experimental data for titanium alloy powder. The agreements between finite element calculations and experimental data for deformation and densification of titanium alloy powder were good during hot isostatic pressing,

Vibration mode separation of transient phenomena using multi-pulse digital holography

A rectangular flat metal plate is made to randomly vibrate when excited by a shaker. A digital holographic interferometry out-of- plane optical system is used to investigate the temporal development of the induced transient deformations. The system relies on two and four laser pulses emitted within a single envelope of the flashlamp contained in the oscillator cavity of a ruby laser, and also on three CCD cameras used to record two or four digital images resulting from the same number of holographic interferograms. Hologram data reconstruction is per- formed digitally and Fourier evaluated to obtain quantitative deformation data for each of the formed interferograms. The deformation data is bro- ken down into resonant mode components, sums of which are used to computer reconstruct the experimental deformation data. The error pro- duced when using a finite sum of resonant mode components is consid- ered. Experimental and computer reconstruction results for the transient vibration deformation of the plate are presented and compared. © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)01712-2)

Primary slip system of ε-iron and anisotropy of the Earth's inner core

Models which attribute the seismic anisotropy of the Earth's inner core to lattice preferred orientation due to plastic deformation, rely on the assumption that the slip systems are the same for hexagonal ε-iron and for titanium, taken as an analogue because of a similar c/ a ratio. However, metals with similar c/ a ratio may predominantly slip on different planes. In the absence of experimental deformation data on ε-iron, we have estimated its primary slip system using a theoretical criterion which has been shown to give correct results in all the cases where it has been tested. The criterion depends on the values of the stacking fault energies on basal and prism planes, which we have calculated from first principles. We find it probable that ε-iron predominantly slips on the basal plane, rather than on the prism planes as titanium. The consequences on the seismic anisotropy of the preferred orientation caused by plastic deformation are analyzed. It is suggested that the observed seismic anisotropy is unlikely to be produced by low-order convection in the inner core.

Dislocations in mantle peeidotite nodules

Dislocation microstructures were investigated in 110 mantle peridotite nodules from basalts and kimberlites. Such an extensive study was made possible by the use of a powerful decoration technique. High voltage electron microscopy has also been used in several cases. Slip planes, dislocation wall spacings and dislocation densities were determined. The most frequent glide system is (010) [100], as expected from extrapolations of experimental deformation data and previous studies. The {110} 〈001〉 system is present in several samples but appears as a result of a late superimposed deformation. The nodules exhibit various degrees of recovery. Dynamic as well as static recrystallization is present. Dislocation densities and wall spacings are on average respectively of 6.10 6 cm −2 and 100μ for basalt nodules and 10 7 cm −2 and 16μ for kimberlite nodules. These results indicate a high temperature deformation under stresses in the 100–1000 bars range.