Nonlinear viscoelastic characterization of polymer materials using a dynamic-mechanical methodology

NASA Technical Reports Server (NTRS)

Strganac, Thomas W.; Payne, Debbie Flowers; Biskup, Bruce A.; Letton, Alan

1995-01-01

Polymer materials retrieved from LDEF exhibit nonlinear constitutive behavior; thus the authors present a method to characterize nonlinear viscoelastic behavior using measurements from dynamic (oscillatory) mechanical tests. Frequency-derived measurements are transformed into time-domain properties providing the capability to predict long term material performance without a lengthy experimentation program. Results are presented for thin-film high-performance polymer materials used in the fabrication of high-altitude scientific balloons. Predictions based upon a linear test and analysis approach are shown to deteriorate for moderate to high stress levels expected for extended applications. Tests verify that nonlinear viscoelastic response is induced by large stresses. Hence, an approach is developed in which the stress-dependent behavior is examined in a manner analogous to modeling temperature-dependent behavior with time-temperature correspondence and superposition principles. The development leads to time-stress correspondence and superposition of measurements obtained through dynamic mechanical tests. Predictions of material behavior using measurements based upon linear and nonlinear approaches are compared with experimental results obtained from traditional creep tests. Excellent agreement is shown for the nonlinear model.

A numerical evaluation of the dynamical systems approach to wall layer turbulence

NASA Technical Reports Server (NTRS)

Berkooz, Gal

1990-01-01

This work attempts to test predictions based on the Dynamical Systems approach to Wall Layer Turbulence. We analyze the Dynamical Systems model for the nonlinear interaction mechanisms between the coherent structures and deduce qualitative behavior as expected. We then test for this behavior in data sets from D.N.S. The agreement is good, given the suboptimal conditions for the test. We discuss implications of this test and work to be done to deepen the understanding of control of turbulent boundary layers.

Developing, mechanizing and testing of a digital active flutter suppression system for a modified B-52 wind-tunnel model

NASA Technical Reports Server (NTRS)

Matthew, J. R.

1980-01-01

A digital flutter suppression system was developed and mechanized for a significantly modified version of the 1/30-scale B-52E aeroelastic wind tunnel model. A model configuration was identified that produced symmetric and antisymmetric flutter modes that occur at 2873N/sq m (60 psf) dynamic pressure with violent onset. The flutter suppression system, using one trailing edge control surface and the accelerometers on each wing, extended the flutter dynamic pressure of the model beyond the design limit of 4788N/sq m (100 psf). The hardware and software required to implement the flutter suppression system were designed and mechanized using digital computers in a fail-operate configuration. The model equipped with the system was tested in the Transonic Dynamics Tunnel at NASA Langley Research Center and results showed the flutter dynamic pressure of the model was extended beyond 4884N/sq m (102 psf).

Crash Padding Research : Vol. I. Material Mechanical Properties.

DOT National Transportation Integrated Search

1986-08-01

The dynamic mechanical properties of Uniroyal Ensolite AAC, a viscoelastic closed-cell foam rubber, are investigated by means of materials tests. Sufficient test data is presented to form a basis for one-dimensional (uniform compression) empirical co...

Mechanical performance of cervical intervertebral body fusion devices: A systematic analysis of data submitted to the Food and Drug Administration.

PubMed

Peck, Jonathan H; Sing, David C; Nagaraja, Srinidhi; Peck, Deepa G; Lotz, Jeffrey C; Dmitriev, Anton E

2017-03-21

Cervical intervertebral body fusion devices (IBFDs) are utilized to provide stability while fusion occurs in patients with cervical pathology. For a manufacturer to market a new cervical IBFD in the United States, substantial equivalence to a cervical IBFD previously cleared by FDA must be established through the 510(k) regulatory pathway. Mechanical performance data are typically provided as part of the 510(k) process for IBFDs. We reviewed all Traditional 510(k) submissions for cervical IBFDs deemed substantially equivalent and cleared for marketing from 2007 through 2014. To reduce sources of variability in test methods and results, analysis was restricted to cervical IBFD designs without integrated fixation, coatings, or expandable features. Mechanical testing reports were analyzed and results were aggregated for seven commonly performed tests (static and dynamic axial compression, compression-shear, and torsion testing per ASTM F2077, and subsidence testing per ASTM F2267), and percentile distributions of performance measurements were calculated. Eighty-three (83) submissions met the criteria for inclusion in this analysis. The median device yield strength was 10,117N for static axial compression, 3680N for static compression-shear, and 8.6Nm for static torsion. Median runout load was 2600N for dynamic axial compression, 1400N for dynamic compression-shear, and ±1.5Nm for dynamic torsion. In subsidence testing, median block stiffness (Kp) was 424N/mm. The mechanical performance data presented here will aid in the development of future cervical IBFDs by providing a means for comparison for design verification purposes. Published by Elsevier Ltd.

10.2 Thermal-Structural Testing

NASA Technical Reports Server (NTRS)

Hudson, Larry D.

2008-01-01

Objective: Test a C/SiC Ruddervator Subcomponent under relevant thermal, mechanical & dynamic loading a) Thermal-structural mission cycling for re-entry and hypersonic cruise conditions; b) High-temperature modal survey to study the effect of heating on mode shapes, natural frequencies and damping. Supports NASA ARMD Hypersonics Material & Structures Program. Partners: NASA Dryden / Langley / Glenn, Lockheed-Martin, Materials Research & Design, GE CCP Test Phases - Phase 1: Acoustic-Vibration Testing (LaRC) completed - Phase 2: Thermal-Mechanical Testing (DFRC) in assembly - Phase 3: Mechanical Testing (DFRC) in assembly

Fluid mechanics of dynamic stall. II - Prediction of full scale characteristics

NASA Technical Reports Server (NTRS)

Ericsson, L. E.; Reding, J. P.

1988-01-01

Analytical extrapolations are made from experimental subscale dynamics to predict full scale characteristics of dynamic stall. The method proceeds by establishing analytic relationships between dynamic and static aerodynamic characteristics induced by viscous flow effects. The method is then validated by predicting dynamic test results on the basis of corresponding static test data obtained at the same subscale flow conditions, and the effect of Reynolds number on the static aerodynamic characteristics are determined from subscale to full scale flow conditions.

Capture approximations beyond a statistical quantum mechanical method for atom-diatom reactions

NASA Astrophysics Data System (ADS)

Barrios, Lizandra; Rubayo-Soneira, Jesús; González-Lezana, Tomás

2016-03-01

Statistical techniques constitute useful approaches to investigate atom-diatom reactions mediated by insertion dynamics which involves complex-forming mechanisms. Different capture schemes based on energy considerations regarding the specific diatom rovibrational states are suggested to evaluate the corresponding probabilities of formation of such collision species between reactants and products in an attempt to test reliable alternatives for computationally demanding processes. These approximations are tested in combination with a statistical quantum mechanical method for the S + H2(v = 0 ,j = 1) → SH + H and Si + O2(v = 0 ,j = 1) → SiO + O reactions, where this dynamical mechanism plays a significant role, in order to probe their validity.

Testing of Composite Fan Vanes With Erosion-Resistant Coating Accelerated

NASA Technical Reports Server (NTRS)

Bowman, Cheryl L.; Sutter, James K.; Otten, Kim D.; Samorezov, Sergey; Perusek, Gail P.

2004-01-01

The high-cycle fatigue of composite stator vanes provided an accelerated life-state prior to insertion in a test stand engine. The accelerated testing was performed in the Structural Dynamics Laboratory at the NASA Glenn Research Center under the guidance of Structural Mechanics and Dynamics Branch personnel. Previous research on fixturing and test procedures developed at Glenn determined that engine vibratory conditions could be simulated for polymer matrix composite vanes by using the excitation of a combined slip table and electrodynamic shaker in Glenn's Structural Dynamics Laboratory. Bench-top testing gave researchers the confidence to test the coated vanes in a full-scale engine test.

Mechanical performance of hemp fiber polypropylene composites at different operating temperatures

Treesearch

Mehdi Tajvidi; Nazanin Motie; Ghonche Rassam; Robert H. Falk; Colin Felton

2010-01-01

In order to quantify the effect of temperature on the mechanical properties of hemp fiber polypropylene composites, formulations containing 25% and 40% (by weight) hemp fiber were produced and tested at three representative temperatures of 256, 296, and 336 K. Flexural, tensile, and impact tests, as well as dynamic mechanical analysis, were performed and the reduction...

Experimental Research Regarding The Motion Capacity Of A Robotic Arm

NASA Astrophysics Data System (ADS)

Dumitru, Violeta Cristina

2015-09-01

This paper refers to the development of necessary experiments which obtained dynamic parameters (force, displacement) for a modular mechanism with multiple vertebrae. This mechanism performs functions of inspection and intervention in small spaces. Mechanical structure allows functional parameters to achieve precise movements to an imposed target. Will be analyzed the dynamic of the mechanisms using simulation instruments DimamicaRobot.tst under TestPoint programming environment and the elasticity of the tension cables. It will be changes on the mechanism so that spatial movement of the robotic arm is optimal.

The long-term reliability of static and dynamic quantitative sensory testing in healthy individuals.

PubMed

Marcuzzi, Anna; Wrigley, Paul J; Dean, Catherine M; Adams, Roger; Hush, Julia M

2017-07-01

Quantitative sensory tests (QSTs) have been increasingly used to investigate alterations in somatosensory function in a wide range of painful conditions. The interpretation of these findings is based on the assumption that the measures are stable and reproducible. To date, reliability of QST has been investigated for short test-retest intervals. The aim of this study was to investigate the long-term reliability of a multimodal QST assessment in healthy people, with testing conducted on 3 occasions over 4 months. Forty-two healthy people were enrolled in the study. Static and dynamic tests were performed, including cold and heat pain threshold (CPT, HPT), mechanical wind-up [wind-up ratio (WUR)], pressure pain threshold (PPT), 2-point discrimination (TPD), and conditioned pain modulation (CPM). Systematic bias, relative reliability and agreement were analysed using repeated measure analysis of variance, intraclass correlation coefficients (ICCs3,1) and SE of the measurement (SEM), respectively. Static QST (CPT, HPT, PPT, and TPD) showed good-to-excellent reliability (ICCs: 0.68-0.90). Dynamic QST (WUR and CPM) showed poor-to-good reliability (ICCs: 0.35-0.61). A significant linear decrease over time was observed for mechanical QST at the back (PPT and TPD) and for CPM (P < 0.01). Static QST were stable over a period of 4 months; however, a small systematic decrease over time has been observed for mechanical QST. Dynamic QST showed considerable variability over time; in particular, CPM using PPT as the test stimulus did not show adequate reliability, suggesting that this test paradigm may be less useful for monitoring individuals over time.

Systematic development of reduced reaction mechanisms for dynamic modeling

NASA Technical Reports Server (NTRS)

Frenklach, M.; Kailasanath, K.; Oran, E. S.

1986-01-01

A method for systematically developing a reduced chemical reaction mechanism for dynamic modeling of chemically reactive flows is presented. The method is based on the postulate that if a reduced reaction mechanism faithfully describes the time evolution of both thermal and chain reaction processes characteristic of a more complete mechanism, then the reduced mechanism will describe the chemical processes in a chemically reacting flow with approximately the same degree of accuracy. Here this postulate is tested by producing a series of mechanisms of reduced accuracy, which are derived from a full detailed mechanism for methane-oxygen combustion. These mechanisms were then tested in a series of reactive flow calculations in which a large-amplitude sinusoidal perturbation is applied to a system that is initially quiescent and whose temperature is high enough to start ignition processes. Comparison of the results for systems with and without convective flow show that this approach produces reduced mechanisms that are useful for calculations of explosions and detonations. Extensions and applicability to flames are discussed.

A parameters optimization method for planar joint clearance model and its application for dynamics simulation of reciprocating compressor

NASA Astrophysics Data System (ADS)

Hai-yang, Zhao; Min-qiang, Xu; Jin-dong, Wang; Yong-bo, Li

2015-05-01

In order to improve the accuracy of dynamics response simulation for mechanism with joint clearance, a parameter optimization method for planar joint clearance contact force model was presented in this paper, and the optimized parameters were applied to the dynamics response simulation for mechanism with oversized joint clearance fault. By studying the effect of increased clearance on the parameters of joint clearance contact force model, the relation of model parameters between different clearances was concluded. Then the dynamic equation of a two-stage reciprocating compressor with four joint clearances was developed using Lagrange method, and a multi-body dynamic model built in ADAMS software was used to solve this equation. To obtain a simulated dynamic response much closer to that of experimental tests, the parameters of joint clearance model, instead of using the designed values, were optimized by genetic algorithms approach. Finally, the optimized parameters were applied to simulate the dynamics response of model with oversized joint clearance fault according to the concluded parameter relation. The dynamics response of experimental test verified the effectiveness of this application.

Accelerated Testing of Polymeric Composites Using the Dynamic Mechanical Analyzer

NASA Technical Reports Server (NTRS)

Abdel-Magid, Becky M.; Gates, Thomas S.

2000-01-01

Creep properties of IM7/K3B composite material were obtained using three accelerated test methods at elevated temperatures. Results of flexural creep tests using the dynamic mechanical analyzer (DMA) were compared with results of conventional tensile and compression creep tests. The procedures of the three test methods are described and the results are presented. Despite minor differences in the time shift factor of the creep compliance curves, the DMA results compared favorably with the results from the tensile and compressive creep tests. Some insight is given into establishing correlations between creep compliance in flexure and creep compliance in tension and compression. It is shown that with careful consideration of the limitations of flexure creep, a viable and reliable accelerated test procedure can be developed using the DMA to obtain the viscoelastic properties of composites in extreme environments.

Review: mechanical behavior of metal/ceramic interfaces in nanolayered composites—experiments and modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Nan; Liu, Xiang-Yang

In this study, recent experimental and modeling studies in nanolayered metal/ceramic composites are reviewed, with focus on the mechanical behaviors of metal/nitrides interfaces. The experimental and modeling studies of the slip systems in bulk TiN are reviewed first. Then, the experimental studies of interfaces, including co-deformation mechanism by micropillar compression tests, in situ TEM straining tests for the dynamic process of the co-deformation, thickness-dependent fracture behavior, and interrelationship among the interfacial bonding, microstructure, and mechanical response, are reviewed for the specific material systems of Al/TiN and Cu/TiN multilayers at nanoscale. The modeling studies reviewed cover first-principles density functional theory-based modeling,more » atomistic molecular dynamics simulations, and mesoscale modeling of nanolayered composites using discrete dislocation dynamics. The phase transformation between zinc-blende and wurtzite AlN phases in Al/AlN multilayers at nanoscale is also reviewed. Finally, a summary and perspective of possible research directions and challenges are given.« less

Review: mechanical behavior of metal/ceramic interfaces in nanolayered composites—experiments and modeling

DOE PAGES

Li, Nan; Liu, Xiang-Yang

2017-11-03

In this study, recent experimental and modeling studies in nanolayered metal/ceramic composites are reviewed, with focus on the mechanical behaviors of metal/nitrides interfaces. The experimental and modeling studies of the slip systems in bulk TiN are reviewed first. Then, the experimental studies of interfaces, including co-deformation mechanism by micropillar compression tests, in situ TEM straining tests for the dynamic process of the co-deformation, thickness-dependent fracture behavior, and interrelationship among the interfacial bonding, microstructure, and mechanical response, are reviewed for the specific material systems of Al/TiN and Cu/TiN multilayers at nanoscale. The modeling studies reviewed cover first-principles density functional theory-based modeling,more » atomistic molecular dynamics simulations, and mesoscale modeling of nanolayered composites using discrete dislocation dynamics. The phase transformation between zinc-blende and wurtzite AlN phases in Al/AlN multilayers at nanoscale is also reviewed. Finally, a summary and perspective of possible research directions and challenges are given.« less

Viscoelastic characterization of soft biological materials

NASA Astrophysics Data System (ADS)

Nayar, Vinod Timothy

Progressive and irreversible retinal diseases are among the primary causes of blindness in the United States, attacking the cells in the eye that transform environmental light into neural signals for the optic pathway. Medical implants designed to restore visual function to afflicted patients can cause mechanical stress and ultimately damage to the host tissues. Research shows that an accurate understanding of the mechanical properties of the biological tissues can reduce damage and lead to designs with improved safety and efficacy. Prior studies on the mechanical properties of biological tissues show characterization of these materials can be affected by environmental, length-scale, time, mounting, stiffness, size, viscoelastic, and methodological conditions. Using porcine sclera tissue, the effects of environmental, time, and mounting conditions are evaluated when using nanoindentation. Quasi-static tests are used to measure reduced modulus during extended exposure to phosphate-buffered saline (PBS), as well as the chemical and mechanical analysis of mounting the sample to a solid substrate using cyanoacrylate. The less destructive nature of nanoindentation tests allows for variance of tests within a single sample to be compared to the variance between samples. The results indicate that the environmental, time, and mounting conditions can be controlled for using modified nanoindentation procedures for biological samples and are in line with averages modulus values from previous studies but with increased precision. By using the quasi-static and dynamic characterization capabilities of the nanoindentation setup, the additional stiffness and viscoelastic variables are measured. Different quasi-static control methods were evaluated along with maximum load parameters and produced no significant difference in reported reduced modulus values. Dynamic characterization tests varied frequency and quasi-static load, showing that the agar could be modeled as a linearly elastic material. The effects of sample stiffness were evaluated by testing both the quasi-static and dynamic mechanical properties of different concentration agar samples, ranging from 0.5% to 5.0%. The dynamic nanoindentation protocol showed some sensitivity to sample stiffness, but characterization remained consistently applicable to soft biological materials. Comparative experiments were performed on both 0.5% and 5.0% agar as well as porcine eye tissue samples using published dynamic macrocompression standards. By comparing these new tests to those obtained with nanoindentation, the effects due to length-scale, stiffness, size, viscoelastic, and methodological conditions are evaluated. Both testing methodologies can be adapted for the environmental and mounting conditions, but the limitations of standardized macro-scale tests are explored. The factors affecting mechanical characterization of soft and thin viscoelastic biological materials are researched and a comprehensive protocol is presented. This work produces material mechanical properties for use in improving future medical implant designs on a wide variety of biological tissue and materials.

Reduced Nucleus Pulposus Glycosaminoglycan Content Alters Intervertebral Disc Dynamic Viscoelastic Mechanics

PubMed Central

Boxberger, John I.; Orlansky, Amy S.; Sen, Sounok; Elliott, Dawn M.

2009-01-01

The intervertebral disc functions over a range of dynamic loading regimes including axial loads applied across a spectrum of frequencies at varying compressive loads. Biochemical changes occurring in early degeneration, including reduced nucleus pulposus glycosaminoglycan content, may alter disc mechanical behavior and thus may contribute to the progression of degeneration. The objective of this study was to determine disc dynamic viscoelastic properties under several equilibrium loads and loading frequencies, and further, to determine how reduced nucleus glycosaminglycan content alters dynamic mechanics. We hypothesized (1) that dynamic stiffness would be elevated with increasing equilibrium load and increasing frequency, (2) that the disc would behave more elastically at higher frequencies, and finally, (3) that dynamic stiffness would be reduced at low equilibrium loads under all frequencies due to nucleus glycosaminoglycan loss. We mechanically tested control and chondroitinase-ABC injected rat lumbar motion segments at several equilibrium loads using oscillatory loading at frequencies ranging from 0.05 to 5 Hz. The rat lumbar disc behaved non-linearly with higher dynamic stiffness at elevated compressive loads irrespective of frequency. Phase angle was not affected by equilibrium load, although it decreased as frequency was increased. Reduced glycosaminoglycan decreased dynamic stiffness at low loads but not at high equilibrium loads and led to increased phase angle at all loads and frequencies. The findings of this study demonstrate the effect of equilibrium load and loading frequencies on dynamic disc mechanics and indicate possible mechanical mechanisms through which disc degeneration can progress. PMID:19539936

Simultaneous Contact Sensing and Characterizing of Mechanical and Dynamic Heat Transfer Properties of Porous Polymeric Materials

PubMed Central

Yao, Bao-Guo; Peng, Yun-Liang; Zhang, De-Pin

2017-01-01

Porous polymeric materials, such as textile fabrics, are elastic and widely used in our daily life for garment and household products. The mechanical and dynamic heat transfer properties of porous polymeric materials, which describe the sensations during the contact process between porous polymeric materials and parts of the human body, such as the hand, primarily influence comfort sensations and aesthetic qualities of clothing. A multi-sensory measurement system and a new method were proposed to simultaneously sense the contact and characterize the mechanical and dynamic heat transfer properties of porous polymeric materials, such as textile fabrics in one instrument, with consideration of the interactions between different aspects of contact feels. The multi-sensory measurement system was developed for simulating the dynamic contact and psychological judgment processes during human hand contact with porous polymeric materials, and measuring the surface smoothness, compression resilience, bending and twisting, and dynamic heat transfer signals simultaneously. The contact sensing principle and the evaluation methods were presented. Twelve typical sample materials with different structural parameters were measured. The results of the experiments and the interpretation of the test results were described. An analysis of the variance and a capacity study were investigated to determine the significance of differences among the test materials and to assess the gage repeatability and reproducibility. A correlation analysis was conducted by comparing the test results of this measurement system with the results of Kawabata Evaluation System (KES) in separate instruments. This multi-sensory measurement system provides a new method for simultaneous contact sensing and characterizing of mechanical and dynamic heat transfer properties of porous polymeric materials. PMID:29084152

Simultaneous Contact Sensing and Characterizing of Mechanical and Dynamic Heat Transfer Properties of Porous Polymeric Materials.

PubMed

Yao, Bao-Guo; Peng, Yun-Liang; Zhang, De-Pin

2017-10-30

Porous polymeric materials, such as textile fabrics, are elastic and widely used in our daily life for garment and household products. The mechanical and dynamic heat transfer properties of porous polymeric materials, which describe the sensations during the contact process between porous polymeric materials and parts of the human body, such as the hand, primarily influence comfort sensations and aesthetic qualities of clothing. A multi-sensory measurement system and a new method were proposed to simultaneously sense the contact and characterize the mechanical and dynamic heat transfer properties of porous polymeric materials, such as textile fabrics in one instrument, with consideration of the interactions between different aspects of contact feels. The multi-sensory measurement system was developed for simulating the dynamic contact and psychological judgment processes during human hand contact with porous polymeric materials, and measuring the surface smoothness, compression resilience, bending and twisting, and dynamic heat transfer signals simultaneously. The contact sensing principle and the evaluation methods were presented. Twelve typical sample materials with different structural parameters were measured. The results of the experiments and the interpretation of the test results were described. An analysis of the variance and a capacity study were investigated to determine the significance of differences among the test materials and to assess the gage repeatability and reproducibility. A correlation analysis was conducted by comparing the test results of this measurement system with the results of Kawabata Evaluation System (KES) in separate instruments. This multi-sensory measurement system provides a new method for simultaneous contact sensing and characterizing of mechanical and dynamic heat transfer properties of porous polymeric materials.

Acoustic emission: A useful tool for damage evaluation in composite materials

NASA Astrophysics Data System (ADS)

Mouzakis, Dionysios E.; Dimogianopoulos, Dimitrios G.

2018-02-01

High performance composites for aviation-related structures are prone to constant aging by environmental agents. Previous data from our work reported on the stiffening behaviour of glass fibre polyester composites used in the manufacturing of wind turbine blades. Airplanes from such composites are already on service nowadays. This justifies the detailed study of the exposure of high performance materials to environmental conditions such as varying temperature, humidity, ultraviolet radiation, in order to assess the impact of these important aging factors on their mechanical behaviour. The dramatic changes in the dynamic mechanical response of polymer matrix carbon fibre composites upon exposure to acceleration aging has been assessed in the present study. In order to assess the synergistic effect action of temperature and humidity on composites subjected to changes of temperature from -35 to +40 °C and humidity variations from <10% to 95% RH (non-condensing) specimens were stored in a climatic chamber for 60 days. Conditions were cycled, as if actual flight cycles of 3-4 hours per flight, were to be simulated. Dynamic mechanical analysis tests were performed in three point bending mode. Scanning of frequency and temperature were performed in order to determine both the viscoelastic response as well as the time-dependent behaviour of the aged materials. All tests were run both for aged and pristine materials for comparison purposes. Three point bending testing was performed in both static as well as in Dynamic mechanical analysis, for a range of temperatures and frequencies. Acoustic Emission damage detection was also performed during the three point bending test both in static and dynamic mode. The aged materials had gained in dynamic stiffness. In addition, that, the gain in the storage moduli, was accompanied by a decrease in the material damping ability, as determined by the tanδ parameter. In the final stages of the study, impact testing was performed on both pristine and aged specimens. The experimentally recorded force/time signals were utilized for concluding on the specimens' condition, by means of signal based damage detection methodologies. Effort was invested in utilizing signal analysis in order to get comparative aging-related information on the tested specimens in order to ultimately validate results of mechanical testing.

Small, high-pressure ratio compressor mechanical acceptance test, volume 2

NASA Technical Reports Server (NTRS)

Metty, G. R.; Shoup, W. I.

1973-01-01

The fabrication and mechanical testing of the high-pressure-ratio compressor are reported. Mechanical testing was performed to demonstrate overspeed capability, adequate rotor dynamics, electrical isolation of the gas bearing trunnion mounted diffuser and shroud and the effect of operating parameters (speed and pressure ratio) on clearance of the compressor test rig. The speed range covered was 20 to 120 percent of rated speed (80,000 rpm). Following these tests an acceptance test which consisted of a 5 hour run at 80,000 rpm was made with approximately design impeller to shroud clearances. For Vol. 1, see N73-26483.

Piezoelectric Response of Ferroelectric Ceramics Under Mechanical Stress

DTIC Science & Technology

2015-09-17

dynamic response, and predict mechanical breakdown of electronic materials, numerous testing techniques such as very high-g machines , drop towers...James C. Hierholzer for building the custom test fixture, Michael D. Craft for his help with static capacitance measurements, Bryan J. Turner, Scott D...ISOLA 370HR Board Specimen Test Set-Up . . . . . . . . . . . . . . . . . . 59 3.3 Printed Circuit Board Electrical Layout

High Gain Antenna System Deployment Mechanism Integration, Characterization, and Lessons Learned

NASA Technical Reports Server (NTRS)

Parong, Fil; Russell, Blair; Garcen, Walter; Rose, Chris; Johnson, Chris; Huber, Craig

2014-01-01

The integration and deployment testing of the High Gain Antenna System (HGAS) for the Global Precipitation Measurement mission is summarized. The HGAS deployment mechanism is described. The gravity negation system configuration and its influence on vertical, ground-based deployment tests are presented with test data and model predictions. A focus is made on the late discovery and resolution of a potentially mission-degrading deployment interference condition. The interaction of the flight deployment mechanism, gravity-negation mechanism, and use of dynamic modeling is described and lessons learned presented

High Gain Antenna System Deployment Mechanism Integration, Characterization, and Lessons Learned

NASA Technical Reports Server (NTRS)

Parong, Fil; Russell, Blair; Garcen, Walter; Rose, Chris; Johnson, Chris; Huber, Craig

2014-01-01

The integration and deployment testing of the High Gain Antenna System for the Global Precipitation Measurement mission is summarized. The HGAS deployment mechanism is described. The gravity negation system configuration and its influence on vertical, ground-based, deployment tests are presented with test data and model predictions. A focus is made on the late discovery and resolution of a potentially mission degrading deployment interference condition. The interaction of the flight deployment mechanism, gravity negation mechanism, and use of dynamic modeling is described and lessons learned presented.

Finite element simulation of location- and time-dependent mechanical behavior of chondrocytes in unconfined compression tests.

PubMed

Wu, J Z; Herzog, W

2000-03-01

Experimental evidence suggests that cells are extremely sensitive to their mechanical environment and react directly to mechanical stimuli. At present, it is technically difficult to measure fluid pressure, stress, and strain in cells, and to determine the time-dependent deformation of chondrocytes. For this reason, there are no data in the published literature that show the dynamic behavior of chondrocytes in articular cartilage. Similarly, the dynamic chondrocyte mechanics have not been calculated using theoretical models that account for the influence of cell volumetric fraction on cartilage mechanical properties. In the present investigation, the location- and time-dependent stress-strain state and fluid pressure distribution in chondrocytes in unconfined compression tests were simulated numerically using a finite element method. The technique involved two basic steps: first, cartilage was approximated as a macroscopically homogenized material and the mechanical behavior of cartilage was obtained using the homogenized model; second, the solution of the time-dependent displacements and fluid pressure fields of the homogenized model was used as the time-dependent boundary conditions for a microscopic submodel to obtain average location- and time-dependent mechanical behavior of cells. Cells and extracellular matrix were assumed to be biphasic materials composed of a fluid phase and a hyperelastic solid phase. The hydraulic permeability was assumed to be deformation dependent and the analysis was performed using a finite deformation approach. Numerical tests were made using configurations similar to those of experiments described in the literature. Our simulations show that the mechanical response of chondrocytes to cartilage loading depends on time, fluid boundary conditions, and the locations of the cells within the specimen. The present results are the first to suggest that chondrocyte deformation in a stress-relaxation type test may exceed the imposed system deformation by a factor of 3-4, that chondrocyte deformations are highly dynamic and do not reach a steady state within about 20 min of steady compression (in an unconfined test), and that cell deformations are very much location dependent.

Impact evaluation of composite floor sections

NASA Technical Reports Server (NTRS)

Boitnott, Richard L.; Fasanella, Edwin L.

1989-01-01

Graphite-epoxy floor sections representative of aircraft fuselage construction were statically and dynamically tested to evaluate their response to crash loadings. These floor sections were fabricated using a frame-stringer design typical of present aluminum aircraft without features to enhance crashworthiness. The floor sections were tested as part of a systematic research program developed to study the impact response of composite components of increasing complexity. The ultimate goal of the research program is to develop crashworthy design features for future composite aircraft. Initially, individual frames of six-foot diameter were tested both statically and dynamically. The frames were then used to construct built-up floor sections for dynamic tests at impact velocities of approximately 20 feet/sec to simulate survivable crash velocities. In addition, static tests were conducted to gain a better understanding of the failure mechanisms seen in the dynamic tests.

Utilization of the waste from the marble industry for application in transport infrastructure: mechanical properties of cement pastes

NASA Astrophysics Data System (ADS)

Prošek, Zdeněk; Trejbal, Jan; Topič, Jaroslav; Plachý, Tomáš; Tesárek, Pavel

2017-09-01

This article is focused on the mechanical testing of cement-based samples containing a micronized waste marble powder used as replacement of standard binders. Tested materials consisted of cement CEM I 42.5 R (Radotín, Czech Republic) and three different amounts of the marbles (25, 50 and 70 wt. %). Standard bending and compressive tests of the prismatic samples having dimensions equal to 40 × 40 × 160 mm were done in order to reveal an influence of marble amount on flexural and compressive strength, respectively. Moreover, the dynamic modulus of elasticity and dynamic shear modulus were examined and compared after 7 and 28 days of mixture curing.

Experimental analysis and constitutive modelling of steel of A-IIIN strength class

NASA Astrophysics Data System (ADS)

Kruszka, Leopold; Janiszewski, Jacek

2015-09-01

Fundamentally important is the better understanding of behaviour of new building steels under impact loadings, including plastic deformations. Results of the experimental analysis in wide range of strain rates in compression at room temperature, as well as constitutive modelling for and B500SP structural steels of new A-IIIN Polish strength class, examined dynamically by split Hopkinson pressure bar technique at high strain rates, are presented in table and graphic forms. Dynamic mechanical characteristics of compressive strength for tested building structural steel are determined as well as dynamic mechanical properties of this material are compared with 18G2-b steel of A-II strength class, including effects of the shape of tested specimens, i.e. their slenderness. The paper focuses the attention on those experimental tests, their interpretation, and constitutive semi-empirical modelling of the behaviour of tested steels based on Johnson-Cook's model. Obtained results of analyses presented here are used for designing and numerical simulations of reinforced concrete protective structures.

Modeling of light dynamic cone penetration test - Panda 3 ® in granular material by using 3D Discrete element method

NASA Astrophysics Data System (ADS)

Tran, Quoc Anh; Chevalier, Bastien; Benz, Miguel; Breul, Pierre; Gourvès, Roland

2017-06-01

The recent technological developments made on the light dynamic penetration test Panda 3 ® provide a dynamic load-penetration curve σp - sp for each impact. This curve is influenced by the mechanical and physical properties of the investigated granular media. In order to analyze and exploit the load-penetration curve, a numerical model of penetration test using 3D Discrete Element Method is proposed for reproducing tests in dynamic conditions in granular media. All parameters of impact used in this model have at first been calibrated by respecting mechanical and geometrical properties of the hammer and the rod. There is a good agreement between experimental results and the ones obtained from simulations in 2D or 3D. After creating a sample, we will simulate the Panda 3 ®. It is possible to measure directly the dynamic load-penetration curve occurring at the tip for each impact. Using the force and acceleration measured in the top part of the rod, it is possible to separate the incident and reflected waves and then calculate the tip's load-penetration curve. The load-penetration curve obtained is qualitatively similar with that obtained by experimental tests. In addition, the frequency analysis of the measured signals present also a good compliance with that measured in reality when the tip resistance is qualitatively similar.

A dynamic integrated fault diagnosis method for power transformers.

PubMed

Gao, Wensheng; Bai, Cuifen; Liu, Tong

2015-01-01

In order to diagnose transformer fault efficiently and accurately, a dynamic integrated fault diagnosis method based on Bayesian network is proposed in this paper. First, an integrated fault diagnosis model is established based on the causal relationship among abnormal working conditions, failure modes, and failure symptoms of transformers, aimed at obtaining the most possible failure mode. And then considering the evidence input into the diagnosis model is gradually acquired and the fault diagnosis process in reality is multistep, a dynamic fault diagnosis mechanism is proposed based on the integrated fault diagnosis model. Different from the existing one-step diagnosis mechanism, it includes a multistep evidence-selection process, which gives the most effective diagnostic test to be performed in next step. Therefore, it can reduce unnecessary diagnostic tests and improve the accuracy and efficiency of diagnosis. Finally, the dynamic integrated fault diagnosis method is applied to actual cases, and the validity of this method is verified.

A Dynamic Integrated Fault Diagnosis Method for Power Transformers

PubMed Central

Gao, Wensheng; Liu, Tong

2015-01-01

In order to diagnose transformer fault efficiently and accurately, a dynamic integrated fault diagnosis method based on Bayesian network is proposed in this paper. First, an integrated fault diagnosis model is established based on the causal relationship among abnormal working conditions, failure modes, and failure symptoms of transformers, aimed at obtaining the most possible failure mode. And then considering the evidence input into the diagnosis model is gradually acquired and the fault diagnosis process in reality is multistep, a dynamic fault diagnosis mechanism is proposed based on the integrated fault diagnosis model. Different from the existing one-step diagnosis mechanism, it includes a multistep evidence-selection process, which gives the most effective diagnostic test to be performed in next step. Therefore, it can reduce unnecessary diagnostic tests and improve the accuracy and efficiency of diagnosis. Finally, the dynamic integrated fault diagnosis method is applied to actual cases, and the validity of this method is verified. PMID:25685841

Spatiotemporal properties of microsaccades: Model predictions and experimental tests

NASA Astrophysics Data System (ADS)

Zhou, Jian-Fang; Yuan, Wu-Jie; Zhou, Zhao

2016-10-01

Microsaccades are involuntary and very small eye movements during fixation. Recently, the microsaccade-related neural dynamics have been extensively investigated both in experiments and by constructing neural network models. Experimentally, microsaccades also exhibit many behavioral properties. It’s well known that the behavior properties imply the underlying neural dynamical mechanisms, and so are determined by neural dynamics. The behavioral properties resulted from neural responses to microsaccades, however, are not yet understood and are rarely studied theoretically. Linking neural dynamics to behavior is one of the central goals of neuroscience. In this paper, we provide behavior predictions on spatiotemporal properties of microsaccades according to microsaccade-induced neural dynamics in a cascading network model, which includes both retinal adaptation and short-term depression (STD) at thalamocortical synapses. We also successfully give experimental tests in the statistical sense. Our results provide the first behavior description of microsaccades based on neural dynamics induced by behaving activity, and so firstly link neural dynamics to behavior of microsaccades. These results indicate strongly that the cascading adaptations play an important role in the study of microsaccades. Our work may be useful for further investigations of the microsaccadic behavioral properties and of the underlying neural dynamical mechanisms responsible for the behavioral properties.

Dynamic Crushing Response of Closed-cell Aluminium Foam at Variable Strain Rates

NASA Astrophysics Data System (ADS)

Islam, M. A.; Kader, M. A.; Escobedo, J. P.; Hazell, P. J.; Appleby-Thomas, G. J.; Quadir, M. Z.

2015-06-01

The impact response of aluminium foams is essential for assessing their crashworthiness and energy absorption capacity for potential applications. The dynamic compactions of closed-cell aluminium foams (CYMAT) have been tested at variable strain rates. Microstructural characterization has also been carried out. The low strain rate impact test has been carried out using drop weight experiments while the high strain compaction test has been carried out via plate impact experiments. The post impacted samples have been examined using optical and electron microscopy to observe the microstructural changes during dynamic loading. This combination of dynamic deformation during impact and post impact microstructural analysis helped to evaluate the pore collapse mechanism and impact energy absorption characteristics.

Measurement of the time-temperature dependent dynamic mechanical properties of boron/aluminum composites

NASA Technical Reports Server (NTRS)

Dicarlo, J. A.; Maisel, J. E.

1978-01-01

A flexural vibration test and associated equipment were developed to accurately measure the low strain dynamic modulus and damping of composite materials from -200 C to over 500 C. The basic test method involves the forced vibration of composite bars at their resonant free-free flexural modes in a high vacuum cryostat furnace. The accuracy of these expressions and the flexural test was verified by dynamic moduli and damping capacity measurements on 50 fiber volume percent boron/aluminum (B/Al) composites vibrating near 2000 Hz. The phase results were summarized to permit predictions of the B/Al dynamic behavior as a function of frequency, temperature, and fiber volume fraction.

Study on mechanical properties of steel honeycomb panel three-point bending specimen under in-plane and out-plane transverse dynamic impact load

NASA Astrophysics Data System (ADS)

Zou, Guangping; Chang, Zhongliang; Xia, Xingyou; Zhang, Xueyi

2010-03-01

The metal honeycomb material has high strength and high stiffness, as a high-performance sandwich panel, it is an ideal lightweight structural material, and widely used in aviation, aerospace, shipbuilding and other fields. In this paper, the improved SHPB instrument is used for testing the in-plane and out-plane mechanical properties of the steel honeycomb panel three-point bending specimen, and also compare the results with the static in-plane and out-plane three-point bending experiments results which is tested by the INSTRON 4505 electronic universal testing machine, and then study the mechanical properties of the steel honeycomb panel three-point bending specimen under transverse dynamic impact load. From the results it can be see that, for the out-plane three point bending experiment, L direction mechanical properties is better than the W direction, and the honeycomb core play an important role during the specimen deformation, while for the in-plane three point bending experiment, the honeycomb core mechanical role is not distinctness.

Investigation of transonic region of high dynamic response encountered on an elastic supercritical wing

NASA Technical Reports Server (NTRS)

Seidel, David A.; Eckstrom, Clinton V.; Sandford, Maynard C.

1987-01-01

Unsteady aerodynamic data were measured on an aspect ratio 10.3 elastic supercritical wing while undergoing high dynamic response above Mach number of 0.90. These tests were conducted in the NASA Langley Transonic Dynamics Tunnel. A previous test of this wing predicted an unusual instability boundary based upon subcritical response data. During the present test no instability was found, but an angle of attack dependent narrow Mach number region of high dynamic wing response was observed over a wide range of dynamic pressures. The effect on dynamic wing response of wing angle of attack, static outboard control surface deflection and a lower surface spanwise fence located near the 60 percent local chordline was investigated. The driving mechanism of the dynamic wing response appears to be related to chordwise shock movement in conjunction with flow separation and reattachment on both the upper and lower surfaces.

Investigation of transonic region of high dynamic response encountered on an elastic supercritical wing

NASA Technical Reports Server (NTRS)

Seidel, David A.; Eckstrom, Clinton V.; Sandford, Maynard C.

1987-01-01

Unsteady aerodynamic data were measured on an aspect ratio 10.3 elastic supercritical wing while undergoing high dynamic response above a Mach number of 0.90. These tests were conducted in the NASA Langley Transonic Dynamics Tunnel. A previous test of this wing predicted an unusual instability boundary based on subcritical response data. During the present test no instability was found, but an angle of attack dependent narrow Mach number region of high dynamic wing response was observed over a wide range of dynamic pressures. The effect on dynamic wing response of wing angle of attack, static outbound control surface deflection and a lower surface spanwise fence located near the 60 percent local chordline was investigated. The driving mechanism of the dynamic wing response appears to be related to chordwise shock movement in conjunction with flow separation and reattachment on both the upper and lower surfaces.

Strain rate sensitivity of autoclaved aerated concrete from quasi-static regime to shock loading

NASA Astrophysics Data System (ADS)

Mespoulet, Jérôme; Plassard, Fabien; Hereil, Pierre Louis

2015-09-01

The quasi-static mechanical behavior of autoclaved aerated concrete is well-known and can be expressed as a function of its density. There are however not much studies dealing with its dynamic behavior and its damping ability when subjected to a mechanical shock or a blast. This study presents experimental results obtained at the Shock Physics Laboratory of THIOT INGENIERIE company. The test specimens are made of YTONG(TM ) cellular concrete with porosity in the range of 75 to 80%. Experimental tests cover a large strain rate amplitude (higher than 104 s-1) for specimens up to 250 mm. They were carried out with a small compression press and with two facilities dedicated to dynamic material characterization: JUPITER dynamic large press (2 MN, 3 ms rising time) and TITAN multi-caliber single-stage gas gun. Results in un-confined conditions show an increase of the compressive strength when strain rate increases (45% increase at 5.102 s-1) but dynamic tests induce damage early in the experiment. This competition between dynamic strength raise and specimen fracture makes the complete compaction curve determination not to be done in unconfined dynamic condition. A 25% increase of the compressive strength has been observed between unconfined and confined condition in Q.S. regime.

Modeling dynamic acousto-elastic testing experiments: validation and perspectives.

PubMed

Gliozzi, A S; Scalerandi, M

2014-10-01

Materials possessing micro-inhomogeneities often display a nonlinear response to mechanical solicitations, which is sensitive to the confining pressure acting on the sample. Dynamic acoustoelastic testing allows measurement of the instantaneous variations in the elastic modulus due to the change of the dynamic pressure induced by a low-frequency wave. This paper shows that a Preisach-Mayergoyz space based hysteretic multi-state elastic model provides an explanation for experimental observations in consolidated granular media and predicts memory and nonlinear effects comparable to those measured in rocks.

Fish population dynamics in a seasonally varying wetland

USGS Publications Warehouse

DeAngelis, Donald L.; Trexler, Joel C.; Cosner, Chris; Obaza, Adam; Jopp, Fred

2010-01-01

Small fishes in seasonally flooded environments such as the Everglades are capable of spreading into newly flooded areas and building up substantial biomass. Passive drift cannot account for the rapidity of observed population expansions. To test the reaction-diffusion mechanism for spread of the fish, we estimated their diffusion coefficient and applied a reaction-diffusion model. This mechanism was also too weak to account for the spatial dynamics. Two other hypotheses were tested through modeling. The first--the 'refuge mechanism--hypothesizes that small remnant populations of small fishes survive the dry season in small permanent bodies of water (refugia), sites where the water level is otherwise below the surface. The second mechanism, which we call the 'dynamic ideal free distribution mechanism' is that consumption by the fish creates a prey density gradient and that fish taxis along this gradient can lead to rapid population expansion in space. We examined the two alternatives and concluded that although refugia may play an important role in recolonization by the fish population during reflooding, only the second, taxis in the direction of the flooding front, seems capable of matching empirical observations. This study has important implications for management of wetlands, as fish biomass is an essential support of higher trophic levels.

Static and yawed-rolling mechanical properties of two type 7 aircraft tires

NASA Technical Reports Server (NTRS)

Tanner, J. A.; Stubbs, S. M.; Mccarty, J. L.

1981-01-01

Selected mechanical properties of 18 x 5.5 and 49 x 17 size, type 7 aircraft tires were evaluated. The tires were subjected to pure vertical loads and to combined vertical and lateral loads under both static and rolling conditions. Parameters for the static tests consisted of tire load in the vertical and lateral directions, and parameters for the rolling tests included tire vertical load, yaw angle, and ground speed. Effects of each of these parameters on the measured tire characteristics are discussed and, where possible, compared with previous work. Results indicate that dynamic tire properties under investigation were generally insensitive to speed variations and therefore tend to support the conclusion that many tire dynamic characteristics can be obtained from static and low speed rolling tests. Furthermore, many of the tire mechanical properties are in good agreement with empirical predictions based on earlier research.

Overview of Glenn Mechanical Components Branch Research

NASA Astrophysics Data System (ADS)

Zakrajsek, James

2002-09-01

Mr. James Zakrajsek, chief of the Mechanical Components Branch, gave an overview of research conducted by the branch. Branch members perform basic research on mechanical components and systems, including gears and bearings, turbine seals, structural and thermal barrier seals, and space mechanisms. The research is focused on propulsion systems for present and advanced aerospace vehicles. For rotorcraft and conventional aircraft, we conduct research to develop technology needed to enable the design of low noise, ultra safe geared drive systems. We develop and validate analytical models for gear crack propagation, gear dynamics and noise, gear diagnostics, bearing dynamics, and thermal analyses of gear systems using experimental data from various component test rigs. In seal research we develop and test advanced turbine seal concepts to increase efficiency and durability of turbine engines. We perform experimental and analytical research to develop advanced thermal barrier seals and structural seals for current and next generation space vehicles. Our space mechanisms research involves fundamental investigation of lubricants, materials, components and mechanisms for deep space and planetary environments.

Algorithms to automate gap-dependent integral tuning for the 2.8-meter long horizontal field undulator with a dynamic force compensation mechanism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Joseph Z., E-mail: x@anl.gov; Vasserman, Isaac; Strelnikov, Nikita

2016-07-27

A 2.8-meter long horizontal field prototype undulator with a dynamic force compensation mechanism has been developed and tested at the Advanced Photon Source (APS) at Argonne National Laboratory (Argonne). The magnetic tuning of the undulator integrals has been automated and accomplished by applying magnetic shims. A detailed description of the algorithms and performance is reported.

Viscoelastic properties of addition-cured polyimides used in high temperature polymer matrix composites

NASA Technical Reports Server (NTRS)

Roberts, Gary D; Malarik, Diane C.; Robaidek, Jerrold O.

1991-01-01

Viscoelastic properties of the addition cured polyimide, PMR-15, were studied using dynamic mechanical and stress relaxation tests. For temperatures below the glass transition temperature, T sub g, the dynamic mechanical properties measured using a temperature scan rate of 10 C/min were strongly affected by the presence of absorbed moisture in the resin. Dynamic mechanical properties measured as a function of time during an isothermal hold provided an indication of chemical changes occurring in the resin. For temperatures above (T sub g + 20 C), the storage modulus increased continuously as a function of time indicating that additional crosslinking is occurring in the resin. Because of these changes in chemical structures, the stress relaxation modulus could not be measured over any useful time interval for temperatures above T sub g. For temperatures below T sub g, dynamic mechanical properties appeared to be unaffected by chemical changes for times exceeding 1 hr. Since the duration of the stress relaxation tests was less than 1 hr, the stress relaxation modulus could be measured. As long as the moisture content of the resin was less than 2 pct, stress relaxation curves measured at different temperatures could be superimposed using horizontal shifts along the log(time) axis with only small shifts along the vertical axis.

Investigation of Dynamic Crack Coalescence Using a Gypsum-Like 3D Printing Material

NASA Astrophysics Data System (ADS)

Jiang, Chao; Zhao, Gao-Feng; Zhu, Jianbo; Zhao, Yi-Xin; Shen, Luming

2016-10-01

Dynamic crack coalescence attracts great attention in rock mechanics. However, specimen preparation in experimental study is a time-consuming and difficult procedure. In this work, a gypsum-like material by powder bed and inkjet 3D printing technique was applied to produce specimens with preset cracks for split Hopkinson pressure bar (SHPB) test. From micro X-ray CT test, it was found that the 3D printing technique could successfully prepare specimens that contain preset cracks with width of 0.2 mm. Basic mechanical properties of the 3D printing material, i.e., the elastic modulus, the Poisson's ratio, the density, the compressive strength, the indirect tensile strength, and the fracture toughness, were obtained and reported. Unlike 3D printed specimens using polylactic acid, these gypsum-like specimens can produce failure patterns much closer to those observed in classical rock mechanical tests. Finally, the dynamic crack coalescence of the 3D printed specimens with preset cracks were captured using a high-speed camera during SHPB tests. Failure patterns of these 3D printed specimens are similar to the specimens made by Portland cement concrete. Our results indicate that sample preparation by 3D printing is highly competitive due to its quickness in prototyping, precision and flexibility on the geometry, and high material homogeneity.

Test of the diffusing-diffusivity mechanism using near-wall colloidal dynamics

NASA Astrophysics Data System (ADS)

Matse, Mpumelelo; Chubynsky, Mykyta V.; Bechhoefer, John

2017-10-01

The mechanism of diffusing diffusivity predicts that, in environments where the diffusivity changes gradually, the displacement distribution becomes non-Gaussian, even though the mean-square displacement grows linearly with time. Here, we report single-particle tracking measurements of the diffusion of colloidal spheres near a planar substrate. Because the local effective diffusivity is known, we have been able to carry out a direct test of this mechanism for diffusion in inhomogeneous media.

Scott Dana | NREL

Science.gov Websites

Dana Scott Dana Mechanical and Vibrations Engineer Scott.Dana@nrel.gov | 303-384-7036 Scott focuses on field testing of wind turbines and components for mechanical loads and power performance structural health monitoring using dynamic-based sensing methods. Education B.S. and M.S. in Mechanical

Effect of thermally reduced graphene oxide on dynamic mechanical properties of carbon fiber/epoxy composite

NASA Astrophysics Data System (ADS)

Adak, Nitai Chandra; Chhetri, Suman; Murmu, Naresh Chandra; Samanta, Pranab; Kuila, Tapas

2018-03-01

The Carbon fiber (CF)/epoxy composites are being used in the automotive and aerospace industries owing to their high specific mechanical strength to weight ratio compared to the other conventional metal and alloys. However, the low interfacial adhesion between fiber and polymer matrix results the inter-laminar fracture of the composites. Effects of different carbonaceous nanomaterials i.e., carbon nanotubes (CNT), graphene nanosheets (GNPs), graphene oxide (GO) etc. on the static mechanical properties of the composites were investigated in detail. Only a few works focused on the improvement of the dynamic mechanical of the CF/epoxy composites. Herein, the effect of thermally reduced grapheme oxide (TRGO) on the dynamic mechanical properties of the CF/epoxy composites was investigated. At first, GO was synthesized using modified Hummers method and then reduced the synthesized GO inside a vacuum oven at 800 °C for 5 min. The prepared TRGO was dispersed in the epoxy resin to modify the epoxy matrix. Then, a number of TRGO/CF/epoxy laminates were manufactured incorporating different wt% of TRGO by vacuum assisted resin transfer molding (VARTM) technique. The developed laminates were cured at room temperature for 24 h and then post cured at 120 °C for 2 h. The dynamic mechanical analyzer (DMA 8000 Perkin Elmer) was used to examine the dynamic mechanical properties of the TRGO/CF/epoxy composites according to ASTM D7028. The dimension of the specimen was 44×10×2.4 mm3 for the DMA test. This test was carried out under flexural loading mode (duel cantilever) at a frequency of 1 Hz and amplitude of 50 μm. The temperature was ramped from 30 to 200 °C with a heating rate of 5 °C min-1. The dynamic mechanical analysis of the 0.2 wt% TRGO incorporated CF/epoxy composites showed ~ 96% enhancement in storage modulus and ~ 12 °C increments in glass transition temperature (Tg) compared to the base CF/epoxy composites. The fiber-matrix interaction was studied by Cole-Cole plot analysis. It proved the homogeneous dispersion of the epoxy resin and TRGO. The homogeneous dispersion of the TRGO in the epoxy matrix increased the overall enhancement of the dynamic mechanical properties of the hybrid composites.

Ergodicity convergence test suggests telomere motion obeys fractional dynamics

NASA Astrophysics Data System (ADS)

Kepten, E.; Bronshtein, I.; Garini, Y.

2011-04-01

Anomalous diffusion, observed in many biological processes, is a generalized description of a wide variety of processes, all obeying the same law of mean-square displacement. Identifying the basic mechanisms of these observations is important for deducing the nature of the biophysical systems measured. We implement a previously suggested method for distinguishing between fractional Langevin dynamics, fractional Brownian motion, and continuous time random walk based on the ergodic nature of the data. We apply the method together with the recently suggested P-variation test and the displacement correlation to the lately measured dynamics of telomeres in the nucleus of mammalian cells and find strong evidence that the telomeres motion obeys fractional dynamics. The ergodic dynamics are observed experimentally to fit fractional Brownian or Langevin dynamics.

Standardized static and dynamic evaluation of myocardial tissue properties.

PubMed

Ramadan, Sherif; Paul, Narinder; Naguib, Hani E

2017-03-20

Quantifying the mechanical behaviors of soft biological tissues is of considerable research interest. However, validity and reproducibility between different researchers and apparatus is questionable. This study aims to quantify the mechanical properties of myocardium while investigating methodologies that can standardize biological tissue testing. Tensile testing was performed to obtain Young's modulus and a dynamic mechanical analysis (DMA) determined the viscoelastic properties. A frequency range of 0.5 Hz (30bpm) to 3.5 Hz (210bpm) was analyzed. For tensile testing three different preconditioning settings were tested: no load, 0.05 N preload, and a cyclic preload at 2.5% strain and 10 cycles. Samples were placed in saline and tested at 37 °C. Five ovine and five porcine hearts were tested. Cyclic loading results in the most consistent moduli values. The modulus of ovine/porcine tissue was mean = 0.05/.06 MPa, SD = 0.02/0.03 MPa. The storage/loss modulus varied from = 0.02/0.003 MPa at 0.5 Hz to 0.04/0.008 MPa at 3.5 Hz; Stiffness increases linearly from 400 to 800 N m -1 with a tan delta around 0.175. Static analysis of the mechanical properties of myocardial tissue confirms that; preconditioning is necessary for reproducibility, and DMA provides a platform for reproducible testing of soft biological tissues.

Dynamic characterization of small fibers based on the flexural vibrations of a piezoelectric cantilever probe

NASA Astrophysics Data System (ADS)

Zhang, Xiaofei; Ye, Xuan; Li, Xide

2016-08-01

In this paper, we present a cantilever-probe system excited by a piezoelectric actuator, and use it to measure the dynamic mechanical properties of a micro- and nanoscale fiber. Coupling the fiber to the free end of the cantilever probe, we found the dynamic stiffness and damping coefficient of the fiber from the resonance frequency and the quality factor of the fiber-cantilever-probe system. The properties of Bacillus subtilis fibers measured using our proposed system agreed with tensile measurements, validating our method. Our measurements show that the piezoelectric actuator coupled to cantilever probe can be made equivalent to a clamped cantilever with an effective length, and calculated results show that the errors of measured natural frequency of the system can be ignored if the coupled fiber has an inclination angle of alignment of less than 10°. A sensitivity analysis indicates that the first or second resonant mode is the sensitive mode to test the sample’s dynamic stiffness, while the damping property has different sensitivities for the first four modes. Our theoretical analysis demonstrates that the double-cantilever probe is also an effective sensitive structure that can be used to perform dynamic loading and characterize dynamic response. Our method has the advantage of using amplitude-frequency curves to obtain the dynamic mechanical properties without directly measuring displacements and forces as in tensile tests, and it also avoids the effects of the complex surface structure and deformation presenting in contact resonance method. Our method is effective for measuring the dynamic mechanical properties of fiber-like one-dimensional (1D) materials.

Spatio-temporal correlations in models of collective motion ruled by different dynamical laws.

PubMed

Cavagna, Andrea; Conti, Daniele; Giardina, Irene; Grigera, Tomas S; Melillo, Stefania; Viale, Massimiliano

2016-11-15

Information transfer is an essential factor in determining the robustness of biological systems with distributed control. The most direct way to study the mechanisms ruling information transfer is to experimentally observe the propagation across the system of a signal triggered by some perturbation. However, this method may be inefficient for experiments in the field, as the possibilities to perturb the system are limited and empirical observations must rely on natural events. An alternative approach is to use spatio-temporal correlations to probe the information transfer mechanism directly from the spontaneous fluctuations of the system, without the need to have an actual propagating signal on record. Here we test this method on models of collective behaviour in their deeply ordered phase by using ground truth data provided by numerical simulations in three dimensions. We compare two models characterized by very different dynamical equations and information transfer mechanisms: the classic Vicsek model, describing an overdamped noninertial dynamics and the inertial spin model, characterized by an underdamped inertial dynamics. By using dynamic finite-size scaling, we show that spatio-temporal correlations are able to distinguish unambiguously the diffusive information transfer mechanism of the Vicsek model from the linear mechanism of the inertial spin model.

An application of holographic interferometry for dynamic vibration analysis of a jet engine turbine compressor rotor

NASA Astrophysics Data System (ADS)

Fein, Howard

2003-09-01

Holographic Interferometry has been successfully employed to characterize the materials and behavior of diverse types of structures under dynamic stress. Specialized variations of this technology have also been applied to define dynamic and vibration related structural behavior. Such applications of holographic technique offer some of the most effective methods of modal and dynamic analysis available. Real-time dynamic testing of the modal and mechanical behavior of jet engine turbine, rotor, vane, and compressor structures has always required advanced instrumentation for data collection in either simulated flight operation test or computer-based modeling and simulations. Advanced optical holography techniques are alternate methods which result in actual full-field behavioral data in a noninvasive, noncontact environment. These methods offer significant insight in both the development and subsequent operational test and modeling of advanced jet engine turbine and compressor rotor structures and their integration with total vehicle system dynamics. Structures and materials can be analyzed with very low amplitude excitation and the resultant data can be used to adjust the accuracy of mathematically derived structural and behavioral models. Holographic Interferometry offers a powerful tool to aid in the developmental engineering of turbine rotor and compressor structures for high stress applications. Aircraft engine applications in particular most consider operational environments where extremes in vibration and impulsive as well as continuous mechanical stress can affect both operation and structural stability. These considerations present ideal requisites for analysis using advanced holographic methods in the initial design and test of turbine rotor components. Holographic techniques are nondestructive, real-time, and definitive in allowing the identification of vibrational modes, displacements, and motion geometries. Such information can be crucial to the determination of mechanical configurations and designs as well as critical operational parameters of turbine structural components or unit turbine components fabricated from advanced and exotic new materials or using new fabrication methods. Anomalous behavioral characteristics can be directly related to hidden structural or mounting anomalies and defects.

Dynamic mechanical characterization of aluminum: analysis of strain-rate-dependent behavior

NASA Astrophysics Data System (ADS)

Rahmat, Meysam

2018-05-01

A significant number of materials show different mechanical behavior under dynamic loads compared to quasi-static (Salvado et al. in Prog. Mater. Sci. 88:186-231, 2017). Therefore, a comprehensive study of material dynamic behavior is essential for applications in which dynamic loads are dominant (Li et al. in J. Mater. Process. Technol. 255:373-386, 2018). In this work, aluminum 6061-T6, as an example of ductile alloys with numerous applications including in the aerospace industry, has been studied under quasi-static and dynamic tensile tests with strain rates of up to 156 s^{-1}. Dogbone specimens were designed, instrumented and tested with a high speed servo-hydraulic load frame, and the results were validated with the literature. It was observed that at a strain rate of 156 s^{-1} the yield and ultimate strength increased by 31% and 33% from their quasi-static values, respectively. Moreover, the failure elongation and fracture energy per unit volume also increased by 18% and 52%, respectively. A Johnson-Cook model was used to capture the behavior of the material at different strain rates, and a modified version of this model was presented to enhance the capabilities of the original model, especially in predicting material properties close to the failure point. Finally, the fracture surfaces of specimens tested under quasi-static and dynamic loads were compared and conclusions about the differences were drawn.

Influence of Rapid Freeze-Thaw Cycling on the Mechanical Properties of Sustainable Strain-Hardening Cement Composite (2SHCC)

PubMed Central

Jang, Seok-Joon; Rokugo, Keitetsu; Park, Wan-Shin; Yun, Hyun-Do

2014-01-01

This paper provides experimental results to investigate the mechanical properties of sustainable strain-hardening cement composite (2SHCC) for infrastructures after freeze-thaw actions. To improve the sustainability of SHCC materials in this study, high energy-consumptive components—silica sand, cement, and polyvinyl alcohol (PVA) fibers—in the conventional SHCC materials are partially replaced with recycled materials such as recycled sand, fly ash, and polyethylene terephthalate (PET) fibers, respectively. To investigate the mechanical properties of green SHCC that contains recycled materials, the cement, PVA fiber and silica sand were replaced with 10% fly ash, 25% PET fiber, and 10% recycled aggregate based on preliminary experimental results for the development of 2SHCC material, respectively. The dynamic modulus of elasticity and weight for 2SHCC material were measured at every 30 cycles of freeze-thaw. The effects of freeze-thaw cycles on the mechanical properties of sustainable SHCC are evaluated by conducting compressive tests, four-point flexural tests, direct tensile tests and prism splitting tests after 90, 180, and 300 cycles of rapid freeze-thaw. Freeze-thaw testing was conducted according to ASTM C 666 Procedure A. Test results show that after 300 cycles of freezing and thawing actions, the dynamic modulus of elasticity and mass loss of damaged 2SHCC were similar to those of virgin 2SHCC, while the freeze-thaw cycles influence mechanical properties of the 2SHCC material except for compressive behavior. PMID:28788522

Validation of a Laboratory Method for Evaluating Dynamic Properties of Reconstructed Equine Racetrack Surfaces

PubMed Central

Setterbo, Jacob J.; Chau, Anh; Fyhrie, Patricia B.; Hubbard, Mont; Upadhyaya, Shrini K.; Symons, Jennifer E.; Stover, Susan M.

2012-01-01

Background Racetrack surface is a risk factor for racehorse injuries and fatalities. Current research indicates that race surface mechanical properties may be influenced by material composition, moisture content, temperature, and maintenance. Race surface mechanical testing in a controlled laboratory setting would allow for objective evaluation of dynamic properties of surface and factors that affect surface behavior. Objective To develop a method for reconstruction of race surfaces in the laboratory and validate the method by comparison with racetrack measurements of dynamic surface properties. Methods Track-testing device (TTD) impact tests were conducted to simulate equine hoof impact on dirt and synthetic race surfaces; tests were performed both in situ (racetrack) and using laboratory reconstructions of harvested surface materials. Clegg Hammer in situ measurements were used to guide surface reconstruction in the laboratory. Dynamic surface properties were compared between in situ and laboratory settings. Relationships between racetrack TTD and Clegg Hammer measurements were analyzed using stepwise multiple linear regression. Results Most dynamic surface property setting differences (racetrack-laboratory) were small relative to surface material type differences (dirt-synthetic). Clegg Hammer measurements were more strongly correlated with TTD measurements on the synthetic surface than the dirt surface. On the dirt surface, Clegg Hammer decelerations were negatively correlated with TTD forces. Conclusions Laboratory reconstruction of racetrack surfaces guided by Clegg Hammer measurements yielded TTD impact measurements similar to in situ values. The negative correlation between TTD and Clegg Hammer measurements confirms the importance of instrument mass when drawing conclusions from testing results. Lighter impact devices may be less appropriate for assessing dynamic surface properties compared to testing equipment designed to simulate hoof impact (TTD). Potential Relevance Dynamic impact properties of race surfaces can be evaluated in a laboratory setting, allowing for further study of factors affecting surface behavior under controlled conditions. PMID:23227183

Response of DP 600 products to dynamic impact loads

NASA Astrophysics Data System (ADS)

Clark, Deidra Darcell

The objective of this study was to compare the microstructural response of various DP 600 products subjected to low velocity, dynamic impact tests, typically encountered in a car crash. Since the response of steel is sensitive to its microstructure as controlled by the alloying elements, phase content, and processing; various DP 600 products may respond differently to crashes. The microstructure before and after dynamic impact deformation at 5 and 10 mph was characterized with regards to grain size, morphology, and phase content among vendors A, B, and C to evaluate efficiency in absorbing energy mechanisms during a crash simulated by dynamic impact testing in a drop tower.

On the dynamic behavior of mineralized tissues

NASA Astrophysics Data System (ADS)

Kulin, Robb Michael

Mineralized tissues, such as bone and antler, are complex hierarchical materials that have adapted over millennia to optimize strength and fracture resistance for their in vivo applications. As a structural support, skeletal bone primarily acts as a rigid framework that is resistant to fracture, and able to repair damage and adapt to sustained loads during its lifetime. Antler is typically deciduous and subjected to large bending moments and violent impacts during its annual cycle. To date, extensive characterization of the quasi-static mechanical properties of these materials has been performed. However, very little has been done to characterize their dynamic properties, despite the fact that the majority of failures in these materials occur under impact loads. Here, an in depth analysis of the dynamic mechanical behavior of these two materials is presented, using equine bone obtained post-mortem from donors ranging in age from 6 months to 28 years, and antler from the North American Elk. Specimens were tested under compressive strain rates of 10-3, 100, and 103 sec-1 in order to investigate their strain rate dependent compressive response. Fracture toughness experiments were performed using a four-point bending geometry on single and double-notch specimens in order to measure fracture toughness, as well as observe differences in crack propagation between dynamic (˜2x105 MPa˙m1/2/s) and quasi-static (˜0.25 MPa˙m1/2/s) loading rates. After testing, specimens were analyzed using a combination of optical, electron and confocal microscopy. Results indicated that the mechanical response of these materials is highly dependent on loading rate. Decreasing quasi-static fracture toughness is observed with age in bone specimens, while dynamic specimens show no age trends, yet universally decreased fracture toughness compared to those tested quasi-statically. For the first time, rising R-curve behavior in bone was also shown to exist under both quasi-static and dynamic loading. Antler demonstrated itself to be extremely resistant to impact loading, often requiring multiple impacts to fracture a specimen. Microscopy observations of deformation and crack propagation mechanisms indicate that differences in mechanical behavior between bone and antler, and at varying strain rates, are the result of subtle differences in bulk composition and active microstructural toughening mechanisms.

Space-resolved diffusing wave spectroscopy measurements of the macroscopic deformation and the microscopic dynamics in tensile strain tests

NASA Astrophysics Data System (ADS)

Nagazi, Med-Yassine; Brambilla, Giovanni; Meunier, Gérard; Marguerès, Philippe; Périé, Jean-Noël; Cipelletti, Luca

2017-01-01

We couple a laser-based, space-resolved dynamic light scattering apparatus to a universal traction machine for mechanical extensional tests. We perform simultaneous optical and mechanical measurements on polyether ether ketone, a semi-crystalline polymer widely used in the industry. Due to the high turbidity of the sample, light is multiply scattered by the sample and the diffusing wave spectroscopy (DWS) formalism is used to interpret the data. Space-resolved DWS yields spatial maps of the sample strain and of the microscopic dynamics. An excellent agreement is found between the strain maps thus obtained and those measured by a conventional stereo-digital image correlation technique. The microscopic dynamics reveals both affine motion and plastic rearrangements. Thanks to the extreme sensitivity of DWS to displacements as small as 1 nm, plastic activity and its spatial localization can be detected at an early stage of the sample strain, making the technique presented here a valuable complement to existing material characterization methods.

Subcritical crack growth in SiNx thin-film barriers studied by electro-mechanical two-point bending

NASA Astrophysics Data System (ADS)

Guan, Qingling; Laven, Jozua; Bouten, Piet C. P.; de With, Gijsbertus

2013-06-01

Mechanical failure resulting from subcritical crack growth in the SiNx inorganic barrier layer applied on a flexible multilayer structure was studied by an electro-mechanical two-point bending method. A 10 nm conducting tin-doped indium oxide layer was sputtered as an electrical probe to monitor the subcritical crack growth in the 150 nm dielectric SiNx layer carried by a polyethylene naphthalate substrate. In the electro-mechanical two-point bending test, dynamic and static loads were applied to investigate the crack propagation in the barrier layer. As consequence of using two loading modes, the characteristic failure strain and failure time could be determined. The failure probability distribution of strain and lifetime under each loading condition was described by Weibull statistics. In this study, results from the tests in dynamic and static loading modes were linked by a power law description to determine the critical failure over a range of conditions. The fatigue parameter n from the power law reduces greatly from 70 to 31 upon correcting for internal strain. The testing method and analysis tool as described in the paper can be used to understand the limit of thin-film barriers in terms of their mechanical properties.

Passiflora incarnata attenuation of neuropathic allodynia and vulvodynia apropos GABA-ergic and opioidergic antinociceptive and behavioural mechanisms.

PubMed

Aman, Urooj; Subhan, Fazal; Shahid, Muhammad; Akbar, Shehla; Ahmad, Nisar; Ali, Gowhar; Fawad, Khwaja; Sewell, Robert D E

2016-02-24

Passiflora incarnata is widely used as an anxiolytic and sedative due to its putative GABAergic properties. Passiflora incarnata L. methanolic extract (PI-ME) was evaluated in an animal model of streptozotocin-induced diabetic neuropathic allodynia and vulvodynia in rats along with antinociceptive, anxiolytic and sedative activities in mice in order to examine possible underlying mechanisms. PI-ME was tested preliminary for qualitative phytochemical analysis and then quantitatively by proximate and GC-MS analysis. The antinociceptive property was evaluated using the abdominal constriction assay and hot plate test. The anxiolytic activity was performed in a stair case model and sedative activity in an open field test. The antagonistic activities were evaluated using naloxone and/or pentylenetetrazole (PTZ). PI-ME was evaluated for prospective anti-allodynic and anti-vulvodynic properties in a rat model of streptozotocin induced neuropathic pain using the static and dynamic testing paradigms of mechanical allodynia and vulvodynia. GC-MS analysis revealed that PI-ME contained predominant quantities of oleamide (9-octadecenamide), palmitic acid (hexadecanoic acid) and 3-hydroxy-dodecanoic acid, among other active constituents. In the abdominal constriction assay and hot plate test, PI-ME produced dose dependant, naloxone and pentylenetetrazole reversible antinociception suggesting an involvement of opioidergic and GABAergic mechanisms. In the stair case test, PI-ME at 200 mg/kg increased the number of steps climbed while at 600 mg/kg a significant decrease was observed. The rearing incidence was diminished by PI-ME at all tested doses and in the open field test, PI-ME decreased locomotor activity to an extent that was analagous to diazepam. The effects of PI-ME were antagonized by PTZ in both the staircase and open field tests implicating GABAergic mechanisms in its anxiolytic and sedative activities. In the streptozotocin-induced neuropathic nociceptive model, PI-ME (200 and 300 mg/kg) exhibited static and dynamic anti-allodynic effects exemplified by an increase in paw withdrawal threshold and paw withdrawal latency. PI-ME relieved only the dynamic component of vulvodynia by increasing flinching response latency. These findings suggest that Passiflora incarnata might be useful for treating neuropathic pain. The antinociceptive and behavioural findings inferring that its activity may stem from underlying opioidergic and GABAergic mechanisms though a potential oleamide-sourced cannabimimetic involvement is also discussed.

Narrative review of the in vivo mechanics of the cervical spine after anterior arthrodesis as revealed by dynamic biplane radiography.

PubMed

Anderst, William

2016-01-01

Arthrodesis is the standard of care for numerous pathologic conditions of the cervical spine and is performed over 150,000 times annually in the United States. The primary long-term concern after this surgery is adjacent segment disease (ASD), defined as new clinical symptoms adjacent to a previous fusion. The incidence of adjacent segment disease is approximately 3% per year, meaning that within 10 years of the initial surgery, approximately 25% of cervical arthrodesis patients require a second procedure to address symptomatic adjacent segment degeneration. Despite the high incidence of ASD, until recently, there was little data available to characterize in vivo adjacent segment mechanics during dynamic motion. This manuscript reviews recent advances in our knowledge of adjacent segment mechanics after cervical arthrodesis that have been facilitated by the use of dynamic biplane radiography. The primary observations from these studies are that current in vitro test paradigms often fail to replicate in vivo spine mechanics before and after arthrodesis, that intervertebral mechanics vary among cervical motion segments, and that joint arthrokinematics (i.e., the interactions between adjacent vertebrae) are superior to traditional kinematics measurements for identifying altered adjacent segment mechanics after arthrodesis. Future research challenges are identified, including improving the biofidelity of in vitro tests, determining the natural history of in vivo spine mechanics, conducting prospective longitudinal studies on adjacent segment kinematics and arthrokinematics after single and multiple-level arthrodesis, and creating subject-specific computational models to accurately estimate muscle forces and tissue loading in the spine during dynamic activities. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

Effects of age and loading rate on equine cortical bone failure.

PubMed

Kulin, Robb M; Jiang, Fengchun; Vecchio, Kenneth S

2011-01-01

Although clinical bone fractures occur predominantly under impact loading (as occurs during sporting accidents, falls, high-speed impacts or other catastrophic events), experimentally validated studies on the dynamic fracture behavior of bone, at the loading rates associated with such events, remain limited. In this study, a series of tests were performed on femoral specimens obtained post-mortem from equine donors ranging in age from 6 months to 28 years. Fracture toughness and compressive tests were performed under both quasi-static and dynamic loading conditions in order to determine the effects of loading rate and age on the mechanical behavior of the cortical bone. Fracture toughness experiments were performed using a four-point bending geometry on single and double-notch specimens in order to measure fracture toughness, as well as observe differences in crack initiation between dynamic and quasi-static experiments. Compressive properties were measured on bone loaded parallel and transverse to the osteonal growth direction. Fracture propagation was then analyzed using scanning electron and scanning confocal microscopy to observe the effects of microstructural toughening mechanisms at different strain rates. Specimens from each horse were also analyzed for dry, wet and mineral densities, as well as weight percent mineral, in order to investigate possible influences of composition on mechanical behavior. Results indicate that bone has a higher compressive strength, but lower fracture toughness when tested dynamically as compared to quasi-static experiments. Fracture toughness also tends to decrease with age when measured quasi-statically, but shows little change with age under dynamic loading conditions, where brittle "cleavage-like" fracture behavior dominates. Copyright © 2010 Elsevier Ltd. All rights reserved.

Dynamic Redox Regulation of IL-4 Signaling.

PubMed

Dwivedi, Gaurav; Gran, Margaret A; Bagchi, Pritha; Kemp, Melissa L

2015-11-01

Quantifying the magnitude and dynamics of protein oxidation during cell signaling is technically challenging. Computational modeling provides tractable, quantitative methods to test hypotheses of redox mechanisms that may be simultaneously operative during signal transduction. The interleukin-4 (IL-4) pathway, which has previously been reported to induce reactive oxygen species and oxidation of PTP1B, may be controlled by several other putative mechanisms of redox regulation; widespread proteomic thiol oxidation observed via 2D redox differential gel electrophoresis upon IL-4 treatment suggests more than one redox-sensitive protein implicated in this pathway. Through computational modeling and a model selection strategy that relied on characteristic STAT6 phosphorylation dynamics of IL-4 signaling, we identified reversible protein tyrosine phosphatase (PTP) oxidation as the primary redox regulatory mechanism in the pathway. A systems-level model of IL-4 signaling was developed that integrates synchronous pan-PTP oxidation with ROS-independent mechanisms. The model quantitatively predicts the dynamics of IL-4 signaling over a broad range of new redox conditions, offers novel hypotheses about regulation of JAK/STAT signaling, and provides a framework for interrogating putative mechanisms involving receptor-initiated oxidation.

Dynamic Redox Regulation of IL-4 Signaling

PubMed Central

Dwivedi, Gaurav; Gran, Margaret A.; Bagchi, Pritha; Kemp, Melissa L.

2015-01-01

Quantifying the magnitude and dynamics of protein oxidation during cell signaling is technically challenging. Computational modeling provides tractable, quantitative methods to test hypotheses of redox mechanisms that may be simultaneously operative during signal transduction. The interleukin-4 (IL-4) pathway, which has previously been reported to induce reactive oxygen species and oxidation of PTP1B, may be controlled by several other putative mechanisms of redox regulation; widespread proteomic thiol oxidation observed via 2D redox differential gel electrophoresis upon IL-4 treatment suggests more than one redox-sensitive protein implicated in this pathway. Through computational modeling and a model selection strategy that relied on characteristic STAT6 phosphorylation dynamics of IL-4 signaling, we identified reversible protein tyrosine phosphatase (PTP) oxidation as the primary redox regulatory mechanism in the pathway. A systems-level model of IL-4 signaling was developed that integrates synchronous pan-PTP oxidation with ROS-independent mechanisms. The model quantitatively predicts the dynamics of IL-4 signaling over a broad range of new redox conditions, offers novel hypotheses about regulation of JAK/STAT signaling, and provides a framework for interrogating putative mechanisms involving receptor-initiated oxidation. PMID:26562652

OTEC riser cable model and prototype testing

NASA Astrophysics Data System (ADS)

Kurt, J. P.; Schultz, J. A.; Roblee, L. H. S.

1981-12-01

Two different OTEC riser cables have been developed to span the distance between a floating OTEC power plant and the ocean floor. The major design concerns for a riser cable in the dynamic OTEC environment are fatigue, corrosion, and electrical/mechanical aging of the cable components. The basic properties of the cable materials were studied through tests on model cables and on samples of cable materials. Full-scale prototype cables were manufactured and were tested to measure their electrical and mechanical properties and performance. The full-scale testing was culminated by the electrical/mechanical fatigue test, which exposes full-scale cables to simultaneous tension, bending and electrical loads, all in a natural seawater environment.

Fluid-structural dynamics of ground-based and microgravity caloric tests

NASA Technical Reports Server (NTRS)

Kassemi, M.; Oas, J. G.; Deserranno, Dimitri

2005-01-01

Microgravity caloric tests aboard the 1983 SpaceLab1 mission produced nystagmus results with an intensity comparable to those elicited during post- and pre- flight tests, thus contradicting the basic premise of Barany's convection hypothesis for caloric stimulation. In this work, we present a dynamic fluid structural analysis of the caloric stimulation of the lateral semicircular canal based on two simultaneous driving forces for the endolymphatic flow: natural convection driven by the temperature-dependent density variation in the bulk fluid and expansive convection caused by direct volumetric displacement of the endolymph during the thermal irrigation. Direct numerical simulations indicate that on earth, the natural convection mechanism is dominant. But in the microgravity environment of orbiting spacecraft, where buoyancy effects are mitigated, expansive convection becomes the sole mechanism for producing cupular displacement. A series of transient 1 g and microgravity case studies are presented to delineate the differences between the dynamics of the 1 g and microgravity endolymphatic flows. The impact of these different flow dynamics on the endolymph-cupula fluid-structural interactions is also analyzed based on the time evolutions of cupular displacement and velocity and the transcupular pressure differences.

Fluid-structural dynamics of ground-based and microgravity caloric tests.

PubMed

Kassemi, M; Oas, J G; Deserranno, Dimitri

2005-01-01

Microgravity caloric tests aboard the 1983 SpaceLab1 mission produced nystagmus results with an intensity comparable to those elicited during post- and pre- flight tests, thus contradicting the basic premise of Barany's convection hypothesis for caloric stimulation. In this work, we present a dynamic fluid structural analysis of the caloric stimulation of the lateral semicircular canal based on two simultaneous driving forces for the endolymphatic flow: natural convection driven by the temperature-dependent density variation in the bulk fluid and expansive convection caused by direct volumetric displacement of the endolymph during the thermal irrigation. Direct numerical simulations indicate that on earth, the natural convection mechanism is dominant. But in the microgravity environment of orbiting spacecraft, where buoyancy effects are mitigated, expansive convection becomes the sole mechanism for producing cupular displacement. A series of transient 1 g and microgravity case studies are presented to delineate the differences between the dynamics of the 1 g and microgravity endolymphatic flows. The impact of these different flow dynamics on the endolymph-cupula fluid-structural interactions is also analyzed based on the time evolutions of cupular displacement and velocity and the transcupular pressure differences.

Constitutive modeling and dynamic softening mechanism during hot deformation of an ultra-pure 17%Cr ferritic stainless steel stabilized with Nb

NASA Astrophysics Data System (ADS)

Gao, Fei; Liu, Zhenyu; Misra, R. D. K.; Liu, Haitao; Yu, Fuxiao

2014-09-01

The hot deformation behavior of an ultra-pure 17%Cr ferritic stainless steel was studied in the temperature range of 750-1000 °C and strain rates of 0.5 to 10 s-1 using isothermal hot compression tests in a thermomechanical simulator. The microstructural evolution was investigated using electron backscattered diffraction and transmission electron microscopy. A modified constitutive equation considering the effect of strain on material constant was developed, which predicted the flow stress for the deformation conditions studied, except at 950 °C in 1 s-1 and 900 °C in 10 s-1. Decreasing deformation temperature and increasing strain was beneficial in refining the microstructure. Decreasing deformation temperature, the in-grain shear bands appeared in the microstructure. It is suggested that the dynamic softening mechanism is closely related to deformation temperature. At low deformation temperature, dynamic recovery was major softening mechanism and no dynamic recrystallization occurred. At high deformation temperature, dynamic softening was explained in terms of efficient dynamic recovery and limited continuous dynamic recrystallization. A drop in the flow stress was not found due to very small fraction of new grains nucleated during dynamic recrystallization.

A tribo-mechanical analysis of PVA-based building-blocks for implementation in a 2-layered skin model.

PubMed

Morales Hurtado, M; de Vries, E G; Zeng, X; van der Heide, E

2016-09-01

Poly(vinyl) alcohol hydrogel (PVA) is a well-known polymer widely used in the medical field due to its biocompatibility properties and easy manufacturing. In this work, the tribo-mechanical properties of PVA-based blocks are studied to evaluate their suitability as a part of a structure simulating the length scale dependence of human skin. Thus, blocks of pure PVA and PVA mixed with Cellulose (PVA-Cel) were synthesised via freezing/thawing cycles and their mechanical properties were determined by Dynamic Mechanical Analysis (DMA) and creep tests. The dynamic tests addressed to elastic moduli between 38 and 50kPa for the PVA and PVA-Cel, respectively. The fitting of the creep compliance tests in the SLS model confirmed the viscoelastic behaviour of the samples with retardation times of 23 and 16 seconds for the PVA and PVA-Cel, respectively. Micro indentation tests were also achieved and the results indicated elastic moduli in the same range of the dynamic tests. Specifically, values between 45-55 and 56-81kPa were obtained for the PVA and PVA-Cel samples, respectively. The tribological results indicated values of 0.55 at low forces for the PVA decreasing to 0.13 at higher forces. The PVA-Cel blocks showed lower friction even at low forces with values between 0.2 and 0.07. The implementation of these building blocks in the design of a 2-layered skin model (2LSM) is also presented in this work. The 2LSM was stamped with four different textures and their surface properties were evaluated. The hydration of the 2LSM was also evaluated with a corneometer and the results indicated a gradient of hydration comparable to the human skin. Copyright © 2016 Elsevier Ltd. All rights reserved.

Phase separated microstructure and dynamics of polyurethane elastomers under strain

NASA Astrophysics Data System (ADS)

Iacob, Ciprian; Padsalgikar, Ajay; Runt, James

The molecular mobility of polyurethane elastomers is of the utmost importance in establishing physical properties for uses ranging from automotive tires and shoe soles to more sophisticated aerospace and biomedical applications. In many of these applications, chain dynamics as well as mechanical properties under external stresses/strains are critical for determining ultimate performance. In order to develop a more complete understanding of their mechanical response, we explored the effect of uniaxial strain on the phase separated microstructure and molecular dynamics of the elastomers. We utilize X-ray scattering to investigate soft segment and hard domain orientation, and broadband dielectric spectroscopy for interrogation of the dynamics. Uniaxial deformation is found to significantly perturb the phase-separated microstructure and chain orientation, and results in a considerable slowing down of the dynamics of the elastomers. Attenuated total reflectance Fourier transform infrared spectroscopy measurements of the polyurethanes under uniaxial deformation are also employed and the results are quantitatively correlated with mechanical tensile tests and the degree of phase separation from small-angle X-ray scattering measurements.

Classical Electrodynamics: Lecture notes

NASA Astrophysics Data System (ADS)

Likharev, Konstantin K.

2018-06-01

Essential Advanced Physics is a series comprising four parts: Classical Mechanics, Classical Electrodynamics, Quantum Mechanics and Statistical Mechanics. Each part consists of two volumes, Lecture notes and Problems with solutions, further supplemented by an additional collection of test problems and solutions available to qualifying university instructors. This volume, Classical Electrodynamics: Lecture notes is intended to be the basis for a two-semester graduate-level course on electricity and magnetism, including not only the interaction and dynamics charged point particles, but also properties of dielectric, conducting, and magnetic media. The course also covers special relativity, including its kinematics and particle-dynamics aspects, and electromagnetic radiation by relativistic particles.

A Multi-Scale Method for Dynamics Simulation in Continuum Solvent Models I: Finite-Difference Algorithm for Navier-Stokes Equation.

PubMed

Xiao, Li; Cai, Qin; Li, Zhilin; Zhao, Hongkai; Luo, Ray

2014-11-25

A multi-scale framework is proposed for more realistic molecular dynamics simulations in continuum solvent models by coupling a molecular mechanics treatment of solute with a fluid mechanics treatment of solvent. This article reports our initial efforts to formulate the physical concepts necessary for coupling the two mechanics and develop a 3D numerical algorithm to simulate the solvent fluid via the Navier-Stokes equation. The numerical algorithm was validated with multiple test cases. The validation shows that the algorithm is effective and stable, with observed accuracy consistent with our design.

Improved Healing of Large, Osseous, Segmental Defects by Reverse Dynamization: Evaluation in a Sheep Model

DTIC Science & Technology

2017-12-01

reverse dynamization. This was supplemented by finite element analysis and the use of a strain gauge. This aim was successfully completed, with the...testing deformation results for model validation. Development of a Finite Element (FE) model was conducted through ANSYS 16 to help characterize...Fixators were characterized through mechanical testing by sawbone and ovine cadaver tibiae samples, and data was used to validate a finite element

Preparation and Dynamic Mechanical Properties at Elevated Temperatures of a Tungsten/Glass Composite

NASA Astrophysics Data System (ADS)

Gao, Chong; Wang, Yingchun; Ma, Xueya; Liu, Keyi; Wang, Yubing; Li, Shukui; Cheng, Xingwang

2018-03-01

Experiments were conducted to prepare a borosilicate glass matrix composite containing 50 vol.% tungsten and examine its dynamic compressive behavior at elevated temperatures in the range of 450-775 °C. The results show that the homogenous microstructure of the tungsten/glass composite with relative density of 97% can be obtained by hot-pressing sintering at 800 °C for 1 h under pressure of 30 MPa. Dynamic compressive testing was carried out by a separate Hopkinson pressure bar system with a synchronous device. The results show that the peak stress decreases and the composite transforms from brittle to ductile in nature with testing temperature increasing from 450 to 750 °C. The brittle-ductile transition temperature is about 500 °C. Over 775 °C, the composite loses load-bearing capacity totally because of the excessive softening of the glass phase. In addition, the deformation and failure mechanism were analyzed.

Evaluation of wheel/rail contact mechanics : roller rig concept design review.

DOT National Transportation Integrated Search

2014-07-01

A need exists for a new test rig design with advanced sensing technologies that will allow the railroad industry and regulatory : agencies to better understand the wheel-rail contact dynamics and mechanics, especially as it pertains to high-speed rai...

Experimental study on dynamic mechanical behaviors of polycarbonate

NASA Astrophysics Data System (ADS)

Zhang, Wei; Gao, Yubo; Ye, Nan; Huang, Wei; Li, Dacheng

2017-01-01

Polycarbonate (PC) is a widely used engineering material in aerospace field, since it has excellent mechanical and optical property. In present study, both compressive and tensile tests of PC were conducted at high strain rates by using a split Hopkinson pressure bar. The high-speed camera and 2D Digital Image Correlation method (DIC) were used to analyze the dynamic deformation behavior of PC. Meanwhile, the plate impact experiment was carried out to measure the equation of state of PC in a single-stage gas gun, which consists of asymmetric impact technology, manganin gauges, PVDF, electromagnetic particle velocity gauges. The results indicate that the yield stress of PC increased with the strain rates in both dynamic compression and tension tests. The same phenomenon was similar to elasticity modulus at different strain rate. A constitutive model was used to describe the mechanical behaviors of PC accurately in different strain rates by contrast with the results of 2D-DIC. At last, The D-u Hugoniot curve of polycarbonate in high pressure was fitted by the least square method.

The Effect of Small Additions of Carbon Nanotubes on the Mechanical Properties of Epoxy Polymers under Static and Dynamic Loads

NASA Astrophysics Data System (ADS)

Tarasov, A. E.; Badamshina, E. R.; Anokhin, D. V.; Razorenov, S. V.; Vakorina, G. S.

2018-01-01

The results of measurements of the mechanical characteristics of cured epoxy composites containing small and ultrasmall additions of single-walled carbon nanotubes in the concentration range from 0 to 0.133 wt % under static and dynamic loads are presented. Static measurements of strength characteristics have been carried out under standard test conditions. Measurements of the Hugoniot elastic limit and spall strength were performed under a shock wave loading of the samples at a deformation rate of (0.8-1.5) ß 105 s-1 before the fracture using explosive devices by recording and subsequent analyzing the evolution of the full wave profiles. It has been shown that agglomerates of nanotubes present in the structure of the composites after curing cause a significant scatter of the measured strength parameters, both in the static and in the dynamic test modes. However, the effects of carbon nanotube additions in the studied concentration interval on the physical and mechanical characteristics of the parameters were not revealed for both types of loading.

Dynamic calibration of a wheelchair dynamometer.

PubMed

DiGiovine, C P; Cooper, R A; Boninger, M L

2001-01-01

The inertia and resistance of a wheelchair dynamometer must be determined in order to compare the results of one study to another, independent of the type of device used. The purpose of this study was to describe and implement a dynamic calibration test for characterizing the electro-mechanical properties of a dynamometer. The inertia, the viscous friction, the kinetic friction, the motor back-electromotive force constant, and the motor constant were calculated using three different methods. The methodology based on a dynamic calibration test along with a nonlinear regression analysis produced the best results. The coefficient of determination comparing the dynamometer model output to the measured angular velocity and torque was 0.999 for a ramp input and 0.989 for a sinusoidal input. The inertia and resistance were determined for the rollers and the wheelchair wheels. The calculation of the electro-mechanical parameters allows for the complete description of the propulsive torque produced by an individual, given only the angular velocity and acceleration. The measurement of the electro-mechanical properties of the dynamometer as well as the wheelchair/human system provides the information necessary to simulate real-world conditions.

Porous media fracturing dynamics: stepwise crack advancement and fluid pressure oscillations

NASA Astrophysics Data System (ADS)

Cao, Toan D.; Hussain, Fazle; Schrefler, Bernhard A.

2018-02-01

We present new results explaining why fracturing in saturated porous media is not smooth and continuous but is a distinct stepwise process concomitant with fluid pressure oscillations. All exact solutions and almost all numerical models yield smooth fracture advancement and fluid pressure evolution, while recent experimental results, mainly from the oil industry, observation from geophysics and a very few numerical results for the quasi-static case indeed reveal the stepwise phenomenon. We summarize first these new experiments and these few numerical solutions for the quasi-static case. Both mechanical loading and pressure driven fractures are considered because their behaviours differ in the direction of the pressure jumps. Then we explore stepwise crack tip advancement and pressure fluctuations in dynamic fracturing with a hydro-mechanical model of porous media based on the Hybrid Mixture Theory. Full dynamic analyses of examples dealing with both hydraulic fracturing and mechanical loading are presented. The stepwise fracture advancement is confirmed in the dynamic setting as well as in the pressure fluctuations, but there are substantial differences in the frequency contents of the pressure waves in the two loading cases. Comparison between the quasi-static and fully dynamic solutions reveals that the dynamic response gives much more information such as the type of pressure oscillations and related frequencies and should be applied whenever there is a doubt about inertia forces playing a role - the case in most fracturing events. In the absence of direct relevant dynamic tests on saturated media some experimental results on dynamic fracture in dry materials, a fast hydraulic fracturing test and observations from geophysics confirm qualitatively the obtained results such as the type of pressure oscillations and the substantial difference in the behaviour under the two loading cases.

Dynamic mechanical analysis of carbon nanotube-reinforced nanocomposites.

PubMed

Her, Shiuh-Chuan; Lin, Kuan-Yu

2017-06-16

To predict the mechanical properties of multiwalled carbon nanotube (MWCNT)-reinforced polymers, it is necessary to understand the role of the nanotube-polymer interface with regard to load transfer and the formation of the interphase region. The main objective of this study was to explore and attempt to clarify the reinforcement mechanisms of MWCNTs in epoxy matrix. Nanocomposites were fabricated by adding different amounts of MWCNTs to epoxy resin. Tensile test and dynamic mechanical analysis (DMA) were conducted to investigate the effect of MWCNT contents on the mechanical properties and thermal stability of nanocomposites. Compared with the neat epoxy, nanocomposite reinforced with 1 wt% of MWCNTs exhibited an increase of 152% and 54% in Young's modulus and tensile strength, respectively. Dynamic mechanical analysis demonstrates that both the storage modulus and glass transition temperature tend to increase with the addition of MWCNTs. Scanning electron microscopy (SEM) observations reveal that uniform dispersion and strong interfacial adhesion between the MWCNTs and epoxy are achieved, resulting in the improvement of mechanical properties and thermal stability as compared with neat epoxy.

Analysis and testing of a space crane articulating joint testbed

NASA Technical Reports Server (NTRS)

Sutter, Thomas R.; Wu, K. Chauncey

1992-01-01

The topics are presented in viewgraph form and include: space crane concept with mobile base; mechanical versus structural articulating joint; articulating joint test bed and reference truss; static and dynamic characterization completed for space crane reference truss configuration; improved linear actuators reduce articulating joint test bed backlash; 1-DOF space crane slew maneuver; boom 2 tip transient response finite element dynamic model; boom 2 tip transient response shear-corrected component modes torque driver profile; peak root member force vs. slew time torque driver profile; and open loop control of space crane motion.

Characterization of LaRC-CPI semicrystalline polyimide using thermal, dynamic mechanical and dielectric relaxation techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rich, D.C.; Huo, P.P.; Liu, C.

1993-12-31

The thermal, dynamic mechanical, and dielectric properties of the semicrystalline thermoplastic polyimide LaRC-CPI were studied. Using differential scanning calorimetry to measure heats of fusion and WAXS to measure crystallinity, the heat of fusion of perfect crystalline LaRC-CPI was determined to be 92 {+-} 2 J/g. DMA and dielectric measurements were performed on three LaRC-CPI films (as received, annealed, and amorphous). Crystallinity was found to reinforce the rubbery state resulting in a higher modulus and broader distribution of relaxation times. Broader relaxation for the crystalline LaRC-CPI was also observed in the dielectric tests. Processing strain and the thermal history were foundmore » to have a significant impact in both dynamic mechanical and dielectric relaxation measurements.« less

Application of holographic interferometry for analysis of the dynamic and modal characteristics of an advanced exotic metal airfoil structure

NASA Astrophysics Data System (ADS)

Fein, Howard

1999-03-01

Holographic Interferometry has been successfully employed to characterize the materials and behavior of diverse types of structures under stress. Specialized variations of this technology have also been applied to define dynamic and vibration related structural behavior. Such applications of holographic technique offer some of the most effective methods of modal and dynamic analysis available. Real-time dynamic testing of the modal and mechanical behavior of aerodynamic control and airfoil structures for advanced aircraft has always required advanced instrumentation for data collection in either actual flight test or wind-tunnel simulations. Advanced optical holography techniques are alternate methods which result in actual full-field behavioral data on the ground in a noninvasive environment. These methods offer significant insight in both the development and subsequent operational test and modeling of advanced exotic metal control structures and their integration with total vehicle system dynamics. Structures and materials can be analyzed with very low amplitude excitation and the resultant data can be used to adjust the accuracy mathematically derived structural and behavioral models. Holographic Interferometry offers a powerful tool to aid in the developmental engineering of exotic metal structures for high stress applications. Advanced Titanium alloy is a significant example of these sorts of materials which has found continually increased use in advanced aerodynamic, undersea, and other highly mobil platforms. Aircraft applications in particular must consider environments where extremes in vibration and impulsive mechanical stress can affect both operation and structural stability. These considerations present ideal requisites for analysis using advanced holographic methods in the initial design and test of structures made with such advanced materials. Holographic techniques are nondestructive, real- time, and definitive in allowing the identification of vibrational modes, displacements, and motion geometries. Such information can be crucial to the determination of mechanical configurations and designs as well as operational parameters of structural components fabricated from advanced and exotic materials. Anomalous behavioral characteristics can be directly related to hidden structural or mounting anomalies and defects. Deriving such information can be crucial to the determination of mechanical configurations and designs, as well as critical operational parameters of structural components fabricated from advanced and exotic materials.

Experimental Trapped-ion Quantum Simulation of the Kibble-Zurek dynamics in momentum space

PubMed Central

Cui, Jin-Ming; Huang, Yun-Feng; Wang, Zhao; Cao, Dong-Yang; Wang, Jian; Lv, Wei-Min; Luo, Le; del Campo, Adolfo; Han, Yong-Jian; Li, Chuan-Feng; Guo, Guang-Can

2016-01-01

The Kibble-Zurek mechanism is the paradigm to account for the nonadiabatic dynamics of a system across a continuous phase transition. Its study in the quantum regime is hindered by the requisite of ground state cooling. We report the experimental quantum simulation of critical dynamics in the transverse-field Ising model by a set of Landau-Zener crossings in pseudo-momentum space, that can be probed with high accuracy using a single trapped ion. We test the Kibble-Zurek mechanism in the quantum regime in the momentum space and find the measured scaling of excitations is in accordance with the theoretical prediction. PMID:27633087

Language Test as Boundary Object: Perspectives from Test Users in the Healthcare Domain

ERIC Educational Resources Information Center

Macqueen, Susy; Pill, John; Knoch, Ute

2016-01-01

Objects that sit between intersecting social worlds, such as Language for Specific Purposes (LSP) tests, are "boundary objects"--dynamic, historically derived mechanisms which maintain coherence between worlds (Star & Griesemer, 1989). They emerge initially from sociopolitical mandates, such as the need to ensure a safe and efficient…

A Model to Study Articular Cartilage Mechanical and Biological Responses to Sliding Loads.

PubMed

Schätti, Oliver R; Gallo, Luigi M; Torzilli, Peter A

2016-08-01

In physiological conditions, joint function involves continuously moving contact areas over the tissue surface. Such moving contacts play an important role for the durability of the tissue. It is known that in pathological joints these motion paths and contact mechanics change. Nevertheless, limited information exists on the impact of such physiological and pathophysiological dynamic loads on cartilage mechanics and its subsequent biological response. We designed and validated a mechanical device capable of applying simultaneous compression and sliding forces onto cartilage explants to simulate moving joint contact. Tests with varying axial loads (1-4 kg) and sliding speeds (1-20 mm/s) were performed on mature viable bovine femoral condyles to investigate cartilage mechanobiological responses. High loads and slow sliding speeds resulted in highest cartilage deformations. Contact stress and effective cartilage moduli increased with increasing load and increasing speed. In a pilot study, changes in gene expression of extracellular matrix proteins were correlated with strain, contact stress and dynamic effective modulus. This study describes a mechanical test system to study the cartilage response to reciprocating sliding motion and will be helpful in identifying mechanical and biological mechanisms leading to the initiation and development of cartilage degeneration.

Dynamic impact testing with servohydraulic testing machines

NASA Astrophysics Data System (ADS)

Bardenheier, R.; Rogers, G.

2006-08-01

The design concept of “Crashworthiness” requires the information on material behaviour under dynamic impact loading in order to describe and predict the crash behaviour of structures. Especially the transport related industries, like car, railway or aircraft industry, pursue the concept of lightweight design for a while now. The materials' maximum constraint during loading is pushed to permanently increasing figures. This means in terms of crashworthiness that the process of energy absorption in structures and the mechanical behaviour of materials must well understood and can be described appropriately by material models. In close cooperation with experts from various industries and research institutes Instron has developed throughout the past years a new family of servohydraulic testing machines specifically designed to cope with the dynamics of high rate testing. Main development steps are reflected versus their experimental necessities.

Notes on Earth Atmospheric Entry for Mars Sample Return Missions

NASA Technical Reports Server (NTRS)

Rivell, Thomas

2006-01-01

The entry of sample return vehicles (SRVs) into the Earth's atmosphere is the subject of this document. The Earth entry environment for vehicles, or capsules, returning from the planet Mars is discussed along with the subjects of dynamics, aerodynamics, and heat transfer. The material presented is intended for engineers and scientists who do not have strong backgrounds in aerodynamics, aerothermodynamics and flight mechanics. The document is not intended to be comprehensive and some important topics are omitted. The topics considered in this document include basic principles of physics (fluid mechanics, dynamics and heat transfer), chemistry and engineering mechanics. These subjects include: a) fluid mechanics (aerodynamics, aerothermodynamics, compressible fluids, shock waves, boundary layers, and flow regimes from subsonic to hypervelocity; b) the Earth s atmosphere and gravity; c) thermal protection system design considerations; d) heat and mass transfer (convection, radiation, and ablation); e) flight mechanics (basic rigid body dynamics and stability); and f) flight- and ground-test requirements; and g) trajectory and flow simulation methods.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bernardin, John D; Baca, Allen G

This paper presents the mechanical design, fabrication and dynamic testing of an electrostatic analyzer spacecraft instrument. The functional and environmental requirements combined with limited spacecraft accommodations, resulted in complex component geometries, unique material selections, and difficult fabrication processes. The challenging aspects of the mechanical design and several of the more difficult production processes are discussed. In addition, the successes, failures, and lessons learned from acoustic and random vibration testing of a full-scale prototype instrument are presented.

Mechanical properties of kenaf composites using dynamic mechanical analysis

NASA Astrophysics Data System (ADS)

Loveless, Thomas A.

Natural fibers show potential to replace glass fibers in thermoset and thermoplastic composites. Kenaf is a bast-type fiber with high specific strength and great potential to compete with glass fibers. In this research kenaf/epoxy composites were analyzed using Dynamic Mechanical Analysis (DMA). A three-point bend apparatus was used in the DMA testing. The samples were tested at 1 hertz, at a displacement of 10 ?m, and at room temperature. The fiber volume content of the kenaf was varied from 20% - 40% in 5% increments. Ten samples of each fiber volume fraction were manufactured and tested. The flexural storage modulus, the flexural loss modulus, and the loss factor were reported. Generally as the fiber volume fraction of kenaf increased, the flexural storage and flexural loss modulus increased. The loss factor remained relatively constant with increasing fiber volume fraction. Woven and chopped fiberglass/epoxy composites were manufactured and tested to be compared with the kenaf/epoxy composites. Both of the fiberglass/epoxy composites reported higher flexural storage and flexural loss modulus values. The kenaf/epoxy composites reported higher loss factor values. The specific flexural storage and specific flexural loss modulus were calculated for both the fiberglass and kenaf fiber composites. Even though the kenaf composites reported a lower density, the fiberglass composites reported higher specific mechanical properties.

Design and application of permanent magnet flux sources for mechanical testing of magnetoactive elastomers at variable field directions.

PubMed

Hiptmair, F; Major, Z; Haßlacher, R; Hild, S

2015-08-01

Magnetoactive elastomers (MAEs) are a class of smart materials whose mechanical properties can be rapidly and reversibly changed by an external magnetic field. Due to this tunability, they are useable for actuators or in active vibration control applications. An extensive magnetomechanical characterization is necessary for MAE material development and requires experiments under cyclic loading in uniform but variable magnetic fields. MAE testing apparatus typically rely on fields of adjustable strength, but fixed (transverse) direction, often provided by electromagnets. In this work, two permanent magnet flux sources were developed as an add-on for a modular test stand, to allow for mechanical testing in uniform fields of variable direction. MAE specimens, based on a silicone matrix with isotropic and anisotropic carbonyl iron particle distributions, were subjected to dynamic mechanical analysis under different field and loading configurations. The magneto-induced increase of stiffness and energy dissipation was determined by the change of the hysteresis loop area and dynamic modulus values. A distinct influence of the composite microstructure and the loading state was observed. Due to the very soft and flexible matrix used for preparing the MAE samples, the material stiffness and damping behavior could be varied over a wide range via the applied field direction and intensity.

Aging and loading rate effects on the mechanical behavior of equine bone

NASA Astrophysics Data System (ADS)

Kulin, Robb M.; Jiang, Fengchun; Vecchio, Kenneth S.

2008-06-01

Whether due to a sporting accident, high-speed impact, fall, or other catastrophic event, the majority of clinical bone fractures occur under dynamic loading conditions. However, although extensive research has been performed on the quasi-static fracture and mechanical behavior of bone to date, few high-quality studies on the fracture behavior of bone at high strain rates have been performed. Therefore, many questions remain regarding the material behavior, including not only the loading-rate-dependent response of bone, but also how this response varies with age. In this study, tests were performed on equine femoral bone taken post-mortem from donors 6 months to 28 years of age. Quasi-static and dynamic tests were performed to determine the fracture toughness and compressive mechanical behavior as a function of age at varying loading rates. Fracture paths were then analyzed using scanning confocal and scanning-electron microscopy techniques to assess the role of various microstructural features on toughening mechanisms.

Verification and implementation of set-up empirical models in pile design : research project capsule.

DOT National Transportation Integrated Search

2016-08-01

The primary objectives of this research include: performing static and dynamic load tests on : newly instrumented test piles to better understand the set-up mechanism for individual soil : layers, verifying or recalibrating previously developed empir...

An investigation into the mechanism of the polygonal wear of metro train wheels and its effect on the dynamic behaviour of a wheel/rail system

NASA Astrophysics Data System (ADS)

Jin, Xuesong; Wu, Lei; Fang, Jianying; Zhong, Shuoqiao; Ling, Liang

2012-12-01

This paper presents a detailed investigation conducted into the mechanism of the polygonal wear of metro train wheels through extensive experiments conducted at the sites. The purpose of the experimental investigation is to determine from where the resonant frequency that causes the polygonal wear of the metro train wheels originates. The experiments include the model tests of a vehicle and its parts and the tracks, the dynamic behaviour test of the vehicle in operation and the observation test of the polygonal wear development of the wheels. The tracks tested include the viaducts and the tunnel tracks. The structure model tests show that the average passing frequency of a polygonal wheel is approximately close to the first bending resonant frequency of the wheelset that is found by the wheelset model test and verified by the finite element analysis of the wheelset. Also, the dynamic behaviour test of the vehicle in operation indicates the main frequencies of the vertical acceleration vibration of the axle boxes, which are dominant in the vertical acceleration vibration of the axle boxes and close to the passing frequency of a polygonal wheel, which shows that the first bending resonant frequency of the wheelset is very exciting in the wheelset operation. The observation test of the polygonal wear development of the wheels indicates an increase in the rate of the polygonal wear of the wheels after their re-profiling. This paper also describes the dynamic models used for the metro vehicle coupled with the ballasted track and the slab track to analyse the effect of the polygonal wear of the wheels on the wheel/rail normal forces.

Growth plate cartilage shows different strain patterns in response to static versus dynamic mechanical modulation.

PubMed

Kaviani, Rosa; Londono, Irene; Parent, Stefan; Moldovan, Florina; Villemure, Isabelle

2016-08-01

Longitudinal growth of long bones and vertebrae occurs in growth plate cartilage. This process is partly regulated by mechanical forces, which are one of the underlying reasons for progression of growth deformities such as idiopathic adolescent scoliosis and early-onset scoliosis. This concept of mechanical modulation of bone growth is also exploited in the development of fusionless treatments of these deformities. However, the optimal loading condition for the mechanical modulation of growth plate remains to be identified. The objective of this study was to evaluate the effects of in vitro static versus dynamic modulation and of dynamic loading parameters, such as frequency and amplitude, on the mechanical responses and histomorphology of growth plate explants. Growth plate explants from distal ulnae of 4-week-old swines were extracted and randomly distributed among six experimental groups: baseline ([Formula: see text]), control ([Formula: see text]), static ([Formula: see text]) and dynamic ([Formula: see text]). For static and dynamic groups, mechanical modulation was performed in vitro using an Indexed CartiGen bioreactor. A stress relaxation test combined with confocal microscopy and digital image correlation was used to characterize the mechanical responses of each explant in terms of peak stress, equilibrium stress, equilibrium modulus of elasticity and strain pattern. Histomorphometrical measurements were performed on toluidine blue tissue sections using a semi-automatic custom-developed MATLAB toolbox. Results suggest that compared to dynamic modulation, static modulation changes the strain pattern of the tissue and thus is more detrimental for tissue biomechanics, while the histomorphological parameters are not affected by mechanical modulation. Also, under dynamic modulation, changing the frequency or amplitude does not affect the biomechanical response of the tissue. Results of this study will be useful in finding optimal and non-damaging parameters for the mechanical modulation of growth plate in fusionless treatments.

Correlation of microstructure with dynamic deformation behavior and penetration performance of tungsten heavy alloys fabricated by mechanical alloying

NASA Astrophysics Data System (ADS)

Kim, Dong-Kuk; Lee, Sunghak; Ryu, Ho Jin; Hyunghong, Soon; Noh, Joon-Woong

2000-10-01

In this study, tungsten heavy alloy specimens were fabricated by mechanical alloying (MA), and their dynamic torsional properties and penetration performance were investigated. Dynamic torsional tests were conducted on the specimens fabricated with different sintering temperatures after MA, and then the test data were compared with those of a conventionally processed specimen. Refinement of tungsten particles was obtained after MA, but contiguity was seriously increased, thereby leading to low ductility and impact energy. Specimens in which both particle size and contiguity were simultaneously reduced by MA and two-step sintering and those having higher matrix fraction by partial MA were successfully fabricated. The dynamic test results indicated that the formation of adiabatic shear bands was expected because of the plastic localization at the central area of the gage section. Upon highspeed impact testing of these specimens, self-sharpening was promoted by the adiabatic shear band formation, but their penetration performance did not improve since much of kinetic energy of the penetrators was consumed for the microcrack formation due to interfacial debonding and cleavage fracture of tungsten particles. In order to improve penetration performance as well as to achieve selfsharpening by applying MA, conditions of MA and sintering process should be established so that alloy densification, particle refinement, and contiguity reduction can be simultaneously achieved.

Structural Dynamic Analyses And Test Predictions For Spacecraft Structures With Non-Linearities

NASA Astrophysics Data System (ADS)

Vergniaud, Jean-Baptiste; Soula, Laurent; Newerla, Alfred

2012-07-01

The overall objective of the mechanical development and verification process is to ensure that the spacecraft structure is able to sustain the mechanical environments encountered during launch. In general the spacecraft structures are a-priori assumed to behave linear, i.e. the responses to a static load or dynamic excitation, respectively, will increase or decrease proportionally to the amplitude of the load or excitation induced. However, past experiences have shown that various non-linearities might exist in spacecraft structures and the consequences of their dynamic effects can significantly affect the development and verification process. Current processes are mainly adapted to linear spacecraft structure behaviour. No clear rules exist for dealing with major structure non-linearities. They are handled outside the process by individual analysis and margin policy, and analyses after tests to justify the CLA coverage. Non-linearities can primarily affect the current spacecraft development and verification process on two aspects. Prediction of flights loads by launcher/satellite coupled loads analyses (CLA): only linear satellite models are delivered for performing CLA and no well-established rules exist how to properly linearize a model when non- linearities are present. The potential impact of the linearization on the results of the CLA has not yet been properly analyzed. There are thus difficulties to assess that CLA results will cover actual flight levels. Management of satellite verification tests: the CLA results generated with a linear satellite FEM are assumed flight representative. If the internal non- linearities are present in the tested satellite then there might be difficulties to determine which input level must be passed to cover satellite internal loads. The non-linear behaviour can also disturb the shaker control, putting the satellite at risk by potentially imposing too high levels. This paper presents the results of a test campaign performed in the frame of an ESA TRP study [1]. A bread-board including typical non-linearities has been designed, manufactured and tested through a typical spacecraft dynamic test campaign. The study has demonstrate the capabilities to perform non-linear dynamic test predictions on a flight representative spacecraft, the good correlation of test results with respect to Finite Elements Model (FEM) prediction and the possibility to identify modal behaviour and to characterize non-linearities characteristics from test results. As a synthesis for this study, overall guidelines have been derived on the mechanical verification process to improve level of expertise on tests involving spacecraft including non-linearity.

Double Trouble at High Density: Cross-Level Test of Resource-Related Adaptive Plasticity and Crowding-Related Fitness

PubMed Central

Gergs, André; Preuss, Thomas G.; Palmqvist, Annemette

2014-01-01

Population size is often regulated by negative feedback between population density and individual fitness. At high population densities, animals run into double trouble: they might concurrently suffer from overexploitation of resources and also from negative interference among individuals regardless of resource availability, referred to as crowding. Animals are able to adapt to resource shortages by exhibiting a repertoire of life history and physiological plasticities. In addition to resource-related plasticity, crowding might lead to reduced fitness, with consequences for individual life history. We explored how different mechanisms behind resource-related plasticity and crowding-related fitness act independently or together, using the water flea Daphnia magna as a case study. For testing hypotheses related to mechanisms of plasticity and crowding stress across different biological levels, we used an individual-based population model that is based on dynamic energy budget theory. Each of the hypotheses, represented by a sub-model, is based on specific assumptions on how the uptake and allocation of energy are altered under conditions of resource shortage or crowding. For cross-level testing of different hypotheses, we explored how well the sub-models fit individual level data and also how well they predict population dynamics under different conditions of resource availability. Only operating resource-related and crowding-related hypotheses together enabled accurate model predictions of D. magna population dynamics and size structure. Whereas this study showed that various mechanisms might play a role in the negative feedback between population density and individual life history, it also indicated that different density levels might instigate the onset of the different mechanisms. This study provides an example of how the integration of dynamic energy budget theory and individual-based modelling can facilitate the exploration of mechanisms behind the regulation of population size. Such understanding is important for assessment, management and the conservation of populations and thereby biodiversity in ecosystems. PMID:24626228

A Multi-Scale Method for Dynamics Simulation in Continuum Solvent Models I: Finite-Difference Algorithm for Navier-Stokes Equation

PubMed Central

Xiao, Li; Cai, Qin; Li, Zhilin; Zhao, Hongkai; Luo, Ray

2014-01-01

A multi-scale framework is proposed for more realistic molecular dynamics simulations in continuum solvent models by coupling a molecular mechanics treatment of solute with a fluid mechanics treatment of solvent. This article reports our initial efforts to formulate the physical concepts necessary for coupling the two mechanics and develop a 3D numerical algorithm to simulate the solvent fluid via the Navier-Stokes equation. The numerical algorithm was validated with multiple test cases. The validation shows that the algorithm is effective and stable, with observed accuracy consistent with our design. PMID:25404761

Dynamical mechanical characteristic simulation and analysis of the low voltage switch under vibration and shock conditions

NASA Astrophysics Data System (ADS)

Miao, Xiaodan; Han, Feng

2017-04-01

The low voltage switch has widely application especially in the hostile environment such as large vibration and shock conditions. In order to ensure the validity of the switch in the hostile environment, it is necessary to predict its mechanical characteristic. In traditional method, the complex and expensive testing system is build up to verify its validity. This paper presented a method based on finite element analysis to predict the dynamic mechanical characteristic of the switch by using ANSYS software. This simulation could provide the basis for the design and optimization of the switch to shorten the design process to improve the product efficiency.

Classical Electrodynamics: Problems with solutions; Problems with solutions

NASA Astrophysics Data System (ADS)

Likharev, Konstantin K.

2018-06-01

l Advanced Physics is a series comprising four parts: Classical Mechanics, Classical Electrodynamics, Quantum Mechanics and Statistical Mechanics. Each part consists of two volumes, Lecture notes and Problems with solutions, further supplemented by an additional collection of test problems and solutions available to qualifying university instructors. This volume, Classical Electrodynamics: Lecture notes is intended to be the basis for a two-semester graduate-level course on electricity and magnetism, including not only the interaction and dynamics charged point particles, but also properties of dielectric, conducting, and magnetic media. The course also covers special relativity, including its kinematics and particle-dynamics aspects, and electromagnetic radiation by relativistic particles.

Mathematical modeling and computational prediction of cancer drug resistance.

PubMed

Sun, Xiaoqiang; Hu, Bin

2017-06-23

Diverse forms of resistance to anticancer drugs can lead to the failure of chemotherapy. Drug resistance is one of the most intractable issues for successfully treating cancer in current clinical practice. Effective clinical approaches that could counter drug resistance by restoring the sensitivity of tumors to the targeted agents are urgently needed. As numerous experimental results on resistance mechanisms have been obtained and a mass of high-throughput data has been accumulated, mathematical modeling and computational predictions using systematic and quantitative approaches have become increasingly important, as they can potentially provide deeper insights into resistance mechanisms, generate novel hypotheses or suggest promising treatment strategies for future testing. In this review, we first briefly summarize the current progress of experimentally revealed resistance mechanisms of targeted therapy, including genetic mechanisms, epigenetic mechanisms, posttranslational mechanisms, cellular mechanisms, microenvironmental mechanisms and pharmacokinetic mechanisms. Subsequently, we list several currently available databases and Web-based tools related to drug sensitivity and resistance. Then, we focus primarily on introducing some state-of-the-art computational methods used in drug resistance studies, including mechanism-based mathematical modeling approaches (e.g. molecular dynamics simulation, kinetic model of molecular networks, ordinary differential equation model of cellular dynamics, stochastic model, partial differential equation model, agent-based model, pharmacokinetic-pharmacodynamic model, etc.) and data-driven prediction methods (e.g. omics data-based conventional screening approach for node biomarkers, static network approach for edge biomarkers and module biomarkers, dynamic network approach for dynamic network biomarkers and dynamic module network biomarkers, etc.). Finally, we discuss several further questions and future directions for the use of computational methods for studying drug resistance, including inferring drug-induced signaling networks, multiscale modeling, drug combinations and precision medicine. © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Development of Fracture Mechanics Maps for Composite Materials. Volume 2.

DTIC Science & Technology

1985-12-01

AD-A169 663 DEP 1/3UR OIOST l uNCL~ss~~n HUCI S I B M 11 1*2 AF,:P,.-TR-?5,-4150 DEVELOPMENT OF FRACTURE MECHANICS MAPS FOR COMPOSITE MATERIALS Dr. H...coIo. Development of N/A N/A N/A N/A Fracture Mechanics Maps for Composite Materials 12. PERSONAL AUTHORISI Editor (Dr. H. W. Bergmann) 13. TYPE OF...GROUP SUB GR. Fiber Reinforced Composites , Dynamic Test, Thermal Cycling, 1I1 04 Quality Control, Static Test, Stress Concentrations 01 03 19

Hydrogen gas embrittlement and the disc pressure test

NASA Technical Reports Server (NTRS)

Bachelet, E. J.; Troiano, A. R.

1973-01-01

A disc pressure test has been used to study the influenced of a hydrogen gas environment on the mechanical properties of three high strength superalloys, Inconel 718, L-605 and A-286, in static and dynamic conditions. The influence of the hydrogen pressure, loading rate, temperature, mechanical and thermal fatigue has investigated. The permeation characteristics of Inconel 718 have been determined in collaboration with the French AEC. The results complemented by a fractographic study are consistent either with a stress-sorption or with an internal embrittlement type of mechanism.

Development of a crashworthy seat for commuter aircraft.

DOT National Transportation Integrated Search

1990-09-01

A series of dynamic impact tests were conducted using a prototype seat with an energy absorbing mechanism as part of the seat pan. The seat frame was designed to represent a typical commuter aircraft passenger seat. Tests were conducted in an orienta...

Dynamic Behavior of Spiral-Groove and Rayleigh-Step Self-Acting Face Seals

NASA Technical Reports Server (NTRS)

Dirusso, Eliseo

1984-01-01

Tests were performed to determine the dynamic behavior and establish baseline dynamic data for five self-acting face seals employing Rayleigh-step lift-pads and inward pumping as well as outward-pumping spiral grooves for the lift-generating mechanism. The primary parameters measured in the tests were film thickness, seal seat axial motion, and seal frictional torque. The data show the dynamic response of the film thickness to the motion of the seal seat. The inward-pumping spiral-groove seals exhibited a high-amplitude film thickness vibratory mode with a frequency of four times the shaft speed. This mode was not observed in the other seals tested. The tests also revealed that high film thickness vibration amplitude produces considerably higher average film thickness than do low amplitude film thickness vibrations. The seals were tested at a constant face load of 73 N (16.4 lb) with ambient air at room temperature and atmospheric pressure as the fluid medium. The test speed range was from 7000 to 17000 rpm. Seal tangential speed range was 34.5 to 83.7 m/sec (113 to 274 ft/sec).

Dynamic Properties of Human Tympanic Membrane Based on Frequency-Temperature Superposition

PubMed Central

Zhang, Xiangming; Gan, Rong Z.

2012-01-01

The human tympanic membrane (TM) transfers sound in the ear canal into the mechanical vibration of the ossicles in the middle ear. The dynamic properties of TM directly affect the middle ear transfer function. The static or quasi-static mechanical properties of TM were reported in the literature, but the dynamic properties of TM over the auditory frequency range are very limited. In this paper, a new method was developed to measure the dynamic properties of human TM using the Dynamic-Mechanical Analyzer (DMA). The test was conducted at the frequency range of 1 to 40 Hz at three different temperatures: 5°, 25° and 37°C. The frequency-temperature superposition was applied to extend the testing frequency range to a much higher level (at least 3800 Hz). The generalized linear solid model was employed to describe the constitutive relation of the TM. The storage modulus E’ and the loss modulus E” were obtained from 11 specimens. The mean storage modulus was 15.1 MPa at 1 Hz and 27.6 MPa at 3800 Hz. The mean loss modulus was 0.28 MPa at 1 Hz and 4.1 MPa at 3800 Hz. The results show that the frequency-temperature superposition is a feasible approach to study the dynamic properties of the ear soft tissues. The dynamic properties of human TM obtained in this study provide a better description of the damping behavior of ear tissues. The properties can be transferred into the finite element (FE) model of the human ear to replace the Rayleigh type damping. The data reported here contribute to the biomechanics of the middle ear and improve the accuracy of the FE model for the human ear. PMID:22820983

Impact compressive and bending behaviour of rocks accompanied by electromagnetic phenomena.

PubMed

Kobayashi, Hidetoshi; Horikawa, Keitaro; Ogawa, Kinya; Watanabe, Keiko

2014-08-28

It is well known that electromagnetic phenomena are often observed preceding earthquakes. However, the mechanism by which these electromagnetic waves are generated during the fracture and deformation of rocks has not been fully identified. Therefore, in order to examine the relationship between the electromagnetic phenomena and the mechanical properties of rocks, uniaxial compression and three-point bending tests for two kinds of rocks with different quartz content, granite and gabbro, have been carried out at quasi-static and dynamic rates. Especially, in the bending tests, pre-cracked specimens of granite were also tested. Using a split Hopkinson pressure bar and a ferrite-core antenna in close proximity to the specimens, both the stress-strain (load-displacement) curve and simultaneous electromagnetic wave magnitude were measured. It was found that the dynamic compressive and bending strengths and the stress increase slope of both rocks were higher than those observed in static tests; therefore, there is a strain-rate dependence in their strength and stress increase rate. It was found from the tests using the pre-cracked bending specimens that the intensity of electromagnetic waves measured during crack extension increased almost proportionally to the increase of the maximum stress intensity factor of specimens. This tendency was observed in both the dynamic and quasi-static three-point bending tests for granite. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Research on Equivalent Tests of Dynamics of On-orbit Soft Contact Technology Based on On-Orbit Experiment Data

NASA Astrophysics Data System (ADS)

Yang, F.; Dong, Z. H.; Ye, X.

2018-05-01

Currently, space robots have been become a very important means of space on-orbit maintenance and support. Many countries are taking deep research and experiment on this. Because space operation attitude is very complicated, it is difficult to model them in research lab. This paper builds up a complete equivalent experiment framework according to the requirement of proposed space soft-contact technology. Also, this paper carries out flexible multi-body dynamics parameters verification for on-orbit soft-contact mechanism, which combines on-orbit experiment data, the built soft-contact mechanism equivalent model and flexible multi-body dynamics equivalent model that is based on KANE equation. The experiment results approve the correctness of the built on-orbit soft-contact flexible multi-body dynamics.

Development and characterization of a synthetic PVC/DEHP myocardial tissue analogue material for CT imaging applications.

PubMed

Ramadan, Sherif; Paul, Narinder; Naguib, Hani E

2018-04-01

A simple myocardial analogue material has great potential to help researchers in the creation of medical CT Imaging phantoms. This work aims to outline a Bis(2-ethylhexyl) phthalate (DEHP) plasticizer/PVC material to achieve this. DEHP-PVC was manufactured in three ratios, 75, 80, and 85% DEHP by heating at 110 °C for 10 min to promote DEHP-PVC binding followed by heating at 150 °C to melt the blend. The material was then tested utilizing FTIR, tensile testing, dynamic mechanical analysis and imaged with computed tomography. The FTIR testing finds the presence of C-CL and carbonyl bonds that demonstrate the binding required in this plasticized material. The tensile testing finds a modulus of 180-20 kPa that increases with the proportion of plasticizer. The dynamic mechanical analysis finds a linear increase in viscoelastic properties with a storage/loss modulus of 6/.5-120/18 kPa. Finally, the CT number of the material increases with higher PVC content from 55 to 144HU. The 80% DEHP-PVC ratio meets the mechanical and CT properties necessary to function as a myocardial tissue analogue.

Mechanical properties of water desalination and wastewater treatment membranes

DOE PAGES

Wang, Kui; Abdalla, Ahmed A.; Khaleel, Mohammad A.; ...

2017-07-13

Applications of membrane technology in water desalination and wastewater treatment have increased significantly in the past fewdecades due to itsmany advantages over otherwater treatment technologies.Water treatment membranes provide high flux and contaminant rejection ability and require good mechanical strength and durability. Thus, assessing the mechanical properties of water treatment membranes is critical not only to their design, but also for studying their failure mechanisms, including the surface damage, mechanical and chemical ageing, delamination and loss of dimensional stability of the membranes. The various experimental techniques to assess themechanical properties ofwastewater treatment and desalinationmembranes are reviewed. Uniaxial tensile test, bending test,more » dynamic mechanical analysis, nanoindentation and bursting tests are the most widely used mechanical characterization methods for water treatment membranes. Mechanical degradations induced by fouling, chemical cleaning as well as membrane delamination are then discussed. Moreover, in order to study the membranesmechanical responses under similar loading conditions, the stress-state of the membranes are analyzed and advanced mechanical testing approaches are proposed. Lastly, some perspectives are highlighted to study the structure-properties relationship for wastewater treatment and water desalination membranes.« less

Mechanical properties of water desalination and wastewater treatment membranes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Kui; Abdalla, Ahmed A.; Khaleel, Mohammad A.

Applications of membrane technology in water desalination and wastewater treatment have increased significantly in the past fewdecades due to itsmany advantages over otherwater treatment technologies.Water treatment membranes provide high flux and contaminant rejection ability and require good mechanical strength and durability. Thus, assessing the mechanical properties of water treatment membranes is critical not only to their design, but also for studying their failure mechanisms, including the surface damage, mechanical and chemical ageing, delamination and loss of dimensional stability of the membranes. The various experimental techniques to assess themechanical properties ofwastewater treatment and desalinationmembranes are reviewed. Uniaxial tensile test, bending test,more » dynamic mechanical analysis, nanoindentation and bursting tests are the most widely used mechanical characterization methods for water treatment membranes. Mechanical degradations induced by fouling, chemical cleaning as well as membrane delamination are then discussed. Moreover, in order to study the membranesmechanical responses under similar loading conditions, the stress-state of the membranes are analyzed and advanced mechanical testing approaches are proposed. Lastly, some perspectives are highlighted to study the structure-properties relationship for wastewater treatment and water desalination membranes.« less

Complex patterns of abnormal heartbeats

NASA Technical Reports Server (NTRS)

Schulte-Frohlinde, Verena; Ashkenazy, Yosef; Goldberger, Ary L.; Ivanov, Plamen Ch; Costa, Madalena; Morley-Davies, Adrian; Stanley, H. Eugene; Glass, Leon

2002-01-01

Individuals having frequent abnormal heartbeats interspersed with normal heartbeats may be at an increased risk of sudden cardiac death. However, mechanistic understanding of such cardiac arrhythmias is limited. We present a visual and qualitative method to display statistical properties of abnormal heartbeats. We introduce dynamical "heartprints" which reveal characteristic patterns in long clinical records encompassing approximately 10(5) heartbeats and may provide information about underlying mechanisms. We test if these dynamics can be reproduced by model simulations in which abnormal heartbeats are generated (i) randomly, (ii) at a fixed time interval following a preceding normal heartbeat, or (iii) by an independent oscillator that may or may not interact with the normal heartbeat. We compare the results of these three models and test their limitations to comprehensively simulate the statistical features of selected clinical records. This work introduces methods that can be used to test mathematical models of arrhythmogenesis and to develop a new understanding of underlying electrophysiologic mechanisms of cardiac arrhythmia.

Mechanisms driving postfire abundance of a generalist mammal

Treesearch

R. Zwolak; D. E. Pearson; Y. K. Ortega; E. E. Crone

2012-01-01

Changes in vertebrate abundance following disturbance are commonly attributed to shifts in food resources or predation pressure, but underlying mechanisms have rarely been tested. We examined four hypotheses for the commonly reported increase in abundance of deer mouse (Peromyscus maniculatus (Wagner, 1845)) following forest fires: source-sink dynamics, decreased...

High-throughput methods for characterizing the mechanical properties of coatings

NASA Astrophysics Data System (ADS)

Siripirom, Chavanin

The characterization of mechanical properties in a combinatorial and high-throughput workflow has been a bottleneck that reduced the speed of the materials development process. High-throughput characterization of the mechanical properties was applied in this research in order to reduce the amount of sample handling and to accelerate the output. A puncture tester was designed and built to evaluate the toughness of materials using an innovative template design coupled with automation. The test is in the form of a circular free-film indentation. A single template contains 12 samples which are tested in a rapid serial approach. Next, the operational principles of a novel parallel dynamic mechanical-thermal analysis instrument were analyzed in detail for potential sources of errors. The test uses a model of a circular bilayer fixed-edge plate deformation. A total of 96 samples can be analyzed simultaneously which provides a tremendous increase in efficiency compared with a conventional dynamic test. The modulus values determined by the system had considerable variation. The errors were observed and improvements to the system were made. A finite element analysis was used to analyze the accuracy given by the closed-form solution with respect to testing geometries, such as thicknesses of the samples. A good control of the thickness of the sample was proven to be crucial to the accuracy and precision of the output. Then, the attempt to correlate the high-throughput experiments and conventional coating testing methods was made. Automated nanoindentation in dynamic mode was found to provide information on the near-surface modulus and could potentially correlate with the pendulum hardness test using the loss tangent component. Lastly, surface characterization of stratified siloxane-polyurethane coatings was carried out with X-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, transmission electron microscopy, and nanoindentation. The siloxane component segregates to the surface during curing. The distribution of siloxane as a function of thickness into the sample showed differences depending on the formulation parameters. The coatings which had higher siloxane content near the surface were those coatings found to perform well in field tests.

Space Shuttle Tail Service Mast Concept Verification

NASA Technical Reports Server (NTRS)

Uda, R. T.

1976-01-01

Design studies and analyses were performed to describe the loads and dynamics of the space shuttle tail service masts (TSMs). Of particular interest are the motion and interaction of the umbilical carrier plate, lanyard system, vacuum jacketed hoses, latches, links, and masthead. A development test rig was designed and fabricated to obtain experimental data. The test program is designed to (1) verify the theoretical dynamics calculations, (2) prove the soundness of design concepts, and (3) elucidate problem areas (if any) in the design of mechanisms and structural components. Design, fabrication, and initiation of TSM development testing at Kennedy Space Center are described.

Microcellular nanocomposite injection molding process

Treesearch

Mingjun Yuan; Lih-Sheng Turng; Rick Spindler; Daniel Caulfield; Chris Hunt

2003-01-01

This study aims to explore the processing benefits and property improvements of combining nanocomposites with microcellular injection molding. The molded parts produced based on the Design of Experiments (DOE) matrices were subjected to tensile testing, impact testing, and Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Dynamic Mechanical...

Research and test facilities

NASA Technical Reports Server (NTRS)

1993-01-01

A description is given of each of the following Langley research and test facilities: 0.3-Meter Transonic Cryogenic Tunnel, 7-by 10-Foot High Speed Tunnel, 8-Foot Transonic Pressure Tunnel, 13-Inch Magnetic Suspension & Balance System, 14-by 22-Foot Subsonic Tunnel, 16-Foot Transonic Tunnel, 16-by 24-Inch Water Tunnel, 20-Foot Vertical Spin Tunnel, 30-by 60-Foot Wind Tunnel, Advanced Civil Transport Simulator (ACTS), Advanced Technology Research Laboratory, Aerospace Controls Research Laboratory (ACRL), Aerothermal Loads Complex, Aircraft Landing Dynamics Facility (ALDF), Avionics Integration Research Laboratory, Basic Aerodynamics Research Tunnel (BART), Compact Range Test Facility, Differential Maneuvering Simulator (DMS), Enhanced/Synthetic Vision & Spatial Displays Laboratory, Experimental Test Range (ETR) Flight Research Facility, General Aviation Simulator (GAS), High Intensity Radiated Fields Facility, Human Engineering Methods Laboratory, Hypersonic Facilities Complex, Impact Dynamics Research Facility, Jet Noise Laboratory & Anechoic Jet Facility, Light Alloy Laboratory, Low Frequency Antenna Test Facility, Low Turbulence Pressure Tunnel, Mechanics of Metals Laboratory, National Transonic Facility (NTF), NDE Research Laboratory, Polymers & Composites Laboratory, Pyrotechnic Test Facility, Quiet Flow Facility, Robotics Facilities, Scientific Visualization System, Scramjet Test Complex, Space Materials Research Laboratory, Space Simulation & Environmental Test Complex, Structural Dynamics Research Laboratory, Structural Dynamics Test Beds, Structures & Materials Research Laboratory, Supersonic Low Disturbance Pilot Tunnel, Thermal Acoustic Fatigue Apparatus (TAFA), Transonic Dynamics Tunnel (TDT), Transport Systems Research Vehicle, Unitary Plan Wind Tunnel, and the Visual Motion Simulator (VMS).

Dynamic Model of Aircraft Passenger Seats for Vibration Comfort Evaluation and Control

NASA Astrophysics Data System (ADS)

Šika, Z.; Valášek, Michael; Vampola, T.; Füllekrug, U.; Klimmek, T.

The paper deals with the development of the seat dynamical model for vibration comfort evaluation and control. The aircraft seats have been tested extensively by vibrations on the 6 DOF vibrating platform. The importance of the careful comfort control together with the flight mechanics control is namely stressed for the blended wing body (BWB) aircrafts. They have a very large fuselage, where the mechanical properties (accelerations, angular accelerations) vary considerably for different seat places. The model have been improved by adding of dynamical models of the aircraft passenger seats identified by the measurements on the 6 DOF vibrating platform. The experiments, their results and the identification of the dynamical seat model are described. The model is further modified by adding of the comfort evaluation norms represented by dynamical filters. The structure and identification of the seat model is briefly described and discussed.

A Mathematical Model to study the Dynamics of Epithelial Cellular Networks

PubMed Central

Abate, Alessandro; Vincent, Stéphane; Dobbe, Roel; Silletti, Alberto; Master, Neal; Axelrod, Jeffrey D.; Tomlin, Claire J.

2013-01-01

Epithelia are sheets of connected cells that are essential across the animal kingdom. Experimental observations suggest that the dynamical behavior of many single-layered epithelial tissues has strong analogies with that of specific mechanical systems, namely large networks consisting of point masses connected through spring-damper elements and undergoing the influence of active and dissipating forces. Based on this analogy, this work develops a modeling framework to enable the study of the mechanical properties and of the dynamic behavior of large epithelial cellular networks. The model is built first by creating a network topology that is extracted from the actual cellular geometry as obtained from experiments, then by associating a mechanical structure and dynamics to the network via spring-damper elements. This scalable approach enables running simulations of large network dynamics: the derived modeling framework in particular is predisposed to be tailored to study general dynamics (for example, morphogenesis) of various classes of single-layered epithelial cellular networks. In this contribution we test the model on a case study of the dorsal epithelium of the Drosophila melanogaster embryo during early dorsal closure (and, less conspicuously, germband retraction). PMID:23221083

A comparison of some static and dynamic mechanical properties of 18 x 5.5 and 49 x 17 type 7 aircraft tires as measured by three test facilities

NASA Technical Reports Server (NTRS)

Dodge, R. N.; Clark, S. K.

1981-01-01

The properties were measured during static, slow rolling, and high-speed tests, and comparisons were made between data as acquired on indoor drum dynamometers and on an outdoor test track. In addition, mechanical properties were also obtained from scale model tires and compared with corresponding properties from full-size tires. While the tests covered a wide range of tire properties, results seem to indicate that speed effects are not large, scale models may be used for obtaining some but not all tire properties, and that predictive equations developed in NASA TR R-64 are still useful in estimating most mechanical properties.

Dynamic Fracture Behavior of Plastic-Bonded Explosives

NASA Astrophysics Data System (ADS)

Fu, Hua; Li, Jun-Ling; Tan, Duo-Wang; Ifp, Caep Team

2011-06-01

Plastic-Bonded Explosives (PBX) are used as important energetic materials in nuclear or conventional weapons. Arms Warhead in the service process and the ballistic phase, may experience complex process such as long pulse and higher loading, compresson, tension and reciprocating compression - tension, friction with the projectile shell, which would lead to explosive deformation and fracture.And the dynamic deformation and fracture behavior of PBX subsequently affect reaction characteristics and initiation mechanism in explosives, then having influence on explosives safety. The dynamic fracure behavior of PBX are generally complex and not well studied or understood. In this paper, the dynamic fracture of explosives are conducted using a Kolsky bar. The Brazilian test, also known as a indirect tensile test or splitting test, is chosen as the test method. Tensile strength under different strain rates are obtained using quartz crystal embedded in rod end. The dynamic deformation and fracture process are captured in real-time by high-speed digital camera, and the displacement and strain fields distribution before specimen fracture are obtained by digital correlation method. Considering the non-uniform microstructure of explosives,the dynamic fracture behavior of explosive are simulated by discrete element method, the simulation results can reproduce the deformation and fracture process in Brazilian test using a maximum tensile strain criterion.

On the origins of the universal dynamics of endogenous granules in mammalian cells.

PubMed

Vanapalli, Siva A; Li, Yixuan; Mugele, Frieder; Duits, Michel H G

2009-12-01

Endogenous granules (EGs) that consist of lipid droplets and mitochondria have been commonly used to assess intracellular mechanical properties via multiple particle tracking microrheology (MPTM). Despite their widespread use, the nature of interaction of EGs with the cytoskeletal network and the type of forces driving their dynamics--both of which are crucial for the interpretation of the results from MPTM technique--are yet to be resolved. In this report, we study the dynamics of endogenous granules in mammalian cells using particle tracking methods. We find that the ensemble dynamics of EGs is diffusive in three types of mammalian cells (endothelial cells, smooth muscle cells and fibroblasts), thereby suggesting an apparent universality in their dynamical behavior. Moreover, in a given cell, the amplitude of the mean-squared displacement for EGs is an order of magnitude larger than that of injected particles. This observation along with results from ATP depletion and temperature intervention studies suggests that cytoskeletal active forces drive the dynamics of EGs. To elucidate the dynamical origin of the diffusive-like nonthermal motion, we consider three active force generation mechanisms--molecular motor transport, actomyosin contractility and microtubule polymerization forces. We test these mechanisms using pharmacological interventions. Experimental evidence and model calculations suggest that EGs are intimately linked to microtubules and that microtubule polymerization forces drive their dynamics. Thus, endogenous granules could serve as non-invasive probes for microtubule network dynamics in mammalian cells.

Stirling System Modeling for Space Nuclear Power Systems

NASA Technical Reports Server (NTRS)

Lewandowski, Edward J.; Johnson, Paul K.

2008-01-01

A dynamic model of a high-power Stirling convertor has been developed for space nuclear power systems modeling. The model is based on the Component Test Power Convertor (CTPC), a 12.5-kWe free-piston Stirling convertor. The model includes the fluid heat source, the Stirling convertor, output power, and heat rejection. The Stirling convertor model includes the Stirling cycle thermodynamics, heat flow, mechanical mass-spring damper systems, and the linear alternator. The model was validated against test data. Both nonlinear and linear versions of the model were developed. The linear version algebraically couples two separate linear dynamic models; one model of the Stirling cycle and one model of the thermal system, through the pressure factors. Future possible uses of the Stirling system dynamic model are discussed. A pair of commercially available 1-kWe Stirling convertors is being purchased by NASA Glenn Research Center. The specifications of those convertors may eventually be incorporated into the dynamic model and analysis compared to the convertor test data. Subsequent potential testing could include integrating the convertors into a pumped liquid metal hot-end interface. This test would provide more data for comparison to the dynamic model analysis.

Torsion pendulum measurements on viscoelastic materials during vacuum exposure

NASA Technical Reports Server (NTRS)

Ward, T. C.; Evans, M. L.

1972-01-01

A torsional pendulum apparatus designed for testing in situ in vacuum, the dynamic mechanical properties of materials is described. The application of this apparatus to an experimental program to measure the effects of vacuum on the mechanical properties of two ablator materials (a foamed material and a filled elastomer) and a solid rocket propellant (a filled elastomer) is presented. Results from the program are discussed as to the effects of vacuum on the mechanical properties of these three materials. In addition, time-temperature-superposition, as a technique for accelerating vacuum induced changes in mechanical properties, is discussed with reference to the three materials tested in the subject program.

Using magnetic resonance elastography to assess the dynamic mechanical properties of cartilage

NASA Astrophysics Data System (ADS)

Lopez, Orlando; Amrami, Kimberly; Rossman, Phillip; Ehman, Richard L.

2004-04-01

This work explored the feasibility of using Magnetic Resonance Elastography (MRE) technology to enable in vitro quantification of dynamic mechanical behavior of cartilage through its thickness. A customized system for MRE of cartilage was designed to include components for adequate generation and detection of high frequency mechanical shear waves within small and stiff materials. The system included components for mechanical excitation, motion encoding, and imaging of small samples. Limitations in sensitivity to motion encoding of high frequency propagating mechanical waves using a whole body coil (i.e. Gmax = 2.2 G/cm) required the design of a local gradient coil system to achieve a gain in gradient strength of at least 5 times. The performance of the new system was tested using various cartilage-mimicking phantom materials. MRE of a stiff 5% agar gelatin phantom demonstrated gains in sensitivity to motion encoding of high frequency mechanical waves in cartilage like materials. MRE of fetal bovine cartilage samples yielded a distribution of shear stiffness within the thickness of the cartilage similar to values found in the literature, hence, suggesting the feasibility of using MRE to non-invasively and directly assess the dynamic mechanical properties of cartilage.

Is hefting to perceive the affordance for throwing a smart perceptual mechanism?

PubMed

Zhu, Qin; Bingham, Geoffrey P

2008-08-01

G. P. Bingham, R. C. Schmidt, and L. D. Rosenblum (1989) found that, by hefting objects of different sizes and weights, people could choose the optimal weight in each size for throwing to a maximum distance. In Experiment 1, the authors replicated this result. G. P. Bingham et al. hypothesized that hefting is a smart mechanism that allows objects to be perceived in the context of throwing dynamics. This hypothesis entails 2 assumptions. First, hefting by hand is required for information about throwing by hand. The authors tested and confirmed this in Experiments 2 and 3. Second, optimal objects are determined by the dynamics of throwing. In Experiment 4, the authors tested this by measuring throwing release angles and using them with mean thrown distances from Experiment 1 and object sizes and weights to simulate projectile motion and recover release velocities. The results showed that only weight, not size, affects throwing. This failed to provide evidence supporting the particular smart mechanism hypothesis of G. P. Bingham et al. Because the affordance relation is determined in part by the dynamics of projectile motion, the results imply that the affordance is learned from knowledge of results of throwing.

Free Flight Ground Testing of ADEPT in Advance of the Sounding Rocket One Flight Experiment

NASA Technical Reports Server (NTRS)

Smith, B. P.; Dutta, S.

2017-01-01

The Adaptable Deployable Entry and Placement Technology (ADEPT) project will be conducting the first flight test of ADEPT, titled Sounding Rocket One (SR-1), in just two months. The need for this flight test stems from the fact that ADEPT's supersonic dynamic stability has not yet been characterized. The SR-1 flight test will provide critical data describing the flight mechanics of ADEPT in ballistic flight. These data will feed decision making on future ADEPT mission designs. This presentation will describe the SR-1 scientific data products, possible flight test outcomes, and the implications of those outcomes on future ADEPT development. In addition, this presentation will describe free-flight ground testing performed in advance of the flight test. A subsonic flight dynamics test conducted at the Vertical Spin Tunnel located at NASA Langley Research Center provided subsonic flight dynamics data at high and low altitudes for multiple center of mass (CoM) locations. A ballistic range test at the Hypervelocity Free Flight Aerodynamics Facility (HFFAF) located at NASA Ames Research Center provided supersonic flight dynamics data at low supersonic Mach numbers. Execution and outcomes of these tests will be discussed. Finally, a hypothesized trajectory estimate for the SR-1 flight will be presented.

Individual differences in the perception of biological motion and fragmented figures are not correlated

PubMed Central

Jung, Eunice L.; Zadbood, Asieh; Lee, Sang-Hun; Tomarken, Andrew J.; Blake, Randolph

2013-01-01

We live in a cluttered, dynamic visual environment that poses a challenge for the visual system: for objects, including those that move about, to be perceived, information specifying those objects must be integrated over space and over time. Does a single, omnibus mechanism perform this grouping operation, or does grouping depend on separate processes specialized for different feature aspects of the object? To address this question, we tested a large group of healthy young adults on their abilities to perceive static fragmented figures embedded in noise and to perceive dynamic point-light biological motion figures embedded in dynamic noise. There were indeed substantial individual differences in performance on both tasks, but none of the statistical tests we applied to this data set uncovered a significant correlation between those performance measures. These results suggest that the two tasks, despite their superficial similarity, require different segmentation and grouping processes that are largely unrelated to one another. Whether those processes are embodied in distinct neural mechanisms remains an open question. PMID:24198799

Individual differences in the perception of biological motion and fragmented figures are not correlated.

PubMed

Jung, Eunice L; Zadbood, Asieh; Lee, Sang-Hun; Tomarken, Andrew J; Blake, Randolph

2013-01-01

WE LIVE IN A CLUTTERED, DYNAMIC VISUAL ENVIRONMENT THAT POSES A CHALLENGE FOR THE VISUAL SYSTEM: for objects, including those that move about, to be perceived, information specifying those objects must be integrated over space and over time. Does a single, omnibus mechanism perform this grouping operation, or does grouping depend on separate processes specialized for different feature aspects of the object? To address this question, we tested a large group of healthy young adults on their abilities to perceive static fragmented figures embedded in noise and to perceive dynamic point-light biological motion figures embedded in dynamic noise. There were indeed substantial individual differences in performance on both tasks, but none of the statistical tests we applied to this data set uncovered a significant correlation between those performance measures. These results suggest that the two tasks, despite their superficial similarity, require different segmentation and grouping processes that are largely unrelated to one another. Whether those processes are embodied in distinct neural mechanisms remains an open question.

Thermalization and its mechanism for generic quantum isolated systems

NASA Astrophysics Data System (ADS)

Olshanii, Maxim; Dunjko, Vanja; Rigol, Marcos

2008-05-01

Time dynamics of isolated many-body quantum systems has long been an elusive subject, perhaps most urgently needed in the foundations of quantum statistical mechanics. In generic systems, one expects the nonequilibrium dynamics to lead to thermalization: a relaxation to states where the values of macroscopic quantities are stationary, universal with respect to widely differing initial conditions, and predictable through the time-tested recipe of statistical mechanics. The relaxation mechanism is not obvious, however; dynamical chaos cannot play the key role as it does in classical systems since quantum evolution is linear. Here we demonstrateootnotetextM. Rigol, V. Dunjko, and M. Olshanii, to appear in Nature (2008), using the results of an ab initio numerical experiment with 5 hard-core bosons moving in a 5x5 lattice, that in quantum systems thermalization happens not in course of time evolution but instead at the level of individual eigenstates, as first proposed by DeutschootnotetextJ. M. Deutsch, Phys.Rev. A 43, 2046 (1991) and SrednickiootnotetextM. Srednicki, Phys. Rev. E 50, 888 (1994).

Quiet Clean Short-haul Experimental Engine (QCSEE). Under-The-Wing (UTW) engine boilerplate nacelle test report. Volume 3: Mechanical performance

NASA Technical Reports Server (NTRS)

1977-01-01

Results of initial tests of the under the wing experimental engine and boilerplate nacelle are presented. The mechanical performance of the engine is reported with emphasis on the advanced technology components. Technology elements of the propulsion system covered include: system dynamics, composite fan blades, reduction gear, lube and accessory drive system, fan frame, inlet, core cowl cooling, fan exhaust nozzle, and digital control system.

1000540

NASA Image and Video Library

2010-04-13

ERIC EARHART (AEROSPACE ENGINEER, ER41 PROPULSION STRUCTURAL & DYNAMICS ANALYSIS BRANCH) DISCUSSES DATA PRODUCED BY A UNIQUE MECHANICAL TEST SETUP THAT MEASURES STRAIN ON A SINGLE SAMPLE, USING TWO DIFFERENT TECHNIQUES AT THE SAME TIME. THE TEST FIXTURE HOLDS A SPECIMEN THAT REPRESENTS A LIQUID OXYGEN (LOX) BEARING FROM THE J2-X ENGINE

Aircraft landing dynamics facility carriage weld test program

NASA Technical Reports Server (NTRS)

Lawson, A. G.

1984-01-01

A welded tubular structure constructed of low alloy high strength quenched and tempered steel was tested. The consistency of the mechanical strengths and chemical composition and the degree of difficulty of obtaining full strength welds with these steels is characterized. The results of constructing and testing two typical connections which are used in the structure design are reported.

1000539

NASA Image and Video Library

2010-04-13

AYMAN GIRGIS (EM10 MATERIALS TEST ENGINEER, JACOBS ESTS GROUP/JTI) AND ERIC EARHART (AEROSPACE ENGINEER, ER41 PROPULSION STRUCTURAL & DYNAMICS ANALYSIS BRANCH) DISCUSS DATA PRODUCED BY A UNIQUE MECHANICAL TEST SETUP THAT MEASURES STRAIN ON A SINGLE SAMPLE, USING TWO DIFFERENT TECHNIQUES AT THE SAME TIME. THE TEST FIXTURE HOLDS A SPECIMEN THAT REPRESENTS A LIQUID OXYGEN (LOX) BEARING FROM THE J2-X ENGINE.

Effects of Heavy Ion Exposure on Nanocrystal Nonvolatile Memory

NASA Technical Reports Server (NTRS)

Oldham, Timothy R.; Suhail, Mohammed; Kuhn, Peter; Prinz, Erwin; Kim, Hak; LaBel, Kenneth A.

2004-01-01

We have irradiated engineering samples of Freescale 4M nonvolatile memories with heavy ions. They use Silicon nanocrystals as the storage element, rather than the more common floating gate. The irradiations were performed using the Texas A&M University cyclotron Single Event Effects Test Facility. The chips were tested in the static mode, and in the dynamic read mode, dynamic write (program) mode, and dynamic erase mode. All the errors observed appeared to be due to single, isolated bits, even in the program and erase modes. These errors appeared to be related to the micro-dose mechanism. All the errors corresponded to the loss of electrons from a programmed cell. The underlying physical mechanisms will be discussed in more detail later. There were no errors, which could be attributed to malfunctions of the control circuits. At the highest LET used in the test (85 MeV/mg/sq cm), however, there appeared to be a failure due to gate rupture. Failure analysis is being conducted to confirm this conclusion. There was no unambiguous evidence of latchup under any test conditions. Generally, the results on the nanocrystal technology compare favorably with results on currently available commercial floating gate technology, indicating that the technology is promising for future space applications, both civilian and military.

Dynamic Mechanical Testing Techniques for Cortical and Cancellous Bone

NASA Astrophysics Data System (ADS)

Cloete, Trevor

2017-06-01

Bone fracture typically occurs as an impact loading event (sporting accidents, vehicle collisions), the simulation of which requires in-depth understanding of dynamic bone behavior. Bone is a natural composite material with a complex multi length-scale hierarchical microstructure. At a macroscopic level, it is classified into hard/compact cortical bone and soft/spongy cancellous (trabecular) bone, though both are low-impedance materials relative to steels. Cortical bone is predominant in long bones, while in complex bone geometries (joints, flat bones) a cancellous bone core supports a thin cortical shell. Bone has primarily been studied at quasi-static strain rates (ɛ˙ < 1s-1), with some dynamic studies (300s-1 <ɛ˙ < 3000s-1), but rarely at intermediate strain rates (ISR) (1s-1 <ɛ˙ < 100s-1). The data shows bone to be viscoelastic, which suggests that more dynamic and ISR data is required. Furthermore, bone exhibits quasi-brittle failure, with interrupted quasi-static tests revealing a strong microstructure dependence. However, bone specimens are typically destroyed during dynamic tests, leading to a lack of dynamic microstructural damage investigations. In this paper, a short overview of dynamic bone testing is presented to give context to the challenges of testing low impedance, strain-rate dependent, non-linear, visco-elastic-brittle materials. Recent state-of-the-art experimental developments in dynamic bone testing are reviewed, with emphasis on pulse shaping, momentum trapping and ISR testing. These techniques allow for dynamic bone testing at small strains and near-constant strain rates with intact specimen recovery. The results are compared to those obtained with varying strain rate tests. Interrupted dynamic test results with microstructural analysis of the recovered specimens are presented and discussed. The paper concludes with a discussion of the experimental and modeling challenges that lie ahead in the field of dynamic bone behavior. The financial assistance of the National Research Foundation and the University of Cape Town towards this research is hereby acknowledged. Opinions expressed and conclusions arrived at are those of the author alone.

Impact resistance of fiber composites - Energy-absorbing mechanisms and environmental effects

NASA Technical Reports Server (NTRS)

Chamis, C. C.; Sinclair, J. H.

1985-01-01

Energy absorbing mechanisms were identified by several approaches. The energy absorbing mechanisms considered are those in unidirectional composite beams subjected to impact. The approaches used include: mechanic models, statistical models, transient finite element analysis, and simple beam theory. Predicted results are correlated with experimental data from Charpy impact tests. The environmental effects on impact resistance are evaluated. Working definitions for energy absorbing and energy releasing mechanisms are proposed and a dynamic fracture progression is outlined. Possible generalizations to angle-plied laminates are described.

Impact resistance of fiber composites: Energy absorbing mechanisms and environmental effects

NASA Technical Reports Server (NTRS)

Chamis, C. C.; Sinclair, J. H.

1983-01-01

Energy absorbing mechanisms were identified by several approaches. The energy absorbing mechanisms considered are those in unidirectional composite beams subjected to impact. The approaches used include: mechanic models, statistical models, transient finite element analysis, and simple beam theory. Predicted results are correlated with experimental data from Charpy impact tests. The environmental effects on impact resistance are evaluated. Working definitions for energy absorbing and energy releasing mechanisms are proposed and a dynamic fracture progression is outlined. Possible generalizations to angle-plied laminates are described.

An apparatus to estimate the hydrodynamic coefficients of autonomous underwater vehicles using water tunnel testing.

PubMed

Nouri, N M; Mostafapour, K; Bahadori, R

2016-06-01

Hydrodynamic coefficients or hydrodynamic derivatives of autonomous underwater vehicles (AUVs) play an important role in their development and maneuverability. The most popular way of estimating their coefficients is to implement captive model tests such as straight line tests and planar motion mechanism (PMM) tests in the towing tanks. This paper aims to develop an apparatus based on planar experiments of water tunnel in order to estimate hydrodynamic derivatives due to AUVs' acceleration and velocity. The capability of implementing straight line tests and PMM ones using mechanical oscillators located in the downstream flow of the model is considered in the design procedure of the system. The hydrodynamic derivatives that resulted from the acceleration and velocity of the AUV model were estimated using the apparatus that we developed. Static and dynamics test results were compared for the similar derivatives. The findings showed that the system provided the basis for conducting static tests, i.e., straight-line and dynamic tests that included pure pitch and pure heave. By conducting such tests in a water tunnel, we were able to eliminate errors related to the time limitation of the tests and the effects of surface waves in the towing tank on AUVs with applications in the deep sea.

An approach for generating trajectory-based dynamics which conserves the canonical distribution in the phase space formulation of quantum mechanics. II. Thermal correlation functions.

PubMed

Liu, Jian; Miller, William H

2011-03-14

We show the exact expression of the quantum mechanical time correlation function in the phase space formulation of quantum mechanics. The trajectory-based dynamics that conserves the quantum canonical distribution-equilibrium Liouville dynamics (ELD) proposed in Paper I is then used to approximately evaluate the exact expression. It gives exact thermal correlation functions (of even nonlinear operators, i.e., nonlinear functions of position or momentum operators) in the classical, high temperature, and harmonic limits. Various methods have been presented for the implementation of ELD. Numerical tests of the ELD approach in the Wigner or Husimi phase space have been made for a harmonic oscillator and two strongly anharmonic model problems, for each potential autocorrelation functions of both linear and nonlinear operators have been calculated. It suggests ELD can be a potentially useful approach for describing quantum effects for complex systems in condense phase.

Mechanical Engineering at KSC: 'How I spend My Hours from 9 to 5 and Draw a Paycheck'

NASA Technical Reports Server (NTRS)

Randazzo, John; Steinrock. Todd (Technical Monitor)

2003-01-01

This viewgraph presentation provides an overview of a senior mechanical engineer's role in designing and testing sensors to fly aboard the shuttle Discovery during STS-95 and STS-98. Topics covered include: software development tools, computation fluid dynamics, structural analysis, housing design, and systems integration.

Structure and mechanical properties of parts obtained by selective laser melting of metal powder based on intermetallic compounds Ni3Al

NASA Astrophysics Data System (ADS)

Smelov, V. G.; Sotov, A. V.; Agapovichev, A. V.; Nosova, E. A.

2018-03-01

The structure and mechanical properties of samples are obtained from metal powder based on intermetallic compound by selective laser melting. The chemical analysis of the raw material and static tensile test of specimens were made. Change in the samples’ structure and mechanical properties after homogenization during four and twenty-four hours were investigated. A small-sized combustion chamber of a gas turbine engine was performed by the selective laser melting method. The print combustion chamber was subjected to the gas-dynamic test in a certain temperature and time range.

Development tests for the 2.5 megawatt Mod-2 wind turbine generator

NASA Technical Reports Server (NTRS)

Andrews, J. S.; Baskin, J. M.

1982-01-01

The 2.5 megawatt MOD-2 wind turbine generator test program is discussed. The development of the 2.5 megawatt MOD-2 wind turbine generator included an extensive program of testing which encompassed verification of analytical procedures, component development, and integrated system verification. The test program was to assure achievement of the thirty year design operational life of the wind turbine system as well as to minimize costly design modifications which would otherwise have been required during on site system testing. Computer codes were modified, fatigue life of structure and dynamic components were verified, mechanical and electrical component and subsystems were functionally checked and modified where necessary to meet system specifications, and measured dynamic responses of coupled systems confirmed analytical predictions.

Development of drive mechanism for an oscillating airfoil

NASA Technical Reports Server (NTRS)

Sticht, Clifford D.

1988-01-01

The design and development of an in-draft wind tunnel test section which will be used to study the dynamic stall of airfoils oscillating in pitch is described. The hardware developed comprises a spanned airfoil between schleiren windows, a four bar linkage, flywheels, a drive system and a test section structure.

Achilles tendons from decorin- and biglycan-null mouse models have inferior mechanical and structural properties predicted by an image-based empirical damage model

PubMed Central

Gordon, J.A.; Freedman, B.R.; Zuskov, A.; Iozzo, R.V.; Birk, D.E.; Soslowsky, L.J.

2015-01-01

Achilles tendons are a common source of pain and injury, and their pathology may originate from aberrant structure function relationships. Small leucine rich proteoglycans (SLRPs) influence mechanical and structural properties in a tendon-specific manner. However, their roles in the Achilles tendon have not been defined. The objective of this study was to evaluate the mechanical and structural differences observed in mouse Achilles tendons lacking class I SLRPs; either decorin or biglycan. In addition, empirical modeling techniques based on mechanical and image-based measures were employed. Achilles tendons from decorin-null (Dcn−/−) and biglycan-null (Bgn−/−) C57BL/6 female mice (N=102) were used. Each tendon underwent a dynamic mechanical testing protocol including simultaneous polarized light image capture to evaluate both structural and mechanical properties of each Achilles tendon. An empirical damage model was adapted for application to genetic variation and for use with image based structural properties to predict tendon dynamic mechanical properties. We found that Achilles tendons lacking decorin and biglycan had inferior mechanical and structural properties that were age dependent; and that simple empirical models, based on previously described damage models, were predictive of Achilles tendon dynamic modulus in both decorin- and biglycan-null mice. PMID:25888014

Achilles tendons from decorin- and biglycan-null mouse models have inferior mechanical and structural properties predicted by an image-based empirical damage model.

PubMed

Gordon, J A; Freedman, B R; Zuskov, A; Iozzo, R V; Birk, D E; Soslowsky, L J

2015-07-16

Achilles tendons are a common source of pain and injury, and their pathology may originate from aberrant structure function relationships. Small leucine rich proteoglycans (SLRPs) influence mechanical and structural properties in a tendon-specific manner. However, their roles in the Achilles tendon have not been defined. The objective of this study was to evaluate the mechanical and structural differences observed in mouse Achilles tendons lacking class I SLRPs; either decorin or biglycan. In addition, empirical modeling techniques based on mechanical and image-based measures were employed. Achilles tendons from decorin-null (Dcn(-/-)) and biglycan-null (Bgn(-/-)) C57BL/6 female mice (N=102) were used. Each tendon underwent a dynamic mechanical testing protocol including simultaneous polarized light image capture to evaluate both structural and mechanical properties of each Achilles tendon. An empirical damage model was adapted for application to genetic variation and for use with image based structural properties to predict tendon dynamic mechanical properties. We found that Achilles tendons lacking decorin and biglycan had inferior mechanical and structural properties that were age dependent; and that simple empirical models, based on previously described damage models, were predictive of Achilles tendon dynamic modulus in both decorin- and biglycan-null mice. Copyright © 2015 Elsevier Ltd. All rights reserved.

3D fiber-deposited scaffolds for tissue engineering: influence of pores geometry and architecture on dynamic mechanical properties.

PubMed

Moroni, L; de Wijn, J R; van Blitterswijk, C A

2006-03-01

One of the main issues in tissue engineering is the fabrication of scaffolds that closely mimic the biomechanical properties of the tissues to be regenerated. Conventional fabrication techniques are not sufficiently suitable to control scaffold structure to modulate mechanical properties. Within novel scaffold fabrication processes 3D fiber deposition (3DF) showed great potential for tissue engineering applications because of the precision in making reproducible 3D scaffolds, characterized by 100% interconnected pores with different shapes and sizes. Evidently, these features also affect mechanical properties. Therefore, in this study we considered the influence of different structures on dynamic mechanical properties of 3DF scaffolds. Pores were varied in size and shape, by changing fibre diameter, spacing and orientation, and layer thickness. With increasing porosity, dynamic mechanical analysis (DMA) revealed a decrease in elastic properties such as dynamic stiffness and equilibrium modulus, and an increase of the viscous parameters like damping factor and creep unrecovered strain. Furthermore, the Poisson's ratio was measured, and the shear modulus computed from it. Scaffolds showed an adaptable degree of compressibility between sponges and incompressible materials. As comparison, bovine cartilage was tested and its properties fell in the fabricated scaffolds range. This investigation showed that viscoelastic properties of 3DF scaffolds could be modulated to accomplish mechanical requirements for tailored tissue engineered applications.

Validation of Slosh Model Parameters and Anti-Slosh Baffle Designs of Propellant Tanks by Using Lateral Slosh Testing

NASA Technical Reports Server (NTRS)

Perez, Jose G.; Parks, Russel, A.; Lazor, Daniel R.

2012-01-01

The slosh dynamics of propellant tanks can be represented by an equivalent mass-pendulum-dashpot mechanical model. The parameters of this equivalent model, identified as slosh mechanical model parameters, are slosh frequency, slosh mass, and pendulum hinge point location. They can be obtained by both analysis and testing for discrete fill levels. Anti-slosh baffles are usually needed in propellant tanks to control the movement of the fluid inside the tank. Lateral slosh testing, involving both random excitation testing and free-decay testing, are performed to validate the slosh mechanical model parameters and the damping added to the fluid by the anti-slosh baffles. Traditional modal analysis procedures were used to extract the parameters from the experimental data. Test setup of sub-scale tanks will be described. A comparison between experimental results and analysis will be presented.

Deformation effect simulation and optimization for double front axle steering mechanism

NASA Astrophysics Data System (ADS)

Wu, Jungang; Zhang, Siqin; Yang, Qinglong

2013-03-01

This paper research on tire wear problem of heavy vehicles with Double Front Axle Steering Mechanism from the flexible effect of Steering Mechanism, and proposes a structural optimization method which use both traditional static structural theory and dynamic structure theory - Equivalent Static Load (ESL) method to optimize key parts. The good simulated and test results show this method has high engineering practice and reference value for tire wear problem of Double Front Axle Steering Mechanism design.

Microstructure-failure mode correlations in braided composites

NASA Technical Reports Server (NTRS)

Filatovs, G. J.; Sadler, Robert L.; El-Shiekh, Aly

1992-01-01

Explication of the fracture processes of braided composites is needed for modeling their behavior. Described is a systematic exploration of the relationship between microstructure, loading mode, and micro-failure mechanisms in carbon/epoxy braided composites. The study involved compression and fracture toughness tests and optical and scanning electron fractography, including dynamic in-situ testing. Principal failure mechanisms of low sliding, buckling, and unstable crack growth are correlated to microstructural parameters and loading modes; these are used for defining those microstructural conditions which are strength limiting.

Multifunctional structural lithium ion batteries for electrical energy storage applications

NASA Astrophysics Data System (ADS)

Javaid, Atif; Zeshan Ali, Muhammad

2018-05-01

Multifunctional structural batteries based on carbon fiber-reinforced polymer composites are fabricated that can bear mechanical loads and act as electrochemical energy storage devices simultaneously. Structural batteries, containing woven carbon fabric anode; lithium cobalt oxide/graphene nanoplatelets coated aluminum cathode; filter paper separator and cross-linked polymer electrolyte, were fabricated through resin infusion under flexible tooling (RIFT) technique. Compression tests, dynamic mechanical thermal analysis, thermogravimetric analysis and impedance spectroscopy were done on the cross-linked polymer electrolytes while cyclic voltammetry, impedance spectroscopy, dynamic mechanical thermal analysis and in-plane shear tests were conducted on the fabricated structural batteries. A range of solid polymer electrolytes with increasing concentrations of lithium perchlorate salt in crosslinked polymer epoxies were formulated. Increased concentrations of electrolyte salt in cross-linked epoxy increased the ionic conductivity, although the compressive properties were compromised. A structural battery, exhibiting simultaneously a capacity of 0.16 mAh L‑1, an energy density of 0.32 Wh L‑1 and a shear modulus of 0.75 GPa have been reported.

Influence of Structure and Composition on Dynamic Viscoelastic Property of Cartilaginous Tissue: Criteria for Classification between Hyaline Cartilage and Fibrocartilage Based on Mechanical Function

NASA Astrophysics Data System (ADS)

Miyata, Shogo; Tateishi, Tetsuya; Furukawa, Katsuko; Ushida, Takashi

Recently, many types of methodologies have been developed to regenerate articular cartilage. It is important to assess whether the reconstructed cartilaginous tissue has the appropriate mechanical functions to qualify as hyaline (articular) cartilage. In some cases, the reconstructed tissue may become fibrocartilage and not hyaline cartilage. In this study, we determined the dynamic viscoelastic properties of these two types of cartilage by using compression and shear tests, respectively. Hyaline cartilage specimens were harvested from the articular surface of bovine knee joints and fibrocartilage specimens were harvested from the meniscus tissue of the same. The results of this study revealed that the compressive energy dissipation of hyaline cartilage showed a strong dependence on testing frequency at low frequencies, while that of fibrocartilage did not. Therefore, the compressive energy dissipation that is indicated by the loss tangent could become the criterion for the in vitro assessment of the mechanical function of regenerated cartilage.

Atomic and vibrational origins of mechanical toughness in bioactive cement during setting

PubMed Central

Tian, Kun V.; Yang, Bin; Yue, Yuanzheng; Bowron, Daniel T.; Mayers, Jerry; Donnan, Robert S.; Dobó-Nagy, Csaba; Nicholson, John W.; Fang, De-Cai; Greer, A. Lindsay; Chass, Gregory A.; Greaves, G. Neville

2015-01-01

Bioactive glass ionomer cements (GICs) have been in widespread use for ∼40 years in dentistry and medicine. However, these composites fall short of the toughness needed for permanent implants. Significant impediment to improvement has been the requisite use of conventional destructive mechanical testing, which is necessarily retrospective. Here we show quantitatively, through the novel use of calorimetry, terahertz (THz) spectroscopy and neutron scattering, how GIC's developing fracture toughness during setting is related to interfacial THz dynamics, changing atomic cohesion and fluctuating interfacial configurations. Contrary to convention, we find setting is non-monotonic, characterized by abrupt features not previously detected, including a glass–polymer coupling point, an early setting point, where decreasing toughness unexpectedly recovers, followed by stress-induced weakening of interfaces. Subsequently, toughness declines asymptotically to long-term fracture test values. We expect the insight afforded by these in situ non-destructive techniques will assist in raising understanding of the setting mechanisms and associated dynamics of cementitious materials. PMID:26548704

Balance decrements are associated with age-related muscle property changes.

PubMed

Hasson, Christopher J; van Emmerik, Richard E A; Caldwell, Graham E

2014-08-01

In this study, a comprehensive evaluation of static and dynamic balance abilities was performed in young and older adults and regression analysis was used to test whether age-related variations in individual ankle muscle mechanical properties could explain differences in balance performance. The mechanical properties included estimates of the maximal isometric force capability, force-length, force-velocity, and series elastic properties of the dorsiflexors and individual plantarflexor muscles (gastrocnemius and soleus). As expected, the older adults performed more poorly on most balance tasks. Muscular maximal isometric force, optimal fiber length, tendon slack length, and velocity-dependent force capabilities accounted for up to 60% of the age-related variation in performance on the static and dynamic balance tests. In general, the plantarflexors had a stronger predictive role than the dorsiflexors. Plantarflexor stiffness was strongly related to general balance performance, particularly in quiet stance; but this effect did not depend on age. Together, these results suggest that age-related differences in balance performance are explained in part by alterations in muscular mechanical properties.

Comparison of infrared and 3D digital image correlation techniques applied for mechanical testing of materials

NASA Astrophysics Data System (ADS)

Krstulović-Opara, Lovre; Surjak, Martin; Vesenjak, Matej; Tonković, Zdenko; Kodvanj, Janoš; Domazet, Željko

2015-11-01

To investigate the applicability of infrared thermography as a tool for acquiring dynamic yielding in metals, a comparison of infrared thermography with three dimensional digital image correlation has been made. Dynamical tension tests and three point bending tests of aluminum alloys have been performed to evaluate results obtained by IR thermography in order to detect capabilities and limits for these two methods. Both approaches detect pastification zone migrations during the yielding process. The results of the tension test and three point bending test proved the validity of the IR approach as a method for evaluating the dynamic yielding process when used on complex structures such as cellular porous materials. The stability of the yielding process in the three point bending test, as contrary to the fluctuation of the plastification front in the tension test, is of great importance for the validation of numerical constitutive models. The research proved strong performance, robustness and reliability of the IR approach when used to evaluate yielding during dynamic loading processes, while the 3D DIC method proved to be superior in the low velocity loading regimes. This research based on two basic tests, proved the conclusions and suggestions presented in our previous research on porous materials where middle wave infrared thermography was applied.

Energetics and dynamics of simple impulsive solar flares

NASA Technical Reports Server (NTRS)

Starr, R.; Heindl, W. A.; Crannell, C. J.; Thomas, R. J.; Batchelor, D. A.; Magun, A.

1987-01-01

Flare energetics and dynamics were studied using observations of simple impulsive spike bursts. A large, homogeneous set of events was selected to enable the most definite tests possible of competing flare models, in the absence of spatially resolved observations. The emission mechanisms and specific flare models that were considered in this investigation are described, and the derivations of the parameters that were tested are presented. Results of the correlation analysis between soft and hard X-ray energetics are also presented. The ion conduction front model and tests of that model with the well-observed spike bursts are described. Finally, conclusions drawn from this investigation and suggestions for future studies are discussed.

Design and testing of an electromagnetic coupling

NASA Technical Reports Server (NTRS)

Anderson, William J.

1986-01-01

Hostile environments such as the hard vacuum of space, and exposure to water or caustic fluids have fostered the development of devices which allow mechanical rotary feed throughs with positive sealing without the use of conventional dynamic seals. One such device is an electromagnetic coupling which transfers motion across a hermetic seal by means of a rotating magnetic field. Static pull-out torque and dynamic heat build-up and pull-out torque tests of a synchronous reluctance homopolar coupling are reported herein. Coupling efficiencies are estimated for a range of speeds and torques.

Robotic joint experiments under ultravacuum

NASA Technical Reports Server (NTRS)

Borrien, A.; Petitjean, L.

1988-01-01

First, various aspects of a robotic joint development program, including gearbox technology, electromechanical components, lubrication, and test results, are discussed. Secondly, a test prototype of the joint allowing simulation of robotic arm dynamic effects is presented. This prototype is tested under vacuum with different types of motors and sensors to characterize the functional parameters: angular position error, mechanical backlash, gearbox efficiency, and lifetime.

Investigation of Dynamic Force/Vibration Transmission Characteristics of Four-Square Type Gear Durability Test Machines

NASA Technical Reports Server (NTRS)

Kahraman, Ahmet

2002-01-01

In this study, design requirements for a dynamically viable, four-square type gear test machine are investigated. Variations of four-square type gear test machines have been in use for durability and dynamics testing of both parallel- and cross-axis gear set. The basic layout of these machines is illustrated. The test rig is formed by two gear pairs, of the same reduction ratio, a test gear pair and a reaction gear pair, connected to each other through shafts of certain torsional flexibility to form an efficient, closed-loop system. A desired level of constant torque is input to the circuit through mechanical (a split coupling with a torque arm) or hydraulic (a hydraulic actuator) means. The system is then driven at any desired speed by a small DC motor. The main task in hand is the isolation of the test gear pair from the reaction gear pair under dynamic conditions. Any disturbances originated at the reaction gear mesh might potentially travel to the test gearbox, altering the dynamic loading conditions of the test gear mesh, and hence, influencing the outcome of the durability or dynamics test. Therefore, a proper design of connecting structures becomes a major priority. Also, equally important is the issue of how close the operating speed of the machine is to the resonant frequencies of the gear meshes. This study focuses on a detailed analysis of the current NASA Glenn Research Center gear pitting test machine for evaluation of its resonance and vibration isolation characteristics. A number of these machines as the one illustrated has been used over last 30 years to establish an extensive database regarding the influence of the gear materials, processes surface treatments and lubricants on gear durability. This study is intended to guide an optimum design of next generation test machines for the most desirable dynamic characteristics.

Social costs enforce honesty of a dynamic signal of motivation.

PubMed

Ligon, Russell A; McGraw, Kevin J

2016-10-26

Understanding the processes that promote signal reliability may provide important insights into the evolution of diverse signalling strategies among species. The signals that animals use to communicate must comprise mechanisms that prohibit or punish dishonesty, and social costs of dishonesty have been demonstrated for several fixed morphological signals (e.g. colour badges of birds and wasps). The costs maintaining the honesty of dynamic signals, which are more flexible and potentially cheatable, are unknown. Using an experimental manipulation of the dynamic visual signals used by male veiled chameleons (Chamaeleo calyptratus) during aggressive interactions, we tested the idea that the honesty of rapid colour change signals is maintained by social costs. Our results reveal that social costs are an important mechanism maintaining the honesty of these dynamic colour signals-'dishonest' chameleons whose experimentally manipulated coloration was incongruent with their contest behaviour received more physical aggression than 'honest' individuals. This is the first demonstration, to the best our knowledge, that the honesty of a dynamic signal of motivation-physiological colour change-can be maintained by the social costliness of dishonesty. Behavioural responses of signal receivers, irrespective of any specific detection mechanisms, therefore prevent chameleon cheaters from prospering. © 2016 The Author(s).

Social costs enforce honesty of a dynamic signal of motivation

PubMed Central

McGraw, Kevin J.

2016-01-01

Understanding the processes that promote signal reliability may provide important insights into the evolution of diverse signalling strategies among species. The signals that animals use to communicate must comprise mechanisms that prohibit or punish dishonesty, and social costs of dishonesty have been demonstrated for several fixed morphological signals (e.g. colour badges of birds and wasps). The costs maintaining the honesty of dynamic signals, which are more flexible and potentially cheatable, are unknown. Using an experimental manipulation of the dynamic visual signals used by male veiled chameleons (Chamaeleo calyptratus) during aggressive interactions, we tested the idea that the honesty of rapid colour change signals is maintained by social costs. Our results reveal that social costs are an important mechanism maintaining the honesty of these dynamic colour signals—‘dishonest’ chameleons whose experimentally manipulated coloration was incongruent with their contest behaviour received more physical aggression than ‘honest’ individuals. This is the first demonstration, to the best our knowledge, that the honesty of a dynamic signal of motivation—physiological colour change—can be maintained by the social costliness of dishonesty. Behavioural responses of signal receivers, irrespective of any specific detection mechanisms, therefore prevent chameleon cheaters from prospering. PMID:27798310

Experimental investigations of visco-plastic properties of the aluminium and tungsten alloys used in KE projectiles

NASA Astrophysics Data System (ADS)

Kruszka, L.; Magier, M.

2012-08-01

The main aim of studies on dynamic behaviour of construction materials at high strain rates is to determine the variation of mechanical properties (strength, plasticity) in function of the strain rate and temperature. On the basis of results of dynamic tests on the properties of constructional materials the constitutive models are formulated to create numerical codes applied to solve constructional problems with computer simulation methods. In the case of military applications connected with the phenomena of gunshot and terminal ballistics it's particularly important to develop a model of strength and armour penetration with KE projectile founded on reliable results of dynamic experiments and constituting the base for further analyses and optimization of projectile designs in order to achieve required penetration depth. Static and dynamic results of strength investigations of the EN AW-7012 aluminium alloy (sabot) and tungsten alloy (penetrator) are discussed in this paper. Static testing was carried out with the INSTRON testing machine. Dynamic tests have been conducted using the split Hopkinson pressure bars technique at strain rates up to 1,2 ṡ 104s-1 (for aluminium alloy) and 6 ṡ 103s-1 (for tungsten alloy).

Deck and Cable Dynamic Testing of a Single-span Bridge Using Radar Interferometry and Videometry Measurements

NASA Astrophysics Data System (ADS)

Piniotis, George; Gikas, Vassilis; Mpimis, Thanassis; Perakis, Harris

2016-03-01

This paper presents the dynamic testing of a roadway, single-span, cable-stayed bridge for a sequence of static load and ambient vibration monitoring scenarios. Deck movements were captured along both sideways of the bridge using a Digital Image Correlation (DIC) and a Ground-based Microwave Interfererometer (GBMI) system. Cable vibrations were measured at a single point location on each of the six cables using the GBMI technique. Dynamic testing involves three types of analyses; firstly, vibration analysis and modal parameter estimation (i. e., natural frequencies and modal shapes) of the deck using the combined DIC and GBMI measurements. Secondly, dynamic testing of the cables is performed through vibration analysis and experimental computation of their tension forces. Thirdly, the mechanism of cable-deck dynamic interaction is studied through their Power Spectra Density (PSD) and the Short Time Fourier Transform (STFT) analyses. Thereby, the global (deck and cable) and local (either deck or cable) bridge modes are identified, serving a concrete benchmark of the current state of the bridge for studying the evolution of its structural performance in the future. The level of synergy and complementarity between the GBMI and DIC techniques for bridge monitoring is also examined and assessed.

Deciphering Mechanical Regulation of Chondrogenesis in Fibrin–Polyurethane Composite Scaffolds Enriched with Human Mesenchymal Stem Cells: A Dual Computational and Experimental Approach

PubMed Central

Stoddart, Martin; Lezuo, Patrick; Forkmann, Christoph; Wimmmer, Markus A.; Alini, Mauro; Van Oosterwyck, Hans

2014-01-01

Fibrin–polyurethane composite scaffolds support chondrogenesis of human mesenchymal stem cells (hMSCs) derived from bone marrow and due to their robust mechanical properties allow mechanical loading in dynamic bioreactors, which has been shown to increase the chondrogenic differentiation of MSCs through the transforming growth factor beta pathway. The aim of this study was to use the finite element method, mechanical testing, and dynamic in vitro cell culture experiments on hMSC-enriched fibrin–polyurethane composite scaffolds to quantitatively decipher the mechanoregulation of chondrogenesis within these constructs. The study identified compressive principal strains as the key regulator of chondrogenesis in the constructs. Although dynamic uniaxial compression did not induce chondrogenesis, multiaxial loading by combined application of dynamic compression and interfacial shear induced significant chondrogenesis at locations where all the three principal strains were compressive and had a minimum magnitude of 10%. In contrast, no direct correlation was identified between the level of pore fluid velocity and chondrogenesis. Due to the high permeability of the constructs, the pore fluid pressures could not be increased sufficiently by mechanical loading, and instead, chondrogenesis was induced by triaxial compressive deformations of the matrix with a minimum magnitude of 10%. Thus, it can be concluded that dynamic triaxial compressive deformations of the matrix is sufficient to induce chondrogenesis in a threshold-dependent manner, even where the pore fluid pressure is negligible. PMID:24199606

Elastic Multi-scale Mechanisms: Computation and Biological Evolution.

PubMed

Diaz Ochoa, Juan G

2018-01-01

Explanations based on low-level interacting elements are valuable and powerful since they contribute to identify the key mechanisms of biological functions. However, many dynamic systems based on low-level interacting elements with unambiguous, finite, and complete information of initial states generate future states that cannot be predicted, implying an increase of complexity and open-ended evolution. Such systems are like Turing machines, that overlap with dynamical systems that cannot halt. We argue that organisms find halting conditions by distorting these mechanisms, creating conditions for a constant creativity that drives evolution. We introduce a modulus of elasticity to measure the changes in these mechanisms in response to changes in the computed environment. We test this concept in a population of predators and predated cells with chemotactic mechanisms and demonstrate how the selection of a given mechanism depends on the entire population. We finally explore this concept in different frameworks and postulate that the identification of predictive mechanisms is only successful with small elasticity modulus.

Fairness and dynamic pricing: comments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hogan, William W.

2010-07-15

In ''The Ethics of Dynamic Pricing,'' Ahmad Faruqui lays out a case for improved efficiency in using dynamic prices for retail electricity tariffs and addresses various issues about the distributional effects of alternative pricing mechanisms. The principal contrast is between flat or nearly constant energy prices and time-varying prices that reflect more closely the marginal costs of energy and capacity. The related issues of fairness criteria, contracts, risk allocation, cost allocation, means testing, real-time pricing, and ethical policies of electricity market design also must be considered. (author)

Evaluation and Analysis of F-16XL Wind Tunnel Data From Static and Dynamic Tests

NASA Technical Reports Server (NTRS)

Kim, Sungwan; Murphy, Patrick C.; Klein, Vladislav

2004-01-01

A series of wind tunnel tests were conducted in the NASA Langley Research Center as part of an ongoing effort to develop and test mathematical models for aircraft rigid-body aerodynamics in nonlinear unsteady flight regimes. Analysis of measurement accuracy, especially for nonlinear dynamic systems that may exhibit complicated behaviors, is an essential component of this ongoing effort. In this report, tools for harmonic analysis of dynamic data and assessing measurement accuracy are presented. A linear aerodynamic model is assumed that is appropriate for conventional forced-oscillation experiments, although more general models can be used with these tools. Application of the tools to experimental data is demonstrated and results indicate the levels of uncertainty in output measurements that can arise from experimental setup, calibration procedures, mechanical limitations, and input errors.

Mechanical Design of a Performance Test Rig for the Turbine Air-Flow Task (TAFT)

NASA Technical Reports Server (NTRS)

Xenofos, George; Forbes, John; Farrow, John; Williams, Robert; Tyler, Tom; Sargent, Scott; Moharos, Jozsef

2003-01-01

To support development of the Boeing-Rocketdyne RS84 rocket engine, a fill-flow, reaction turbine geometry was integrated into the NASA-MSFC turbine air-flow test facility. A mechanical design was generated which minimized the amount of new hardware while incorporating all test and instrUmentation requirements. This paper provides details of the mechanical design for this Turbine Air-Flow Task (TAFT) test rig. The mechanical design process utilized for this task included the following basic stages: Conceptual Design. Preliminary Design. Detailed Design. Baseline of Design (including Configuration Control and Drawing Revision). Fabrication. Assembly. During the design process, many lessons were learned that should benefit future test rig design projects. Of primary importance are well-defined requirements early in the design process, a thorough detailed design package, and effective communication with both the customer and the fabrication contractors. The test rig provided steady and unsteady pressure data necessary to validate the computational fluid dynamics (CFD) code. The rig also helped characterize the turbine blade loading conditions. Test and CFD analysis results are to be presented in another JANNAF paper.

Development of test methodology for dynamic mechanical analysis instrumentation

NASA Technical Reports Server (NTRS)

Allen, V. R.

1982-01-01

Dynamic mechanical analysis instrumentation was used for the development of specific test methodology in the determination of engineering parameters of selected materials, esp. plastics and elastomers, over a broad range of temperature with selected environment. The methodology for routine procedures was established with specific attention given to sample geometry, sample size, and mounting techniques. The basic software of the duPont 1090 thermal analyzer was used for data reduction which simplify the theoretical interpretation. Clamps were developed which allowed 'relative' damping during the cure cycle to be measured for the fiber-glass supported resin. The correlation of fracture energy 'toughness' (or impact strength) with the low temperature (glassy) relaxation responses for a 'rubber-modified' epoxy system was negative in result because the low-temperature dispersion mode (-80 C) of the modifier coincided with that of the epoxy matrix, making quantitative comparison unrealistic.

Cooperative quantum-behaved particle swarm optimization with dynamic varying search areas and Lévy flight disturbance.

PubMed

Li, Desheng

2014-01-01

This paper proposes a novel variant of cooperative quantum-behaved particle swarm optimization (CQPSO) algorithm with two mechanisms to reduce the search space and avoid the stagnation, called CQPSO-DVSA-LFD. One mechanism is called Dynamic Varying Search Area (DVSA), which takes charge of limiting the ranges of particles' activity into a reduced area. On the other hand, in order to escape the local optima, Lévy flights are used to generate the stochastic disturbance in the movement of particles. To test the performance of CQPSO-DVSA-LFD, numerical experiments are conducted to compare the proposed algorithm with different variants of PSO. According to the experimental results, the proposed method performs better than other variants of PSO on both benchmark test functions and the combinatorial optimization issue, that is, the job-shop scheduling problem.

Futurepath: The Story of Research and Technology at NASA Lewis Research Center. Structures for Flight Propulsion, ARC Sprayed Monotape, National Aero-Space Plane

NASA Technical Reports Server (NTRS)

1989-01-01

The story of research and technology at NASA Lewis Research Center's Structures Division is presented. The job and designs of the Structures Division needed for flight propulsion is described including structural mechanics, structural dynamics, fatigue, and fracture. The video briefly explains why properties of metals used in structural mechanics need to be tested. Examples of tests and simulations used in structural dynamics (bodies in motion) are briefly described. Destructive and non-destructive fatigue/fracture analysis is also described. The arc sprayed monotape (a composite material) is explained, as are the programs in which monotape plays a roll. Finally, the National Aero-Space Plane (NASP or x-30) is introduced, including the material development and metal matrix as well as how NASP will reduce costs for NASA.

Dynamic performance and mechanical model analysis of a shear thickening fluid damper

NASA Astrophysics Data System (ADS)

Zhao, Qian; He, Yonghui; Yao, Hongliang; Wen, Bangchun

2018-07-01

This paper presents an experimental study of the dynamic performance of a self-developed shear thickening fluid (STF) damper and its mechanical model was proposed by nonlinear fitting. First, STF samples with different mass fraction and dispersion medium were fabricated by nano fumed silica and polyethylene glycol, and its rheological properties were investigated by a rheometer. Second, a smart STF damper was developed and manufactured. Its dynamic properties were experimentally investigated by establishing a vibration test bench, and results indicated that the STF damper can output variable damping force by controlling the loading frequency, loading amplitude and fluid gap. Third, the Bouc–Wen model was proposed to address the dynamic properties of STF damper, and mechanical model analysis was carried out by comparing several fitting functions. It verified that the Bouc–Wen hysteresis model can be better used to describe the nonlinear stiffness, nonlinear damping and rate-dependence characteristics of the STF damper. All these investigations can offer an effective guidance for further theoretical and application study of the smart STF damper in energy dissipation fields.

Validating early stellar encounters as the cause of dynamically hot planetary systems

NASA Astrophysics Data System (ADS)

Kalas, Paul

2017-08-01

One of the key questions concerning exoplanetary systems is why some are dynamically cold, such as TRAPPIST-1, whereas others are dynamically hot, with highly eccentric planets and/or perturbed debris disks. Dynamical theory describes a variety of plausible mechanisms, but few can be empirically tested since the critical dynamical evolution that sets the final planetary architecture is short-lived. One rare system available for testing dynamical upheaval scenarios is the 400 Myr-old Fomalhaut system. In Cycle 22 we coronagraphically studied Fomalhaut C, which is a wide M-dwarf companion to Fomalhaut A, in order to test our prediction that the unresolved, Herschel-detected debris disk around Fomalhaut C may be highly perturbed because of a recent close interaction with Fomalhaut A. Using HST/STIS we discovered a highly asymmetric feature extending northward of Fomalhaut C by 3 that resembles our model of a dynamically hot disk. However, it may be a background galaxy and the definitive test of its physical relationship to Fomalhaut C is to demonstrate common proper motion. Using Keck adaptive optics follow-up observations in J band, we did not detect the feature, and hence follow-up HST observations are the only way to test for common proper motion. Here we request a very small program to revisit Fomalhaut C with STIS in order to validate the initial discovery as a debris disk (1 proper motion between HST epochs). The astrophysical significance is demonstrating that the Fomalhaut system is a valuable case for studying dynamical upheavals via stellar encounters that are inferred to occur in the evolution of many other planetary systems.

A Dynamic Attitude Measurement System Based on LINS

PubMed Central

Li, Hanzhou; Pan, Quan; Wang, Xiaoxu; Zhang, Juanni; Li, Jiang; Jiang, Xiangjun

2014-01-01

A dynamic attitude measurement system (DAMS) is developed based on a laser inertial navigation system (LINS). Three factors of the dynamic attitude measurement error using LINS are analyzed: dynamic error, time synchronization and phase lag. An optimal coning errors compensation algorithm is used to reduce coning errors, and two-axis wobbling verification experiments are presented in the paper. The tests indicate that the attitude accuracy is improved 2-fold by the algorithm. In order to decrease coning errors further, the attitude updating frequency is improved from 200 Hz to 2000 Hz. At the same time, a novel finite impulse response (FIR) filter with three notches is designed to filter the dither frequency of the ring laser gyro (RLG). The comparison tests suggest that the new filter is five times more effective than the old one. The paper indicates that phase-frequency characteristics of FIR filter and first-order holder of navigation computer constitute the main sources of phase lag in LINS. A formula to calculate the LINS attitude phase lag is introduced in the paper. The expressions of dynamic attitude errors induced by phase lag are derived. The paper proposes a novel synchronization mechanism that is able to simultaneously solve the problems of dynamic test synchronization and phase compensation. A single-axis turntable and a laser interferometer are applied to verify the synchronization mechanism. The experiments results show that the theoretically calculated values of phase lag and attitude error induced by phase lag can both match perfectly with testing data. The block diagram of DAMS and physical photos are presented in the paper. The final experiments demonstrate that the real-time attitude measurement accuracy of DAMS can reach up to 20″ (1σ) and the synchronization error is less than 0.2 ms on the condition of three axes wobbling for 10 min. PMID:25177802

Strain Rate and Anisotropic Microstructure Dependent Mechanical Behaviors of Silkworm Cocoon Shells

PubMed Central

Xu, Jun; Zhang, Wen; Gao, Xiang; Meng, Wanlin; Guan, Juan

2016-01-01

Silkworm cocoons are multi-layered composite structures comprised of high strength silk fiber and sericin, and their mechanical properties have been naturally selected to protect pupas during metamorphosis from various types of external attacks. The present study attempts to gain a comprehensive understanding of the mechanical properties of cocoon shell materials from wild silkworm species Antheraea pernyi under dynamic loading rates. Five dynamic strain rates from 0.00625 s-1 to 12.5 s-1 are tested to show the strain rate sensitivity of the cocoon shell material. In the meantime, the anisotropy of the cocoon shell is considered and the cocoon shell specimens are cut along 0°, 45° and 90° orientation to the short axis of cocoons. Typical mechanical properties including Young’s modulus, yield strength, ultimate strength and ultimate strain are extracted and analyzed from the stress-strain curves. Furthermore, the fracture morphologies of the cocoon shell specimens are observed under scanning electron microscopy to help understand the relationship between the mechanical properties and the microstructures of the cocoon material. A discussion on the dynamic strain rate effect on the mechanical properties of cocoon shell material is followed by fitting our experimental results to two previous models, and the effect could be well explained. We also compare natural and dried cocoon materials for the dynamic strain rate effect and interestingly the dried cocoon shells show better overall mechanical properties. This study provides a different perspective on the mechanical properties of cocoon material as a composite material, and provides some insight for bio-inspired engineering materials. PMID:26939063

A dynamic mechanical analysis technique for porous media

PubMed Central

Pattison, Adam J; McGarry, Matthew; Weaver, John B; Paulsen, Keith D

2015-01-01

Dynamic mechanical analysis (DMA) is a common way to measure the mechanical properties of materials as functions of frequency. Traditionally, a viscoelastic mechanical model is applied and current DMA techniques fit an analytical approximation to measured dynamic motion data by neglecting inertial forces and adding empirical correction factors to account for transverse boundary displacements. Here, a finite element (FE) approach to processing DMA data was developed to estimate poroelastic material properties. Frequency-dependent inertial forces, which are significant in soft media and often neglected in DMA, were included in the FE model. The technique applies a constitutive relation to the DMA measurements and exploits a non-linear inversion to estimate the material properties in the model that best fit the model response to the DMA data. A viscoelastic version of this approach was developed to validate the approach by comparing complex modulus estimates to the direct DMA results. Both analytical and FE poroelastic models were also developed to explore their behavior in the DMA testing environment. All of the models were applied to tofu as a representative soft poroelastic material that is a common phantom in elastography imaging studies. Five samples of three different stiffnesses were tested from 1 – 14 Hz with rough platens placed on the top and bottom surfaces of the material specimen under test to restrict transverse displacements and promote fluid-solid interaction. The viscoelastic models were identical in the static case, and nearly the same at frequency with inertial forces accounting for some of the discrepancy. The poroelastic analytical method was not sufficient when the relevant physical boundary constraints were applied, whereas the poroelastic FE approach produced high quality estimates of shear modulus and hydraulic conductivity. These results illustrated appropriate shear modulus contrast between tofu samples and yielded a consistent contrast in hydraulic conductivity as well. PMID:25248170

Dynamic Loading Assembly for Testing Actuators of Segmented Mirror Telescope

NASA Astrophysics Data System (ADS)

Deshmukh, Prasanna Gajanan; Parihar, Padmakar; Balasubramaniam, Karthik A.; Mishra, Deepta Sundar; Mahesh, P. K.

Upcoming large telescopes are based on Segmented Mirror Telescope (SMT) technology which uses small hexagonal mirror segments placed side by side to form the large monolithic surface. The segments alignment needs to be maintained against external disturbances like wind, gravity, temperature and structural vibration. This is achieved by using three position actuators per segment working at few-nanometer scale range along with a local closed loop controller. The actuator along with a controller is required to meet very stringent performance requirements, such as track rates up to 300nm/s (90mN/s) with tracking errors less than 5nm, dynamical forces of up to ±40N, ability to reject disturbances introduced by the wind as well as by mechanical vibration generated in the mirror cell, etc. To conduct these performance tests in more realistic manner, we have designed and developed a Dynamic Loading Assembly (DLA) at Indian Institute of Astrophysics (IIA), Bangalore. DLA is a computer controlled force-inducing device, designed in a modular fashion to generate different types of user-defined disturbances in extremely precise and controlled manner. Before realizing the device, using a simple spring-mass-damper-based mathematical model, we ensured that the concept would indeed work. Subsequently, simple concept was converted into a detailed mechanical design and parts were manufactured and assembled. DLA has static and dynamic loading capabilities up to 250N and 18N respectively, with a bandwidth sufficient to generate wind disturbances. In this paper, we present various performance requirements of SMT actuators as well as our effort to develop a dynamic loading device which can be used to test these actuators. Well before using DLA for meaningful testing of the actuator, the DLA itself have gone through various tests and improvements phases. We have successfully demonstrated that DLA can be used to check the extreme performance of two different SMT actuators, which are expected to track the position/force with a few nanometer accuracy.

Evolution of microstructure of Haynes 230 and Inconel 617 under mechanical testing at high temperatures

NASA Astrophysics Data System (ADS)

Hrutkay, Kyle

Haynes 230 and Inconel 617 are austenitic nickel based superalloys, which are candidate structural materials for next generation high temperature nuclear reactors. High temperature deformation behavior of Haynes 230 and Inconel 617 have been investigated at the microstructural level in order to gain a better understanding of mechanical properties. Tensile tests were performed at strain rates ranging from 10-3-10-5 s -1 at room temperature, 600 °C, 800 °C and 950 °C. Subsequent microstructural analysis, including Scanning Electron Microscopy, Transmission Electron Microscopy, Energy-Dispersive X-ray Spectroscopy, and X-Ray Diffraction were used to relate the microstructural evolution at high temperatures to that of room temperature samples. Grain sizes and precipitate morphologies were used to determine high temperature behavior and fracture mechanics. Serrated flow was observed at intermediate and high temperatures as a result of discontinuous slip and dynamic recrystallization. The amplitude of serration increased with a decrease in the strain rate and increase in the temperature. Dynamic strain ageing was responsible for serrations at intermediate temperatures by means of a locking and unlocking phenomenon between dislocations and solute atoms. Dynamic recrystallization nucleated by grain and twin bulging resulting in a refinement of grain size. Existing models found in the literature were discussed to explain both of these phenomena.

Quantifying dynamic mechanical properties of human placenta tissue using optimization techniques with specimen-specific finite-element models.

PubMed

Hu, Jingwen; Klinich, Kathleen D; Miller, Carl S; Nazmi, Giseli; Pearlman, Mark D; Schneider, Lawrence W; Rupp, Jonathan D

2009-11-13

Motor-vehicle crashes are the leading cause of fetal deaths resulting from maternal trauma in the United States, and placental abruption is the most common cause of these deaths. To minimize this injury, new assessment tools, such as crash-test dummies and computational models of pregnant women, are needed to evaluate vehicle restraint systems with respect to reducing the risk of placental abruption. Developing these models requires accurate material properties for tissues in the pregnant abdomen under dynamic loading conditions that can occur in crashes. A method has been developed for determining dynamic material properties of human soft tissues that combines results from uniaxial tensile tests, specimen-specific finite-element models based on laser scans that accurately capture non-uniform tissue-specimen geometry, and optimization techniques. The current study applies this method to characterizing material properties of placental tissue. For 21 placenta specimens tested at a strain rate of 12/s, the mean failure strain is 0.472+/-0.097 and the mean failure stress is 34.80+/-12.62 kPa. A first-order Ogden material model with ground-state shear modulus (mu) of 23.97+/-5.52 kPa and exponent (alpha(1)) of 3.66+/-1.90 best fits the test results. The new method provides a nearly 40% error reduction (p<0.001) compared to traditional curve-fitting methods by considering detailed specimen geometry, loading conditions, and dynamic effects from high-speed loading. The proposed method can be applied to determine mechanical properties of other soft biological tissues.

Testing of information condensation in a model reverberating spiking neural network.

PubMed

Vidybida, Alexander

2011-06-01

Information about external world is delivered to the brain in the form of structured in time spike trains. During further processing in higher areas, information is subjected to a certain condensation process, which results in formation of abstract conceptual images of external world, apparently, represented as certain uniform spiking activity partially independent on the input spike trains details. Possible physical mechanism of condensation at the level of individual neuron was discussed recently. In a reverberating spiking neural network, due to this mechanism the dynamics should settle down to the same uniform/ periodic activity in response to a set of various inputs. Since the same periodic activity may correspond to different input spike trains, we interpret this as possible candidate for information condensation mechanism in a network. Our purpose is to test this possibility in a network model consisting of five fully connected neurons, particularly, the influence of geometric size of the network, on its ability to condense information. Dynamics of 20 spiking neural networks of different geometric sizes are modelled by means of computer simulation. Each network was propelled into reverberating dynamics by applying various initial input spike trains. We run the dynamics until it becomes periodic. The Shannon's formula is used to calculate the amount of information in any input spike train and in any periodic state found. As a result, we obtain explicit estimate of the degree of information condensation in the networks, and conclude that it depends strongly on the net's geometric size.

Does the continuum theory of dynamic fracture work?

NASA Astrophysics Data System (ADS)

Kessler, David A.; Levine, Herbert

2003-09-01

We investigate the validity of the linear elastic fracture mechanics approach to dynamic fracture. We first test the predictions in a lattice simulation, using a formula of Eshelby for the time-dependent stress intensity factor. Excellent agreement with the theory is found. We then use the same method to analyze the experiment of Sharon and Fineberg. The data here are not consistent with the theoretical expectation.

The Shock and Vibration Digest, Volume 12, Number 9,

DTIC Science & Technology

1980-09-01

include diesel engine noise, process plant noise, and environ- dynamic mechanical properties of viscoelastic mate- mental noise and planning. rials...new numerical methods are presented in- plant noise control, design of facilities for noise in the twelve articles of the mathematics section. control...International Symposium for Innovative the seminar: 31 16 = ,,-,==. ’d-m w .’ " Dynamic Testing of Nuclear Power Plant Struc- ENVIRONMENTAL STRESS

The Relative Effectiveness of the Use of Static and Dynamic Mechanical Models in Teaching Elementary School Children the Theoretical Concept--The Particle Nature of Matter.

ERIC Educational Resources Information Center

Ziegler, Robert Edward

This study is concerned with determining the relative effectiveness of a static and dynamic theoretical model in teaching elementary school students to use the particle idea of matter when explaining certain physical phenomena. A clinical method of personal individual interview-testing, teaching, and retesting of a random sample population from…

Dispersion of response times reveals cognitive dynamics.

PubMed

Holden, John G; Van Orden, Guy C; Turvey, Michael T

2009-04-01

Trial-to-trial variation in word-pronunciation times exhibits 1/f scaling. One explanation is that human performances are consequent on multiplicative interactions among interdependent processes-interaction dominant dynamics. This article describes simulated distributions of pronunciation times in a further test for multiplicative interactions and interdependence. Individual participant distributions of approximately 1,100 word-pronunciation times were successfully mimicked for each participant in combinations of lognormal and power-law behavior. Successful hazard function simulations generalized these results to establish interaction dominant dynamics, in contrast with component dominant dynamics, as a likely mechanism for cognitive activity. (c) 2009 APA, all rights reserved

Dispersion of Response Times Reveals Cognitive Dynamics

PubMed Central

Holden, John G.; Van Orden, Guy C.; Turvey, Michael T.

2013-01-01

Trial to trial variation in word pronunciation times exhibits 1/f scaling. One explanation is that human performances are consequent on multiplicative interactions among interdependent processes – interaction dominant dynamics. This article describes simulated distributions of pronunciation times in a further test for multiplicative interactions and interdependence. Individual participant distributions of ≈1100 word pronunciation times are successfully mimicked for each participant in combinations of lognormal and power law behavior. Successful hazard function simulations generalize these results to establish interaction dominant dynamics, in contrast with component dominant dynamics, as a likely mechanism for cognitive activity. PMID:19348544

Compensating for intersegmental dynamics across the shoulder, elbow, and wrist joints during feedforward and feedback control.

PubMed

Maeda, Rodrigo S; Cluff, Tyler; Gribble, Paul L; Pruszynski, J Andrew

2017-10-01

Moving the arm is complicated by mechanical interactions that arise between limb segments. Such intersegmental dynamics cause torques applied at one joint to produce movement at multiple joints, and in turn, the only way to create single joint movement is by applying torques at multiple joints. We investigated whether the nervous system accounts for intersegmental limb dynamics across the shoulder, elbow, and wrist joints during self-initiated planar reaching and when countering external mechanical perturbations. Our first experiment tested whether the timing and amplitude of shoulder muscle activity account for interaction torques produced during single-joint elbow movements from different elbow initial orientations and over a range of movement speeds. We found that shoulder muscle activity reliably preceded movement onset and elbow agonist activity, and was scaled to compensate for the magnitude of interaction torques arising because of forearm rotation. Our second experiment tested whether elbow muscles compensate for interaction torques introduced by single-joint wrist movements. We found that elbow muscle activity preceded movement onset and wrist agonist muscle activity, and thus the nervous system predicted interaction torques arising because of hand rotation. Our third and fourth experiments tested whether shoulder muscles compensate for interaction torques introduced by different hand orientations during self-initiated elbow movements and to counter mechanical perturbations that caused pure elbow motion. We found that the nervous system predicted the amplitude and direction of interaction torques, appropriately scaling the amplitude of shoulder muscle activity during self-initiated elbow movements and rapid feedback control. Taken together, our results demonstrate that the nervous system robustly accounts for intersegmental dynamics and that the process is similar across the proximal to distal musculature of the arm as well as between feedforward (i.e., self-initiated) and feedback (i.e., reflexive) control. NEW & NOTEWORTHY Intersegmental dynamics complicate the mapping between applied joint torques and the resulting joint motions. We provide evidence that the nervous system robustly predicts these intersegmental limb dynamics across the shoulder, elbow, and wrist joints during reaching and when countering external perturbations. Copyright © 2017 the American Physiological Society.

Development of a Continuum Damage Mechanics Material Model of a Graphite-Kevlar(Registered Trademark) Hybrid Fabric for Simulating the Impact Response of Energy Absorbing Kevlar(Registered Trademark) Hybrid Fabric for Simulating the Impact Response of Energy Absorbing

NASA Technical Reports Server (NTRS)

Jackson, Karen E.; Fasanella, Edwin L.; Littell, Justin D.

2017-01-01

This paper describes the development of input properties for a continuum damage mechanics based material model, Mat 58, within LS-DYNA(Registered Trademark) to simulate the response of a graphite-Kevlar(Registered Trademark) hybrid plain weave fabric. A limited set of material characterization tests were performed on the hybrid graphite-Kevlar(Registered Trademark) fabric. Simple finite element models were executed in LS-DYNA(Registered Trademark) to simulate the material characterization tests and to verify the Mat 58 material model. Once verified, the Mat 58 model was used in finite element models of two composite energy absorbers: a conical-shaped design, designated the "conusoid," fabricated of four layers of hybrid graphite-Kevlar(Registered Trademark) fabric; and, a sinusoidal-shaped foam sandwich design, designated the "sinusoid," fabricated of the same hybrid fabric face sheets with a foam core. Dynamic crush tests were performed on components of the two energy absorbers, which were designed to limit average vertical accelerations to 25- to 40-g, to minimize peak crush loads, and to generate relatively long crush stroke values under dynamic loading conditions. Finite element models of the two energy absorbers utilized the Mat 58 model that had been verified through material characterization testing. Excellent predictions of the dynamic crushing response were obtained.

1001518

NASA Image and Video Library

2010-09-01

DEVELOPMENT TESTING BEING CONDUCTED AT THE REQUEST OF THE MSFC DYNAMICS, LOADS, AND STRENGTH BRANCH (EV31) TO STUDY THE FAILURE BEHAVIOR OF FASTENERS SUBJECTED TO COMBINED SHEAR AND TENSION LOADING. THE DATA FROM THIS TESTING WILL BE USED TO DEVELOP APPROPRIATE STRUCTURAL ANALYSIS METHODS AS PART OF A FASTENER STANDARDS EFFORT SPONSORED BY THE NASA ENGINEERING SAFETY CENTER (NESC). THE TEST FIXTURE WAS DESIGNED AND FABRICATED THROUGH THE MSFC MECHANICAL FABRICATION BRANCH (ES23). THE TESTING ORGANIZATION IS THE MSFC MATERIALS TEST BRANCH (EM10).

1001519

NASA Image and Video Library

2010-09-01

DEVELOPMENT TESTING BEING CONDUCTED AT THE REQUEST OF THE MSFC DYNAMICS, LOADS, AND STRENGTH BRANCH (EV31) TO STUDY THE FAILURE BEHAVIOR OF FASTENERS SUBJECTED TO COMBINED SHEAR AND TENSION LOADING. THE DATA FROM THIS TESTING WILL BE USED TO DEVELOP APPROPRIATE STRUCTURAL ANALYSIS METHODS AS PART OF A FASTENER STANDARDS EFFORT SPONSORED BY THE NASA ENGINEERING SAFETY CENTER (NESC). THE TEST FIXTURE WAS DESIGNED AND FABRICATED THROUGH THE MSFC MECHANICAL FABRICATION BRANCH (ES23). THE TESTING ORGANIZATION IS THE MSFC MATERIALS TEST BRANCH (EM10).

1001520

NASA Image and Video Library

2010-09-01

DEVELOPMENT TESTING BEING CONDUCTED AT THE REQUEST OF THE MSFC DYNAMICS, LOADS, AND STRENGTH BRANCH (EV31) TO STUDY THE FAILURE BEHAVIOR OF FASTENERS SUBJECTED TO COMBINED SHEAR AND TENSION LOADING. THE DATA FROM THIS TESTING WILL BE USED TO DEVELOP APPROPRIATE STRUCTURAL ANALYSIS METHODS AS PART OF A FASTENER STANDARDS EFFORT SPONSORED BY THE NASA ENGINEERING SAFETY CENTER (NESC). THE TEST FIXTURE WAS DESIGNED AND FABRICATED THROUGH THE MSFC MECHANICAL FABRICATION BRANCH (ES23). THE TESTING ORGANIZATION IS THE MSFC MATERIALS TEST BRANCH (EM10).

1001521

NASA Image and Video Library

2010-09-01

DEVELOPMENT TESTING BEING CONDUCTED AT THE REQUEST OF THE MSFC DYNAMICS, LOADS, AND STRENGTH BRANCH (EV31) TO STUDY THE FAILURE BEHAVIOR OF FASTENERS SUBJECTED TO COMBINED SHEAR AND TENSION LOADING. THE DATA FROM THIS TESTING WILL BE USED TO DEVELOP APPROPRIATE STRUCTURAL ANALYSIS METHODS AS PART OF A FASTENER STANDARDS EFFORT SPONSORED BY THE NASA ENGINEERING SAFETY CENTER (NESC). THE TEST FIXTURE WAS DESIGNED AND FABRICATED THROUGH THE MSFC MECHANICAL FABRICATION BRANCH (ES23). THE TESTING ORGANIZATION IS THE MSFC MATERIALS TEST BRANCH (EM10).

High-strain rate tensile characterization of graphite platelet reinforced vinyl ester based nanocomposites using split-Hopkinson pressure bar

NASA Astrophysics Data System (ADS)

Pramanik, Brahmananda

The dynamic response of exfoliated graphite nanoplatelet (xGnP) reinforced and carboxyl terminated butadiene nitrile (CTBN) toughened vinyl ester based nanocomposites are characterized under both dynamic tensile and compressive loading. Dynamic direct tensile tests are performed applying the reverse impact Split Hopkinson Pressure Bar (SHPB) technique. The specimen geometry for tensile test is parametrically optimized by Finite Element Analysis (FEA) using ANSYS Mechanical APDLRTM. Uniform stress distribution within the specimen gage length has been verified using high-speed digital photography. The on-specimen strain gage installation is substituted by a non-contact Laser Occlusion Expansion Gage (LOEG) technique for infinitesimal dynamic tensile strain measurements. Due to very low transmitted pulse signal, an alternative approach based on incident pulse is applied for obtaining the stress-time history. Indirect tensile tests are also performed combining the conventional SHPB technique with Brazilian disk test method for evaluating cylindrical disk specimens. The cylindrical disk specimen is held snugly in between two concave end fixtures attached to the incident and transmission bars. Indirect tensile stress is estimated from the SHPB pulses, and diametrical transverse tensile strain is measured using LOEG. Failure diagnosis using high-speed digital photography validates the viability of utilizing this indirect test method for characterizing the tensile properties of the candidate vinyl ester based nanocomposite system. Also, quasi-static indirect tensile response agrees with previous investigations conducted using the traditional dog-bone specimen in quasi-static direct tensile tests. Investigation of both quasi-static and dynamic indirect tensile test responses show the strain rate effect on the tensile strength and energy absorbing capacity of the candidate materials. Finally, the conventional compressive SHPB tests are performed. It is observed that both strength and energy absorbing capacity of these candidate material systems are distinctively less under dynamic tension than under compressive loading. Nano-reinforcement appears to marginally improve these properties for pure vinyl ester under dynamic tension, although it is found to be detrimental under dynamic compression.

PATHFINDER ATOMIC POWER PLANT TECHNICAL PROGRESS REPORT FOR JULY 1, 1959- SEPTEMBER 30, 1959

DOE Office of Scientific and Technical Information (OSTI.GOV)

None

1960-10-31

ABS>Fuel Element Research and Development. Dynamic and static corrosion tests on 8001 Al were completed. Annealmmmg of 1100 cladding on 5083 and M400 cladding on X2219 were tested at 500 deg C, and investigation continued on producing X8101 Al alloy cladding in tube plates by extrusion. Boiler fuel element capsule irradiation tests and subassembly tests are described Heat transfer loop studies and fuel fabrication for the critical facility are reported. Boiler fuel element mechanical design and testing progress is desc ribed. and the superheater fuel element temperature evaluating routine is discussed. Low- enrichment superheater fuel element development included design studiesmore » and stainless steel powder and UO/sub 2/ powder fabrication studies Reactor Mechanical Studies. Research is reported on vessel and structure design, fabrication, and testing, recirculation system design, steam separator tests, and control rod studies. Nuclear Analysis. Reactor physics studies are reported on nuclear constants, baffle plate analysis, comparison of core representations, delayed neutron fraction. and shielding analysis of the reactor building. Reactor and system dynamics and critical experiments were also studied. Chemistry. Progress is reported on recombiner. radioactive gas removal and storage, ion exchanger and radiochemical processing. (For preceding period see ACNP-5915.) (T.R.H.)« less

Gas Bubble Dynamics under Mechanical Vibrations

NASA Astrophysics Data System (ADS)

Mohagheghian, Shahrouz; Elbing, Brian

2017-11-01

The scientific community has a limited understanding of the bubble dynamics under mechanical oscillations due to over simplification of Navier-Stockes equation by neglecting the shear stress tensor and not accounting for body forces when calculating the acoustic radiation force. The current work experimental investigates bubble dynamics under mechanical vibration and resulting acoustic field by measuring the bubble size and velocity using high-speed imaging. The experimental setup consists of a custom-designed shaker table, cast acrylic bubble column, compressed air injection manifold and an optical imaging system. The mechanical vibrations resulted in accelerations between 0.25 to 10 times gravitational acceleration corresponding to frequency and amplitude range of 8 - 22Hz and 1 - 10mm respectively. Throughout testing the void fraction was limited to <5%. The bubble size is larger than resonance size and smaller than acoustic wavelength. The amplitude of acoustic pressure wave was estimated using the definition of Bjerknes force in combination with Rayleigh-Plesset equation. Physical behavior of the system was capture and classified. Bubble size, velocity as well as size and spatial distribution will be presented.

Brillouin microspectroscopy of nanostructured biomaterials: photonics assisted tailoring mechanical properties

NASA Astrophysics Data System (ADS)

Meng, Zhaokai; Jaiswal, Manish K.; Chitrakar, Chandani; Thakur, Teena; Gaharwar, Akhilesh K.; Yakovlev, Vladislav V.

2016-03-01

Developing new biomaterials is essential for the next-generation of materials for bioenergy, bioelectronics, basic biology, medical diagnostics, cancer research, and regenerative medicine. Specifically, recent progress in nanotechnology has stimulated the development of multifunctional biomaterials for tissue engineering applications. The physical properties of nanocomposite biomaterials, including elasticity and viscosity, play key roles in controlling cell fate, which underlines therapeutic success. Conventional mechanical tests, including uniaxial compression and tension, dynamic mechanical analysis and shear rheology, require mechanical forces to be directly exerted onto the sample and therefore may not be suitable for in situ measurements or continuous monitoring of mechanical stiffness. In this study, we employ spontaneous Brillouin spectroscopy as a viscoelasticity-specific probing technique. We utilized a Brillouin spectrometer to characterize biomaterial's microscopic elasticity and correlated those with conventional mechanical tests (e.g., rheology).

In vivo dynamical behavior of yeast chromatin modeled as an entangled polymer network with constraint release

NASA Astrophysics Data System (ADS)

Wang, Chenxi; Kilfoil, Maria L.

2013-03-01

The high fidelity segregation of chromatin is the central problem in cell mitosis. The role of mechanics underlying this, however, is undetermined. Work in this area has largely focused on cytoskeletal elements of the process. Preliminary work in our lab suggests the mechanical properties of chromatin are fundamental in this process. Nevertheless, the mechanical properties of chromatin in the cellular context are not well-characterized. For better understanding of the role of mechanics in this cellular process, and of the chromatin mechanics in vivo generally, a systematic dynamical description of chromatin in vivo is required. Accordingly, we label specific sites on chromatin with fluorescent proteins of different wave lengths, enabling us to detect multiple spots separately in 3D and track their displacements in time inside living yeast cells. We analyze the pairwise cross-correlated motion between spots as a function of relative distance along the DNA contour. Comparison between the reptation model and our data serves to test our conjecture that chromatin in the cell is basically an entangled polymer network under constraints to thermal motion, and removal of constraints by non-thermal cellular processes is expected to affect its dynamic behavior.

Five-Axis, Three-Magnetic-Bearing Dynamic Spin Rig

NASA Technical Reports Server (NTRS)

Morrison, Carlos R.; Provenza, Andrew; Kurkov, Anatole; Mehmed, Oral; Johnson, Dexter; Montague, Gerald; Duffy, Kirsten; Jansen, Ralph

2005-01-01

The Five-Axis, Three-Magnetic-Bearing Dynamic Spin Rig is an apparatus for vibration testing of turbomachine blades in a vacuum at rotational speeds from 0 to 40,000 rpm. This rig includes (1) a vertically oriented shaft on which is mounted an assembly comprising a rotor holding the blades to be tested, (2) two actively controlled heteropolar radial magnetic bearings at opposite ends of the shaft, and (3) an actively controlled magnetic thrust bearing at the upper end of the shaft. This rig is a more capable successor to a prior apparatus, denoted the Dynamic Spin Rig (DSR), that included a vertically oriented shaft with a mechanical thrust bearing at the upper end and a single actively controlled heteropolar radial magnetic bearing at the lower end.

Modeling and Testing of Phase Transition-Based Deployable Systems for Small Body Sample Capture

NASA Technical Reports Server (NTRS)

Quadrelli, Marco; Backes, Paul; Wilkie, Keats; Giersch, Lou; Quijano, Ubaldo; Keim, Jason; Mukherjee, Rudranarayan

2009-01-01

This paper summarizes the modeling, simulation, and testing work related to the development of technology to investigate the potential that shape memory actuation has to provide mechanically simple and affordable solutions for delivering assets to a surface and for sample capture and return. We investigate the structural dynamics and controllability aspects of an adaptive beam carrying an end-effector which, by changing equilibrium phases is able to actively decouple the end-effector dynamics from the spacecraft dynamics during the surface contact phase. Asset delivery and sample capture and return are at the heart of several emerging potential missions to small bodies, such as asteroids and comets, and to the surface of large bodies, such as Titan.

Peripheral neuropathic pain: a mechanism-related organizing principle based on sensory profiles

PubMed Central

Baron, Ralf; Maier, Christoph; Attal, Nadine; Binder, Andreas; Bouhassira, Didier; Cruccu, Giorgio; Finnerup, Nanna B.; Haanpää, Maija; Hansson, Per; Hüllemann, Philipp; Jensen, Troels S.; Freynhagen, Rainer; Kennedy, Jeffrey D.; Magerl, Walter; Mainka, Tina; Reimer, Maren; Rice, Andrew S.C.; Segerdahl, Märta; Serra, Jordi; Sindrup, Sören; Sommer, Claudia; Tölle, Thomas; Vollert, Jan; Treede, Rolf-Detlef

2016-01-01

Abstract Patients with neuropathic pain are heterogeneous in etiology, pathophysiology, and clinical appearance. They exhibit a variety of pain-related sensory symptoms and signs (sensory profile). Different sensory profiles might indicate different classes of neurobiological mechanisms, and hence subgroups with different sensory profiles might respond differently to treatment. The aim of the investigation was to identify subgroups in a large sample of patients with neuropathic pain using hypothesis-free statistical methods on the database of 3 large multinational research networks (German Research Network on Neuropathic Pain (DFNS), IMI-Europain, and Neuropain). Standardized quantitative sensory testing was used in 902 (test cohort) and 233 (validation cohort) patients with peripheral neuropathic pain of different etiologies. For subgrouping, we performed a cluster analysis using 13 quantitative sensory testing parameters. Three distinct subgroups with characteristic sensory profiles were identified and replicated. Cluster 1 (sensory loss, 42%) showed a loss of small and large fiber function in combination with paradoxical heat sensations. Cluster 2 (thermal hyperalgesia, 33%) was characterized by preserved sensory functions in combination with heat and cold hyperalgesia and mild dynamic mechanical allodynia. Cluster 3 (mechanical hyperalgesia, 24%) was characterized by a loss of small fiber function in combination with pinprick hyperalgesia and dynamic mechanical allodynia. All clusters occurred across etiologies but frequencies differed. We present a new approach of subgrouping patients with peripheral neuropathic pain of different etiologies according to intrinsic sensory profiles. These 3 profiles may be related to pathophysiological mechanisms and may be useful in clinical trial design to enrich the study population for treatment responders. PMID:27893485

Peripheral neuropathic pain: a mechanism-related organizing principle based on sensory profiles.

PubMed

Baron, Ralf; Maier, Christoph; Attal, Nadine; Binder, Andreas; Bouhassira, Didier; Cruccu, Giorgio; Finnerup, Nanna B; Haanpää, Maija; Hansson, Per; Hüllemann, Philipp; Jensen, Troels S; Freynhagen, Rainer; Kennedy, Jeffrey D; Magerl, Walter; Mainka, Tina; Reimer, Maren; Rice, Andrew S C; Segerdahl, Märta; Serra, Jordi; Sindrup, Sören; Sommer, Claudia; Tölle, Thomas; Vollert, Jan; Treede, Rolf-Detlef

2017-02-01

Patients with neuropathic pain are heterogeneous in etiology, pathophysiology, and clinical appearance. They exhibit a variety of pain-related sensory symptoms and signs (sensory profile). Different sensory profiles might indicate different classes of neurobiological mechanisms, and hence subgroups with different sensory profiles might respond differently to treatment. The aim of the investigation was to identify subgroups in a large sample of patients with neuropathic pain using hypothesis-free statistical methods on the database of 3 large multinational research networks (German Research Network on Neuropathic Pain (DFNS), IMI-Europain, and Neuropain). Standardized quantitative sensory testing was used in 902 (test cohort) and 233 (validation cohort) patients with peripheral neuropathic pain of different etiologies. For subgrouping, we performed a cluster analysis using 13 quantitative sensory testing parameters. Three distinct subgroups with characteristic sensory profiles were identified and replicated. Cluster 1 (sensory loss, 42%) showed a loss of small and large fiber function in combination with paradoxical heat sensations. Cluster 2 (thermal hyperalgesia, 33%) was characterized by preserved sensory functions in combination with heat and cold hyperalgesia and mild dynamic mechanical allodynia. Cluster 3 (mechanical hyperalgesia, 24%) was characterized by a loss of small fiber function in combination with pinprick hyperalgesia and dynamic mechanical allodynia. All clusters occurred across etiologies but frequencies differed. We present a new approach of subgrouping patients with peripheral neuropathic pain of different etiologies according to intrinsic sensory profiles. These 3 profiles may be related to pathophysiological mechanisms and may be useful in clinical trial design to enrich the study population for treatment responders.

Biomechanical investigation of a novel ratcheting arthrodesis nail.

PubMed

McCormick, Jeremy J; Li, Xinning; Weiss, Douglas R; Billiar, Kristen L; Wixted, John J

2010-10-14

Knee or tibiotalocalcaneal arthrodesis is a salvage procedure, often with unacceptable rates of nonunion. Basic science of fracture healing suggests that compression across a fusion site may decrease nonunion. A novel ratcheting arthrodesis nail designed to improve dynamic compression is mechanically tested in comparison to existing nails. A novel ratcheting nail was designed and mechanically tested in comparison to a solid nail and a threaded nail using sawbones models (Pacific Research Laboratories, Inc.). Intramedullary nails (IM) were implanted with a load cell (Futek LTH 500) between fusion surfaces. Constructs were then placed into a servo-hydraulic test frame (Model 858 Mini-bionix, MTS Systems) for application of 3 mm and 6 mm dynamic axial displacement (n = 3/group). Load to failure was also measured. Mean percent of initial load after 3-mm and 6-mm displacement was 190.4% and 186.0% for the solid nail, 80.7% and 63.0% for the threaded nail, and 286.4% and 829.0% for the ratcheting nail, respectively. Stress-shielding (as percentage of maximum load per test) after 3-mm and 6-mm displacement averaged 34.8% and 28.7% (solid nail), 40.3% and 40.9% (threaded nail), and 18.5% and 11.5% (ratcheting nail), respectively. In the 6-mm trials, statistically significant increase in initial load and decrease in stress-shielding for the ratcheting vs. solid nail (p = 0.029, p = 0.001) and vs. threaded nail (p = 0.012, p = 0.002) was observed. Load to failure for the ratcheting nail; 599.0 lbs, threaded nail; 508.8 lbs, and solid nail; 688.1 lbs. With significantly increase of compressive load while decreasing stress-shielding at 6-mm of dynamic displacement, the ratcheting mechanism in IM nails may clinically improve rates of fusion.

Biomechanical investigation of a novel ratcheting arthrodesis nail

PubMed Central

2010-01-01

Background Knee or tibiotalocalcaneal arthrodesis is a salvage procedure, often with unacceptable rates of nonunion. Basic science of fracture healing suggests that compression across a fusion site may decrease nonunion. A novel ratcheting arthrodesis nail designed to improve dynamic compression is mechanically tested in comparison to existing nails. Methods A novel ratcheting nail was designed and mechanically tested in comparison to a solid nail and a threaded nail using sawbones models (Pacific Research Laboratories, Inc.). Intramedullary nails (IM) were implanted with a load cell (Futek LTH 500) between fusion surfaces. Constructs were then placed into a servo-hydraulic test frame (Model 858 Mini-bionix, MTS Systems) for application of 3 mm and 6 mm dynamic axial displacement (n = 3/group). Load to failure was also measured. Results Mean percent of initial load after 3-mm and 6-mm displacement was 190.4% and 186.0% for the solid nail, 80.7% and 63.0% for the threaded nail, and 286.4% and 829.0% for the ratcheting nail, respectively. Stress-shielding (as percentage of maximum load per test) after 3-mm and 6-mm displacement averaged 34.8% and 28.7% (solid nail), 40.3% and 40.9% (threaded nail), and 18.5% and 11.5% (ratcheting nail), respectively. In the 6-mm trials, statistically significant increase in initial load and decrease in stress-shielding for the ratcheting vs. solid nail (p = 0.029, p = 0.001) and vs. threaded nail (p = 0.012, p = 0.002) was observed. Load to failure for the ratcheting nail; 599.0 lbs, threaded nail; 508.8 lbs, and solid nail; 688.1 lbs. Conclusion With significantly increase of compressive load while decreasing stress-shielding at 6-mm of dynamic displacement, the ratcheting mechanism in IM nails may clinically improve rates of fusion. PMID:20942976

A bioreactor test system to mimic the biological and mechanical environment of oral soft tissues and to evaluate substitutes for connective tissue grafts.

PubMed

Mathes, Stephanie H; Wohlwend, Lorenz; Uebersax, Lorenz; von Mentlen, Roger; Thoma, Daniel S; Jung, Ronald E; Görlach, Christoph; Graf-Hausner, Ursula

2010-12-15

Gingival cells of the oral connective tissue are exposed to complex mechanical forces during mastication, speech, tooth movement and orthodontic treatments. Especially during wound healing following surgical procedures, internal and external forces may occur, creating pressure upon the newly formed tissue. This clinical situation has to be considered when developing biomaterials to augment soft tissue in the oral cavity. In order to pre-evaluate a collagen sponge intended to serve as a substitute for autogenous connective tissue grafts (CTGs), a dynamic bioreactor system was developed. Pressure and shear forces can be applied in this bioreactor in addition to a constant medium perfusion to cell-material constructs. Three-dimensional volume changes and stiffness of the matrices were analyzed. In addition, cell responses such as cell vitality and extracellular matrix (ECM) production were investigated. The number of metabolic active cells constantly increased under fully dynamic culture conditions. The sponges remained elastic even after mechanical forces were applied for 14 days. Analysis of collagen type I and fibronectin revealed a statistically significant accumulation of these ECM molecules (P < 0.05-0.001) when compared to static cultures. An increased expression of tenascin-c, indicating tissue remodeling processes, was observed under dynamic conditions only. The results indicate that the tested in vitro cell culture system was able to mimic both the biological and mechanical environments of the clinical situation in a healing wound. © 2010 Wiley Periodicals, Inc.

NASA Common Research Model Test Envelope Extension With Active Sting Damping at NTF

NASA Technical Reports Server (NTRS)

Rivers, Melissa B.; Balakrishna, S.

2014-01-01

The NASA Common Research Model (CRM) high Reynolds number transonic wind tunnel testing program was established to generate an experimental database for applied Computational Fluid Dynamics (CFD) validation studies. During transonic wind tunnel tests, the CRM encounters large sting vibrations when the angle of attack approaches the second pitching moment break, which can sometimes become divergent. CRM transonic test data analysis suggests that sting divergent oscillations are related to negative net sting damping episodes associated with flow separation instability. The National Transonic Facility (NTF) has been addressing remedies to extend polar testing up to and beyond the second pitching moment break point of the test articles using an active piezoceramic damper system for both ambient and cryogenic temperatures. This paper reviews CRM test results to gain understanding of sting dynamics with a simple model describing the mechanics of a sting-model system and presents the performance of the damper under cryogenic conditions.

Vestibular ontogeny: Measuring the influence of the dynamic environment

NASA Technical Reports Server (NTRS)

Jones, Timothy A.; Devries, Sherri M.; Dubois, Linda M.; Nelson, Rick C.

1993-01-01

In comparison to other special senses, we are only meagerly informed about the development of vestibular function and the mechanisms that may operate to control or influence the course of vestibular ontogeny. Perhaps one contributing factor to this disparity is the difficulty of evaluating vestibular sense organs directly and noninvasively. The present report describes a recently developed direct noninvasive vestibular function test that can be used to address many basic questions about the developing vestibular system. More particularly, the test can be used to examine the effects of the dynamic environment (e.g. gravitational field and vibration) on vestibular ontogeny.

Impact of Isothermal Aging and Testing Temperature on Large Flip-Chip BGA Interconnect Mechanical Shock Performance

NASA Astrophysics Data System (ADS)

Lee, Tae-Kyu; Chen, Zhiqiang; Guirguis, Cherif; Akinade, Kola

2017-10-01

The stability of solder interconnects in a mechanical shock environment is crucial for large body size flip-chip ball grid array (FCBGA) electronic packages. Additionally, the junction temperature increases with higher electric power condition, which brings the component into an elevated temperature environment, thus introducing another consideration factor for mechanical stability of interconnection joints. Since most of the shock performance data available were produced at room temperature, the effect of elevated temperature is of interest to ensure the reliability of the device in a mechanical shock environment. To achieve a stable␣interconnect in a dynamic shock environment, the interconnections must tolerate mechanical strain, which is induced by the shock wave input and reaches the particular component interconnect joint. In this study, large body size (52.5 × 52.5 mm2) FCBGA components assembled on 2.4-mm-thick boards were tested with various isothermal pre-conditions and testing conditions. With a heating element embedded in the test board, a test temperature range from room temperature to 100°C was established. The effects of elevated temperature on mechanical shock performance were investigated. Failure and degradation mechanisms are identified and discussed based on the microstructure evolution and grain structure transformations.

Functional Plasticity in the Absence of Structural Change.

PubMed

Krasovsky, Tal; Landa, Jana; Bar, Orly; Jaana, Ahonniska-Assa; Livny, Abigail; Tsarfaty, Galia; Silberg, Tamar

2017-04-01

This work presents a case of a young woman with apraxia and a severe body scheme disorder, 10 years after a childhood frontal and occipitoparietal brain injury. Despite specific limitations, she is independent in performing all activities of daily living. A battery of tests was administered to evaluate praxis and body representations. Specifically, the Hand Laterality Test was used to compare RS's dynamic body representation to that of healthy controls (N = 14). Results demonstrated RS's severe praxis impairment, and the Hand Laterality Test revealed deficits in accuracy and latency of motor imagery, suggesting a significant impairment in dynamic body representation. However, semantic and structural body representations were intact. These results, coupled with frequent use of verbalizations as a strategy, suggest a possible ventral compensatory mechanism (top-down processing) for dorsal stream deficits, which may explain RS's remarkable recovery of activities of daily living. The link between praxis and dynamic body representation is discussed.

Accurate and fast creep test for viscoelastic fluids using disk-probe-type and quadrupole-arrangement-type electromagnetically spinning systems

NASA Astrophysics Data System (ADS)

Hirano, Taichi; Sakai, Keiji

2017-07-01

Viscoelasticity is a unique characteristic of soft materials and describes its dynamic response to mechanical stimulations. A creep test is an experimental method for measuring the strain ratio/rate against an applied stress, thereby assessing the viscoelasticity of the materials. We propose two advanced experimental systems suitable for the creep test, adopting our original electromagnetically spinning (EMS) technique. This technique can apply a constant torque by a noncontact mechanism, thereby allowing more sensitive and rapid measurements. The viscosity and elasticity of a semidilute wormlike micellar solution were determined using two setups, and the consistency between the results was assessed.

Study on Mechanical Properties of Barite Concrete under Impact Load

NASA Astrophysics Data System (ADS)

Chen, Z. F.; Cheng, K.; Wu, D.; Gan, Y. C.; Tao, Q. W.

2018-03-01

In order to research the mechanical properties of Barite concrete under impact load, a group of concrete compression tests was carried out under the impact load by using the drop test machine. A high-speed camera was used to record the failure process of the specimen during the impact process. The test results show that:with the increase of drop height, the loading rate, the peak load, the strain under peak load, the strain rate and the dynamic increase factor (DIF) all increase gradually. The ultimate tensile strain is close to each other, and the time of impact force decreases significantly, showing significant strain rate effect.

Impact of mechanism vibration characteristics by joint clearance and optimization design of its multi-objective robustness

NASA Astrophysics Data System (ADS)

Zeng, Baoping; Wang, Chao; Zhang, Yu; Gong, Yajun; Hu, Sanbao

2017-12-01

Joint clearances and friction characteristics significantly influence the mechanism vibration characteristics; for example: as for joint clearances, the shaft and bearing of its clearance joint collide to bring about the dynamic normal contact force and tangential coulomb friction force while the mechanism works; thus, the whole system may vibrate; moreover, the mechanism is under contact-impact with impact force constraint from free movement under action of the above dynamic forces; in addition, the mechanism topology structure also changes. The constraint relationship between joints may be established by a repeated complex nonlinear dynamic process (idle stroke - contact-impact - elastic compression - rebound - impact relief - idle stroke movement - contact-impact). Analysis of vibration characteristics of joint parts is still a challenging open task by far. The dynamic equations for any mechanism with clearance is often a set of strong coupling, high-dimensional and complex time-varying nonlinear differential equations which are solved very difficultly. Moreover, complicated chaotic motions very sensitive to initial values in impact and vibration due to clearance let high-precision simulation and prediction of their dynamic behaviors be more difficult; on the other hand, their subsequent wearing necessarily leads to some certain fluctuation of structure clearance parameters, which acts as one primary factor for vibration of the mechanical system. A dynamic model was established to the device for opening the deepwater robot cabin door with joint clearance by utilizing the finite element method and analysis was carried out to its vibration characteristics in this study. Moreover, its response model was carried out by utilizing the DOE method and then the robust optimization design was performed to sizes of the joint clearance and the friction coefficient change range so that the optimization design results may be regarded as reference data for selecting bearings and controlling manufacturing process parameters for the opening mechanism. Several optimization objectives such as x/y/z accelerations for various measuring points and dynamic reaction forces of mounting brackets, and a few constraints including manufacturing process were taken into account in the optimization models, which were solved by utilizing the multi-objective genetic algorithm (NSGA-II). The vibration characteristics of the optimized opening mechanism are superior to those of the original design. In addition, the numerical forecast results are in good agreement with the test results of the prototype.

Developing Capture Mechanisms and High-Fidelity Dynamic Models for the MXER Tether System

NASA Technical Reports Server (NTRS)

Canfield, Steven L.

2007-01-01

A team consisting of collaborators from Tennessee Technological University (TTU), Marshall Space Flight Center, BD Systems, and the University of Delaware (herein called the TTU team) conducted specific research and development activities in MXER tether systems during the base period of May 15, 2004 through September 30, 2006 under contract number NNM04AB13C. The team addressed two primary topics related to the MXER tether system: 1) Development of validated high-fidelity dynamic models of an elastic rotating tether and 2) development of feasible mechanisms to enable reliable rendezvous and capture. This contractor report will describe in detail the activities that were performed during the base period of this cycle-2 MXER tether activity and will summarize the results of this funded activity. The primary deliverables of this project were the quad trap, a robust capture mechanism proposed, developed, tested, and demonstrated with a high degree of feasibility and the detailed development of a validated high-fidelity elastic tether dynamic model provided through multiple formulations.

Long residence times of rapidly decomposable soil organic matter: application of a multi-phase, multi-component, and vertically-resolved model (TOUGHREACTv1) to soil carbon dynamics

NASA Astrophysics Data System (ADS)

Riley, W. J.; Maggi, F. M.; Kleber, M.; Torn, M. S.; Tang, J. Y.; Dwivedi, D.; Guerry, N.

2014-01-01

Accurate representation of soil organic matter (SOM) dynamics in Earth System Models is critical for future climate prediction, yet large uncertainties exist regarding how, and to what extent, the suite of proposed relevant mechanisms should be included. To investigate how various mechanisms interact to influence SOM storage and dynamics, we developed a SOM reaction network integrated in a one-dimensional, multi-phase, and multi-component reactive transport solver. The model includes representations of bacterial and fungal activity, multiple archetypal polymeric and monomeric carbon substrate groups, aqueous chemistry, aqueous advection and diffusion, gaseous diffusion, and adsorption (and protection) and desorption from the soil mineral phase. The model predictions reasonably matched observed depth-resolved SOM and dissolved organic carbon (DOC) stocks in grassland ecosystems as well as lignin content and fungi to aerobic bacteria ratios. We performed a suite of sensitivity analyses under equilibrium and dynamic conditions to examine the role of dynamic sorption, microbial assimilation rates, and carbon inputs. To our knowledge, observations do not exist to fully test such a complicated model structure or to test the hypotheses used to explain observations of substantial storage of very old SOM below the rooting depth. Nevertheless, we demonstrated that a reasonable combination of sorption parameters, microbial biomass and necromass dynamics, and advective transport can match observations without resorting to an arbitrary depth-dependent decline in SOM turnover rates, as is often done. We conclude that, contrary to assertions derived from existing turnover time based model formulations, observed carbon content and δ14C vertical profiles are consistent with a representation of SOM dynamics consisting of (1) carbon compounds without designated intrinsic turnover times, (2) vertical aqueous transport, and (3) dynamic protection on mineral surfaces.

Dynamic Brazilian Test of Rock Under Intermediate Strain Rate: Pendulum Hammer-Driven SHPB Test and Numerical Simulation

NASA Astrophysics Data System (ADS)

Zhu, W. C.; Niu, L. L.; Li, S. H.; Xu, Z. H.

2015-09-01

The tensile strength of rock subjected to dynamic loading constitutes many engineering applications such as rock drilling and blasting. The dynamic Brazilian test of rock specimens was conducted with the split Hopkinson pressure bar (SHPB) driven by pendulum hammer, in order to determine the indirect tensile strength of rock under an intermediate strain rate ranging from 5.2 to 12.9 s-1, which is achieved when the incident bar is impacted by pendulum hammer with different velocities. The incident wave excited by pendulum hammer is triangular in shape, featuring a long rising time, and it is considered to be helpful for achieving a constant strain rate in the rock specimen. The dynamic indirect tensile strength of rock increases with strain rate. Then, the numerical simulator RFPA-Dynamics, a well-recognized software for simulating the rock failure under dynamic loading, is validated by reproducing the Brazilian test of rock when the incident stress wave retrieved at the incident bar is input as the boundary condition, and then it is employed to study the Brazilian test of rock under the higher strain rate. Based on the numerical simulation, the strain-rate dependency of tensile strength and failure pattern of the Brazilian disc specimen under the intermediate strain rate are numerically simulated, and the associated failure mechanism is clarified. It is deemed that the material heterogeneity should be a reason for the strain-rate dependency of rock.

Viscoelastic properties of addition-cured polyimides used in high temperature polymer matrix composites

NASA Technical Reports Server (NTRS)

Roberts, Gary D.; Malarik, Diane C.; Robaidek, Jerrold O.

1991-01-01

The viscoelastic properties of an addition-cured polyimide, PMR-15, were evaluated through dynamic mechanical and stress relaxation testing. Below the glass transition temperature, the dynamic mechanical properties of the composites are strongly affected by the absorbed moisture in the resin. At temperature 20 C and more above the glass transition temperature, the storage modulus increases continuously with time, indicating that additional crosslinking is occurring in the resin. For resin moisture contents less than 2 percent, stress relaxation curves measured at different temperatures can be superimposed using horizontal shifts along the log(time) axis with only small shifts along the vertical axis.

Formaldehyde emission from particleboard and plywood paneling : measurement, mechanism, and product standards

Treesearch

George E. Myers

1983-01-01

A number of commercial panel products, primarily particleboard and hardwood plywood, were tested for their formaldehyde emission behavior using desiccator, perforator, and dynamic chamber methods. The results were analyzed in terms of the source of formaldehyde observed in the tests (free vs. hydrolytically produced) and the potential utility of the testa as product...

Simulating the Response of a Composite Honeycomb Energy Absorber. Part 1; Dynamic Crushing of Components and Multi-Terrain Impacts

NASA Technical Reports Server (NTRS)

Jackson, Karen E.; Fasanella, Edwin L.; Polanco, Michael A.

2012-01-01

This paper describes the experimental and analytical evaluation of an externally deployable composite honeycomb structure that is designed to attenuate impact energy during helicopter crashes. The concept, designated the Deployable Energy Absorber (DEA), utilizes an expandable Kevlar (Registered Trademark) honeycomb to dissipate kinetic energy through crushing. The DEA incorporates a unique flexible hinge design that allows the honeycomb to be packaged and stowed until needed for deployment. Experimental evaluation of the DEA included dynamic crush tests of multi-cell components and vertical drop tests of a composite fuselage section, retrofitted with DEA blocks, onto multi-terrain. Finite element models of the test articles were developed and simulations were performed using the transient dynamic code, LSDYNA (Registered Trademark). In each simulation, the DEA was represented using shell elements assigned two different material properties: Mat 24, an isotropic piecewise linear plasticity model, and Mat 58, a continuum damage mechanics model used to represent laminated composite fabrics. DEA model development and test-analysis comparisons are presented.

The NASA Langley Isolator Dynamics Research Lab

NASA Technical Reports Server (NTRS)

Middleton, Troy F.; Balla, Robert J.; Baurle, Robert A.; Humphreys, William M.; Wilson, Lloyd G.

2010-01-01

The Isolator Dynamics Research Lab (IDRL) is under construction at the NASA Langley Research Center in Hampton, Virginia. A unique test apparatus is being fabricated to support both wall and in-stream measurements for investigating the internal flow of a dual-mode scramjet isolator model. The test section is 24 inches long with a 1-inch by 2-inch cross sectional area and is supplied with unheated, dry air through a Mach 2.5 converging-diverging nozzle. The test section is being fabricated with two sets (glass and metallic) of interchangeable sidewalls to support flow visualization and laser-based measurement techniques as well as static pressure, wall temperature, and high frequency pressure measurements. During 2010, a CFD code validation experiment will be conducted in the lab in support of NASA s Fundamental Aerodynamics Program. This paper describes the mechanical design of the Isolator Dynamics Research Lab test apparatus and presents a summary of the measurement techniques planned for investigating the internal flow field of a scramjet isolator model.

[Effect of glyceryl triacetate on properties of PLA/PBAT blends].

PubMed

Yang, Nan; Wang, Xiyuan; Weng, Yunxuan; Jin, Yujuan; Zhang, Min

2016-06-25

Poly lactic acid (PLA)/Poly (butyleneadipate-co-terephthalate)(PBAT) and glyceryl triacetate (GTA) blend were prepared by torque rheometer, and the effect of GTA on thermodynamical performance, mechanical properties and microstructure of PLA/PBAT composites were studied using differential scanning calorimeter(DSC), dynamic mechanical analysis(DMA), universal testing machine, impact testing machine and scanning electron microscope(SEM). After adding GTA, Tg values of the two phases gradually became closer, blends cold crystallization temperature and melting temperature decreased. When with 3 phr GTA, the dispersed phase particle size of PLA/PBAT blend decreased. Mechanics performance test showed that the elongation at break and impact strength of the PLA/PBAT blend was greatly increased with 3 phr GTA, and the elongation at break increased 2.6 times, improved from 17.7% to 64.1%.

Cooperative Quantum-Behaved Particle Swarm Optimization with Dynamic Varying Search Areas and Lévy Flight Disturbance

PubMed Central

Li, Desheng

2014-01-01

This paper proposes a novel variant of cooperative quantum-behaved particle swarm optimization (CQPSO) algorithm with two mechanisms to reduce the search space and avoid the stagnation, called CQPSO-DVSA-LFD. One mechanism is called Dynamic Varying Search Area (DVSA), which takes charge of limiting the ranges of particles' activity into a reduced area. On the other hand, in order to escape the local optima, Lévy flights are used to generate the stochastic disturbance in the movement of particles. To test the performance of CQPSO-DVSA-LFD, numerical experiments are conducted to compare the proposed algorithm with different variants of PSO. According to the experimental results, the proposed method performs better than other variants of PSO on both benchmark test functions and the combinatorial optimization issue, that is, the job-shop scheduling problem. PMID:24851085

Dynamic Mechanical Properties and Fracture Surface Morphologies of Core-Shell Rubber (CSR) Toughened Epoxy at Liquid Nitrogen (Ln2) Temperatures

NASA Technical Reports Server (NTRS)

Wang, J.; Magee, D.; Schneider, J. A.

2009-01-01

The dynamic mechanical properties and fracture surface morphologies were evaluated for a commercial epoxy resin toughened with two types of core-shell rubber (CSR) toughening agents (Kane Ace(Registered TradeMark) MX130 and MX960). The impact resistance (R) was evaluated by the resulting breaking energy measured in Charpy impact tests conducted on an instrumented drop tower. The resulting fracture surface morphologies were examined using Scanning Electron Microscopy (SEM). Fractographic observations of the CSR toughened epoxy tested at ambient temperature, showed a fracture as characterized by slender dendrite textures with large voids. The increasing number of dendrites and decreasing size of scale-like texture with more CSR particles corresponded with increased R. As the temperature decreased to Liquid Nitrogen (LN 2), the fracture surfaces showed a fracture characterized by a rough, torn texture containing many river markings and deep furrows.

Quantitative theory of driven nonlinear brain dynamics.

PubMed

Roberts, J A; Robinson, P A

2012-09-01

Strong periodic stimuli such as bright flashing lights evoke nonlinear responses in the brain and interact nonlinearly with ongoing cortical activity, but the underlying mechanisms for these phenomena are poorly understood at present. The dominant features of these experimentally observed dynamics are reproduced by the dynamics of a quantitative neural field model subject to periodic drive. Model power spectra over a range of drive frequencies show agreement with multiple features of experimental measurements, exhibiting nonlinear effects including entrainment over a range of frequencies around the natural alpha frequency f(α), subharmonic entrainment near 2f(α), and harmonic generation. Further analysis of the driven dynamics as a function of the drive parameters reveals rich nonlinear dynamics that is predicted to be observable in future experiments at high drive amplitude, including period doubling, bistable phase-locking, hysteresis, wave mixing, and chaos indicated by positive Lyapunov exponents. Moreover, photosensitive seizures are predicted for physiologically realistic model parameters yielding bistability between healthy and seizure dynamics. These results demonstrate the applicability of neural field models to the new regime of periodically driven nonlinear dynamics, enabling interpretation of experimental data in terms of specific generating mechanisms and providing new tests of the theory. Copyright © 2012 Elsevier Inc. All rights reserved.

Thermal Fatigue and Fracture Behavior of Ceramic Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Zhu, Dong-Ming; Choi, Sung R.; Miller, Robert A.

2001-01-01

Thermal fatigue and fracture behavior of plasma-sprayed ceramic thermal barrier coatings has been investigated under high heat flux and thermal cyclic conditions. The coating crack propagation is studied under laser heat flux cyclic thermal loading, and is correlated with dynamic fatigue and strength test results. The coating stress response and inelasticity, fatigue and creep interactions, and interface damage mechanisms during dynamic thermal fatigue processes are emphasized.

Microstructure and Mechanical Properties of Laser Solid Formed Ti-6Al-4V Alloy Under Dynamic Shear Loading

NASA Astrophysics Data System (ADS)

Zhou, Ping; Guo, Wei-Guo; Su, Yu; Wang, Jianjun; Lin, Xin; Huang, Weidong

2017-07-01

To investigate the mechanical properties of the Ti-6Al-4V alloy fabricated by laser solid forming technology, both static and dynamic shear tests were conducted on hat-shaped specimens by a servohydraulic testing machine and an enhanced split Hopkinson pressure bar system, over a temperature range of 173-573 K. The microstructure of both the original and deformed specimens was characterized by optical microscopy and scanning electron microscopy. The results show that: (1) the anisotropy of shear properties is not significant regardless of the visible stratification and the prior- β grains that grow epitaxially along the depositing direction; (2) the ultimate shear strength of this material is lower than that of those Ti-6Al-4V alloys fabricated by forging and extrusion; (3) the adiabatic shear bands of approximately 25.6-36.4 μm in width can develop at all selected temperatures during the dynamic shear deformation; and (4) the observed microstructure and measured microhardness indicate that the grains become refined in adiabatic shear band. Estimation of the temperature rise shows that the temperature in shear band exceeds the recrystallization temperature. The process of rotational dynamic recrystallization is considered to be the cause of the grain refinement in shear band.

Development of a Perfusion Platform for Dynamic Cultivation of in vitro Skin Models.

PubMed

Strüver, Kay; Friess, Wolfgang; Hedtrich, Sarah

2017-01-01

Reconstructed skin models are suitable test systems for toxicity testing and for basic investigations on (patho-)physiological aspects of human skin. Reconstructed human skin, however, has clear limitations such as the lack of immune cells and a significantly weaker skin barrier function compared to native human skin. Potential reasons for the latter might be the lack of mechanical forces during skin model cultivation which is performed classically in static well-plate setups. Mechanical forces and shear stress have a major impact on tissue formation and, hence, tissue engineering. In the present work, a perfusion platform was developed allowing dynamic cultivation of in vitro skin models. The platform was designed to cultivate reconstructed skin at the air-liquid interface with a laminar and continuous medium flow below the dermis equivalent. Histological investigations confirmed the formation of a significantly thicker stratum corneum compared to the control cultivated under static conditions. Moreover, the skin differentiation markers involucrin and filaggrin as well as the tight junction proteins claudin 1 and occludin showed increased expression in the dynamically cultured skin models. Unexpectedly, despite improved differentiation, the skin barrier function of the dynamically cultivated skin models was not enhanced compared with the skin models cultivated under static conditions. © 2017 S. Karger AG, Basel.

Strategic avionics technology definition studies. Subtask 3-1A3: Electrical Actuation (ELA) Systems Test Facility

NASA Technical Reports Server (NTRS)

Rogers, J. P.; Cureton, K. L.; Olsen, J. R.

1994-01-01

Future aerospace vehicles will require use of the Electrical Actuator systems for flight control elements. This report presents a proposed ELA Test Facility for dynamic evaluation of high power linear Electrical Actuators with primary emphasis on Thrust Vector Control actuators. Details of the mechanical design, power and control systems, and data acquisition capability of the test facility are presented. A test procedure for evaluating the performance of the ELA Test Facility is also included.

Air Force Dynamic Mechanical Analysis Testing of NATO Round Robin Propellant Testing for Development of AOP-4717

DTIC Science & Technology

2015-08-01

10 minutes. After this, the furnace was opened and the clamps were tightened to 6 in-lb of torque . At the end of the tests, we examined the specimens...to use a different procedure for tightening the clamps in the frequency sweep tests -- this is explained in the next section...procedure to tighten the clamps. This is described next. First, the test applies different frequencies at a large range of temperatures – from -110 C to 70

Comparisons of Kinematics and Dynamics Simulation Software Tools

NASA Technical Reports Server (NTRS)

Shiue, Yeu-Sheng Paul

2002-01-01

Kinematic and dynamic analyses for moving bodies are essential to system engineers and designers in the process of design and validations. 3D visualization and motion simulation plus finite element analysis (FEA) give engineers a better way to present ideas and results. Marshall Space Flight Center (MSFC) system engineering researchers are currently using IGRIP from DELMIA Inc. as a kinematic simulation tool for discrete bodies motion simulations. Although IGRIP is an excellent tool for kinematic simulation with some dynamic analysis capabilities in robotic control, explorations of other alternatives with more powerful dynamic analysis and FEA capabilities are necessary. Kinematics analysis will only examine the displacement, velocity, and acceleration of the mechanism without considering effects from masses of components. With dynamic analysis and FEA, effects such as the forces or torques at the joint due to mass and inertia of components can be identified. With keen market competition, ALGOR Mechanical Event Simulation (MES), MSC visualNastran 4D, Unigraphics Motion+, and Pro/MECHANICA were chosen for explorations. In this study, comparisons between software tools were presented in terms of following categories: graphical user interface (GUI), import capability, tutorial availability, ease of use, kinematic simulation capability, dynamic simulation capability, FEA capability, graphical output, technical support, and cost. Propulsion Test Article (PTA) with Fastrac engine model exported from IGRIP and an office chair mechanism were used as examples for simulations.

Accelerated Testing Methodology in Constant Stress-Rate Testing for Advanced Structural Ceramics: A Preloading Technique

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.; Huebert, Dean; Bartlett, Allen; Choi, Han-Ho

2001-01-01

Preloading technique was used as a means of an accelerated testing methodology in constant stress-rate ('dynamic fatigue') testing for two different brittle materials. The theory developed previously for fatigue strength as a function of preload was further verified through extensive constant stress-rate testing for glass-ceramic and CRT glass in room temperature distilled water. The preloading technique was also used in this study to identify the prevailing failure mechanisms at elevated temperatures, particularly at lower test rate in which a series of mechanisms would be associated simultaneously with material failure, resulting in significant strength increase or decrease. Two different advanced ceramics including SiC whisker-reinforced composite silicon nitride and 96 wt% alumina were used at elevated temperatures. It was found that the preloading technique can be used as an additional tool to pinpoint the dominant failure mechanism that is associated with such a phenomenon of considerable strength increase or decrease.

Accelerated Testing Methodology in Constant Stress-Rate Testing for Advanced Structural Ceramics: A Preloading Technique

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.; Huebert, Dean; Bartlett, Allen; Choi, Han-Ho

2001-01-01

Preloading technique was used as a means of an accelerated testing methodology in constant stress-rate (dynamic fatigue) testing for two different brittle materials. The theory developed previously for fatigue strength as a function of preload was further verified through extensive constant stress-rate testing for glass-ceramic and CRT glass in room temperature distilled water. The preloading technique was also used in this study to identify the prevailing failure mechanisms at elevated temperatures, particularly at lower test rates in which a series of mechanisms would be associated simultaneously with material failure, resulting in significant strength increase or decrease. Two different advanced ceramics including SiC whisker-reinforced composite silicon nitride and 96 wt% alumina were used at elevated temperatures. It was found that the preloading technique can be used as an additional tool to pinpoint the dominant failure mechanism that is associated with such a phenomenon of considerable strength increase or decrease.

True Triaxial Experimental Study of Rockbursts Induced By Ramp and Cyclic Dynamic Disturbances

NASA Astrophysics Data System (ADS)

Su, Guoshao; Hu, Lihua; Feng, Xiating; Yan, Liubin; Zhang, Gangliang; Yan, Sizhou; Zhao, Bin; Yan, Zhaofu

2018-04-01

A modified rockburst testing system was utilized to reproduce rockbursts induced by ramp and cyclic dynamic disturbances with a low-intermediate strain rate of 2 × 10-3-5 × 10-3 s-1 in the laboratory. The experimental results show that both the ramp and cyclic dynamic disturbances play a significant role in inducing rockbursts. In the tests of rockbursts induced by a ramp dynamic disturbance, as the static stress before the dynamic disturbance increases, both the strength of specimens and the kinetic energy of the ejected fragments first increase and then decrease. In the tests of rockbursts induced by a cyclic dynamic disturbance, there exists a rockburst threshold of the static stress and the dynamic disturbance amplitude, and the kinetic energy of the ejected fragments first increases and then decreases as the cyclic dynamic disturbance frequency increases. The main differences between rockbursts induced by ramp dynamic disturbances and those induced by cyclic dynamic disturbances are as follows: the rockburst development process of the former is characterized by an impact failure feature, while that of the latter is characterized by a fatigue failure feature; the damage evolution curve of the specimen of the former has a leap-developing form with a significant catastrophic feature, while that of the latter has an inverted S-shape with a remarkable fatigue damage characteristic; the energy mechanism of the former involves the ramp dynamic disturbance giving extra elastic strain energy to rocks, while that of the latter involves the cyclic dynamic disturbance decreasing the ultimate energy storage capacity of rocks.

Simple green approach to reinforce natural rubber with bacterial cellulose nanofibers.

PubMed

Trovatti, Eliane; Carvalho, Antonio J F; Ribeiro, Sidney J L; Gandini, Alessandro

2013-08-12

Natural rubber (NR) is a renewable polymer with a wide range of applications, which is constantly tailored, further increasing its utilizations. The tensile strength is one of its most important properties susceptible of being enhanced by the simple incorporation of nanofibers. The preparation and characterization of natural-rubber based nanocomposites reinforced with bacterial cellulose (BC) and bacterial cellulose coated with polystyrene (BCPS), yielded high performance materials. The nanocomposites were prepared by a simple and green process, and characterized by tensile tests, dynamical mechanical analysis (DMA), scanning electron microscopy (SEM), and swelling experiments. The effect of the nanofiber content on morphology, static, and dynamic mechanical properties was also investigated. The results showed an increase in the mechanical properties, such as Young's modulus and tensile strength, even with modest nanofiber loadings.

Influence of grain size on the mechanical properties of nano-crystalline copper; insights from molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Rida, A.; Makke, A.; Rouhaud, E.; Micoulaut, M.

2017-10-01

We use molecular dynamics simulations to study the mechanical properties of a columnar nanocrystalline copper with a mean grain size between 8.91 nm and 24 nm. The used samples were generated by using a melting cooling method. These samples were submitted to uniaxial tensile test. The results reveal the presence of a critical mean grain size between 16 and 20 nm, where there is an inversion in the conventional Hall-Petch tendency. This inversion is illustrated by the increase of flow stress with the increase of the mean grain size. This transition is caused by shifting of the deformation mechanism from dislocations to a combination of grain boundaries sliding and dislocations. Moreover, the effect of temperature on the mechanical properties of nanocrystalline copper has been investigated. The results show a decrease of the flow stress and Young's modulus when the temperature increases.

Ensemble Kalman Filter for Dynamic State Estimation of Power Grids Stochastically Driven by Time-correlated Mechanical Input Power

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosenthal, William Steven; Tartakovsky, Alex; Huang, Zhenyu

State and parameter estimation of power transmission networks is important for monitoring power grid operating conditions and analyzing transient stability. Wind power generation depends on fluctuating input power levels, which are correlated in time and contribute to uncertainty in turbine dynamical models. The ensemble Kalman filter (EnKF), a standard state estimation technique, uses a deterministic forecast and does not explicitly model time-correlated noise in parameters such as mechanical input power. However, this uncertainty affects the probability of fault-induced transient instability and increased prediction bias. Here a novel approach is to model input power noise with time-correlated stochastic fluctuations, and integratemore » them with the network dynamics during the forecast. While the EnKF has been used to calibrate constant parameters in turbine dynamical models, the calibration of a statistical model for a time-correlated parameter has not been investigated. In this study, twin experiments on a standard transmission network test case are used to validate our time-correlated noise model framework for state estimation of unsteady operating conditions and transient stability analysis, and a methodology is proposed for the inference of the mechanical input power time-correlation length parameter using time-series data from PMUs monitoring power dynamics at generator buses.« less

Ensemble Kalman Filter for Dynamic State Estimation of Power Grids Stochastically Driven by Time-correlated Mechanical Input Power

DOE PAGES

Rosenthal, William Steven; Tartakovsky, Alex; Huang, Zhenyu

2017-10-31

State and parameter estimation of power transmission networks is important for monitoring power grid operating conditions and analyzing transient stability. Wind power generation depends on fluctuating input power levels, which are correlated in time and contribute to uncertainty in turbine dynamical models. The ensemble Kalman filter (EnKF), a standard state estimation technique, uses a deterministic forecast and does not explicitly model time-correlated noise in parameters such as mechanical input power. However, this uncertainty affects the probability of fault-induced transient instability and increased prediction bias. Here a novel approach is to model input power noise with time-correlated stochastic fluctuations, and integratemore » them with the network dynamics during the forecast. While the EnKF has been used to calibrate constant parameters in turbine dynamical models, the calibration of a statistical model for a time-correlated parameter has not been investigated. In this study, twin experiments on a standard transmission network test case are used to validate our time-correlated noise model framework for state estimation of unsteady operating conditions and transient stability analysis, and a methodology is proposed for the inference of the mechanical input power time-correlation length parameter using time-series data from PMUs monitoring power dynamics at generator buses.« less

Development of procedures for calculating stiffness and damping properties of elastomers in engineering applications. Part 4: Testing of elastomers under a rotating load. [resonance testing

NASA Technical Reports Server (NTRS)

Darlow, M. S.; Smalley, A. J.

1977-01-01

A test rig designed to measure stiffness and damping of elastomer cartridges under a rotating load excitation is described. The test rig employs rotating unbalance in a rotor which runs to 60,000 RPM as the excitation mechanism. A variable resonant mass is supported on elastomer elements and the dynamic characteristics are determined from measurements of input and output acceleration. Five different cartridges are considered: three of these are buttons cartridges having buttons located in pairs, with 120 between each pair. Two of the cartridges consist of 360 elastomer rings with rectangular cross-sections. Dynamic stiffness and damping are measured for each cartridge and compared with predictions at different frequencies and different strains.

Investigation of nucleation processes during dynamic recrystallization of ice using cryo-EBSD.

PubMed

Chauve, T; Montagnat, M; Barou, F; Hidas, K; Tommasi, A; Mainprice, D

2017-02-13

Nucleation mechanisms occurring during dynamic recrystallization play a crucial role in the evolution of microstructures and textures during high temperature deformation. In polycrystalline ice, the strong viscoplastic anisotropy induces high strain heterogeneities between grains which control the recrystallization mechanisms. Here, we study the nucleation mechanisms occurring during creep tests performed on polycrystalline columnar ice at high temperature and stress (T=-5°C;σ=0.5 MPa) by post-mortem analyses of deformation microstructures using cryogenic electron backscatter diffraction. The columnar geometry of the samples enables discrimination of the nuclei from the initial grains. Various nucleation mechanisms are deduced from the analysis of the nuclei relations with the dislocation sub-structures within grains and at grain boundaries. Tilt sub-grain boundaries and kink bands are the main structures responsible for development of polygonization and mosaic sub-structures. Nucleation by bulging at serrated grain boundaries is also an efficient nucleation mechanism near the grain boundaries where strain incompatibilities are high. Observation of nuclei with orientations not related to the 'parent' ones suggests the possibility of 'spontaneous' nucleation driven by the relaxation of the dislocation-related internal stress field. The complexity of the nucleation mechanisms observed here emphasizes the impact of stress and strain heterogeneities on dynamic recrystallization mechanisms.This article is part of the themed issue 'Microdynamics of ice'. © 2016 The Author(s).

Investigation of nucleation processes during dynamic recrystallization of ice using cryo-EBSD

PubMed Central

Barou, F.; Hidas, K.; Tommasi, A.; Mainprice, D.

2017-01-01

Nucleation mechanisms occurring during dynamic recrystallization play a crucial role in the evolution of microstructures and textures during high temperature deformation. In polycrystalline ice, the strong viscoplastic anisotropy induces high strain heterogeneities between grains which control the recrystallization mechanisms. Here, we study the nucleation mechanisms occurring during creep tests performed on polycrystalline columnar ice at high temperature and stress (T=−5°C;σ=0.5 MPa) by post-mortem analyses of deformation microstructures using cryogenic electron backscatter diffraction. The columnar geometry of the samples enables discrimination of the nuclei from the initial grains. Various nucleation mechanisms are deduced from the analysis of the nuclei relations with the dislocation sub-structures within grains and at grain boundaries. Tilt sub-grain boundaries and kink bands are the main structures responsible for development of polygonization and mosaic sub-structures. Nucleation by bulging at serrated grain boundaries is also an efficient nucleation mechanism near the grain boundaries where strain incompatibilities are high. Observation of nuclei with orientations not related to the ‘parent’ ones suggests the possibility of ‘spontaneous’ nucleation driven by the relaxation of the dislocation-related internal stress field. The complexity of the nucleation mechanisms observed here emphasizes the impact of stress and strain heterogeneities on dynamic recrystallization mechanisms. This article is part of the themed issue ‘Microdynamics of ice’. PMID:28025294

Testing Microgravity Flight Hardware Concepts on the NASA KC-135

NASA Technical Reports Server (NTRS)

Motil, Susan M.; Harrivel, Angela R.; Zimmerli, Gregory A.

2001-01-01

This paper provides an overview of utilizing the NASA KC-135 Reduced Gravity Aircraft for the Foam Optics and Mechanics (FOAM) microgravity flight project. The FOAM science requirements are summarized, and the KC-135 test-rig used to test hardware concepts designed to meet the requirements are described. Preliminary results regarding foam dispensing, foam/surface slip tests, and dynamic light scattering data are discussed in support of the flight hardware development for the FOAM experiment.

The Radiation Belt Storm Probes (RBSP) Energetic Particle, Composition, and Thermal plasma (ECT) Suite: Upcoming Opportunties for Testing Radiation Belt Acceleration Mechanisms

NASA Astrophysics Data System (ADS)

Spence, Harlan; Reeves, Geoffrey

2012-07-01

The Radiation Belt Storm Probes (RBSP) mission will launch in late summer 2012 and begin its exploration of acceleration and dynamics of energetic particles in the inner magnetosphere. In this presentation, we discuss opportunities afforded by the RBSP Energetic Particle, Composition, and Thermal plasma (ECT) instrument suite to advance our understanding of acceleration processes in the radiation belts. The RBSP-ECT instrument suite comprehensively measures the electron and major ion populations of the inner magnetosphere, from the lowest thermal plasmas of the plasmasphere, to the hot plasma of the ring current, to the relativistic populations of the radiation belts. Collectively, the ECT measurements will reveal the complex cross-energy coupling of these colocated particle populations, which along with concurrent RBSP wave measurements, will permit various wave-particle acceleration mechanisms to be tested. We review the measurement capabilities of the RBSP-ECT instrument suite, and demonstrate several examples of how these measurements will be used to explore candidate acceleration mechanisms and dynamics of radiation belt particles.

Phenomenological study of a cellular material behaviour under dynamic loadings

NASA Astrophysics Data System (ADS)

Bouix, R.; Viot, Ph.; Lataillade, J.-L.

2006-08-01

Polypropylene foams are cellular materials, which are often use to fill structures subjected to crash or violent impacts. Therefore, it is necessary to know and to characterise in experiments their mechanical behaviour in compression at high strain rates. So, several apparatus have been used in order to highlight the influence of strain rate, material density and also temperature. A split Hopkinson Pressure Bar has been used for impact tests, a fly wheel to test theses materials at medium strain rate and an electro-mechanical testing machine associated to a climatic chamber for temperature tests. Then, a rheological model has been used in order to describe the material behaviour. The mechanical response to compression of these foams presents three typical domains: a linear elastic step, a wide collapse plateau stress, which leads to a densification, which are related to a standard rheological model.

Mechanical strength of an ITER coil insulation system under static and dynamic load after reactor irradiation

NASA Astrophysics Data System (ADS)

Bittner-Rohrhofer, K.; Humer, K.; Weber, H. W.; Hamada, K.; Sugimoto, M.; Okuno, K.

2002-12-01

The insulation system proposed by the Japanese Home Team for the ITER Toroidal Field coil (TF coil) is a T-glass-fiber/Kapton reinforced epoxy prepreg system. In order to assess the material performance under the actual operating conditions of the coils, the insulation system was irradiated in the TRIGA reactor (Vienna) to a fast neutron fluence of 2×10 22 m -2 ( E>0.1 MeV). After measurements of swelling, all mechanical tests were carried out at 77 K. Tensile and short-beam-shear (SBS) tests were performed under static loading conditions. In addition, tension-tension fatigue experiments up to about 10 6 cycles were made. The laminate swells in the through-thickness direction by 0.86% at the highest dose level. The fatigue tests as well as the static tests do not show significant influences of the irradiation on the mechanical behavior of this composite.

Modelling of Mechanical Behavior at High Strain Rate of Ti-6al-4v Manufactured By Means of Direct Metal Laser Sintering Technique

NASA Astrophysics Data System (ADS)

Iannitti, Gianluca; Bonora, Nicola; Gentile, Domenico; Ruggiero, Andrew; Testa, Gabriel; Gubbioni, Simone

2017-06-01

In this work, the mechanical behavior of Ti-6Al-4V obtained by additive manufacturing technique was investigated, also considering the build direction. Dog-bone shaped specimens and Taylor cylinders were machined from rods manufactured by means of the EOSSINT M2 80 machine, based on Direct Metal Laser Sintering technique. Tensile tests were performed at strain rate ranging from 5E-4 s-1 to 1000 s-1 using an Instron electromechanical machine for quasistatic tests and a Direct-Tension Split Hopkinson Bar for dynamic tests. The mechanical strength of the material was described by a Johnson-Cook model modified to account for stress saturation occurring at high strain. Taylor cylinder tests and their corresponding numerical simulations were carried out in order to validate the constitutive model under a complex deformation path, high strain rates, and high temperatures.

Mechanical properties of commercial high strength ceramic core materials.

PubMed

Rizkalla, A S; Jones, D W

2004-02-01

The objective of the present study is to evaluate and compare the flexural strength, dynamic elastic moduli and true hardness (H(o)) values of commercial Vita In-Ceram alumina core and Vita In-Ceram matrix glass with the standard aluminous porcelain (Hi-Ceram and Vitadur), Vitadur N and Dicor glass and glass-ceramic. The flexural strength was evaluated (n=5) using 3-point loading and a servo hydraulic Instron testing machine at a cross head speed of 0.5 mm/min. The density of the specimens (n=3) was measured by means of the water displacement technique. Dynamic Young's shear and bulk moduli and Poisson's ratio (n=3) were measured using a non-destructive ultrasonic technique using 10 MHz lithium niobate crystals. The true hardness (n=3) was measured using a Knoop indenter and the fracture toughness (n=3) was determined using a Vickers indenter and a Tukon hardness tester. Statistical analysis of the data was conducted using ANOVA and a Student-Newman-Keuls (SNK) rank order multiple comparative test. The SNK rank order test analysis of the mean flexural strength was able to separate five commercial core materials into three significant groups at p=0.05. Vita In-Ceram alumina and IPS Empress 2 exhibited significantly higher flexural strength than aluminous porcelains and IPS Empress at p=0.05. The dynamic elastic moduli and true hardness of Vita In-Ceram alumina core were significantly higher than the rest of the commercial ceramic core materials at p=0.05. The ultrasonic test method is a valuable mechanical characterization tool and was able to statistically discriminate between the chemical and structural differences within dental ceramic materials. Significant correlation was obtained between the dynamic Young's modulus and true hardness, p=0.05.

Rheological behaviors of doughs reconstituted from wheat gluten and starch.

PubMed

Yang, Yanyan; Song, Yihu; Zheng, Qiang

2011-08-01

Hydrated starch-gluten reconstituted doughs were prepared and dynamic rheological tests of the reconstituted doughs were performed using dynamic strain and dynamic frequency sweep modes. Influence of starch/gluten ratio on rheological behaviors of the reconstituted doughs was investigated. The results showed that the reconstituted doughs exhibited nonlinear rheological behavior with increasing strain. The mechanical spectra revealed predominantly elastic characteristics in frequency range from 10(-1) rad s(-1) to 10(2) rad s(-1). Cole-Cole functions were applied to fit the mechanical spectra to reveal the influence of starch/gluten ratio on Plateau modulus and longest relaxation time of the dough network. The time-temperature superposition principle was applicable to a narrow temperature range of 25°C ~40°C while it failed at 50°C due to swelling and gelatinization of the starch.

Control of unsteady separated flow associated with the dynamic stall of airfoils

NASA Technical Reports Server (NTRS)

Wilder, Michael C.

1992-01-01

The two principal objectives of this research were to achieve an improved understanding of the mechanisms involved in the onset and development of dynamic stall under compressible flow conditions, and to investigate the feasibility of employing adaptive airfoil geometry as an active flow control device in the dynamic stall engine. Presented here are the results of a quantitative (PDI) study of the compressibility effects on dynamic stall over the transiently pitching airfoil, as well as a discussion of a preliminary technique developed to measure the deformation produced by the adaptive geometry control device, and bench test results obtained using an airfoil equipped with the device.

Thermoplastic coating of carbon fibers

NASA Technical Reports Server (NTRS)

Edie, D. D.; Lickfield, G. C.

1991-01-01

Using a continuous powder coating process, more than 1500 meters of T 300/LaRC-TPI prepreg were produced. Two different types of heating sections in the coating line, namely electrical resistance and convection heating, were utilized. These prepregs were used to fabricate unidirectional composites. During composite fabrication the cure time of the consolidation was varied, and composites samples were produced with and without vacuum. Under these specimens, the effects of the different heating sections and of the variation of the consolidation parameters on mechanical properties and void content were investigated. The void fractions of the various composites were determined from density measurements, and the mechanical properties were measured by tensile testing, short beam shear testing and dynamic mechanical analysis.

ARCADE small-scale docking mechanism for micro-satellites

NASA Astrophysics Data System (ADS)

Boesso, A.; Francesconi, A.

2013-05-01

The development of on-orbit autonomous rendezvous and docking (ARD) capabilities represents a key point for a number of appealing mission scenarios that include activities of on-orbit servicing, automated assembly of modular structures and active debris removal. As of today, especially in the field of micro-satellites ARD, many fundamental technologies are still missing or require further developments and micro-gravity testing. In this framework, the University of Padova, Centre of Studies and Activities for Space (CISAS), developed the Autonomous Rendezvous Control and Docking Experiment (ARCADE), a technology demonstrator intended to fly aboard a BEXUS stratospheric balloon. The goal was to design, build and test, in critical environment conditions, a proximity relative navigation system, a custom-made reaction wheel and a small-size docking mechanism. The ARCADE docking mechanism was designed against a comprehensive set of requirements and it can be classified as small-scale, central, gender mating and unpressurized. The large use of commercial components makes it low-cost and simple to be manufactured. Last, it features a good tolerance to off-nominal docking conditions and a by-design soft docking capability. The final design was extensively verified to be compliant with its requirements by means of numerical simulations and physical testing. In detail, the dynamic behaviour of the mechanism in both nominal and off-nominal conditions was assessed with the multibody dynamics analysis software MD ADAMS 2010 and functional tests were carried out within the fully integrated ARCADE experiment to ensure the docking system efficacy and to highlight possible issues. The most relevant results of the study will be presented and discussed in conclusion to this paper.

Allosteric mechanism of quinoline inhibitors for HIV RT-associated RNase with MD simulation and dynamics fluctuation network.

PubMed

Cai, Yi; Liu, Hao; Chen, Haifeng

2018-03-01

The human immunodeficiency virus (HIV) is a retrovirus which infects T lymphocyte of human body and causes immunodeficiency. Reverse transcriptase inhibitors (RTIs) can inhibit some functions of RT, preventing virus synthesis (double-stranded DNA), so that HIV virus replication can be reduced. Experimental results indicate a series of benzimidazole-based inhibitors which target HIV RT-associated RNase to inhibit the reverse transcription of HIV virus. However, the allosteric mechanism is still unclear. Here, molecular dynamics simulations and dynamics fluctuation network analysis were used to reveal the binding mode between the inhibitors and RT-associated RNase. The most active molecule has more hydrophobic and electrostatic interactions than the less active inhibitor. Dynamics correlation network analysis indicates that the most active inhibitor perturbs the network of RT-associated RNase and decreases the correlation of nodes. 3D-QSAR model suggests that two robust and reliable models were constructed and validated by independent test set. 3D-QSAR model also shows that bulky negatively charged or hydrophilic substituent is favorable to bioactivity. These results reveal the allosteric mechanism of quinoline inhibitors and help to improve the bioactivity. © 2017 John Wiley & Sons A/S.

Coexistence in streams: Do source-sink dynamics allow salamanders to persist with fish predators?

USGS Publications Warehouse

Sepulveda, A.J.; Lowe, W.H.

2011-01-01

Theory suggests that source-sink dynamics can allow coexistence of intraguild predators and prey, but empirical evidence for this coexistence mechanism is limited. We used capture-mark-recapture, genetic methods, and stable isotopes to test whether source-sink dynamics promote coexistence between stream fishes, the intraguild predator, and stream salamanders (Dicamptodon aterrimus), the intraguild prey. Salamander populations from upstream reaches without fish were predicted to maintain or supplement sink populations in downstream reaches with fish. We found instead that downstream reaches with fish were not sinks even though fish consumed salamander larvae-apparent survival, recruitment, and population growth rate did not differ between upstream and downstream reaches. There was also no difference between upstream and downstream reaches in net emigration. We did find that D. aterrimus moved frequently along streams, but believe that this is a response to seasonal habitat changes rather than intraguild predation. Our study provides empirical evidence that local-scale mechanisms are more important than dispersal dynamics to coexistence of streams salamanders and fish. More broadly, it shows the value of empirical data on dispersal and gene flow for distinguishing between local and spatial mechanisms of coexistence. ?? 2011 Springer-Verlag.

Advanced thermoplastic resins, phase 1

NASA Technical Reports Server (NTRS)

Hendricks, C. L.; Hill, S. G.; Falcone, A.; Gerken, N. T.

1991-01-01

Eight thermoplastic polyimide resin systems were evaluated as composite matrix materials. Two resins were selected for more extensive mechanical testing and both were versions of LaRC-TPI (Langley Research Center - Thermoplastic Polyimide). One resin was made with LaRC-TPI and contained 2 weight percent of a di(amic acid) dopant as a melt flow aid. The second system was a 1:1 slurry of semicrystalline LaRC-TPI powder in a polyimidesulfone resin diglyme solution. The LaRC-TPI powder melts during processing and increases the melt flow of the resin. Testing included dynamic mechanical analysis, tension and compression testing, and compression-after-impact testing. The test results demonstrated that the LaRC-TPI resins have very good properties compared to other thermoplastics, and that they are promising matrix materials for advanced composite structures.

Dynamic Mechanical Properties and Microstructure of Graphene Oxide Nanosheets Reinforced Cement Composites.

PubMed

Long, Wu-Jian; Wei, Jing-Jie; Ma, Hongyan; Xing, Feng

2017-11-24

This paper presents an experimental investigation on the effect of uniformly dispersed graphene oxide (GO) nanosheets on dynamic mechanical properties of cement based composites prepared with recycled fine aggregate (RFA). Three different amounts of GO, 0.05%, 0.10%, and 0.20% in mass of cement, were used in the experiments. The visual inspections of GO nanosheets were also carried out after ultrasonication by transmission electron microscope (TEM) atomic force microscope (AFM), and Raman to characterize the dispersion effect of graphite oxide. Dynamic mechanical analyzer test showed that the maximum increased amount of loss factor and storage modulus, energy absorption was 125%, 53%, and 200% when compared to the control sample, respectively. The flexural and compressive strengths of GO-mortar increased up to 22% to 41.3% and 16.2% to 16.4% with 0.20 wt % GO at 14 and 28 days, respectively. However the workability decreased by 7.5% to 18.8% with 0.05% and 0.2% GO addition. Microstructural analysis with environmental scanning electron microscopy (ESEM)/backscattered mode (BSEM) showed that the GO-cement composites had a much denser structure and better crystallized hydration products, meanwhile mercury intrusion porosimetry (MIP) testing and image analysis demonstrated that the incorporation of GO in the composites can help in refining capillary pore structure and reducing the air voids content.

Dynamic Mechanical Properties and Microstructure of Graphene Oxide Nanosheets Reinforced Cement Composites

PubMed Central

Wei, Jing-Jie; Xing, Feng

2017-01-01

This paper presents an experimental investigation on the effect of uniformly dispersed graphene oxide (GO) nanosheets on dynamic mechanical properties of cement based composites prepared with recycled fine aggregate (RFA). Three different amounts of GO, 0.05%, 0.10%, and 0.20% in mass of cement, were used in the experiments. The visual inspections of GO nanosheets were also carried out after ultrasonication by transmission electron microscope (TEM) atomic force microscope (AFM), and Raman to characterize the dispersion effect of graphite oxide. Dynamic mechanical analyzer test showed that the maximum increased amount of loss factor and storage modulus, energy absorption was 125%, 53%, and 200% when compared to the control sample, respectively. The flexural and compressive strengths of GO-mortar increased up to 22% to 41.3% and 16.2% to 16.4% with 0.20 wt % GO at 14 and 28 days, respectively. However the workability decreased by 7.5% to 18.8% with 0.05% and 0.2% GO addition. Microstructural analysis with environmental scanning electron microscopy (ESEM)/backscattered mode (BSEM) showed that the GO-cement composites had a much denser structure and better crystallized hydration products, meanwhile mercury intrusion porosimetry (MIP) testing and image analysis demonstrated that the incorporation of GO in the composites can help in refining capillary pore structure and reducing the air voids content. PMID:29186810

Effects of Kaolin Clay on the Mechanical Properties of Asphaltic Concrete AC14

NASA Astrophysics Data System (ADS)

Abdullah, M. E.; Ramadhansyah, P. J.; Rafsanjani, M. H.; Norhidayah, A. H.; Yaacob, H.; Hainin, M. R.; Warid, M. N. Mohd; Satar, M. K. I. Mohd; Aziz, Md Maniruzzaman A.; Mashros, N.

2018-04-01

This study investigated the effect of kaolin clay on the mechanical properties of asphaltic concrete AC14 through Marshall Stability, resilient modulus, and dynamic creep tests. Four replacement levels of kaolin clay (2%, 4%, 6%, and 8% by weight of the binder) were considered. Kaolin clay functioned as an effective filler replacement material to increase the mechanical properties of asphalt mixtures. Asphaltic concrete with 2% to 4% kaolin clay replacement level exhibited excellent performance with good stability, resilient modulus, and creep stiffness.

Mars Science Laboratory Sample Acquisition, Sample Processing and Handling: Subsystem Design and Test Challenges

NASA Technical Reports Server (NTRS)

Jandura, Louise

2010-01-01

The Sample Acquisition/Sample Processing and Handling subsystem for the Mars Science Laboratory is a highly-mechanized, Rover-based sampling system that acquires powdered rock and regolith samples from the Martian surface, sorts the samples into fine particles through sieving, and delivers small portions of the powder into two science instruments inside the Rover. SA/SPaH utilizes 17 actuated degrees-of-freedom to perform the functions needed to produce 5 sample pathways in support of the scientific investigation on Mars. Both hardware redundancy and functional redundancy are employed in configuring this sampling system so some functionality is retained even with the loss of a degree-of-freedom. Intentional dynamic environments are created to move sample while vibration isolators attenuate this environment at the sensitive instruments located near the dynamic sources. In addition to the typical flight hardware qualification test program, two additional types of testing are essential for this kind of sampling system: characterization of the intentionally-created dynamic environment and testing of the sample acquisition and processing hardware functions using Mars analog materials in a low pressure environment. The overall subsystem design and configuration are discussed along with some of the challenges, tradeoffs, and lessons learned in the areas of fault tolerance, intentional dynamic environments, and special testing

Non-equilibrium dynamics due to moving deflagration front at RDX/HTPB interface

NASA Astrophysics Data System (ADS)

Chaudhuri, Santanu; Joshi, Kaushik; Lacevic, Naida

Reactive dissipative particle dynamics (DPD-RX), a promising tool in characterizing the sensitivity and performance of heterogeneous solid propellants like polymer bonded explosives (PSXs), requires further testing for non-equilibrium dynamics. It is important to understand detailed atomistic chemistry for developing coarse grain reactive models needed for the DPD-RX. In order to obtain insights into combustion chemistry of RDX/HTPB binder, we used reactive molecular dynamics (RMD) to obtain energy up-pumping and reaction mechanisms at RDX/HTPB interface when exposed to a self-sustaining deflagration front. Hot spots are ignited near and away from the heterogeneous interface using the thermal pulse. The results show that the hot spot near interface significantly delays the transition from ignition to deflagration. We will present the mechanical response and the combustion chemistry of HTPB when the propagating deflagration front hits the polymer binder. We will discuss our efforts to incorporate this RMD based chemistry into the DPD-RX which will enable us to perform such non-equilibrium dynamics simulations on large-length scale with microstructural heterogeneities. Funding from DTRA Grant Number HDTRA1-15-1-0034 is acknowledged.

Effect of strain rate and temperature on mechanical properties of selected building Polish steels

NASA Astrophysics Data System (ADS)

Moćko, Wojciech; Kruszka, Leopold

2015-09-01

Currently, the computer programs of CAD type are basic tool for designing of various structures under impact loading. Application of the numerical calculations allows to substantially reduce amount of time required for the design stage of such projects. However, the proper use of computer aided designing technique requires input data for numerical software including elastic-plastic models of structural materials. This work deals with the constitutive model developed by Rusinek and Klepaczko (RK) applied for the modelling of mechanical behaviour of selected grades structural St0S, St3SX, 18GS and 34GS steels and presents here results of experimental and empirical analyses to describe dynamic elastic-plastic behaviours of tested materials at wide range of temperature. In order to calibrate the RK constitutive model, series of compression tests at wide range of strain rates, including static, quasi-static and dynamic investigations at lowered, room and elevated temperatures, were carried out using two testing stands: servo-hydraulic machine and split Hopkinson bar. The results were analysed to determine influence of temperature and strain rate on visco-plastic response of tested steels, and show good correlation with experimental data.

Spatially explicit modelling of cholera epidemics

NASA Astrophysics Data System (ADS)

Finger, F.; Bertuzzo, E.; Mari, L.; Knox, A. C.; Gatto, M.; Rinaldo, A.

2013-12-01

Epidemiological models can provide crucial understanding about the dynamics of infectious diseases. Possible applications range from real-time forecasting and allocation of health care resources to testing alternative intervention mechanisms such as vaccines, antibiotics or the improvement of sanitary conditions. We apply a spatially explicit model to the cholera epidemic that struck Haiti in October 2010 and is still ongoing. The dynamics of susceptibles as well as symptomatic and asymptomatic infectives are modelled at the scale of local human communities. Dissemination of Vibrio cholerae through hydrological transport and human mobility along the road network is explicitly taken into account, as well as the effect of rainfall as a driver of increasing disease incidence. The model is calibrated using a dataset of reported cholera cases. We further model the long term impact of several types of interventions on the disease dynamics by varying parameters appropriately. Key epidemiological mechanisms and parameters which affect the efficiency of treatments such as antibiotics are identified. Our results lead to conclusions about the influence of different intervention strategies on the overall epidemiological dynamics.

Long residence times of rapidly decomposable soil organic matter: application of a multi-phase, multi-component, and vertically resolved model (BAMS1) to soil carbon dynamics

NASA Astrophysics Data System (ADS)

Riley, W. J.; Maggi, F.; Kleber, M.; Torn, M. S.; Tang, J. Y.; Dwivedi, D.; Guerry, N.

2014-07-01

Accurate representation of soil organic matter (SOM) dynamics in Earth system models is critical for future climate prediction, yet large uncertainties exist regarding how, and to what extent, the suite of proposed relevant mechanisms should be included. To investigate how various mechanisms interact to influence SOM storage and dynamics, we developed an SOM reaction network integrated in a one-dimensional, multi-phase, and multi-component reactive transport solver. The model includes representations of bacterial and fungal activity, multiple archetypal polymeric and monomeric carbon substrate groups, aqueous chemistry, aqueous advection and diffusion, gaseous diffusion, and adsorption (and protection) and desorption from the soil mineral phase. The model predictions reasonably matched observed depth-resolved SOM and dissolved organic matter (DOM) stocks and fluxes, lignin content, and fungi to aerobic bacteria ratios. We performed a suite of sensitivity analyses under equilibrium and dynamic conditions to examine the role of dynamic sorption, microbial assimilation rates, and carbon inputs. To our knowledge, observations do not exist to fully test such a complicated model structure or to test the hypotheses used to explain observations of substantial storage of very old SOM below the rooting depth. Nevertheless, we demonstrated that a reasonable combination of sorption parameters, microbial biomass and necromass dynamics, and advective transport can match observations without resorting to an arbitrary depth-dependent decline in SOM turnover rates, as is often done. We conclude that, contrary to assertions derived from existing turnover time based model formulations, observed carbon content and Δ14C vertical profiles are consistent with a representation of SOM consisting of carbon compounds with relatively fast reaction rates, vertical aqueous transport, and dynamic protection on mineral surfaces.

Technology development for cryogenic deployable telescope structures and mechanisms

NASA Astrophysics Data System (ADS)

Atkinson, Charles B.; Gilman, Larry; Reynolds, Paul

2003-12-01

At 6-7 meters in diameter, the James Webb Space Telescope (JWST) will require structures that remain stable to levels that are on the order of 10 nanometers under dynamic and thermal loading while operating at cryogenic temperatures. Moreover, the JWST will be the first telescope in space that is deployed, resulting in an aperture that is not only segmented, but has hinge-lines and the associated joining systems or latches in it. In order to understand the behavior and reduce the risk associated with very large, deployed structures and the stability of the associated structure and latches, we developed and tested the largest cryogenic structure ever built and then characterized its stability. This paper presents a description of the design of the Development Optical Telescope Assembly (DOTA), the testing performed, and the results of the testing performed on it. We discuss the material selection and characterization processes, give a description of the test configurations, describe the metrology equipment and the validation process for it, provide the test results, and summarize the conclusions drawn from the results. The testing and associated results include characterization of the thermal stability of the large-scale structure, characterization of the micro-dynamic stability of the latching system, and measurements of the deployment capability of the mechanisms. We also describe how the DOTA design relates to the JWST design and how the test results relate to the JWST requirements.

Strain rate effects on fracture behavior of Austempered Ductile Irons

NASA Astrophysics Data System (ADS)

Ruggiero, Andrew; Bonora, Nicola; Gentile, Domenico; Iannitti, Gianluca; Testa, Gabriel; Hörnqvist Colliander, Magnus; Masaggia, Stefano; Vettore, Federico

2017-06-01

Austempered Ductile Irons (ADIs), combining high strength, good ductility and low density, are candidates to be a suitable alternative to high-strength steels. Nevertheless, the concern about a low ductility under dynamic loads often leads designers to exclude cast irons for structural applications. However, results from dynamic tensile tests contradict this perception showing larger failure strain with respect to quasistatic data. The fracture behaviour of ADIs depends on damage mechanisms occurring in the spheroids of graphite, in the matrix and at their interface, with the matrix (ausferrite) consisting of acicular ferrite in carbon-enriched austenite. Here, a detailed microstructural analysis was performed on the ADI 1050-6 deformed under different conditions of strain rates, temperatures, and states of stress. Beside the smooth specimens used for uniaxial tensile tests, round notched bars to evaluate the ductility reduction with increasing stress triaxiality and tophat geometries to evaluate the propensity to shear localization and the associated microstructural alterations were tested. The aim of the work is to link the mechanical and fracture behavior of ADIs to the load condition through the microstructural modifications that occur for the corresponding deformation path.

Slow crack growth versus creep cavity coalescence: Competing failure mechanisms during high-temperature deformation of advanced ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jenkins, M.G.; Kohles, S.S.; Stevens, T.L.

1996-12-31

Duality of failure mechanisms (slow crack growth from pre-existing defects versus cumulative creep damage) is examined in a silicon nitride advanced ceramic recently tested at elevated-temperatures. Static (constant stress over time), dynamic (monotonically-increasing stress over time), and cyclic (fluctuating stress over time) fatigue behaviors were evaluated in tension in ambient air at temperatures of 1150, 1260, and 1370{degrees}C for a hot-isostatically pressed monolithic {beta}-silicon nitride. At 1150{degrees}C, all three types of fatigue results showed the similar failure mechanism of slow crack growth (SCG). At 1260 and 1370{degrees}C the failure mechanism was more complex. Failure under static fatigue was dominated bymore » the accumulation of creep damage via diffusion-controlled cavities. In dynamic fatigue, failure occurred by SCG at high stress rates (>10{sup {minus}2}MPa/s) and by creep damage at low stress rates ({le}10{sup {minus}2} MPa/s). For cyclic fatigue, such rate effects influenced the stress rupture results in which times to failure were greater for dynamic and cyclic fatigue than for static fatigue. Elucidation of failure mechanisms is necessary for accurate prediction of long-term survivability and reliability of structural ceramics.« less

Kv1 channels control spike threshold dynamics and spike timing in cortical pyramidal neurones

PubMed Central

Higgs, Matthew H; Spain, William J

2011-01-01

Abstract Previous studies showed that cortical pyramidal neurones (PNs) have a dynamic spike threshold that functions as a high-pass filter, enhancing spike timing in response to high-frequency input. While it is commonly assumed that Na+ channel inactivation is the primary mechanism of threshold accommodation, the possible role of K+ channel activation in fast threshold changes has not been well characterized. The present study tested the hypothesis that low-voltage activated Kv1 channels affect threshold dynamics in layer 2–3 PNs, using α-dendrotoxin (DTX) or 4-aminopyridine (4-AP) to block these conductances. We found that Kv1 blockade reduced the dynamic changes of spike threshold in response to a variety of stimuli, including stimulus-evoked synaptic input, current steps and ramps of varied duration, and noise. Analysis of the responses to noise showed that Kv1 channels increased the coherence of spike output with high-frequency components of the stimulus. A simple model demonstrates that a dynamic spike threshold can account for this effect. Our results show that the Kv1 conductance is a major mechanism that contributes to the dynamic spike threshold and precise spike timing of cortical PNs. PMID:21911608

Mechanical properties and mechanism of single crystal Cu pillar by in situ TEM compression and molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Lin, Kai-Peng; Fang, Te-Hua; Lin, Ying-Jhin

2018-02-01

In this study, we investigate the mechanical properties of single-crystal copper (Cu) nanopillars. Critical deformation variations of Cu-nanopillared structures are estimated using in situ transmission electron microscopy compression tests and molecular dynamics simulations. The Young’s moduli of Cu nanopillars with diameters of 2-6 nm were 90.20-124.47 GPa. The contact stiffnesses of the Cu nanopillars with diameters of 400 and 500 nm were 1.33 and 3.86 N m-1, respectively; the Poisson’s ratios for these nanopillars were 0.32 and 0.33. The yield strength of the nanopillars varied from 0.25 GPa at 500 nm to 0.42 GPa at 400 nm; the yield strength of single-crystal Cu nanopillars decreased with increasing diameter. The values of the indented hardness of the Cu block were 0.27 and 1.06 GPa, respectively. Through experimental work and molecular dynamics simulations, we demonstrate that Cu nanopillars exhibit internal stress transmission during compression. When compression reaches the maximum strain, it can be observed that Cu slips. Our results are useful for understanding the mechanical properties, contact, and local deformation of Cu nanopillars.

Extreme Mechanical Behavior of Nacre-Mimetic Graphene-Oxide and Silk Nanocomposites.

PubMed

Xie, Wanting; Tadepalli, Sirimuvva; Park, Sang Hyun; Kazemi-Moridani, Amir; Jiang, Qisheng; Singamaneni, Srikanth; Lee, Jae-Hwang

2018-02-14

Biological materials have the ability to withstand extreme mechanical forces due to their unique multilevel hierarchical structure. Here, we fabricated a nacre-mimetic nanocomposite comprised of silk fibroin and graphene oxide that exhibits hybridized dynamic responses arising from alternating high-contrast mechanical properties of the components at the nanoscale. Dynamic mechanical behavior of these nanocomposites is assessed through a microscale ballistic characterization using a 7.6 μm diameter silica sphere moving at a speed of approximately 400 m/s. The volume fraction of graphene oxide in these composites is systematically varied from 0 to 32 vol % to quantify the dynamic effects correlating with the structural morphologies of the graphene oxide flakes. Specific penetration energy of the films rapidly increases as the distribution of graphene oxide flakes evolves from noninteracting, isolated sheets to a partially overlapping continuous sheet. The specific penetration energy of the nanocomposite at the highest graphene oxide content tested here is found to be significantly higher than that of Kevlar fabrics and close to that of pure multilayer graphene. This study evidently demonstrates that the morphologies of nanoscale constituents and their interactions are critical to realize scalable high-performance nanocomposites using typical nanomaterial constituents having finite dimensions.

The Proposed Doppler Electron Velocimeter and the Need for Nanoscale Dynamics

DOE PAGES

Reu, Phillip L.

2007-05-01

As engineering challenges grow in the ever-shrinking world of nano-design, methods of making dynamic measurements of nano-materials and systems become more important. The Doppler electron velocimeter (DEV) is a new measurement concept motivated by the increasing importance of nano-dynamics. Nano-dynamics is defined in this context as any phenomenon that causes a dynamically changing phase in an electron beam, and includes traditional mechanical motion, as well as additional phenomena including changing magnetic and electric fields. The DEV is only a theoretical device at this point. Lastly, this article highlights the importance of pursuing nano-dynamics and presents a case that the electronmore » microscope and its associated optics are a viable test bed to develop this new measurement tool.« less

A fully dynamic model of a multi-layer piezoelectric actuator incorporating the power amplifier

NASA Astrophysics Data System (ADS)

Zhu, Wei; Yang, Fufeng; Rui, Xiaoting

2017-12-01

The dynamic input-output characteristics of the multi-layer piezoelectric actuator (PA) are intrinsically rate-dependent and hysteresis. Meanwhile, aiming at the strong capacitive impedance of multi-layer PA, the power amplifier of the actuator can greatly affect the dynamic performances of the actuator. In this paper, a novel dynamic model that includes a model of the electric circuit providing voltage to the actuator, an inverse piezoelectric effect model describing the hysteresis and creep behavior of the actuator, and a mechanical model, in which the vibration characteristics of the multi-layer PA is described, is put forward. Validation experimental tests are conducted. Experimental results show that the proposed dynamic model can accurately predict the fully dynamic behavior of the multi-layer PA with different driving power.

High-rate behaviour of iron ore pellet

NASA Astrophysics Data System (ADS)

Gustafsson, Gustaf; Häggblad, Hans-Åke; Jonsén, Pär; Nishida, Masahiro

2015-09-01

Iron ore pellets are sintered, centimetre-sized spheres of ore with high iron content. Together with carbonized coal, iron ore pellets are used in the production of steel. In the transportation from the pelletizing plants to the customers, the iron ore pellets are exposed to different loading situations, resulting in degradation of strength and in some cases fragmentation. For future reliable numerical simulations of the handling and transportation of iron ore pellets, knowledge about their mechanical properties is needed. This paper describes the experimental work to investigate the dynamic mechanical properties of blast furnace iron ore pellets. To study the dynamic fracture of iron ore pellets a number of split Hopkinson pressure bar tests are carried out and analysed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fasiello, Matteo; Vlah, Zvonimir

A specific value for the cosmological constant Λ can account for late-time cosmic acceleration. However, motivated by the so-called cosmological constant problem(s), several alternative mechanisms have been explored. To date, a host of well-studied dynamical dark energy and modified gravity models exists. Going beyond ΛCDM often comes with additional degrees of freedom (dofs). For these to pass existing observational tests, an efficient screening mechanism must be in place. Furthermore, the linear and quasi-linear regimes of structure formation are ideal probes of such dofs and can capture the onset of screening. We propose here a semi-phenomenological “filter” to account for screeningmore » dynamics on LSS observables, with special emphasis on Vainshtein-type screening.« less

Reliability Issues and Solutions in Flexible Electronics Under Mechanical Fatigue

NASA Astrophysics Data System (ADS)

Yi, Seol-Min; Choi, In-Suk; Kim, Byoung-Joon; Joo, Young-Chang

2018-07-01

Flexible devices are of significant interest due to their potential expansion of the application of smart devices into various fields, such as energy harvesting, biological applications and consumer electronics. Due to the mechanically dynamic operations of flexible electronics, their mechanical reliability must be thoroughly investigated to understand their failure mechanisms and lifetimes. Reliability issue caused by bending fatigue, one of the typical operational limitations of flexible electronics, has been studied using various test methodologies; however, electromechanical evaluations which are essential to assess the reliability of electronic devices for flexible applications had not been investigated because the testing method was not established. By employing the in situ bending fatigue test, we has studied the failure mechanism for various conditions and parameters, such as bending strain, fatigue area, film thickness, and lateral dimensions. Moreover, various methods for improving the bending reliability have been developed based on the failure mechanism. Nanostructures such as holes, pores, wires and composites of nanoparticles and nanotubes have been suggested for better reliability. Flexible devices were also investigated to find the potential failures initiated by complex structures under bending fatigue strain. In this review, the recent advances in test methodology, mechanism studies, and practical applications are introduced. Additionally, perspectives including the future advance to stretchable electronics are discussed based on the current achievements in research.

Reliability Issues and Solutions in Flexible Electronics Under Mechanical Fatigue

NASA Astrophysics Data System (ADS)

Yi, Seol-Min; Choi, In-Suk; Kim, Byoung-Joon; Joo, Young-Chang

2018-03-01

Flexible devices are of significant interest due to their potential expansion of the application of smart devices into various fields, such as energy harvesting, biological applications and consumer electronics. Due to the mechanically dynamic operations of flexible electronics, their mechanical reliability must be thoroughly investigated to understand their failure mechanisms and lifetimes. Reliability issue caused by bending fatigue, one of the typical operational limitations of flexible electronics, has been studied using various test methodologies; however, electromechanical evaluations which are essential to assess the reliability of electronic devices for flexible applications had not been investigated because the testing method was not established. By employing the in situ bending fatigue test, we has studied the failure mechanism for various conditions and parameters, such as bending strain, fatigue area, film thickness, and lateral dimensions. Moreover, various methods for improving the bending reliability have been developed based on the failure mechanism. Nanostructures such as holes, pores, wires and composites of nanoparticles and nanotubes have been suggested for better reliability. Flexible devices were also investigated to find the potential failures initiated by complex structures under bending fatigue strain. In this review, the recent advances in test methodology, mechanism studies, and practical applications are introduced. Additionally, perspectives including the future advance to stretchable electronics are discussed based on the current achievements in research.

Dynamic Reconfiguration of a RGBD Sensor Based on QoS and QoC Requirements in Distributed Systems.

PubMed

Munera, Eduardo; Poza-Lujan, Jose-Luis; Posadas-Yagüe, Juan-Luis; Simó-Ten, José-Enrique; Noguera, Juan Fco Blanes

2015-07-24

The inclusion of embedded sensors into a networked system provides useful information for many applications. A Distributed Control System (DCS) is one of the clearest examples where processing and communications are constrained by the client's requirements and the capacity of the system. An embedded sensor with advanced processing and communications capabilities supplies high level information, abstracting from the data acquisition process and objects recognition mechanisms. The implementation of an embedded sensor/actuator as a Smart Resource permits clients to access sensor information through distributed network services. Smart resources can offer sensor services as well as computing, communications and peripheral access by implementing a self-aware based adaptation mechanism which adapts the execution profile to the context. On the other hand, information integrity must be ensured when computing processes are dynamically adapted. Therefore, the processing must be adapted to perform tasks in a certain lapse of time but always ensuring a minimum process quality. In the same way, communications must try to reduce the data traffic without excluding relevant information. The main objective of the paper is to present a dynamic configuration mechanism to adapt the sensor processing and communication to the client's requirements in the DCS. This paper describes an implementation of a smart resource based on a Red, Green, Blue, and Depth (RGBD) sensor in order to test the dynamic configuration mechanism presented.

Analytical Ultrasonics in Materials Research and Testing

NASA Technical Reports Server (NTRS)

Vary, A.

1986-01-01

Research results in analytical ultrasonics for characterizing structural materials from metals and ceramics to composites are presented. General topics covered by the conference included: status and advances in analytical ultrasonics for characterizing material microstructures and mechanical properties; status and prospects for ultrasonic measurements of microdamage, degradation, and underlying morphological factors; status and problems in precision measurements of frequency-dependent velocity and attenuation for materials analysis; procedures and requirements for automated, digital signal acquisition, processing, analysis, and interpretation; incentives for analytical ultrasonics in materials research and materials processing, testing, and inspection; and examples of progress in ultrasonics for interrelating microstructure, mechanical properites, and dynamic response.

Dynamic load testing on the bearing capacity of prestressed tubular concrete piles in soft ground

NASA Astrophysics Data System (ADS)

Yu, Chuang; Liu, Songyu

2008-11-01

Dynamic load testing (DLT) is a high strain test method for assessing pile performance. The shaft capacity of a driven PTC (prestressed tubular concrete) pile in marine soft ground will vary with time after installation. The DLT method has been successfully transferred to the testing of prestressed pipe piles in marine soft clay of Lianyungang area in China. DLT is investigated to determine the ultimate bearing capacity of single pile at different period after pile installation. The ultimate bearing capacity of single pile was founded to increase more than 70% during the inventing 3 months, which demonstrate the time effect of rigid pile bearing capacity in marine soft ground. Furthermore, the skin friction and axial force along the pile shaft are presented as well, which present the load transfer mechanism of pipe pile in soft clay. It shows the economy and efficiency of DLT method compared to static load testing method.

The effect of deformation temperature on the microstructure evolution of Inconel 625 superalloy

NASA Astrophysics Data System (ADS)

Guo, Qingmiao; Li, Defu; Guo, Shengli; Peng, Haijian; Hu, Jie

2011-07-01

Hot compression tests of Inconel 625 superalloy were conducted using a Gleeble-1500 simulator between 900 °C and 1200 °C with different true strains and a strain rate of 0.1 s -1. Scanning electron microscope (SEM) and electron backscatter diffraction technique (EBSD) were employed to investigate the effect of deformation temperature on the microstructure evolution and nucleation mechanisms of dynamic recrystallization (DRX). It is found that the relationship between the DRX grain size and the peak stress can be expressed by a power law function. Significant influence of deformation temperatures on the nucleation mechanisms of DRX are observed at different deformation stages. At lower deformation temperatures, continuous dynamic recrystallization (CDRX) characterized by progressive subgrain rotation is considered as the main mechanism of DRX at the early deformation stage. However, discontinuous dynamic recrystallization (DDRX) with bulging of the original grain boundaries becomes the operating mechanism of DRX at the later deformation stage. At higher deformation temperatures, DDRX is the primary mechanism of DRX, while CDRX can only be considered as an assistant mechanism at the early deformation stage. Nucleation of DRX can also be activated by the twinning formation. With increasing the deformation temperature, the effect of DDRX accompanied with twinning formation grows stronger, while the effect of CDRX grows weaker. Meanwhile, the position of subgrain formation shifts gradually from the interior of original grains to the vicinity of the original boundaries.

Development of a multistage compliant mechanism with new boundary constraint

NASA Astrophysics Data System (ADS)

Ling, Mingxiang; Cao, Junyi; Jiang, Zhou; Li, Qisheng

2018-01-01

This paper presents a piezo-actuated compliant mechanism with a new boundary constraint to provide concurrent large workspace and high dynamic frequency for precision positioning or other flexible manipulation applications. A two-stage rhombus-type displacement amplifier with the "sliding-sliding" boundary constraint is presented to maximize the dynamic frequency while retaining a large output displacement. The vibration mode is also improved by the designed boundary constraint. A theoretical kinematic model of the compliant mechanism is established to optimize the geometric parameters, and a prototype is fabricated with a compact dimension of 60 mm × 60 mm × 12 mm. The experimental testing shows that the maximum stroke is approximately 0.6 mm and the output stiffness is 1.1 N/μm with the fundamental frequency of larger than 2.2 kHz. Lastly, the excellent performance of the presented compliant mechanism is compared with several mechanisms in the previous literature. As a conclusion, the presented boundary constraint strategy provides a new way to balance the trade-off between the frequency response and the stroke range widely existed in compliant mechanisms.

A novel hybrid actuation mechanism based XY nanopositioning stage with totally decoupled kinematics

NASA Astrophysics Data System (ADS)

Zhu, Wu-Le; Zhu, Zhiwei; Guo, Ping; Ju, Bing-Feng

2018-01-01

This paper reports the design, analysis and testing of a parallel two degree-of-freedom piezo-actuated compliant stage for XY nanopositioning by introducing an innovative hybrid actuation mechanism. It mainly features the combination of two Scott-Russell and a half-bridge mechanisms for double-stage displacement amplification as well as moving direction modulation. By adopting the leaf-type double parallelogram (LTDP) structures at both input and output ends of the hybrid mechanism, the lateral stiffness and dynamic characteristics are significantly improved while the parasitic motions are greatly eliminated. The XY nanopositioning stage is constructed with two orthogonally configured hybrid mechanisms along with the LTDP mechanisms for totally decoupled kinematics at both input and output ends. An analytical model was established to describe the complete elastic deformation behavior of the stage, with further verification through the finite element simulation. Finally, experiments were implemented to comprehensively evaluate both the static and dynamic performances of the proposed stage. Closed-loop control of the piezoelectric actuators (PEA) by integrating strain gauges was also conducted to effectively eliminate the nonlinear hysteresis of the stage.

An Experimental Investigation of Compressible Dynamic Stall on a Pitching Airfoil

NASA Astrophysics Data System (ADS)

Thorne, Katie; Bowles, Patrick

2009-11-01

A new facility has been designed and constructed at the University of Notre Dame to investigate dynamic stall on a 2-D pitching airfoil at high subsonic Mach numbers. This work is motivated by the need to investigate dynamic stall at conditions relevant to military helicopters. One focus of the experiments is to characterize the role of shock/boundary layer interactions during the pitching cycle. The new dynamic stall facility is integrated into a closed-loop, low turbulence wind tunnel capable of achieving test section Mach numbers in excess of M = 0.6. The design of the dynamic stall test section was focused on achieving reduced pitching frequencies of up to k = 0.2 and chord Reynolds numbers up to 5 x10^6. The facility has the unique ability to execute non-harmonic pitching motions through the use of an actuated pitch link mechanism. Optical access is provided to allow the use of high-speed and Schlieren imaging. Thirty-one flush mounted Kulite dynamic pressure transducers provide the instantaneous unsteady surface pressure distribution over the airfoil. Initial dynamic stall measurements obtained in the new facility will be described.

A comparison of take-off dynamics during three different spikes, block and counter-movement jump in female volleyball players.

PubMed

Kabacinski, Jaroslae; Dworak, Lecholslaw B; Murawa, Michal; Ostarello, John; Rzepnicka, Agata; Maczynski, Jacek

2016-12-01

The purpose of the study was to compare the take-off dynamics in counter-movement jump (CMJ), volleyball block and spikes. Twelve professional female players, representing the highest volleyball league in Poland, participated in the laboratory tests. A force platform was used to record ground reaction force (GRF) during take-off phase in CMJ test, block from a run-up and spikes: front row attack, slide attack, back row attack. Vertical (v) GRF (peak: Rmax and integral mean: ), impulse of vGRF (J) and mechanical power (peak: Pmax and integral mean:

) were analyzed. Significant differences (P<0.05) of values of the dynamic parameters (Rmax, , J, Pmax, and

) were found between CMJ, block from a run-up and three different technique spikes. The highest values were recorded during take-off in the back row attack: peak vGRF (2.93±0.05 BW), integral mean vGRF (1.90±0.08 BW), impulse of vGRF (354±40 Ns), peak power (5320±918 W) and integral mean power (3604±683 W). Peak power (2608±217 W) and integral mean power (1417±94 W) were determined in CMJ test to evaluate the force-velocity capabilities of the players. In terms of GRF and the mechanical power, high level of dynamics in take-off influences positively the jumping height and significantly increases the effectiveness of attacks during spike of the ball over the block of the opponent.

Characterization of free volume during vulcanization of styrene butadiene rubber by means of positron annihilation lifetime spectroscopy and dynamic mechanical test.

PubMed

Marzocca, A J; Cerveny, S; Salgueiro, W; Somoza, A; Gonzalez, L

2002-02-01

An experimental investigation was performed to study the effect on the free volume of the advance of the cross-linking reaction in a copolymer of styrene butadiene rubber by sulfur vulcanization. The dynamic modulus and loss tangent were evaluated over samples cured for different times at 433 K by dynamic mechanical tests over a range of frequencies between 5 and 80 Hz at temperatures between 200 and 300 K. Using the William-Landel-Ferry relationship, master curves were obtained at a reference temperature of 298 K and the coefficients c(0)(1) and c(0)(2) were evaluated. From these parameters the dependence of the free volume on the cure time is obtained. Positron annihilation lifetime spectroscopy was also used to estimate the size and number density of free volume sites in the material. The spectra were analyzed in terms of continuous distributions of free volume size. The results suggest an increase of the lower free volume size when cross linking takes place. Both techniques give similar results for the dependence of free volume on the time of cure of the polymer.

Measuring the Influence of Pearlite Dissolution on the Transient Dynamic Strength of Rapidly Heated Plain Carbon Steels

NASA Astrophysics Data System (ADS)

Mates, Steven; Stoudt, Mark; Gangireddy, Sindhura

2016-07-01

Carbon steels containing ferrite-pearlite microstructures weaken dramatically when pearlite dissolves into austenite on heating. The kinetics of this phase transformation, while fast, can play a role during dynamic, high-temperature manufacturing processes, including high-speed machining, when the time scale of this transformation is on the order of the manufacturing process itself. In such a regime, the mechanical strength of carbon steel can become time dependent. The present work uses a rapidly heated, high-strain-rate mechanical test to study the effect of temperature and time on the amount of pearlite dissolved and on the resulting transient effect on dynamic strength of a low and a high carbon (eutectoid) steel. Measurements indicate that the transient effect occurs for heating times less than about 3 s. The 1075 steel loses about twice the strength compared to the 1018 steel (85 MPa to 45 MPa) owing to its higher initial pearlite volume fraction. Pearlite dissolution is confirmed by metallographic examination of tested samples. Despite the different starting pearlite fractions, the kinetics of dissolution are comparable for the two steels, owing to the similarity in their initial pearlite morphology.

High Strain Rate Testing of Rocks using a Split-Hopkinson-Pressure Bar

NASA Astrophysics Data System (ADS)

Zwiessler, Ruprecht; Kenkmann, Thomas; Poelchau, Michael; Nau, Siegfried; Hess, Sebastian

2016-04-01

Dynamic mechanical testing of rocks is important to define the onset of rate dependency of brittle failure. The strain rate dependency occurs through the propagation velocity limit (Rayleigh wave speed) of cracks and their reduced ability to coalesce, which, in turn, significantly increases the strength of the rock. We use a newly developed pressurized air driven Split-Hopkinson-Pressure Bar (SHPB), that is specifically designed for the investigation of high strain rate testing of rocks, consisting of several 10 to 50 cm long strikers and bar components of 50 mm in diameter and 2.5 meters in length each. The whole set up, composed of striker, incident- and transmission bar is available in aluminum, titanium and maraging steel to minimize the acoustic impedance contrast, determined by the change of density and speed of sound, to the specific rock of investigation. Dynamic mechanical parameters are obtained in compression as well as in spallation configuration, covering a wide spectrum from intermediate to high strain rates (100-103 s-1). In SHPB experiments [1] one-dimensional longitudinal compressive pulses of diverse shapes and lengths - formed with pulse shapers - are used to generate a variety of loading histories under 1D states of stress in cylindrical rock samples, in order to measure the respective stress-strain response at specific strain rates. Subsequent microstructural analysis of the deformed samples is aimed at quantification fracture orientation, fracture pattern, fracture density, and fracture surface properties as a function of the loading rate. Linking mechanical and microstructural data to natural dynamic deformation processes has relevance for the understanding of earthquakes, landslides, impacts, and has several rock engineering applications. For instance, experiments on dynamic fragmentation help to unravel super-shear rupture events that pervasively pulverize rocks up to several hundred meters from the fault core [2, 3, 4]. The dynamic, strain rate dependent behavior with strongly increasing strength and changing fracturing process has not been consequently considered in modeling of geo-hazards such as earthquakes, rock falls, landslides or even meteorite impacts [5]. Incorporation of dynamic material data therefore will contribute to improvements of forecast models and the understanding of fast geodynamic processes. References [1] Zhang, Q. B. & Zhao, J. (2013). A Review of Dynamic Experimental Techniques and Mechanical Behaviour of Rock Materials. Rock Mech Rock Eng. DOI 10.1007/s00603-013-0463-y [2] Doan, M. L., & Gary, G. (2009). Rock pulverization at high strain rate near the San Andreas fault. Nature Geosci., 2, 709-712. [3] Reches, Z. E., & Dewers, T. A. (2005). Gouge formation by dynamic pulverization during earthquake rupture. Earth Planet. Sci. Lett., 235, 361-374. [4] Fondriest, M., Aretusini, S., Di Toro, G., & Smith, S. A. (2015). Fracturing and rock pulverization along an exhumed seismogenic fault zone in dolostones: The Foiana Fault Zone (Southern Alps, Italy). Tectonophys.654, 56-74. [5] Kenkmann, T., Poelchau, M. H., & Wulf, G. (2014). Structural Geology of impact craters. J. .Struct. Geol., 62, 156-182.

Modeling and parameter identification of impulse response matrix of mechanical systems

NASA Astrophysics Data System (ADS)

Bordatchev, Evgueni V.

1998-12-01

A method for studying the problem of modeling, identification and analysis of mechanical system dynamic characteristic in view of the impulse response matrix for the purpose of adaptive control is developed here. Two types of the impulse response matrices are considered: (i) on displacement, which describes the space-coupled relationship between vectors of the force and simulated displacement, which describes the space-coupled relationship between vectors of the force and simulated displacement and (ii) on acceleration, which also describes the space-coupled relationship between the vectors of the force and measured acceleration. The idea of identification consists of: (a) the practical obtaining of the impulse response matrix on acceleration by 'impact-response' technique; (b) the modeling and parameter estimation of the each impulse response function on acceleration through the fundamental representation of the impulse response function on displacement as a sum of the damped sine curves applying linear and non-linear least square methods; (c) simulating the impulse provides the additional possibility to calculate masses, damper and spring constants. The damped natural frequencies are used as a priori information and are found through the standard FFT analysis. The problem of double numerical integration is avoided by taking two derivations of the fundamental dynamic model of a mechanical system as linear combination of the mass-damper-spring subsystems. The identified impulse response matrix on displacement represents the dynamic properties of the mechanical system. From the engineering point of view, this matrix can be also understood as a 'dynamic passport' of the mechanical system and can be used for dynamic certification and analysis of the dynamic quality. In addition, the suggested approach mathematically reproduces amplitude-frequency response matrix in a low-frequency band and on zero frequency. This allows the possibility of determining the matrix of the static stiffness due to dynamic testing over the time of 10- 15 minutes. As a practical example, the dynamic properties in view of the impulse and frequency response matrices of the lathe spindle are obtained, identified and investigated. The developed approach for modeling and parameter identification appears promising for a wide range o industrial applications; for example, rotary systems.

Innocuous cooling can produce nociceptive sensations that are inhibited during dynamic mechanical contact.

PubMed

Green, Barry G; Pope, Jennifer V

2003-02-01

In a previous study of the heat grill illusion, sensations of burning and stinging were sometimes reported when the skin was cooled by as little as 2 degrees C. Informal tests subsequently indicated that these nociceptive sensations were experienced if cooling occurred when the stimulating thermode rested on the skin, but not when the thermode was cooled and then touched to the skin. In experiment 1 subjects judged the intensity of thermal (cold/warm) and nociceptive (burning/stinging) sensations when the volar surface of the forearm was cooled to 25 degrees C (1) via a static thermode (Static condition), or (2) via a cold thermode touched to the skin (Dynamic condition). The total area of stimulation was varied from 2.6 to 10.4 cm(2) to determine if the occurrence of nociceptive sensations depended upon stimulus size. Burning/stinging was rated 10.3 times stronger in the Static condition than in the Dynamic condition, and this difference did not vary significantly with stimulus size. In experiment 2, thermal and nociceptive sensations were measured during cooling to just 31 degrees, 29 degrees or 27 degrees C, and data were obtained on the frequency at which different sensation qualities were experienced. Stinging was the most frequently reported nociceptive quality in the Static condition, and stinging and burning were both markedly reduced in the Dynamic condition. In experiment 3 we tested the possibility that dynamic contact might have inhibited burning and stinging not because of mechanical contact per se, but rather because dynamic contact caused higher rates of cooling. However, varying cooling rate over a tenfold range (-0.5 degrees to -5.0 degrees /s) had no appreciable effect on the frequency of stinging and burning. Overall, the data show that mild cooling can produce nociceptive sensations that are suppressed under conditions of dynamic mechanical contact. The latter observation suggests that cold is perceived differently during active contact with objects than during passive heat loss to the environment. Hypotheses about the physiological basis of the nociceptive sensations at mild temperatures and their possible role in the phenomena of paradoxical heat and synthetic heat are discussed.

Investigation of the leaching behavior of lead in stabilized/solidified waste using a two-year semi-dynamic leaching test.

PubMed

Xue, Qiang; Wang, Ping; Li, Jiang-Shan; Zhang, Ting-Ting; Wang, Shan-Yong

2017-01-01

Long-term leaching behavior of contaminant from stabilization/solidification (S/S) treated waste stays unclear. For the purpose of studying long-term leaching behavior and leaching mechanism of lead from cement stabilized soil under different pH environment, semi-dynamic leaching test was extended to two years to investigate leaching behaviors of S/S treated lead contaminated soil. Effectiveness of S/S treatment in different scenarios was evaluated by leachability index (LX) and effective diffusion coefficient (D e ). In addition, the long-term leaching mechanism was investigated at different leaching periods. Results showed that no significant difference was observed among the values of the cumulative release of Pb, D e and LX in weakly alkaline and weakly acidic environment (pH value varied from 5.00 to 10.00), and all the controlling leaching mechanisms of the samples immersed in weakly alkaline and weakly acidic environments turned out to be diffusion. Strong acid environment would significantly affect the leaching behavior and leaching mechanism of lead from S/S monolith. The two-year variation of D e appeared to be time dependent, and D e values increased after the 210 th day in weakly alkaline and weakly acidic environment. Copyright © 2016 Elsevier Ltd. All rights reserved.

Contrast detection in fluid-saturated media with magnetic resonance poroelastography

PubMed Central

Perriñez, Phillip R.; Pattison, Adam J.; Kennedy, Francis E.; Weaver, John B.; Paulsen, Keith D.

2010-01-01

Purpose: Recent interest in the poroelastic behavior of tissues has led to the development of magnetic resonance poroelastography (MRPE) as an alternative to single-phase MR elastographic image reconstruction. In addition to the elastic parameters (i.e., Lamé’s constants) commonly associated with magnetic resonance elastography (MRE), MRPE enables estimation of the time-harmonic pore-pressure field induced by external mechanical vibration. Methods: This study presents numerical simulations that demonstrate the sensitivity of the computed displacement and pore-pressure fields to a priori estimates of the experimentally derived model parameters. In addition, experimental data collected in three poroelastic phantoms are used to assess the quantitative accuracy of MR poroelastographic imaging through comparisons with both quasistatic and dynamic mechanical tests. Results: The results indicate hydraulic conductivity to be the dominant parameter influencing the deformation behavior of poroelastic media under conditions applied during MRE. MRPE estimation of the matrix shear modulus was bracketed by the values determined from independent quasistatic and dynamic mechanical measurements as expected, whereas the contrast ratios for embedded inclusions were quantitatively similar (10%–15% difference between the reconstructed images and the mechanical tests). Conclusions: The findings suggest that the addition of hydraulic conductivity and a viscoelastic solid component as parameters in the reconstruction may be warranted. PMID:20831058

Dynamic Radioactive Source for Evaluating and Demonstrating Time-dependent Performance of Continuous Air Monitors.

PubMed

McLean, Thomas D; Moore, Murray E; Justus, Alan L; Hudston, Jonathan A; Barbé, Benoît

2016-11-01

Evaluation of continuous air monitors in the presence of a plutonium aerosol is time intensive, expensive, and requires a specialized facility. The Radiation Protection Services Group at Los Alamos National Laboratory has designed a Dynamic Radioactive Source, intended to replace plutonium aerosol challenge testing. The Dynamic Radioactive Source is small enough to be inserted into the sampler filter chamber of a typical continuous air monitor. Time-dependent radioactivity is introduced from electroplated sources for real-time testing of a continuous air monitor where a mechanical wristwatch motor rotates a mask above an alpha-emitting electroplated disk source. The mask is attached to the watch's minute hand, and as it rotates, more of the underlying source is revealed. The measured alpha activity increases with time, simulating the arrival of airborne radioactive particulates at the air sampler inlet. The Dynamic Radioactive Source allows the temporal behavior of puff and chronic release conditions to be mimicked without the need for radioactive aerosols. The new system is configurable to different continuous air monitor designs and provides an in-house testing capability (benchtop compatible). It is a repeatable and reusable system and does not contaminate the tested air monitor. Test benefits include direct user control, realistic (plutonium) aerosol spectra, and iterative development of continuous air monitor alarm algorithms. Data obtained using the Dynamic Radioactive Source has been used to elucidate alarm algorithms and to compare the response time of two commercial continuous air monitors.

Dynamic Radioactive Source for Evaluating and Demonstrating Time-dependent Performance of Continuous Air Monitors

DOE PAGES

McLean, Thomas D.; Moore, Murray E.; Justus, Alan L.; ...

2016-01-01

Evaluation of continuous air monitors in the presence of a plutonium aerosol is time intensive, expensive, and requires a specialized facility. The Radiation Protection Services Group at Los Alamos National Laboratory has designed a Dynamic Radioactive Source, intended to replace plutonium aerosol challenge testing. Furthermore, the Dynamic Radioactive Source is small enough to be inserted into the sampler filter chamber of a typical continuous air monitor. Time-dependent radioactivity is introduced from electroplated sources for real-time testing of a continuous air monitor where a mechanical wristwatch motor rotates a mask above an alpha-emitting electroplated disk source. The mask is attached tomore » the watch’s minute hand, and as it rotates, more of the underlying source is revealed. The alpha activity we measured increases with time, simulating the arrival of airborne radioactive particulates at the air sampler inlet. The Dynamic Radioactive Source allows the temporal behavior of puff and chronic release conditions to be mimicked without the need for radioactive aerosols. The new system is configurable to different continuous air monitor designs and provides an in-house testing capability (benchtop compatible). It is a repeatable and reusable system and does not contaminate the tested air monitor. Test benefits include direct user control, realistic (plutonium) aerosol spectra, and iterative development of continuous air monitor alarm algorithms. We also used data obtained using the Dynamic Radioactive Source to elucidate alarm algorithms and to compare the response time of two commercial continuous air monitors.« less

Characterizing RNA ensembles from NMR data with kinematic models

PubMed Central

Fonseca, Rasmus; Pachov, Dimitar V.; Bernauer, Julie; van den Bedem, Henry

2014-01-01

Functional mechanisms of biomolecules often manifest themselves precisely in transient conformational substates. Researchers have long sought to structurally characterize dynamic processes in non-coding RNA, combining experimental data with computer algorithms. However, adequate exploration of conformational space for these highly dynamic molecules, starting from static crystal structures, remains challenging. Here, we report a new conformational sampling procedure, KGSrna, which can efficiently probe the native ensemble of RNA molecules in solution. We found that KGSrna ensembles accurately represent the conformational landscapes of 3D RNA encoded by NMR proton chemical shifts. KGSrna resolves motionally averaged NMR data into structural contributions; when coupled with residual dipolar coupling data, a KGSrna ensemble revealed a previously uncharacterized transient excited state of the HIV-1 trans-activation response element stem–loop. Ensemble-based interpretations of averaged data can aid in formulating and testing dynamic, motion-based hypotheses of functional mechanisms in RNAs with broad implications for RNA engineering and therapeutic intervention. PMID:25114056

Effect of brace design on patients with ACL-ruptures.

PubMed

Strutzenberger, G; Braig, M; Sell, S; Boes, K; Schwameder, H

2012-11-01

Different designs of functional knee braces for ACL-injury rehabilitation exist. In addition to the mechanical stabilization provided by rigid shell braces, sleeve braces also address proprioceptive mechanisms, but little is known if this leads to benefits for ACL-deficient subjects. Therefore the aim of this study was to investigate the effect of 2 different functional brace designs (shell and sleeve brace) on functional achievements in ACL-deficient patients. 28 subjects with ACL-ruptured knees performed tests for knee joint laxity, joint position sense, static and dynamic balance and isometric and dynamic lower limb extension strength in non-braced, sleeve braced and shell braced condition. The results showed a significant decrease in knee joint laxity for sleeve (33%; p<0.001) and rigid shell bracing (14%, p=0.039). The sleeve brace revealed a significant increase in dynamic balance after perturbation (20%; p=0.024) and a significant increase in dynamic lower limb peak rate of force development (17%; p=0.015) compared to the non-braced condition. The effects might be caused by the flexible area of support and the incorporated mechanisms to address proprioceptive aspects. Braces might not be needed in simple daily life tasks, but could provide beneficial support in more dynamic settings when patients return to sporting activities after an ACL-injury. © Georg Thieme Verlag KG Stuttgart · New York.

Assessing the importance of self-regulating mechanisms in diamondback moth population dynamics: application of discrete mathematical models.

PubMed

Nedorezov, Lev V; Löhr, Bernhard L; Sadykova, Dinara L

2008-10-07

The applicability of discrete mathematical models for the description of diamondback moth (DBM) (Plutella xylostella L.) population dynamics was investigated. The parameter values for several well-known discrete time models (Skellam, Moran-Ricker, Hassell, Maynard Smith-Slatkin, and discrete logistic models) were estimated for an experimental time series from a highland cabbage-growing area in eastern Kenya. For all sets of parameters, boundaries of confidence domains were determined. Maximum calculated birth rates varied between 1.086 and 1.359 when empirical values were used for parameter estimation. After fitting of the models to the empirical trajectory, all birth rate values resulted considerably higher (1.742-3.526). The carrying capacity was determined between 13.0 and 39.9DBM/plant, after fitting of the models these values declined to 6.48-9.3, all values well within the range encountered empirically. The application of the Durbin-Watson criteria for comparison of theoretical and experimental population trajectories produced negative correlations with all models. A test of residual value groupings for randomness showed that their distribution is non-stochastic. In consequence, we conclude that DBM dynamics cannot be explained as a result of intra-population self-regulative mechanisms only (=by any of the models tested) and that more comprehensive models are required for the explanation of DBM population dynamics.

Stress-strain state of mechanical rebar couplings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klimenov, Vasilij, E-mail: nauka@tsuab.ru; Tomsk State University of Architecture and Buildings, 2 Solyanaya Sq., Tomsk, 634003; Ovchinnikov, Artem

Mechanical rebar couplers are preferable in the advanced building construction and structural design of anti-seismic elements. The paper presents destructive inspection techniques used to investigate stress fields (tensile and compressive) and deformation curves for mechanical rebar splicing. The properties of mechanical rebar splicing are investigated by the non-destructive testing digital radiography. The behavior of real connections (column-to-column, beam-to-column) is studied under static and dynamic loads. Investigation results allow the elaboration of recommendations on their application in the universal prefabricated anti-seismic structural system developed at Tomsk State University of Architecture and Building, Tomsk, Russia.

Modeling and Characterization of Dynamic Failure of Soda-lime Glass Under High Speed Impact

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Wenning N.; Sun, Xin; Chen, Weinong W.

2012-05-27

In this paper, the impact-induced dynamic failure of a soda-lime glass block is studied using an integrated experimental/analytical approach. The Split Hopkinson Pressure Bar (SHPB) technique is used to conduct dynamic failure test of soda-lime glass first. The damage growth patterns and stress histories are reported for various glass specimen designs. Making use of a continuum damage mechanics (CDM)-based constitutive model, the initial failure and subsequent stiffness reduction of glass are simulated and investigated. Explicit finite element analyses are used to simulate the glass specimen impact event. A maximum shear stress-based damage evolution law is used in describing the glassmore » damage process under combined compression/shear loading. The impact test results are used to quantify the critical shear stress for the soda-lime glass under examination.« less

Investigation of a Water-Pond Arresting of a Dynamic Model of a Jet Transport

NASA Technical Reports Server (NTRS)

Thompson, William C.

1961-01-01

Brief dynamic-model tests have been made at the request of the Federal Aviation Agency to investigate the use of a shallow pond of water at the end of a runway as a means of arresting jet-transport aircraft when they are forced to abort on take-off or overrun on landing. Such a scheme is of particular interest for civil aircraft because it requires no modifications or attachments to the airplane and no mechanical devices in the arresting system. A modification of this scheme that uses a flexible plastic cover over the water surface has also been tested. The purpose of this paper is to present the results of a dynamic model investigation which would aid in determining whether the water-pond arresting system could be used as a means of arresting airplane overrun.

Mathematical model of depolarization mechanism of conducted vasoreactivity

NASA Astrophysics Data System (ADS)

Neganova, Anastasiia Y.; Stiukhina, Elena S.; Postnov, Dmitry E.

2015-03-01

We address the problem of conducted vasodilation, the phenomenon which is also known as functional hyperemia. Specifically, we test the mechanism of nondecremental propagation of electric signals along endothelial cell layer recently hypothesized by Figueroa et al. By means of functional modeling we focus on possible nonlinear mechanisms that can underlie such regenerative pulse transmission (RPT). Since endothelial cells (EC) are generally known as electrically inexcitable, the possible role of ECs in RPT mechanisms is not evident. By means of mathematical modeling we check the dynamical self-consistency of Figueroa's hypothesis, as well as estimate the possible contribution of specific ionic currents to the suggested RPT mechanism.

The mechanisms of plastic strain accommodation and post critical behavior of heterogeneous reactive composites subject to dynamic loading

NASA Astrophysics Data System (ADS)

Olney, Karl L.

The dynamic behavior of granular/porous and laminate reactive materials is of interest due to their practical applications; reactive structural components, reactive fragments, etc. The mesostructural properties control meso- and macro-scale dynamic behavior of these heterogeneous composites including the behavior during the post-critical stage of deformation. They heavily influence mechanisms of fragment generation and the in situ development of local hot spots, which act as sites of ignition in these materials. This dissertation concentrates on understanding the mechanisms of plastic strain accommodation in two representative reactive material systems with different heterogeneous mesostructrues: Aluminum-Tungsten granular/porous and Nickel-Aluminum laminate composites. The main focus is on the interpretation of results of the following dynamic experiments conducted at different strain and strain rates: drop weight tests, explosively expanded ring experiments, and explosively collapsed thick walled cylinder experiments. Due to the natural limitations in the evaluation of the mesoscale behavior of these materials experimentally and the large variation in the size scales between the mesostructural level and the sample, it is extremely difficult, if not impossible, to examine the mesoscale behavior in situ. Therefore, numerical simulations of the corresponding experiments are used as the main tool to explore material behavior at the mesoscale. Numerical models were developed to elucidate the mechanisms of plastic strain accommodation and post critical behavior in these heterogeneous composites subjected to dynamic loading. These simulations were able to reproduce the qualitative and quantitative features that were observable in the experiments and provided insight into the evolution of the mechanisms of plastic strain accommodation and post critical behavior in these materials with complex mesotructure. Additionally, these simulations provided a framework to examine the influence of various mesoscale properties such as the bonding of interfaces, the role of material properties, and the influence of mesoscale geometry. The results of this research are helpful in the design of material mesotructures conducive to the desirable behavior under dynamic loading.

Influence of the strain path on crash properties of a crash-box structure by experimental and numerical approaches

NASA Astrophysics Data System (ADS)

Durrenberger, L.; Even, D.; Molinari, A.; Rusinek, A.

2006-08-01

In order to reduce the gas emission without decreasing the passengers safety, the UHSS (Ultra High Strength Steel) steels are more and more used in the automotive industry. The very high mechanical characteristics of these steels allow to reduce the car weight thanks to the thickness reduction of the structure parts. The aim of this study is to analyse the plastic pre-strain effect (forming) on the crash properties of a crash-box structure. In order to achieve this goal, experimental rheological tests have been performed by combining quasi-static tensile tests followed by dynamic tensile test (8.10 - 3 s - 1 ≤ dot{\\varepsilon} ≤ 1000 s - 1) for a TRIP steel produced by ARCELOR. The combination of these results allows to obtain a better understanding of the steel behaviour in dynamic loading under different strain paths. All these information are necessary for an efficient simulation of crash test by including a pertinent material response. A special attention is given to the influence of the previous forming process on the dynamical response of crash boxes.

Experimental and numerical investigation of the nonlinear dynamics of compliant mechanisms for deployable structures

NASA Astrophysics Data System (ADS)

Dewalque, Florence; Schwartz, Cédric; Denoël, Vincent; Croisier, Jean-Louis; Forthomme, Bénédicte; Brüls, Olivier

2018-02-01

This paper studies the dynamics of tape springs which are characterised by a highly geometrical nonlinear behaviour including buckling, the formation of folds and hysteresis. An experimental set-up is designed to capture these complex nonlinear phenomena. The experimental data are acquired by the means of a 3D motion analysis system combined with a synchronised force plate. Deployment tests show that the motion can be divided into three phases characterised by different types of folds, frequencies of oscillation and damping behaviours. Furthermore, the reproducibility quality of the dynamic and quasi-static results is validated by performing a large number of tests. In parallel, a nonlinear finite element model is developed. The required model parameters are identified based on simple experimental tests such as static deformed configurations and small amplitude vibration tests. In the end, the model proves to be well correlated with the experimental results in opposite sense bending, while in equal sense, both the experimental set-up and the numerical model are particularly sensitive to the initial conditions.

Design of a pulsatile flow facility to evaluate thrombogenic potential of implantable cardiac devices.

PubMed

Arjunon, Sivakkumar; Ardana, Pablo Hidalgo; Saikrishnan, Neelakantan; Madhani, Shalv; Foster, Brent; Glezer, Ari; Yoganathan, Ajit P

2015-04-01

Due to expensive nature of clinical trials, implantable cardiac devices should first be extensively characterized in vitro. Prosthetic heart valves (PHVs), an important class of these devices, have been shown to be associated with thromboembolic complications. Although various in vitro systems have been designed to quantify blood-cell damage and platelet activation caused by nonphysiological hemodynamic shear stresses in these PHVs, very few systems attempt to characterize both blood damage and fluid dynamics aspects of PHVs in the same test system. Various numerical modeling methodologies are also evolving to simulate the structural mechanics, fluid mechanics, and blood damage aspects of these devices. This article presents a completely hemocompatible small-volume test-platform that can be used for thrombogenicity studies and experimental fluid mechanics characterization. Using a programmable piston pump to drive freshly drawn human blood inside a cylindrical column, the presented system can simulate various physiological and pathophysiological conditions in testing PHVs. The system includes a modular device-mounting chamber, and in this presented case, a 23 mm St. Jude Medical (SJM) Regents® mechanical heart valve (MHV) in aortic position was used as the test device. The system was validated for its capability to quantify blood damage by measuring blood damage induced by the tester itself (using freshly drawn whole human blood). Blood damage levels were ascertained through clinically relevant assays on human blood while fluid dynamics were characterized using time-resolved particle image velocimetry (PIV) using a blood-mimicking fluid. Blood damage induced by the tester itself, assessed through Thrombin-anti-Thrombin (TAT), Prothrombin factor 1.2 (PF1.2), and hemolysis (Drabkins assay), was within clinically accepted levels. The hydrodynamic performance of the tester showed consistent, repeatable physiological pressure and flow conditions. In addition, the system contains proximity sensors to accurately capture leaflet motion during the entire cardiac cycle. The PIV results showed skewing of the leakage jet, caused by the asymmetric closing of the two leaflets. All these results are critical to characterizing the blood damage and fluid dynamics characteristics of the SJM Regents® MHV, proving the utility of this tester as a precise system for assessing the hemodynamics and thrombogenicity for various PHVs.

Equations of motion of test particles for solving the spin-dependent Boltzmann–Vlasov equation

DOE PAGES

Xia, Yin; Xu, Jun; Li, Bao-An; ...

2016-06-16

A consistent derivation of the equations of motion (EOMs) of test particles for solving the spin-dependent Boltzmann–Vlasov equation is presented. The resulting EOMs in phase space are similar to the canonical equations in Hamiltonian dynamics, and the EOM of spin is the same as that in the Heisenburg picture of quantum mechanics. Considering further the quantum nature of spin and choosing the direction of total angular momentum in heavy-ion reactions as a reference of measuring nucleon spin, the EOMs of spin-up and spin-down nucleons are given separately. The key elements affecting the spin dynamics in heavy-ion collisions are identified. Themore » resulting EOMs provide a solid foundation for using the test-particle approach in studying spin dynamics in heavy-ion collisions at intermediate energies. Future comparisons of model simulations with experimental data will help to constrain the poorly known in-medium nucleon spin–orbit coupling relevant for understanding properties of rare isotopes and their astrophysical impacts.« less

Design and test of three active flutter suppression controllers

NASA Technical Reports Server (NTRS)

Christhilf, David M.; Waszak, Martin R.; Adams, William M.; Srinathkumar, S.; Mukhopadhyay, Vivek

1991-01-01

Three flutter suppression control law design techniques are presented. Each uses multiple control surfaces and/or sensors. The first uses linear combinations of several accelerometer signals together with dynamic compensation to synthesize the modal rate of the critical mode for feedback to distributed control surfaces. The second uses traditional tools (pole/zero loci and Nyquist diagrams) to develop a good understanding of the flutter mechanism and produce a controller with minimal complexity and good robustness to plant uncertainty. The third starts with a minimum energy Linear Quadratic Gaussian controller, applies controller order reduction, and then modifies weight and noise covariance matrices to improve multi-variable robustness. The resulting designs were implemented digitally and tested subsonically on the Active Flexible Wing (AFW) wind tunnel model. Test results presented here include plant characteristics, maximum attained closed-loop dynamic pressure, and Root Mean Square control surface activity. A key result is that simultaneous symmetric and antisymmetric flutter suppression was achieved by the second control law, with a 24 percent increase in attainable dynamic pressure.

Force reflecting hand controller for manipulator teleoperation

NASA Technical Reports Server (NTRS)

Bryfogle, Mark D.

1991-01-01

A force reflecting hand controller based upon a six degree of freedom fully parallel mechanism, often termed a Stewart Platform, has been designed, constructed, and tested as an integrated system with a slave robot manipulator test bed. A force reflecting hand controller comprises a kinesthetic device capable of transmitting position and orientation commands to a slave robot manipulator while simultaneously representing the environmental interaction forces of the slave manipulator back to the operator through actuators driving the hand controller mechanism. The Stewart Platform was chosen as a novel approach to improve force reflecting teleoperation because of its inherently high ratio of load generation capability to system mass content and the correspondingly high dynamic bandwidth. An additional novelty of the program was to implement closed loop force and torque control about the hand controller mechanism by equipping the handgrip with a six degree of freedom force and torque measuring cell. The mechanical, electrical, computer, and control systems are discussed and system tests are presented.

Cavitation behavior observed in three monoleaflet mechanical heart valves under accelerated testing conditions.

PubMed

Lo, Chi-Wen; Liu, Jia-Shing; Li, Chi-Pei; Lu, Po-Chien; Hwang, Ned H

2008-01-01

Accelerated testing provides a substantial amount of data on mechanical heart valve durability in a short period of time, but such conditions may not accurately reflect in vivo performance. Cavitation, which occurs during mechanical heart valve closure when local flow field pressure decreases below vapor pressure, is thought to play a role in valve damage under accelerated conditions. The underlying flow dynamics and mechanisms behind cavitation bubble formation are poorly understood. Under physiologic conditions, random perivalvular cavitation is difficult to capture. We applied accelerated testing at a pulse rate of 600 bpm and transvalvular pressure of 120 mm Hg, with synchronized videographs and high-frequency pressure measurements, to study cavitation of the Medtronic Hall Standard (MHS), Medtronic Hall D-16 (MHD), and Omni Carbon (OC) valves. Results showed cavitation bubbles between 340 and 360 micros after leaflet/housing impact of the MHS, MHD, and OC valves, intensified by significant leaflet rebound. Squeeze flow, Venturi, and water hammer effects each contributed to cavitation, depending on valve design.

Creep Behavior of Poly(lactic acid) Based Biocomposites

PubMed Central

Morreale, Marco; Mistretta, Maria Chiara; Fiore, Vincenzo

2017-01-01

Polymer composites containing natural fibers are receiving growing attention as possible alternatives for composites containing synthetic fibers. The use of biodegradable matrices obtained from renewable sources in replacement for synthetic ones is also increasing. However, only limited information is available about the creep behavior of the obtained composites. In this work, the tensile creep behavior of PLA based composites, containing flax and jute twill weave woven fabrics, produced through compression molding, was investigated. Tensile creep tests were performed at different temperatures (i.e., 40 and 60 °C). The results showed that the creep behavior of the composites is strongly influenced by the temperature and the woven fabrics used. As preliminary characterization, quasi-static tensile tests and dynamic mechanical tests were carried out on the composites. Furthermore, fabrics (both flax and jute) were tested as received by means of quasi-static tests and creep tests to evaluate the influence of fabrics mechanical behavior on the mechanical response of the resulting composites. The morphological analysis of the fracture surface of the tensile samples showed the better fiber-matrix adhesion between PLA and jute fabric. PMID:28772755

Creep Behavior of Poly(lactic acid) Based Biocomposites.

PubMed

Morreale, Marco; Mistretta, Maria Chiara; Fiore, Vincenzo

2017-04-08

Polymer composites containing natural fibers are receiving growing attention as possible alternatives for composites containing synthetic fibers. The use of biodegradable matrices obtained from renewable sources in replacement for synthetic ones is also increasing. However, only limited information is available about the creep behavior of the obtained composites. In this work, the tensile creep behavior of PLA based composites, containing flax and jute twill weave woven fabrics, produced through compression molding, was investigated. Tensile creep tests were performed at different temperatures (i.e., 40 and 60 °C). The results showed that the creep behavior of the composites is strongly influenced by the temperature and the woven fabrics used. As preliminary characterization, quasi-static tensile tests and dynamic mechanical tests were carried out on the composites. Furthermore, fabrics (both flax and jute) were tested as received by means of quasi-static tests and creep tests to evaluate the influence of fabrics mechanical behavior on the mechanical response of the resulting composites. The morphological analysis of the fracture surface of the tensile samples showed the better fiber-matrix adhesion between PLA and jute fabric.

Hydrocarbon-fuel/combustion-chamber-liner materials compatibility

NASA Technical Reports Server (NTRS)

Gage, Mark L.

1990-01-01

Results of material compatibility experiments using hydrocarbon fuels in contact with copper-based combustion chamber liner materials are presented. Mil-Spec RP-1, n- dodecane, propane, and methane fuels were tested in contact with OFHC, NASA-Z, and ZrCu coppers. Two distinct test methods were employed. Static tests, in which copper coupons were exposed to fuel for long durations at constant temperature and pressure, provided compatibility data in a precisely controlled environment. Dynamic tests, using the Aerojet Carbothermal Test Facility, provided fuel and copper compatibility data under realistic booster engine service conditions. Tests were conducted using very pure grades of each fuel and fuels to which a contaminant, e.g., ethylene or methyl mercaptan, was added to define the role played by fuel impurities. Conclusions are reached as to degradation mechanisms and effects, methods for the elimination of these mechanisms, selection of copper alloy combustion chamber liners, and hydrocarbon fuel purchase specifications.

Microstructure evolution and dynamic recrystallization behavior of a powder metallurgy Ti-22Al-25Nb alloy during hot compression

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jia, Jianbo

The flow behavior of a powder metallurgy (P/M) Ti-22Al-25Nb alloy during hot compression tests has been investigated at a strain rate of 0.01 s{sup −1} and a temperature range of 980–1100 °C up to various true strains from 0.1 to 0.9. The effects of deformation temperature and strain on microstructure characterization and nucleation mechanisms of dynamic recrystallization (DRX) were assessed by means of Optical microscope (OM), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) techniques, respectively. The results indicated that the process of DRX was promoted by increasing deformation temperature and strain. By regression analysis, a power exponent relationshipmore » between peak stresses and sizes of stable DRX grains was developed. In addition, it is suggested that the discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) controlled nucleation mechanisms for DRX grains operated simultaneously during the whole hot process, and which played the leading role varied with hot process parameters of temperature and strain. It was further demonstrated that the CDRX featured by progressive subgrain rotation was weakened by elevating deformation temperatures. - Highlights: •Flow behavior of a P/M Ti-22Al-25Nb is studied by hot compression tests. •Microstructure evolution of alloy is affected by deformation temperature and strain. •The relationship between peak stress and stable DRX grain size was developed. •The process of DRX was promoted by increasing deformation temperature and strain. •Nucleation mechanisms of DRX were identified by EBSD analysis and TEM observation.« less

Subsonic Ultra Green Aircraft Research: Phase II- Volume III-Truss Braced Wing Aeroelastic Test Report

NASA Technical Reports Server (NTRS)

Bradley, Marty K.; Allen, Timothy J.; Droney, Christopher

2014-01-01

This Test Report summarizes the Truss Braced Wing (TBW) Aeroelastic Test (Task 3.1) work accomplished by the Boeing Subsonic Ultra Green Aircraft Research (SUGAR) team, which includes the time period of February 2012 through June 2014. The team consisted of Boeing Research and Technology, Boeing Commercial Airplanes, Virginia Tech, and NextGen Aeronautics. The model was fabricated by NextGen Aeronautics and designed to meet dynamically scaled requirements from the sized full scale TBW FEM. The test of the dynamically scaled SUGAR TBW half model was broken up into open loop testing in December 2013 and closed loop testing from January 2014 to April 2014. Results showed the flutter mechanism to primarily be a coalescence of 2nd bending mode and 1st torsion mode around 10 Hz, as predicted by analysis. Results also showed significant change in flutter speed as angle of attack was varied. This nonlinear behavior can be explained by including preload and large displacement changes to the structural stiffness and mass matrices in the flutter analysis. Control laws derived from both test system ID and FEM19 state space models were successful in suppressing flutter. The control laws were robust and suppressed flutter for a variety of Mach, dynamic pressures, and angle of attacks investigated.

Characterization of structural connections using free and forced response test data

NASA Technical Reports Server (NTRS)

Lawrence, Charles; Huckelbridge, Arthur A.

1989-01-01

The accurate prediction of system dynamic response often has been limited by deficiencies in existing capabilities to characterize connections adequately. Connections between structural components often are complex mechanically, and difficult to accurately model analytically. Improved analytical models for connections are needed to improve system dynamic preditions. A procedure for identifying physical connection properties from free and forced response test data is developed, then verified utilizing a system having both a linear and nonlinear connection. Connection properties are computed in terms of physical parameters so that the physical characteristics of the connections can better be understood, in addition to providing improved input for the system model. The identification procedure is applicable to multi-degree of freedom systems, and does not require that the test data be measured directly at the connection locations.

Modeling and Simulation of Nanoindentation

NASA Astrophysics Data System (ADS)

Huang, Sixie; Zhou, Caizhi

2017-11-01

Nanoindentation is a hardness test method applied to small volumes of material which can provide some unique effects and spark many related research activities. To fully understand the phenomena observed during nanoindentation tests, modeling and simulation methods have been developed to predict the mechanical response of materials during nanoindentation. However, challenges remain with those computational approaches, because of their length scale, predictive capability, and accuracy. This article reviews recent progress and challenges for modeling and simulation of nanoindentation, including an overview of molecular dynamics, the quasicontinuum method, discrete dislocation dynamics, and the crystal plasticity finite element method, and discusses how to integrate multiscale modeling approaches seamlessly with experimental studies to understand the length-scale effects and microstructure evolution during nanoindentation tests, creating a unique opportunity to establish new calibration procedures for the nanoindentation technique.

Development and Testing of a ``Backlash-Free'' Gas-Tight High Precision Sample Handling Mechanism for Combined Science on the ExoMars 2018 Rover

NASA Astrophysics Data System (ADS)

Paul, R.; Redlich, D.; Richter, L.; Zuknik, K.-H.; Muhlbauer, Q.; Thiel, M.; Fowler, L.; Tattusch, T.; Weisz, H.; Musso, F.; Durrant, S.

2015-09-01

This paper presents the development and testing by the OHB System AG of the Powdered Sample Handling Mechanism (PSHS) that is part of the rover of the European Space Agency 2018 ExoMars Mission, a cooperative mission with Roscosmos including a scientific instrument contribution from NASA. The task of this mechanism is to flatten and position powdered Martian soil samples allowing subsequent investigation of selected grains by different optical instruments thus providing combined science in an ultra-clean environment.The exceptional sensitivity of these instruments causes extremely challenging requirements with respect to positioning performance as well as cleanliness and contamination control. The impact of these design drivers is highlighted focusing on specific mechanism features such as the pre-torque device to minimize the backlash and the dynamic feed-through, allowing a gas-tight encapsulation of an ultra-clean zone free of drive-train components.Subsequently the results of the test campaign of an elegant breadboard under Mars-like conditions, as well as first QM test results are described. Furthermore the outcomes of combined tests with an optical instrument are reported.

Testing the effects of adolescent alcohol use on adult conflict-related theta dynamics.

PubMed

Harper, Jeremy; Malone, Stephen M; Iacono, William G

2017-11-01

Adolescent alcohol use (AAU) is associated with brain anomalies, but less is known about long-term neurocognitive effects. Despite theoretical models linking AAU to diminished cognitive control, empirical work testing this relationship with specific cognitive control neural correlates (e.g., prefrontal theta-band EEG dynamics) remains scarce. A longitudinal twin design was used to test the hypothesis that greater AAU is associated with reduced conflict-related EEG theta-band dynamics in adulthood, and to examine the genetic/environmental etiology of this association. In a large (N=718) population-based prospective twin sample, AAU was assessed at ages 11/14/17. Twins completed a flanker task at age 29 to elicit EEG theta-band medial frontal cortex (MFC) power and medial-dorsal prefrontal cortex (MFC-dPFC) connectivity. Two complementary analytic methods (cotwin control analysis; biometric modeling) were used to disentangle the genetic/shared environmental risk towards AAU from possible alcohol exposure effects on theta dynamics. AAU was negatively associated with adult cognitive control-related theta-band MFC power and MFC-dPFC functional connectivity. Genetic influences primarily underlie these associations. Findings provide strong evidence that genetic factors underlie the comorbidity between AAU and diminished cognitive control-related theta dynamics in adulthood. Conflict-related theta-band dynamics appear to be candidate brain-based endophenotypes/mechanisms for AAU. Copyright © 2017 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.

Nonlinear elasticity in rocks: A comprehensive three-dimensional description

DOE PAGES

Lott, Martin; Remillieux, Marcel; Garnier, Vincent; ...

2017-07-17

Here we study theoretically and experimentally the mechanisms of nonlinear and nonequilibrium dynamics in geomaterials through dynamic acoustoelasticity testing. In the proposed theoretical formulation, the classical theory of nonlinear elasticity is extended to include the effects of conditioning. This formulation is adapted to the context of dynamic acoustoelasticity testing in which a low-frequency “pump” wave induces a strain field in the sample and modulates the propagation of a high-frequency “probe” wave. Experiments are conducted to validate the formulation in a long thin bar of Berea sandstone. Several configurations of the pump and probe are examined: the pump successively consists ofmore » the first longitudinal and first torsional mode of vibration of the sample while the probe is successively based on (pressure) $P$ and (shear) $S$ waves. The theoretical predictions reproduce many features of the elastic response observed experimentally, in particular, the coupling between nonlinear and nonequilibrium dynamics and the three-dimensional effects resulting from the tensorial nature of elasticity.« less

Verification of a 2 kWe Closed-Brayton-Cycle Power Conversion System Mechanical Dynamics Model

NASA Technical Reports Server (NTRS)

Ludwiczak, Damian R.; Le, Dzu K.; McNelis, Anne M.; Yu, Albert C.; Samorezov, Sergey; Hervol, Dave S.

2005-01-01

Vibration test data from an operating 2 kWe closed-Brayton-cycle (CBC) power conversion system (PCS) located at the NASA Glenn Research Center was used for a comparison with a dynamic disturbance model of the same unit. This effort was performed to show that a dynamic disturbance model of a CBC PCS can be developed that can accurately predict the torque and vibration disturbance fields of such class of rotating machinery. The ability to accurately predict these disturbance fields is required before such hardware can be confidently integrated onto a spacecraft mission. Accurate predictions of CBC disturbance fields will be used for spacecraft control/structure interaction analyses and for understanding the vibration disturbances affecting the scientific instrumentation onboard. This paper discusses how test cell data measurements for the 2 kWe CBC PCS were obtained, the development of a dynamic disturbance model used to predict the transient torque and steady state vibration fields of the same unit, and a comparison of the two sets of data.

In-vitro development of a temporal abutment screw to protect osseointegration in immediate loaded implants.

PubMed

García-Roncero, Herminio; Caballé-Serrano, Jordi; Cano-Batalla, Jordi; Cabratosa-Termes, Josep; Figueras-Álvarez, Oscar

2015-04-01

In this study, a temporal abutment fixation screw, designed to fracture in a controlled way upon application of an occlusal force sufficient to produce critical micromotion was developed. The purpose of the screw was to protect the osseointegration of immediate loaded single implants. Seven different screw prototypes were examined by fixing titanium abutments to 112 Mozo-Grau external hexagon implants (MG Osseous®; Mozo-Grau, S.A., Valladolid, Spain). Fracture strength was tested at 30° in two subgroups per screw: one under dynamic loading and the other without prior dynamic loading. Dynamic loading was performed in a single-axis chewing simulator using 150,000 load cycles at 50 N. After normal distribution of obtained data was verified by Kolmogorov-Smirnov test, fracture resistance between samples submitted and not submitted to dynamic loading was compared by the use of Student's t-test. Comparison of fracture resistance among different screw designs was performed by the use of one-way analysis of variance. Confidence interval was set at 95%. Fractures occurred in all screws, allowing easy retrieval. Screw Prototypes 2, 5 and 6 failed during dynamic loading and exhibited statistically significant differences from the other prototypes. Prototypes 2, 5 and 6 may offer a useful protective mechanism during occlusal overload in immediate loaded implants.

Fluid Dynamic Characterization of a Polymeric Heart Valve Prototype (Poli-Valve) tested under Continuous and Pulsatile Flow Conditions

PubMed Central

De Gaetano, Francesco; Serrani, Marta; Bagnoli, Paola; Brubert, Jacob; Stasiak, Joanna; Moggridge, Geoff D.; Costantino, Maria Laura

2016-01-01

Introduction Only mechanical and biological heart valve prostheses are currently commercially available. The former show longer durability but require anticoagulant therapy, the latter display better fluid dynamic behaviour but do not have adequate durability. New Polymeric Heart Valves (PHVs) could potentially combine the haemodynamic properties of biological valves with the durability of mechanical valves. This work presents a hydrodynamic evaluation of two groups of newly developed supra-annular tri-leaflet prosthetic heart valves made from styrenic block copolymers (SBC): Poli-Valves. Methods Two types of Poli-Valves made of SBC differing in polystyrene fraction content were tested under continuous and pulsatile flow conditions as prescribed by ISO 5840 Standard. An ad - hoc designed pulse duplicator allowed the valve prototypes to be tested at different flow rates and frequencies. Pressure and flow were recorded; pressure drops, effective orifice area (EOA), and regurgitant volume were computed to assess the valve’s behaviour. Results Both types Poli-Valves met the minimum requirements in terms of regurgitation and EOA as specified by ISO 5840 Standard. Results were compared with five mechanical heart valves (MHVs) and five tissue heart valves (THVs), currently available on the market. Conclusion Based on these results, polymeric heart valves based on styrenic block copolymers, as Poli-Valves are, can be considered as promising alternative for heart valve replacement in near future. PMID:26689146

Fluid dynamic characterization of a polymeric heart valve prototype (Poli-Valve) tested under continuous and pulsatile flow conditions.

PubMed

De Gaetano, Francesco; Serrani, Marta; Bagnoli, Paola; Brubert, Jacob; Stasiak, Joanna; Moggridge, Geoff D; Costantino, Maria Laura

2015-11-01

Only mechanical and biological heart valve prostheses are currently commercially available. The former show longer durability but require anticoagulant therapy; the latter display better fluid dynamic behavior but do not have adequate durability. New Polymeric Heart Valves (PHVs) could potentially combine the hemodynamic properties of biological valves with the durability of mechanical valves. This work presents a hydrodynamic evaluation of 2 groups of newly developed supra-annular, trileaflet prosthetic heart valves made from styrenic block copolymers (SBC): Poli-Valves. 2 types of Poli-Valves made of SBC and differing in polystyrene fraction content were tested under continuous and pulsatile flow conditions as prescribed by ISO 5840 Standard. A pulse duplicator designed ad hoc allowed the valve prototypes to be tested at different flow rates and frequencies. Pressure and flow were recorded; pressure drops, effective orifice area (EOA), and regurgitant volume were computed to assess the behavior of the valve. Both types of Poli-Valves met the minimum requirements in terms of regurgitation and EOA as specified by the ISO 5840 Standard. Results were compared with 5 mechanical heart valves (MHVs) and 5 tissue heart valves (THVs), currently available on the market. Based on these results, PHVs based on styrenic block copolymers, as are Poli-Valves, can be considered a promising alternative for heart valve replacement in the near future.

Contact dynamics math model

NASA Technical Reports Server (NTRS)

Glaese, John R.; Tobbe, Patrick A.

1986-01-01

The Space Station Mechanism Test Bed consists of a hydraulically driven, computer controlled six degree of freedom (DOF) motion system with which docking, berthing, and other mechanisms can be evaluated. Measured contact forces and moments are provided to the simulation host computer to enable representation of orbital contact dynamics. This report describes the development of a generalized math model which represents the relative motion between two rigid orbiting vehicles. The model allows motion in six DOF for each body, with no vehicle size limitation. The rotational and translational equations of motion are derived. The method used to transform the forces and moments from the sensor location to the vehicles' centers of mass is also explained. Two math models of docking mechanisms, a simple translational spring and the Remote Manipulator System end effector, are presented along with simulation results. The translational spring model is used in an attempt to verify the simulation with compensated hardware in the loop results.

A unified design space of synthetic stripe-forming networks

PubMed Central

Schaerli, Yolanda; Munteanu, Andreea; Gili, Magüi; Cotterell, James; Sharpe, James; Isalan, Mark

2014-01-01

Synthetic biology is a promising tool to study the function and properties of gene regulatory networks. Gene circuits with predefined behaviours have been successfully built and modelled, but largely on a case-by-case basis. Here we go beyond individual networks and explore both computationally and synthetically the design space of possible dynamical mechanisms for 3-node stripe-forming networks. First, we computationally test every possible 3-node network for stripe formation in a morphogen gradient. We discover four different dynamical mechanisms to form a stripe and identify the minimal network of each group. Next, with the help of newly established engineering criteria we build these four networks synthetically and show that they indeed operate with four fundamentally distinct mechanisms. Finally, this close match between theory and experiment allows us to infer and subsequently build a 2-node network that represents the archetype of the explored design space. PMID:25247316

Chemical and Thermal Analysis

NASA Technical Reports Server (NTRS)

Bulluck, J. W.; Rushing, R. A.

1995-01-01

During the past six months we have conducted significant research in several domains in order to clarify and understanding the aging and chemical failure mechanism of thermoplastics (PVDF or Tefzel) for pipes. We organized numerous analytical studies with methods including Fourier Transform Infrared Spectroscopy, Dynamic Mechanical Analysis, Differential Scanning Calorimetry, and Stress Relaxation experiments. In addition we have reanalyzed previous thermogravimetric data concerning the rate of deplasticization of Coflon pipe. We investigated a number of aged samples of both Tefzel and Coflon that were forwarded from MERL. We conducted stress relaxation experiments of Coflon pipe at several temperatures and determined an activation energy. We also examined the dynamic mechanical response PVDF during deplasticization and during methanol plasticization. We performed numerous DSC analyses to research the changing crystalline morphology. We have noted significant changes in crystallinity upon aging for both PVDF and Tefzel. Little variation in elemental composition was noted for many of the aged Coflon and Tefzel samples tested.

Physicochemical, mechanical and thermal properties of chitosan films with and without sorbitol.

PubMed

Liu, Mei; Zhou, Yibin; Zhang, Yang; Yu, Chen; Cao, Shengnan

2014-09-01

The effect of sorbitol on the physicochemical, mechanical and thermal properties of chitosan films with different degrees of deacetylation (DD; i.e., DD85% and DD95%) was investigated. The thickness, moisture content (MC), water solubility (WS) and water-vapor permeability (WVP) of the films were evaluated. Sorbitol addition reduced MC, increased WS and significantly (p<0.01) reduced WVP of both film types. DD95% films had lower MC and WVP, and higher WS than DD85% films. Static (thermomechanical analysis) and dynamic (dynamic mechanical analysis) tests indicated that sorbitol increased the strain and decreased stress for both DD films, but DD95% could sustain higher strain and DD85% could sustain higher stress. Thermogravimetrics analysis and differential scanning calorimetry showed that sorbitol elicited a lower degradation temperature for both films, and that DD95% films exhibited higher thermal stability than DD85% films. Copyright © 2014 Elsevier B.V. All rights reserved.

Characterization of vibration transfer paths in nose gearboxes of an AH-64 Apache

NASA Astrophysics Data System (ADS)

Islam, A. K. M. Anwarul; Dempsey, Paula J.; Feldman, Jason; Larsen, Chris

2014-03-01

Health monitoring of rotorcraft components, which is currently being performed by Health and Usage Monitoring Systems (HUMS) through analyzing vibration signatures of dynamic mechanical components, is very important for their safe and economic operation. Vibration diagnostic algorithms in HUMS analyze vibration signatures associated with faults and quantify them as condition indicators (CI) to predict component behavior. Vibration transfer paths (VTP) play important roles in CI response and are characterized by frequency response functions (FRF) derived from vibration signatures of dynamic mechanical components of a helicopter. With an objective to investigate the difference in VTP of a component in a helicopter and test stand, and to relate that to the CI response, VTP measurements were recorded from 0-50 kHz under similar conditions in the left and right nose gearboxes (NGBs) of an AH-64 Apache and an isolated left NGB in a test stand at NASA Glenn Research Center. The test fixture enabled the application of measured torques - common during an actual operation. Commercial and lab piezo shakers, and an impact hammer were used in both systems to collect the vibration response using two types of commercially available accelerometers under various test conditions. The FRFs of both systems were found to be consistent, and certain real-world installation and maintenance issues, such as sensor alignments, locations and installation torques, had minimal effect on the VTP. However, gear vibration transfer path dynamics appeared to be somewhat dependent on presence of oil, and the lightly-damped ring gear produced sharp and closer transfer path resonances.

Incorporating Vibration Test Results for the Advanced Stirling Convertor into the System Dynamic Model

NASA Technical Reports Server (NTRS)

Meer, David W.; Lewandowski, Edward J.

2010-01-01

The U.S. Department of Energy (DOE), Lockheed Martin Corporation (LM), and NASA Glenn Research Center (GRC) have been developing the Advanced Stirling Radioisotope Generator (ASRG) for use as a power system for space science missions. As part of the extended operation testing of this power system, the Advanced Stirling Convertors (ASC) at NASA GRC undergo a vibration test sequence intended to simulate the vibration history that an ASC would experience when used in an ASRG for a space mission. During these tests, a data system collects several performance-related parameters from the convertor under test for health monitoring and analysis. Recently, an additional sensor recorded the slip table position during vibration testing to qualification level. The System Dynamic Model (SDM) integrates Stirling cycle thermodynamics, heat flow, mechanical mass, spring, damper systems, and electrical characteristics of the linear alternator and controller. This Paper presents a comparison of the performance of the ASC when exposed to vibration to that predicted by the SDM when exposed to the same vibration.

Identifying and correcting non-Markov states in peptide conformational dynamics

NASA Astrophysics Data System (ADS)

Nerukh, Dmitry; Jensen, Christian H.; Glen, Robert C.

2010-02-01

Conformational transitions in proteins define their biological activity and can be investigated in detail using the Markov state model. The fundamental assumption on the transitions between the states, their Markov property, is critical in this framework. We test this assumption by analyzing the transitions obtained directly from the dynamics of a molecular dynamics simulated peptide valine-proline-alanine-leucine and states defined phenomenologically using clustering in dihedral space. We find that the transitions are Markovian at the time scale of ≈50 ps and longer. However, at the time scale of 30-40 ps the dynamics loses its Markov property. Our methodology reveals the mechanism that leads to non-Markov behavior. It also provides a way of regrouping the conformations into new states that now possess the required Markov property of their dynamics.

Recycling of asbestos tailings used as reinforcing fillers in polypropylene based composites.

PubMed

Zhai, Wensi; Wang, Yao; Deng, Yuan; Gao, Hongli; Lin, Zhen; Li, Mao

2014-04-15

In this work, asbestos tailings were recycled and used as reinforcing fillers to enhance the mechanical properties of polypropylene (PP). A silane coupling agent was used to chemically modify the asbestos tailings to increase the compatibility between asbestos tailings and polypropylene matrix. Both raw and chemically treated asbestos tailings with different loading levels (from 3 to 30 wt%) were utilized to fabricate composites. Mechanical properties of these composites have been investigated by dynamic mechanical analysis, tensile test and notched impact test. Results showed that hybridization of asbestos tailings in the composites enhanced the mechanical properties of neat PP evidently, and treated asbestos tailings/PP composites yielded even better mechanical properties compared with those of raw asbestos tailings/PP composites. This recycling method of asbestos tailings not only reduces disposal costs and avoids secondary pollution but also produces a new PP-based composite material with enhanced mechanical properties. Copyright © 2014 Elsevier B.V. All rights reserved.

Constitutive modeling of polycarbonate over a wide range of strain rates and temperatures

NASA Astrophysics Data System (ADS)

Wang, Haitao; Zhou, Huamin; Huang, Zhigao; Zhang, Yun; Zhao, Xiaoxuan

2017-02-01

The mechanical behavior of polycarbonate was experimentally investigated over a wide range of strain rates (10^{-4} to 5× 103 s^{-1}) and temperatures (293 to 353 K). Compression tests under these conditions were performed using a SHIMADZU universal testing machine and a split Hopkinson pressure bar. Falling weight impact testing was carried out on an Instron Dynatup 9200 drop tower system. The rate- and temperature-dependent deformation behavior of polycarbonate was discussed in detail. Dynamic mechanical analysis (DMA) tests were utilized to observe the glass (α ) transition and the secondary (β ) transition of polycarbonate. The DMA results indicate that the α and β transitions have a dramatic influence on the mechanical behavior of polycarbonate. The decompose/shift/reconstruct (DSR) method was utilized to decompose the storage modulus into the α and β components and extrapolate the entire modulus, the α-component modulus and the β-component modulus. Based on three previous models, namely, Mulliken-Boyce, G'Sell-Jonas and DSGZ, an adiabatic model is proposed to predict the mechanical behavior of polycarbonate. The model considers the contributions of both the α and β transitions to the mechanical behavior, and it has been implemented in ABAQUS/Explicit through a user material subroutine VUMAT. The model predictions are proven to essentially coincide with the experimental results during compression testing and falling weight impact testing.

Measurement of the mechanical properties of car body sheet steels at high strain rates and non ambient temperature

NASA Astrophysics Data System (ADS)

Bleck, W.; Larour, P.

2003-09-01

Crash behaviour and light weight have become the major design criteria for car bodies. Modem high strength steels offer appropriate solutions for these requirements. The prediction of the crash behaviour in simulation programs requires the information on materials behaviour during dynamic testing. The reduction of the signal waviness and the inertia effects at strain rates above 50s^{-1} are major issues in dynamic tensile testing. Damping techniques or load measurement on the sample itself are the common way to reduce oscillations. Strain measurement from the piston displacement or from optical devices on the specimen itself are also compared. Advantages and drawbacks of those various measurement techniques are presented.

Toward a comprehensive model of antisocial development: a dynamic systems approach.

PubMed

Granic, Isabela; Patterson, Gerald R

2006-01-01

The purpose of this article is to develop a preliminary comprehensive model of antisocial development based on dynamic systems principles. The model is built on the foundations of behavioral research on coercion theory. First, the authors focus on the principles of multistability, feedback, and nonlinear causality to reconceptualize real-time parent-child and peer processes. Second, they model the mechanisms by which these real-time processes give rise to negative developmental outcomes, which in turn feed back to determine real-time interactions. Third, they examine mechanisms of change and stability in early- and late-onset antisocial trajectories. Finally, novel clinical designs and predictions are introduced. The authors highlight new predictions and present studies that have tested aspects of the model

Comment on “The reduction of friction in long-runout landslides as an emergent phenomenon” by Brandon C. Johnson et al.

USGS Publications Warehouse

Iverson, Richard M.

2016-01-01

Results from a highly idealized, 2-D computational model indicate that dynamic normal-stress rarefactions might cause friction reduction in long-runout landslides, but the physical relevance of the idealized dynamics has not been confirmed by experimental tests. More importantly, the model results provide no evidence that refutes alternative hypotheses about friction reduction mechanisms. One alternative hypothesis, which is strongly supported by field evidence, experimental data, and the predictions of a well-constrained computational model, involves development of high pore fluid pressures in deforming landslide material or overridden bed material. However, no scientific basis exists for concluding that a universal mechanism is responsible for friction reduction in all long-runout landslides.

Screening in perturbative approaches to LSS

DOE PAGES

Fasiello, Matteo; Vlah, Zvonimir

2017-08-24

A specific value for the cosmological constant Λ can account for late-time cosmic acceleration. However, motivated by the so-called cosmological constant problem(s), several alternative mechanisms have been explored. To date, a host of well-studied dynamical dark energy and modified gravity models exists. Going beyond ΛCDM often comes with additional degrees of freedom (dofs). For these to pass existing observational tests, an efficient screening mechanism must be in place. Furthermore, the linear and quasi-linear regimes of structure formation are ideal probes of such dofs and can capture the onset of screening. We propose here a semi-phenomenological “filter” to account for screeningmore » dynamics on LSS observables, with special emphasis on Vainshtein-type screening.« less

Effects of tritium gas exposure on the dynamic mechanical properties of EPDM elastomer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clark, E. A.; Staack, G. C.

2008-07-15

Samples of ethylene propylene diene monomer (EPDM) elastomer were exposed to tritium gas in closed containers at 101 kPa (1 atmosphere) pressure and ambient temperature for about one week. Tritium exposure effects on the samples were characterized by dynamic mechanical analysis (DMA) and radiolysis products were characterized by measuring the total final pressure and composition in the exposure containers at the end of exposure period. There was no effect of one week tritium exposure on the glass transition temperature, Tg, of the samples tested. Impurity gases produced in the closed containers included HT and lesser amounts of H{sub 2}, DTO,more » and CT{sub 4}. The total pressure remained the same during exposure. (authors)« less

EFFECTS OF TRITIUM GAS EXPOSURE ON THE DYNAMIC MECHANICAL PROPERTIES OF EPDM ELASTOMER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clark, E; Gregory Staack, G

2007-08-13

Samples of ethylene propylene diene monomer (EPDM) elastomer were exposed to tritium gas in closed containers initially at 101 kPa (1 atmosphere) pressure and ambient temperature for about one week. Tritium exposure effects on the samples were characterized by dynamic mechanical analysis (DMA) and radiolysis products were characterized by measuring the total final pressure and composition in the exposure containers at the end of exposure period. There was no effect of one week tritium exposure on the glass transition temperature, Tg, of the samples tested. Impurity gases produced in the closed containers included HT and lesser amounts of H{sub 2},more » DTO, and CT{sub 4}. The total pressure remained the same during exposure.« less

High strain rate behavior of saturated and non-saturated sandstone: implications for earthquake mechanisms.

NASA Astrophysics Data System (ADS)

Aben, F. M.; Doan, M. L.; Gratier, J. P.; Renard, F.

2015-12-01

Damage zones of active faults control their resistance to rupture and transport properties. Hence, knowing the damage's origin is crucial to shed light on the (paleo)seismic behavior of the fault. Coseismic damage in the damage zone occurs by stress-wave loading of a passing earthquake rupture tip, resulting in dynamic (high strain rate) loading and subsequent dynamic fracturing or pulverization. Recently, interest in this type of damage has increased and several experimental studies were performed on dry rock specimens to search for pulverization-controlling parameters. However, the influence of fluids in during dynamic loading needs to be constrained. Hence, we have performed compressional dynamic loading experiments on water saturated and oven dried Vosges sandstone samples using a Split Hopkinson Pressure Bar apparatus. Due to the high porosity in these rocks, close to 20%, the effect of fluids should be clear. Afterwards, microstructural analyses have been applied on thin sections. Water saturated samples reveal dynamic mechanical behavior that follows linear poro-elasticity for undrained conditions: the peak strength of the sample decreases by 30-50% and the accumulated strain increases relative to the dry samples that were tested under similar conditions. The mechanical behavior of partially saturated samples falls in between. Microstructural studies on thin section show that fractures are restricted to some quartz grains while other quartz grains remain intact, similar to co-seismically damaged sandstones observed in the field. Most deformation is accommodated by inter-granular processes, thereby appointing an important role to the cement matrix in between grains. Intra-granular fracture damage is highest for the saturated samples. The presence of pore fluids in the rocks lower the dynamic peak strength, especially since fast dynamic loading does not allow for time-dependent fluid dissipation. Thus, fluid-saturated rocks would show undrained mechanical behavior, creating local overpressure in the pore that breaks the inter-granular cement. This strength-decreasing effect provides an explanation for the presence of pulverized and coseismically damaged rocks at depth and extends the range of dynamic stress where dynamic damage can occur in fault zones.

Alternating air-medium exposure in rotating bioreactors optimizes cell metabolism in 3D novel tubular scaffold polyurethane foams.

PubMed

Tresoldi, Claudia; Stefani, Ilaria; Ferracci, Gaia; Bertoldi, Serena; Pellegata, Alessandro F; Farè, Silvia; Mantero, Sara

2017-04-26

In vitro dynamic culture conditions play a pivotal role in developing engineered tissue grafts, where the supply of oxygen and nutrients, and waste removal must be permitted within construct thickness. For tubular scaffolds, mass transfer is enhanced by introducing a convective flow through rotating bioreactors with positive effects on cell proliferation, scaffold colonization and extracellular matrix deposition. We characterized a novel polyurethane-based tubular scaffold and investigated the impact of 3 different culture configurations over cell behavior: dynamic (i) single-phase (medium) rotation and (ii) double-phase exposure (medium-air) rotation; static (iii) single-phase static culture as control. A new mixture of polyol was tested to create polyurethane foams (PUFs) as 3D scaffold for tissue engineering. The structure obtained was morphologically and mechanically analyzed tested. Murine fibroblasts were externally seeded on the novel porous PUF scaffold, and cultured under different dynamic conditions. Viability assay, DNA quantification, SEM and histological analyses were performed at different time points. The PUF scaffold presented interesting mechanical properties and morphology adequate to promote cell adhesion, highlighting its potential for tissue engineering purposes. Results showed that constructs under dynamic conditions contain enhanced viability and cell number, exponentially increased for double-phase rotation; under this last configuration, cells uniformly covered both the external surface and the lumen. The developed 3D structure combined with the alternated exposure to air and medium provided the optimal in vitro biochemical conditioning with adequate nutrient supply for cells. The results highlight a valuable combination of material and dynamic culture for tissue engineering applications.

Dynamic self-cleaning in gecko setae via digital hyperextension

PubMed Central

Hu, Shihao; Lopez, Stephanie; Niewiarowski, Peter H.; Xia, Zhenhai

2012-01-01

Gecko toe pads show strong adhesion on various surfaces yet remain remarkably clean around everyday contaminants. An understanding of how geckos clean their toe pads while being in motion is essential for the elucidation of animal behaviours as well as the design of biomimetic devices with optimal performance. Here, we test the self-cleaning of geckos during locomotion. We provide, to our knowledge, the first evidence that geckos clean their feet through a unique dynamic self-cleaning mechanism via digital hyperextension. When walking naturally with hyperextension, geckos shed dirt from their toes twice as fast as they would if walking without hyperextension, returning their feet to nearly 80 per cent of their original stickiness in only four steps. Our dynamic model predicts that when setae suddenly release from the attached substrate, they generate enough inertial force to dislodge dirt particles from the attached spatulae. The predicted cleaning force on dirt particles significantly increases when the dynamic effect is included. The extraordinary design of gecko toe pads perfectly combines dynamic self-cleaning with repeated attachment/detachment, making gecko feet sticky yet clean. This work thus provides a new mechanism to be considered for biomimetic design of highly reuseable and reliable dry adhesives and devices. PMID:22696482

Dynamic adaptive chemistry for turbulent flame simulations

NASA Astrophysics Data System (ADS)

Yang, Hongtao; Ren, Zhuyin; Lu, Tianfeng; Goldin, Graham M.

2013-02-01

The use of large chemical mechanisms in flame simulations is computationally expensive due to the large number of chemical species and the wide range of chemical time scales involved. This study investigates the use of dynamic adaptive chemistry (DAC) for efficient chemistry calculations in turbulent flame simulations. DAC is achieved through the directed relation graph (DRG) method, which is invoked for each computational fluid dynamics cell/particle to obtain a small skeletal mechanism that is valid for the local thermochemical condition. Consequently, during reaction fractional steps, one needs to solve a smaller set of ordinary differential equations governing chemical kinetics. Test calculations are performed in a partially-stirred reactor (PaSR) involving both methane/air premixed and non-premixed combustion with chemistry described by the 53-species GRI-Mech 3.0 mechanism and the 129-species USC-Mech II mechanism augmented with recently updated NO x pathways, respectively. Results show that, in the DAC approach, the DRG reduction threshold effectively controls the incurred errors in the predicted temperature and species concentrations. The computational saving achieved by DAC increases with the size of chemical kinetic mechanisms. For the PaSR simulations, DAC achieves a speedup factor of up to three for GRI-Mech 3.0 and up to six for USC-Mech II in simulation time, while at the same time maintaining good accuracy in temperature and species concentration predictions.

An experimental test of well-described vegetation patterns across slope aspects using woodland herb transplants and manipulated abiotic drivers

Treesearch

Robert J. Warren

2010-01-01

• The ubiquitous transition of plant communities across slope aspects is a welldescribed, but rarely tested, ecological dynamic. Aspect position is often used as a proxy for microclimate changes in moisture, light and temperature, but these abiotic drivers are seldom decoupled and very rarely manipulated across slope aspects. • To investigate the mechanisms...

Study Modules for Calculus-Based General Physics. [Includes Modules 11-14: Collisions; Equilibrium of Rigid Bodies; Rotational Dynamics; and Fluid Mechanics].

ERIC Educational Resources Information Center

Fuller, Robert G., Ed.; And Others

This is part of a series of 42 Calculus Based Physics (CBP) modules totaling about 1,000 pages. The modules include study guides, practice tests, and mastery tests for a full-year individualized course in calculus-based physics based on the Personalized System of Instruction (PSI). The units are not intended to be used without outside materials;…

Chemo-physical properties of renal capsules under ultraviolet-c exposure

NASA Astrophysics Data System (ADS)

Baghapour, Sh.; Parvin, P.; Reyhani, A.; Mortazavi, S. Z.; Mokhtari, S.; Amjadi, A.

2014-08-01

The renal capsule tissue of lamb was irradiated with ultraviolet-C light and the treated samples were analyzed by uniaxial tensile test, dynamic mechanical analysis, attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and contact angle measurements. It was shown that the skin cross-linking is dominant in low doses in accordance with the contact angle assessment. Conversely, the strong bulk degradation takes place at high doses. Similarly, the bulk cross-linking affects the mechanical tests as to enhance the stiffness at low doses, whereas strong degradation occurs at high doses that mainly arises from the strong bulk chain scission.

The role of shear and tensile failure in dynamically triggered landslides

USGS Publications Warehouse

Gipprich, T.L.; Snieder, R.K.; Jibson, R.W.; Kimman, W.

2008-01-01

Dynamic stresses generated by earthquakes can trigger landslides. Current methods of landslide analysis such as pseudo-static analysis and Newmark's method focus on the effects of earthquake accelerations on the landslide mass to characterize dynamic landslide behaviour. One limitation of these methods is their use Mohr-Coulomb failure criteria, which only accounts for shear failure, but the role of tensile failure is not accounted for. We develop a limit-equilibrium model to investigate the dynamic stresses generated by a given ground motion due to a plane wave and use this model to assess the role of shear and tensile failure in the initiation of slope instability. We do so by incorporating a modified Griffith failure envelope, which combines shear and tensile failure into a single criterion. Tests of dynamic stresses in both homogeneous and layered slopes demonstrate that two modes of failure exist, tensile failure in the uppermost meters of a slope and shear failure at greater depth. Further, we derive equations that express the dynamic stress in the near-surface in the acceleration measured at the surface. These equations are used to approximately define the depth range for each mechanism of failure. The depths at which these failure mechanisms occur suggest that shear and tensile failure might collaborate in generating slope failure. ?? 2007 The Authors Journal compilation ?? 2007 RAS.

Static and Dynamic Moduli of Malm Carbonate: A Poroelastic Correlation

NASA Astrophysics Data System (ADS)

Hassanzadegan, Alireza; Guérizec, Romain; Reinsch, Thomas; Blöcher, Guido; Zimmermann, Günter; Milsch, Harald

2016-08-01

The static and poroelastic moduli of a porous rock, e.g., the drained bulk modulus, can be derived from stress-strain curves in rock mechanical tests, and the dynamic moduli, e.g., dynamic Poisson's ratio, can be determined by acoustic velocity and bulk density measurements. As static and dynamic elastic moduli are different, a correlation is often required to populate geomechanical models. A novel poroelastic approach is introduced to correlate static and dynamic bulk moduli of outcrop analogues samples, representative of Upper-Malm reservoir rock in the Molasse basin, southwestern Germany. Drained and unjacketed poroelastic experiments were performed at two different temperature levels (30 and 60°C). For correlating the static and dynamic elastic moduli, a drained acoustic velocity ratio is introduced, corresponding to the drained Poisson's ratio in poroelasticity. The strength of poroelastic coupling, i.e., the product of Biot and Skempton coefficients here, was the key parameter. The value of this parameter decreased with increasing effective pressure by about 56 ~% from 0.51 at 3 MPa to 0.22 at 73 MPa. In contrast, the maximum change in P- and S-wave velocities was only 3 % in this pressure range. This correlation approach can be used in characterizing underground reservoirs, and can be employed to relate seismicity and geomechanics (seismo-mechanics).

From phase drift to synchronisation - pedestrian stepping behaviour on laterally oscillating structures and consequences for dynamic stability

NASA Astrophysics Data System (ADS)

Bocian, Mateusz; Burn, Jeremy F.; Macdonald, John H. G.; Brownjohn, James M. W.

2017-03-01

The subject of this paper pertains to the contentious issue of synchronisation of walking pedestrians to lateral structural motion, which is the mechanism most commonly purported to cause lateral dynamic instability. Tests have been conducted on a custom-built experimental setup consisting of an instrumented treadmill laterally driven by a hydraulic shaking table. The experimental setup can accommodate adaptive pedestrian behaviour via a bespoke speed feedback control mechanism that allows automatic adjustment of the treadmill belt speed to that of the walker. 15 people participated in a total of 137 walking tests during which the treadmill underwent lateral sinusoidal motion. The amplitude of this motion was set from 5 to 15 mm and the frequency was set from 0.54 to 1.1 Hz. A variety of stepping behaviours are identified in the kinematic data obtained using a motion capture system. The most common behaviour is for the timing of footsteps to be essentially unaffected by the structural motion, but a few instances of synchronisation are found. A plausible mechanism comprising an intermediate state between unsynchronised and synchronised pedestrian and structural motion is observed. This mechanism, characterised by a weak form of modulation of the timing of footsteps, could possibly explain the under-estimation of negative damping coefficients in models and laboratory trials compared with previously reported site measurements. The results from tests conducted on the setup for which synchronisation is identified are evaluated in the context of structural stability and related to the predictions of the inverted pendulum model, providing insight into fundamental relations governing pedestrian behaviour on laterally oscillating structures.

A multiscale red blood cell model with accurate mechanics, rheology, and dynamics.

PubMed

Fedosov, Dmitry A; Caswell, Bruce; Karniadakis, George Em

2010-05-19

Red blood cells (RBCs) have highly deformable viscoelastic membranes exhibiting complex rheological response and rich hydrodynamic behavior governed by special elastic and bending properties and by the external/internal fluid and membrane viscosities. We present a multiscale RBC model that is able to predict RBC mechanics, rheology, and dynamics in agreement with experiments. Based on an analytic theory, the modeled membrane properties can be uniquely related to the experimentally established RBC macroscopic properties without any adjustment of parameters. The RBC linear and nonlinear elastic deformations match those obtained in optical-tweezers experiments. The rheological properties of the membrane are compared with those obtained in optical magnetic twisting cytometry, membrane thermal fluctuations, and creep followed by cell recovery. The dynamics of RBCs in shear and Poiseuille flows is tested against experiments and theoretical predictions, and the applicability of the latter is discussed. Our findings clearly indicate that a purely elastic model for the membrane cannot accurately represent the RBC's rheological properties and its dynamics, and therefore accurate modeling of a viscoelastic membrane is necessary. Copyright 2010 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Functional connectivity dynamically evolves on multiple time-scales over a static structural connectome: Models and mechanisms.

PubMed

Cabral, Joana; Kringelbach, Morten L; Deco, Gustavo

2017-10-15

Over the last decade, we have observed a revolution in brain structural and functional Connectomics. On one hand, we have an ever-more detailed characterization of the brain's white matter structural connectome. On the other, we have a repertoire of consistent functional networks that form and dissipate over time during rest. Despite the evident spatial similarities between structural and functional connectivity, understanding how different time-evolving functional networks spontaneously emerge from a single structural network requires analyzing the problem from the perspective of complex network dynamics and dynamical system's theory. In that direction, bottom-up computational models are useful tools to test theoretical scenarios and depict the mechanisms at the genesis of resting-state activity. Here, we provide an overview of the different mechanistic scenarios proposed over the last decade via computational models. Importantly, we highlight the need of incorporating additional model constraints considering the properties observed at finer temporal scales with MEG and the dynamical properties of FC in order to refresh the list of candidate scenarios. Copyright © 2017 Elsevier Inc. All rights reserved.

A Multiscale Red Blood Cell Model with Accurate Mechanics, Rheology, and Dynamics

PubMed Central

Fedosov, Dmitry A.; Caswell, Bruce; Karniadakis, George Em

2010-01-01

Abstract Red blood cells (RBCs) have highly deformable viscoelastic membranes exhibiting complex rheological response and rich hydrodynamic behavior governed by special elastic and bending properties and by the external/internal fluid and membrane viscosities. We present a multiscale RBC model that is able to predict RBC mechanics, rheology, and dynamics in agreement with experiments. Based on an analytic theory, the modeled membrane properties can be uniquely related to the experimentally established RBC macroscopic properties without any adjustment of parameters. The RBC linear and nonlinear elastic deformations match those obtained in optical-tweezers experiments. The rheological properties of the membrane are compared with those obtained in optical magnetic twisting cytometry, membrane thermal fluctuations, and creep followed by cell recovery. The dynamics of RBCs in shear and Poiseuille flows is tested against experiments and theoretical predictions, and the applicability of the latter is discussed. Our findings clearly indicate that a purely elastic model for the membrane cannot accurately represent the RBC's rheological properties and its dynamics, and therefore accurate modeling of a viscoelastic membrane is necessary. PMID:20483330

Hybrid Residual Flexibility/Mass-Additive Method for Structural Dynamic Testing

NASA Technical Reports Server (NTRS)

Tinker, M. L.

2003-01-01

A large fixture was designed and constructed for modal vibration testing of International Space Station elements. This fixed-base test fixture, which weighs thousands of pounds and is anchored to a massive concrete floor, initially utilized spherical bearings and pendulum mechanisms to simulate Shuttle orbiter boundary constraints for launch of the hardware. Many difficulties were encountered during a checkout test of the common module prototype structure, mainly due to undesirable friction and excessive clearances in the test-article-to-fixture interface bearings. Measured mode shapes and frequencies were not representative of orbiter-constrained modes due to the friction and clearance effects in the bearings. As a result, a major redesign effort for the interface mechanisms was undertaken. The total cost of the fixture design, construction and checkout, and redesign was over $2 million. Because of the problems experienced with fixed-base testing, alternative free-suspension methods were studied, including the residual flexibility and mass-additive approaches. Free-suspension structural dynamics test methods utilize soft elastic bungee cords and overhead frame suspension systems that are less complex and much less expensive than fixed-base systems. The cost of free-suspension fixturing is on the order of tens of thousands of dollars as opposed to millions, for large fixed-base fixturing. In addition, free-suspension test configurations are portable, allowing modal tests to be done at sites without modal test facilities. For example, a mass-additive modal test of the ASTRO-1 Shuttle payload was done at the Kennedy Space Center launch site. In this Technical Memorandum, the mass-additive and residual flexibility test methods are described in detail. A discussion of a hybrid approach that combines the best characteristics of each method follows and is the focus of the study.

Decreased lung compliance increases preload dynamic tests in a pediatric acute lung injury model.

PubMed

Erranz, Benjamín; Díaz, Franco; Donoso, Alejandro; Salomón, Tatiana; Carvajal, Cristóbal; Torres, María Fernanda; Cruces, Pablo

2015-01-01

Preload dynamic tests, pulse pressure variation (PPV) and stroke volume variation (SVV) have emerged as powerful tools to predict response to fluid administration. The influence of factors other than preload in dynamic preload test is currently poorly understood in pediatrics. The aim of our study was to assess the effect of tidal volume (VT) on PPV and SVV in the context of normal and reduced lung compliance in a piglet model. Twenty large-white piglets (5.2±0.4kg) were anesthetized, paralyzed and monitored with pulse contour analysis. PPV and SVV were recorded during mechanical ventilation with a VT of 6 and 12mL/kg (low and high VT, respectively), both before and after tracheal instillation of polysorbate 20. Before acute lung injury (ALI) induction, modifications of VT did not significantly change PPV and SVV readings. After ALI, PPV and SVV were significantly greater during ventilation with a high VT compared to a low VT (PPV increased from 8.9±1.2 to 12.4±1.1%, and SVV from 8.5±1.0 to 12.7±1.2%, both P<0.01). This study found that a high VT and reduced lung compliance due to ALI increase preload dynamic tests, with a greater influence of the latter. In subjects with ALI, lung compliance should be considered when interpreting the preload dynamic tests. Copyright © 2015 Sociedad Chilena de Pediatría. Publicado por Elsevier España, S.L.U. All rights reserved.

Triggering of repeating earthquakes in central California

USGS Publications Warehouse

Wu, Chunquan; Gomberg, Joan; Ben-Naim, Eli; Johnson, Paul

2014-01-01

Dynamic stresses carried by transient seismic waves have been found capable of triggering earthquakes instantly in various tectonic settings. Delayed triggering may be even more common, but the mechanisms are not well understood. Catalogs of repeating earthquakes, earthquakes that recur repeatedly at the same location, provide ideal data sets to test the effects of transient dynamic perturbations on the timing of earthquake occurrence. Here we employ a catalog of 165 families containing ~2500 total repeating earthquakes to test whether dynamic perturbations from local, regional, and teleseismic earthquakes change recurrence intervals. The distance to the earthquake generating the perturbing waves is a proxy for the relative potential contributions of static and dynamic deformations, because static deformations decay more rapidly with distance. Clear changes followed the nearby 2004 Mw6 Parkfield earthquake, so we study only repeaters prior to its origin time. We apply a Monte Carlo approach to compare the observed number of shortened recurrence intervals following dynamic perturbations with the distribution of this number estimated for randomized perturbation times. We examine the comparison for a series of dynamic stress peak amplitude and distance thresholds. The results suggest a weak correlation between dynamic perturbations in excess of ~20 kPa and shortened recurrence intervals, for both nearby and remote perturbations.

Greek Participation to Solar Orbiter Development

NASA Astrophysics Data System (ADS)

Katsiyannis, A.

2012-01-01

Greece, via its PRODEX membership intends to meaningfully participate to the instrument development of a flagship ESA mission, the Solar Orbiter (SolO). This involvement pertains to hardware development for SolO's Spectrometer/Telescope for Imaging X-rays (STIX), namely, STIX's movable attenuator. SolO will allow close-up and high-latitude studies of our mother star, the Sun, based mostly on remote-sensing measurements (imaging). STIX is a critical SolO instrument, enabling one of its major science goals: understanding and acceleration of electrons at the Sun and their transport into interplanetary space. The attenuator, or shutter, that will be developed by the Greek team, is a critical component of the STIX instrument. Attenuators are dictated by the substantial dynamical range of incident X-ray fluxes from solar flares: the largest X-ray flares can give as many as 105 more count rates in X-ray photons compared to those of the smallest microflare that STIX can detect. It is proposed that two mechanisms are developed for a comparative study. First, a mechanism based on sensitive Shape Memory Alloy actuators and, second, one based on a piezoelectric actuator module. Both mechanisms will be designed and manufactured and then tested in vacuum and alternating high-low temperature conditions. Evaluation of reliability and accuracy in assembly and operation will follow. A vibrating table will be used for the dynamical analysis of the mechanism and independent strength tests of the various parts of the mechanism will follow.

Simulated and Experimental Damping Properties of a SMA/Fiber Glass Laminated Composite

NASA Astrophysics Data System (ADS)

Arnaboldi, S.; Bassani, P.; Biffi, C. A.; Tuissi, A.; Carnevale, M.; Lecis, N.; Loconte, A.; Previtali, B.

2011-07-01

In this article, an advanced laminated composite is developed, combining the high damping properties of shape memory alloy (SMA) with mechanical properties and light weight of a glass-fiber reinforced polymer. The composite is formed by stacking a glass-fiber reinforced epoxy core between two thin patterned strips of SMA alloy, and two further layers of fiber-glass reinforced epoxy. The bars of the laminated composite were assembled and cured in autoclave. The patterning was designed to enhance the interface adhesion between matrix and SMA inserts and optimally exploit the damping capacity of the SMA thin ribbons. The patterned ribbons of the SMA alloy were cut by means of a pulsed fiber laser source. Damping properties at different amplitudes on full scale samples were investigated at room temperature with a universal testing machine through dynamic tension tests, while temperature dependence was investigated by dynamic mechanical analyses (DMA) on smaller samples. Experimental results were used in conjunction with FEM analysis to optimize the geometry of the inserts. Experimental decay tests on the laminated composite have been carried out to identify the adimensional damping value related to their first flexural mode.

Longitudinal train dynamics model for a rail transit simulation system

DOE PAGES

Wang, Jinghui; Rakha, Hesham A.

2018-01-01

The paper develops a longitudinal train dynamics model in support of microscopic railway transportation simulation. The model can be calibrated without any mechanical data making it ideal for implementation in transportation simulators. The calibration and validation work is based on data collected from the Portland light rail train fleet. The calibration procedure is mathematically formulated as a constrained non-linear optimization problem. The validity of the model is assessed by comparing instantaneous model predictions against field observations, and also evaluated in the domains of acceleration/deceleration versus speed and acceleration/deceleration versus distance. A test is conducted to investigate the adequacy of themore » model in simulation implementation. The results demonstrate that the proposed model can adequately capture instantaneous train dynamics, and provides good performance in the simulation test. Thus, the model provides a simple theoretical foundation for microscopic simulators and will significantly support the planning, management and control of railway transportation systems.« less

Longitudinal train dynamics model for a rail transit simulation system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jinghui; Rakha, Hesham A.

The paper develops a longitudinal train dynamics model in support of microscopic railway transportation simulation. The model can be calibrated without any mechanical data making it ideal for implementation in transportation simulators. The calibration and validation work is based on data collected from the Portland light rail train fleet. The calibration procedure is mathematically formulated as a constrained non-linear optimization problem. The validity of the model is assessed by comparing instantaneous model predictions against field observations, and also evaluated in the domains of acceleration/deceleration versus speed and acceleration/deceleration versus distance. A test is conducted to investigate the adequacy of themore » model in simulation implementation. The results demonstrate that the proposed model can adequately capture instantaneous train dynamics, and provides good performance in the simulation test. Thus, the model provides a simple theoretical foundation for microscopic simulators and will significantly support the planning, management and control of railway transportation systems.« less

Verification Challenges of Dynamic Testing of Space Flight Hardware

NASA Technical Reports Server (NTRS)

Winnitoy, Susan

2010-01-01

The Six Degree-of-Freedom Dynamic Test System (SDTS) is a test facility at the National Aeronautics and Space Administration (NASA) Johnson Space Center in Houston, Texas for performing dynamic verification of space structures and hardware. Some examples of past and current tests include the verification of on-orbit robotic inspection systems, space vehicle assembly procedures and docking/berthing systems. The facility is able to integrate a dynamic simulation of on-orbit spacecraft mating or demating using flight-like mechanical interface hardware. A force moment sensor is utilized for input to the simulation during the contact phase, thus simulating the contact dynamics. While the verification of flight hardware presents many unique challenges, one particular area of interest is with respect to the use of external measurement systems to ensure accurate feedback of dynamic contact. There are many commercial off-the-shelf (COTS) measurement systems available on the market, and the test facility measurement systems have evolved over time to include two separate COTS systems. The first system incorporates infra-red sensing cameras, while the second system employs a laser interferometer to determine position and orientation data. The specific technical challenges with the measurement systems in a large dynamic environment include changing thermal and humidity levels, operational area and measurement volume, dynamic tracking, and data synchronization. The facility is located in an expansive high-bay area that is occasionally exposed to outside temperature when large retractable doors at each end of the building are opened. The laser interferometer system, in particular, is vulnerable to the environmental changes in the building. The operational area of the test facility itself is sizeable, ranging from seven meters wide and five meters deep to as much as seven meters high. Both facility measurement systems have desirable measurement volumes and the accuracies vary within the respective volumes. In addition, because this is a dynamic facility with a moving test bed, direct line-of-sight may not be available at all times between the measurement sensors and the tracking targets. Finally, the feedback data from the active test bed along with the two external measurement systems must be synchronized to allow for data correlation. To ensure the desired accuracy and resolution of these systems, calibration of the systems must be performed regularly. New innovations in sensor technology itself are periodically incorporated into the facility s overall measurement scheme. In addressing the challenges of the measurement systems, the facility is able to provide essential position and orientation data to verify the dynamic performance of space flight hardware.

Mechanical properties of MEMS materials: reliability investigations by mechanical- and HRXRD-characterization related to environmental testing

NASA Astrophysics Data System (ADS)

Bandi, T.; Shea, H.; Neels, A.

2014-06-01

The performance and aging of MEMS often rely on the stability of the mechanical properties over time and under harsh conditions. An overview is given on methods to investigate small variations of the mechanical properties of structural MEMS materials by functional characterization, high-resolution x-ray diffraction methods (HR-XRD) and environmental testing. The measurement of the dynamical properties of micro-resonators is a powerful method for the investigation of elasticity variations in structures relevant to microtechnology. X-ray diffraction techniques are used to analyze residual strains and deformations with high accuracy and in a non-destructive manner at surfaces and in buried micro-structures. The influence of elevated temperatures and radiation damage on the performance of resonant microstructures with a focus on quartz and single crystal silicon is discussed and illustrated with examples including work done in our laboratories at CSEM and EPFL.

Attenuation of cryocooler induced vibration using multimodal tuned dynamic absorbers

NASA Astrophysics Data System (ADS)

Veprik, Alexander; Babitsky, Vladimir; Tuito, Avi

2017-05-01

Modern infrared imagers often rely on split Stirling linear cryocoolers comprising compressor and expander, the relative position of which is governed by the optical design and packaging constraints. A force couple generated by imbalanced reciprocation of moving components inside both compressor and expander result in cryocooler induced vibration comprising angular and translational tonal components manifesting itself in the form of line of sight jitter and dynamic defocusing. Since linear cryocooler is usually driven at a fixed and precisely adjustable frequency, a tuned dynamic absorber is a well suited tool for vibration control. It is traditionally made in the form of lightweight single degree of freedom undamped mechanical resonator, the frequency of which is essentially matched with the driving frequency or vice versa. Unfortunately, the performance of such a traditional approach is limited in terms of simultaneous attenuating translational and angular components of cooler induced vibration. The authors are enhancing the traditional concept and consider multimodal tuned dynamic absorber made in the form of weakly damped mechanical resonator, where the frequencies of useful dynamic modes are essentially matched with the driving frequency. Dynamic analysis and experimental testing show that the dynamic reactions (forces and moments) produced by such a device may simultaneously attenuate both translational and angular components of cryocoolerinduced vibration. The authors are considering different embodiments and their suitability for different packaging concepts. The outcomes of theoretical predictions are supported by full scale experimentation.

Dynamic Loading of Carrara Marble in a Heated State

NASA Astrophysics Data System (ADS)

Wong, Louis Ngai Yuen; Li, Zhihuan; Kang, Hyeong Min; Teh, Cee Ing

2017-06-01

Useable land is a finite space, and with a growing global population, countries have been exploring the use of underground space as a strategic resource to sustain the growth of their society and economy. However, the effects of impact loading on rocks that have been heated, and hence the integrity of the underground structure, are still not fully understood and has not been included in current design standards. Such scenarios include traffic accidents and explosions during an underground fire. This study aims to provide a better understanding of the dynamic load capacity of Carrara marble at elevated temperatures. Dynamic uniaxial compression tests are performed on Carrara marble held at various temperatures using a split-Hopkinson Pressure Bar (SHPB) setup with varying input force. A customized oven is included in the SHPB setup to allow for testing of the marble specimens in a heated state. After the loading test, a three-wave analysis is performed to obtain the dynamic stress-strain curve of the specimen under loading. The fragments of the failed specimens were also collected and dry-sieved to obtain the particle size distribution. The results reveal that the peak stress of specimens that have been heated is negatively correlated with the heating temperature. However, the energy absorbed by the specimens at peak stress at all temperatures is similar, indicating that a significant amount of energy is dissipated via plastic deformation. Generally, fragment size is also found to show a negative correlation with heating temperature and loading pressure. However, in some cases this relationship does not hold true, probably due to the occurrence of stress shadowing. Linear Elastic Fracture Mechanics has been found to be generally applicable to specimens tested at low temperatures; but at higher temperatures, Elastic-Plastic Fracture Mechanics will give a more accurate prediction. Another contribution of this study is to show that other than the peak stress of the rock failure type, the strain history experienced by the rock during impact and the post-impact fragment size distribution are also significant distinguishing features of damage caused by dynamic loading on heated rocks.

Performance Analysis of Retrofitted Tribo-Corrosion Test Rig for Monitoring In Situ Oil Conditions.

PubMed

Siddaiah, Arpith; Khan, Zulfiqar Ahmad; Ramachandran, Rahul; Menezes, Pradeep L

2017-09-28

Oils and lubricants, once extracted after use from a mechanical system, can hardly be reused, and should be refurbished or replaced in most applications. New methods of in situ oil and lubricant efficiency monitoring systems have been introduced for a wide variety of mechanical systems, such as automobiles, aerospace aircrafts, ships, offshore wind turbines, and deep sea oil drilling rigs. These methods utilize electronic sensors to monitor the "byproduct effects" in a mechanical system that are not indicative of the actual remaining lifecycle and reliability of the oils. A reliable oil monitoring system should be able to monitor the wear rate and the corrosion rate of the tribo-pairs due to the inclusion of contaminants. The current study addresses this technological gap, and presents a novel design of a tribo-corrosion test rig for oils used in a dynamic system. A pin-on-disk tribometer test rig retrofitted with a three electrode-potentiostat corrosion monitoring system was used to analyze the corrosion and wear rate of a steel tribo-pair in industrial grade transmission oil. The effectiveness of the retrofitted test rig was analyzed by introducing various concentrations of contaminants in an oil medium that usually leads to a corrosive working environment. The results indicate that the retrofitted test rig can effectively monitor the in situ tribological performance of the oil in a controlled dynamic corrosive environment. It is a useful method to understand the wear-corrosion synergies for further experimental work, and to develop accurate predictive lifecycle assessment and prognostic models. The application of this system is expected to have economic benefits and help reduce the ecological oil waste footprint.

Performance Analysis of Retrofitted Tribo-Corrosion Test Rig for Monitoring In Situ Oil Conditions

PubMed Central

Ramachandran, Rahul; Menezes, Pradeep L.

2017-01-01

Oils and lubricants, once extracted after use from a mechanical system, can hardly be reused, and should be refurbished or replaced in most applications. New methods of in situ oil and lubricant efficiency monitoring systems have been introduced for a wide variety of mechanical systems, such as automobiles, aerospace aircrafts, ships, offshore wind turbines, and deep sea oil drilling rigs. These methods utilize electronic sensors to monitor the “byproduct effects” in a mechanical system that are not indicative of the actual remaining lifecycle and reliability of the oils. A reliable oil monitoring system should be able to monitor the wear rate and the corrosion rate of the tribo-pairs due to the inclusion of contaminants. The current study addresses this technological gap, and presents a novel design of a tribo-corrosion test rig for oils used in a dynamic system. A pin-on-disk tribometer test rig retrofitted with a three electrode-potentiostat corrosion monitoring system was used to analyze the corrosion and wear rate of a steel tribo-pair in industrial grade transmission oil. The effectiveness of the retrofitted test rig was analyzed by introducing various concentrations of contaminants in an oil medium that usually leads to a corrosive working environment. The results indicate that the retrofitted test rig can effectively monitor the in situ tribological performance of the oil in a controlled dynamic corrosive environment. It is a useful method to understand the wear–corrosion synergies for further experimental work, and to develop accurate predictive lifecycle assessment and prognostic models. The application of this system is expected to have economic benefits and help reduce the ecological oil waste footprint. PMID:28956819

Dynamical ejections of stars due to an accelerating gas filament

NASA Astrophysics Data System (ADS)

Boekholt, T. C. N.; Stutz, A. M.; Fellhauer, M.; Schleicher, D. R. G.; Matus Carrillo, D. R.

2017-11-01

Observations of the Orion A integral shaped filament (ISF) have shown indications of an oscillatory motion of the gas filament. This evidence is based on both the wave-like morphology of the filament and the kinematics of the gas and stars, where the characteristic velocities of the stars require a dynamical heating mechanism. As proposed by Stutz & Gould, such a heating mechanism (the `Slingshot') may be the result of an oscillating gas filament in a gas-dominated (as opposed to stellar-mass dominated) system. Here we test this hypothesis with the first stellar-dynamical simulations in which the stars are subjected to the influence of an oscillating cylindrical potential. The accelerating, cylindrical background potential is populated with a narrow distribution of stars. By coupling the potential to N-body dynamics, we are able to measure the influence of the potential on the stellar distribution. The simulations provide evidence that the slingshot mechanism can successfully reproduce several stringent observational constraints. These include the stellar spread (both in projected position and in velocity) around the filament, the symmetry in these distributions, and a bulk motion of the stars with respect to the filament. Using simple considerations, we show that star-star interactions are incapable of reproducing these spreads on their own when properly accounting for the gas potential. Thus, properly accounting for the gas potential is essential for understanding the dynamical evolution of star-forming filamentary systems in the era of Gaia (Gaia Collaboration 2016).

Dynamic oxidation behavior of TD-NiCr alloy with different surface pretreatments

NASA Technical Reports Server (NTRS)

Young, C. T.; Tenney, D. R.; Herring, H. W.

1975-01-01

Oxidation tests of TD-NiCr alloy with different surface pretreatments were conducted in a Mach-5 arc-jet at 1200 C and 0.002 lb/sec flowing air environment. The mechanisms responsible for the observed oxidation behavior are examined. The presence of atomic oxygen in the air stream plays a significant role in determining the oxidation characteristic of the alloy. The rate of Cr2O3 vaporization by formation of volatile CrO3 is greatly enhanced by the flowing conditions. The typical microstructure of oxides formed in the dynamic tests consists of an external layer of NiO with a porous mushroom-type morphology, an intermediate layer of NiO and Cr2O3 oxide mixture, and a continuous inner layer of Cr2O3 in contact with the Cr-depleted alloy substrate. Three basic processes underlying the formation of mushroom-type NiO are identified and discussed. The oxidation rate is determined by the rate of vaporization of NiO. Surface pretreatment has a significant effect on the oxidation behavior of the alloy in the early stage of oxidation, but becomes less important as exposure time increases. Mechanical polishing induces surface recrystallization, but promotes the concurrence of external growth of NiO and internal oxidation of the alloy in the dynamic atmosphere.

Dynamic wind-tunnel tests of an aeromechanical gust-alleviation system using several different combinations of control surfaces

NASA Technical Reports Server (NTRS)

Stewart, E. C.; Doggett, R. V., Jr.

1978-01-01

Some experimental results are presented from wind tunnel studies of a dynamic model equipped with an aeromechanical gust alleviation system for reducing the normal acceleration response of light airplanes. The gust alleviation system consists of two auxiliary aerodynamic surfaces that deflect the wing flaps through mechanical linkages when a gust is encountered to maintain nearly constant airplane lift. The gust alleviation system was implemented on a 1/6-scale, rod mounted, free flying model that is geometrically and dynamically representative of small, four place, high wing, single engine, light airplanes. The effects of flaps with different spans, two size of auxiliary aerodynamic surfaces, plain and double hinged flaps, and a flap elevator interconnection were studied. The model test results are presented in terms of predicted root mean square response of the full scale airplane to atmospheric turbulence. The results show that the gust alleviation system reduces the root mean square normal acceleration response by 30 percent in comparison with the response in the flaps locked condition. Small reductions in pitch-rate response were also obtained. It is believed that substantially larger reductions in normal acceleration can be achieved by reducing the rather high levels of mechanical friction which were extant in the alleviation system of the present model.

Perceived Sexual Control, Sex-Related Alcohol Expectancies and Behavior Predict Substance-Related Sexual Revictimization

ERIC Educational Resources Information Center

Walsh, Kate; Messman-Moore, Terri; Zerubavel, Noga; Chandley, Rachel B.; DeNardi, Kathleen A.; Walker, Dave P.

2013-01-01

Objectives: Although numerous studies have documented linkages between childhood sexual abuse (CSA) and later sexual revictimization, mechanisms underlying revictimization, particularly assaults occurring in the context of substance use, are not well-understood. Consistent with Traumagenic Dynamics theory, the present study tested a path model…

Research on hysteresis loop considering the prestress effect and electrical input dynamics for a giant magnetostrictive actuator

NASA Astrophysics Data System (ADS)

Zhu, Yuchuan; Yang, Xulei; Wereley, Norman M.

2016-08-01

In this paper, focusing on the application-oriented giant magnetostrictive material (GMM)-based electro-hydrostatic actuator, which features an applied magnetic field at high frequency and high amplitude, and concentrating on the static and dynamic characteristics of a giant magnetostrictive actuator (GMA) considering the prestress effect on the GMM rod and the electrical input dynamics involving the power amplifier and the inductive coil, a methodology for studying the static and dynamic characteristics of a GMA using the hysteresis loop as a tool is developed. A GMA that can display the preforce on the GMM rod in real-time is designed, and a magnetostrictive model dependent on the prestress on a GMM rod instead of the existing quadratic domain rotation model is proposed. Additionally, an electrical input dynamics model to excite GMA is developed according to the simplified circuit diagram, and the corresponding parameters are identified by the experimental data. A dynamic magnetization model with the eddy current effect is deduced according to the Jiles-Atherton model and the Maxwell equations. Next, all of the parameters, including the electrical input characteristics, the dynamic magnetization and the mechanical structure of GMA, are identified by the experimental data from the current response, magnetization response and displacement response, respectively. Finally, a comprehensive comparison between the model results and experimental data is performed, and the results show that the test data agree well with the presented model results. An analysis on the relation between the GMA displacement response and the parameters from the electrical input dynamics, magnetization dynamics and mechanical structural dynamics is performed.

Proportional and Integral Thermal Control System for Large Scale Heating Tests

NASA Technical Reports Server (NTRS)

Fleischer, Van Tran

2015-01-01

The National Aeronautics and Space Administration Armstrong Flight Research Center (Edwards, California) Flight Loads Laboratory is a unique national laboratory that supports thermal, mechanical, thermal/mechanical, and structural dynamics research and testing. A Proportional Integral thermal control system was designed and implemented to support thermal tests. A thermal control algorithm supporting a quartz lamp heater was developed based on the Proportional Integral control concept and a linearized heating process. The thermal control equations were derived and expressed in terms of power levels, integral gain, proportional gain, and differences between thermal setpoints and skin temperatures. Besides the derived equations, user's predefined thermal test information generated in the form of thermal maps was used to implement the thermal control system capabilities. Graphite heater closed-loop thermal control and graphite heater open-loop power level were added later to fulfill the demand for higher temperature tests. Verification and validation tests were performed to ensure that the thermal control system requirements were achieved. This thermal control system has successfully supported many milestone thermal and thermal/mechanical tests for almost a decade with temperatures ranging from 50 F to 3000 F and temperature rise rates from -10 F/s to 70 F/s for a variety of test articles having unique thermal profiles and test setups.

A novel representation of groundwater dynamics in large-scale land surface modelling

NASA Astrophysics Data System (ADS)

Rahman, Mostaquimur; Rosolem, Rafael; Kollet, Stefan

2017-04-01

Land surface processes are connected to groundwater dynamics via shallow soil moisture. For example, groundwater affects evapotranspiration (by influencing the variability of soil moisture) and runoff generation mechanisms. However, contemporary Land Surface Models (LSM) generally consider isolated soil columns and free drainage lower boundary condition for simulating hydrology. This is mainly due to the fact that incorporating detailed groundwater dynamics in LSMs usually requires considerable computing resources, especially for large-scale applications (e.g., continental to global). Yet, these simplifications undermine the potential effect of groundwater dynamics on land surface mass and energy fluxes. In this study, we present a novel approach of representing high-resolution groundwater dynamics in LSMs that is computationally efficient for large-scale applications. This new parameterization is incorporated in the Joint UK Land Environment Simulator (JULES) and tested at the continental-scale.

Application of Micro-ramp Flow Control Devices to an Oblique Shock Interaction

NASA Technical Reports Server (NTRS)

Hirt, Stefanie; Anderson, Bernhard

2007-01-01

Tests are planned in the 15cm x 15cm supersonic wind tunnel at NASA Glenn to demonstrate the applicability of micro-ramp flow control to the management of shock wave boundary layer interactions. These tests will be used as a database for computational fluid dynamics (CFD) validation and Design of Experiments (DoE) design information. Micro-ramps show potential for mechanically simple and fail-safe boundary layer control.

Field monitoring of static, dynamic, and statnamic pile loading tests using fibre Bragg grating strain sensors

NASA Astrophysics Data System (ADS)

Li, Jin; Correia, Ricardo P.; Chehura, Edmon; Staines, Stephen; James, Stephen W.; Tatam, Ralph; Butcher, Antony P.; Fuentes, Raul

2009-10-01

Pile loading test plays an important role in the field of piling engineering. In order to gain further insight into the load transfer mechanism, strain gauges are often used to measure local strains along the piles. This paper reports a case whereby FBG strain sensors was employed in a field trial conducted on three different types of pile loading tests in a glacial till. The instrumentation systems were configured to suit the specific characteristic of each type of test. Typical test results are presented. The great potential of using FBG sensors for pile testing is shown.

Application of the time-temperature superposition principle to the mechanical characterization of elastomeric adhesives for crash simulation purposes

NASA Astrophysics Data System (ADS)

Rauh, A.; Hinterhölzl, R.; Drechsler, K.

2012-05-01

In the automotive industry, finite element simulation is widely used to ensure crashworthiness. Mechanical material data over wide strain rate and temperature ranges are required as a basis. This work proposes a method reducing the cost of mechanical material characterization by using the time-temperature superposition principle on elastomeric adhesives. The method is based on the time and temperature interdependence which is characteristic for mechanical properties of polymers. Based on the assumption that polymers behave similarly at high strain rates and at low temperatures, a temperature-dominated test program is suggested, which can be used to deduce strain rate dependent material behavior at different reference temperatures. The temperature shift factor is found by means of dynamic mechanical analysis according to the WLF-equation, named after Williams, Landel and Ferry. The principle is applied to the viscoelastic properties as well as to the failure properties of the polymer. The applicability is validated with high strain rate tests.

Characterization of fine abrasive particles for optical fabrication

NASA Astrophysics Data System (ADS)

Funkenbusch, Paul D.; Zhou, Y. Y.; Takahashi, Toshio; Quesnel, David J.; Lambropoulos, John C.

1995-08-01

Material removal during fine grinding operations is accomplished primarily by the action of individual abrasive particles on the glass surface. The mechanical properties of the abrasive are therefore important. Unfortunately it is difficult to directly measure the mechanical response of abrasives once they reach the scale of approximately 10 microns. As a result mechanical properties of fine abrasives are sometimes characterized in terms of an empirical `friability', based on the response of the abrasive to crushing by a metal ball in a vial. In this paper we report on modeling/experiments designed to more precisely quantify the mechanical properties of fine abrasives and ultimately to relate them to the conditions experienced by bound particles during grinding. Experiments have been performed on various types and sizes of diamond abrasives. The response of the particles is a strong function of the loading conditions and can be tracked by changing the testing parameters. Diamond size is also found to play a critical role, with finer diamonds less susceptible to fracture. A micromechanical model from the literature is employed estimate the forces likely to be seen during testing. We are also developing dynamic models to better predict the forces experienced during `friability' testing as a function of the testing parameters.

Research on dynamic routing mechanisms in wireless sensor networks.

PubMed

Zhao, A Q; Weng, Y N; Lu, Y; Liu, C Y

2014-01-01

WirelessHART is the most widely applied standard in wireless sensor networks nowadays. However, it does not provide any dynamic routing mechanism, which is important for the reliability and robustness of the wireless network applications. In this paper, a collection tree protocol based, dynamic routing mechanism was proposed for WirelessHART network. The dynamic routing mechanism was evaluated through several simulation experiments in three aspects: time for generating the topology, link quality, and stability of network. Besides, the data transmission efficiency of this routing mechanism was analyzed. The simulation and evaluation results show that this mechanism can act as a dynamic routing mechanism for the TDMA-based wireless sensor network.

Semi-dynamic leaching tests of nickel containing wastes stabilized/solidified with magnesium potassium phosphate cements.

PubMed

Torras, Josep; Buj, Irene; Rovira, Miquel; de Pablo, Joan

2011-02-28

Herein is presented a study on the long-term leaching behaviour of nickel containing wastes stabilized/solidified with magnesium potassium phosphate cements. Two different semi-dynamic leaching tests were carried out on monolithic materials: ANS 16.1 test with liquid-to-solid ratio (L/S) of 10 dm(3) kg(-1) and increasing renewal times, and ASTM C1308 test with liquid-to-solid ratio (L/S) of 100 dm(3) kg(-1) and constant renewal time of 1 day. ASTM C1308 provides a lower degree of saturation of the leachant with respect to the leached material. The effectiveness of magnesium potassium phosphate cements for the inertization of nickel was proved. XRD analyses showed the presence of bobierrite on the monolith's surface after the leaching test, which had not been detected prior to the leaching test. In addition, the calculated cumulative release of the main components of the stabilization matrix (Mg(2+), total P and K(+)) was represented versus time in logarithmic scale and it was determined if the leaching mechanism corresponds to diffusion. Potassium is released by diffusion, while total phosphorous and magnesium show dissolution. Magnesium release in ANS 16.1 is slowed down because of saturation of the leachant. Experimental results demonstrate the importance of L/S ratio and renewal times in semi-dynamic leaching tests. Copyright © 2010 Elsevier B.V. All rights reserved.

Advanced radial inflow turbine rotor program: Design and dynamic testing

NASA Technical Reports Server (NTRS)

Rodgers, C.

1976-01-01

The advancement of small, cooled, radial inflow turbine technology in the area of operation at higher turbine inlet temperature is discussed. The first step was accomplished by designing, fabricating, and subjecting to limited mechanical testing an advanced gas generator rotating assembly comprising a radial inflow turbine and two-stage centrifugal compressor. The radial inflow turbine and second-stage compressor were designed as an integrally machined monorotor with turbine cooling taking place basically by conduction to the compressor. Design turbine inlet rotor gas temperature, rotational speed, and overall gas generator compressor pressure ratio were 1422 K (2560 R), 71,222 rpm, and 10/1 respectively. Mechanical testing on a fabricated rotating assembly and bearing system covered 1,000 cold start/stop cycles and three spins to 120 percent design speed (85,466 rpm).

Progress on Fault Mechanisms for Gear Transmissions in Coal Cutting Machines: From Macro to Nano Models.

PubMed

Jiang, Yu; Zhang, Xiaogang; Zhang, Chao; Li, Zhixiong; Sheng, Chenxing

2017-04-01

Numerical modeling has been recognized as the dispensable tools for mechanical fault mechanism analysis. Techniques, ranging from macro to nano levels, include the finite element modeling boundary element modeling, modular dynamic modeling, nano dynamic modeling and so forth. This work firstly reviewed the progress on the fault mechanism analysis for gear transmissions from the tribological and dynamic aspects. Literature review indicates that the tribological and dynamic properties were separately investigated to explore the fault mechanism in gear transmissions. However, very limited work has been done to address the links between the tribological and dynamic properties and scarce researches have been done for coal cutting machines. For this reason, the tribo-dynamic coupled model was introduced to bridge the gap between the tribological and dynamic models in fault mechanism analysis for gear transmissions in coal cutting machines. The modular dynamic modeling and nano dynamic modeling techniques are expected to establish the links between the tribological and dynamic models. Possible future research directions using the tribo dynamic coupled model were summarized to provide potential references for researchers in the field.

CFD Simulations of the Supersonic Inflatable Aerodynamic Decelerator (SIAD) Ballistic Range Tests

NASA Technical Reports Server (NTRS)

Brock, Joseph; Stern, Eric; Wilder, Michael

2017-01-01

A series of ballistic range tests were performed on a scaled model of the Supersonic Flight Demonstration Test (SFDT) intended to test the Supersonic Inflatable Aerodynamic Decelerator (SIAD) geometry. The purpose of these experiments were to provide aerodynamic coefficients of the vehicle to aid in mission and vehicle design. The experimental data spans the moderate Mach number range, $3.8-2.0$, with a total angle of attack ($alpha_T$) range, $10o-20o$. These conditions are intended to span the Mach-$alpha$ space for the majority of the SFDT experiment. In an effort to validate the predictive capabilities of Computational Fluid Dynamics (CFD) for free-flight aerodynamic behavior, numerical simulations of the ballistic range experiment are performed using the unstructured finite volume Navier-Stokes solver, US3D. Comparisons to raw vehicle attitude, and post-processed aerodynamic coefficients are made between simulated results and experimental data. The resulting comparisons for both raw model attitude and derived aerodynamic coefficients show good agreement with experimental results. Additionally, near body pressure field values for each trajectory simulated are investigated. Extracted surface and wake pressure data gives further insights into dynamic flow coupling leading to a potential mechanism for dynamic instability.

Stability and Evolution of Multiple Planet and Satellite Systems

NASA Astrophysics Data System (ADS)

Quillen, Alice

Numerous multiple planet systems have recently been discovered with the Kepler Mission, suggesting that multiple planet systems are common. Multiple- body nearly coplanar satellite systems are also found in the Solar system. Multiple planet and satellite systems exhibit rich dynamics as they are affected by three-body and secular resonances affecting short timescale behavior and long timescale stability. Interactions with debris disks and planetesimal belts and tidal interactions can both reduce and induce instability. Using both numerical and analytical studies, we propose to develop a broadly applicable framework to estimate diffusion rates and stability regimes both in resonant and non- resonant configurations. Understanding of resonant dynamics is needed to understand each of these systems and a broader general theory would cover scenarios and mechanisms that are relevant for all of them. Architectures and dynamical mechanisms will be used to test scenarios for formation and evolution of multiple body systems and constrain poorly known quantities such as masses, eccentricities, inclinations, radii, and the existence of undetected bodies.

Effects of high energy radiation on the mechanical properties of epoxy-graphite fiber reinforced composites

NASA Technical Reports Server (NTRS)

Fornes, R. E.; Gilbert, R. D.; Memory, J. D.

1984-01-01

The effects of high energy radiation on the mechanical properties and on the molecular and structural properties of graphite fiber reinforced composites were assessed so that the durability of such composites in space applications could be predicted. Investigative techniques including ESR and infrared spectroscopy, ESCA, contact angle measurements, and dynamic and static mechanical testing (3-point bending and interlaminar shear) were employed. The results using these different techniques are individually described, and the implications of the data are discussed. The proposed plan of work for the next fiscal year is outlined.

A neural coding scheme reproducing foraging trajectories

NASA Astrophysics Data System (ADS)

Gutiérrez, Esther D.; Cabrera, Juan Luis

2015-12-01

The movement of many animals may follow Lévy patterns. The underlying generating neuronal dynamics of such a behavior is unknown. In this paper we show that a novel discovery of multifractality in winnerless competition (WLC) systems reveals a potential encoding mechanism that is translatable into two dimensional superdiffusive Lévy movements. The validity of our approach is tested on a conductance based neuronal model showing WLC and through the extraction of Lévy flights inducing fractals from recordings of rat hippocampus during open field foraging. Further insights are gained analyzing mice motor cortex neurons and non motor cell signals. The proposed mechanism provides a plausible explanation for the neuro-dynamical fundamentals of spatial searching patterns observed in animals (including humans) and illustrates an until now unknown way to encode information in neuronal temporal series.

Materials science. Dynamic mechanical behavior of multilayer graphene via supersonic projectile penetration.

PubMed

Lee, Jae-Hwang; Loya, Phillip E; Lou, Jun; Thomas, Edwin L

2014-11-28

Multilayer graphene is an exceptional anisotropic material due to its layered structure composed of two-dimensional carbon lattices. Although the intrinsic mechanical properties of graphene have been investigated at quasi-static conditions, its behavior under extreme dynamic conditions has not yet been studied. We report the high-strain-rate behavior of multilayer graphene over a range of thicknesses from 10 to 100 nanometers by using miniaturized ballistic tests. Tensile stretching of the membrane into a cone shape is followed by initiation of radial cracks that approximately follow crystallographic directions and extend outward well beyond the impact area. The specific penetration energy for multilayer graphene is ~10 times more than literature values for macroscopic steel sheets at 600 meters per second. Copyright © 2014, American Association for the Advancement of Science.

In-vitro development of a temporal abutment screw to protect osseointegration in immediate loaded implants

PubMed Central

2015-01-01

PURPOSE In this study, a temporal abutment fixation screw, designed to fracture in a controlled way upon application of an occlusal force sufficient to produce critical micromotion was developed. The purpose of the screw was to protect the osseointegration of immediate loaded single implants. MATERIALS AND METHODS Seven different screw prototypes were examined by fixing titanium abutments to 112 Mozo-Grau external hexagon implants (MG Osseous®; Mozo-Grau, S.A., Valladolid, Spain). Fracture strength was tested at 30° in two subgroups per screw: one under dynamic loading and the other without prior dynamic loading. Dynamic loading was performed in a single-axis chewing simulator using 150,000 load cycles at 50 N. After normal distribution of obtained data was verified by Kolmogorov-Smirnov test, fracture resistance between samples submitted and not submitted to dynamic loading was compared by the use of Student's t-test. Comparison of fracture resistance among different screw designs was performed by the use of one-way analysis of variance. Confidence interval was set at 95%. RESULTS Fractures occurred in all screws, allowing easy retrieval. Screw Prototypes 2, 5 and 6 failed during dynamic loading and exhibited statistically significant differences from the other prototypes. CONCLUSION Prototypes 2, 5 and 6 may offer a useful protective mechanism during occlusal overload in immediate loaded implants. PMID:25932315

Towards a standardized grasping and refuelling on-orbit servicing for geo spacecraft

NASA Astrophysics Data System (ADS)

Medina, Alberto; Tomassini, Angelo; Suatoni, Matteo; Avilés, Marcos; Solway, Nick; Coxhill, Ian; Paraskevas, Iosif S.; Rekleitis, Georgios; Papadopoulos, Evangelos; Krenn, Rainer; Brito, André; Sabbatinelli, Beatrice; Wollenhaupt, Birk; Vidal, Christian; Aziz, Sarmad; Visentin, Gianfranco

2017-05-01

Exploitation of space must benefit from the latest advances in robotics. On-orbit servicing is a clear candidate for the application of autonomous rendezvous and docking mechanisms. However, during the last three decades most of the trials took place combining extravehicular activities (EVAs) with telemanipulated robotic arms. The European Space Agency (ESA) considers that grasping and refuelling are promising near-mid-term capabilities that could be performed by servicing spacecraft. Minimal add-ons on spacecraft to enhance their serviceability may protect them for a changing future in which satellite servicing may become mainstream. ESA aims to conceive and promote standard refuelling provisions that can be installed in present and future European commercial geostationary orbit (GEO) satellite platforms and scientific spacecraft. For this purpose ESA has started the ASSIST activity addressing the analysis, design and validation of internal provisions (such as modifications to fuel, gas, electrical and data architecture to allow servicing) and external provisions (such as integrated berthing fixtures with peripheral electrical, gas, liquid connectors, leak check systems and corresponding optical and radio markers for cooperative rendezvous and docking). This refuelling approach is being agreed with European industry (OHB, Thales Alenia Space) and expected to be consolidated with European commercial operators as a first step to become an international standard; this approach is also being considered for on-orbit servicing spacecraft, such as the SpaceTug, by Airbus DS. This paper describes in detail the operational means, structure, geometry and accommodation of the system. Internal and external provisions will be designed with the minimum possible impact on the current architecture of GEO satellites without introducing additional risks in the development and commissioning of the satellite. End-effector and berthing fixtures are being designed in the range of few kilos and linear dimensions around 15 cm. A central mechanical part is expected to perform first a soft docking followed by a motorized retraction ending during a hard docking phase using aligning pins. Mating and de-mating will be exhaustively analysed to ensure robustness of operations. Leakage-free valves would allow for the transfer of fuel to the serviced spacecraft. The validation of the ASSIST system through dedicated environmental tests in a vacuum chamber together with dynamic testing using an air-bearing table will allow for the demonstration of concept feasibility and its suitability for becoming a standard of the on-orbit space industry. Failure during the injection of the payload into the nominal target or transfer orbit. In most cases the satellite cannot accomplish this on its own; an orbit transfer vehicle could provide support. Necessity for support unfinished operations during the test and commissioning phase. Typical example can be incomplete deployment mechanism of solar arrays or of antenna dishes. Premature end of life of the satellite due to equipment obsolescence or wear. Extension of the expected duration of the satellite operative life through a refuelling of propellant tanks devoted to attitude/orbit control. This scenario will be the main subject of this ASSIST project and will be fully explored. This activity is led by GMV (coordinator and dynamics simulator) together with MOOG (mechanical design, breadboard manufacturing and environmental testing), NTUA (air-bearing table dynamics and testing), DLR (contact dynamics), OHB (mission requirements and propulsion provisions) and TAS (mission requirements).This paper is organized as follows: Section 1 provides an introduction, Section 2 introduces the ASSIST concept, Section 3 provides a review on servicing/refuelling systems, Section 4 describes the operational scenarios and phases, Section 5 presents the ASSIST design while Section 6 describes the step-by-step refuelling operations, Sections 7 and 8 present the internal and external provisions respectively, Section 9 introduces the Kinematic and Dynamic simulator, Section 10 shows the air-bearing test set-up, Section 11 describes the dynamic test cases and validation results and finally Sections 12 present the conclusions.

Design and implementation of a novel mechanical testing system for cellular solids.

PubMed

Nazarian, Ara; Stauber, Martin; Müller, Ralph

2005-05-01

Cellular solids constitute an important class of engineering materials encompassing both man-made and natural constructs. Materials such as wood, cork, coral, and cancellous bone are examples of cellular solids. The structural analysis of cellular solid failure has been limited to 2D sections to illustrate global fracture patterns. Due to the inherent destructiveness of 2D methods, dynamic assessment of fracture progression has not been possible. Image-guided failure assessment (IGFA), a noninvasive technique to analyze 3D progressive bone failure, has been developed utilizing stepwise microcompression in combination with time-lapsed microcomputed tomographic imaging (microCT). This method allows for the assessment of fracture progression in the plastic region, where much of the structural deformation/energy absorption is encountered in a cellular solid. Therefore, the goal of this project was to design and fabricate a novel micromechanical testing system to validate the effectiveness of the stepwise IGFA technique compared to classical continuous mechanical testing, using a variety of engineered and natural cellular solids. In our analysis, we found stepwise compression to be a valid approach for IGFA with high precision and accuracy comparable to classical continuous testing. Therefore, this approach complements the conventional mechanical testing methods by providing visual insight into the failure propagation mechanisms of cellular solids. (c) 2005 Wiley Periodicals, Inc.

Studies on microstructure, mechanical and corrosion properties of high nitrogen stainless steel shielded metal arc welds

NASA Astrophysics Data System (ADS)

Mohammed, Raffi; Madhusudhan Reddy, G.; Srinivasa Rao, K.

2018-03-01

The present work is aimed at studying the microstructure, mechanical and corrosion properties of high nitrogen stainless steel shielded metal arc (SMA) welds made with Cromang-N electrode. Basis for selecting this electrode is to increase the solubility of nitrogen in weld metal due to high chromium and manganese content. Microstructures of the welds were characterized using optical microscopy (OM), field emission scanning electron microscopy (FESEM) and electron back scattered diffraction (EBSD) mainly to determine the morphology, phase analysis, grain size and orientation image mapping. Hardness, tensile and ductility bend tests were carried out to determine mechanical properties. Potentio-dynamic polarization testing was carried out to study the pitting corrosion resistance using a GillAC basic electrochemical system. Constant load type testing was carried out to study stress corrosion cracking (SCC) behaviour of welds. The investigation results shown that the selected Cr–Mn–N type electrode resulted in favourable microstructure and completely solidified as single phase coarse austenite. Mechanical properties of SMA welds are found to be inferior when compared to that of base metal and is due to coarse and dendritic structure.

Dynamic Aftershock Triggering Correlated with Cyclic Loading in the Slip Direction

NASA Astrophysics Data System (ADS)

Hardebeck, J.

2014-12-01

Dynamic stress changes have been shown to contribute to aftershock triggering, but the physical triggering mechanisms are not fully understood. Some proposed mechanisms are based on dynamic stress loading of the target fault in a direction that encourages earthquake slip (e.g. dynamic Coulomb stress triggering), while other mechanisms are based on fault weakening due to shaking. If dynamic stress loading in the fault slip direction plays a role in aftershock triggering, we would expect to see a relationship between the dynamic stress orientations and the aftershock focal mechanisms. Alternatively, if dynamic stress change triggering functions only through a fault weakening mechanism that is independent of the slip direction of the target fault, no such relationship is expected. I study aftershock sequences of 4 M≥6.7 mainshocks in southern California, and find a small but significant relationship between modeled dynamic stress direction and aftershock focal mechanisms. The mainshock dynamic stress changes have two observed impacts: changing the focal mechanisms in a given location to favor those aligned with the dynamic stress change, and changing the spatial distribution of seismicity to favor locations where the dynamic stress change aligns with the background stress. The aftershock focal mechanisms are significantly more aligned with the dynamic stress changes than the preshock mechanisms for only the first 0.5-1 year following most mainshocks, although for at least 10 years following Hector Mine. Dynamic stress effects on focal mechanisms are best observed at long periods (30-60 sec). Dynamic stress effects are only observed when using metrics based on repeated stress cycling in the same direction, for example considering the dominant stress orientation over the full time series, and not for the peak dynamic stress. These results imply that dynamic aftershock triggering operates at least in part through cyclic loading in the direction of fault slip, although non-directional fault weakening may be important as well. This suggests that the orientation of the dynamic stresses, as well as their amplitude, should be considered in the development of physics-based aftershock forecasting models.

A piezoelectric six-DOF vibration energy harvester based on parallel mechanism: dynamic modeling, simulation, and experiment

NASA Astrophysics Data System (ADS)

Yuan, G.; Wang, D. H.

2017-03-01

Multi-directional and multi-degree-of-freedom (multi-DOF) vibration energy harvesting are attracting more and more research interest in recent years. In this paper, the principle of a piezoelectric six-DOF vibration energy harvester based on parallel mechanism is proposed to convert the energy of the six-DOF vibration to single-DOF vibrations of the limbs on the energy harvester and output voltages. The dynamic model of the piezoelectric six-DOF vibration energy harvester is established to estimate the vibrations of the limbs. On this basis, a Stewart-type piezoelectric six-DOF vibration energy harvester is developed and explored. In order to validate the established dynamic model and the analysis results, the simulation model of the Stewart-type piezoelectric six-DOF vibration energy harvester is built and tested with different vibration excitations by SimMechanics, and some preliminary experiments are carried out. The results show that the vibration of the limbs on the piezoelectric six-DOF vibration energy harvester can be estimated by the established dynamic model. The developed Stewart-type piezoelectric six-DOF vibration energy harvester can harvest the energy of multi-directional linear vibration and multi-axis rotating vibration with resonance frequencies of 17 Hz, 25 Hz, and 47 Hz. Moreover, the resonance frequencies of the developed piezoelectric six-DOF vibration energy harvester are not affected by the direction changing of the vibration excitation.

Modeling the dynamic crush of impact mitigating materials

NASA Astrophysics Data System (ADS)

Logan, R. W.; McMichael, L. D.

1995-05-01

Crushable materials are commonly utilized in the design of structural components to absorb energy and mitigate shock during the dynamic impact of a complex structure, such as an automobile chassis or drum-type shipping container. The development and application of several finite-element material models which have been developed at various times at LLNL for DYNA3D are discussed. Between the models, they are able to account for several of the predominant mechanisms which typically influence the dynamic mechanical behavior of crushable materials. One issue we addressed was that no single existing model would account for the entire gambit of constitutive features which are important for crushable materials. Thus, we describe the implementation and use of an additional material model which attempts to provide a more comprehensive model of the mechanics of crushable material behavior. This model combines features of the pre-existing DYNA models and incorporates some new features as well in an invariant large-strain formulation. In addition to examining the behavior of a unit cell in uniaxial compression, two cases were chosen to evaluate the capabilities and accuracy of the various material models in DYNA. In the first case, a model for foam filled box beams was developed and compared to test data from a four-point bend test. The model was subsequently used to study its effectiveness in energy absorption in an aluminum extrusion, spaceframe, vehicle chassis. The second case examined the response of the AT-400A shipping container and the performance of the overpack material during accident environments selected from 10CFR71 and IAEA regulations.

Development of procedures for calculating stiffness and damping properties of elastomers in engineering applications. Part 1: Verification of basic methods

NASA Technical Reports Server (NTRS)

Chiang, T.; Tessarzik, J. M.; Badgley, R. H.

1972-01-01

The primary aim of this investigation was verification of basic methods which are to be used in cataloging elastomer dynamic properties (stiffness and damping) in terms of viscoelastic model constants. These constants may then be used to predict dynamic properties for general elastomer shapes and operating conditions, thereby permitting optimum application of elastomers as energy absorption and/or energy storage devices in the control of vibrations in a broad variety of applications. The efforts reported involved: (1) literature search; (2) the design, fabrication and use of a test rig for obtaining elastomer dynamic test data over a wide range of frequencies, amplitudes, and preloads; and (3) the reduction of the test data, by means of a selected three-element elastomer model and specialized curve fitting techniques, to material properties. Material constants thus obtained have been used to calculate stiffness and damping for comparison with measured test data. These comparisons are excellent for a number of test conditions and only fair to poor for others. The results confirm the validity of the basic approach of the overall program and the mechanics of the cataloging procedure, and at the same time suggest areas in which refinements should be made.

Mechanical characterization and durability of sintered porous transport layers for polymer electrolyte membrane electrolysis

NASA Astrophysics Data System (ADS)

Borgardt, Elena; Panchenko, Olha; Hackemüller, Franz Josef; Giffin, Jürgen; Bram, Martin; Müller, Martin; Lehnert, Werner; Stolten, Detlef

2018-01-01

Differential pressure electrolysis offers the potential for more efficient hydrogen compression. Due to the differential pressures acting within the electrolytic cell, the porous transport layer (PTL) is subjected to high stress. For safety reasons, the PTL's mechanical stability must be ensured. However, the requirements for high porosity and low thickness stand in contrast to that for mechanical stability. Porous transport layers for polymer electrolyte membrane (PEM) electrolysis are typically prepared by means of the thermal sintering of titanium powder. Thus far, the factors that influence the mechanical strength of the sintered bodies and how all requirements can be simultaneously fulfilled have not been investigated. Here, the static and dynamic mechanical properties of thin sintered titanium sheets are investigated ex-situ via tensile tests and periodic loading in a test cell, respectively. In order for a sintered PTL with a thickness of 500 μm and porosities above 25% to be able to withstand 50 bar differential pressure in the cell, the maximum flow field width should be limited to 3 mm. Thus, a method was developed to test the suitability of PTL materials for use in electrolysis for various differential pressures and flow field widths.

Variable threshold algorithm for division of labor analyzed as a dynamical system.

PubMed

Castillo-Cagigal, Manuel; Matallanas, Eduardo; Navarro, Iñaki; Caamaño-Martín, Estefanía; Monasterio-Huelin, Félix; Gutiérrez, Álvaro

2014-12-01

Division of labor is a widely studied aspect of colony behavior of social insects. Division of labor models indicate how individuals distribute themselves in order to perform different tasks simultaneously. However, models that study division of labor from a dynamical system point of view cannot be found in the literature. In this paper, we define a division of labor model as a discrete-time dynamical system, in order to study the equilibrium points and their properties related to convergence and stability. By making use of this analytical model, an adaptive algorithm based on division of labor can be designed to satisfy dynamic criteria. In this way, we have designed and tested an algorithm that varies the response thresholds in order to modify the dynamic behavior of the system. This behavior modification allows the system to adapt to specific environmental and collective situations, making the algorithm a good candidate for distributed control applications. The variable threshold algorithm is based on specialization mechanisms. It is able to achieve an asymptotically stable behavior of the system in different environments and independently of the number of individuals. The algorithm has been successfully tested under several initial conditions and number of individuals.

What dynamics can be expected for mixed states in two-slit experiments?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luis, Alfredo; Sanz, Ángel S., E-mail: asanz@iff.csic.es

2015-06-15

Weak-measurement-based experiments (Kocsis et al., 2011) have shown that, at least for pure states, the average evolution of independent photons in Young’s two-slit experiment is in compliance with the trajectories prescribed by the Bohmian formulation of quantum mechanics. But, what happens if the same experiment is repeated assuming that the wave function associated with each particle is different, i.e., in the case of mixed (incoherent) states? This question is investigated here by means of two alternative numerical simulations of Young’s experiment, purposely devised to be easily implemented and tested in the laboratory. Contrary to what could be expected a priori, itmore » is found that even for conditions of maximal mixedness or incoherence (total lack of interference fringes), experimental data will render a puzzling and challenging outcome: the average particle trajectories will still display features analogous to those for pure states, i.e., independently of how mixedness arises, the associated dynamics is influenced by both slits at the same time. Physically this simply means that weak measurements are not able to discriminate how mixedness arises in the experiment, since they only provide information about the averaged system dynamics. - Highlights: • The dynamics associated with mixture states in investigated by means of two simple Young’s two-slit models. • The models are prepared to be easily implemented and tested in the laboratory by means of weak measurements. • Bohmian mechanics has been generalized to encompass statistical mixtures. • Even for conditions of maximal mixedness numerical simulations show that the dynamics is strongly influenced by both slits. • Accordingly, weak measurements are unable to discriminate how mixedness arises in an experiment.« less

Mechanical properties characterization of polymethyl methacrylate polymer optical fibers after thermal and chemical treatments

NASA Astrophysics Data System (ADS)

Leal-Junior, Arnaldo; Frizera, Anselmo; Marques, Carlos; Pontes, Maria José

2018-07-01

This paper presents the dynamic mechanical analysis (DMA) in polymer optical fibers (POFs) made of Polymethyl Methacrylate (PMMA) that were submitted to different thermal and chemical treatments, namely annealing and etching processes. The prepared samples were submitted to stress-strain cycles to evaluate the Young's modulus of each fiber. Also, test with constant stress and temperature variation were performed to estimate the thermal expansion coefficient of the fibers submitted to each thermal and chemical treatment. The samples were also tested under different temperature, humidity and strain cycle frequency conditions to analyze the variation of their mechanical properties with these parameters. Results show that the thermal and chemical treatments lead to a reduction of Young's modulus and an increase of the thermal expansion coefficient, which can produce sensors based on intensity variation or fiber Bragg grating with higher dynamic range, stress and temperature sensitivity. Furthermore, the etching and annealing resulted in fiber that presents lower Young's modulus variation with temperature, humidity and strain cycling frequency in most cases. However, the annealing made under water and the combinations of etching and annealing resulted in POFs with higher modulus variation with humidity, which enable their application as intensity variation or FBG-based sensors in humidity/moisture assessment.

A Dynamic Simulation of Musculoskeletal Function in the Mouse Hindlimb During Trotting Locomotion

PubMed Central

Charles, James P.; Cappellari, Ornella; Hutchinson, John R.

2018-01-01

Mice are often used as animal models of various human neuromuscular diseases, and analysis of these models often requires detailed gait analysis. However, little is known of the dynamics of the mouse musculoskeletal system during locomotion. In this study, we used computer optimization procedures to create a simulation of trotting in a mouse, using a previously developed mouse hindlimb musculoskeletal model in conjunction with new experimental data, allowing muscle forces, activation patterns, and levels of mechanical work to be estimated. Analyzing musculotendon unit (MTU) mechanical work throughout the stride allowed a deeper understanding of their respective functions, with the rectus femoris MTU dominating the generation of positive and negative mechanical work during the swing and stance phases. This analysis also tested previous functional inferences of the mouse hindlimb made from anatomical data alone, such as the existence of a proximo-distal gradient of muscle function, thought to reflect adaptations for energy-efficient locomotion. The results do not strongly support the presence of this gradient within the mouse musculoskeletal system, particularly given relatively high negative net work output from the ankle plantarflexor MTUs, although more detailed simulations could test this further. This modeling analysis lays a foundation for future studies of the control of vertebrate movement through the development of neuromechanical simulations. PMID:29868576

Preparation of a Strong Gelatin-Short Linear Glucan Nanocomposite Hydrogel by an in Situ Self-Assembly Process.

PubMed

Ge, Shengju; Li, Man; Ji, Na; Liu, Jing; Mul, Hongyan; Xiong, Liu; Sun, Qingjie

2018-01-10

Gelatin hydrogels exhibit excellent biocompatibility, nonimmunogenicity, and biodegradability, but they have limited applications in the food and medical industries because of their poor mechanical properties. Herein, we first developed an in situ self-assembly process for the preparation of gelatin-short linear glucan (SLG) nanocomposite hydrogels with enhanced mechanical strength. The microstructure, dynamic viscoelasticity, compression behavior, and thermal characteristics of the gelatin-SLG nanocomposite hydrogels were determined using scanning electron microscopy (SEM), dynamic rheological experiments, compression tests, and texture profile analysis tests. The SEM images revealed that nanoparticles were formed by the in situ self-assembly of SLG in the gelatin matrix and that the size of these nanoparticles ranged between 200 and 600 nm. The pores of the nanocomposite hydrogels were smaller than those of the pure gelatin hydrogels. Transmission electron microscopy images and X-ray diffraction further confirmed the presence of SLG nanoparticles with spherical shapes and B-type structures. Compared with pure gelatin hydrogels, the nanocomposite hydrogels exhibited improved mechanical behavior. Notably, the hardness and maximum values of the compressive stress of gelatin-SLG nanocomposites containing 5% SLG increased by about 2-fold and 3-fold, respectively, compared to the corresponding values of pure gelatin hydrogels.

Berthing simulator for space station and orbiter

NASA Technical Reports Server (NTRS)

Veerasamy, Sam

1991-01-01

The development of a real-time man-in-the-loop berthing simulator is in progress at NASA Lyndon B. Johnson Space Center (JSC) to conduct a parametric study and to measure forces during contact conditions of the actual docking mechanisms for the Space Station Freedom and the orbiter. In berthing, the docking ports of the Space Station and the orbiter are brought together using the orbiter robotic arm to control the relative motion of the vehicles. The berthing simulator consists of a dynamics docking test system (DDTS), computer system, simulator software, and workstations. In the DDTS, the Space Station, and the orbiter docking mechanisms are mounted on a six-degree-of-freedom (6 DOF) table and a fixed platform above the table. Six load cells are used on the fixed platform to measure forces during contact conditions of the docking mechanisms. Two Encore Concept 32/9780 computers are used to simulate the orbiter robotic arm and to operate the berthing simulator. A systematic procedure for a real-time dynamic initialization is being developed to synchronize the Space Station docking port trajectory with the 6 DOF table movement. The berthing test can be conducted manually or automatically and can be extended for any two orbiting vehicles using a simulated robotic arm. The real-time operation of the berthing simulator is briefly described.

Mountain bicycle frame testing as an example of practical implementation of hybrid simulation using RTFEM

NASA Astrophysics Data System (ADS)

Mucha, Waldemar; Kuś, Wacław

2018-01-01

The paper presents a practical implementation of hybrid simulation using Real Time Finite Element Method (RTFEM). Hybrid simulation is a technique for investigating dynamic material and structural properties of mechanical systems by performing numerical analysis and experiment at the same time. It applies to mechanical systems with elements too difficult or impossible to model numerically. These elements are tested experimentally, while the rest of the system is simulated numerically. Data between the experiment and numerical simulation are exchanged in real time. Authors use Finite Element Method to perform the numerical simulation. The following paper presents the general algorithm for hybrid simulation using RTFEM and possible improvements of the algorithm for computation time reduction developed by the authors. The paper focuses on practical implementation of presented methods, which involves testing of a mountain bicycle frame, where the shock absorber is tested experimentally while the rest of the frame is simulated numerically.

Advanced Nanoindentation Testing for Studying Strain-Rate Sensitivity and Activation Volume

NASA Astrophysics Data System (ADS)

Maier-Kiener, Verena; Durst, Karsten

2017-11-01

Nanoindentation became a versatile tool for testing local mechanical properties beyond hardness and modulus. By adapting standard nanoindentation test methods, simple protocols capable of probing thermally activated deformation processes can be accomplished. Abrupt strain-rate changes within one indentation allow determining the strain-rate dependency of hardness at various indentation depths. For probing lower strain-rates and excluding thermal drift influences, long-term creep experiments can be performed by using the dynamic contact stiffness for determining the true contact area. From both procedures hardness and strain-rate, and consequently strain-rate sensitivity and activation volume can be reliably deducted within one indentation, permitting information on the locally acting thermally activated deformation mechanism. This review will first discuss various testing protocols including possible challenges and improvements. Second, it will focus on different examples showing the direct influence of crystal structure and/or microstructure on the underlying deformation behavior in pure and highly alloyed material systems.

Dynamic Network Logistic Regression: A Logistic Choice Analysis of Inter- and Intra-Group Blog Citation Dynamics in the 2004 US Presidential Election

PubMed Central

2013-01-01

Methods for analysis of network dynamics have seen great progress in the past decade. This article shows how Dynamic Network Logistic Regression techniques (a special case of the Temporal Exponential Random Graph Models) can be used to implement decision theoretic models for network dynamics in a panel data context. We also provide practical heuristics for model building and assessment. We illustrate the power of these techniques by applying them to a dynamic blog network sampled during the 2004 US presidential election cycle. This is a particularly interesting case because it marks the debut of Internet-based media such as blogs and social networking web sites as institutionally recognized features of the American political landscape. Using a longitudinal sample of all Democratic National Convention/Republican National Convention–designated blog citation networks, we are able to test the influence of various strategic, institutional, and balance-theoretic mechanisms as well as exogenous factors such as seasonality and political events on the propensity of blogs to cite one another over time. Using a combination of deviance-based model selection criteria and simulation-based model adequacy tests, we identify the combination of processes that best characterizes the choice behavior of the contending blogs. PMID:24143060

Stressed but Stable: Canopy Loss Decreased Species Synchrony and Metabolic Variability in an Intertidal Hard-Bottom Community

PubMed Central

Valdivia, Nelson; Golléty, Claire; Migné, Aline; Davoult, Dominique; Molis, Markus

2012-01-01

The temporal stability of aggregate community properties depends on the dynamics of the component species. Since species growth can compensate for the decline of other species, synchronous species dynamics can maintain stability (i.e. invariability) in aggregate properties such as community abundance and metabolism. In field experiments we tested the separate and interactive effects of two stressors associated with storminess–loss of a canopy-forming species and mechanical disturbances–on species synchrony and community respiration of intertidal hard-bottom communities on Helgoland Island, NE Atlantic. Treatments consisted of regular removal of the canopy-forming seaweed Fucus serratus and a mechanical disturbance applied once at the onset of the experiment in March 2006. The level of synchrony in species abundances was assessed from estimates of species percentage cover every three months until September 2007. Experiments at two sites consistently showed that canopy loss significantly reduced species synchrony. Mechanical disturbance had neither separate nor interactive effects on species synchrony. Accordingly, in situ measurements of CO2-fluxes showed that canopy loss, but not mechanical disturbances, significantly reduced net primary productivity and temporal variation in community respiration during emersion periods. Our results support the idea that compensatory dynamics may stabilise aggregate properties. They further suggest that the ecological consequences of the loss of a single structurally important species may be stronger than those derived from smaller-scale mechanical disturbances in natural ecosystems. PMID:22574181

Shock-driven fluid-structure interaction for civil design

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wood, Stephen L; Deiterding, Ralf

The multiphysics fluid-structure interaction simulation of shock-loaded structures requires the dynamic coupling of a shock-capturing flow solver to a solid mechanics solver for large deformations. The Virtual Test Facility combines a Cartesian embedded boundary approach with dynamic mesh adaptation in a generic software framework of flow solvers using hydrodynamic finite volume upwind schemes that are coupled to various explicit finite element solid dynamics solvers (Deiterding et al., 2006). This paper gives a brief overview of the computational approach and presents first simulations that utilize the general purpose solid dynamics code DYNA3D for complex 3D structures of interest in civil engineering.more » Results from simulations of a reinforced column, highway bridge, multistory building, and nuclear reactor building are presented.« less

Molecular dynamics calculation on structures, stabilities, mechanical properties, and energy density of CL-20/FOX-7 cocrystal explosives.

PubMed

Hang, Gui-Yun; Yu, Wen-Li; Wang, Tao; Wang, Jin-Tao; Li, Zhen

2017-11-30

In this article, different CL-20/FOX-7 cocrystal models were established by the substitution method based on the molar ratios of CL-20:FOX-7. The structures and comprehensive properties, including mechanical properties, stabilities, and energy density, of different cocrystal models were obtained and compared with each other. The main aim was to estimate the influence of molar ratios on properties of cocrystal explosives. The molecular dynamics (MD) simulation results show that the cocrystal model with molar ratio 1:1 has the best mechanical properties and highest binding energy, so the CL-20/FOX-7 cocrystal model is more likely to form in 1:1 M ratio. The detonation parameters show that the cocrystal explosive exhibited preferable energy density and excellent detonation performance. In a word, the 1:1 cocrystal model has the best comprehensive properties, is very promising, and worth more theoretical investigations and experimental tests. This paper gives some original theories to better understand the cocrystal mechanism and provides some helpful guidance and useful instructions to help design CL-20 cocrystal explosives.

The Significance of Small Cracks in Fatigue Design Concepts as Related to Rotorcraft Metallic Dynamic Components

NASA Technical Reports Server (NTRS)

Everett, R. A., Jr.; Elber, W.

2000-01-01

In this paper the significance of the "small" crack effect as defined in fracture mechanics will be discussed as it relates to life managing rotorcraft dynamic components using the conventional safe-life, the flaw tolerant safe-life, and the damage tolerance design philosophies. These topics will be introduced starting with an explanation of the small-crack theory, then showing how small-crack theory has been used to predict the total fatigue life of fatigue laboratory test coupons with and without flaws, and concluding with how small cracks can affect the crack-growth damage tolerance design philosophy. As stated in this paper the "small" crack effect is defined in fracture mechanics where it has been observed that cracks on the order of 300 microns or less in length will propagate at higher growth rates than long cracks and also will grow at AK values below the long crack AK threshold. The small-crack effect is illustrated herein as resulting from a lack of crack closure and is explained based on continuum mechanics principles using crack-closure concepts in fracture mechanics.

Effect of filler content on mechanical and dynamic mechanical properties of particulate biphasic calcium phosphate--polylactide composites.

PubMed

Bleach, N C; Nazhat, S N; Tanner, K E; Kellomäki, M; Törmälä, P

2002-04-01

A bioabsorbable self-reinforced polylactide/biphasic calcium phosphate (BCP) composite is being developed for fracture fixation plates. One manufacturing route is to produce preimpregnated sheets by pulling polylactide (PLA) fibres through a suspension of BCP filler in a PLA solution and compression moulding the prepreg to the desired shape. To aid understanding of the process, interactions between the matrix and filler were investigated. Composite films containing 0-0.25 volume fraction filler, produced by solvent casting, were analysed using SEM, tensile testing and dynamic mechanical analysis (DMA). Homogeneous films could be made, although some particle agglomeration was seen at higher filler volume fractions. As the filler content increased, the failure strain decreased due to a reduction in the amount of ductile polymer present and the ultimate tensile strength (UTS) decreased because of agglomeration and void formation at higher filler content. The matrix glass transition temperature increased due to polymer chain adsorption and immobilization onto the BCP particles. Complex damping mechanisms, such as particle-particle agglomeration, may exist at the higher BCP volume fractions.

Molecular-dynamics simulations of crosslinking and confinement effects on structure, segmental mobility and mechanics of filled elastomers

NASA Astrophysics Data System (ADS)

Davris, Theodoros; Lyulin, Alexey V.

2016-05-01

The significant drop of the storage modulus under uniaxial deformation (Payne effect) restrains the performance of the elastomer-based composites and the development of possible new applications. In this paper molecular-dynamics (MD) computer simulations using LAMMPS MD package have been performed to study the mechanical properties of a coarse-grained model of this family of nanocomposite materials. Our goal is to provide simulational insights into the viscoelastic properties of filled elastomers, and try to connect the macroscopic mechanics with composite microstructure, the strength of the polymer-filler interactions and the polymer mobility at different scales. To this end we simulate random copolymer films capped between two infinite solid (filler aggregate) walls. We systematically vary the strength of the polymer-substrate adhesion interactions, degree of polymer confinement (film thickness), polymer crosslinking density, and study their influence on the equilibrium and non-equilibrium structure, segmental dynamics, and the mechanical properties of the simulated systems. The glass-transition temperature increases once the mesh size became smaller than the chain radius of gyration; otherwise it remained invariant to mesh-size variations. This increase in the glass-transition temperature was accompanied by a monotonic slowing-down of segmental dynamics on all studied length scales. This observation is attributed to the correspondingly decreased width of the bulk density layer that was obtained in films whose thickness was larger than the end-to-end distance of the bulk polymer chains. To test this hypothesis additional simulations were performed in which the crystalline walls were replaced with amorphous or rough walls.

Modeling of abnormal mechanical properties of nickel-based single crystal superalloy by three-dimensional discrete dislocation dynamics

NASA Astrophysics Data System (ADS)

Yang, Hui; Li, Zhenhuan; Huang, Minsheng

2014-12-01

Unlike common single crystals, the nickel-based single crystal superalloy shows surprisingly anomalous flow strength (i.e. with the increase of temperature, the yield strength first increases to a peak value and then decreases) and tension-compression (TC) asymmetry. A comprehensive three-dimensional discrete dislocation dynamics (3D-DDD) procedure was developed to model these abnormal mechanical properties. For this purpose, a series of complicated dynamic evolution details of Kear-Wilsdorf (KW) locks, which are closely related to the flow strength anomaly and TC asymmetry, were incorporated into this 3D-DDD framework. Moreover, the activation of the cubic slip system, which is the origin of the decrease in yield strength with increasing temperature at relatively high temperatures, was especially taken into account by introducing a competition criterion between the unlocking of the KW locks and the activation of the cubic slip system. To test our framework, a series of 3D-DDD simulations were performed on a representative volume cell model with a cuboidal Ni3Al precipitate phase embedded in a nickel matrix. Results show that the present 3D-DDD procedure can successfully capture the dynamic evolution of KW locks, the flow strength anomaly and TC asymmetry. Then, the underlying dislocation mechanisms leading to these abnormal mechanical responses were investigated and discussed in detail. Finally, a cyclic deformation of the nickel-based single crystal superalloy was modeled by using the present DDD model, with a special focus on the influence of KW locks on the Bauschinger effect and cyclic softening.

Examining Fundamental Movement Competency and Closed-Chain Upper-Extremity Dynamic Balance in Swimmers.

PubMed

Bullock, Garrett S; Brookreson, Nate; Knab, Amy M; Butler, Robert J

2017-06-01

Abnormal fundamental movement patterns and upper-quarter dynamic balance are proposed mechanisms affecting athletic performance and injury risk. There are few studies investigating functional movement and closed-chain upper-extremity dynamic stability in swimmers. The purpose of this study was to determine differences in fundamental movement competency and closed-chain upper-extremity dynamic balance, using the Functional Movement Screen (FMS) and Upper-Quarter Y Balance Test (YBT-UQ), of high school (HS; n = 70) and collegiate (COL; n = 70) swimmers. Variables included the individual movement tests on the FMS and the average normalized reach (percent limb length [%LL]) for each direction, with the YBT-UQ. Statistical analysis was completed using a chi square for the independent test scores on the FMS while independent samples t-test to examine performance on the YBT-UQ (p ≤ 0.05). HS swimmers exhibited a statistically significant greater percentage of below average performance (score of 0 or 1) on the following FMS tests: lunge (HS: 22.9%, COL: 4.3%), hurdle step (HS: 31.4%, COL: 7.1%), and push-up (HS: 61.4%, COL: 31.4%). Furthermore, COL males performed worse in the lunge (male: 9%, female: 0%), whereas COL females had poorer efficiency in the push-up (male: 17.6%, female: 44%). Significant effects of competition level and sex were observed in YBT-UQ medial reach (HS: female 92.06, male 101.63; COL: female 101.3, male 101.5% LL). Individual fundamental movement patterns that involved lumbopelvic neuromuscular control differed between HS and COL swimmers. General upper-extremity dynamic balance differed between competition levels. These data may be helpful in understanding injury and performance-based normative data for participation and return to swimming.

Pressure calculation in hybrid particle-field simulations

NASA Astrophysics Data System (ADS)

Milano, Giuseppe; Kawakatsu, Toshihiro

2010-12-01

In the framework of a recently developed scheme for a hybrid particle-field simulation techniques where self-consistent field (SCF) theory and particle models (molecular dynamics) are combined [J. Chem. Phys. 130, 214106 (2009)], we developed a general formulation for the calculation of instantaneous pressure and stress tensor. The expressions have been derived from statistical mechanical definition of the pressure starting from the expression for the free energy functional in the SCF theory. An implementation of the derived formulation suitable for hybrid particle-field molecular dynamics-self-consistent field simulations is described. A series of test simulations on model systems are reported comparing the calculated pressure with those obtained from standard molecular dynamics simulations based on pair potentials.

Models Provide Specificity: Testing a Proposed Mechanism of Visual Working Memory Capacity Development

ERIC Educational Resources Information Center

Simmering, Vanessa R.; Patterson, Rebecca

2012-01-01

Numerous studies have established that visual working memory has a limited capacity that increases during childhood. However, debate continues over the source of capacity limits and its developmental increase. Simmering (2008) adapted a computational model of spatial cognitive development, the Dynamic Field Theory, to explain not only the source…

Feedback Mechanisms in Learning Virtual Community Settings

ERIC Educational Resources Information Center

Colazzo, Luigi; Comai, Alessio; Davi, Filippo; Molinari, Andrea; Villa, Nicola

2010-01-01

This paper introduces a set of services for the creation of on-line surveys, questionnaires, exams and self-assessment tests within a virtual community system used in e-learning settings. The system, called "Online Communities", is a dynamic web application used as platform for blended learning activities by the Faculty of Economics of…

Force Project Technology Presentation to the NRCC

DTIC Science & Technology

2014-02-04

Functional Bridge components Smart Odometer Adv Pretreatment Smart Bridge Multi-functional Gap Crossing Fuel Automated Tracking System Adv...comprehensive matrix of candidate composite material systems and textile reinforcement architectures via modeling/analyses and testing. Product(s...Validated Dynamic Modeling tool based on parametric study using material models to reliably predict the textile mechanics of the hose

Learning, Retention, and Forgetting of Newton's Third Law throughout University Physics

ERIC Educational Resources Information Center

Sayre, Eleanor C.; Franklin, Scott V.; Dymek, Stephanie; Clark, Jessica; Sun, Yifei

2012-01-01

We present data from a between-student study on student response to questions on Newton's third law given in two introductory calculus-based physics classes (Mechanics and Electromagnetism) at a large northeastern university. Construction of a response curve reveals subtle dynamics in student learning not capturable by pretesting and post-testing.…

Ability-Training-Oriented Automated Assessment in Introductory Programming Course

ERIC Educational Resources Information Center

Wang, Tiantian; Su, Xiaohong; Ma, Peijun; Wang, Yuying; Wang, Kuanquan

2011-01-01

Learning to program is a difficult process for novice programmers. AutoLEP, an automated learning and assessment system, was developed by us, to aid novice programmers to obtain programming skills. AutoLEP is ability-training-oriented. It adopts a novel assessment mechanism, which combines static analysis with dynamic testing to analyze student…

The deformable secondary mirror of VLT: final electro-mechanical and optical acceptance test results

NASA Astrophysics Data System (ADS)

Briguglio, Runa; Biasi, Roberto; Xompero, Marco; Riccardi, Armando; Andrighettoni, Mario; Pescoller, Dietrich; Angerer, Gerald; Gallieni, Daniele; Vernet, Elise; Kolb, Johann; Arsenault, Robin; Madec, Pierre-Yves

2014-07-01

The Deformable Secondary Mirror (DSM) for the VLT ended the stand-alone electro-mechanical and optical acceptance process, entering the test phase as part of the Adaptive Optics Facility (AOF) at the ESO Headquarter (Garching). The VLT-DSM currently represents the most advanced already-built large-format deformable mirror with its 1170 voice-coil actuators and its internal metrology based on co-located capacitive sensors to control the shape of the 1.12m-diameter 2mm-thick convex shell. The present paper reports the final results of the electro-mechanical and optical characterization of the DSM executed in a collaborative effort by the DSM manufacturing companies (Microgate s.r.l. and A.D.S. International s.r.l.), INAF-Osservatorio Astrofisico di Arcetri and ESO. The electro-mechanical acceptance tests have been performed in the company premises and their main purpose was the dynamical characterization of the internal control loop response and the calibration of the system data that are needed for its optimization. The optical acceptance tests have been performed at ESO (Garching) using the ASSIST optical test facility. The main purpose of the tests are the characterization of the optical shell flattening residuals, the corresponding calibration of flattening commands, the optical calibration of the capacitive sensors and the optical calibration of the mirror influence functions.

On the Comparison of the Long Penetration Mode (LPM) Supersonic Counterflowing Jet to the Supersonic Screech Jet

NASA Technical Reports Server (NTRS)

Farr, Rebecca A.; Chang, Chau-Lyan.; Jones, Jess H.; Dougherty, N. Sam

2015-01-01

The authors provide a brief overview of the classic tonal screech noise problem created by underexpanded supersonic jets, briefly describing the fluid dynamic-acoustics feedback mechanism that has been long established as the basis for this well-known aeroacoustics problem. This is followed by a description of the Long Penetration Mode (LPM) supersonic underexpanded counterflowing jet phenomenon which has been demonstrated in several wind tunnel tests and modeled in several computational fluid dynamics (CFD) simulations. The authors provide evidence from test and CFD analysis of LPM that indicates that acoustics feedback and fluid interaction seen in LPM are analogous to the aeroacoustics interactions seen in screech jets. Finally, the authors propose applying certain methodologies to LPM which have been developed and successfully demonstrated in the study of screech jets and mechanically induced excitation in fluid oscillators for decades. The authors conclude that the large body of work done on jet screech, other aeroacoustic phenomena, and fluid oscillators can have direct application to the study and applications of LPM counterflowing supersonic cold flow jets.

A cyber-physical approach to experimental fluid mechanics

NASA Astrophysics Data System (ADS)

Mackowski, Andrew Williams

This Thesis documents the design, implementation, and use of a novel type of experimental apparatus, termed Cyber-Physical Fluid Dynamics (CPFD). Unlike traditional fluid mechanics experiments, CPFD is a general-purpose technique that allows one to impose arbitrary forces on an object submerged in a fluid. By combining fluid mechanics with robotics, we can perform experiments that would otherwise be incredibly difficult or time-consuming. More generally, CPFD allows a high degree of automation and control of the experimental process, allowing for much more efficient use of experimental facilities. Examples of CPFD's capabilites include imposing a gravitational force in the horizontal direction (allowing a test object to "fall" sideways in a water channel), simulating nonlinear springs for a vibrating fluid-structure system, or allowing a self-propelled body to move forward under its own force. Because experimental parameters (including forces and even the mass of the test object) are defined in software, one can define entire ensembles of experiments to run autonomously. CPFD additionally integrates related systems such as water channel speed control, LDV flow speed measurements, and PIV flowfield measurements. The end result is a general-purpose experimental system that opens the door to a vast array of fluid-structure interaction problems. We begin by describing the design and implementation of CPFD, the heart of which is a high-performance force-feedback control system. Precise measurement of time-varying forces (including removing effects of the test object's inertia) is more critical here than in typical robotic force-feedback applications. CPFD is based on an integration of ideas from control theory, fluid dynamics, computer science, electrical engineering, and solid mechanics. We also describe experiments using the CPFD experimental apparatus to study vortex-induced vibration (VIV) and oscillating-airfoil propulsion. We show how CPFD can be used to simulate a hypothetical VIV energy harvesting device. By replacing standard linear springs with nonlinear ones, we can broaden the system's frequency response. Next, we transition from bluff bodies to unsteady airfoils, where we begin by measuring the thrust and efficiency of an airfoil pitching about its quarter-chord point. Finally, we examine how the propulsive performance of an oscillating airfoil is improved by the addition of passive dynamics.

Low-Velocity Impact Wear Behavior of Ball-to-Flat Contact Under Constant Kinetic Energy

NASA Astrophysics Data System (ADS)

Wang, Zhang; Cai, Zhen-bing; Chen, Zhi-qiang; Sun, Yang; Zhu, Min-hao

2017-11-01

The impact tests were conducted on metallic materials with different bulk hardness and Young's moduli. Analysis of the dynamics response during the tribological process showed that the tested materials had similar energy absorption, where the peak contact force increased as the tests continued. Moreover, wear volume decreased with the increase in Young's modulus of metals, except for Cr with a relatively low hardness. Wear rate was gradually reduced to a steady stage with increasing cycles, which was attributed to the decrease in contact stress and work-hardening effect. The main wear mechanism of impact was characterized by delamination, and the specific surface degradation mechanisms were depending on the mechanical properties of materials. The absorbed energy was used to the propagation of micro-cracks in the subsurface instead of plastic deformation, when resistance of friction wear and plastic behavior was improved. Hence, both the hardness and Young's modulus played important roles in the impact wear of metallic materials.

An Improved Model of Heat-Induced Hyperalgesia—Repetitive Phasic Heat Pain Causing Primary Hyperalgesia to Heat and Secondary Hyperalgesia to Pinprick and Light Touch

PubMed Central

Henrich, Florian; Magerl, Walter; May, Arne

2014-01-01

This study tested a modified experimental model of heat-induced hyperalgesia, which improves the efficacy to induce primary and secondary hyperalgesia and the efficacy-to-safety ratio reducing the risk of tissue damage seen in other heat pain models. Quantitative sensory testing was done in eighteen healthy volunteers before and after repetitive heat pain stimuli (60 stimuli of 48°C for 6 s) to assess the impact of repetitive heat on somatosensory function in conditioned skin (primary hyperalgesia area) and in adjacent skin (secondary hyperalgesia area) as compared to an unconditioned mirror image control site. Additionally, areas of flare and secondary hyperalgesia were mapped, and time course of hyperalgesia determined. After repetitive heat pain conditioning we found significant primary hyperalgesia to heat, and primary and secondary hyperalgesia to pinprick and to light touch (dynamic mechanical allodynia). Acetaminophen (800 mg) reduced pain to heat or pinpricks only marginally by 11% and 8%, respectively (n.s.), and had no effect on heat hyperalgesia. In contrast, the areas of flare (−31%) and in particular of secondary hyperalgesia (−59%) as well as the magnitude of hyperalgesia (−59%) were significantly reduced (all p<0.001). Thus, repetitive heat pain induces significant peripheral sensitization (primary hyperalgesia to heat) and central sensitization (punctate hyperalgesia and dynamic mechanical allodynia). These findings are relevant to further studies using this model of experimental heat pain as it combines pronounced peripheral and central sensitization, which makes a convenient model for combined pharmacological testing of analgesia and anti-hyperalgesia mechanisms related to thermal and mechanical input. PMID:24911787

The dynamic failure behavior of tungsten heavy alloys subjected to transverse loads

NASA Astrophysics Data System (ADS)

Tarcza, Kenneth Robert

Tungsten heavy alloys (WHA), a category of particulate composites used in defense applications as kinetic energy penetrators, have been studied for many years. Even so, their dynamic failure behavior is not fully understood and cannot be predicted by numerical models presently in use. In this experimental investigation, a comprehensive understanding of the high-rate transverse-loading fracture behavior of WHA has been developed. Dynamic fracture events spanning a range of strain rates and loading conditions were created via mechanical testing and used to determine the influence of surface condition and microstructure on damage initiation, accumulation, and sample failure under different loading conditions. Using standard scanning electron microscopy metallographic and fractographic techniques, sample surface condition is shown to be extremely influential to the manner in which WHA fails, causing a fundamental change from externally to internally nucleated failures as surface condition is improved. Surface condition is characterized using electron microscopy and surface profilometry. Fracture surface analysis is conducted using electron microscopy, and linear elastic fracture mechanics is used to understand the influence of surface condition, specifically initial flaw size, on sample failure behavior. Loading conditions leading to failure are deduced from numerical modeling and experimental observation. The results highlight parameters and considerations critical to the understanding of dynamic WHA fracture and the development of dynamic WHA failure models.

Semiclassical Monte Carlo: A first principles approach to non-adiabatic molecular dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

White, Alexander J.; Center for Nonlinear Studies; Gorshkov, Vyacheslav N.

2014-11-14

Modeling the dynamics of photophysical and (photo)chemical reactions in extended molecular systems is a new frontier for quantum chemistry. Many dynamical phenomena, such as intersystem crossing, non-radiative relaxation, and charge and energy transfer, require a non-adiabatic description which incorporate transitions between electronic states. Additionally, these dynamics are often highly sensitive to quantum coherences and interference effects. Several methods exist to simulate non-adiabatic dynamics; however, they are typically either too expensive to be applied to large molecular systems (10's-100's of atoms), or they are based on ad hoc schemes which may include severe approximations due to inconsistencies in classical and quantummore » mechanics. We present, in detail, an algorithm based on Monte Carlo sampling of the semiclassical time-dependent wavefunction that involves running simple surface hopping dynamics, followed by a post-processing step which adds little cost. The method requires only a few quantities from quantum chemistry calculations, can systematically be improved, and provides excellent agreement with exact quantum mechanical results. Here we show excellent agreement with exact solutions for scattering results of standard test problems. Additionally, we find that convergence of the wavefunction is controlled by complex valued phase factors, the size of the non-adiabatic coupling region, and the choice of sampling function. These results help in determining the range of applicability of the method, and provide a starting point for further improvement.« less

A consumer-resource approach to the density-dependent population dynamics of mutualism.

PubMed

Holland, J Nathaniel; DeAngelis, Donald L

2010-05-01

Like predation and competition, mutualism is now recognized as a consumer-resource (C-R) interaction, including, in particular, bi-directional (e.g., coral, plant-mycorrhizae) and uni-directional (e.g., ant-plant defense, plant-pollinator) C-R mutualisms. Here, we develop general theory for the density-dependent population dynamics of mutualism based on the C-R mechanism of interspecific interaction. To test the influence of C-R interactions on the dynamics and stability of bi- and uni-directional C-R mutualisms, we developed simple models that link consumer functional response of one mutualistic species with the resources supplied by another. Phase-plane analyses show that the ecological dynamics of C-R mutualisms are stable in general. Most transient behavior leads to an equilibrium of mutualistic coexistence, at which both species densities are greater than in the absence of interactions. However, due to the basic nature of C-R interactions, certain density-dependent conditions can lead to C-R dynamics characteristic of predator-prey interactions, in which one species overexploits and causes the other to go extinct. Consistent with empirical phenomena, these results suggest that the C-R interaction can provide a broad mechanism for understanding density-dependent population dynamics of mutualism. By unifying predation, competition, and mutualism under the common ecological framework of consumer-resource theory, we may also gain a better understanding of the universal features of interspecific interactions in general.

A consumer-resource approach to the density-dependent population dynamics of mutualism

USGS Publications Warehouse

Holland, J. Nathaniel; DeAngelis, Donald L.

2010-01-01

Like predation and competition, mutualism is now recognized as a consumer resource (C-R) interaction, including, in particular, bi-directional (e.g., coral, plant- mycorrhizae) and uni-directional (e.g., ant-plant defense, plant-pollinator) C-R mutualisms. Here, we develop general theory for the density-dependent population dynamics of mutualism based on the C-R mechanism of interspecific interaction. To test the influence of C-R interactions on the dynamics and stability of bi- and uni-directional C-R mutualisms, we developed simple models that link consumer functional response of one mutualistic species with the resources supplied by another. Phase-plane analyses show that the ecological dynamics of C-R mutualisms are stable in general. Most transient behavior leads to an equilibrium of mutualistic coexistence, at which both species densities are greater than in the absence of interactions. However, due to the basic nature of C-R interactions, certain density-dependent conditions can lead to C-R dynamics characteristic of predator-prey interactions, in which one species overexploits and causes the other to go extinct. Consistent with empirical phenomena, these results suggest that the C-R interaction can provide a broad mechanism for understanding density-dependent population dynamics of mutualism. By unifying predation, competition, and mutualism under the common ecological framework of consumer-resource theory, we may also gain a better understanding of the universal features of interspecific interactions in general.

Personalized hip implants manufacturing and testing

NASA Astrophysics Data System (ADS)

Croitoru, A. Sorin Mihai; Pacioga, B. Adrian; Comsa, C. Stanca

2017-09-01

Two models of Ti6Al4V personalized femoral stems for hip replacement have been designed and laser sintered with different sizes of fenestrated architecture that mimics the natural structure of bone, ensuring postoperative bone ingrowth and increasing the elasticity of the entire structure. They were tested statically and dynamically versus a commercial femoral stem. Mechanical tests were performed in order to determine the fatigue limit using the Locati method. The tests were conducted in a thermostatic bath (37°±1°) with the implants immersed in distilled water salted solution 0.91%. For probe embedment poly-methyl methacrylate (PMMA) was used. The characteristic curves of the two personalized fenestrated implants reveal an elastic behaviour by their nonlinear appearance. After dynamic tests an inverse relationship between displacements obtained in the static tests and the fatigue limit was observed. Large fenestrations conferred the desired elasticity to the implant, but contributed to a life service reduction. The fatigue limit for both implants was much above the minimum value specified by ISO 7602: 2010, so both models can be safely used in the medical practice, leading to increased life service of implants.

Human-Robot Collaboration Dynamic Impact Testing and Calibration Instrument for Disposable Robot Safety Artifacts

PubMed Central

Dagalakis, Nicholas G.; Yoo, Jae Myung; Oeste, Thomas

2017-01-01

The Dynamic Impact Testing and Calibration Instrument (DITCI) is a simple instrument with a significant data collection and analysis capability that is used for the testing and calibration of biosimulant human tissue artifacts. These artifacts may be used to measure the severity of injuries caused in the case of a robot impact with a human. In this paper we describe the DITCI adjustable impact and flexible foundation mechanism, which allows the selection of a variety of impact force levels and foundation stiffness. The instrument can accommodate arrays of a variety of sensors and impact tools, simulating both real manufacturing tools and the testing requirements of standards setting organizations. A computer data acquisition system may collect a variety of impact motion, force, and torque data, which are used to develop a variety of mathematical model representations of the artifacts. Finally, we describe the fabrication and testing of human abdomen soft tissue artifacts, used to display the magnitude of impact tissue deformation. Impact tests were performed at various maximum impact force and average pressure levels. PMID:28579658

Human-Robot Collaboration Dynamic Impact Testing and Calibration Instrument for Disposable Robot Safety Artifacts.

PubMed

Dagalakis, Nicholas G; Yoo, Jae Myung; Oeste, Thomas

2016-01-01

The Dynamic Impact Testing and Calibration Instrument (DITCI) is a simple instrument with a significant data collection and analysis capability that is used for the testing and calibration of biosimulant human tissue artifacts. These artifacts may be used to measure the severity of injuries caused in the case of a robot impact with a human. In this paper we describe the DITCI adjustable impact and flexible foundation mechanism, which allows the selection of a variety of impact force levels and foundation stiffness. The instrument can accommodate arrays of a variety of sensors and impact tools, simulating both real manufacturing tools and the testing requirements of standards setting organizations. A computer data acquisition system may collect a variety of impact motion, force, and torque data, which are used to develop a variety of mathematical model representations of the artifacts. Finally, we describe the fabrication and testing of human abdomen soft tissue artifacts, used to display the magnitude of impact tissue deformation. Impact tests were performed at various maximum impact force and average pressure levels.

The release of nickel from orthodontic NiTi wires is increased by dynamic mechanical loading but not constrained by surface nitridation.

PubMed

Peitsch, T; Klocke, A; Kahl-Nieke, B; Prymak, O; Epple, M

2007-09-01

The influence of dynamic mechanical loading and of surface nitridation on the nickel release from superelastic nickel-titanium orthodontic wires was investigated under ultrapure conditions. Commercially available superelastic NiTi arch wires (size 0.018 x 0.025'') without surface modification (Neo Sentalloy) and with nitrogen ion implantation surface treatment (Neo Sentalloy Ionguard) were analyzed. Mechanical loading of wire segments with a force similar to the physiological situation was performed with a frequency of 5 Hz in ultrapure water and saline solution, respectively. The release of nickel was monitored by atomic absorption spectroscopy for up to 36 days. The mechanically loaded wires released significantly more nickel ( approximately 45 ng cm(-2) d(-1)) than did nonloaded wires (<1 ng cm(-2) d(-1)). There was no statistically significant effect of the testing solution (water or NaCl) or of the surface nitridation. The total amount of released nickel was small in all cases, but may nevertheless account for the occasional clinical observations of adverse reactions during application of NiTi-based orthodontic appliances. The surface nitridation did not constrain the release of nickel from NiTi under continuous mechanical stress.

The History and Implications of Design Standards for Underwater Breathing Apparatus - 1954 to 2015

DTIC Science & Technology

2015-02-11

respiratory loading using both simple models of fluid mechanics and experimental evidence. An understanding of the influence of both respiratory ventilatory... fluid dynamics of flow in divers’ airways. It allows testing laboratories to make maximum use of all of their testing data, and lo present that data in...tireless efforts of numerous military divers at Navy Experimental Diving Unit in Panama City, FL and Naval Medical Research Institute, Bethesda, MD

Application of the Wavy Mechanical Face Seal to Submarine Seal Design.

DTIC Science & Technology

1982-07-01

to Stainless Steel Bond Strength Tests. . . 31 3-1 Seal Design ...... .................... ... 54 3-2 Offset and Tilt Results...primer, Loctite Superbonder 420 with the addi- tion of two stainless steel rings for the inner and outer diam- eter of the carbon insert to give a...near zero clearance fit, and the use of the 3M 1838 B/A epoxy also with the same stainless steel rings. Static and dynamic tests on the seal under water

Laser-Induced Thermal Acoustics Theory and Expected Experimental Errors when Applied to a Scramjet Isolator Model

NASA Technical Reports Server (NTRS)

Middleton, Troy F.; Balla, Robert Jeffrey; Baurle, Robert A.; Wilson, Lloyd G.

2011-01-01

A scramjet isolator model test apparatus is being assembled in the Isolator Dynamics Research Lab (IDRL) at the NASA Langley Research Center in Hampton, Virginia. The test apparatus is designed to support multiple measurement techniques for investigating the flow field in a scramjet isolator model. The test section is 1-inch high by 2-inch wide by 24-inch long and simulates a scramjet isolator with an aspect ratio of two. Unheated, dry air at a constant stagnation pressure and temperature is delivered to the isolator test section through a Mach 2.5 planar nozzle. The isolator test section is mechanically back-pressured to contain the resulting shock train within the 24-inch isolator length and supports temperature, static pressure, and high frequency pressure measurements at the wall. Additionally, nonintrusive methods including laser-induced thermal acoustics (LITA), spontaneous Raman scattering, particle image velocimetry, and schlieren imaging are being incorporated to measure off-wall fluid dynamic, thermodynamic, and transport properties of the flow field. Interchangeable glass and metallic sidewalls and optical access appendages permit making multiple measurements simultaneously. The measurements will be used to calibrate computational fluid dynamics turbulence models and characterize the back-pressured flow of a scramjet isolator. This paper describes the test apparatus, including the optical access appendages; the physics of the LITA method; and estimates of LITA measurement uncertainty for measurements of the speed of sound and temperature.

Mechanical Properties of Materials with Nanometer Scale Microstructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

William D. Nix

2004-10-31

We have been engaged in research on the mechanical properties of materials with nanometer-scale microstructural dimensions. Our attention has been focused on studying the mechanical properties of thin films and interfaces and very small volumes of material. Because the dimensions of thin film samples are small (typically 1 mm in thickness, or less), specialized mechanical testing techniques based on nanoindentation, microbeam bending and dynamic vibration of micromachined structures have been developed and used. Here we report briefly on some of the results we have obtained over the past three years. We also give a summary of all of the dissertations,more » talks and publications completed on this grant during the past 15 years.« less

Planetary Migration and Kuiper Belt Dynamics

NASA Astrophysics Data System (ADS)

Malhotra, Renu

The Kuiper belt holds memory of the dynamical processes that shaped the architecture of the solar system, including the orbital migration history of the giant planets. We propose studies of the orbital dynamics of the Kuiper Belt in order to understand the origin of its complex dynamical structure and its link to the orbital migration history of the giant planets. By means of numerical simulations, statistical tests, as well as analytical calculations we will (1) investigate the origin of resonant Kuiper belt objects to test alternative scenarios of Neptune's migration history, (2) investigate the long term dynamical evolution of the Haumea family of Kuiper Belt objects in order to improve the age estimate of this family, and (3) investigate resonance-sticking behavior and the Kozai-Lidov mechanism and its role in the origin of the extended scattered disk. These studies directly support the goals of the NASA-OSS program by improving our understanding of the origin of the solar system's architecture. Our results will provide constraints on the nature and timing of the dynamical excitation event that is thought to have occurred in early solar system history and to have determined the architecture of the present-day solar system; our results will also provide deeper theoretical understanding of sticky mean motion resonances which contribute greatly to the longevity of many small bodies, improve our understanding of dynamical transport of planetesimals in planetary systems, and help interpret observations of other planetary systems.

Spectral Dynamics Inc., ships hybrid, 316-channel data acquisition system to Sandia Labs.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwartz, Douglas

2003-09-01

Spectral Dynamics announced the shipment of a 316-channel data acquisition system. The system was custom designed for the Light Initiated High Explosive (LIHE) facility at Sandia Labs in Albuquerque, New Mexico by Spectral Dynamics Advanced Research Products Group. This Spectral Dynamics data acquisition system was tailored to meet the unique LIHE environmental and testing requirements utilizing Spectral Dynamics commercial off the shelf (COTS) Jaguar and VIDAS products supplemented by SD Alliance partner's (COTS) products. 'This system is just the beginning of our cutting edge merged technology solutions,' stated Mark Remelman, Manager for the Spectral Dynamics Advanced Research Products Group. 'Thismore » Hybrid system has 316-channels of data acquisition capability, comprised of 102.4kHz direct to disk acquisition and 2.5MHz, 200Mhz & 500Mhz RAM based capabilities. In addition it incorporates the advanced bridge conditioning and dynamic configuration capabilities offered by Spectral Dynamics new Smart Interface Panel System (SIPS{trademark}).' After acceptance testing, Tony King, the Instrumentation Engineer facilitating the project for the Sandia LIHE group commented; 'The LIHE staff was very impressed with the design, construction, attention to detail and overall performance of the instrumentation system'. This system combines VIDAS, a leading edge fourth generation SD-VXI hardware and field-proven software system from SD's Advanced Research Products Group with SD's Jaguar, a multiple Acquisition Control Peripheral (ACP) system that allows expansion to hundreds of channels without sacrificing signal processing performance. Jaguar incorporates dedicated throughput disks for each ACP providing time streaming to disk at up to the maximum sample rate. Spectral Dynamics, Inc. is a leading worldwide supplier of systems and software for advanced computer-automated data acquisition, vibration testing, structural dynamics, explosive shock, high-speed transient capture, acoustic analysis, monitoring, measurement, control and backup. Spectral Dynamics products are used for research, design verification, product testing and process improvement by manufacturers of all types of electrical, electronic and mechanical products, as well as by universities and government-funded agencies. The Advanced Research Products Group is the newest addition to the Spectral Dynamics family. Their newest VXI data acquisition hardware pushes the envelope on capabilities and embodies the same rock solid design methodologies, which have always differentiated Spectral Dynamics from its competition.« less

Computational analysis of nonlinearities within dynamics of cable-based driving systems

NASA Astrophysics Data System (ADS)

Anghelache, G. D.; Nastac, S.

2017-08-01

This paper deals with computational nonlinear dynamics of mechanical systems containing some flexural parts within the actuating scheme, and, especially, the situations of the cable-based driving systems were treated. It was supposed both functional nonlinearities and the real characteristic of the power supply, in order to obtain a realistically computer simulation model being able to provide very feasible results regarding the system dynamics. It was taken into account the transitory and stable regimes during a regular exploitation cycle. The authors present a particular case of a lift system, supposed to be representatively for the objective of this study. The simulations were made based on the values of the essential parameters acquired from the experimental tests and/or the regular practice in the field. The results analysis and the final discussions reveal the correlated dynamic aspects within the mechanical parts, the driving system, and the power supply, whole of these supplying potential sources of particular resonances, within some transitory phases of the working cycle, and which can affect structural and functional dynamics. In addition, it was underlines the influences of computational hypotheses on the both quantitative and qualitative behaviour of the system. Obviously, the most significant consequence of this theoretical and computational research consist by developing an unitary and feasible model, useful to dignify the nonlinear dynamic effects into the systems with cable-based driving scheme, and hereby to help an optimization of the exploitation regime including a dynamics control measures.

Universal effect of dynamical reinforcement learning mechanism in spatial evolutionary games

NASA Astrophysics Data System (ADS)

Zhang, Hai-Feng; Wu, Zhi-Xi; Wang, Bing-Hong

2012-06-01

One of the prototypical mechanisms in understanding the ubiquitous cooperation in social dilemma situations is the win-stay, lose-shift rule. In this work, a generalized win-stay, lose-shift learning model—a reinforcement learning model with dynamic aspiration level—is proposed to describe how humans adapt their social behaviors based on their social experiences. In the model, the players incorporate the information of the outcomes in previous rounds with time-dependent aspiration payoffs to regulate the probability of choosing cooperation. By investigating such a reinforcement learning rule in the spatial prisoner's dilemma game and public goods game, a most noteworthy viewpoint is that moderate greediness (i.e. moderate aspiration level) favors best the development and organization of collective cooperation. The generality of this observation is tested against different regulation strengths and different types of network of interaction as well. We also make comparisons with two recently proposed models to highlight the importance of the mechanism of adaptive aspiration level in supporting cooperation in structured populations.

Investigation on temporal evolution of the grain refinement in copper under high strain rate loading via in-situ synchrotron measurement and predictive modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shah, Pooja Nitin; Shin, Yung C.; Sun, Tao

Synchrotron X-rays are integrated with a modified Kolsky tension bar to conduct in situ tracking of the grain refinement mechanism operating during the dynamic deformation of metals. Copper with an initial average grain size of 36 μm is refined to 6.3 μm when loaded at a constant high strain rate of 1200 s -1. The synchrotron measurements revealed the temporal evolution of the grain refinement mechanism in terms of the initiation and rate of refinement throughout the loading test. A multiscale coupled probabilistic cellular automata based recrystallization model has been developed to predict the microstructural evolution occurring during dynamic deformationmore » processes. The model accurately predicts the initiation of the grain refinement mechanism with a predicted final average grain size of 2.4 μm. As a result, the model also accurately predicts the temporal evolution in terms of the initiation and extent of refinement when compared with the experimental results.« less

Dynamic stress effects in technical superconductors and the ''training'' problem of superconducting magnets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pasztor, G.; Schmidt, C.

The behavior of NbTi superconductors under dynamic mechanical stress was investigated. A training effect was found in short-sample tests when the conductor was strained in a magnetic field and with a transport current applied. Possible mechanisms are discussed which were proposed to explain training in short samples and in magnets. A stress-induced microplastic as well as an incomplete pseudoelastic behavior of NbTi was detected by monitoring acoustic emission. The experiments support the hypothesis that microplastic or shape memory effects in NbTi involving dislocation processes are responsible for training. The minimum energy needed to induce a normal transition in short-sample testsmore » is calculated with a computer program, which gives the exact solution of the heat equation. A prestrain treatment of the conductor at room temperature is shown to be a simple method of reducing training of short samples and of magnets. This is a direct proof that the same mechanisms are involved in both cases.« less

Investigation on temporal evolution of the grain refinement in copper under high strain rate loading via in-situ synchrotron measurement and predictive modeling

DOE PAGES

Shah, Pooja Nitin; Shin, Yung C.; Sun, Tao

2017-10-03

Synchrotron X-rays are integrated with a modified Kolsky tension bar to conduct in situ tracking of the grain refinement mechanism operating during the dynamic deformation of metals. Copper with an initial average grain size of 36 μm is refined to 6.3 μm when loaded at a constant high strain rate of 1200 s -1. The synchrotron measurements revealed the temporal evolution of the grain refinement mechanism in terms of the initiation and rate of refinement throughout the loading test. A multiscale coupled probabilistic cellular automata based recrystallization model has been developed to predict the microstructural evolution occurring during dynamic deformationmore » processes. The model accurately predicts the initiation of the grain refinement mechanism with a predicted final average grain size of 2.4 μm. As a result, the model also accurately predicts the temporal evolution in terms of the initiation and extent of refinement when compared with the experimental results.« less

Microstructural Characteristic of the Al-Fe-Cu Alloy During High-Speed Repetitive Continuous Extrusion Forming

NASA Astrophysics Data System (ADS)

Hu, Jiamin; Teng, Jie; Ji, Xiankun; Kong, Xiangxin; Jiang, Fulin; Zhang, Hui

2016-11-01

High-speed repetitive continuous extrusion forming process (R-Conform process) was performed on the Al-Fe-Cu alloy. The microstructural evolution and mechanical properties were studied by x-ray diffraction, electron backscatter diffraction, transmission electron microscopy and tensile testing. The results show that a significant improvement of tensile ductility concurs with a considerable loss of tensile strength before four passes, after that the process on mechanical properties variation tends to be steady, indicating an accelerated mechanical softening occurs when comparing to low-speed R-Conform process. Microstructure characterization indicates that the accumulated strain promotes the transformation of low angle boundaries to high angle boundaries, thus leading to the acceleration of continuous dynamic recrystallization process, and the precipitates are broken, spheroidized and homogeneously distribute in Al matrix as increasing R-Conform passes. Massive microshear bands are observed after initial passes of R-Conform process, which may promote continuous dynamic recrystallization and further grain refinement during high-speed R-Conform process.

RELATING ACCUMULATOR MODEL PARAMETERS AND NEURAL DYNAMICS

PubMed Central

Purcell, Braden A.; Palmeri, Thomas J.

2016-01-01

Accumulator models explain decision-making as an accumulation of evidence to a response threshold. Specific model parameters are associated with specific model mechanisms, such as the time when accumulation begins, the average rate of evidence accumulation, and the threshold. These mechanisms determine both the within-trial dynamics of evidence accumulation and the predicted behavior. Cognitive modelers usually infer what mechanisms vary during decision-making by seeing what parameters vary when a model is fitted to observed behavior. The recent identification of neural activity with evidence accumulation suggests that it may be possible to directly infer what mechanisms vary from an analysis of how neural dynamics vary. However, evidence accumulation is often noisy, and noise complicates the relationship between accumulator dynamics and the underlying mechanisms leading to those dynamics. To understand what kinds of inferences can be made about decision-making mechanisms based on measures of neural dynamics, we measured simulated accumulator model dynamics while systematically varying model parameters. In some cases, decision- making mechanisms can be directly inferred from dynamics, allowing us to distinguish between models that make identical behavioral predictions. In other cases, however, different parameterized mechanisms produce surprisingly similar dynamics, limiting the inferences that can be made based on measuring dynamics alone. Analyzing neural dynamics can provide a powerful tool to resolve model mimicry at the behavioral level, but we caution against drawing inferences based solely on neural analyses. Instead, simultaneous modeling of behavior and neural dynamics provides the most powerful approach to understand decision-making and likely other aspects of cognition and perception. PMID:28392584

Dynamic modeling and experiment of a new type of parallel servo press considering gravity counterbalance

NASA Astrophysics Data System (ADS)

He, Jun; Gao, Feng; Bai, Yongjun; Wu, Shengfu

2013-11-01

The large capacity servo press is traditionally realized by means of redundant actuation, however there exist the over-constraint problem and interference among actuators, which increases the control difficulty and the product cost. A new type of press mechanism with parallel topology is presented to develop the mechanical servo press with high stamping capacity. The dynamic model considering gravity counterbalance is proposed based on the virtual work principle, and then the effect of counterbalance cylinder on the dynamic performance of the servo press is studied. It is found that the motor torque required to operate the press is a lot less than the others when the ratio of the counterbalance force to the gravity of ram is in the vicinity of 1.0. The stamping force of the real press prototype can reach up to 25 MN on the position of 13 mm away from the bottom dead center. The typical deep-drawing process with 1 200 mm stroke at 8 strokes per minute is proposed by means of five order polynomial. On this process condition, the driving torques are calculated based on the above dynamic model and the torque measuring test is also carried out on the prototype. It is shown that the curve trend of calculation torque is consistent to the measured result and that the average error is less than 15%. The parallel mechanism is introduced into the development of large capacity servo press to avoid the over-constraint and interference of traditional redundant actuation, and its dynamic characteristics with gravity counterbalance are presented.

In Vivo Patellofemoral Contact Mechanics During Active Extension Using a Novel Dynamic MRI-based Methodology

PubMed Central

Borotikar, Bhushan S.; Sheehan, Frances T.

2017-01-01

Objectives To establish an in vivo, normative patellofemoral cartilage contact mechanics database acquired during voluntary muscle control using a novel dynamic magnetic resonance (MR) imaging-based computational methodology and validate the contact mechanics sensitivity to the known sub-millimeter methodological inaccuracies. Design Dynamic cine phase-contrast and multi-plane cine images were acquired while female subjects (n=20, sample of convenience) performed an open kinetic chain (knee flexion-extension) exercise inside a 3-Tesla MR scanner. Static cartilage models were created from high resolution three-dimensional static MR data and accurately placed in their dynamic pose at each time frame based on the cine-PC data. Cartilage contact parameters were calculated based on the surface overlap. Statistical analysis was performed using paired t-test and a one-sample repeated measures ANOVA. The sensitivity of the contact parameters to the known errors in the patellofemoral kinematics was determined. Results Peak mean patellofemoral contact area was 228.7±173.6mm2 at 40° knee angle. During extension, contact centroid and peak strain locations tracked medially on the femoral and patellar cartilage and were not significantly different from each other. At 30°, 35°, and 40° of knee extension, contact area was significantly different. Contact area and centroid locations were insensitive to rotational and translational perturbations. Conclusion This study is a first step towards unfolding the biomechanical pathways to anterior patellofemoral pain and OA using dynamic, in vivo, and accurate methodologies. The database provides crucial data for future studies and for validation of, or as an input to, computational models. PMID:24012620

Dynamic mechanical analysis of storage modulus development in light-activated polymer matrix composites.

PubMed

Sakaguchi, Ronald L; Shah, Nilam C; Lim, Bum Soon; Ferracane, Jack L; Borgersen, Svenn E

2002-05-01

The goal of this study was to evaluate the potential for using dynamic mechanical analysis of tubular geometry in a three-point flexure fixture for monitoring the storage modulus development of a light-activated polymer matrix composite. Composite samples were inserted into PTFE tubes and tested in a three-point bend fixture in a dynamic mechanical analyzer (DMA) at 200 Hz with 20 microm amplitude. Samples were light activated for 60s (385 mW/cm(2) at the composite surface) and storage modulus (E') was measured continuously for the seven light-activated composites studied (one microfill, four hybrids and two unfilled resins). Cores of composite were removed from the PTFE sheath after 13.5 min and evaluated with the same parameters in the DMA. A finite element model of the test configuration was created and used to estimate operating parameters for the DMA. Degree of conversion (DC) was measured using micro-Fourier Transform Infrared (FTIR) spectroscopy for the microfilled composite samples and one hybrid 13.5 and 60 min after light activation. The E' for a generic hybrid and microfilled composite was 13,400+/-1100 and 5900+/-200 MPa, respectively, when cured within the tube and then removed and tested in the DMA. DC was 54.6% for the hybrid and 60.6% for the microfill. A linear regression of E' for the sheath and core vs core alone (r(2)=0.986) indicated a linear scaling of the sheath and core values for E' enabling a correction for estimated E' values of the composite core. This method estimates the storage modulus growth during light-activated polymerization of highly filled dimethacrylates. Although the approach is phenomenological in that quantitative measurements of E' are not made directly from the DMA, estimates of early polymerization kinetics appear to be validated by three different approaches.

Development of a simulation model for dynamic derailment analysis of high-speed trains

NASA Astrophysics Data System (ADS)

Ling, Liang; Xiao, Xin-Biao; Jin, Xue-Song

2014-12-01

The running safety of high-speed trains has become a major concern of the current railway research with the rapid development of high-speed railways around the world. The basic safety requirement is to prevent the derailment. The root causes of the dynamic derailment of high-speed trains operating in severe environments are not easy to identify using the field tests or laboratory experiments. Numerical simulation using an advanced train-track interaction model is a highly efficient and low-cost approach to investigate the dynamic derailment behavior and mechanism of high-speed trains. This paper presents a three-dimensional dynamic model of a high-speed train coupled with a ballast track for dynamic derailment analysis. The model considers a train composed of multiple vehicles and the nonlinear inter-vehicle connections. The ballast track model consists of rails, fastenings, sleepers, ballasts, and roadbed, which are modeled by Euler beams, nonlinear spring-damper elements, equivalent ballast bodies, and continuous viscoelastic elements, in which the modal superposition method was used to reduce the order of the partial differential equations of Euler beams. The commonly used derailment safety assessment criteria around the world are embedded in the simulation model. The train-track model was then used to investigate the dynamic derailment responses of a high-speed train passing over a buckled track, in which the derailment mechanism and train running posture during the dynamic derailment process were analyzed in detail. The effects of train and track modelling on dynamic derailment analysis were also discussed. The numerical results indicate that the train and track modelling options have a significant effect on the dynamic derailment analysis. The inter-vehicle impacts and the track flexibility and nonlinearity should be considered in the dynamic derailment simulations.

Jitter Test Program and On-Orbit Mitigation Strategies for Solar Dynamic Observatory

NASA Technical Reports Server (NTRS)

Liu, Kuo-Chia; Kenney, Thomas; Maghami, Peiman; Mule, Pete; Blaurock, Carl; Haile, William B.

2007-01-01

The Solar Dynamic Observatory (SDO) aims to study the Sun's influence on the Earth, the source, storage, and release of the solar energy, and the interior structure of the Sun. During science observations, the jitter stability at the instrument focal plane must be maintained to less than a fraction of an arcsecond for two of the SDO instruments. To meet these stringent requirements, a significant amount of analysis and test effort has been devoted to predicting the jitter induced from various disturbance sources. This paper presents an overview of the SDO jitter analysis approach and test effort performed to date. It emphasizes the disturbance modeling, verification, calibration, and validation of the high gain antenna stepping mechanism and the reaction wheels, which are the two largest jitter contributors. This paper also describes on-orbit mitigation strategies to protect the system from analysis model uncertainties. Lessons learned from the SDO jitter analyses and test programs are included in the paper to share the knowledge gained with the community.

Drop Weight Impact Behavior of Al-Si-Cu Alloy Foam-Filled Thin-Walled Steel Pipe Fabricated by Friction Stir Back Extrusion

NASA Astrophysics Data System (ADS)

Hangai, Yoshihiko; Nakano, Yukiko; Utsunomiya, Takao; Kuwazuru, Osamu; Yoshikawa, Nobuhiro

2017-02-01

In this study, Al-Si-Cu alloy ADC12 foam-filled thin-walled stainless steel pipes, which exhibit metal bonding between the ADC12 foam and steel pipe, were fabricated by friction stir back extrusion. Drop weight impact tests were conducted to investigate the deformation behavior and mechanical properties of the foam-filled pipes during dynamic compression tests, which were compared with the results of static compression tests. From x-ray computed tomography observation, it was confirmed that the fabricated foam-filled pipes had almost uniform porosity and pore size distributions. It was found that no scattering of the fragments of collapsed ADC12 foam occurred for the foam-filled pipes owing to the existence of the pipe surrounding the ADC12 foam. Preventing the scattering of the ADC12 foam decreases the drop in stress during dynamic compression tests and therefore improves the energy absorption properties of the foam.

Noradrenergic activation of the basolateral amygdala maintains hippocampus-dependent accuracy of remote memory.

PubMed

Atucha, Erika; Vukojevic, Vanja; Fornari, Raquel V; Ronzoni, Giacomo; Demougin, Philippe; Peter, Fabian; Atsak, Piray; Coolen, Marcel W; Papassotiropoulos, Andreas; McGaugh, James L; de Quervain, Dominique J-F; Roozendaal, Benno

2017-08-22

Emotional enhancement of memory by noradrenergic mechanisms is well-described, but the long-term consequences of such enhancement are poorly understood. Over time, memory traces are thought to undergo a neural reorganization, that is, a systems consolidation, during which they are, at least partly, transferred from the hippocampus to neocortical networks. This transfer is accompanied by a decrease in episodic detailedness. Here we investigated whether norepinephrine (NE) administration into the basolateral amygdala after training on an inhibitory avoidance discrimination task, comprising two distinct training contexts, alters systems consolidation dynamics to maintain episodic-like accuracy and hippocampus dependency of remote memory. At a 2-d retention test, both saline- and NE-treated rats accurately discriminated the training context in which they had received footshock. Hippocampal inactivation with muscimol before retention testing disrupted discrimination of the shock context in both treatment groups. At 28 d, saline-treated rats showed hippocampus-independent retrieval and lack of discrimination. In contrast, NE-treated rats continued to display accurate memory of the shock-context association. Hippocampal inactivation at this remote retention test blocked episodic-like accuracy and induced a general memory impairment. These findings suggest that the NE treatment altered systems consolidation dynamics by maintaining hippocampal involvement in the memory. This shift in systems consolidation was paralleled by time-regulated DNA methylation and transcriptional changes of memory-related genes, namely Reln and Pkm ζ, in the hippocampus and neocortex. The findings provide evidence suggesting that consolidation of emotional memories by noradrenergic mechanisms alters systems consolidation dynamics and, as a consequence, influences the maintenance of long-term episodic-like accuracy of memory.

Energy absorption capability of foam-based composite materials and their applications as seat cushions in aircraft crashworthiness

NASA Astrophysics Data System (ADS)

Kh. Beheshti, Hamid

This study is focusing on the application of foam materials in aviation. These materials are being used for acoustic purposes, as padding in the finished interior panels of the aircraft, and as seat cushions. Foams are mostly used in seating applications. Since seat cushion is directly interacting with the body of occupant, it has to be ergonomically comfortable beside of absorbing the energy during the impact. All the seats and seat cushions have to pass regulations defined by Federal Aviation Administration (FAA). In fact, all airplane companies are required to certify the subcomponents of aircrafts before installing them on the main structure, fuselage. Current Federal Aviation Administration Regulations require a dynamic sled test of the entire seat system for certifying the seat cushions. This dynamic testing is required also for replacing the deteriorated cushions with new cushions. This involves a costly and time-consuming certification process. AGATE group has suggested a procedure based on quasi-static testing in order to certify new seat cushions without conducting full-scale dynamic sled testing. AGATE subcomponent methodology involves static tests of the energy-absorbing foam cushions and design validation by conducting a full-scale dynamic seat test. Microscopic and macroscopic studies are necessary to provide a complete understanding about performance of foams during the crash. Much investigation has been done by different sources to obtain the reliable modeling in terms of demonstration of mechanical behavior of foams. However, rate sensitivity of foams needs more attention. A mathematical hybrid dynamic model for the cushion underneath of the human body will be taken into consideration in this research. Analytical and finite element codes such as MADYMO and LS-DYNA codes have the potential to greatly speed up the crashworthy design process, to help certify seats and aircraft to dynamic crash loads, to predict seat and occupant response to impact with the probability of injury, and to evaluate numerous crash scenarios not economically feasible with full-scale crash testing. Therefore, these codes are being used to find the accurate response of spinal load during the impact of model including human body, seat cushion and seat under different acceleration pulses. (Abstract shortened by UMI.)

Dynamic visual acuity using "far" and "near" targets

NASA Technical Reports Server (NTRS)

Peters, Brian T.; Bloomberg, Jacob J.

2005-01-01

CONCLUSIONS: DVA may be useful for assessing the functional consequences of an impaired gaze stabilization mechanism or for testing the effectiveness of a rehabilitation paradigm. Because target distance influences the relative contributions of canal and otolith inputs, the ability to measure DVA at near and far viewing distances may also lead to tests that will independently assess canal and otolith function. OBJECTIVE: To present and test a methodology that uses dynamic visual acuity (DVA) to assess the efficacy of compensatory gaze mechanisms during a functionally relevant activity that differentially measures canal and otolith function. MATERIAL AND METHODS: The effect of treadmill walking at a velocity of 1.79 m/s on subjects' visual acuity was assessed at each of two viewing distances. A custom-written threshold determination program was used to display Landolt C optotypes on a laptop computer screen during a "far" (4 m) target condition and on a micro-display for a "near" (50 cm) target condition. The walking acuity scores for each target distance were normalized by subtracting a corresponding acuity measure obtained while standing still on the treadmill belt. RESULTS: As predicted by subjective reports of relative target motion, the decrease in visual acuity was significantly greater (p < 0.00001) for the near compared to the far condition.

Delay-dependent stability and added damping of SDOF real-time dynamic hybrid testing

NASA Astrophysics Data System (ADS)

Chi, Fudong; Wang, Jinting; Jin, Feng

2010-09-01

It is well-recognized that a transfer system response delay that reduces the test stability inevitably exists in real-time dynamic hybrid testing (RTDHT). This paper focuses on the delay-dependent stability and added damping of SDOF systems in RTDHT. The exponential delay term is transferred into a rational fraction by the Padé approximation, and the delay-dependent stability conditions and instability mechanism of SDOF RTDHT systems are investigated by the root locus technique. First, the stability conditions are discussed separately for the cases of stiffness, mass, and damping experimental substructure. The use of root locus plots shows that the added damping effect and instability mechanism for mass are different from those for stiffness. For the stiffness experimental substructure case, the instability results from the inherent mode because of an obvious negative damping effect of the delay. For the mass case, the delay introduces an equivalent positive damping into the inherent mode, and instability occurs at an added high frequency mode. Then, the compound stability condition is investigated for a general case and the results show that the mass ratio may have both upper and lower limits to remain stable. Finally, a high-emulational virtual shaking table model is built to validate the stability conclusions.

Damage Mechanisms and Controlled Crack Propagation in a Hot Pressed Silicon Nitride Ceramic. Ph.D. Thesis - Northwestern Univ., 1993

NASA Technical Reports Server (NTRS)

Calomino, Anthony Martin

1994-01-01

The subcritical growth of cracks from pre-existing flaws in ceramics can severely affect the structural reliability of a material. The ability to directly observe subcritical crack growth and rigorously analyze its influence on fracture behavior is important for an accurate assessment of material performance. A Mode I fracture specimen and loading method has been developed which permits the observation of stable, subcritical crack extension in monolithic and toughened ceramics. The test specimen and procedure has demonstrated its ability to generate and stably propagate sharp, through-thickness cracks in brittle high modulus materials. Crack growth for an aluminum oxide ceramic was observed to be continuously stable throughout testing. Conversely, the fracture behavior of a silicon nitride ceramic exhibited crack growth as a series of subcritical extensions which are interrupted by dynamic propagation. Dynamic initiation and arrest fracture resistance measurements for the silicon nitride averaged 67 and 48 J/sq m, respectively. The dynamic initiation event was observed to be sudden and explosive. Increments of subcritical crack growth contributed to a 40 percent increase in fracture resistance before dynamic initiation. Subcritical crack growth visibly marked the fracture surface with an increase in surface roughness. Increments of subcritical crack growth loosen ceramic material near the fracture surface and the fracture debris is easily removed by a replication technique. Fracture debris is viewed as evidence that both crack bridging and subsurface microcracking may be some of the mechanisms contributing to the increase in fracture resistance. A Statistical Fracture Mechanics model specifically developed to address subcritical crack growth and fracture reliability is used together with a damaged zone of material at the crack tip to model experimental results. A Monte Carlo simulation of the actual experiments was used to establish a set of modeling input parameters. It was demonstrated that a single critical parameter does not characterize the conditions required for dynamic initiation. Experimental measurements for critical crack lengths, and the energy release rates exhibit significant scatter. The resulting output of the model produces good agreement with both the average values and scatter of experimental measurements.

Experimental investigation of the formaldehyde removal mechanisms in a dynamic botanical filtration system for indoor air purification.

PubMed

Wang, Zhiqiang; Pei, Jingjing; Zhang, Jensen S

2014-09-15

Botanical filtration has been proved to be effective for indoor gas pollutant removal. To understand the roles of different transport, storage and removal mechanism by a dynamic botanical air filter, a series of experimental investigations were designed and conducted in this paper. Golden Pothos (Epipremnum aureum) plants was selected for test, and its original soil or activated/pebbles root bed was used in different test cases. It was found that flowing air through the root bed with microbes dynamically was essential to obtain meaningful formaldehyde removal efficiency. For static potted plant as normally place in rooms, the clean air delivery rate (CADR), which is often used to quantify the air cleaning ability of portable air cleaners, was only ∼ 5.1m(3)/h per m(2) bed, while when dynamically with air flow through the bed, the CADR increased to ∼ 233 m(3)/h per m(2) bed. The calculated CADR due to microbial activity is ∼ 108 m(3)/h per m(2) bed. Moisture in the root bed also played an important role, both for maintaining a favorable living condition for microbes and for absorbing water-soluble compounds such as formaldehyde. The role of the plant was to introduce and maintain a favorable microbe community which effectively degraded the volatile organic compounds adsorbed or absorbed by the root bed. The presence of the plant increased the removal efficiency by a factor of two based on the results from the bench-scale root bed experiments. Copyright © 2014 Elsevier B.V. All rights reserved.

High Strain Rate Tensile Testing of Silver Nanowires: Rate-Dependent Brittle-to-Ductile Transition.

PubMed

Ramachandramoorthy, Rajaprakash; Gao, Wei; Bernal, Rodrigo; Espinosa, Horacio

2016-01-13

The characterization of nanomaterials under high strain rates is critical to understand their suitability for dynamic applications such as nanoresonators and nanoswitches. It is also of great theoretical importance to explore nanomechanics with dynamic and rate effects. Here, we report in situ scanning electron microscope (SEM) tensile testing of bicrystalline silver nanowires at strain rates up to 2/s, which is 2 orders of magnitude higher than previously reported in the literature. The experiments are enabled by a microelectromechanical system (MEMS) with fast response time. It was identified that the nanowire plastic deformation has a small activation volume (<10b(3)), suggesting dislocation nucleation as the rate controlling mechanism. Also, a remarkable brittle-to-ductile failure mode transition was observed at a threshold strain rate of 0.2/s. Transmission electron microscopy (TEM) revealed that along the nanowire, dislocation density and spatial distribution of plastic regions increase with increasing strain rate. Furthermore, molecular dynamic (MD) simulations show that deformation mechanisms such as grain boundary migration and dislocation interactions are responsible for such ductility. Finally, the MD and experimental results were interpreted using dislocation nucleation theory. The predicted yield stress values are in agreement with the experimental results for strain rates above 0.2/s when ductility is pronounced. At low strain rates, random imperfections on the nanowire surface trigger localized plasticity, leading to a brittle-like failure.

Impact Damage and Strain Rate Effects for Toughened Epoxy Composite Structures

NASA Technical Reports Server (NTRS)

Chamis, Christos C.; Minnetyan, Levon

2006-01-01

Structural integrity of composite systems under dynamic impact loading is investigated herein. The GENOA virtual testing software environment is used to implement the effects of dynamic loading on fracture progression and damage tolerance. Combinations of graphite and glass fibers with a toughened epoxy matrix are investigated. The effect of a ceramic coating for the absorption of impact energy is also included. Impact and post impact simulations include verification and prediction of (1) Load and Impact Energy, (2) Impact Damage Size, (3) Maximum Impact Peak Load, (4) Residual Strength, (5) Maximum Displacement, (6) Contribution of Failure Modes to Failure Mechanisms, (7) Prediction of Impact Load Versus Time, and (8) Damage, and Fracture Pattern. A computer model is utilized for the assessment of structural response, progressive fracture, and defect/damage tolerance characteristics. Results show the damage progression sequence and the changes in the structural response characteristics due to dynamic impact. The fundamental premise of computational simulation is that the complete evaluation of composite fracture requires an assessment of ply and subply level damage/fracture processes as the structure is subjected to loads. Simulation results for the graphite/epoxy composite were compared with the impact and tension failure test data, correlation and verification was obtained that included: (1) impact energy, (2) damage size, (3) maximum impact peak load, (4) residual strength, (5) maximum displacement, and (6) failure mechanisms of the composite structure.

A neural coding scheme reproducing foraging trajectories

PubMed Central

Gutiérrez, Esther D.; Cabrera, Juan Luis

2015-01-01

The movement of many animals may follow Lévy patterns. The underlying generating neuronal dynamics of such a behavior is unknown. In this paper we show that a novel discovery of multifractality in winnerless competition (WLC) systems reveals a potential encoding mechanism that is translatable into two dimensional superdiffusive Lévy movements. The validity of our approach is tested on a conductance based neuronal model showing WLC and through the extraction of Lévy flights inducing fractals from recordings of rat hippocampus during open field foraging. Further insights are gained analyzing mice motor cortex neurons and non motor cell signals. The proposed mechanism provides a plausible explanation for the neuro-dynamical fundamentals of spatial searching patterns observed in animals (including humans) and illustrates an until now unknown way to encode information in neuronal temporal series. PMID:26648311

Molecular dynamics computer simulation of permeation in solids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pohl, P.I.; Heffelfinger, G.S.; Fisler, D.K.

1997-12-31

In this work the authors simulate permeation of gases and cations in solid models using molecular mechanics and a dual control volume grand canonical molecular dynamics technique. The molecular sieving nature of microporous zeolites are discussed and compared with that for amorphous silica made by sol-gel methods. One mesoporous and one microporous membrane model are tested with Lennard-Jones gases corresponding to He, H{sub 2}, Ar and CH{sub 4}. The mesoporous membrane model clearly follows a Knudsen diffusion mechanism, while the microporous model having a hard-sphere cutoff pore diameter of {approximately}3.4 {angstrom} demonstrates molecular sieving of the methane ({sigma} = 3.8more » {angstrom}) but anomalous behavior for Ar ({sigma} = 3.4 {angstrom}). Preliminary results of Ca{sup +} diffusion in calcite and He/H{sub 2} diffusion in polyisobutylene are also presented.« less

Augmenting static and dynamic mechanical strength of carbon nanotube/epoxy soft nanocomposites via modulation of purification and functionalization routes.

PubMed

Billing, Beant Kaur; Dhar, Purbarun; Singh, Narinder; Agnihotri, Prabhat K

2018-01-03

A detailed experimental investigation was carried out to establish the relationship between CNT purification and functionalization routes and the average response of CNT/epoxy nanocomposites under static and dynamic loading. It was shown that the relative improvement in the mechanical properties of the epoxy matrix due to the addition of CNTs depends on the choice of purification and functionalization steps. A better dispersion of CNTs was recorded for the functionalized CNTs as compared to the oxidized and CVD grown CNTs. Moreover, tensile, 3-point bending and nanoDMA testing performed on nanocomposites processed with CVD-grown, oxidized and functionalized CNTs revealed that COOH functionalization after the oxidation of CNTs at 350 °C is the optimized processing route to harness the excellent properties of CNTs in CNT/epoxy nanocomposites.

A Bioreactor to Identify the Driving Mechanical Stimuli of Tissue Growth and Remodeling.

PubMed

van Kelle, Mathieu A J; Oomen, Pim J A; Bulsink, Jurgen A; Janssen-van den Broek, Marloes W J T; Lopata, Richard G P; Rutten, Marcel C M; Loerakker, Sandra; Bouten, Carlijn V C

2017-06-01

Tissue growth and remodeling are essential processes that should ensure long-term functionality of tissue-engineered (TE) constructs. Even though it is widely recognized that these processes strongly depend on mechanical stimuli, the underlying mechanisms of mechanically induced growth and remodeling are only partially understood. It is generally accepted that cells sense mechanical changes and respond by altering their surroundings, by means of extracellular matrix growth and remodeling, in an attempt to return to a certain preferred mechanical homeostatic state. However, the exact mechanical cues that trigger cells to synthesize and remodel their environment remain unclear. To identify the driving mechanical stimuli of these processes, it is critical to be able to temporarily follow the mechanical state of developing tissues under physiological loading conditions. Therefore, a novel "versatile tissue growth and remodeling" (Vertigro) bioreactor was developed that is capable of tissue culture and mechanical stimulation for a prolonged time period, while simultaneously performing mechanical testing. The Vertigro's unique two-chamber design allows easy, sterile handling of circular 3D TE constructs in a dedicated culture chamber, while a separate pressure chamber facilitates a pressure-driven dynamic loading regime during culture. As a proof-of-concept, temporal changes in the mechanical state of cultured tissues were quantified using nondestructive mechanical testing by means of a classical bulge test, in which the tissue displacement was tracked using ultrasound imaging. To demonstrate the successful development of the bioreactor system, compositional, structural, and geometrical changes were qualitatively and quantitatively assessed using a series of standard analysis techniques. With this bioreactor and associated mechanical analysis technique, a powerful toolbox has been developed to quantitatively study and identify the driving mechanical stimuli of engineered tissue growth and remodeling.

Effect of cyclic fatigue on the fracture toughness of Polyoxymethylene

NASA Astrophysics Data System (ADS)

Ramoa, B.; Berer, M.; Schwaiger, M.; Pinter, G.

2017-05-01

Polymers are used in a wide range of applications and their properties are dependent upon the morphological development during processing and the specimen configuration which in turn define the mechanical properties. In this context fatigue and monotonic testing are part of the standard procedure to assess relevant mechanical and material parameters to ensure a better part design. The present work addresses the performance issues of a real component made of Polyoxymethylene (POM) which is subjected to cyclic loads from intermediate levels to high peak values inside a damping mechanism. For this linear elastic fracture mechanics concepts were used to characterize the behavior of a POM homopolymer resin used in this application. Injection molded compact tension specimens, with sharp and blunt notches, were tested under a combination of cyclic and monotonic loads and the fracture surfaces were examined. The critical stress intensity factor obtained by monotonic tests was evaluated as a function of the cycle number, where an increase after the first 1000 cycles followed by a continuous decrease with higher numbers of cycles was observed. A variation of approximately 50% and 70% were obtained along the duration of the tests for the sharp and blunt notch specimens, respectively. In light of the obtained results, a discussion is presented considering the dynamic specimen compliance and the structural features observed on the fracture surfaces in combination with the fracture mechanical response.

CFD Fuel Slosh Modeling of Fluid-Structure Interaction in Spacecraft Propellant Tanks with Diaphragms

NASA Technical Reports Server (NTRS)

Sances, Dillon J.; Gangadharan, Sathya N.; Sudermann, James E.; Marsell, Brandon

2010-01-01

Liquid sloshing within spacecraft propellant tanks causes rapid energy dissipation at resonant modes, which can result in attitude destabilization of the vehicle. Identifying resonant slosh modes currently requires experimental testing and mechanical pendulum analogs to characterize the slosh dynamics. Computational Fluid Dynamics (CFD) techniques have recently been validated as an effective tool for simulating fuel slosh within free-surface propellant tanks. Propellant tanks often incorporate an internal flexible diaphragm to separate ullage and propellant which increases modeling complexity. A coupled fluid-structure CFD model is required to capture the damping effects of a flexible diaphragm on the propellant. ANSYS multidisciplinary engineering software employs a coupled solver for analyzing two-way Fluid Structure Interaction (FSI) cases such as the diaphragm propellant tank system. Slosh models generated by ANSYS software are validated by experimental lateral slosh test results. Accurate data correlation would produce an innovative technique for modeling fuel slosh within diaphragm tanks and provide an accurate and efficient tool for identifying resonant modes and the slosh dynamic response.

Experimental metaphysics2 : The double standard in the quantum-information approach to the foundations of quantum theory

NASA Astrophysics Data System (ADS)

Hagar, Amit

Among the alternatives of non-relativistic quantum mechanics (NRQM) there are those that give different predictions than quantum mechanics in yet-untested circumstances, while remaining compatible with current empirical findings. In order to test these predictions, one must isolate one's system from environmental induced decoherence, which, on the standard view of NRQM, is the dynamical mechanism that is responsible for the 'apparent' collapse in open quantum systems. But while recent advances in condensed-matter physics may lead in the near future to experimental setups that will allow one to test the two hypotheses, namely genuine collapse vs. decoherence, hence make progress toward a solution to the quantum measurement problem, those philosophers and physicists who are advocating an information-theoretic approach to the foundations of quantum mechanics are still unwilling to acknowledge the empirical character of the issue at stake. Here I argue that in doing so they are displaying an unwarranted double standard.

Development of a High-speed Electromagnetic Repulsion Mechanism for High-voltage Vacuum Circuit Breakers

NASA Astrophysics Data System (ADS)

Tsukima, Mitsuru; Takeuchi, Toshie; Koyama, Kenichi; Yoshiyasu, Hajimu

This paper presents a design and testing of a new high-speed electromagnetic driving mechanism for a high-voltage vacuum circuit breaker (VCB). This mechanism is based on a high-speed electromagnetic repulsion and a permanent magnet spring (PMS). This PMS is introduced instead of the conventional disk spring due to its low spring energy and more suitable force characteristics for VCB application. The PMS has been optimally designed by the 3d non-linear finite-elements magnetic field analysis and investigated its internal friction and eddy-current effect. Furthermore, we calculated the dynamic of this mechanism coupling with the electromagnetic field and circuit analysis, in order to satisfy the operating characteristics—contact velocity, response time and so on, required for the high-speed VCB. A prototype VCB, which was built based on the above analysis shows sufficient operating performance. Finally, the short circuit interruption tests were carried out with this prototype breaker, and we have been able to verify its satisfying performance.

Dynamic Stiffness Transfer Function of an Electromechanical Actuator Using System Identification

NASA Astrophysics Data System (ADS)

Kim, Sang Hwa; Tahk, Min-Jea

2018-04-01

In the aeroelastic analysis of flight vehicles with electromechanical actuators (EMAs), an accurate prediction of flutter requires dynamic stiffness characteristics of the EMA. The dynamic stiffness transfer function of the EMA with brushless direct current (BLDC) motor can be obtained by conducting complicated mathematical calculations of control algorithms and mechanical/electrical nonlinearities using linearization techniques. Thus, system identification approaches using experimental data, as an alternative, have considerable advantages. However, the test setup for system identification is expensive and complex, and experimental procedures for data collection are time-consuming tasks. To obtain the dynamic stiffness transfer function, this paper proposes a linear system identification method that uses information obtained from a reliable dynamic stiffness model with a control algorithm and nonlinearities. The results of this study show that the system identification procedure is compact, and the transfer function is able to describe the dynamic stiffness characteristics of the EMA. In addition, to verify the validity of the system identification method, the simulation results of the dynamic stiffness transfer function and the dynamic stiffness model were compared with the experimental data for various external loads.

Processing and Characterization of Cellulose Nanocrystals/Polylactic Acid Nanocomposite Films

PubMed Central

Sullivan, Erin M.; Moon, Robert J.; Kalaitzidou, Kyriaki

2015-01-01

The focus of this study is to examine the effect of cellulose nanocrystals (CNC) on the properties of polylactic acid (PLA) films. The films are fabricated via melt compounding and melt fiber spinning followed by compression molding. Film fracture morphology, thermal properties, crystallization behavior, thermo-mechanical behavior, and mechanical behavior were determined as a function of CNC content using scanning electron microscopy, differential scanning calorimetry, X-ray diffraction, dynamic mechanical analysis, and tensile testing. Film crystallinity increases with increasing CNC content indicating CNC act as nucleating agents, promoting crystallization. Furthermore, the addition of CNC increased the film storage modulus and slightly broadened the glass transition region. PMID:28793701

Ballistic and diffusive dynamics in a two-dimensional ideal gas of macroscopic chaotic Faraday waves.

PubMed

Welch, Kyle J; Hastings-Hauss, Isaac; Parthasarathy, Raghuveer; Corwin, Eric I

2014-04-01

We have constructed a macroscopic driven system of chaotic Faraday waves whose statistical mechanics, we find, are surprisingly simple, mimicking those of a thermal gas. We use real-time tracking of a single floating probe, energy equipartition, and the Stokes-Einstein relation to define and measure a pseudotemperature and diffusion constant and then self-consistently determine a coefficient of viscous friction for a test particle in this pseudothermal gas. Because of its simplicity, this system can serve as a model for direct experimental investigation of nonequilibrium statistical mechanics, much as the ideal gas epitomizes equilibrium statistical mechanics.

Standards for Radiation Effects Testing: Ensuring Scientific Rigor in the Face of Budget Realities and Modern Device Challenges

NASA Technical Reports Server (NTRS)

Lauenstein, J M.

2015-01-01

An overview is presented of the space radiation environment and its effects on electrical, electronic, and electromechanical parts. Relevant test standards and guidelines are listed. Test standards and guidelines are necessary to ensure best practices, minimize and bound systematic and random errors, and to ensure comparable results from different testers and vendors. Test standards are by their nature static but exist in a dynamic environment of advancing technology and radiation effects research. New technologies, failure mechanisms, and advancement in our understanding of known failure mechanisms drive the revision or development of test standards. Changes to standards must be weighed against their impact on cost and existing part qualifications. There must be consensus on new best practices. The complexity of some new technologies exceeds the scope of existing test standards and may require development of a guideline specific to the technology. Examples are given to illuminate the value and limitations of key radiation test standards as well as the challenges in keeping these standards up to date.

A Method for Testing the Dynamic Accuracy of Micro-Electro-Mechanical Systems (MEMS) Magnetic, Angular Rate, and Gravity (MARG) Sensors for Inertial Navigation Systems (INS) and Human Motion Tracking Applications

DTIC Science & Technology

2010-06-01

32 2. Low-Cost Framework........................................................................33 3. Low Magnetic Field ...that have a significant impact on the magnetic field measured by a MARG, which could potentially add errors that are due entirely to the test...minimize the impact on the local magnetic field , and the apparatus was made as rigidly as possible using 2 x 4s to minimize any out of plane motions that

Numerical simulation study on thermal response of PBX 9501 to low velocity impact

NASA Astrophysics Data System (ADS)

Lou, Jianfeng; Zhou, Tingting; Zhang, Yangeng; Zhang, Xiaoli

2017-01-01

Impact sensitivity of solid high explosives, an important index in evaluating the safety and performance of explosives, is an important concern in handling, storage, and shipping procedures. It is a great threat for either bare dynamite or shell charge when subjected to low velocity impact involved in traffic accidents or charge piece drops. The Steven test is an effective tool to study the relative sensitivity of various explosives. In this paper, we built the numerical simulation method involving mechanical, thermo and chemical properties of Steven test based on the thermo-mechanical coupled material model. In the model, the stress-strain relationship is described by dynamic plasticity model, the thermal effect of the explosive induced by impact is depicted by isotropic thermal material model, the chemical reaction of explosives is described by Arrhenius reaction rate law, and the effects of heating and melting on mechanical properties and thermal properties of materials are also taken into account. Specific to the standard Steven test, the thermal and mechanical response rules of PBX 9501 at various impact velocities were numerically analyzed, and the threshold velocity of explosive initiation was obtained, which is in good agreement with experimental results. In addition, the effect of confine condition of test device to the threshold velocity was explored.

Influence of Water Content on Mechanical Properties of Rock in Both Saturation and Drying Processes

NASA Astrophysics Data System (ADS)

Zhou, Zilong; Cai, Xin; Cao, Wenzhuo; Li, Xibing; Xiong, Cheng

2016-08-01

Water content has a pronounced influence on the properties of rock materials, which is responsible for many rock engineering hazards, such as landslides and karst collapse. Meanwhile, water injection is also used for the prevention of some engineering disasters like rock-bursts. To comprehensively investigate the effect of water content on mechanical properties of rocks, laboratory tests were carried out on sandstone specimens with different water contents in both saturation and drying processes. The Nuclear Magnetic Resonance technique was applied to study the water distribution in specimens with variation of water contents. The servo-controlled rock mechanics testing machine and Split Hopkinson Pressure Bar technique were used to conduct both compressive and tensile tests on sandstone specimens with different water contents. From the laboratory tests, reductions of the compressive and tensile strength of sandstone under static and dynamic states in different saturation processes were observed. In the drying process, all of the saturated specimens could basically regain their mechanical properties and recover its strength as in the dry state. However, for partially saturated specimens in the saturation and drying processes, the tensile strength of specimens with the same water content was different, which could be related to different water distributions in specimens.

Study on creep properties of Japonica cooked rice and its relationship with rice chemical compositions and sensory evaluation

USDA-ARS?s Scientific Manuscript database

Creep properties of four varieties japonica cooked rice were tested using a Dynamic Mechanical Analyser (DMA Q800). The creep curve was described by Burgers model. The creep process of japonica cooked rice mainly consisted of retarded elastic deformation, epsilonR and viscous flow deformation, epsil...

Subjective Well-Being as an Indicator for Clinical Depression

ERIC Educational Resources Information Center

Gargiulo, R.; Stokes, Mark A.

2009-01-01

The Theory of Homeostasis posits that Subjective Well-being (SWB) is regulated by a dynamic biological mechanism, assisting to maintain a positive view of life. Further, the theory suggests that clinical depression is the loss of SWB due to the defeat of this homeostatic defence system. To test this hypothesis it was predicted that people who were…

Computational Methods for Structural Mechanics and Dynamics

NASA Technical Reports Server (NTRS)

Stroud, W. Jefferson (Editor); Housner, Jerrold M. (Editor); Tanner, John A. (Editor); Hayduk, Robert J. (Editor)

1989-01-01

Topics addressed include: transient dynamics; transient finite element method; transient analysis in impact and crash dynamic studies; multibody computer codes; dynamic analysis of space structures; multibody mechanics and manipulators; spatial and coplanar linkage systems; flexible body simulation; multibody dynamics; dynamical systems; and nonlinear characteristics of joints.

Performance of a Single Liquid Column Damper for the Control of Dynamic Responses of a Tension Leg Platform

NASA Astrophysics Data System (ADS)

Jaksic, V.; Wright, C.; Chanayil, Afeef; Faruque Ali, Shaikh; Murphy, Jimmy; Pakrashi, Vikram

2015-07-01

Tuned liquid column dampers have been proved to be successful in mitigating the dynamic responses of civil infrastructure. There have been some recent applications of this concept on wind turbines and this passive control system can help to mitigate responses of offshore floating platforms and wave devices. The control of dynamic responses of these devices is important for reducing loads on structural elements and facilitating operations and maintenance (O&M) activities. This paper outlines the use of a tuned single liquid column damper for the control of a tension leg platform supported wind turbine. Theoretical studies were carried out and a scaled model was tested in a wave basin to assess the performance of the damper. The tests on the model presented in this paper correspond to a platform with a very low natural frequency for surge, sway and yaw motions. For practical purposes, it was not possible to tune the liquid damper exactly to this frequency. The consequent approach taken and the efficiency of such approach are presented in this paper. Responses to waves of a single frequency are investigated along with responses obtained from wave spectra characterising typical sea states. The extent of control is quantified using peak and root mean squared dynamic responses respectively. The tests present some guidelines and challenges for testing scaled devices in relation to including response control mechanisms. Additionally, the results provide a basis for dictating future research on tuned liquid column damper based control on floating platforms.

Reverse Dynamization

PubMed Central

Glatt, Vaida; Bartnikowski, Nicole; Quirk, Nicholas; Schuetz, Michael; Evans, Christopher

2016-01-01

Background: Reverse dynamization is a technology for enhancing the healing of osseous defects. With use of an external fixator, the axial stiffness across the defect is initially set low and subsequently increased. The purpose of the study described in this paper was to explore the efficacy of reverse dynamization under different conditions. Methods: Rat femoral defects were stabilized with external fixators that allowed the stiffness to be modulated on living animals. Recombinant human bone morphogenetic protein-2 (rhBMP-2) was implanted into the defects on a collagen sponge. Following a dose-response experiment, 5.5 μg of rhBMP-2 was placed into the defect under conditions of very low (25.4-N/mm), low (114-N/mm), medium (185-N/mm), or high (254-N/mm) stiffness. Reverse dynamization was evaluated with 2 different starting stiffnesses: low (114 N/mm) and very low (25.4 N/mm). In both cases, high stiffness (254 N/mm) was imposed after 2 weeks. Healing was assessed with radiographs, micro-computed tomography (μCT), histological analysis, and mechanical testing. Results: In the absence of dynamization, the medium-stiffness fixators provided the best healing. Reverse dynamization starting with very low stiffness was detrimental to healing. However, with low initial stiffness, reverse dynamization considerably improved healing with minimal residual cartilage, enhanced cortication, increased mechanical strength, and smaller callus. Histological analysis suggested that, in all cases, healing provoked by rhBMP-2 occurred by endochondral ossification. Conclusions: These data confirm the potential utility of reverse dynamization as a way of improving bone healing but indicate that the stiffness parameters need to be selected carefully. Clinical Relevance: Reverse dynamization may reduce the amount of rhBMP-2 needed to induce healing of recalcitrant osseous lesions, reduce the time to union, and decrease the need for prolonged external fixation. PMID:27098327

A Dynamical Approach Toward Understanding Mechanisms of Team Science: Change, Kinship, Tension, and Heritage in a Transdisciplinary Team

PubMed Central

2013-01-01

Abstract Since the concept of team science gained recognition among biomedical researchers, social scientists have been challenged with investigating evidence of team mechanisms and functional dynamics within transdisciplinary teams. Identification of these mechanisms has lacked substantial research using grounded theory models to adequately describe their dynamical qualities. Research trends continue to favor the measurement of teams by isolating occurrences of production over relational mechanistic team tendencies. This study uses a social constructionist‐grounded multilevel mixed methods approach to identify social dynamics and mechanisms within a transdisciplinary team. A National Institutes of Health—funded research team served as a sample. Data from observations, interviews, and focus groups were qualitatively coded to generate micro/meso level analyses. Social mechanisms operative within this biomedical scientific team were identified. Dynamics that support such mechanisms were documented and explored. Through theoretical and emergent coding, four social mechanisms dominated in the analysis—change, kinship, tension, and heritage. Each contains relational social dynamics. This micro/meso level study suggests such mechanisms and dynamics are key features of team science and as such can inform problems of integration, praxis, and engagement in teams. PMID:23919361

A dynamical approach toward understanding mechanisms of team science: change, kinship, tension, and heritage in a transdisciplinary team.

PubMed

Lotrecchiano, Gaetano R

2013-08-01

Since the concept of team science gained recognition among biomedical researchers, social scientists have been challenged with investigating evidence of team mechanisms and functional dynamics within transdisciplinary teams. Identification of these mechanisms has lacked substantial research using grounded theory models to adequately describe their dynamical qualities. Research trends continue to favor the measurement of teams by isolating occurrences of production over relational mechanistic team tendencies. This study uses a social constructionist-grounded multilevel mixed methods approach to identify social dynamics and mechanisms within a transdisciplinary team. A National Institutes of Health-funded research team served as a sample. Data from observations, interviews, and focus groups were qualitatively coded to generate micro/meso level analyses. Social mechanisms operative within this biomedical scientific team were identified. Dynamics that support such mechanisms were documented and explored. Through theoretical and emergent coding, four social mechanisms dominated in the analysis-change, kinship, tension, and heritage. Each contains relational social dynamics. This micro/meso level study suggests such mechanisms and dynamics are key features of team science and as such can inform problems of integration, praxis, and engagement in teams. © 2013 Wiley Periodicals, Inc.

Determination of mechanical properties of some glass fiber reinforced plastics suitable to Wind Turbine Blade construction

NASA Astrophysics Data System (ADS)

Steigmann, R.; Savin, A.; Goanta, V.; Barsanescu, P. D.; Leitoiu, B.; Iftimie, N.; Stanciu, M. D.; Curtu, I.

2016-08-01

The control of wind turbine's components is very rigorous, while the tower and gearbox have more possibility for revision and repairing, the rotor blades, once they are deteriorated, the defects can rapidly propagate, producing failure, and the damages can affect large regions around the wind turbine. This paper presents the test results, performed on glass fiber reinforced plastics (GFRP) suitable to construction of wind turbine blades (WTB). The Young modulus, shear modulus, Poisson's ratio, ultimate stress have been determined using tensile and shear tests. Using Dynamical Mechanical Analysis (DMA), the activation energy for transitions that appear in polyester matrix as well as the complex elastic modulus can be determined, function of temperature.

Investigation of steady and fluctuating pressures associated with the transonic buffeting and wing rock of a one-seventh scale model of the F-5A aircraft

NASA Technical Reports Server (NTRS)

Hwang, C.; Pi, W. S.

1978-01-01

A wind tunnel test of a 1/7 scale F-5A model is described. The pressure, force, and dynamic response measurements during buffet and wing rock are evaluated. Effects of Mach number, angle of attack, sideslip angle, and control surface settings were investigated. The mean and fluctuating static pressure data are presented and correlated with some corresponding flight test data of a F-5A aircraft. Details of the instrumentation and the specially designed support system which allowed the model to oscillate in roll to simulate wing rock are also described. A limit cycle mechanism causing wing rock was identified from this study, and this mechanism is presented.

Characterization of tissue biomechanics and mechanical signaling in uterine leiomyoma☆

PubMed Central

Norian, John M.; Owen, Carter M.; Taboas, Juan; Korecki, Casey; Tuan, Rocky; Malik, Minnie; Catherino, William H.; Segars, James H.

2012-01-01

Leiomyoma are common tumors arising within the uterus that feature excessive deposition of a stiff, disordered extracellular matrix (ECM). Mechanical stress is a critical determinant of excessive ECM deposition and increased mechanical stress has been shown to be involved in tumorigenesis. Here we tested the viscoelastic properties of leiomyoma and characterized dynamic and static mechanical signaling in leiomyoma cells using three approaches, including measurement of active RhoA. We found that the peak strain and pseudo-dynamic modulus of leiomyoma tissue was significantly increased relative to matched myometrium. In addition, leiomyoma cells demonstrated an attenuated response to applied cyclic uniaxial strain and to variation in substrate stiffness, relative to myometrial cells. However, on a flexible pronectin-coated silicone substrate, basal levels and lysophosphatidic acid-stimulated levels of activated RhoA were similar between leiomyoma and myometrial cells. In contrast, leiomyoma cells plated on a rigid polystyrene substrate had elevated levels of active RhoA, compared to myometrial cells. The results indicate that viscoelastic properties of the ECM of leiomyoma contribute significantly to the tumor’s inherent stiffness and that leiomyoma cells have an attenuated sensitivity to mechanical cues. The findings suggest there may be a fundamental alteration in the communication between the external mechanical environment (extracellular forces) and reorganization of the actin cytoskeleton mediated by RhoA in leiomyoma cells. Additional research will be needed to elucidate the mechanism(s) responsible for the attenuated mechanical signaling in leiomyoma cells. PMID:21983114

On the foundations of general relativistic celestial mechanics

NASA Astrophysics Data System (ADS)

Battista, Emmanuele; Esposito, Giampiero; Dell'Agnello, Simone

2017-09-01

Towards the end of nineteenth century, Celestial Mechanics provided the most powerful tools to test Newtonian gravity in the solar system and also led to the discovery of chaos in modern science. Nowadays, in light of general relativity, Celestial Mechanics leads to a new perspective on the motion of satellites and planets. The reader is here introduced to the modern formulation of the problem of motion, following what the leaders in the field have been teaching since the nineties, in particular, the use of a global chart for the overall dynamics of N bodies and N local charts describing the internal dynamics of each body. The next logical step studies in detail how to split the N-body problem into two sub-problems concerning the internal and external dynamics, how to achieve the effacement properties that would allow a decoupling of the two sub-problems, how to define external-potential-effacing coordinates and how to generalize the Newtonian multipole and tidal moments. The review paper ends with an assessment of the nonlocal equations of motion obtained within such a framework, a description of the modifications induced by general relativity on the theoretical analysis of the Newtonian three-body problem, and a mention of the potentialities of the analysis of solar-system metric data carried out with the Planetary Ephemeris Program.

Development of a semi-active dynamic vibration absorber for longitudinal vibration of propulsion shaft system based on magnetorheological elastomer

NASA Astrophysics Data System (ADS)

Liu, Gaoyu; Lu, Kun; Zou, Donglin; Xie, Zhongliang; Rao, Zhushi; Ta, Na

2017-07-01

The control of the longitudinal pulsating force and the vibration generated is very important to improve the stealth performance of a submarine. Magnetorheological elastomer (MRE) is a kind of intelligent composite material, whose mechanical properties can be continuously, rapidly and reversibly controlled by an external magnetic field. It can be used as variable-stiffness components in the design of a semi-active dynamic vibration absorber (SDVA), which is one of the effective means of longitudinal vibration control. In this paper, an SDVA is designed based on the MRE’s magnetic-induced variable stiffness characteristic. Firstly, a mechanical model of the propulsion shaft system with the SDVA is proposed, theoretically discussed and numerically validated. Then, the mechanical performance of the MRE under different magnetic fields is tested. In addition, the magnetic circuit and the overall structure of the SDVA are designed. Furthermore, electromagnetic and thermodynamic simulations are carried out to guarantee the structural design. The frequency shift property of the SDVA is found through dynamic simulations and validated by a frequency shift experiment. Lastly, the vibration absorption capacity of the SDVA is investigated. The results show that the magnetorheological effect of the MRE and the frequency shift of the SDVA are obvious; the SDVA has relatively acceptable vibration absorption capacity.