Mechanical Response of Brain Stem in Compression and the Differential Scanning Calorimetry and FTIR Analyses

2016 ◽  
Vol 83 (9) ◽  
Author(s):  
Wei Zhang ◽  
Run-run Zhang ◽  
Liang-liang Feng ◽  
Yang Li ◽  
Fan Wu ◽  
...  
Keyword(s):  
Differential Scanning Calorimetry ◽  
Strain Rate ◽  
Brain Stem ◽  
Mechanical Response ◽  
Viscoelastic Behavior ◽  
Transitional Region ◽  
Rate Dependency ◽  
Scanning Calorimetry ◽  
Polar Functional Groups ◽  
The Brain

The stress–strain curves of brain stem in uniaxial compression demonstrate strain rate dependency and can be characterized with three regions: initial toe region, transitional region, and high strain region, suggesting strong viscoelastic behavior. To investigate the origin of this viscoelasticity at microscale, differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectra of brain stem tissue were recorded and analyzed. The emergence of endotherm thermal domains in DSC indicates that the conformation change of biomolecules can absorb and dissipate energy, explaining the viscous behavior of the brain stem. FTIR analyses indicate that the presence of polar functional groups such as amide, phosphate, and carboxyl groups in the biomolecules takes responsibility for the viscous performance of brain stem. Ogden, Fung, and Gent models were adopted to fit the experimental data, and Ogden model is the most apt one in capturing the stiffening of the brain stem with the increasing strain rate.

Dynamic Globularization of α-Phase in Ti6Al4V Alloy during Hot Compression

2014 ◽  
Vol 783-786 ◽  
pp. 584-590 ◽  
Author(s):  
Kalenda Mutombo ◽  
C. Siyasiya ◽  
W.E. Stumpf
Keyword(s):  
Differential Scanning Calorimetry ◽  
Transition Temperature ◽  
Strain Rate ◽  
Alpha Phase ◽  
Ti6al4v Alloy ◽  
Thermodynamic Calculations ◽  
Scanning Calorimetry ◽  
Temperature Range ◽  
Α Phase ◽  
Dsc Thermograms

Ti6Al4V samples were isothermally compressed using a Gleeble(TM) 1500D thermo-mechanical simulator. Differential scanning calorimetry (DSC), microstructural analyses, and thermodynamic calculations were used to investigate the sequence of transformation of β into α or vice-versa and the presence of different phases in the compressed Ti6Al4V sample. Globular alpha phase was revealed in the isothermally compressed sample in addition to martensitic and lamellar α/β structures. The transition temperature range of β into α-phase was determined using the DSC thermograms and thermodynamic calculated diagrams. The fraction of α-phase globulized increased as the strain rate decreased from 0.01s-1 to 10-3s-1, and the spheroidization of the α-phase is only possible in a specific range of deformation temperatures.

scholarly journals Anisotropic mechanical behaviour of calendered nonwoven fabrics: Strain-rate dependency

2020 ◽  
pp. 002199832097679
Author(s):  
V Cucumazzo ◽  
E Demirci ◽  
B Pourdeyhimi ◽  
VV Silberschmidt
Keyword(s):  
Strain Rate ◽  
Mechanical Behaviour ◽  
Mechanical Response ◽  
Tensile Tests ◽  
Elastic Response ◽  
Uniaxial Tensile ◽  
Rate Dependency ◽  
Fibrous Matrix ◽  
Nonwoven Fabrics ◽  
Linear Elastic

Calendered nonwovens, formed by polymeric fibres, are three-phase heterogeneous materials, comprising a fibrous matrix, bond-areas and interface regions. As a result, two main factors of anisotropy can be identified. The first one is ascribable to a random fibrous microstructure, with the second one related to orientation of a bond pattern. This paper focuses on the first type of anisotropy in thin and thick nonwovens under uniaxial tensile loading. Individual and combined effects of anisotropy and strain rate were studied by conducting uniaxial tensile tests in various loading directions (0°, 30°, 45°, 60° and 90° with regard to the main fabric’s direction) and strain rate (0.01, 0.1 and 0.5 s−1). Fabrics exhibited an initial linear elastic response, followed by nonlinear strain hardening up to necking and final softening. The studied allowed assessment of the extent the effects of loading direction (anisotropy), planar density and strain rate on the mechanical response of the calendered fabrics. The evidence supported the conclusion that anisotropy is the most crucial factor, also delineating the balance between the fabric’s load-bearing capacity and extension level along various directions. The strain rate produced a marked effect on the fibre’s response, with increased stress at higher strain rate while this effect in the fabric was small. The results demonstrated the differences of the mechanical behaviour of fabrics from that of their constituent fibres.

Strain-Rate Sensitive Constitutive Modeling of Anisotropic Visco-Hyperelastic Materials

2012 ◽  
Author(s):  
Sahand Ahsanizadeh ◽  
LePing Li
Keyword(s):  
Strain Rate ◽  
Evolution Equations ◽  
Mechanical Response ◽  
Viscoelastic Behavior ◽  
Biological Tissues ◽  
Internal Variables ◽  
Current Configuration ◽  
Hyperelastic Materials ◽  
History Of ◽  
Viscoelastic Constitutive Model

Integral-based formulations of viscoelasticity have been widely used to describe the mechanical behavior of soft biological tissues and polymers. However, it is suggested that they are not suitable to be used under high strain rates. On the other hand, strain-rate sensitive models with an explicit dependence on the strain-rate have been developed for a certain class of materials. They predict the viscoelastic behavior during ramp loading more accurately while fail to account for the relaxation response. In order to overcome these drawbacks, a viscoelastic constitutive model has been proposed in this study based on the concept of internal variables. While the behavior of elastic materials is uniquely determined by the current state of deformation or external variables, the mechanical response of inelastic materials are regulated also by internal variables. The internal variables are associated with the dissipative mechanisms in the material and along with the evolution equations introduce the effect of history of the deformation to the current configuration. The current study employs short-term and long-term internal variables to account for the viscoelastic response during loading and relaxation respectively.

Non-Isothermal Crystallization and Viscoelastic Behavior of Polypropylene/Nanoclay Composites Fabricated from Masterbatch by Using a Mini Extruder

2018 ◽  
Vol 382 ◽  
pp. 89-93
Author(s):  
Achmad Chafidz ◽  
R.M. Faisal ◽  
Mujtahid Kaavessina ◽  
Dhoni Hartanto
Keyword(s):  
Differential Scanning Calorimetry ◽  
Isothermal Crystallization ◽  
Viscoelastic Behavior ◽  
Test Results ◽  
Dsc Analysis ◽  
Scanning Calorimetry ◽  
Frequency Sweep ◽  
Melt Compounding ◽  
Frequency Sweep Test ◽  
Scanning Electron

Polypropylene(PP)/nanoclay composites samples have been fabricated by melt compounding the PP pellets with nanoclay masterbatch (i.e. 50 wt% of nanoclay) using a mini extruder. The effect of three loadings of nanoclay (i.e. 5, 10, and 15 wt%) on the morphology, non-isothermal crystallization, and viscoelastic behavior of the PP/nanoclay composites were investigated. All the nanocomposites samples were characterized by using Scanning Electron Microscope (SEM), Differential Scanning Calorimetry (DSC), and an oscillatory rheometer. The SEM results showed that the distribution of nanoclay in the PP was relatively good at all level of loadings. The DSC analysis results showed that the nanoclay has dramatically enhanced the crystallization temperature, from 117°C (for neat PP) to 127-129°C (for nanocomposites). Additionally, the frequency sweep test results exhibited that the presence of nanoclay increased the viscoelastic behavior of the PP matrix.

Crystallization kinetics of amorphous Ga–Sb–Te chalcogenide films: Part I. Nonisothermal studies by differential scanning calorimetry

2004 ◽  
Vol 19 (10) ◽  
pp. 2929-2937 ◽  
Author(s):  
Chain-Ming Lee ◽  
Yeong-Iuan Lin ◽  
Tsung-Shune Chin
Keyword(s):  
Activation Energy ◽  
Differential Scanning Calorimetry ◽  
Crystallization Kinetics ◽  
Crystallization Temperature ◽  
Ternary Phase Diagram ◽  
Film Deposition ◽  
Rate Dependency ◽  
Scanning Calorimetry ◽  
Kinetics Parameters ◽  
Kinetics Of

Nonisothermal crystallization kinetics of amorphous chalcogenide Ga–Sb–Te films with compositions along the pseudo-binary tie-lines connecting Sb7Te3−GaSb and Sb2Te3–GaSb of the ternary phase diagram were investigated by means of differential scanning calorimetry. Powder samples were prepared firstly by film deposition using a co-sputtering method; the films were then stripped from the substrate. The activation energy (Ea) and rate factor (Ko) were evaluated from the heating rate dependency of the crystallization temperature using the Kissinger method. The kinetic exponent (n) was deduced from the exothermic peak integrals using the Ozawa method. The crystallization temperature (Tx = 181 to 327 °C) and activation energy (Ea= 2.8 to 6.5 eV) increased monotonically with increasing GaSb content and reached a maximum value in compositions located at the vicinity of GaSb. The kinetic exponent is temperature dependent and shows higher values in the SbTe-rich compositions. Promising media compositions worthy of further studies were identified through the determined kinetics parameters.

Experimental identification of the subarachnoid and subpial compartments by intracranial pressure measurements

1974 ◽  
Vol 40 (5) ◽  
pp. 609-616 ◽  
Author(s):  
Alfonso Schettini ◽  
Edward K. Walsh
Keyword(s):  
Intracranial Pressure ◽  
Viscoelastic Behavior ◽  
Experimental Methods ◽  
Transitional Region ◽  
Pressure Measurements ◽  
Correct Interpretation ◽  
Content Type ◽  
Experimental Identification ◽  
Depth Determination ◽  
The Brain

✓ Because of the range of pressures associated with the intracranial system, correct interpretation of epidural intracranial pressure measurements requires an accurate means of measuring the pressure, the depth at which the pressure is measured, and the region of the system associated with that depth. A measurement system is described that provides such an accurate pressure/depth determination and maintains a uniform rate-of-insertion of the pressure transducer; the latter provision is important because of the viscoelastic behavior of the brain tissue. Use of these experimental methods to determine the pressure in three distinct intracranial regions is described, namely, in the subarachnoid and the subpial compartments and a transitional region between these two.

scholarly journals The effect of matrix morphology on dynamic-mechanical properties of polypropylene/layered silicate nanocomposites

2017 ◽  
Vol 36 (2) ◽  
pp. 251
Author(s):  
Gordana Bogoeva-Gaceva ◽  
Lujleta Raka ◽  
Andrea Sorrentino
Keyword(s):  
Mechanical Response ◽  
Viscoelastic Behavior ◽  
Layered Silicate ◽  
Clay Content ◽  
Dynamic Mechanical Properties ◽  
Scanning Calorimetry ◽  
Slow Cooling ◽  
Dynamic Mechanical ◽  
Melting Temperatures ◽  
Matrix Morphology

In this work, the influence on the morphology and viscoelastic behavior of polypropylene/clay nanocomposites of clay, in combination with different crystallization rates applied in compression molding, is reported. By deconvolution of differential scanning calorimetry (DSC) melting endotherms, it was found that the slowly cooled samples had slightly higher melting temperatures, and the crystal dimensions decreased progressively with the clay content; while, in contrast, the presence of clay particles had no influence on the crystal dimensions in fast-cooled samples. Dynamic mechanical thermal analysis (DMTA) has shown that above the glass transition temperature, nanocomposites obtained by slow cooling exhibited better mechanical response compared to the fast-cooled samples. The value of dynamic modulus E’ of slow-cooled samples increased by ~55 % with addition of only 1 wt% clay, which was attributed to the better reinforcing effect achieved during prolonged time of crystallization.  

A Constitutive Material Model With Strain-Rate Dependency for Brain Tissue

2019 ◽  
Author(s):  
Mohammad Hosseini Farid ◽  
Mohammadreza Ramzanpour ◽  
Mariusz Ziejewski ◽  
Ghodrat Karami
Keyword(s):  
Constitutive Model ◽  
Brain Tissue ◽  
Brain Injuries ◽  
Viscoelastic Behavior ◽  
Strain Rates ◽  
Compression Tests ◽  
Rate Dependency ◽  
Rate Dependent ◽  
Constitutive Material Model ◽  
The Brain

Abstract In almost all scenarios of traumatic brain injuries (TBIs), the brain tissue goes under mechanical loading at high strain rates. In experimental works, it has also shown that brain tissue behavior is highly rate-dependent. We are presenting here the results of a study on mechanical properties of bovine brain tissue under unconfined compression tests at different rates. The tissue specimens are compressed with deformation rates of 10, 100, and 1000 mm/sec, respectively. We observed the tissue is showing a viscoelastic behavior and become stiffer under increasing strain rates. We developed a nonlinear viscoelastic rate-dependent constitutive model to be calibrated with the test results. The material parameters for this constitutive model have been validated for the above tested results. The model was examined against other rates and agrees well. The study will provide new insight into a better understanding of the rate-dependency behavior of the brain tissue under dynamic conditions. The work is a step forward in understanding the material characteristics of brain tissue for TBI analysis and prediction under loading or high kinematical motions.

scholarly journals Triaxial tests to determine a microstructure-based snow viscosity law

2000 ◽  
Vol 31 ◽  
pp. 457-462 ◽  
Author(s):  
Perry Bartelt ◽  
Markus Von Moos
Keyword(s):  
Strain Rate ◽  
Constitutive Relations ◽  
Viscoelastic Behavior ◽  
Final Analysis ◽  
Sample Volume ◽  
Triaxial Tests ◽  
Strain Rates ◽  
Rate Dependency ◽  
Tension And Compression ◽  
Ice Lattice

AbstractThis paper describes a new triaxial testing apparatus designed to determine the creep (viscoelastic) behavior of snow. The device is deformation-controlled and can apply strain rates between 10–7 s–1 and 10–2s–1 in tension and compression. The sample volume change is determined by measuring the displaced pore-air volume. During winters 1997/98 and 1998/99, >100 compression and tension tests were carried out. It is shown that snow is a highly non-linear but ideal viscoelastic material with a strong strain-rate dependency. A selection of test results is provided. We show how snow viscosity varies with density and strain rate. In a final analysis we interpret our results with respect to snow microstructure in order to develop microstructure-based constitutive relations which can be implemented in finite-element programs. Our results clearly show that for snow densities and strain rates tested, straining of the grain bonds is the primary mechanism of deformation within the snow ice lattice.

Permeability of the microcirculation in area postrema of rat

1988 ◽  
Vol 46 ◽  
pp. 348-349
Author(s):  
Shams M. Ghoneim ◽  
Frank M. Faraci ◽  
Gary L. Baumbach
Keyword(s):  
Brain Stem ◽  
Area Postrema ◽  
Upper Body ◽  
Sprague Dawley ◽  
Sodium Cacodylate ◽  
Acute Hypertension ◽  
Sprague Dawley Rats ◽  
Ultrastructural Characteristics ◽  
The Brain ◽  
Adjacent Brain

The area postrema is a circumventricular organ in the brain stem and is one of the regions in the brain that lacks a fully functional blood-brain barrier. Recently, we found that disruption of the microcirculation during acute hypertension is greater in area postrema than in the adjacent brain stem. In contrast, hyperosmolar disruption of the microcirculation is greater in brain stem. The objective of this study was to compare ultrastructural characteristics of the microcirculation in area postrema and adjacent brain stem.We studied 5 Sprague-Dawley rats. Horseradish peroxidase was injected intravenously and allowed to circulate for 1, 5 or 15 minutes. Following perfusion of the upper body with 2.25% glutaraldehyde in 0.1 M sodium cacodylate, the brain stem was removed, embedded in agar, and chopped into 50-70 μm sections with a TC-Sorvall tissue chopper. Sections of brain stem were incubated for 1 hour in a solution of 3,3' diaminobenzidine tetrahydrochloride (0.05%) in 0.05M Tris buffer with 1% H2O2.

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