Microstructure and Defects Evaluation of Varistors by Ultrasonic Waves in Low Frequency Range

2013 ◽  
Vol 592-593 ◽  
pp. 688-691
Author(s):  
Pavel Tofel ◽  
Pavel Škarvada ◽  
Josef Sikula ◽  
Gabriel Cséfalvay
Keyword(s):  
Mechanical Properties ◽  
Mass Density ◽  
Low Frequency ◽  
Sample Volume ◽  
Ultrasonic Signal ◽  
Ultrasonic Waves ◽  
Ultrasonic Vibrations ◽  
Ultrasonic Spectroscopy ◽  
Resistance Change ◽  
Acoustic Effect

Each material contains defects and in-homogeneities in a structure volume. It has influence on the properties of material (conductivity, mass density, mechanical properties). Interaction of the ultrasonic waves with defects or in-homogeneities in the solid state is not clear. Electro-ultrasonic spectroscopy can help to clarify this phenomenon. The electro-ultrasonic spectroscopy describes defects and un-homogeneities inside the sample structure. This method is quite different from electro-acoustic effect. Ultrasonic signal is in range from 20 kHz to 150 kHz. Ultrasonic signal changes geometry of the sample in elastic range only. The sizes of cracks are changing also in the sample volume. Conductivity near the area of cracks is strongly changing due to ultrasonic vibrations. It has influence on resistance of the sample which is changing along with a frequency of ultrasonic vibrations. The amplitude of the resistance change depends on the material, number of cracks, size of cracks and Eigen frequencies of the sample excited by ultrasonic wave. We applied the electro-ultrasonic spectroscopy on two types of varistors. It can be useful for understanding the relation between microstructure and mechanical properties of these types of varistors.

Ultrasonic Non Destructive Evaluation of Microstructural Changes and Degradation of Ceramics at High Temperature

1988 ◽  
Vol 142 ◽  
Author(s):  
Christian Gault
Keyword(s):  
High Temperature ◽  
Thermal Stresses ◽  
Low Frequency ◽  
Ultrasonic Waves ◽  
Phase Changes ◽  
Ultrasonic Spectroscopy ◽  
Microstructural Changes ◽  
Porosity Evolution ◽  
Non Destructive ◽  
Pulsed Ultrasonic

AbstractThis paper deals with the use of pulsed ultrasonic waves to monitor microstructural changes and degradation of ceramics in the field of high temperature. Two types of devices are described. One is a low frequency system for the measurement of Young's modulus at temperatures up to 1800°C. The second is an ultrasonic spectroscopy system for the evaluation of damage in structural ceramics during thermal fatigue experiments. Applications concern phase changes, porosity evolution or microcracking induced by thermal stresses when heating monolithic or composite ceramics.

MECHANICAL PROPERTIES PREDICTION OF PHENOLIC RESIN: A MOLECULAR DYNAMICS STUDY

2021 ◽  
Author(s):  
IVAN GALLEGOS ◽  
JOSHUA KEMPPAINEN ◽  
SAGAR U. PATIL ◽  
PRATHAMESH DESHPANDE ◽  
JACOB GISSINER ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Phenolic Resin ◽  
Mass Density ◽  
Carbon Composites ◽  
Mechanical And Thermal Properties ◽  
Phenolic Resins ◽  
Suitable Candidate ◽  
Mechanical Properties Prediction ◽  
Experimental Values

Carbon-carbon composites (CCCs) widely used in the aerospace and automotive industries due to their excellent mechanical and thermal properties. Phenolic resins have a relatively high carbon yield, which makes them a suitable candidate for CCCs manufacturing. Molecular Dynamics (MD) can further reduce costs by predicting properties of a material before manufacturing and testing. In the present work, a Molecular Dynamics (MD) model of a crosslinked phenolic resin was developed to predict mechanical properties by implementing the fix bond/react algorithm in LAMMPS. The predicted mass density (ρ) and Young’s Modulus (E) agree well with experimental values and highlights the validity of the topologybased approach to building stable molecular models of phenolic resins.

EFFECTS OF STOICHIOMETRY ON PROPERTIES OF DGEBF/DETDA EPOXY USING MOLECULAR DYNAMICS

2021 ◽  
Author(s):  
SAGAR PATIL ◽  
MICHAEL OLAYA ◽  
PRATHAMESH DESHPANDE ◽  
MARIANNA MAIARÙ ◽  
GREGORY ODEGARD
Keyword(s):  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Molecular Modeling ◽  
Bulk Modulus ◽  
Mass Density ◽  
Strong Dependence ◽  
Crosslinking Density ◽  
Mechanical Deformation ◽  
Epoxy System ◽  
Reactive Interface

This article details the molecular modeling of full and off-stoichiometry models of the DGEBF/DETDA epoxy system using Molecular Dynamics to predict the mechanical properties as a function of the crosslinking density. The Reactive Interface Force Field (IFF-R) is implemented in this work to simulate mechanical deformation. The “fix bond/react” command in LAMMPS is used to simulate crosslinking between epoxy monomers. The results show that the predicted mass density, volumetric shrinkage, and bulk modulus have a strong dependence on the stoichiometry of the epoxy.

A Study on Thermal and Electrical Conductivities of Ethylene-Butene Copolymer Composites with Carbon Fibers

2021 ◽  
Vol 36 (4) ◽  
pp. 417-422
Author(s):  
Y. Hamid ◽  
P. Svoboda
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Carbon Fiber ◽  
Electric Conductivity ◽  
Carbon Fibers ◽  
Mechanical Strain ◽  
Electric Resistance ◽  
Resistance Change ◽  
Electrical Conductivities ◽  
Fiber Sample

Abstract Ethylene-butene copolymer (EBC)/carbon-fiber (CF) composites can be utilized as an electromechanical material due to their ability to change electric resistance with mechanical strain. The electro-mechanical properties and thermal conductivity of ethylene butene copolymer (EBC) composites with carbon fibers were studied. Carbon fibers were introduced to EBC with various concentrations (5 to 25 wt%). The results showed that carbon fibers’ addition to EBC improves the electric conductivity up to 10 times. Increasing the load up to 2.9 MPa will raise the electric resistance change by 4 500% for a 25% fiber sample. It is also noted that the EBC/CF composites’ electric resistance underwent a dramatic increase in raising the strain. For example, the resistance change was around 13 times higher at 15% strain compared to 5% strain. The thermal conductivity tests showed that the addition of carbon fibers increases the thermal conductivity by 40%, from 0.19 to 0.27 Wm–1K–1.

Novel Ultrasonic Technology for Devulcanization of Waste Rubbers

1995 ◽  
Vol 68 (2) ◽  
pp. 267-280 ◽  
Author(s):  
A. I. Isayev ◽  
J. Chen ◽  
A. Tukachinsky
Keyword(s):  
Mechanical Properties ◽  
Structural Characteristics ◽  
Three Dimensional ◽  
Ultrasonic Waves ◽  
Styrene Butadiene Rubber ◽  
Butadiene Rubber ◽  
Processing Conditions ◽  
Laboratory Reactor ◽  
Plant Level ◽  
Theological Properties

Abstract A novel patented process and several reactors have been developed for devulcanization of waste rubbers. The technology is based on the use of the high power ultrasonics. The ultrasonic waves of certain levels in the presence of pressure and heat rapidly break up the three-dimensional network in crosslinked rubbers. The devulcanized rubber can be reprocessed, shaped and revulcanized in much the same way as a virgin rubber. The first laboratory reactor has been scaled up to pilot-plant level by the National Feedscrew and Machining, Inc. Various devulcanization experiments were carried out with model styrene-butadiene rubber (SBR) and with ground rubber tire (GRT). Curing behavior, Theological properties, and structural characteristics of rubbers devulcanized at various processing conditions were studied, as well as mechanical properties of revulcanized rubber samples. A possible mechanism of the devulcanization is discussed. The performed measurements indicate that the rubbers are partially devulcanized, and the devulcanization process is accompanied by certain degradation of the macromolecular chains. In spite of these observations, the processing conditions are identified at which the retention of the mechanical properties is found to be good. A further work is in progress to find the optimal conditions of devulcanization and to improve the selectivity of the process towards breaking up the chemical network only.

scholarly journals Diagnostics of concrete plate in bending with ultrasonic waves modulated by low frequency oscillations

2013 ◽  
Vol 12 (1) ◽  
pp. 243-250
Author(s):  
Błażej Meronk ◽  
Krzysztof Wilde
Keyword(s):  
Experimental Study ◽  
Low Frequency ◽  
Ultrasonic Waves ◽  
Modulation Method ◽  
Frequency Spectra ◽  
Concrete Plate ◽  
Low Frequency Oscillations ◽  
Damaged Zone ◽  
Nonlinear Acoustic ◽  
Concrete Elements

The paper presents the experimental study on the inter-modulation method for the diagnostics of concrete elements. The tests were conducted on a concrete plate subjected to ultrasonic waves and low frequency vibrations. The nonlinear acoustic effects, recorded in the experiments, made it possible to detect the presence of damaged zones. Further studies are necessary to establish the relation between the sidebanes of frequency spectra and the size of the damaged zone.

Age-Dependent Acoustic and Microelastic Properties of Red Blood Cells Determined by Vector Contrast Acoustic Microscopy

2012 ◽  
Vol 18 (3) ◽  
pp. 436-444 ◽  
Author(s):  
Esam T. Ahmed Mohamed ◽  
Albert E. Kamanyi ◽  
Mieczysław Pluta ◽  
Wolfgang Grill
Keyword(s):  
Red Blood Cells ◽  
Blood Cells ◽  
Mass Density ◽  
Healthy Person ◽  
Ultrasonic Waves ◽  
Acoustic Microscopy ◽  
Cell Parameters ◽  
Different Ages ◽  
The Individual

AbstractVariations of the mechanical properties of red blood cells that occur during their life span have long been an intriguing task for investigations. The research presented is based on noninvasive monitoring of red blood cells of different ages performed by scanning acoustic microscopy with magnitude and phase contrast. The characteristic signature of fixed cells from groups of three different ages fractionated according to mass density is obtained from the acoustic microscope images, with the data represented in polar graphs. The analysis of these data enables the determination of averaged values for the velocities of ultrasound propagating in the cells from the different groups ranging from (1,681 ± 16) m s−1in the youngest to (1,986 ± 20) m s−1in the oldest group. The determined bulk modulus varies with age from (3.04 ± 0.05) GPa to (4.34 ± 0.08) GPa. An approach to determine for an age-mixed population of red blood cells, collected from a healthy person, the age of the individual cells and the age dependence of the cell parameters including density, velocity, and attenuation of longitudinal polarized ultrasonic waves traveling in the cells is demonstrated.

scholarly journals Phononic Band Gaps of Elastic Periodic Structures: A Homogenization Theory Study

2007 ◽  
Author(s):  
Ying-Hong Liu ◽  
Chien C. Chang ◽  
Ruey-Lin Chern ◽  
C. Chung Chang
Keyword(s):  
Elastic Constants ◽  
Periodic Structures ◽  
Mass Density ◽  
Density Ratio ◽  
Low Frequency ◽  
Phononic Crystals ◽  
Band Gaps ◽  
Homogenization Theory ◽  
Dominant Factor ◽  
Phononic Band Gaps

In this study, we investigate band structures of phononic crystals with particular emphasis on the effects of the mass density ratio and of the contrast of elastic constants. The phononic crystals consist of arrays of different media embedded in a rubber or epoxy. It is shown that the density ratio rather than the contrast of elastic constants is the dominant factor that opens up phononic band gaps. The physical background of this observation is explained by applying the theory of homogenization to investigate the group velocities of the low-frequency bands at the center of symmetry Γ.

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