• Geomechanics and Engineering
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• v.33 no.5
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• pp.427-437
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• 2023

The objective of this work is to study the wave propagation of an FGM plate via a new integral inverse shear model with temperature-dependent material properties. In this contribution, a new model based on a high-order theory field of displacement is included by introducing indeterminate integral variables and inverse co-tangential functions for the presentation of shear stress. The temperature-dependent properties of the FGM plate are assumed mixture of metal and ceramic, and its properties change by the power functions of the thickness of the plate. By applying Hamilton's principle, general formulas of wave propagation were obtained to plot the phase velocity curves and wave modes of the FGM plate with simply supported edges. The effects of the temperature and volume fraction by distributions on wave propagation of the FGM plate are investigated in detail. The results of the dispersion and the phase velocity curves of the propagation wave in the functionally graded plate are compared with previous research.

• Geomechanics and Engineering
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• v.17 no.1
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• pp.57-67
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• 2019

Water-induced strength reduction is one of the most critical causes for rock deformation and failure. Understanding the effects of water on the strength, toughness and deformability of rocks are of a great importance in rock fracture mechanics and design of structures in rock. However, only a few studies have been conducted to understand the effects of water on fracture properties such as fracture toughness, crack propagation velocity, consumed energy, and microstructural damage. Thus, in this study, we focused on the understanding of how microscale damages induced by water saturation affect mesoscale mechanical and fracture properties compared with oven dried specimens along three notch orientations-divider, arrester, and short transverse. The mechanical properties of calcite-cemented sandstone were examined using standard uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) tests. In addition, fracture properties such as fracture toughness, consumed energy and crack propagation velocity were examined with cracked chevron notched Brazilian disk (CCNBD) tests. Digital Image Correlation (DIC), a non-contact optical measurement technique, was used for both strain and crack propagation velocity measurements along the bedding plane orientations. Finally, environmental scanning electron microscope (ESEM) was employed to investigate the microstructural damages produced in calcite-cemented sandstone specimens before and after CCNBD tests. As results, both mechanical and fracture properties reduced significantly when specimens were saturated. The effects of water on fracture properties (fracture toughness and consumed energy) were predominant in divider specimens when compared with arrester and short transverse specimens. Whereas crack propagation velocity was faster in short transverse and slower in arrester, and intermediate in divider specimens. Based on ESEM data, water in the calcite-cemented sandstone induced microstructural damages (microcracks and voids) and increased the strength disparity between cement/matrix and rock forming mineral grains, which in turn reduced the crack propagation resistance of the rock, leading to lower both consumed energy and fracture toughness ($K_{IC}$).

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.55 no.8
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• pp.378-385
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• 2006

In this study, a method measuring signal propagation direction in human body was developed by using passive electrical properties of the body. The measured method of the signal propagation direction is to apply basic characteristic of electricity to the human body; when a voltage is set to a conducted medium, according to the polarity of the conducted voltage, the voltage rising or drop is generated. And using this concept, it is able to estimate the direction of electrical signal on the human body. The passive electrical properties were measured and the direction of signal propagation was estimated on the followings; between the flexor carpi radialis, between arms, between legs, between an arm and a leg, between the cervical vertebra and the upper limb, between the sacral vertebra and the leg, between the cervical vertebra and the tendon of triceps brachii, and between the sacral vertebra and the calcaneal tendon. As the result of experiments, the passive electrical properties were increased from l[Hz] to 50[kHz] of the inputted frequencies and showed at saturating tendency after that. And also, the estimated signal propagation directions using the developed method in this study agreed with the expected directions exactly at each part of the human body.

• Journal of Mechanical Science and Technology
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• v.18 no.11
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• pp.2058-2065
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• 2004

A light collecting probe named Multi-color Integrated Cassegrain Receiving Optics (MICRO) is applied to spark-ignited spherical spray flames to obtain the flame propagation speed in freely falling droplet suspension produced by an ultrasonic atomizer. Two MICRO probes are used to monitor time-series signals of OH chemiluminescence from two different locations in the flame. By detecting the arrival time difference of the propagating flame front, the flame propagation speed is calculated with a two-point delay-time method. In addition, time-series images of OH chemiluminescence are simultaneously obtained by a high-speed digital CCD camera to ensure the validity of the two-point delay-time method by the MICRO system. Furthermore, the relationship between the spray properties measured by phase Doppler anemometer (PDA) and the flame propagation speed are discussed with three different experimental conditions by changing the fuel injection rate. It was confirmed that the two-point delay-time method with two MICRO probes is useful and convenient to obtain the flame propagation speed and that the flame propagation speed depends on the spray properties.

• Journal of the Korean Society of Safety
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• v.19 no.3 s.67
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• pp.20-25
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• 2004

In order to obtain the flame Propagation speed in freely falling droplet suspension Produced by an ultrasonic atomizer, a light collecting probe named Multi-color Integrated Cassegrain Receiving Optics (MICRO) is applied to spark-ignited spherical spray flames. Two MICRO probes are used to monitor time-series signals of OH chemilumine-scence from two different locations in the flame. The flame propagation speed is calculated by detecting the arrival time difference of the propagating flame front. In addition, time-series images of OH chemiluminescence are simultaneously obtained by a high-speed digital CCD camera to ensure the validity of the MICRO system. Furthermore, relationship between the spray properties measured by phase Doppler anemometer (PDA) and the flame propagation speed are discussed with k different experimental conditions by changing the fuel injection rate. It was confirmed that the MICRO probe system was very useful and convenient to obtain the flame propagation speed and that the flame propagation speed was different depending on the spray properties.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1347-1352
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• 2001

In this study, the acoustic properties of polyester sound absorbing materials with three different bulk densities were investigated by calculating and measuring the acoustic parameters in terms of characteristic impedance, propagation constant, and absorption coefficient. For the calculations, Delany and Bazley's empirical equation was used together with the experimentally obtained specific flow resistivities under steady flow conditions. For the experimental measurements, the well-known two-thickness method was accessed. The experimentally measured values of characteristic impedance and propagation constant were generally agreed well with the corresponding calculated values. Based on the comparisons between the calculations and measurements, it was found that the magnitude of the absorption coefficient was closely related to the characteristic impedance and the real part of the propagation constant. Especially, the maximum magnitude of the absorption coefficient was depended upon the imaginary part of the propagation constant indicating the phase change of the propagation constant.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.311-314
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• 2007

The experimental method of measuring dynamic properties of structures was presented. The method is based on the flexural wave propagation characteristics. Using the method, change in structural dynamic properties due to damage is measured. The crack has much more significant impact on the strain energy than the inertial effects. From this, the sensitivity of the dynamic stiffness on the crack location is estimated by calculating the strain energy. When the wave propagates, the strain and kinetic energies shows cyclic changed over space. The crack that occurred at locations where the wave energy is in the form of the potential energy affected most significantly the wave propagation characteristics. The effects of crack location on the wave propagation were used to determine the crack location.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.3
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• pp.61-67
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• 1998

To find out the reason of fracture, specimens were made from the fractured winding shaft and the mechanical properties as well as their microstructures were investigated. Several heat treatments. including caburizing and tempering were carried out to improve the microstructure, mechanical properties, fatigue crack propagation and rotating bending fatigue characteristics. Through these experiments, following conclusions were obtained. (1) Carburized and tempered specimens showed greatly improved mechanical properties including impact energy, hardness and strength. (2) The fatigue strength of the carburized and tempered specimens increased more than twice than that of the original fractured winding shaft. (3) Crack propagation of the carburized and tempered specimens were faster than that of the original fractured speciens under the same △K. However, it is believed that, in the early stage, the fatigue crack initiation and growth for the carburized and tempered specimen is more difficult.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.950-953
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• 2006

The floor impact noise of concrete structures in apartments buildings is affected from the flexural wave propagation characteristics. Accordingly, the measurement of wave propagation characteristics is required for suggestion of efficient method to reduce the impact noise. The purpose of this article is to propose an experimental technique to measure dynamic properties of concrete structures. The method was proposed using the flexural wave propagation characteristics. Wave speeds, bending stiffness and their loss factors are estimated from which the vibration dissipation capabilities are investigated. Several different concrete beam structures were custom-built for measurement. The damping treatments using viscoelastic materials for reducing noise generation are also tested. The beam transfer function of the damped beam is predicted using the compressional damping model from which the mechanism of the vibration energy dissipation is investigated.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.3
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• pp.181-189
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• 2001

For the Tailor Welded Blank sheet used fur automobile body panel, the characteristics of fatigue crack propagation behavior were studied. The thickness of specimen was machined to be same (0.9+0.9mm) and different (0.9+2.0mm). As a base test, mechanical properties around welding zone were examined. The results indicated that there were no significant decreases in mechanical properties, but hardness around welding bead is 2.3 times greater than base material. The crack propagation rate was noticeably decreased around welding line and rapidly increased as it passed by welding line. Reviewing the shape of the crack propagation, crack width around welding line was wide around the welding zone due to retardation of crack growth, but it became narrow passing welding line due to decreased toughness. Elasto-Plastic analysis was performed by finite element analysis fur explaining the test results.