• 한국해양공학회지
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• 제23권6호
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• pp.124-130
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• 2009

This study presents a finite element simulation of elastic waves for detecting anti-symmetric damages in an adhesively-bonded single lap joint. Plane strain elements were used for modeling adherents (aluminum) and adhesives (epoxy). Three types of damage were introduced: thickness reduction, elasticity deterioration, and voids in the adhesive layers, and two excitation and reception arrangements (ER1 and ER2) were used to investigate the detectability of the damage. The simulation showed that symmetrically located damage, such as a thickness reduction, can be detected by one excitation and one reception arrangement (ER1) and anti-symmetric damages, such as elasticity deterioration and voids, can be detected by modified two-point elastic wave excitation (ER2). Compared with the ER1 arrangement, the ER2 arrangement does not require a baseline signal for damage detection; hence, an efficient method of anti-symmetric damage detection in an adhesively-bonded single lap joint is proposed.

• Structural Engineering and Mechanics
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• 제58권2호
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• pp.347-378
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• 2016

Within the scope of the plane-strain state, by utilizing the three-dimensional linearized theory of elastic waves in initially stressed piezoelectric and elastic materials, Lamb wave propagation and the influence of the initial stresses on this propagation in a sandwich plate with pre-stressed piezoelectric face and pre-stressed metal elastic core layers are investigated. Dispersion equations are derived for the extensional and flexural Lamb waves and, as a result of numerical solution to these equations, the corresponding dispersion curves for the first (fundamental) and second modes are constructed. Concrete numerical results are obtained for the cases where the face layers' materials are PZT-2 or PZT-6B, but the material of the middle layer is Steel (St) or Aluminum (Al). Sandwich plates PZT-2/St/PZT-2, PZT-2/Al/PZT-2, PZT-6B/St/PZT-6B and PZT-6B/Al/PZT-6B are examined and the influence of the problem parameters such as piezoelectric and dielectric constants, layer thickness ratios and third order elastic constants of the St and Al on the effects of the initial stresses on the wave propagation velocity is studied.

• Geomechanics and Engineering
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• 제15권2호
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• pp.775-781
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• 2018

Shake table tests were conducted on scaled tunnel model to investigate the mechanism and effect of seismic loadings on horseshoe scaled tunnel model in ground fissure site. Key technical details of the experimental test were set up, including similarity relations, boundary conditions, sensor layout, modelling methods were presented. Synthetic waves and El Centro waves were adopted as the input earthquake waves. Results measured from hanging wall and foot wall were compared and analyzed. It is found that the seismic loadings increased the subsidence of hanging wall and lead to the appearance and propagation of cracks. The values of acceleration, earth pressure and strain were greater in the hanging wall than those in the foot wall. The tunnel exhibited the greatest earth pressure on right and left arches, however, the earth pressure on the crown of arch is the second largest and the inverted arch has the least earth pressure in the same tunnel section. Therefore, the effect of the hanging wall on the seismic performance of metro tunnel in earth fissure ground should be considered in the seismic design.

• Smart Structures and Systems
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• 제26권2호
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• pp.157-174
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• 2020

The guided wave technique is commonly used in structural health monitoring as the guided waves can propagate far in the structures without much energy loss. The guided waves are conventionally generated by the surface-mounted piezoelectric wafer active sensor (PWAS). However, there is still lack of understanding of the wave propagation in layered structures, especially in structures made of anisotropic materials such as carbon fiber reinforced polymer (CFRP) composites. In this paper, the Rayleigh-Lamb wave strain tuning curves in a PWAS-mounted unidirectional CFRP plate are analytically derived using the normal mode expansion (NME) method. The excitation frequency spectrum is then multiplied by the tuning curves to calculate the frequency response spectrum. The corresponding time domain responses are obtained through the inverse Fourier transform. The theoretical calculations are validated through finite element analysis and an experimental study. The PWAS responses under the free, debonded and bonded CFRP conditions are investigated and compared. The results demonstrate that the amplitude and travelling time of wave packet can be used to evaluate the CFRP bonding conditions. The method can work on a baseline-free manner.

• 한국지역사회생활과학회지
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• 제21권4호
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• pp.595-603
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• 2010

The present study was performed on humans to investigate the physiological strain of wearing protective clothing for shielding electromagnetic waves and to compare control clothing that are currently on the market and new clothing that are developed for improving thermal comfort and material weight. Experiments were conducted in a climatic chamber of $28.8{\pm}0.6^{\circ}C$, $37{\pm}5%$RH under three differed experimental clothing conditions: None, Control, New. The results were as follows. Mean skin temperature and rectal temperature in New were significantly lower than that in None and Control (p<.05). The temperature and humidity inside clothing were lower in None (p<.05). Total weight loss was lower in New. Thermal sensation and thermal comfort were less hot and more comfortable in New than those in Control. It was concluded that wearing the protective clothing for shielding electromagnetic waves affects physiological responses such as distribution of body temperature, sweat rate, etc.

• Smart Structures and Systems
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• 제5권4호
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• pp.329-344
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• 2009

Ultrasonic chaotic excitations combined with sensor prediction algorithms have shown the ability to identify incipient damage (loss of preload) in a bolted joint. In this study we examine a physical experiment on a single-bolt aluminum lap joint as well as a three-dimensional physics-based simulation designed to model the behavior of guided ultrasonic waves through a similarly configured joint. A multiple bolt frame structure is also experimentally examined. In the physical experiment each signal is imparted to the structure through a macro-fiber composite (MFC) patch on one side of the lap joint and sensed using an equivalent MFC patch on the opposite side of the joint. The model applies the waveform via direct nodal displacement and 'senses' the resulting displacement using an average of the nodal strain over an area equivalent to the MFC patch. A novel statistical classification feature is developed from information theory concepts of cross-prediction and interdependence. This damage detection algorithm is used to evaluate multiple damage levels and locations.

• 한국자동차공학회논문집
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• 제13권2호
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• pp.58-64
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• 2005

An infinite element for impact problem has been developed using ABAQUS/Standard UEL. 4-node plane strain element was considered, and the constitutive equation was derived from properties of propagation plane body waves. The element acts as unbounded domain to the plane waves generated by impact. The numerical method was tested for the simulation of plate impact. The results show the effectiveness of the infinite element.

• Structural Engineering and Mechanics
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• 제56권5호
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• pp.767-785
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• 2015

The stochastic finite element method is employed to obtain a stochastic dynamic model of angled beams subjected to impact loads when uncertain material properties are described by random fields. Using the perturbation technique in conjunction with a precise time integration method, a random analysis approach is developed for efficient analysis of random elastic waves. Formulas for the mean, variance and covariance of displacement, strain and stress are introduced. Statistics of displacement and stress waves is analyzed and effects of bend angle and material stochasticity on wave propagation are studied. It is found that the elastic wave correlation in the angled section is the most significant. The mean, variance and covariance of the stress wave amplitude decrease with an increase in bend angle. The standard deviation of the beam material density plays an important role in longitudinal displacement wave covariance.

• 한국전기전자재료학회논문지
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• 제30권4호
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• pp.235-240
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• 2017

The effect of particle sizes on the aerosol deposition (AD) of Cu films is investigated in order to understand the deposition behaviors of metal powder during the AD process. The Cu coatings fabricated by using $2{\mu}m$ Cu powders had a dense microstructure, a high deposition rate ($1.6{\pm}0.2{\mu}m/min$), and low resistance ($9.42{\pm}0.4{\mu}{\Omega}{\cdot}cm$) compared to that from using Cu powder with a particle size greater than $5{\mu}m$. Also, from estimating the internal micro-strain of Cu films, the Cu coatings fabricated by using $2{\mu}m$ Cu particles exhibited a high micro-strain value of $3.307{\times}10^{-3}$. On the other hand, the strain of Cu coatings fabricated with $5{\mu}m$ particles was decreased to $2.76{\times}10^{-3}$. These results seem to show that the impacted Cu particles are compressed and flattened by shock waves, and that their bonding is associated with the high internal micro-strain caused by plastic deformation.

• 한국해양공학회지
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• 제28권2호
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• pp.133-139
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• 2014

Offshore wind turbines have been constructed extensively throughout the world. These turbines are subjected to approximately $10^8$ horizontal load cycles produced from wind, waves, and current during their lifetimes. Therefore, the accumulated displacement of the foundation under horizontal cyclic loading has significant effects on the foundation design of a wind turbine. Akili(2006) and Achmus et al.(2009) performed cyclic triaxial tests on dry sands and proposed an empirical model for predicting the accumulated plastic strain of sands under long-term cyclic loading. In this study, cyclic triaxial tests were performed to analyze the cyclic loading behaviors of dry sands. A total of 27 test cases were performed by varying three parameters: the relative density of the sands, cyclic load level, and confining stress. The test results showed that the accumulated plastic strain increased with an increase in the cyclic load level and a decrease in the relative density of the sand. The confining stress had less effect on the plastic strain. In addition, the plastic strain at the 1st loading cycle was about 57% of the accumulated strain at 1,000 cycles. Finally, the input parameters of the empirical models of Akili(2006) and Achmus et al.(2009) were evaluated by using the relative density of the sand and the cyclic load level.