• Smart Structures and Systems
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• v.13 no.1
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• pp.55-80
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• 2014

The present work pays emphasis on investigating the effect of different types of debonding on the bending behaviour of active sandwich beam, consisting of both extension and shear actuators. An active sandwich beam finite element is formulated by using Timoshenko's beam theory, characterized by first order shear deformation for the core and Euler-Bernoulli's beam theory for the top and bottom faces. The problem of debondings of extension actuator and face are dealt with by employing four-region model for inner debonding and three-region model for the edge debonding respectively. Displacement based continuity conditions are enforced at the interfaces of different regions using penalty method. Firstly, piezoelectric actuation of healthy sandwich beam is assessed through deflection analysis. Then the effect of actuators' debondings with different boundary conditions on bending behavior is computationally evaluated and experimentally clamped-free case is validated. The results generated will be useful to address the damage tolerant design procedures for smart sandwich beam structures with structural control and health monitoring applications.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.649-656
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• 2000

Consolidation of the ground surrounding the sand piles is delayed by well resistance and smear effect. This study is executed to understand the factors that affect the characteristics of consolidation. This was accomplished by utilizing the estimated and measured values of the soil properties through the monitoring of the ground surrounding the sand piles. When it is assumed that the horizontal coefficient is equal to the vertical coefficient of consolidation, the estimated values is exceedingly similar to the measured values. The properties of the initially disturbed soil by the sand pile installation seemed to improve through the process of consolidation with the passage of time. From the results of the analysis of the settlement measurement, the measured values occurred about 60～90% of the predicted values. Considering the initial radical compression deformation, according to the theory of cavity expansion, the difference between the two appears to be in good agreement. In this study, to understand the behavioral characteristics of the ground surrounding the sand piles requires estimation through considering the initial radial compression as well as smear effect of the soil disturbance and well resistance.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• v.4 no.1
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• pp.51-55
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• 2001

The characteristics of elastic waves emanating from crack initiation in 2024 and 5052 aluminum alloys subject to static and fatigue loading are investigated through laboratory experiments. The objective of the study is to determine difference in the properties of the signals generated from static and fatigue tests and also to examine if the sources of the waves could be identified from the temporal and spectral characteristics of the acoustic emission (AE) waveforms. The signals are recoded using non-resonant, flat, broadband transducers attached to the surface of the alloy specimens. The time dependence and power spectra of the signals recorded during the tests were examined and classified according to their special features. Three distinct types of signals were observed. The waveforms and their power spectra were found to be dependent on the material and the type of fracture associated with the signals. Analysis of the waveforms indicated that some signals could be attributed to plastic deformation associated with static tests. The potential application of the approach in health monitoring of aging aircraft structures using a network of surface mounted broadband sensors is discussed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.61-67
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• 1997

The electronic speckle pattern interferometer (ESPI) has been applied to many technical problems such as deformation and displacement measurement, strain visualization and surface roughness monitoring. In this study, we used an ESPI system based on the dual beam speckle interferometer method in order to measure in-plane displacement and vibration mode using the ESIP technique. This research was carried out for the purpose of applying the vibration analysis method employing Electro-Optic holographic interference technique to the vibration analysis of uniform rectangular cantilevers plate(SS400,STS304) with cantilevers span to breadth ratio of 150 by 75. And thickness of 1mm and 0.8mm respectively. We improved the ESPI technique in order to obtain the distribution of displacement component resolved in one direction through a CCD camera combined with an image processing system. To certify and to assess the accuracy in measuring by this ESPI, the results obtained with the speckle method and vibration mode analysis are to be compared with those results by Warbuton's Theoretical expression and vibration made in FEM analysis.

• Smart Structures and Systems
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• v.8 no.5
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• pp.471-486
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• 2011

Various types of strain sensors have been developed and widely used in the field for monitoring the mechanical deformation of structures. However, conventional strain sensors are not suited for measuring large strains associated with impact damage and local crack propagation. In addition, strain sensors are resistive-type transducers, which mean that the sensors require an external electrical or power source. In this study, a gold nanoparticle (GNP)-based polymer composite is proposed for large strain sensing. Fabrication of the composites relies on a novel and simple in situ GNP reduction technique that is performed directly within the elastomeric poly(dimethyl siloxane) (PDMS) matrix. First, the reducing and stabilizing capacities of PDMS constituents and mixtures are evaluated via visual observation, ultraviolet-visible (UV-Vis) spectroscopy, and transmission electron microscopy. The large strain sensing capacity of the GNP-PDMS thin film is then validated by correlating changes in thin film optical properties (e.g., maximum UV-Vis light absorption) with applied tensile strains. Also, the composite's strain sensing performance (e.g., sensitivity and sensing range) is also characterized with respect to gold chloride concentrations within the PDMS mixture.

• Structural Engineering and Mechanics
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• v.65 no.2
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• pp.155-162
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• 2018

A smart glass fiber reinforced polymer (SMFRP) reinforcing bar with a fiber Bragg grating (FBG) sensor was fabricated using a pultrusion technique, while ribs were formed to improve bonding between concrete and SMFRP. Then, strain of SMFRP bars were measured for a uniaxial tension test of an SMFRP bar, and a four-point bending test of concrete beams reinforced with SMFRP bars. The results of a uniaxial tension test illustrate that the strain obtained from an FBG sensor agrees well with that obtained from electrical resistance strain gauge (ERSG). Additionally, concrete beams reinforced with SMFRP bars were fabricated, and actual flexural test were performed while the strain of with an FBG sensor was compared with that of ERSG. The experimental results demonstrate that SMFRP bars can be used as reinforcement of concrete member while providing deformation information. Furthermore, SMFRP bars may provide stronger durability and smart monitoring to reinforced concrete members under corrosive environments during a service life.

• Geomechanics and Engineering
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• v.20 no.5
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• pp.447-459
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• 2020

Based on the literature statistical method, the paper publication status of the isolated working face and the distribution of the rockburst coal mine were obtained. The numerical simulation method is used to study the stress distribution law of working face under different mining range. In addition, based on the similar material simulation test, the overlying strata failure modes and the deformation characteristics of coal pillars during the mining process of the isolated working face with thick-hard key strata are analyzed. The research shows that, under the influence of the key strata, the overlying strata formation above the isolated working face is a long arm T-type spatial structure. With the mining of the isolated working face, a series of damages occur in the coal pillars, causing the key strata to break and inducing the rockburst occurs. Combined with the mechanism of rockburst induced by the dynamic and static combined load, the source of dynamic and static load on the isolated working face is analyzed, and the rockburst monitoring methods and the prevention and control measures are proposed. Through the above research, the occurrence probability of rockburst can be effectively reduced, which is of great significance for the safe mining of deep coal mines.

• Tribology and Lubricants
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• v.33 no.6
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• pp.282-287
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• 2017

SU-8 is an epoxy-type photoresist widely used for the fabrication of high-aspect-ratio (HAR) micro-structures in micro-electro-mechanical systems (MEMS). To fabricate highly integrated structures, chemical mechanical polishing (CMP) has emerged as the preferred manufacturing process for planarizing the MEMS structure. In SU-8 CMP, an oxidizer decomposes organic impurities and particles in the CMP slurry remove the chemically reacted surface of SU-8. To fabricate HAR microstructures using the CMP process, the adhesion between SU-8 and substrate material is important to avoid the delamination of the SU-8 film caused by the mechanical-dominant material removal characteristic. In this study, the friction force during the CMP process is measured with a CMP monitoring system to detect the delamination phenomenon and investigate the delamination of the SU-8 film from the silicon substrate under various pressure conditions. The increase in applied pressure causes an increase in the frictional force and wafer-edge stress concentration. The frictional force measurement shows that the friction force changes according to the delamination phenomenon of the SU-8 film, and that it is possible to monitor the delamination phenomenon during the SU-8 CMP process. The delamination at a high applied pressure is explained by the effect of stress distribution and pad deformation. Consequently, it is necessary to control the pressure of polishing, which can avoid the delamination in SU-8 CMP.

• Smart Structures and Systems
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• v.1 no.4
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• pp.369-384
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• 2005

The main objectives of this paper are to demonstrate the feasibility of using newly developed smart GFRP reinforcements to effectively monitor reinforced concrete beams subjected to flexural and creep loads, and to develop non-linear numerical models to predict the behavior of these beams. The smart glass fiber-reinforced polymer (GFRP) rebars are fabricated using a modified pultrusion process, which allows the simultaneous embeddement of Fabry-Perot fiber-optic sensors within them. Two beams are subjected to static and repeated loads (until failure), and a third one is under long-term investigation for assessment of its creep behavior. The accuracy and reliability of the strain readings from the embedded sensors are verified by comparison with corresponding readings from surface attached electrical strain gages. Nonlinear finite element modeling of the smart concrete beams is subsequently performed. These models are shown to be effective in predicting various parameters of interest such as crack patterns, failure loads, strains and stresses. The strain values computed by these numerical models agree well with corresponding readings from the embedded fiber-optic sensors.

• Geomechanics and Engineering
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• v.16 no.5
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• pp.539-545
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• 2018

Longitudinal Displacement Profile (LDP) is an appropriate tool for determination of the displacement magnitude of the tunnel walls as a function of the distance to the tunnel face. Some useful formulations for calculation of LDP have been developed based on the monitoring data on site or by 3D numerical simulations. However, the presented equations are only based on the tunnel dimensions and for different quality of rock masses proposed a unique LDP. In the present study, it is tried to present a new formulation, for calculation of LDP, on the basis of Rock mass quality. For this purpose, a comprehensive numerical simulation program was developed to investigate the effect of rock mass quality on the LDP. Results of the numerical modelling were analyzed and the least square technique was used for fitting an appropriate curve on the derived data from the numerical simulations. The proposed formulation in the present study, is a logistic function and the constants of the logistic function were predicted by rock mass quality index (GSI). Results of this study revealed that, the LDP curves of the tunnel surrounded by rock masses with high quality (GSI>60) match together; because the rock mass deformation varies over an elastic range.