• Journal of Korean Elementary Science Education
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• v.35 no.4
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• pp.389-405
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• 2016

The purpose of this study was to analyze elementary school teachers' understanding, certainty, and familiarity with 13 key concepts of wave physics that are presented in textbook and teacher's guidebook. 123 elementary school teachers answered concept tests and questionnaires. In the results to these tests and questionnaires, teachers demonstrated a high level of understanding and high certainty in understanding with regard to the concepts of sound generation, effect of medium on wave, timbre, wavelength, and trough and crest of wave. For the topics of sound velocity, wave reflection and wave transmission, teachers demonstrated a high level of understanding but low certainty in understanding. With regard to sound propagation, teachers demonstrated a low level of understanding and an improperly high certainty in that low understanding. Teachers lacked knowledge, i.e., displayed a low level of understanding and low certainty in sound strength, sound frequency, constructive interference and destructive interference. In constructive and destructive interference, the teachers also displayed a low level of familiarity. We analyzed the differences in teacher's understanding, certainty, and familiarity according to teacher demographics defined by the teacher's gender, teaching experience with concepts of sound, career, curriculum track while in high school, and major in university. There were no significant differences in understanding, certainty, or familiarity as defined by gender, teaching experience, and career. However, these displays of knowledge were affected by the teacher's curriculum track in high school and their major. These results suggest that the teacher's understanding of, familiarity with, and certainty in wave physics concepts are more influenced by their learning experience than by their teaching experience. Therefore, we suggest additional learning opportunities for teachers (such as teacher training programs) in order to improve teacher knowledge and correct teacher misconceptions in wave physics.

• Journal of Korean Institute of Industrial Engineers
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• v.41 no.5
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• pp.481-487
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• 2015

In the product development stage, it is very important to ensure demanded quality level before moving to the full-scale manufacturing. For example, in developing guided weapons, live-fire tests are required to verify the final performance of the weapons which are very expensive. The quality evaluation of the guided weapons needs destructive testing, which makes it necessary to test as small number of samples as possible. This paper presents sampling inspection plans and calculating system for finite population guided weapons, which can meet the demanded quality level and confidence level with the minimum number of performance tests. The result of this paper can be useful for any kind of costly destructive testing.

• Earthquakes and Structures
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• v.10 no.3
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• pp.523-538
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• 2016

Besides their spiritual significance, minarets are humanity's cultural heritage to the future generations due to their historical and architectural attraction. Currently, many historical masonry minarets are damaged and destroyed due to several reasons such as earthquakes and wind. Therefore, safety of these religiously significant buildings needs to be thoroughly investigated. The utmost care must be taken into account while investigating these structures. Our study investigated earthquake behavior of historical masonry minaret of Haci Mahmut Mosque. Destructive and non-destructive tests were carried out to determine earthquake safety of this structure. Brick-stone masonry material properties of structure were determined by accomplishing ultrasonic wave velocity, Schmidt Hammer, uniaxial compression (UAC) and indirect tension (Brazilian) tests. Determined material properties were used in the finite element analysis of the structure. To validate the numerical analysis, Operational Modal Analysis was applied to the structure and dynamic characteristics of the structure were determined. To this end, accelerometers were placed on the structure and vibrations due to environmental effects were followed. Finite element model of the minaret was updated using dynamic characteristics of the structure and the realistic numerical model of the structure was obtained. This numerical model was solved by using earthquake records of Turkey with time history analysis (THA) and the realistic earthquake behavior of the structure was introduced.

• Composite Materials and Engineering
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• v.3 no.3
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• pp.167-178
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• 2021

In the present paper, the destructive behavior of distilled water, salty water, sulfuric acid, and heat on glass/vinyl ester composites was investigated by experimental methods. Hetron 922 vinyl ester resin and two types of mat and woven glass fibers as the reinforcements were used to fabricate composite test samples. All samples were immersed in distilled water, salty water, and sulfuric acid with three different concentrations. The tests were performed at 20℃ and 70℃ for the exposure duration of 1, 2, 4, and 8 weeks. Bending tests were performed after aging for all composite samples to check the degradation of the bending modulus and strength. The results show that the effect of distilled water, in comparison with salty water, on the degradation of composite samples was significant. On the other hand, almost non-sensitivity of concentrations of salty water on the weight gain of specimens has been observed. In addition, it was also observed that the degradation of samples at 70℃ temperature is much more than that of at 20℃. Also, it was observed that the flexural modulus of virgin specimens exposed to salty water (2% concentration) has been recovered just after two weeks of immersion. Furthermore, in some cases, composite samples under the sulfuric acid solution have lost almost 80% of their mechanical properties.

• Journal of the Korean Geotechnical Society
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• v.24 no.8
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• pp.13-23
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• 2008

The evaluation of soundness of pile is very important for the safety of super structure. In this paper, the HWAW(Harmonic Wavelet Analysis of Wave) method which is developed to determine phase and group velocities of waves is applied to evaluate integrity of pile non-destructivly. The proposed method can evaluate a soundness of pile and pile end condition which is very important factor for pile behaviour. To verity the applicability of HWAW method in non-destructive test for pile, the numerical simulation test using ABAQUS was performed. And the model pile was made and the proposed non-destructive pile tests were applied to evaluate soundness and end boundary condition of model pile in the air and soil box. Through a numerical simulation and model tests, it is shown that the HWAW method has good potential of applying to the evaluation of pile integrity.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.766-777
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• 2008

Currently in increasing number of urban tunnels with small overburden are excavated according to the principle of the New Austrian Tunneling Method (NATM). Successful design, construction and maintenance of NATM tunnel demands prediction, control and monitoring of ground displacement and support stress high accuracy. A magnetic anisotropy sensor is used for nondestructive measurement of stress on surfaces of a ferromagnetic material, such as steel. The sensor is built on the principle of the magneto-strictive effect in which changes in magnetic permeability due to deformation of a ferromagnetic material is measured in a nondestructive manner, which then can be translated into the absolute values of stresses existing on the surface of the material. This technique was applied to measure stresses of H-beams, used as tunnel support structures, to confirm expected measurement accuracy with reading error of about 10 to 20 MPa, which was confirmed by monitoring strains released during cutting tests The results show that this method could be one of the promising technologies for non-destructive stress measurement for safe construction and maintenance of underground rock structures encountered in civil and mining engineering.

• Computers and Concrete
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• v.34 no.1
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• pp.33-48
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• 2024

This paper presents the detailed experimental and analytical investigation on the evolution of static (E_s) and dynamic modulus of elasticity (E_d) of concrete having 0%, 35%, and 50% FA used as partial cement replacement. Destructive and non-destructive tests were conducted on cylindrical specimens to evaluate the compressive strength and MoE of concrete in compression at the age of 28, 56, 90, and 150 days for all mixes. Experimental results show that the concrete having 35% FA achieved compressive strength and MoE similar to plain concrete at the age of 90 days, while 50% FA concrete attained satisfactory compressive strength and MoE at the age of 150 days. The comprehensive statistical analysis has been carried out in two ways on the basis of the experimental results. Firstly, the 28-day crushing strength of plain concrete in compression was used to design the models for the prediction of E_s and E_d of fly ash concrete at any age and percentage replacement of FA. Secondly, using the values of UPV and RHN, models have been developed to predict the age or time-dependent E_s and E_d of fly ash concrete. These models will be helpful in assessing the E_s and E_d of fly ash concrete without knowing the 28-day crushing strength of plain concrete in compression in the laboratory. Hence, the suggested models in the present study will be beneficial in conducting the health assessment of fly ash based concrete structures.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.6
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• pp.427-439
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• 2006

Accurate estimates of in place thickness of early age (3 to 28 days after casting) concrete pavements are needed, where a thickness accuracy of ${\pm}6mm$ is desired. The impact-echo method is a standardized non-destructive technique that has been applied for this task. However, the ability of impact-echo to achieve this precision goal is affected by Vp (measured) and ${\beta}$ (assumed) values that are applied in the computation. A deeper understanding of the effects of these parameters on the accuracy of impact-echo should allow the technique to be improved to meet the desired accuracy goal. In this paper, the results of experimental tests carried out on a range of concrete slabs are reported. Impact-echo thickness estimation errors caused by material property gradients and sensor type are identified. Correction factors to the standard analysis method are proposed to correct the identified errors and to increase the accuracy of the standard method. Results show that improved accuracy can be obtained in the field by applying these recommendations with the standard impact-echo method.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.26 no.4
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• pp.436-440
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• 2017

This study evaluated the design and structural integrity of a three-axle bogie frame in a railway freight car through a numerical analysis and an experimental evaluation. A three-axle bogie frame, which supports the weight of the car body and load, is required to transport heavier cargo because two-axle vehicles have structural limitations. Therefore, this study performed a structural analysis and static load tests to evaluate the design and structural integrity of a three-axle bogie frame. The results obtained from the numerical analysis were compared to those of the experiments. For the bogie frame used in the experiments, a failure evaluation was performed using non-destructive methods. The numerical analysis and experimental evaluation were satisfactory for the structural integrity evaluation.

• International Journal of Railway
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• v.1 no.1
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• pp.1-5
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• 2008

The railway system requires safety and reliability of service of all railway vehicles. Suitable technical systems and working methods adapted to it, which meet the requirements on safety and good order of traffic, should be maintained. For detection of defects, non-destructive testing methods-which should be quick, reliable and cost-effective - are most often used. Since failure in railway wheelset can cause a disaster, regular inspection of defects in wheels and axles are mandatory. Ultrasonic testing, acoustic emission and eddy current testing method and so on regularly check railway wheelset in service. However, it is difficult to detect a crack initiation clearly with ultrasonic testing due to noise echoes. It is necessary to develop a non-destructive technique that is superior to conventional NDT techniques in order to ensure the safety of railway wheelset. In the present paper, the new NDT technique is applied to the detection of surface defects for railway wheelset. To detect the defects for railway wheelset, the sensor for defect detection is optimized and the tests are carried out with respect to surface and internal defects each other. The results show that the surface crack depth of 1.5 mm in press fitted axle and internal crack in wheel could be detected by using the new method. The ICFPD method is useful to detect the defect that initiated in railway wheelset.