• Structural Engineering and Mechanics
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• v.26 no.5
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• pp.499-516
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• 2007

An experimental method denoted as Impulse Method is proposed as a cost-effective non-destructive technique for the on-site evaluation of concrete elastic modulus in existing structures: on the basis of Hertz's quasi-static theory of elastic impact and with the aid of a simple portable testing equipment, it makes it possible to collect series of local measurements of the elastic modulus in an easy way and in a very short time. A Hypothesis Testing procedure is developed in order to provide a statistical tool for processing the data collected by means of the Impulse Method and assessing the possible occurrence of significant variations in the elastic modulus without exceeding some prescribed error probabilities. It is based on a particular formulation of the renowned sequential probability ratio test and reveals to be optimal with respect to the error probabilities and the required number of observations, thus further improving the time-effectiveness of the Impulse Method. The results of an experimental investigation on different types of plain concrete prove the validity of the Impulse Method in estimating the unknown value of the elastic modulus and attest the effectiveness of the proposed Hypothesis Testing procedure in identifying significant variations in the elastic modulus.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.47-56
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• 2009

Rock bolts and shotcrete play a crucial role as a main support system in the underground space. Thus, the safety of the underground space may be affected by the defect of rock bolts. In order to evaluate the rock bolt integrity by using non-destructive technique, the transmission method of the guided ultrasonic waves, which are generated by using the piezo disk elements has been successfully performed. The energy generated by the piezo disk elements, however, is not enough for the rock bolts in the field. In addition, the piezo disk elements should be installed at the end of the steel bar during construction of the rock bolts. The purpose of this study is the devolvement of the reflection method, which may generate enough energy, and the application in the field rock bolts. Both laboratory and field tests are carried out. The guided ultrasonic waves with high energy are generated by the hammer impact with the center punch, and the AE sensor is used to measure the reflected guided waves. The received guided waves are analyzed by the wavelet transform. The peak value of the wavelet transform produces the energy velocity, which is used for the evaluation of the rock bolt integrity. The energy velocity increases with an increase in the defect ratio in both laboratory and field rock bolts. This study demonstrates that the hammer-impact reflection method may be a suitable method for the evaluation of the rock bolt in the field.

• Smart Structures and Systems
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• v.29 no.3
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• pp.445-455
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• 2022

Steel anchor bolts are installed in concrete using a variety of methods. One of the most common methods of anchor bolt installation is using epoxy resin as an infill material injected into the drilled hole to act as a bonding material between the steel bolt and the surrounding concrete. Typical design standards assume uniform stress distribution along the length of the anchor bolt accompanied with single crack leading to pull-out failure. Experimental evidence has shown that the steel anchor bolts fail owing to the multiple failure patterns, hence these design assumptions are not realistic. In this regard, the presented research work details the analytical model that takes into consideration multiple micro cracks in the infill material induced via impact loading. The impact loading from the Schmidt hammer is used to evaluate the bond condition bond condition of anchor bolt and the epoxy material. The added advantage of the presented analytical model is that it is able to take into account the various type of end conditions of the anchor bolts such as bent or U-shaped anchors. Through sensitivity analysis the optimum stiffness and shear strength properties of the epoxy infill material is achieved, which have shown to achieve lower displacement coupled with reduced damage to the surrounding concrete. The accuracy of the presented model is confirmed by comparing the simulated deformational responses with the experimental evidence. From the comparison it was found that the model was successful in simulating the experimental results. The proposed model can be adopted by professionals interested in predicting and controlling the deformational response of anchor bolts.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.7
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• pp.1241-1249
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• 2002

The extent of materials deterioration can be evaluated accurately by mechanical test such as impact test or creep test. But it is almost impossible to extract a large test specimen from in-service components. Thus material degradation evaluation by non-destructive method is earnestly required. In this paper, the material degradation for virgin and several aged materials of a Cr-Mo-V steel, which is an candidated as structural material of the turbine casing components for electric power plant, is nondestructively evaluated by reactivation polarization testing method. And, the results obtained from the test are compared with those in small punch(SP) tests recommended as a semi-nondestructive testing method using miniaturized specimen. In contrast to the aged materials up to 1,000hrs which exhibit the degradation behaviors with increased ${\Delta}[DBTT]_{SP}$, the improvement of mechanical property can be observed on the 2,000hrs and 3,000hrs aged materials. This is because of the softening of material due to the carbide precipitation, the increase of ferritic structures and the recovery of dislocation microstructure by long-time heat treatment. The reactivation rates($I_R/I_{Crit},\;Q_R/Q_{Crit}$) calculated by reactivation current densityt ($I_R$) and charge($Q_R$) in the polarization curves exhibit a good correlation with ${\Delta}[DBTT]_{SP}$ behaviors.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.11 s.170
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• pp.2014-2021
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• 1999

The present investigation is concerned with the degradation characteristics of cast stainless steel(CF8M), exposed to the $\sigma$-phase degradation at $700^{\circ}C$. In the present paper, the degradation of CF8 M at $700^{\circ}C$ is evaluated by a non-destructive test, DL-EPR(double loop electrochemical potentiokinetic reactivation). The surface of specimens is observed by using scanning electron microscopy after DL-EPR test. Also. chromium contents of matrix, grain boundary and ferrite phase are analyzed by electron probe X-ray micro analyzer. Through the experiments, the following results are obtained 1) The degree of sensitization(DOS) of CF8M aged up to 15hr at $700^{\circ}C$ is increased with acing time while that is decreased with aging time from 15hr to 150hr. 2) The impact energy decreases with increase of $\sigma$-phase while DOS increases with $\sigma$-phase until aging time reaches to 15hr. After the aging time. 15hr, the $\sigma$-phase and the rate of impact energy with respect to aging time decreases. Therefore the degradation behavior of the CF8M can be evaluated by comparing SEM micrographs and the value of DOS.

• Tunnel and Underground Space
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• v.19 no.1
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• pp.19-30
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• 2009

For the purpose of determining the thickness of concrete lining and detect of the cavity where may be located behind tunnel lining, IE (Impact-Echo) method it effectively useful in the tunnel safety diagnosis and the quality control during the construction. As a part of case study, we applied IE method to various tunnel structure types such as road tunnel and subway tunnel constructed by NATM (New Austrian Tunnelling Method) and ASSM (American Steel Support Method). As tunnel specifications estimated from this method were compared with coring data, design drawing and other survey results, it was very good agreement with each other. In conclusion, we verified that IE method shows an accurate and reliable result. The conventional interpretation of IE method in frequency domain gives only vertical information at a certain point. However, the interpretation using time-frequency analysis and depth section imaging technique from two dimensional profiling surveys can show more reliable information about structure inside.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.1
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• pp.96-102
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• 2012

The current establishment of car engineering plastic piping polyethylene (PE) tube used as bonding state or part of the health or safety of fusion is very important. A part of these fusion methods to determine the soundness of the short-term trials and long-term tests can be largely classified. Typical tests included short-term strength, tensile strength, impact strength, compressive strength, resiliency and compression. Polyethylene (PE) pipes installed in the domestic terms of overall penetration rate of 45% has been used. However, polyethylene (PE) pipes have reliability problems, and these occurs mostly in part by defective welding. Therefore, the test is necessary for safety. Non-destructive methods (ultrasonic testing) are difficult to be used. Therefore, Polyethylene (PE) pipe are used. Fusion of thses materilas is necessary in these field however, its technical, and basic research has not been studied well. In this research, short-term strength of welding parts, its tensile strength, hardness, fatigue, and microstructure have been analyzed to find the optimum process conditions to improve mechanical properties.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.5
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• pp.564-569
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• 2011

The current establishment of city gas piping polyethylene (PE) tube used as bonding state or part of the health or safety of fusion is very important. A part of these fusion methods to determine the soundness of the short-term trials and long-term tests can be largely classified. Typical tests include short-term strength, tensile strength, impact strength, compressive strength, resiliency and compression. Polyethylene (PE) pipes installed in the domestic terms of overall penetration rate of 45% has been used. However, polyethylene (PE) pipes have reliability problems, and these occurs mostly in part by defective welding. Therefore, the test is necessary for safety. Non-destructive methods (ultrasonic testing) are difficult to be used. Therefore, Polypropylene copolymer (PP-C), polypropylene homopolymer (PP-H), and polyethylene (PE) pipe are used. Fusion of these materials is necessary in these field however, its technical, and basic research has not been studied well. In this research, short-term strength of welding parts, its tensile strength, hardness, fatigue, and microstructure have been analyzed to find the optimum process conditions to improve mechanical properties.

• Journal of the Korea Institute of Building Construction
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• v.23 no.5
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• pp.519-526
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• 2023

This research endeavors to explore the nuances in apparent resistivity readings in concrete specimens due to the proximity of embedded reinforcement. To systematically gauge this, concrete samples incorporating singular and paired rebars were meticulously crafted. These rebars were strategically positioned at intervals of 0.03m, 0.04m, and 0.05m from each specimen's midpoint. Subsequent resistivity assessments were conducted at 0.01m increments up to the predetermined rebar location for each sample. A consistent observation was the nadir in apparent resistivity manifesting at the rebar's epicenter. Notably, dual-rebar configurations registered lower resistivity values at this central juncture compared to their single-rebar counterparts. This metric underscores the palpable impact of surrounding reinforcement on resistivity readings. Further, as the spatial separation between rebars increased, the distinctness in their locational identification via resistivity became increasingly pronounced.

• Land and Housing Review
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• v.15 no.3
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• pp.153-164
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• 2024

Structural health monitoring involves performance evaluation based on measurements for maintenance purposes. By back-calculating measured Frequency Response Function (FRF) data, the concept of effective mass was introduced and applied to the performance evaluation of structural members. An identification method was proposed that uses participation factors to estimate the dynamic parameters and the strength of concrete of structural members. The appropriateness of these methods for identifying dynamic parameters and concrete strength of structural members was validated through experimental results, proving their utility in non-destructive testing for concrete strength.