• Journal of the Korean Wood Science and Technology
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• 제31권6호
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• pp.45-54
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• 2003

The density and strength of wood is affected by degradations and defects, such as voids and knots. Old wooden structures such as traditional cultural properties have been deteriorated by these types of defects. They were evaluated by a visual observation that is difficult to evaluate the inner deterioration in structures. In this study, three nondestructive testing techniques were investigated to detect the wooden structural members. Ultrasonic stress wave tests, drilling resistance tests and visual inspections were used to examine the structural wood members. Patterns of Resistograph using by drilling resistance tests could indicate the features of internal wood such as voids, knots, decay, fungi, and so on. The technique just like as ultrasonic stress wave tests, however, difficult to detect exactly area where small amounts of internal deterioration in logs are. In spite of results of ultrasonic stress wave test, the internal deterioration of wooden structural members could be evaluated by the relationship between ultrasonic stress wave tests and drilling resistance tests.

• Journal of the Korean Wood Science and Technology
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• 제32권3호
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• pp.33-41
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• 2004

In ancient wooden structures, the mechanical properties of the structural members have been reduced by time-dependent degradations such as fatigue or creep. Also, the external and internal deterioration was caused by environmental condition, fungi, bacteria, or insect, and then reduced the quality of structural members. However, the previous methods for evaluating the deterioration have been mainly depended on the visual inspection. In this study, therefore, ultrasonic stress wave test, accelerometer stress wave test were used to evaluate the deterioration of structural wood members in ancient wooden structures. Based on the results, the quantitative criteria of stress wave transmitted velocity were proposed to evaluate the deterioration of structural member. The proposed criteria were related to the degree of deterioration. In accelerometer stress wave, the criteria of deterioration of wave reciprocal velocity was below 1800 ㎲/m at incipient deterioration (below 12% ratio of deterioration), between 1800 and 2200 ㎲/m at moderate deterioration (12~17%) and above 2200 ㎲/m at severe deterioration (above 17%). The ultrasonic stress wave, the criteria of deterioration were 800 and 950 ㎲/m at below 8% and above 15% of the degree of deterioration respectively.

• 한국정밀공학회지
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• 제20권3호
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• pp.157-164
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• 2003

The pulse-echo method is one of the most widely used ultrasonic techniques for application of nondestructive evaluation. Particularly, quantitative nondestructive evaluation of defects has been considered more important to assure the reliability and the safety of structure. Frequency energy in adhesive joints is based on the ultrasonic wave analysis. The attenuation coefficient upon wave amplitude and the frequency energy that is expressed in the term of wave pressure amplitude were utilized for the primary wave experiment. By means of a control experiment, it was confirmed that the variation of the frequency energy in adhesive joints depends on transition by stress variation. In this paper, the ultrasonic characteristics were measured for single lap joint and Double Cantilever Beam specimen with different fracture modes that was subjected to stress. Consequently, the data that was obtained from the adhesive specimen was analytically compared to the fracture mechanics parameter

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.348-352
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• 1995

In the conventional linear elasticity, ultrasonic velocity is determined by elastic modulus and density of te medium which ultrasonic wave propagates through. But, practical ultrsonic wave depends on the stress acting in the medium, and as the stress increases such dependency becomes nonlinear. This nonlinear dependencyof ultrasonic velocity on stress can be identified by using nonlinear elastic modulus up to 4th order. In thid paper, with the above background relationships between nonlinear elastic modulus and the internalstatus of materials, normal, plastic deformed or heat stressed, are discussed. For this purpose, a new type of measuring system extended from the general nondestructive UT(ultrasonic test) equipment is constructed.

• 한국정밀공학회지
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• 제13권4호
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• pp.53-60
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• 1996

In the conventional linear elasticity, sound speed is determined by only elastic modulus and density of the medium. In actual, however, sound speed depends on the stress and this dependency becomes nonlinear as the stress increases. These phenomena can be introducing nonlinear elastic modulus. In this paper, relationships between nonlinear elastic modulus up to 4th order and the internal status of materials are discussed through computer simulations and experiments. For the measurement of sound speed, a new type of measurement system using ultrasonic wave is proposed on the basis of ultrasonic pulse echo method which has been generally used in nondestructive ultrasonic test equipment. In order to confirm the stress dependency of sound speed, several experiments are carried out for alumina specimen.

• Geomechanics and Engineering
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• 제25권3호
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• pp.253-266
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• 2021

In this paper, we discuss a mathematical method for determining the return energy of the wave from the sample and comparing it with the mechanical energy consumed to change the dimension of the sample in the triaxial test of the rock. We represent a method to determine the mechanical energy and then we provide how to calculate the return energy of the wave. However, the static energy and pulse return energy will show higher amounts with axial pressure increase. Three types of clastic sedimentary rocks including sandstone, pyroclastic rock, and argillitic tuff were selected. The sandstone showed the highest strength, Young's modulus and ultrasonic P and S waves' velocities versus others in the triaxial test. Also, from the received P wavelet, the calculated pulse wave returning energy indicated the best correlation between axial stress compared to wave velocities in all specimens. The fact that the return energy decreases or increases is related to increasing lateral stress and depends on the geological characteristics of the rock. This method can be used to determine the stresses on the rock as well as its in-situ modulus in projects that are located at high depths of the earth.

• 한국가스학회지
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• 제4권1호
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• pp.55-62
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• 2000

Pit형 표면결함으로부터 발생하는 작은 피로균열의 거동을 초음파의 표면파를 이용하여 이를 위하여 피로시험중인 Al 2024-T3를 시험재료, 피로시험도중 초음파를 이용하여 피로균열의 거동을 조사하였다. 즉, 피로시험에서 균열이나 Pit로부터 발생하는 작은 피로균열을 여러 응력조건하에서 나타나는 표면파의 반사특성에 관하여 연구하였다. 또한 이론적 결과와 실험적 결과를 상호 비교, 분석하였고, SEM을 사용하여 이들 작은 피로균열을 관찰하였다. 초음파를 이용한 피로균열의 균열 개구 거동에 관한 연구에서 피로균열의 유효균열 특성을 초음파법으로 평가 할 수 있었다.

• 한국지반공학회논문집
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• 제18권6호
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• pp.17-24
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• 2002

본 연구에서는 초음파실험을 통하여 카올린 점토 시료의 초음파 전파 속도와 감쇠특성을 조사하였다. 슬러리 압밀 방법을 이용하여 이산구조와 면모구조를 갖는 두 종류의 카올린 점토를 인공적으로 제작하였다. 초음파를 이용하여 각 구조를 가진 점토의 압축파 속도 및 감쇠 거동을 측정하였다. 측정시 가진 주파수, 시료 길이, 측정 방향 등을 변화시키며 그에 대한 영향을 조사하였다. 실험 결과 전파속도는 같은 압축 응력 조건에서 제작된 본 시료의 경우 미세구조의 영향이 크지 않았으나 감쇠 특성은 미세구조의 영향이 큰 것으로 나타났다.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2000년도 창립총회 및 춘계학술발표회
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• pp.37-40
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• 2000

Acoustically enhanced soil flushing method is a newly developed in-situ remediation technique. However, there has not been an analytical method that can be used to evaluate the effectiveness of ultrasonic wave under different conditions. This study was undertaken to investigate the degree of enhancement in contaminant removal due to ultrasonic energy on the soil flushing method. The test conditions included different levels of ultrasonic power and hydraulic gradient. The test soils were Ottawa sand, a fine aggregate, and a natural soil, and the surrogate contaminant was a Crisco Vegetable Oil. The test results showed that sonication could increase contaminant removal significantly. Increasing sonication power increased pollutant removal. The faster the flow is, the smaller the degree of enhancement will be. The pollutants in dense soils are more difficult to be removed than in loose soils.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 추계학술대회 논문집
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• pp.127-132
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• 2003

In a today industry, the welding is doing a many portion in structure manufacture. This study is simulated heat of heat-effected zone and researched a mechanical properties and ultrasonic characteristic in used the SS400 and the STS304. As the result mechanical properties of steel that become drawing decreased because of remaining stress by strain gardening according as simulated heat temperature rises, but according as temperature rises in material that do simulated heat after have done annealing, mechanical propensity was improved. The velocity and attenuation become different by effect of remaining stress than effect of material internal microstructure in ultrasonic wave test. In the case of STS304, there was change in mechanical properties by effect that is by strain hardening, but there was no change in material that simulated heat after annealing. When become drawing in ultrasonic waves test, according as simulated heat temperatures rise, change of attenuation coefficient is looked, but material that simulated heat after annealing was no change almost both the volocity and attenuation.