• 한국안전학회지
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• 제17권4호
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• pp.11-18
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• 2002

We proposed a new experimental method which is required to easily observe the growth behavior of fatigue cracks. In the proposed method, the image data of cracks were stored into the computer while the cyclic loading was interrupted. After testing, crack length was determined using an image processing software which was developed by authors. By comparing the data measured by the image processing system with those by the manual measurement with a microscope, the effectiveness of the image processing system was established. If the proposed method is used to monitor and observe the crack growth behavior automatically, the time and efforts for fatigue test could be dramatically reduced.

• 대한기계학회논문집A
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• 제28권4호
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• pp.386-393
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• 2004

In this paper, the ultrasonic attenuation coefficient was measured by variation of crack length for double-cantilever beam(DCB) specimen. The energy release rate, G, was obtained by the experimental measurement of compliance. The experimental results represents that the crack length for the ultrasonic attenuation coefficient and energy release rate is increases proportionally From the experimental results, we proposed a detecting method of the crack length by the ultrasonic attenuation coefficient and discussed it.

• 한국세라믹학회지
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• 제33권1호
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• pp.83-91
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• 1996

Monolithic AlN and AlN-W composites were fabricated by pressure-less sintering at 190$0^{\circ}C$ under nitrogen atmosphere and the influences of tungsten phase on the microstructure and mechanical properties were investi-gated. In the fabrication of sintered specimen no additive was used. And monolithic AlN showed substantial grain growth and low relative density. AlN-W composites were fully densified and grain growths of matrix were inhibited. The densification behavior of composites were inferred to be achieved through the liquid phase sintering process such as particle-rearrangement and solutino-reprecipitation. Also the oxid phases which is expected to form liquid phases duringsintering process were detected by XRD analysis. As the tungsten volume content increases fracture strength was decreased and fracture toughness was increased. It was suppo-sed that the strength decrease of composites with tungsten content was due to existence of interface phases. The subcritical crack growth behavior was observed from the stress-strain curve of composites. The effect of the secondary phase and interface phases on toughness in crease were studied through observation of crack propagation path and the influence of residual stress on crack propagation was investigated by X-ray residual stress measurement. In the result of residual stress measurement the compressive stress of matrix in composi-test was increased with tungsten volume content and the compressive stress distribution of matrix must have contributed to the inhibition of crack propagation.

• 비파괴검사학회지
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• 제27권2호
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• pp.173-182
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• 2007

콘크리트 구조물에 발생한 균열은 내구성과 사용성 측면의 문제가 발생할 수 있기 때문에 정기적으로 관리하여야 한다. 대부분의 균열 측정은 균열 현미경과 균열 게이지와 같은 장비를 이용하여 균열의 폭, 길이, 방향 등과 같은 균열의 특징을 육안조사나 수작업에 의해 수행되고 있다. 그러나 기존의 방법들은 시간과 인력이 많이 필요할 뿐만 아니라 계측자의 주관이 개입될 여지가 많다. 따라서 이 연구에서는 이미지 프로세싱과 인공신경회로망을 이용하여 콘크리트 표면 균열 평가 기법을 제시하고자 한다. 개발된 기법은 세부분(균열 검출, 균열 분석, 균열 패턴인식)으로 나누어진다. 개발된 기법의 유효성을 검증하기 위하여 실험을 수행하였고, 실험 결과 개발된 기법은 콘크리트 표면 균열을 효과적으로 검출, 분석할 수 있었고, 5가지 균열 패턴을 정확히 인식하였다.

• 한국안전학회지
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• 제19권2호
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• pp.16-20
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• 2004

This paper aims to analyze fatigue fracture mechnisms with high strength aluminum alloys, which are widely used in vehicles or airplanes to prevent accidents. Usefulness of the crack opening point was proposed by using an effective stress intensity facor when evaluating the fatigue crack propagaion rate. Therefore an exact crack opening ratio can be measured for a more exact fatigue crack propagation rate. It is found that the fatigue crack propagation rate was valid within the range of experimentation as an effective stress intensity factor. Summarizing the results are as follows in this paper ; (1) It is found that the value of the crack opening ratio is constant at the rear of the specimen, U'=0.25 at the crack mouth and U'=0.45 at the crack tip, respectively regardless of the stress ratio. (2) The crack opening ratio is different according to measurement locations. The crack opening ratio value was measured at the crack mouth by a clip gage or measured behind the specimen by a strain gage. It is found that the crack opening ratio value is more accurate that any other measuring test for evaluating the crack propagation ratio test by effective stress intensity factor.

• Journal of Mechanical Science and Technology
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• 제17권11호
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• pp.1659-1664
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• 2003

A cracked plate with a patch bonded on one side was treated with a crack-bridging model using weight function: assuming continuous distribution of springs acting between th crack surfaces, the stress intensity factor of the patched crack was numerically obtained. Especially in the case of a patched crack subjected to residual non-uniform stress, the stress intensity factor was easily with the corresponding approximate weight function. This paper presented the stress intensity factors for a crack partially patched within a finite plate or a patched crack initiated from a notch.

• 한국정밀공학회지
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• 제24권2호
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• pp.103-109
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• 2007

In fatigue life prediction, it is important that fatigue life is affected by crack closure phenomenon in thin sheet Al alloy. In this research, we attempt to (1)analyze the characteristics of fatigue crack propagation in constant loading condition for thin sheet Al 2024-T3 alloy which is generally used in transportation structures, (2)identify the crack closure phenomenon in thin sheet comparing experimental results of thin and thick sheet specimen under same fatigue loading condition. In using the fatigue related material constants from these fatigue crack propagation analysis, we attempt to (3)operate the fatigue life estimating process with considering crack closure phenomenon and (4)analyze the experimental and prediction results of fatigue life in thin sheet Al alloy.

• 한국구조물진단유지관리공학회 논문집
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• 제6권4호
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• pp.181-188
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• 2002

The objective of this study is to determine crack depth located under steel reinforcement in concrete specimens using ultrasonic method. Experimental studies were performed on concrete specimens containing vertical and inclined surface-opening cracks with known depths. The other studies were carried out on specimens with flexural crack. Experimental results have shown that the crack depth is effectually measured when the distance between the probes is less than the crack depth. The effect of steel on crack depth estimation is studied through a model by considering P-waves diffaction at the tip of crack and steel. In addition, experimental results show that the ultrasonic method is one of useful methods to evaluate the crack depth in reinforced concrete.

• Smart Structures and Systems
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• 제32권4호
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• pp.219-233
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• 2023

Crack width is an important indicator to evaluate the health condition of the concrete structure. The crack width is measured by manual using crack width gauge commonly, which is time-consuming and laborious. In this paper, we have proposed a fast and simplified crack width quantification method via deep Q learning and geometric calculation. Firstly, the crack edge is extracted by using U-Net network and edge detection operator. Then, the intelligent decision of is made by the deep Q learning model. Further, the geometric calculation method based on endpoint and curvature extreme point detection is proposed. Finally, a case study is carried out to demonstrate the effectiveness of the proposed method, achieving high precision in the real crack width quantification.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1991년도 봄 학술발표회 논문집
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• pp.117-120
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• 1991

Cracks of concrete structure must be analyzed and estimated synthetically in order to have a maintenance and to insure the safety and the durability of structure. Concrete cracks have to be surveyed with respect to depth, width, shape and direction etc, but crack depth among these items is not measured easily. Occasionally, it needs to measure the crack depth of concrete structure for the purpose of evaulating the safe capacity and the necessity of repair. Therefore, this research is performed to verify the applicability and the accuracy of Ultra-sonic Pulse Velocity Technique(Tester), in non-destructive testing methods of concrete crack depth.