• Nuclear Engineering and Technology
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• 제54권4호
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• pp.1167-1174
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• 2022

Cast austenitic stainless steels (CASSs) are widely used as structural materials in the nuclear industry. The main drawback of CASSs is the reduction in fracture toughness due to long-term exposure to operating environment. Even though ultrasonic non-destructive testing has been conducted in major nuclear components and pipes, the detection of cracks is difficult due to the scattering and attenuation of ultrasonic waves by the coarse grains and the inhomogeneity of CASS materials. In this study, the ultrasonic signals measured in thermally aged CASS were discriminated for the first time with the simple ultrasonic technique (UT) and machine learning (ML) models. Several different ML models, specifically the K-nearest neighbors (KNN), Support Vector Machine (SVM), and Multi-Layer Perceptron (MLP) models, were used to classify the ultrasonic signals as thermal aging condition of CASS specimens. We identified that the ML models can predict the category of ultrasonic signals effectively according to the aging condition.

• Smart Structures and Systems
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• 제21권6호
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• pp.751-759
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• 2018

Glass fibre reinforced polymers (GFRP) are widely exploited in many industrial branches. Due to this Structural Health Monitoring systems containing embedded fibre optics sensors are applied. One of the problems that can influence on composite element durability is water contamination that can be introduced into material structure during manufacturing. Such inclusion can be a damage origin significantly decreasing mechanical properties of an element. A non-destructive method that can be applied for inspection of an internal structure of elements is THz spectroscopy. It can be used for identifications of material discontinuities that results in changes of absorption, refractive index or scattering of propagating THz waves. The limitations of THz propagation through water makes this technique a promising solution for detection of a water inclusion. The paper presents an application of THz spectroscopy for detection and localisation of a water drop inclusion embedded in a GFRP material between two fibre optics with fibre Bragg grating sensors. The proposed filtering method allowed to determine a 3D shape of the water drop.

• Smart Structures and Systems
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• 제19권2호
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• pp.195-202
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• 2017

The aim of this paper is to develop a novel method to determine the severity of a damage in a thin plate. This paper presents a novel fault detection and diagnosis approach employing a new electromagnetic acoustic transducer, called EMAT, together with a complex signal processing method. The method consists in the recognition of a fault that exists within the structure, the fault location, i.e. the identification of the geometric position of damage, and the determining the significance of the damage, which indicates the importance or severity of the defect. The main scientific novelties presented in this paper is: to develop of a new type of electromagnetic acoustic transducer; to incorporate wavelet transforms for signal representation enhancements; to investigate multi-parametric analysis for noise identification and defect classification; to study attenuation curves properties for defect localization improvement; flaw sizing and location algorithm development.

• 한국추진공학회지
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• 제11권1호
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• pp.34-42
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• 2007

초음파를 이용한 추진기관의 비파괴검사는 X-ray 검사에 비하여 경제성이 우수하고, X-ray 검사 시 취약한 미접착, 손상 등의 결함 검출이 우수한 편이다. 그리고 전용 시설 없이 현장에서 실시간으로 검사가 가능하며 방사선 작업에 비하여 안전한 방법이다. 본 논문에서는 고체 추진제에 대한 초음파 특성을 분석하고, 추진제/라이너 미접착에 대한 내측과 외측 검사 방법 및 추진제 손상에 의한 미세 크랙 검출에 대하여 실험 및 분석하였다. 실험 결과, 추진제/라이너 미접착에 대한 내.외측 검사에 있어서 검출 가능성을 보였으며, 그리고 손상에 의한 추진제 미세 크랙도 초음파의 감쇠특성을 이용하여 검출 가능함을 보였다.

• 대한기계학회논문집
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• 제17권8호
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• pp.2061-2068
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• 1993

Condition monitoring technology is of great importance for the maintenance of complex machinery in view of its early monitoring of the abnormal condition and the protection against failure. Several methods have been used for the detection of failure of journal bearings, one of the main elements of mechanical system. The methods most frequently used are vibration and temperature monitoring, but these are unable to monitor the wear conditions exactly. In this study, an ultrasonic measument method, one of the non-destructive testing methods, was introduced as the monitoring technology. Furtermore a pattem recognition method was applied to analyze the ultrasonic signal. The monitoring system using the pattern recognition method is composed of digital signal processing units and uses Hamming net algorithm for the recognition of ultrasonic waves. From the journal bearing wear test, the occurrence of adhesive wear of the white metal in rubbing contact with the shaft was exactly detected by this system, and the wear status of the journal bearing was monitored by measuring the wear thickness.

• 한국정밀공학회지
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• 제23권6호
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• pp.119-127
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• 2006

A non-destructive time domain approach to examine structural damage using parameterized partial differential equations and Galerkin approximation techniques is presented. The time domain analysis for damage detection is independent of modal parameters and analytical models unlike frequency domain methods which generally rely on analytical models. The time history of the vibration response of the structure was used to identify the presence of damage. Damage in a structure causes changes in the physical coefficients of mass density, elastic modulus and damping coefficients. This is a part of our ongoing effort on the general problem of modeling and parameter estimation for internal damping mechanisms in a composite beam. Namely, in detecting damage through time-domain or frequency-domain data from smart sensors, the common damages are changed in modal properties such as natural frequencies, mode shapes, and mode shape curvature. This paper examines the use of beam-like structures with piezoceramic sensors and actuators to perform identification of those physical parameters, and detect the damage. Experimental results are presented from tests on cantilevered composite beams damaged at different locations and different dimensions. It is demonstrated that the method can sense the presence of damage and obtain the position of a damage.

• 한국정밀공학회지
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• 제27권11호
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• pp.30-36
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• 2010

Previous researches show that linearly integrated Hall sensor arrays (LIHaS) can detect cracks in the steel structure fast and effectively This paper proposes an algorithm that estimates the size and shape of cracks for the developed LIHaS. In most nondestructive testing (NDT), just crack existence and location are obtained by processing 1-dimensional data from the sensor that scans the object with relative speed in single direction. The proposed method is composed with two steps. The first step is constructing 2-dimensionally mapped data space by combining the converted position data from the time-based scan data with the position information of sensor arrays those are placed in the vertical direction to the scan direction. The second step is applying designed Laplacian filter and smoothing filter to estimate the size and shape of cracks. The experimental results of express train wheels show that the proposed algorithm is not only more reliable and accurate to detecting cracks but also effective to estimate the size and shape of cracks.

• 비파괴검사학회지
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• 제31권4호
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• pp.398-413
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• 2011

철도 레일의 주기적인 탐상은 레일 결함으로 인해 발생할 수 있는 철도 중대사고를 미연에 방지할 수 있는, 철도 안전 유지의 중요한 요소 중 하나이다. 본 논문은 현재 철도 레일 탐상에 적용되고 있거나, 적용을 위해 연구 중인 비파괴탐상 기법들에 관해 기술하였다. 레일에 발생하는 결함 유형에 대해 우선 언급하였고, 레일 탐상에 가장 많이 적용되고 있는 압전형 탐촉자 기반의 초음파탐상 기술에 대해 정리하였다. 접촉식 초음파 레일 탐상 기술에 대한 대안으로서 연구 중이거나 시험 중인 비파괴탐상 기법들에 대해 기술하고, 각 기법 별로 레일의 표면 및 내부 결함 검출 가능 여부에 대해 살펴보았으며 여러 탐상 기법들에 대한 비교를 통해 향후 레일 탐상 기술 개발에 활용하고자 하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제26회 춘계학술대회논문집
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• pp.11-16
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• 2006

본 연구는 이종 접착 재질의 접착계면에서 미접착 결함을 검출하기 위한 새로운 시험 기법을 개발하기 위함이다. 접착계면과 미접착계면에서의 초음파 전달 현상을 이론적으로 해석하여 초음파 신호를 모델링하였고, 이론적 분석에 기초하여 미접착계면에서의 위상 반전 현상을 애용한 검사 방법을 FRP/고무 시편에 적용하였다. 정량적으로 결함의 최소 검출 능력을 평가하기 위하여 알루미늄/고무 시편에 평저공을 가공하여 제작하였고 일반적으로 사용하고 있는 펄스에코반사법과 새로운 시험 기법인 위상반전법을 상호 비교하였으며 이론적으로 예측한 초음파 신호와 실험에서 얻은 초음파 신호를 근거로 위상반전법으로 미접착 결함을 검출할 수 있다고 판단하였다.

• 한국공간구조학회:학술대회논문집
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• 한국공간구조학회 2008년도 춘계 학술발표회 논문집
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• pp.179-183
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• 2008

콘크리트에서의 손상 검증법은 비파괴 시험법을 주로 이용한다. 이러한 비파괴시험법은 다양한 센서를 이용하지만, 대부분의 손상을 검사하는 방법은 육안으로 확인한다. 비파괴 시험법에서 가속도계를 이용하여 철근 콘크리트 부재 내부의 불규칙한 균열 손상을 측정하기에는 철근의 방향성과 경계조건으로 어려움이 많다. 본 연구에서는 3축 가속도센서를 이용하고 탄성파를 가진하여, 콘크리트 부재 내부에 철근의 배치방향에 따른 영향 검토와 강도가 저하된 부재의 손상을 검토하기 위한 기초적 연구이다.