고장력 강판의 초음파 피로시험

염현호(Hyunho Yeom),정용찬(Yongchan Jung),김차영(Chayeong Kim),강기영(Ki-Young Kangb),이문구(Moon Gu Lee),홍민성(Min-Sung Hong),전용호(Yongho Jeon) 한국생산제조학회 2015 한국생산제조학회지 Vol.24 No.6

The demand of high cycle fatigue behavior on plate material is increasing because of its various applications. However, the high-cycle fatigue life data of the plate material is very rare compared to the rod material. Thus, in this study, a plate specimen is designed for the ultrasonic fatigue test because it is time efficient as compared to the conventional fatigue test. To apply the ultrasonic fatigue test, the specimen design is required to resonate at 20 kHz. Therefore, the dynamic elastic modulus was determined by measuring the resonance frequency with a piezoelectric element and laser doppler vibrometer (LDV). As a result, the plate specimen is designed and demonstrated using the ultrasonic fatigue testing machine. The ultrasonic fatigue test results were compared with the hydraulic fatigue test results.

초음파 피로시험법을 이용한 A356-T6 합금의 초고주파 피로특성 평가

김정호 ( Jeong Ho Kim ),김정식 ( Jung Sik Kim ),이종주 ( Jong Ju Lee ),윤형석 ( Hyung Seok Yoon ),진영준 ( Young Jun Jin ),어순철 ( Soon Chul Ur ) 대한설비관리학회 2013 대한설비관리학회지 Vol.18 No.3

The behavior of very high cycle fatigue in automotive alloy wheels have become a critical issue for safety, due to their prolonged service life. For the test, a specially designed, dedicated ultrasonic fatigue test (UFT)system was utilized to investigate the high cycle fatigue behavior of A356-T6 aluminium alloys. The hourglass-shaped specimens were specifically designed according to the alloy``s dynamic elastic modulus and fatigue-tested up to 109 cycles at room temperature under completely reversed loading conditions of R=-1. SN curve was plotted, showing monotonic decrease in the test range. Cracked area and fracture surface after tests were investigated using a scanning electron microscope(SEM). It was shown that cracks were initiated from a surface flaw and then propagated into the internal area. Fracture surfaces consist of mostly dimples, typically as in other ductile fracture mode. This test method can be an alternative test methods, since it shows several merits over conventional fatigue testing methods such as fast test speed and effectiveness.

열피로 균열에 대한 위상배열 초음파 탐상 검사 정확도 및 유용성 평가

안형근,황웅기,김재성,박익근 한국비파괴검사학회 2019 한국비파괴검사학회지 Vol.39 No.4

Thermal fatigue cracking is one of the flaws that can occur in nuclear power plant components and cause problems in maintaining the integrity of nuclear power plants. Therefore, to prevent such problems, nondestructive testing of nuclear power plant components is being performed. Radiographic testing and ultrasonic testing are the primary applied as the inspection methods for components. However, radiographic testing is decreasing in proportion because of radiation exposure and nuclear safety regulations. Alternatively, the proportion of ultrasonic testing is increasing. In particular, phased array ultrasonic testing is applied, replacing a wide range of tests, such as radiographic testing. In this study, the accuracy and usefulness of phased array ultrasonic depth sizing of weldment cracks and artificial flaws are investigated through the evaluation of the average error and RMS error values. 열피로 균열은 원자력 발전소 주요기기에서 발생될 수 있는 결함 중 하나로, 균열 발생 시 원전의 건전성 유지에 문제를 야기할 수 있다. 이에 따라, 이러한 문제가 발생되지 않도록 원전에서는 주요기기에 대해 비파괴 검사를 수행하고 있다. 주로 적용되는 검사 방법으로는 방사선투과 검사와 초음파탐상 검사가 있으나, 최근 방사선투과 검사는 방사선 피폭에 의한 사건·사고와 원자력 안전 규제에 따라 활용 비중이 줄어들고 있으며, 대안으로 초음파 검사의 비중이 높아지고 있다. 특히, 방사선투과 검사와 같이 넓은 범위의 검사가 가능한 위상배열 초음파 탐상 검사가 대두되고 있다. 본 논문에서는 STS 304 배관에 인공결함을 제작한 시험편과 동종 용접한 배관에 열피로 균열을 제작하여, 위상배열 초음파 탐상 깊이 측정 결과의 Average error와 RMS error를 평가하여 정확도와 유용성을 검토하고자 한다.

초음파 피로시험편 결정법의 연구동향

명노준(No-Jun Myeong),한승욱(Seung-Wook Han),박정훈(Jung-Hoon Park),최낙삼(Nak-Sam Choi) 대한기계학회 2013 大韓機械學會論文集A Vol.37 No.8

본 논문에서는 초고주기피로영역(VHCF)에 대한 가속시험 방법인 초음파 피로시험을 소개하고 이와 관련된 이론을 검토하였다. 초음파피로시험은 20 kHz 영역에서 시험편의 공진을 이용하므로 동탄성계수와 파장을 고려하여 시험편의 길이와 형상을 설계하여야 한다. 공진시험을 통하여 20 kHz 에 맞는 파장을 구하고 시험편의 길이와 동탄성계수를 계산한다. 이렇게 계산된 시험편의 형상과 시험시 형성되는 변위값을 측정하여 응력을 구한다. 초음파 피로시험결과는 기존의 피로시험법에 따른 결과와 비교되어 주파수 및 시험편 형상의 효과가 검증되어야 한다. An accelerated ultrasonic fatigue test(UFT) has been used for analyzing very high cycle fatigue(VHCF, Nf >10?). This study reviews how the test specimen is to be determined. We focus on UFT using a resonance of 20 kHz. The specimen geometry is determined by selecting test materials by using a dynamic Young’s modulus and wavelength of 20 kHz. The dynamic Young’s modulus is calculated at the resonant frequency. Through a resonant vibration test at 20 kHz, the length of the specimen is calculated. By determining the shape of the specimen, the stress during the UFT is calculated. The UFT results should be comparable at the test frequency and the specimen geometry obtained by the conventional fatigue tests.

기계부품소재분야에서 적용된 초음파피로시험법의 새로운 장치시스템과 연구분야

서대석(DaeSeok Seo),이중권(JungGwon Lee),이창순(ChangSoon Lee),박인규(InGyu Park),조인식(InSik Cho) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12

The Ultrasonic fatigue tests(UFTs) are typically the accelerated fatigue testing of 20 ㎑, which have resulted in the substantial reduction of the application period of newly developed processes and materials for various machine parts and materials sectors. In this study, the UFT results have been evaluated for the conventional ferrous and non-ferrous materials including the polymer composits. Particularly, the welded plate specimens for the automobiles have been analyzed in detail. Furthermore, the data for the environmental research fields have also been reviewed and evaluated, such as corrosion and fretting fatigue. Finally, the future research orientation in UFTs has been suggested with the recent research developments in the advanced countries.

동적 유한요소해석을 이용한 모래시계형 초음파 피로시험편의 응력계산식 보정

명노준(NohJun Myung),최낙삼(Nak-Sam Choi) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11

The stress analysis of an hourglass specimen was performed for the ultrasonic fatigue test (UFT) at resonance frequency around 20 ㎑. Local stresses at the gauge portion of the specimen were calculated using the coventional stress equation with the assumption of an hourglass-shaped gauge portion that had the form of a hyperbolic cosine. For the actual specimen that had a circular arc shape used in the test. Stress distribution through a finite element analysis (FEA) is calculated in comparison to real test results. FEA focuses on the behaviors of local stress concentration occurring in the gauge portion during UFT. The stress concentration effect in the specimen was clarified to compensate for the actual fatigue strength.

Ti-6Al-4V 합금의 초고주기 피로특성 평가

조인식(Insik Cho),전용호(Yongho Jeon),신충식(Choongshig Shin),곽동호(Dongho Kwak),이지용(Jiyong Lee) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10

Due to the extensive long service life for aero-space components, the behavior of very high cycle fatigue(VHCF) is gained attention. For this reason, the newly developed piezoelectric ultrasonic fatigue test (UFT) system by Mbrosiatec Co. Ltd is used to investigate the high cycle fatigue (HCF) strength of Ti-6Al-4V alloy. The hourglass-shaped specimens are investigated in the range of 10<SUP>6</SUP> to 10<SUP>9</SUP> cycles at room temperature under completely reversed loading conditions R=-1. Scanning electron microscopy(SEM) analysis revealed that failures occur right up to the gigacycle regime, with the fractures being found to initiate from the surface unlike in steels. In addition, SEM micrographs showed that micro-cracks were transformed into intergranular fracture. Additionally, this test method can be applicable on commercialized parts of automotive and rail road which are required high cycle fatigue. In addition, SEM micrographs showed that micro-cracks were transformed into intergranular fracture.

초음파피로시험법을 이용한 엔지니어링 플라스틱(POM)의 내구성평가

황정호(JungHo Hwang),오주연(JooYeon Oh),김현창(HyunChang Kim),오세훈(SaeHoon Oh),조인식(InSik Cho),이창순(ChangSoon Lee),박인규(InGyu Park) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12

Due to the extensive long service life for automotive components, the behavior of very high cycle fatigue(VHCF) is gained attention. For this reason, the newly developed piezoelectric ultrasonic fatigue test (UFT) system by Mbrosiatec Co. Ltd<SUP>1</SUP> is used to investigate the high cycle fatigue (HCF) strength of Engineering Plastic(EP). The plate-shaped specimens are investigated in the range of 10<SUP>6</SUP> to 10<SUP>9</SUP> cycles at room temperature under completely reversed loading conditions R=-1. Scanning electron microscopy(SEM) analysis revealed that failures occur right up to the high cycle regime, with the fractures being found to initiate from the surface unlike in EP. In addition, SEM micrographs showed that micro-dimples were transformed. Additionally, this test method can be applicable on commercialized parts of automotive and rail road which are required high cycle fatigue. In addition, SEM micrographs showed that micro-dimples were transformed into EP fracture.

VHCF Characteristics of UNSM treated A7075-T651 Aluminum Alloy under Rotary Bending and Ultrasonic Fatigue Testing M/C

Chang-Min Suh(서창민),Seung-Hoon Nahm(남승훈),Min-Soo Suh(서민수),Young-sik Pyun(편영식) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.4

The fatigue characteristics of A7075-T651 aluminum alloy were studied and compared with surface treatments of UNSM (Ultrasonic Nano-Crystal Surface Modification) technology. Fatigue characteristics of those are unearthed by using various fatigue testing machines of followings; the ultrasonic fatigue testing machine (UFT, 20KHz), and the rotary bending fatigue testing machines (RFT, 53Hz) with a single-spindle (simple beam type) and a multi-spindles (Cantilever type). The fatigue strength of a Cantilever type rotary bending fatigue testing machines and a simple beam Ohno type rotary bending fatigue testing machine showed the same fatigue properties. The improvement of fatigue life was confirmed for rotary bending fatigue testing machines with the specimens treated under UNSM-30N. However, the effect of surface modification as fatigue life improvement of UNSM-50N and - 60N has decreased rather than UNSM-30N. The fatigue strength of ultrasonic fatigue test (UFT, 20KHz) is lower than that of rotary bending fatigue testing (RFT, 53Hz).

VHCF Characteristics of A7075-T651 Alloy Depending on Fatigue Testing Methods and Shot Peening Conditions

Chang-Min Suh,Jong-Hyoung Kim,Min-Soo Suh 한국자동차공학회 2014 한국자동차공학회 지부 학술대회 논문집 Vol.2014 No.4

In this paper, the fatigue characteristics of A7075-T651 aluminum specimens were obtained and compared with those of the treated specimens with shot peening (SP) conditions by using ultrasonic fatigue testing machine (20KHz), a multi-spindle (Cantilever type) and single spindle (simple beam type) rotary bending fatigue testing machines (RFT, 53Hz). The improvement of fatigue lives of the treated specimens with SP were appeared at both of rotary bending fatigue testing machines, but the effects of surface modification was not appeared at ultrasonic fatigue testing machine. The fatigue lives of a Cantilever type rotary bending fatigue testing machines and a single spindle rotary bending fatigue testing machine showed the same fatigue properties. The fatigue strength of ultrasonic fatigue test(UFT, 20KHz) is lower than that of rotary bending fatigue testing (RFT, 53Hz). The mechanical characteristics including hardness and fatigue strength of RFT specimen improved by the effects of shot peening surface modification of structure.