탄소섬유직물/에폭시 복합재의 혼합모우드 층간파괴 거동

윤성호(Sung-Ho Yoon),허광수(Kwang-Soo Heo),오진오(Jin-Oh Oh) 한국항공우주학회 2007 韓國航空宇宙學會誌 Vol.35 No.1

MMF 시험을 적용하여 혼합모우드 비율을 20%~90%의 범위 내에서 변화시키면서 탄소섬유직물/에폭시 복합재의 혼합모우드 층간파괴 거동을 조사하였다. 혼합모우드 층간파괴 거동을 예측하기 위해 NL점과 5% offset점에 근거한 혼합모우드 층간파괴 결정식을 제시하였다. 파단면 양상과 균열진전 거동은 이동식 현미경과 전자현미경을 통해 조사하였다. 연구결과에 따르면 혼합모우드 층간파괴 거동은 NL점에 근거한 경우 매개변수 m=1.5와 n=0.5, 5% offset점에 근거한 경우 매개변수 m=2와 n=3인 혼합모우드 충간파괴 결정식에 의해 잘 예측되어진다. 파단면 양상과 균열진전 거동은 혼합모우드 비율에 매우 민감하게 변하며 MMF 시험은 혼합모우드 층간파괴인성의 평가에 성공적으로 적용됨을 알 수 있었다. Mixed mode interlaminar fracture behaviors of carbon fabric/epoxy composites were investigated through MMF (Mixed Mode Flexural) test by varying mixed mode ratio ranging from 20% to 90%. Mixed mode interlaminar fracture criteria based on NL point and 5% offset point were also suggested in order to predict mixed mode interlaminar fracture behaviors. Fracture surfaces and crack propagating behaviors were examined through a travelling scope and a scanning electron microscope. According to the results, mixed mode interlaminar fracture behaviors can be predicted by mixed mode interiaminar fracture criterion with m=1.5 and n=0.5 on the basis of NL point or mixed mode interlaminar fracture criterion with m=2 and n=3 on the basis of 5% offset point. Fracture surfaces and crack propagating behaviors are sensitive to mixed mode ratios. MMF test can be successfully applicable in evaluating mixed mode interiaminar fracture toughness of carbon fabric/epoxy composites.

The study of fractural behavior of repaired composite

박상순,남욱,엄아향,김덕수,최기운,최경규 大韓齒科保存學會 2010 Restorative Dentistry & Endodontics Vol.35 No.6

Objectives: This study evaluated microtensile bond strength () and short-rod fracture toughness to explain fractural behavior of repaired composite restorations according to different surface treatments. Materials and Methods: Thirty composite blocks for test and sixty short-rod specimens for fracture toughness test were fabricated and were allocated to 3 groups according to the combination of surface treatment (none-treated, sand blasting, bur roughening). Each group was repaired immediately and 2 weeks later. Twenty-four hours later from repair, and fracture toughness test were conducted. Mean values analyzed with two-way ANOVA / Tukey's B test (= 0.05) and correlation analysis was done between and fracture toughness. FE-SEM was employed on fractured surface to examine the crack propagation. Results: The fresh composite resin showed higher than the aged composite resin (p < 0.001). Mechanically treated groups showed higher bond strength than non-mechanically treated groups except none-treated fresh group in (p < 0.05). The fracture toughness value of mechanically treated surface was higher than that of non-mechanically treated surface (p < 0.05). There was no correlation between fracture toughness and microtensile bond strength values. Specimens having high KIC showed toughening mechanism including crack deviation, microcracks and crack bridging in FE-SEM. Conclusions: Surface treatment by mechanical interlock is more important for effective composite repair, and the fracture toughness test could be used as an appropriate tool to examine the fractural behavior of the repaired composite with microtensile bond strength. 연구목적: 본 연구는 미세인장결합강도와 파괴인성을 통해 복합 레진 수복물의 수리 시기와 표면 처리 방법에 따른 파괴 거동을 알아보고자 시행되었다. 연구 재료 및 방법: Short rod 시편과 composite resin specimen block을 준비하여 표면 처리 방법에 따라 none-treated, sand blasting, bur roughening 군으로 나누고 이를 다시 즉시군과 2주 지연군으로 나누어 수리했다. 결과: 미세인장결합강도와 파괴인성을 측정한 결과, 두 실험 모두에서 즉시군이 지연군보다 높은 값을 보였다. 기계적 표면 처리군이 none-treated군보다 높은 값을 보였고, sand blasting과 bur roughening 사이에 유의한 차이는 없었다. 파괴인성과 미세인장결합강도는 상관 관계가 없었다. FE-SEM을 보아 수복물의 탈락은 균열 전도와 관계가 있는 것으로 보인다. 결론: 수리된 복합 레진의 파괴 거동 평가에는 파괴인성 실험이 적합하다.

NRC 증기압 암석 파쇄제에 의한 PMMA 블록의 동적 파괴 과정에 관한 실험 및 수치해석적 연구

민경조(Gyeongjo Min) 한국방재안전학회 2023 한국방재안전학회 논문집 Vol.16 No.1

본 연구의 목적은 테르밋 반응으로 결정화된 액체혼합물을 순간적으로 기화시켜, 이에 따라 발생되는 증기압을 이용하여 암석 및 콘크리트를 파쇄시키는 Nonex Rock Cracker(NRC) 암석 파쇄제의 동적 파괴 특성을 분석하고 파괴패턴을 예측할 수 있는 해석기법을 개발하기 위함이다. NRC 암석 파쇄제의 순간적의 증기압 발생 특성을 분석하기 위하여 인공취성재료로 알려진 Polymethyl methacrylate(PMMA) 블록을 대상으로 NRC를 장전하여 파쇄시험을 수행하였다. NRC의 증기압 발생순간을 촬영하기 위하여 초고속 카메라를 활용하였으며, 장약실과 연결된 관측공에 동적압력게이지를 부착하여 장약공 압력-시간이력을 계측하였다. 증기압 암석 파쇄제에 의한 PMMA 블록의 파괴패턴을 모사하기 위하여 2차원 동적 파괴 과정 해석 기법인 2D Dynamic Fracture Process Analysis(2DDFPA)가 활용되었으며, 계측된 장약공 압력-시간이력을 고려한 입사압력함수를 결정하였다. 제안된 해석조건을 활용하여 화강암재료와 고성능 폭약에 의하여 발생될 수 있는 파괴패턴에 대하여 고찰하였다. This study aims to investigate the dynamic fracture characteristics of rocks and rock-like materials subjected to the Nonex Rock Cracker (NRC), a vapor pressure crushing agent that produces vapor pressure by instantaneously vaporizing a liquid mixture crystallized through the thermite reaction. Furthermore, the study seeks to develop an analytical technique for predicting the fracture pattern. A dynamic fracture test was performed on a PMMA block, an artificial brittle material, using the NRC. High-speed cameras and dynamic pressure gauges were employed to capture the moment of vapor pressure generation and measure the vapor pressure-time history, respectively. The 2-dimensional Dynamic Fracture Process Analysis (2D DFPA) was used to simulate the fracture process caused by the vapor pressure, with the applied pressure determined based on the vapor pressure-time history. The proposed analytical method was used to examine various fracture patterns with respect to granite material and high-performance explosives.

반구형과 평탄형 선단 비상체의 충돌을 받는 콘크리트의 파괴특성

이상규,김규용,김홍섭,손민재,남정수 한국구조물진단유지관리공학회 2016 한국구조물진단유지관리공학회 논문집 Vol.20 No.6

본 연구에서는 반구형과 평탄형의 비상체를 이용하여 일반콘크리트와 섬유보강콘크리트에 충격시험을 진행한 후 파괴깊이와 형 태, 파괴직경, 배면의 인장변형을 평가하였다. 선단면적이 작을수록 충격력의 집중에 의해 파괴깊이는 크고 표면파괴 직경은 작게 되는 것으로 확인되었다. 반면에 선단면적이 클수록 파괴깊이는 작지만 표면파괴직경은 크게 되었다. 일반콘크리트와 섬유보강 콘크리트에서 유사한 표 면파괴와 배면변형이 발생하였으나 인장변형의 크기는 일반콘크리트에 비해 섬유보강 콘크리트가 작은 것으로 나타났다. 또한, 비상체의 선 단형상에 따른 표면관입의 형태와 배면의 인장변형 사이에 직접적인 연관이 있는 것으로 사료된다. 따라서 콘크리트의 배면박리한계두께 예 측 시에는 표면관입깊이뿐만 아니라 배면의 변형거동 또한 고려할 필요성이 있을 것으로 사료된다. In this study, projectiles with 2 kinds of nose shape: spherical and flat were impacted into normal concrete and fiber reinforced concrete panels. The fracture depth and form, crater diameter, tensile strain at rear face were evaluated. It was confirmed that smaller projectile nose areas resulted in deeper penetrations associated with concentrated impact forces and small front-face crater diameters in impact test. Conversely, larger projectile nose areas resulted in shallower penetrations and larger front-face fracture diameters. Similar front-face failure and strain distribution relationships based on the projectile nose shape were observed for normal and fiber-reinforced concrete although the rear-face tensile strain and scabbing were significantly reduced by the fiber reinforcement. In addition, a direct relationship was confirmed between the penetration depth based on the projectile nose shape and the tensile strain on the rear face. Thus the impact strain behavior is required to predict the scabbing behavior with penetration depth.

음향방출법을 이용한 CFRP 복합재의 모드 1 : 파괴거동에 관한 연구

이장규,우창기 한국기계기술학회 2013 한국기계기술학회지 Vol.15 No.2

In this study, carbon/epoxy composite DCB(double cantilever beam) specimens based on K-means clustering and wavelet transform analyses are presented. For the fracture Mode I, the fiber orientation θ = [0 ]24 and θ = [±45]12 both shown up stable crack growth in DCB testing. For the fiber orientation θ = [0 ]24 , the continuous type AE signal showed at central frequency 130~270kHz, which means that matrix micro cracking was occurred. The Burst type AE signal was occurred at central frequency 200~300kHz due to fiber bridging and fiber breaking. Other burst type AE signals were occurred at central frequency 130~180kHz with very high amplitude due to fiber bridging. For the fiber orientation θ = [±45]12 , the burst type signal showed at central frequency 220~300kHz, which means that fiber breaking was occurred. Mixed type of burst and continuous signals were captured at central frequency 250~480kHz due to fiber friction.

굽힘하중을 받는 감육배관의 파괴거동 및 유한요소해석

안석환(Seok-Hwan Ahn),남기우(Ki-Woo Nam) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11

Fracture behaviors of pipes with local wall thinning are very important for the integrity of nuclear power plant. In pipes of energy plants, sometimes, the local wall thinning may result from severe erosion-corrosion (E/C) damage. In this paper, the monotonic bending tests were performed of full-scale welded and unwelded carbon steel pipes with local wall thinning. A monotonic bending load was applied to straight pipe specimens by four-point loading at ambient temperature without internal pressure. The observed failure modes were divided into four types; ovalization, crack initiation/growth after ovalization, local buckling and crack initiation/growth after local buckling. Also, the strengths of welded and unwelded piping system with local wall thinning were evaluated. Also, the elasto-plastic analysis is performed by FE code ANSIS. We compared the simulated results by finite element analysis with experimental ones. The failure mode, fracture strength and fracture behavior obtained from tests showed well agrees with analytic results.

세라믹 돔포트 커버 상사모델의 파괴거동에 관한 연구

황권태(Kwontae Hwang),김재훈(Jaehoon Kim),이영신(Youngshin Lee),박종호(Jongho Park),송기혁(Keehyuck Song),윤수진(Soojin Yoon) 한국추진공학회 2009 한국추진공학회지 Vol.13 No.4

Fracture behavior of ceramic dome port cover on air breathing engine using liquid and solid fuel propulsion system was carried out in this study. Fracture characteristics was tested and estimated using scaled model of ceramic dome port cover by Shock tube . Fracture behavior was obtained by the fracture pressure from pressure sensor and observed the scattering phenomena of fracture specimen using high speed camera. Results obtained from this study can be used in the base data of dome port cover design for an air breathing engine.

KS D 3504에 따라 제작된 철근의 항복강도의 다양성을 고려한 RC보의 파괴거동 평가

우태련 ( Woo Tae-ryeon ),정치영 ( Jung Chi-young ),이종한 ( Lee Jong-han ),정진환 ( Cheung Jin-hwan ) 한국구조물진단유지관리공학회 2019 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.23 No.2

철근콘크리트 구조물의 설계 시 구조물의 연성거동을 보장할 수 있도록 한다. 연성거동에 영향을 미치는 주요 인자 중 하나는 철근이다. 철근콘크리트에 사용되는 철근은 KS D 3504에 따라 제작되어지는데, 설계 시 사용되는 철근의 항복강도는 KS D 3504에서 제시하는 기준 항복강도이다. 항복강도가 달라짐에 따라 구조물의 파괴거동 또한 달라질 수 있다. 본 연구에서는 기준 항복강도와 KS D 3504에서 허용하고 있는 허용 최대항복강도를 적용하였을 때의 구조물의 파괴거동 차이를 비교 및 분석하였다.

감육배관의 유한요소해석에 의한 변형 및 강도 평가

안석환(SEOK-HWAN AHN),이수식(SOO-SIG LEE),김진욱(JIN-WOOK KIM),윤자문(JA-MUN YOON),남기우(KI-WOO NAM) 한국해양공학회 2005 韓國海洋工學會誌 Vol.19 No.5

Fracture behavior and pipe strength are very important to the integrity of energy plants, ocean structures, and so forth. The pipes of energy plants and ocean structures are subject to local wall thinning, resulting from severe erosion-corrosion damage. Recently, the effects of local wall thinning on fracture strength and fracture behavior of piping systems have been the focus of many studies. In this paper, the elasto-plastic analysis is performed by FE code ANSYS on straight pipes with wall thinning. We evaluated the failure mode, fracture strength and fracture behavior, using FE analysis. Also, the effect of the axial strain on deformations and failure modes was estimated by FE analysis.

원전 배관재료의 파괴거동에 미치는 지진하중의 영향

김진원(Jin Weon Kim),최명락(Myung Rak Choi),김윤재(Yun Jae Kim) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11

This study performs J-R fracture toughness tests under monotonic loading with various displacement-rates and cyclic loading conditions at room temperature (RT) and 316℃ to investigate the effect of seismic loading on the fracture behavior of nuclear piping materials. SA508 Gr.1a low alloy steel and SA312 TP316 stainless steel piping materials were used for the tests. The fracture toughness of SA312 TP316 stainless steel was independent of displacement-rate for both test temperatures. The fracture toughness of SA508 Gr.1a low alloy steel under dynamic displacement-rate corresponding to seismic loading rate was nearly the same as that under quasi-static displacement-rate, although it was affected by displacement-rate at 316℃. Under cyclic loading condition, the fracture toughness were considerably decreased regardless of types of pipe material and test temperatures.