• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2002년도 춘계학술발표대회 논문집
• /
• pp.109-113
• /
• 2002

Interfacial and electrical properties for the carbon fiber reinforced epoxy-amine terminated (AT) PEI composites were performed using microdroplet test and electrical resistance measurements. As AT PEI content increased, the fracture toughness of epoxy-AT PEI matrix increased, and IFSS was improved due to the improved toughness and energy absorption mechanisms of AT PEI. The microdroplet in the carbon fiber/neat epoxy composite showed brittle microfailure mode. At 15 wt% AT PEI content, ductile microfailure mode appeared because of improved fracture toughness. After curing, the changes of electrical resistance (ΔR) with increasing AT PEI content increased gradually because of thermal shrinkage. The matrix fracture toughness was correlated to IFSS, TEC and electrical resistance. In cyclic strain test, the maximum stress and their slope of the neat epoxy case were higher than those of 15 wt% AT PEI. The results obtained from electrical resistance measurements under curing process and reversible stress and strain were consistent well with matrix toughness properties.

• 한국해양공학회지
• /
• 제29권6호
• /
• pp.445-453
• /
• 2015

The stress triaxiality and lode angle are known to be most dominant fracture parameters in ductile materials. This paper proposes a three-dimensional failure strain surface for a ductile steel, called a low-temperature high-tensile steel (EH36), using average stress triaxiality and average normalized lode parameter, along with briefly introducing their theoretical background. It is an extension of previous works by Choung et al. (2011; 2012; 2014a; 2014b) and Choung and Nam (2013), in which a two-dimensional failure strain locus was presented. A series of tests for specially designed specimens that were expected to fail in the shear mode, shear-tension mode, and compression mode was conducted to develop a three-dimensional fracture surface covering wide ranges for the two parameters. This paper discusses the test procedures for three different tests in detail. The tensile force versus stroke data are presented as the results of these tests and will be used for the verification of numerical simulations and fracture identifications in Part II.

• 대한기계학회논문집A
• /
• 제26권2호
• /
• pp.300-307
• /
• 2002

Partial penetration welding joint is defined as groove welds welded from one side, without steel backing or groove welds welded from both sides but without back gouging. So it has an unwelded portion at the root of the weld. Study of partial penetration weldment fracture behavior includes residual stress analysis and fracture analysis. The J-integral loses its path independency in residual stress field. Therefore, it is necessary to introduce a new J-integral, J, which is defined including the effect of plastic deformation and thermal strain. In this study, theoretical formulation and program were developed for the evaluation of J-integral for the crack tip located in the weldment. Evaluations of fracture behavior were performed for partial penetration multi-pass weldment of 25.4mm thick plate by J-integral. From a point of fracture in partial penetration multi-pass welding, it seemed to be better to control root face smaller than 6.35mm.

• 한국정밀공학회지
• /
• 제17권12호
• /
• pp.76-81
• /
• 2000

Analysis on failure of the panel glass under mechanical shock is the main topic of this study. Since the glass for the LCD panel is thin, it needs to be designed to have enough toughness against mechanical shock. In this paper, a process of estimating fracture of the panel glass is proposed to guarantee reliability of the product. The fracture toughness of the panel glass is used as a criterion of the fracture based on an experimental approach. The stress intensity factor was calculated considering a model with the largest initial crack size on a cut surface and with the boundary force obtained from a dynamic finite element analysis. Critical surface roughness on the cut surface of a typical glass panel, to prevent fracture in case of bending mode, is obtained.

• 터널과지하공간
• /
• 제31권6호
• /
• pp.593-609
• /
• 2021

본 연구에서는 입자기반 개별요소모델(grain-based distinct element model, GBDEM)을 이용하여 결정질 암석 내 포함된 균열의 열-역학적 거동을 평가할 수 있는 수치해석기법을 제시하고 열에 의한 균열의 미끄러짐 거동을 해석하였다. 이는 DECOVALEX-2023 프로젝트 Task G의 일환으로 수행된 벤치마크 모델링 연구로, Task G는 결정질 암반 내 균열의 열-수리-역학적 복합거동을 해석하기 위한 수치해석기법을 개발하는 데에 목표가 있다. 여기에서는 Voronoi diagram을 이용하여 다면체 개별입자의 집합체로서 해석모델을 생성하고, 입자 및 입자간 접촉에서 발생하는 열-역학적 거동을 개별요소프로그램인 3DEC을 통해 해석하였다. 암석 시험편의 탄성거동을 재현하기 위하여 등가연속체 개념을 적용하여 입자와 접촉의 미시물성을 산정하였으며, 균열에 상응하는 접촉에는 Coulomb slip model을 부여하여 인장강도와 전단강도를 갖는 불연속면을 모사하였다. 경계응력과 열응력에 의한 균열의 거동을 수치적으로 모델링하였으며, 경계조건에 따라 균열의 미끄러짐이 발생하는 열-역학적 메커니즘을 정량적으로 분석하였다. 해석 결과, 본 연구에서 제시한 해석모델이 암석 내 열팽창과 열응력의 증가, 균열 응력과 변위, 경계조건의 영향 등을 합리적으로 재현하고 있음을 확인하였다. 본 연구의 해석모델은 Task G에 참여하는 국외 연구팀들과의 의견 교류와 워크숍을 통해 지속적으로 개선하는 한편, 향후 실내실험에 적용하여 타당성을 검증할 예정이다.

• 한국소음진동공학회논문집
• /
• 제23권9호
• /
• pp.850-856
• /
• 2013

Torsional interaction between electrical network phenomena and turbine-generator shaft cause torsional stress on turbine-generator shaft and torsional fatigue fracture on vulnerable component, but the prediction of the torsional stress is difficult because the torsional stress is occurred instantly and randomly. Therefore continuous monitoring of the torsional stress on turbine-generator shaft is necessary to predict the torsional fatigue, but installing the sensors on the surface of the shaft directly to monitor the stress is impossible practically. In this study torsional vibration was measured using magnetic sensor at a point of turbine-generator rotor kit, the torsional stress of whole train of rotor kit was calculated using rotor kit's stress model and the calculated results were verified in comparison with the measured results using strain gauge at several point of turbine-generator rotor kit. It is expected that these experiment results will be used effectively to calculate the torsional stress of whole train of turbine-generator rotor in power plants.

• 대한족부족관절학회지
• /
• 제15권1호
• /
• pp.22-26
• /
• 2011

Purpose: To report the effectiveness of adding distal fibular external rotation stress test on the traditional lateral stress Cotton test in evaluating distal tibiofibular syndesmotic injuries. Materials and Methods: We evaluated syndesmotic injuries with intraoperative stress test during treating ankle fractures from March 2009 to September 2010. External rotation of distal fibula using small elevator was added on traditional stress test in case of suspicious syndesmotic injury. We retrospectively reviewed and compared the results of each test in 44 cases for which we tried both tests. Results: In 9 cases of positive traditional lateral stress tests, positive results were obtained in all cases by additional external rotation tests. In 21 cases of negative traditional stress tests, additional stress tests results were also negative. But there were 10 cases of positive additional tests and 4 of negative additional tests in equivocal results cases by the traditional stress tests. Conclusion: Using additional external rotation stress test in case of equivocal test result by the traditional lateral stress Cotton test for evaluation of syndesmotic injury during operation for ankle fracture can be a supplemental method to clarify syndesmotic injury needs fixation.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2013년도 추계학술대회 논문집
• /
• pp.862-867
• /
• 2013

Torsional interaction between electrical network phenomena and turbine-generator shaft cause torsional stress on turbine-generator shaft and torsional fatigue fracture on vulnerable component, but the prediction of the torsional stress is difficult because the torsional stress is occurred instantly and randomly. Therefore continuous monitoring of the torsional stress on turbine-generator shaft is necessary to predict the torsional fatigue, but installing the sensors on the surface of the shaft directly to monitor the stress is impossible practically. In this study torsional vibration was measured using magnetic sensor at a point of turbine-generator rotor kit, the torsional stress of whole train of rotor kit was calculated using rotor kit's stress model and the calculated results were verified in comparison with the measured results using strain gauge at several point of turbine-generator rotor kit. It is expected that these experiment results will be used effectively to calculate the torsional stress of whole train of turbine-generator rotor in power plants.

• 한국안전학회지
• /
• 제21권4호
• /
• pp.19-24
• /
• 2006

Fatigue crack propagation tests for the brake disc cast iron were conducted for investigating fatigue crack propagation rate(da/dN), crack propagation path and fracture toughness($K_c$) of the material. The threshold stress intensity factor range, ${\Delta}K_{th}$, was found to be about $6MPa{\sqrt{m}}$ at the stress ratio of R = 0.1. Also, fracture toughness value was determined to be $24.7MPa{\sqrt{m}}$. Irregular fatigue fracture surfaces were observed, indicating that fatigue crack growth occurred at the interface between randomly scattered flak graphite and ferrite, where the interfacial strength was relatively weak.

• Journal of Mechanical Science and Technology
• /
• 제18권12호
• /
• pp.2158-2173
• /
• 2004

In this paper, the higher order terms in the crack tip stress fields are investigated macroscopically for more realistic assessment of structural material behaviors. For reactor pressure vessel material of A533B ferritic steel, effects of crack size and temperature have been evaluated using 3-point SENB specimens through a series of finite element analyses, tensile tests and fracture toughness tests. The T-stress, Q-parameter and q-parameter as well as the K and J-integral are calculated and mutual relationships are investigated also. Based on the evaluation, it has proven that the effect of crack size from standard length (a/W=0.53) to shallow length (a/W=0.11) is remarkable whilst the effect of temperature from -20$^{\circ}C$ to -60$^{\circ}C$ is negligible. Finally, the cleavage fracture toughness loci as a function of the promising Q-parameter or q-parameter are developed using specific test results as well as finite element analysis results, which can be applicable for structural integrity evaluation considering constraint effects.