• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.579-584
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• 2001

As the huge energy transfer systems like as nuclear power plant and steam power plant are operated for a long time, mechanical properties are changed and ductile-brittle transition temperature is raised by degradation. So it is required to estimate degradation in order to assess the safety, remaining life, and further operation parameters. The sub-sized specimen test method using surveillance specimen was developed for evaluating the integrity of metallic components. In this study, we would like to present the evaluation technique of the ductile-brittle transition temperature by the sub-sired specimen test. The four classes of the thermally aged 1Cr-1Mo-0.25V specimens were prepared using an artificially accelerated aging method. The tensile test and fracture toughness test were performed. The results of the fracture toughness tests using the sub-sized specimens were compared with the evaluation technique of the ductile-brittle transition temperature.

• 대한치과보철학회지
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• 제43권4호
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• pp.415-425
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• 2005

Statement of problem : Fracture of composite resin core will be occulted by progress of crack. Bonding interface of different materials has large possibility of starting point of crack line. Therefore, the bond strength of glass fiber post to composite resin core is important for prevention of fracture. Purpose: This in vitro study tried to find out how to get the higher strength of glass fiber post to composite resin core through surveying the maximum load that fractures the post and cote complex. Materials and methods: 40 specimens made with glass fiber Posts(Style $post^{(R)}$, Metalor, Swiss) and composite resin core ($Z-100^{(R)}$, 3M, USA) were prepared and loaded to failure with push-out type shear-bond strength test in a universal test machine. The maximum fracture load and fracture mode were investigated in the specimens that were restored with four different surface treatments. With the data. ANOVA test was used to validate the significance between the test groups, and Bonferroni method was used to check if there is any significant statistical difference between each test group. Evely analysis was approved with 95% reliance. Results: On measuring the maximum fracture load of specimens, both the treatments of sandblasted and acid-etched one statistically showed the strength increase rather than the control group (p<0.005). The scanning electric microscope revealed that sand blasting made more micro-retention form not only on the resin matrix but on the glass fiber, and acid-etching contributed to increase in surface retention form, eliminated the inorganic particles in resin matrix. Specimen fracture modes investigation represented that sand blasted groups showed lower bonding failure than no-sand blasted groups. Conclusion: Referring to the values of maximum fracture load of specimens, the bonding strength was increased by sand blasting and acid-etching.

• 터널과지하공간
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• 제11권3호
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• pp.237-247
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• 2001

이 연구에서는 수압파쇄시험 결과의 해석에 대한 파괴역학모델의 적용성을 검토하기 위해 시험결과의 해석에 주로 이용되고 있는 탄성모델과 함게 파괴역학모델을 이론적으로 고찰하였으며, 국내에서 실시된 4개 현장의 측정결과를 이용하여 각 모델의 해석 결과를 비교·검토하였다. 파괴역학모델로부터 얻어진 해석 결과는 탄성모델에 의한 계산 값과 차이를 보였으며, 이러한 차이는 기존 균열의 길이가 작을수록 크게 나타났다. 파괴역학모델은 균열 길이의 판단이 가능한 경우와 같이 특수한 조건에 대해서만 적용이 가능할 것으로 판단된다. 암석의 인장강도는 파괴역학모델에 의한 값이 가장 크게 나타났으며, 압열인장시험, 탄성모델에 의한 값의 순서로 크게 나타났다. 이러한 현상은 시험규모에 따른 크기효과 때문이며, 따라서 수압파쇄시험의 탄성모델로부터 얻어진 암석의 인장강도는 현지암반의 인장강도를 추정할 때 이용될 수 있을 것으로 보인다.

• 지질공학
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• 제6권1호
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• pp.1-13
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• 1996

단열암반(fractured rock mass)에서 분리단열망(Discrete Fracture Network;DFN)개념을 적용한 지하수유 동해석 과정 및 결과에 가장 크게 영향을 미치는 인자 중의 하나느 단열투수량계수(fracture transmissivity;$T_f$)이다. $T_f$는 단열특성, 방향성(orientation),단열틈(aperture),크기(size),조도(roughness) 및 충전물질(filling materiral)등에 크게 좌우된다. 본 연구에서는 DFN모델링 과정에서 가장 민감성을 나타내는 인자중 하나인 Tf의 도출을 위해서 초음파주사검층(Borehole Acouist Scanning;Televiewer)과 구가별 정압주입시험(Fixed Inter Length test in constant head;FIL)을 이용하였다. 이 값을 이용하여 해석한 결과, 연구지역의 지하수유동모델링 과정의 신뢰성은 물론 단열투수량계수,터널내 지하수유입량등,해석 전반에 걸쳐 상당한 신뢰성을 부여할 수 있었다.따라서 DFN모델에 의한 지하수유동해석시 Cubic law의 기본전제를 만족하는 단열특성의 경우, televiewer와 FIL시험과의 결과분석을 통하여 도출한 단열조별 Tf는 지하수유동 해석결과에 대한 신로성을 한 단계 제고할 수 있는 방법으로서 의의가 있다.

• International Journal of Concrete Structures and Materials
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• 제10권2호
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• pp.163-175
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• 2016

This paper presents a revised procedure for computation of double-K fracture parameters of concrete split-tension cube specimen using weight function of the centrally cracked plate of finite strip with a finite width. This is an improvement over the previous work of the authors in which the determination of double-K fracture parameters of concrete for split-tension cube test using weight function of the centrally cracked plate of infinite strip with a finite width was presented. In a recent research, it was pointed out that there are great differences between a finite strip and an infinite strip regarding their weight function and the solution of infinite strip can be utilized in the split-tension specimens when the notch size is very small. In the present work, improved version of LEFM formulas for stress intensity factor, crack mouth opening displacement and crack opening displacement profile presented in the recent research work are incorporated. The results of the double-K fracture parameters obtained using revised procedure and the previous work of the authors is compared. The double-K fracture parameters of split-tension cube specimen are also compared with those obtained for standard three point bend test specimen. The input data required for determining double-K fracture parameters for both the specimen geometries for laboratory size specimens are obtained using well known version of the Fictitious Crack Model.

• 비파괴검사학회지
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• 제21권3호
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• pp.251-260
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• 2001

단조인장시험하에서 CFRP적층재의 손상과정을 음향방출과 초음파시험에 의해 평가하였다. 시험편으로부터의 음항방출신호의 진폭 분포는 기지재 균열(matrix crack), 박리(debonding), 섬유 pull-out 및 섬유 과단(fiber fracture)과 같은 CFRP에서의 파괴기구를 분석하는데 도움을 주며, 초음파 진폭감쇠의 특성 또한 각각의 파괴기구를 분석하는데 유용하다. 여러종류의 CFRP시험편을 사용하여 음향방출신호와 초음파신호의 진폭감쇠를 조사하였다. 끝으로 하중 제하중(loading-unloading) 시험이 초음파내의 진폭비에 대한 Felicity effect와 감쇠를 조사하기 위해서 수행되었다. 전 실험에 걸쳐 초음파신호의 진폭감쇠와 음향방출 파라미터(parameter)들은 동시에 검출되었다. 이로써 음향방출과 초음파시험의 두 파라미터들이 CERP에서의 파괴기구를 분석하기 위해 효과적으로 사용될 수 있음이 확인되었다.

• Restorative Dentistry and Endodontics
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• 제15권2호
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• pp.17-33
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• 1990

The purpose of this study was to evaluate the fracture toughness of dental composite resins and to investigate the filler factor affecting the fracture behaviour on which the degree of fracture toughness depends. Six kinds of commercially available composite resin;, including two of each macrofilled, microfilled, and hybrid type were used for this study, The plane strain fracture toughness ($K_{10}$) was determined by three-point bending test using the single edge notch specimen according to the ASTM-E399. The specimens were fabricated with visible light curing or self curing of each composite resin previously inserted into a metal mold, and three-point bending test was conducted with cross-head speed of 0.1mm/min following a day's storage of the specimens in $37^{\circ}C$ distilled water. The filler volume fractions were determined by the standard ashing test according to the ISO-4049. Acoustic Emission(AE), a nondestructive testing method detecting the elastic wave released from the localized sources In material under a certain stress, was detected during three-point bending test and its analyzed data was compared with, canning electron fractographs of each specimen. The results were as follows : 1. The filler content of composite resin material was found to be highest in the hybrid type followed by the macrofilled type, and the microfilled type. 2. It was found that the value of plane strain fracture toughness of composite resin material was in the range from 0.69 MPa$\sqrt{m}$ to 1 46 MPa$\sqrt{m}$ and highest In the macrofilled type followed by the hybrid type, and the microfilled type. 3. The consequence of Acoustic Emission analysis revealed that the plane strain fracture toughness increased according as the count of Acoustic Emission events increased. 4. The higher the plane strain fracture toughness became, the higher degree of surface roughness and irregularity the fractographs demonstrated.

• 대한기계학회논문집A
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• 제22권2호
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• pp.311-320
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• 1998

The cryogenic fracture behaviors of austenitic stainless steel HN2 developed for nuclear fusion reactor were evaluated quantitatively by using the small punch(SP) test. The electrochemical polarization test was applied to study thermal aging degradation of HN2 steel. The X-ray diffraction(XRD) analysis was conducted to detect carbides and nitrides precipitated on the grain boundary of the heat treated HN2 steel. The mechanical properties of the HN2 steel significantly decreased with increasing time and temperature of heat treatment or with decreasing testing temperature. The integrated charge(Q) obtained from electrochemical polarization test showed a good correlation with the SP energy(ESP) obtained by means of SP tests. From the results observed in the x-ray diffraction and anodic polarization curve, it was known that the material the grain boundary. Combining SP test and electrochemical polarization test, it could be useful tools to non-destructively evaluate the cryogenic fracture behaviors and the aging degradation for cryogenic structural material.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1-6
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• 2004

In this study, the intrinsic static/dynamic fracture toughness of Al 7175=T74 is evaluated from the apparent static/ dynamic toughness of notched specimen, The critical average stress fracture model is suggested to establish the relationship to predict the intrinsic fracture toughness from the apparent fracture toughness of a notched specimen. The critical average stress fracture model is established using the relation between the notch root radius and the effective distance calculated by finite element analysis. Also, effective distance is applied to estimate the failure criterion for the combustion pipe with notch. It is conclude that the true fracture toughness can be estimated from test results of apparent fracture toughness measured by using a notched specimen. Also, the effective In this study, the intrinsic static/dynamic fracture toughness of Al 7175=T74 is evaluated from the apparent static/ dynamic toughness of notched specimen, The critical average stress fracture model is suggested to establish the relationship to predict the intrinsic fracture toughness from the apparent fracture toughness of a notched specimen. The critical average stress fracture model is established using the relation between the notch root radius and the effective distance calculated by finite element analysis. Also, effective distance is applied to estimate the failure criterion for the combustion pipe with notch. It is conclude that the true fracture toughness can be estimated from test results of apparent fracture toughness measured by using a notched specimen. Also, the effective distance can be used to evaluate the failure criterion of structure with notch.

• Advances in concrete construction
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• 제2권3호
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• pp.229-247
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• 2014

A numerical study of the influence of shear-span/depth ratio on the cohesive crack fracture parameters and double - K fracture parameters of concrete is carried out in this paper. For the study the standard bending specimen geometry loaded with four point bending test is used. For four point loading, the shear - span/depth ratio is varied as 0.4, 1 and 1.75 and the ao/D ratio is varied from 0.2, 0.3 and 0.4 for laboratory specimens having size range from 100 - 500 mm. The input parameters for determining the double - K fracture parameters are taken from the developed fictitious crack model. It is found that the cohesive crack fracture parameters are independent of shear-span/depth ratio. Further, the unstable fracture toughness of double-K fracture model is independent of shear-span/depth ratio whereas, the initial cracking toughness of the material is dependent on the shear-span/depth ratio.