• 한국재료학회지
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• 제24권2호
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• pp.87-92
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• 2014

The Notched Ring Test(NRT) has proven to be very useful in determining the slow crack growth behavior of polyethylene pressure pipes. In particular, the test is simple and an order of magnitude shorter in experimental times as compared to the currently used Notched Pipe Test(NPT), which makes this method attractive for use as the accelerated slow crack growth test. In addition, since the NRT specimen is taken directly from the pipe, having maintained the cross-section, processing induced artifacts that would affect the slow crack growth behavior are not altered. This makes the direct comparison to the slow crack growth specimen in pipe from more meaningful. In this study, for comparison with other available slow crack growth methods, including the NPT, the stress intensity factor equation for NRT specimen was developed and demonstrated of its accuracy within 3% of that obtained from the finite element analysis. The equation was derived using a flexure formula of curved beam bending along with numerically determined geometric factors. The accuracy of the equation was successfully tested on 63, 110, 140, 160, 250, and 400 mm nominal pipe diameters, with crack depth ranging from 15 % to 45 % of the pipe wall thickness, and for standard dimensional ratio(SDR) of 9, 11, and 13.6. Using this equation the slow crack results from 110SDR11 NRT specimen were compared to that from the NPT specimen, which demonstrated that the NRT specimen was equivalent to the NPT specimen in creating the slow crack, however in much shorter experimental times.

• 한국세라믹학회지
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• 제19권3호
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• pp.229-235
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• 1982

This paper deals with the electric insulator in terms of its toughness. The toughness is determined by the notched beam test and it is found that the toughness of electric insulator largely depends on the porosity as well as crystalline phases. This study also indicates that the Korean electric insulators have improved its toughness for last seven years and the recent products show comparable properties with imported insulator.

• Structural Engineering and Mechanics
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• 제62권2호
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• pp.225-236
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• 2017

The purpose of this work is to predict ductile fracture of structural steel under extremely low cyclic loading experienced in earthquake. A cumulative damage model is proposed on the basis of an existing damage model originally aiming to predict fracture under monotonic loading. The cumulative damage model assumes that damage does not grow when stress triaxiality is below a threshold and fracture occurs when accumulated damage reach unit. The model was implemented in ABAQUS software. The cumulative damage model parameters for steel base metal, weld metal and heat affected zone were calibrated, respectively, through testing and finite element analyses of notched coupon specimens. The damage evolution law in the notched coupon specimens under different loads was compared. Finally, in order to examine the engineering applicability of the proposed model, the fracture performance of beam-column welded joints reported by previous researches was analyzed based on the cumulative damage model. The analysis results show that the cumulative damage model is able to successfully predict the cracking location, fracture process, the crack initiation life, and the total fatigue life of the joints.

• 수산해양기술연구
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• 제35권4호
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• pp.410-420
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• 1999

The value of the mode I interlamina fracture toughness, GIC, is calculated by experimental compliance method, modified compliance method and beam theory. The value of the mode II interlamina fracture toughness, GIC, is evaluated by beam method, theory beam theory and compliance method. This paper describes the effect of load pint displacement rate and speicimen geometries for mode I and II interlaminar fracture toughness of glass fiber reinforced plastic composites by using double cantilever beam (DCB) and end notched flexure (ENF) specimen. For the load point displacement rate of increases whereas the value of 2,6 and 10 mm/min the value of GIC decrease as load point displacement rate increases whereas the value of GIC is found to be no significant effect. The value of GIC decreases as initial crack length increases. The fractured surface of the DCB and ENF samples are examined by scanning electron microscopy (SEM).

• Computers and Concrete
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• 제23권3호
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• pp.171-188
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• 2019

This study proposed a new and efficient 2D damage-plasticity model within the framework of Isogeometric analysis (IGA) for the geometrically nonlinear damage analysis of concrete. Since concrete exhibits complicated material properties, two internal variables are introduced to measure the hardening/softening behavior of concrete in tension and compression, and an implicit gradient-enhanced formulation is adopted to restore the well-posedness of the boundary value problem. The numerical results calculated by the model is compared with the experimental data of three benchmark problems of plain concrete (three-point and four-point bending single-notched beams and four-point bending double-notched beam) to illustrate the geometrical flexibility, accuracy, and robustness of the proposed approach. In addition, the influence of the characteristic length on the numerical results of each problem is investigated.

• 콘크리트학회논문집
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• 제24권5호
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• pp.525-533
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• 2012

이 연구에서는 UHPCC에서 섬유혼입률에 따른 초기균열강도 및 휨인장강도의 변화를 0~5 vol.% 범위에서 조사하였으며, 노치의 여부에 따른 영향을 파악하기 위해 노치가 없는 보에 대한 4점 재하실험 및 노치 낸 보에 대한 3점 재하실험을 같이 실시하였다. 실험 결과로부터 섬유혼입률이 증가함에 따라 휨인장강도는 선형적으로 강도가 향상됨을 확인할 수 있었고, 초기균열강도의 경우에는 1 vol.% 이상에서는 강도향상을 나타내었으나 그 이하의 섬유혼입에서는 강도향상 효과가 거의 없는 것으로 나타났다. 노치 유무에 따른 휨 실험으로부터 구한 UHPCC의 초기균열발생강도 및 휨 인장강도를 비교했을 때, 섬유혼입률에 따라 노치의 영향이 변하는 것으로 나타났다. 섬유혼입률이 증가함에 따라 노치에서의 응력집중의 영향이 감소하여 강도 차이가 점차 줄어들었으며, 높은 섬유혼입률에서는 노치에 의한 응력집중효과는 없어지고 균열면의 상태 및 크기효과의 영향이 지배적으로 작용하여 노치낸 보의 강도가 좀 더 크게 나타났다.

• Composites Research
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• 제29권2호
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• pp.45-52
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• 2016

섬유금속적층판과 같은 하이브리드 소재는 여러 방향의 하중에 의한 접착층의 파괴로 인해 층간분리가 발생할 수 있다. 모든 하중은 수직 방향의 응력과 면내 두 방향의 전단 응력으로 분해할 수 있으며, 이러한 하중은 접착층의 모드 I, II, III 파괴를 일으킨다. 따라서 하중에 의한 층간분리 현상을 예측하기 위해, 접착층의 모드별 임계 에너지 해방률을 도출하는 것이 중요하다. 본 연구에서는 접착층의 모드 I 임계 에너지 해방률을 측정하기 위해 double cantilever beam 시험을 수행하였으며, 모드 II 임계 에너지 해방률을 측정하기 위해 end-notched flexure 시험을 수행하였다. 또한, 실험으로부터 도출한 임계 에너지 해방률을 ABAQUS의 응집영역모델에 적용하여 유한요소해석을 수행하였으며, 실제 실험 결과와의 비교를 통해 층간분리 현상에 대한 수치해석 기법 적용의 유효성을 입증하였다.

• Steel and Composite Structures
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• 제29권2호
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• pp.187-200
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• 2018

This paper handles the repairing of deficient square Concrete-Filled Steel-Tube (CFST) beams subject to bending through an experimental and numerical program. Eight square-CFST beams were tested. A 5-mm artificial notch was induced at mid-span of seven beams, four of them were repaired by using CFRP sheets and two were repaired by using GFRP sheets. The beam deflection, strain and ultimate moments were recorded. It was found that providing different cut-off points for the different layers of FRP sheets prohibited failure at termination points due to stress concentrations. Using different lengths of FRP sheets around the notch retarded crack propagation and prevented FRP rupture at the crack position. Finite element analysis was then conducted and the proposed FE model was verified against the recorded experimental data. The influence of various parameters as FRP sheet length, tensile modulus and the number of layers were studied. The moment capacity of damaged square-CFST beams was improved up to 77.6% when repaired by using four layers of CFRP, however, this caused a dramatic decrease in beam deflection. U-wrapping of notched-CFST beam with 0.75 of its length provided a comparable behaviour as wrapping the full length of the beam.

• 한국세라믹학회지
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• 제24권4호
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• pp.313-320
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• 1987

Fracture toughness of hot pressed cordierite-SiC whisker ceramic composites contained up to 40vol.% SiC whiskers were determined by using the indentation crack length(IC), indentation strengthin-bending(IS), and single-edge notched-beam(SENB) methods. The results were compared to stress intensity factor, KB, at the crack branching boundary measured by using the mirror zone radius (MZ) method. IS method seems to provide a more reasonable estimation of fracture toughness than other methods for these composites.

• 한국소음진동공학회논문집
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• 제22권1호
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• pp.9-14
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• 2012

This paper investigates the prediction of the dynamic strain response using acceleration response only. Two methods are proposed for the strain prediction; one is based on beam theory and the other is calculated by the frequency response function between acceleration and strain. First, it is estimated the dynamics of the simple notched beam, including the non-linearity, through the uni-axial vibration testing. Then, the dynamic strain response is predicted under two different methods using acceleration response. The validation of proposed methods is conducted by the comparison between measured strain and predicted values. The comparison reveals that the proposed method based on the FRF between acceleration and strain is more reliable one than that stemmed from beam theory and the maximum relative error is less than 8 %.