• Title/Summary/Keyword: cracking and brittle fracture

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Structural Integrity Assessment of High-Strength Anchor Bolt in Nuclear Power Plant based on Fracture Mechanics Concept (원자력발전소 고강도 앵커 볼트의 파괴역학적 건전성평가)

  • Lim, Eun-Mo;Huh, Nam-Su;Shim, Hee-Jin;Oh, Chang-Kyun;Kim, Hyun-Su
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.37 no.7
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    • pp.875-881
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    • 2013
  • The failure of a bolted joint owing to stress corrosion cracking (SCC) has been considered one of the most important structural integrity issues in a nuclear power plant. In this study, the failure possibility of bolting, which is used to support the steam generator of a pressurized water reactor, owing to SCC and brittle fracture was evaluated in accordance with guidelines proposed by the Electric Power Research Institute, which are called the Reference Flaw Factor method. For this evaluation, first, detailed finite element stress analyses were conducted to obtain the actual nominal stresses of bolting in which either service loads or bolt preloads were considered. Based on these nominal stresses, the structural integrity of bolting was addressed from the viewpoints of SCC and toughness. In addition, the accuracy of the EPRI Reference Flaw Factor for assessing bolting failure was investigated using finite element fracture mechanics analyses.

Shake Table Test on Seismic Performance Evaluation of the Bolted Connection Type Paneling System with Exterior Finish Material (외부마감재가 부착된 볼트접합 방식 패널링 시스템의 내진성능평가를 위한 진동대 실험)

  • Oh, Sang Hoon;Park, Jong Won;Park, Hae Yong
    • Journal of the Earthquake Engineering Society of Korea
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    • v.22 no.1
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    • pp.23-32
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    • 2018
  • In this study, we conducted a shake table test to verify the seismic performance of the paneling system with steel truss composed of bolt connections. The control group was set to the traditional paneling system with steel truss connected by spot welding method. Test results showed that the bolted connection type paneling system has excellent deformation capacity without cracking or brittle fracture of the steel truss connection parts compared to the welding type paneling system. Furthermore, in the bolted connection type, slight damage occurred at the time of occurrence of the same story drift angle as compared with the existing method, it is considered that it has excellent seismic performance. In compliance with the performance-based design recommended for the current code (ASCE 41-13) on non-structural components, it is judged that in the case of the bolted connection type paneling system, it can be applied to all risk category structures without restriction. However, in the case of traditional paneling system with spot welding method, it is considered that it can be applied limitedly.

Investigating the effect of using three pozzolans (including the nanoadditive) in combination on the formation and development of cracks in concretes using non-contact measurement method

  • Grzegorz Ludwik Golewski
    • Advances in nano research
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    • v.16 no.3
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    • pp.217-229
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    • 2024
  • This paper presents results of visual analysis of cracks formation and propagation of concretes made of quaternary binders (QBC). A composition of the two most commonly used mineral additives, i.e. fly ash (FA) and silica fume (SF) in combination with nanosilica (nS), has been proposed as a partial replacement of the cement. The principal objective of the present study is to achieve information about the effect of simultaneous incorporation of three pozzolans as partial replacement to the OPC on the fracture processes in concretes made from quaternary binders (QBC). The modern and precise non-contact measurement method (NCMM) via digital image correlation (DIC) technique was used, during the studies. In the course of experiments it was established that the substitution of OPC with three pozzolans including the nanoadditive in FA+SF+nS FA+SF+nS combination causes a clear change of brittleness and behavior during fractures in QBCs. It was found that the shape of cracks in unmodified concrete was quasi-linear. Substitution of the binder by SCMs resulted in a slight heterogeneity of the structure of the QBC, including only SF and nS, and clear heterogeneity for concretes with the FA additive. In addition, as content of FA rises throughout each of QBC series, material becomes more ductile and shows less brittle failure. It means that an increase in the FA content in the concrete mix causes a significant change in fracture process in this composite in comparison to concrete with the addition of silica modifiers only.

Characterization of Acoustic Emission Signal for Welding Flaw and Stress Corrosion of SPPH Steels (SPPH강의 용접결함과 응력부식에 따른 음향 방출 신호의 특성)

  • Kim, Sung-Dai;Jung, Woo-Gwang;Lee, Jong-O;Jung, Yu-Jin
    • Journal of the Korean Society for Nondestructive Testing
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    • v.27 no.2
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    • pp.97-104
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    • 2007
  • An investigation has been made on the relationship between characteristics of Acoustic Emission (AE) signal in welding flaw and the stress corrosion defect in-service for the high pressure pipe steel. In order to tackle the problem of welding flaw in high pressure pipe, specimens were made by the aid of the application of both corrosion liquid usage and a quenching method after local heating. The amplitude of signal was $60{\sim}75\;dB$ in the territory which is suspected for defect, and the specimens which only have welding flaw showed gradients of 0.034, 0.034, 0.035. Moreover, there is a certain increase in gradient even though the differences are very slight. That is, corrosion specimens showed new gradients of 0.040, 0.039, 0.041 which put welding flaw and corrosion mechanism together. After pressurizing 3 minutes, AE signal has been detected from welding flaw easily in each part of the section. It is possible to predict the occurrence and also prevent the damage of stress corrosion crack which has characteristics of cleavage fracture.

Experimental and numerical study on mechanical behaviour of grouted splices with light-weight sleeves

  • Quanwei Liu;Tao Wu;Zhengyi Kong;Xi Liu;Ran Chen;Kangxiang Hu;Tengfei Xiang;Yingkang Zhou
    • Steel and Composite Structures
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    • v.52 no.2
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    • pp.165-182
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    • 2024
  • Grouted sleeve splice (GSS) is an effective type of connection applied in the precast concrete structures as it has the advantages of rapidly assembly and reliable strength. To decrease the weight and cost of vertical rebar connection in precast shear walls, a light-weight sleeve is designed according to the thick-cylinder theory. Mechanical behaviour of the light-weighted GSS is investigated through experimental analysis. Two failure modes, such as rebar fracture failure and rebar pull-out failure, are found. The load-displacement curves exhibit four different stages: elastic stage, yield stage, strengthening stage, and necking stage. The bond strength between the rebar and the grout increases gradually from outer position to inner position of the sleeve, and it reaches the maximum value at the centre of the anchorage length. A finite element model predicting the mechanical properties of the light-weighted GSS is developed based on the Concrete Damage Plasticity (CDP) model and the Brittle Cracking (BC) model. The effect of the rebar anchorage length is significant, while the increase of the thickness of sleeve and the grout strength are not very effective. A model for estimating ultimate load, including factors of inner diameter of sleeves, anchorage length, and rebar diameter, is proposed. The proposed model shows good agreement with various test data.

Mechanical Modeling of Pen Drop Test for Protection of Ultra-Thin Glass Layer (초박형 유리층 보호를 위한 펜 낙하 시험의 기계적 모델링)

  • Oh, Eun Sung;Oh, Seung Jin;Lee, Sun-Woo;Jeon, Seung-Min;Kim, Taek-Soo
    • Journal of the Microelectronics and Packaging Society
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    • v.29 no.3
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    • pp.49-53
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    • 2022
  • Ultra-thin glass (UTG) has been widely used in foldable display as a cover window for the protection of display and has a great potential for rollable display and various flexible electronics. The foldable display is under impact loading by bending and touch pen and exposed to other external impact loads such as drop while people are using it. These external impact loads can cause cracks or fracture to UTG because it is very thin under 100 ㎛ as well as brittle. Cracking and fracture lead to severe reliability problems for foldable smartphone. Thus, this study constructs finite element analysis (FEA) model for the pen drop test which can measure the impact resistance of UTG and conducts mechanical modeling to improve the reliability of UTG under impact loading. When a protective layer is placed to an upper layer or lower layer of UTG layer, stress mechanism which is applied to the UTG layer by pen drop is analyzed and an optimized structure is suggested for reliability improvement of UTG layer. Furthermore, maximum principal stress values applied at the UTG layer are analyzed according to pen drop height to obtain maximum pen drop height based on the strength of UTG.

Resistance Curves of Concrete CLWL-DCB Specimens (콘크리트 CLWL-DCB 시험편의 저항곡선)

  • 연정흠
    • Journal of the Korea Concrete Institute
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    • v.14 no.3
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    • pp.357-364
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    • 2002
  • The resistance curves (R-curves) for 381 m crack extension of CLWL-DCB specimens had been determined. The average velocities of the crack extension measured with strain gages were 0.70 and 55 ㎜/sec. The measured rotation angle of the notch faces showed the existence of the singularity at least before 171 and 93 mm crack extensions for the 0.70 and 55 ㎜/sec crack velocities, respectively. The maximum slopes of the R-curves occurred between 25 and 89 ㎜ crack extensions for 0.70 ㎜/sec crack velocity and between 51 and 127 ㎜ crack extensions for 55 ㎜/sec crack velocity During the maximum slopes of the R-curves, the micro-crack localization can be expected, and faster crack velocity may form longer micro-cracking and micro-crack localizing zones. The fracture resistance of 0.70 ㎜/sec crack velocity reached a roughly constant maximum value of 143 N/m at 152 ㎜ crack extension, while that of 55 ㎜/sec crack velocity increased continuously to 245 N/m at 254 ㎜ crack extension and then decreased to the value of 0.70 ㎜/sec crack velocity. The R-curve of 55 ㎜/sec crack velocity was similar to that of the small size three-point bend test, and it showed that small size specimen or fast crack velocity could cause more brittle behavior.