• 터널과지하공간
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• 제19권4호
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• pp.304-317
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• 2009

대부분의 결정질 암석은 압축강도에 비해 인장강도가 현저하게 낮으므로 근본적으로는 인장에 의한 취성파괴의 형태를 나타낸다. 암반이 충분한 강도와 지지력을 가진다 하더라도 현지 암반응력이 크거나 암반 구조물 형상에 따른 유도응력의 작용방향에 의해 암반의 강도를 초과하는 응력집중이 발생될 경우 취성파괴가 발생할 수 있다. 따라서 심부 암반 구조물의 안정성평가를 위해서는 암반의 취성파괴 거동특성 규명이 반드시 필요하다. 암반이 충분한 강도와 지지력을 가진다 하더라도 현지 암반응력이 크거나 암반 구조물 형상에 따른 유도응력의 작용방향에 의해 암반의 강도를 초과하는 응력집중이 발생될 경우 취성파괴가 발생할 수 있다. 따라서 심부 암반 구조물의 안정성평가를 위해서는 암반의 취성파괴 거동특성 규명이 반드시 필요하다. 본 논문에서는 과지압을 받는 심부터널 주변 암반의 취성파괴 특성을 파악하기 위하여 국내 대표 암종인 흑운모 화강암과 화강암질 편마암의 대심도 암석시료에 대한 손상제어시험을 수행하고, 이로부터 점착력과 마찰각의 변화특성을 파악하였다. 또한 그 결과를 이용하여 CWFS 모델을 구성하고, 이 모델을 지하심부에 굴착되는 터널에 적용하여 터널주변 암반에 발생하는 취성파괴 양상 및 파괴가능 심도를 M-C 모델 결과와 비교 및 분석하였다.

• Geomechanics and Engineering
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• 제22권3호
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• pp.219-226
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• 2020

Unconfined compression test (UCT) is widely conducted in laboratories to evaluate the mechanical behavior of frozen soils. However, its results are sensitive to the initial conditions of sample creation by freezing as well as the end-surface conditions during loading of the specimen into the apparatus for testing. This work compared ice samples prepared by three-dimensional and one-dimensional freezing. The latter created more-homogenous ice samples containing fewer entrapped air bubbles or air nuclei, leading to relatively stable UCT results. Three end-surface conditions were compared for UCT on ice specimens made by one-dimensional freezing. Steel disc cap with embedded rubber was found most appropriate for UCT. Three frozen materials (ice, frozen sand, and frozen silt) showed different failure patterns, which were classified as brittle failure and ductile failure. Ice and frozen sand showed strain-softening, while frozen silt showed strain-hardening. Subsequent investigation considered the influence of fines content on the unconfined compression behavior of frozen soil mixtures with fines contents of 0-100%. The mixtures showed a brittle-to-ductile transition of failure patterns at 10%-20% fines content.

• Structural Engineering and Mechanics
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• 제75권5호
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• pp.559-569
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• 2020

In the present study, the fracture toughness of U-shaped notches made of aluminum alloy Al7075-T6 under combined tension/out-of-plane shear loading conditions (mixed mode I/III) is studied by theoretical and experimental methods. In the experimental part, U-notched test samples are loaded using a previously developed fixture under mixed mode I/III loading and their load-carrying capacity (LCC) is measured. Then, due to the presence of considerable plasticity in the notch vicinity at crack initiation instance, using the Equivalent Material Concept (EMC) and with the help of the point stress (PS) and mean stress (MS) brittle failure criteria, the LCC of the tested samples is predicted theoretically. The EMC equates a ductile material with a virtual brittle material in order to avoid performing elastic-plastic analysis. Because of the very good match between the EMC-PS and EMC-MS combined criteria with the experimental results, the use of the combination of the criteria with EMC is recommended for designing U-notched aluminum plates in engineering structures. Meanwhile, because of nearly the same accuracy of the two criteria and the simplicity of the PS criterion relations, the use of EMC-PS failure model in design of notched Al7075-T6 components is superior to the EMC-MS criterion.

• Computers and Concrete
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• 제30권1호
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• pp.19-32
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• 2022

This paper presents an investigation into the failure of RC columns under impact loadings. A numerical simulation of 19 identical RC columns subjected to single and repeated impact loadings was performed. A free-falling hammer was dropped at midspan with the same total kinetic energy input but varying mass and momentum. The specimens under the repeated impact test were struck two times at the same location. The colliding index, defined as the impact energy-momentum ratio, was proposed to explain the different impact responses under equal-energy impacts. The increase of colliding index from low to high indicates the transition of the impact response from static to dynamic and failure mode from flexure to shear. This phenomenon was more evident when the column had a greater axial load and was impacted with a high colliding index. The existence of the axial load had an inhibitory effect on the crack development and increased the shear resistance. The second impact changes the failure mode from flexural to brittle shear as found in the specimen with 20% axial load subjected to high a colliding index. Moreover, a deflection prediction equation based on the impact energy and force was limited to the low colliding index impact.

• Computers and Concrete
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• 제25권1호
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• pp.15-27
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• 2020

During the past decades, the application of acoustic emission techniques (AET) through the diagnosis and monitoring of the fracture process in materials has been attracting considerable attention. AET proved to be operative among the other non-destructive testing methods for various reasons including their practicality and cost-effectiveness. Concrete and rock structures often demand thorough and real-time assessment to predict and prevent their damage nucleation and evolution. This paper presents an overview of the work carried out on the use of AE as a monitoring technique to form a comprehensive insight into its potential application in brittle materials. Reported properties in this study are crack growth behavior, localization, damage evolution, dynamic character and structures monitoring. This literature review provides practicing engineers and researchers with the main AE procedures to follow when examining the possibility of failure in civil/resource structures that rely on brittle materials.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권8호
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• pp.342-347
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• 2003

The suspension insulators are subjected to harsh environment in service for a long time. Long term reliability of the insulators is required for both mechanical and electrical performances. We studied an analysing method to find out a deformation of brittle porcelain with a thermal expansion of simulation analysis and experimental results show that cement volume growths affect severely to b mechanical failure ageing.

• 콘크리트학회지
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• 제7권3호
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• pp.164-174
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• 1995

ACI규준에 의하여 설계된 철근콘크리트 보의 휨보강의 신뢰성을 분석하였다. 분석된 결과를 기존의 연구와 비교하였다. 인장철근비가 변함에 따라 일관된 신뢰성이 보장되지 못하고 부적합하게 변하는 것으로 분석되었다. 규준의 최대철근비 조항에 적합하게 설계된 보라도 취성파괴가 매우 높은 것으로 분석되었다. 특히 국내의 철근콘트리트구조물에서는 이러한 현상이 두드러지는 것으로 분석되었다. 이와 같은 현상의 원인을 규명하였고 그 대책을 제시하였다.

• 한국암반공학회:학술대회논문집
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• 한국암반공학회 2008년도 국제학술회의
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• pp.3-16
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• 2008

The underground construction and mining are facing many geomechanics challenges stemming from, geological complexities and stress-driven rock mass degradation processes. Brittle failing rock at depth poses unique problems as stress-driven failure processes often dominate the tunnel behaviour. Such failure processes can lead to shallow unravelling or strainbursting modes of instability that cause difficult conditions for tunnel contractors. This keynote address focuses on the challenge of anticipating the actual behaviour of brittle rocks in laboratory testing, for empirical rock mass strength estimation, and by back-analysis of field observations. This paper summarizes lessons learned during the construction of deep Alpine tunnels and highlights implications that are of practical importance with respect to constructability. It builds on a recent presentation made at the $1^{st}$ Southern Hemisphere International Rock Mechanics Symposium held in Perth, Australia, in September this year, and includes results from recent developments.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.331-334
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• 2003

Since regulation or specification for the reinforcing method are quite ambiguous, structural design for the reinforcement can be subjectively and arbitrarily conducted. Thus, reasonable limitation and guide for the quantity of the reinforcement are required for the safe use of the structure after repair. In order to guarantee the safety of the structural member several items should be considered; reinforcing limit to avoid the brittle failure, least required strength of the existing member before reinforcement in order not to fail under the new serviceability load condition when reinforcing steel plates or CFRP sheets are harmed or subjected to fire.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.339-342
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• 2003

The bridge columns with lap-splice reinforcements in earthquake suffered a brittle bond-slip failure due to deterioration of the lap-spliced longitudinal reinforcements without developing its flexural capacity or ductility. In this case, such a brittle failure can be controlled by the seismic retrofit using FRP wrapping. The retrofitted columns using FRP wrapping showed significant improvement in seismic performance due to FRP's confinement effect. This paper presents the circumferential confinement effect of existing circular bridge pier strengthened with FRP wrapping for poor lap-splice details. The effects on the confinement of FRP wrapping, such as gap lengths between footing and FRP, fiber orientations, and thicknesses of FRP, were investigated by quasi-static experiments.