• 제목/요약/키워드: tensile cracks

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Comparison of macrosynthetic and steel FRC shear-critical beams with similar residual flexure tensile strengths

  • Ortiz-Navas, Francisco;Navarro-Gregori, Juan;Leiva, Gabriel;Serna, Pedro
    • Structural Engineering and Mechanics
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    • v.76 no.4
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    • pp.491-503
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    • 2020
  • This study extends previous experimental research on the shear behaviour of macrosynthetic fibre-reinforced concrete beams and compares them to steel fibre-reinforced concrete beams with similar mechanical and geometrical properties. This work employed two fibre types: 60/0.9 (long/diameter) double hooked-end steel fibre and 60/85 monofilament polypropylene fibre. Beams were tested by shear loading covering parameters, such as two different cross-section widths, two shear-span-to-effective-depth ratios, two fibre types and using repetitions with and without transverse reinforcement. For quantitative comparison purposes, crack pattern evolution was studied along increasing loads levels. Effects were studied by photogrammetry, including influence of fibres on crack propagation in uncracked and dowel zones, influence of fibres on stirrup behaviour, and shear deformation or kinematics of critical shear cracks. The results evidenced similar effectiveness for both fibre types in controlling shear crack propagation and horizontal dowel cracking. Both fibres provided similar shear ductility and shear deflections. Consequently, the authors confirm that residual flexural tensile strengths are a convenient parameter for characterising the shear behaviour of fibre-reinforced concrete beams.

Performance of concrete structures with a combination of normal SCC and fiber SCC

  • Farhang, Kianoosh;Fathi, Hamoon
    • Computers and Concrete
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    • v.20 no.6
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    • pp.655-661
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    • 2017
  • Fiber reinforced concretes exhibit higher tensile strength depending on the percent and type of the fiber used. These concretes are used to reduce cracks and improve concrete behavior. The use of these fibers increases the production costs and reduces the compressive strength to a certain extent. Therefore, the use of fiber reinforced concrete in regions where higher tensile strength is required can cut costs and improve the overall structural strength. The behavior of fiber reinforced concrete and normal concrete adjacent to each other was investigated in the present study. The concrete used was self-compacting and did not require vibration. The samples had 0, 1, 2 and 4 wt% polypropylene fibers. 15 cm sample cubes were subjected to uniaxial loads to investigate their compressive strength. Fiber Self-Compacting Concrete was poured in the mold up to 0, 30, 50, 70 and 100 percent of the mold height, and then Self-Compacting Concrete without fiber was added to the empty section of that mold. In order to investigate concrete behavior under bending moment, concrete beam samples with similar conditions were prepared and subjected to the three-point bending flexural test. The results revealed that normal Self-Compacting Concrete and Fiber Self-Compacting Concrete may be used in adjacent to each other in structures and structural members. Moreover, no separation was observed at the interface of Fiber Self-Compacting Concrete and Self-Compacting Concrete, either in the cubic samples under compression or in the concrete beams under bending moment.

Automatic Detection and Characterization of Cracked Constituent Particles/Inclusions in Al-Alloys under Uniaxial Tensile Loading (인장하중에 의한 Al 합금내 크랙형성 복합상의 자동검출 및 정량분석)

  • Lee, Soon Gi;Jang, Sung Ho;Kim, Yong Chan
    • Korean Journal of Metals and Materials
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    • v.47 no.1
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    • pp.7-12
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    • 2009
  • The detailed quantitative microstructural data on the cracking of coarse constituent particles in 7075 (T651) series wrought Al-alloys have been studied using the utility of a novel digital image processing technique, where the particle cracks are generated due to monotonic loading. The microstructural parameters such as number density, volume fraction, size distribution, first nearest neighbor distribution, and two-point correlation function have been quantitatively characterized using the developed technique and such data are very useful to verify and study the theoretical models for the damage evolution and fracture of Al-alloys. The data suggests useful relationships for damage modeling such as a linear relationship between particle cracking and strain exists for the uniaxial tensile loading condition, where the larger particles crack preferentially.

Fabrication and Mechanical Characterization of the Mg-Zn-RE/Al1050 Clad Sheet (Mg-Zn-RE/Al1050 클래드재의 제조 및 기계적 특성)

  • Shin, Beomsoo;Yoon, Sockyeon;Ha, Changseong;Yun, Seungkwan;Bae, Donghyun
    • Korean Journal of Metals and Materials
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    • v.48 no.2
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    • pp.116-121
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    • 2010
  • The Mg-Zn-RE alloy cladded with the thin Al1050 sheet was fabricated by means of a roll bonding process at $280^{\circ}C$.Microstructures and mechanical properties of the clad sheets were investigated. After heat treatment at $230^{\circ}C$ for 30 min, an Mg-rich diffusion layer with about $2{\mu}m$ in thickness was developed at the Mg and Al interface. Tensile tests were carried out in a temperature range up to $300^{\circ}C$. The clad sheet exhibits superior elongation to failure not only at room temperature but also at elevated temperatures compared with those of the Mg alloy sheet. For the deformed specimens, interface debonding does not occur and the diffusion layer shows only a few cracks.

Failure Analysis of Stress Reliever in Heat-Transport Pipe of District Heating System

  • Cho, Jeongmin;Chae, Hobyung;Kim, Heesan;Kim, Jung-Gu;Kim, Woo Cheol;Lee, Soo Yeol
    • Corrosion Science and Technology
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    • v.21 no.4
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    • pp.243-249
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    • 2022
  • The objective of the present study was to perform failure analysis of double-layered bellow (expansion joint), a core part of stress reliever, used to relieve axial stresses induced by thermal expansion of heat-transport pipes in a district heating system. The bellow underwent tensile or compressive stresses due to its structure in terms of position. A leaked position sufferred a fatigue with a tensile component for decades. A cracked bellow contained a higher fraction of martensitic phase because of manufacturing and usage histories, which induced more brittleness on the component. Inclusions in the inner layer of the bellow acted as a site of stress concentration, from which cracks initiated and then propagated along the hoop direction from the inner surface of the inner layer under fatigue loading conditions. As the crack reached critical thickness, the crack propagated to the outer surface at a higher rate, resulting in leakage of the stress reliever.

Tensile damage of reinforced concrete and simulation of the four-point bending test based on the random cracking theory

  • Chang, Yan-jun;Wan, Li-yun;Mo, De-kai;Hu, Dan;Li, Shuang-bei
    • Computers and Concrete
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    • v.30 no.4
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    • pp.289-299
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    • 2022
  • Based on the random cracking theory, the cylinder RVE model of reinforced concrete is established and the damage process is divided into three stages as the evolution of the cracks. The stress distribution along longitude direction of the concrete and the steel bar in the cylinder model are derived. The equivalent elastic modulus of the RVE are derived and the user-defined field variable subroutine (USDFLD) for the equivalent elastic modulus is well integrated into the ABAQUS. Regarding the tensile rebars and the concrete surrounding the rebars as the equivalent homogeneous transversely isotropic material, and the FEM analysis for the reinforced concrete beams is conducted with the USDFLD subroutine. Considering the concrete cracking and interfacial debonding, the macroscopic damage process of the reinforced concrete beam under four-point bending loading in the simulation. The volume fraction of rebar and the cracking degree are mainly discussed to reveal their influence on the macro-performance and they are calibrated with experimental results. Comparing with the bending experiment performed with 8 reinforced concrete beams, the bending stiffness of the second stage and the ultimate load simulated are in good agreement with the experimental values, which verifies the effectiveness and the accuracy of the improved finite element method for reinforced concrete beam.

Crack-controlled design methods of RC beams for ensuring serviceability and reparability

  • Chiu, Chien-Kuo;Saputra, Jodie;Putra, Muhammad Dachreza Tri Kurnia
    • Structural Engineering and Mechanics
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    • v.82 no.6
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    • pp.757-770
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    • 2022
  • For the design of flexural and shear crack control for reinforced concrete (RC) beams related to serviceability and reparability ensuring, eight simply-supported normal-strength reinforced concrete (NSRC) beam specimens are tested and the existing high-strength reinforced concrete (HSRC) experimental data are included in the investigation of this work. According to the investigation results of flexural and shear cracks, this works modifies the existing design formulas to determine the spacing of the tensile reinforcement for the flexural crack control of a HSRC/NSRC beam design. Additionally, for a specified shear crack width of 0.4 mm, the allowable stresses of the shear reinforcement are also identified. For the serviceability and reparability ensuring of HSRC/NSRC beams, this works proposes the relationship curves between the maximum flexural width and allowable stress of the tensile reinforcement, and the relationship curves between the shear crack width and allowable shear force that can be used to do the crack width control directly.

Stress Intensity Factor Measurement of Inclined Crack in Tensile Plates by Use of Photoelasticity (광탄성법을 이용한 인장판의 경사균열 응력확대계수 측정)

  • Baek, Tae-Hyun;Lee, Chun-Tae;Kim, Young-Chul
    • Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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    • v.5 no.2
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    • pp.215-222
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    • 2015
  • This paper presents the measurement of stress intensity factors of inclined cracks by use of photoelasticity. The distributions of isochromatics near a crack tip of the specimen loaded by uniaxially tensile load are used for analysis. Accuracy and reliability is enhanced by twice multiplying and sharpening the measured isochromatics using digital image processing. Photoelastic results are compared with those obtained by finite element method. Good agreement between them shows that the photoelastic analysis is reliable.

Examination of Stress Changes Depending on the Size of the Repaired Part of a Partially Repaired RC Beam (부분보수한 RC보의 보수부 크기에 따른 응력 변화 검토)

  • Kwon, Hyeong-Soon;Lee, Sang-Soo
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2023.11a
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    • pp.47-48
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    • 2023
  • Reinforced concrete structures are an integrated structure in which reinforcing bars are placed on the tensile side of the beam to compensate for concrete that is strong in compression but weak in tension, so that the concrete receives compressive force and the reinforcing bars receive tensile force. It is durable, fire-resistant, economical, and adapts to the shape and dimensions of the structure. It has been widely used for a long time because it can be made freely without restrictions. However, reinforced concrete structures have the disadvantage that cracks occur easily, so they are repaired using a cross-sectional construction method. During this process, problems such as the repair part falling off occurred, so in order to solve the problem, stress changes due to changes in the size of the repair part were examined. As a result, based on the elastic modulus ratio of 1.0, the stress tended to increase as the size of the repair part decreased when it was less than 1.0, and the opposite tendency was seen when it was more than 1.0. This is believed to be due to an increase in the area of the part with a large elastic modulus.

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Effect of Adhesion Strength Between Flexible Substrates and Electrodes on the Durability of Electrodes (유연 기판과 전극 사이의 접합력이 전극의 내구성에 미치는 영향)

  • Doyeon Im;Byoung-Joon Kim;Geon Hwee Kim;Taechang An
    • Journal of Sensor Science and Technology
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    • v.33 no.2
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    • pp.86-92
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    • 2024
  • Flexible electronic devices are exposed to repeated mechanical deformation; therefore, electrode performance is an important element. Recently, a new technology has been developed to improve the adhesion strength between polymer substrates and metal thin films through the cross-linking reaction of bovine serum albumin (BSA) bioconjugation proteins; however, additional performance evaluation as an electrode is necessary. Therefore, in this study, we investigated the effect of adhesive strength between a flexible substrate and a metal thin film on the performance of a flexible electrode. Cracks and changes in the electrical resistance of the electrode surface were observed through outer bending fatigue tests and tensile tests. As a result of a bending fatigue test of 50,000 cycles and a tensile test at 10% strain, the change in the electrical resistance of the flexible electrode with a high adhesion strength was less than 40%, and only a few microcracks were formed on the surface; thus, the electrical performance did not significantly deteriorate. Through this study, the relationship between the adhesion strength and electrical performance was identified. This study will provide useful information for analyzing the performance of flexible electrodes in the commercialization of flexible electronic devices in the future.