Papers by Keyword: Multiple Cracking

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Authors: Zhi Hua Li, Wei Kang Chen, Xu Zhou, Feng Quan Chen
Abstract: Polyvinyl alcohol (PVA) fiber reinforced cementitious material (called PVA-ECC) has been intensively studied as a promising alternative to ordinary cement materials. While PVA-ECC has high stain capacity and ductility, its extreme high cost mainly caused by the high unit cost of used Japanese fiber has hindered its application in China. In order to reduce the cost of PVA-ECC, one type of inexpensive PVA fiber produced in China was used to develop a ductile ECC with deflection hardening and multiple cracking behaviors in this research. Compressive strength test, four-point bending test and uniaxial tension test were conducted to investigate the mechanical properties of the newly developed composites. The results show that ECC made with domestic ingredients exhibits large deformation and multiple cracking, revealing that it is feasible to produce low cost ECC material employing local PVA fibers.
Authors: Milan Rydval, Jiří Kolísko, Šárka Nenadálová
Abstract: This paper is focused on a mechanical properties of fine-grained cement based composite materials reinforced by short PVA fibers. Cementitious materials are characterized by their fragile matrix. Reinforcing by fibers (e.g. steel fibers, PVA fibers, PP fibers, glass fibers) increase the tensile strength. The behavior of the elements after developing and spreading of micro cracks under load should be described as a strain-softening, strain-hardening, etc. The multiple cracking under load is typical deformations of composite materials reinforced by short PVA fibers, that is worldwide known as a ECC.
Authors: Jian Ping Han, Jin Yu Tao
Abstract: As one kind of Engineering Cementitious Composites (ECC), polyvinyl alcohol (PVA) fiber reinforced cement-based composites has specific strain hardening characteristics and multiple cracking properties. Thus it can exhibit excellent ductile properties and damage tolerance, which makes it being a potential material for critical components of seismic resistant structures. In order to investigate the flexural performance of PVA fiber reinforced cement-based composites, beam-type and sheet-type specimens made from PVA fiber reinforced cement-based composites were designed and four-point bending tests were conducted. The flexural toughness and flexural strength of PVA fiber reinforced cement-based composites were assessed via load-deflection curves. Experimental results indicate that PVA fiber reinforced cement-based composites can be used in critical structural components to mitigate the seismic response and to improve the seismic performance of structures.
Authors: Xin Hua Cai, Shi Lang Xu, Zhen He
Abstract: Ultra high toughness cementitious composite (UHTCC) is a newly developed, high performance, fiber-reinforced cementitious composite with substantial benefit in both high ductility and improved durability due to its tight crack width. The failure pattern of UHTCC exhibits saturated multiple fine cracks, so the durability of structures will be improved markedly by utilizing UHTCC partly or entirely instead of concrete. In this study, a total of 20 beams, including reinforced concrete beams that the cover zone was replaced by UHTCC (the thickness is 15mm, not containing reinforcement, and 50mm, containing reinforcement, respectively), reinforced concrete beams and reinforced UHTCC beams, had been manufactured. A power supply was used to accelerate the corrosion process of reinforcing bars, inducing different degrees of corrosion (the corrosion ratio was 1%, 2%, 4% and 5%) into reinforcing bars. The time of the cracks occurred and the crack width were recorded and the beams having different corrosion ratios of reinforcing bars were then tested under four-point bending for their load-deflection relations. The results showed that UHTCC could restrict the corrosion expansive crack of cover effectively, convert the crack pattern, and delay the appearance of first corrosion expansive crack, thereby to raise the service life of reinforcement concrete structures or components. Meanwhile, the bending test of beams after accelerated corrosion showed that the beams with a cover replaced by 50mm UHTCC and reinforced UHTCC having smaller amount of strength reduction and a reasonable ductile failure after corrosion. The experimental results showed that UHTCC could effectively delay the cover expansive cracking due to corrosion of reinforcing bars retain the ductile properties of reinforced concrete beams after reinforcing bar corroded.
Authors: Shojiro Ochiai, T. Tomida, Toyomitsu Nakamura, S. Iwamoto, Hiroshi Okuda, Masashi Tanaka, M. Hojo
Abstract: The compressive fracture and spalling of multiply-cracked brittle coating layer on metal substrate under tensile stress was studied for the anodic-oxidized aluminum wire with the Al2O3 coating layer and galvannealed IF steel plate with the intermetallic compound coating layer consisting of ζ, δ1 and Γ1 and Γ phases. The thin Al2O3 coating layer on Al wire was fractured by buckling in the circumferential direction by the compressive hoop stress, but thick layer was debonded by the tensile radial stress at interface. The thickness of the coating layer at the transition from the compressive fracture to interfacial debonding was around 30 µm. In the galvannealed steel plate sample, the (ζ+δ1) phases were fractured by buckling in the width direction, resulting spalling of the (ζ+δ1) phases in the first stage, and the remained (δ1+Γ1+ Γ) phases or (Γ1+Γ) phase was again fractured by buckling, followed by the spalling of the remained phase.
Authors: Michal Přinosil, Petr Kabele
Abstract: In the study, the bending behavior of high-performance fiber reinforced lime-based mortars is experimentally investigated using four-point bending test. From the experimental data, the influence of the mortar’s composition on its stiffness, cracking strength and ultimate strength are investigated. It is also studied, whether the response has strain-softening or strain-hardening character and whether the material exhibits multiple cracking. Such behavior is very important for the durability of the material, because it allows carrying load during imposed deformations (due to thermal effects, movements of foundations, seismicity, etc.). The number of formed cracks is examined using digital image correlation method. The mortar composition is considered with two types of binder (pure lime, lime-metakaolin), with two types of polyvinyl alcohol fibers in four volume fractions (0.5÷2.0%). As the reference, we consider two sets of specimens made of plain mortar without fiber reinforcement.
Authors: Wilson Nguyen, Jacob F. Duncan, Paulo J.M. Monteiro, Claudia P. Ostertag
Abstract: Many reinforced concrete structures susceptible to corrosion damage are subjected to externally applied loads, causing cracking. These cracks increase the permeability of the material, accelerating the ingress of corrosion-inducing deleterious agents. In this paper, the effect of multiple microcracking and macrocrack formation on corrosion initiation was investigated. A hybrid fiber-reinforced concrete (HyFRC), which forms ductile, distributed microcracking prior to dominant crack localization due to multiple tiers of fiber reinforcement, is being studied for its performance against corrosion damage. The effect of matrix cracking on corrosion initiation was studied with beam specimens preloaded in flexure prior to long-term corrosion exposure. Reinforced HyFRC composites were found to have a delayed corrosion initiation response due to reductions in crack widths and suppression of splitting cracks, compared to conventional reinforced concrete. The influence of microcracks on corrosion is studied using X-ray micro-computed tomography (μCT) on reinforced fiber-reinforced cementitious composites and reinforced mortar preloaded in tension.
Authors: Iliya Vlasov, Sergey V. Panin, Viktor Sergeev, Vladimir Titkov, Pavlo Maruschak
Abstract: Surface modification is an effective way both to protect structural materials and to improve their mechanical properties. However under mechanical loading the distinction of elastic moduli of a modified surface layer and adjacent bulk material causes the stress concentrators to occur, whose relaxation may give rise to localized development of plastic deformation or fracture [1]. Under cyclic loading such distinction of the properties brings to multiple microcracking of strengthened surface layer, to act as structural micronotches [2, 3]. Therefore, optimized modes and parameters for surface layer modification are to be determined being a certain compromise between strength/ductility of the layer and its thickness etc.
Authors: Ilya Vlasov, Sergey Panin, Viktor Sergeev, Vasilii Naidfeld, Pavlo Maruschak
Abstract: Cyclic tension and alternating bending tests of 12Cr1MoV and 30CrMnSiNi2 steels specimens in as–supplied state and after surface irradiation by Zr+ ion beam have been carried out. Distinctions in formation of strain induced relief, as well as cracking pattern of modified surface layer are illustrated by methods of optical microscopy and interferential profilometry. Changes to occur in subsurface layer are characterized by means of nanoindentation and scanning electron microscopy of fracture surfaces. The description of differences of deformation behavior is carried out with use of the multiple cracking concepts.
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