• Title, Summary, Keyword: Fracture behavior

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A Study on Fracture Behavior and Impact Stability of Sintered Rare-earth Permanent Magnets

  • Li, Wei;Li, Anhua;Wang, Huijie;Dong, Shengzhi;Guo, Yongquan
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • pp.790-791
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    • 2006
  • The fracture behavior and mechanical characteristics of sintered rare-earth magnets were investigated. It shows that the fracture behavior and bending strength of the magnets obviously exhibit anisotropy. Sm-Co magnets tend to cleavage fracture in the close-packed (0001) plane or in the ($10\bar{1}1$) plane. The fracture mechanism of $Nd_2Fe_{14}B$ magnet mainly appears to be intergranular fracture. The anisotropy of fracture behavior and mechanical strength of sintered rare-earth magnets is caused mainly by the strong crystal-structure anisotropy and the grain alignment texture. The effects of Nd content, and Pr, Dy substitution on the impact stability of $Nd_2Fe_{14}B$ magnets were also reported.

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Crack Growth Behaviors of Cement Composites by Fractal Analysis

  • Won, Jong-Pil;Kim, Sung-Ae
    • KCI Concrete Journal
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    • v.14 no.1
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    • pp.30-35
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    • 2002
  • The fractal geometry is a non-Euclidean geometry which describes the naturally irregular or fragmented shapes, so that it can be applied to fracture behavior of materials to investigate the fracture process. Fractal curves have a characteristic that represents a self-similarity as an invariant based on the fractal dimension. This fractal geometry was applied to the crack growth of cementitious composites in order to correlate the fracture behavior to microstructures of cementitious composites. The purpose of this study was to find relationships between fractal dimensions and fracture energy. Fracture test was carried out in order to investigate the fracture behavior of plain and fiber reinforced cement composites. The load-CMOD curve and fracture energy of the beams were observed under the three point loading system. The crack profiles were obtained by the image processing system. Box counting method was used to determine the fractal dimension, D$_{f}$. It was known that the linear correlation exists between fractal dimension and fracture energy of the cement composites. The implications of the fractal nature for the crack growth behavior on the fracture energy, G$_{f}$ is apparent.ent.

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Flexural Fracture Behavior of Reinforced Concrete Beam Based on Fracture Mechanics Approach (파괴역학에 근거한 철근콘크리트 보의 휨 파괴거동)

  • 어석홍;최덕진;홍기호;김희성
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.149-154
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    • 2002
  • An analytical fracture mechanics approach was used to investigate the fracture behavior of reinforced concrete beams. By use of this approach based on fracture mechanics concepts, the crack width and length as well as the strength and cracking stability of reinforced concrete beams were investigated. The results obtained from the analytical studies were also discussed in terms of the minimum reinforcement ratio and crack width specified in design code provisions. The analytical approach based on fracture mechanics concepts are very useful to predict the fracture behavior of reinforced concrete beams.

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Effect of Loading Rate on the Fracture Behavior of Nuclear Piping Materials Under Cyclic Loading Conditions

  • Kim, Jin Weon;Choi, Myung Rak;Kim, Yun Jae
    • Nuclear Engineering and Technology
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    • v.48 no.6
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    • pp.1376-1386
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    • 2016
  • This study investigated the loading rate effect on the fracture resistance under cyclic loading conditions to understand clearly the fracture behavior of piping materials under seismic conditions. J-R fracture toughness tests were conducted under monotonic and cyclic loading conditions at various displacement rates at room temperature and the operating temperature of nuclear power plants (i.e., $316^{\circ}C$). SA508 Gr.1a low-alloy steel and SA312 TP316 stainless steel piping materials were used for the tests. The fracture resistance under a reversible cyclic load was considerably lower than that under monotonic load regardless of test temperature, material, and loading rate. Under both cyclic and monotonic loading conditions, the fracture behavior of SA312 TP316 stainless steel was independent of the loading rate at both room temperature and $316^{\circ}C$. For SA508 Gr.1a lowalloy steel, the loading rate effect on the fracture behavior was appreciable at $316^{\circ}C$ under cyclic and monotonic loading conditions. However, the loading rate effect diminished when the cyclic load ratio of the load (R) was -1. Thus, it was recognized that the fracture behavior of piping materials, including seismic loading characteristics, can be evaluated when tested under a cyclic load of R = -1 at a quasistatic loading rate.

The Effect of residual stress for fracture behavior in the laser weldment (레이저용접부의 파괴에 미치는 잔류응력의 영향)

  • Jo, Seong-Gyu;Yang, Yeong-Su
    • Proceedings of the Korean Society of Laser Processing Conference
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    • pp.3-8
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    • 2006
  • The integrity of laser welded structures is decided with fracture strength and fatigue strength. This study presents fracture behavior considering residual stress in the laser welding. Experiments are conducted and analyses are performed to explore the influence of residual stress on fracture behavior of bead-on laser welded compact specimen. Fracture experiments are performed using ASTM 1820. The performed analyses included thermo-elasto-plastic analyses for residual stress and subsequent J-integral calculation. A modified J integral is calculated in the presence of residual stresses. The J-integral is path-independent for combination of residual stress field and stress due to mechanical loading. The results indicates that the tensile residual stress near crack front bring the low fracture load while the compressive residual stress bring the high fracture load compared to no residual stress specimen. These results quantitatively understand the influence of residual stress on fracture behavior.

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The Effect of residual stress on fracture behavior in the laser weldment (레이저용접부의 파괴에 미치는 잔류응력의 영향)

  • Cho, Sung-Kyu;Yang, Young-Soo;Noh, Young-Jin
    • Journal of Korean Society of Laser Processing
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    • v.11 no.2
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    • pp.1-7
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    • 2008
  • The integrity of laser welded structures is decided in fracture strength and fatigue strength. This study made an effort to understand the fracture behavior considering residual stress. Experiments are conducted and analyses are performed to explore the influence of residual stress on fracture behavior of bead-on laser welded compact specimen. Fracture experiments are performed using ASTM 1820. The performed analyses included thermo-elasto-plastic analyses for residual stress and subsequent J-integral calculation. A modified J integral is calculated in the presence of residual stresses. The J-integral is path-independent for combination of residual stress field and stress due to mechanical loading. The results indicates that the tensile residual stress near crack front bring the low fracture load while the compressive residual stress bring the high fracture load compared to no residual stress specimen. These results quantitatively understand the influence of residual stress on fracture behavior.

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A Study on the Influence of Fiber Orientation on the Mode I Interlaminar Fracture Behavior of Carbon/Epoxy Composite materials (탄소섬유/에폭시 복합재료의 Mode I 층간파괴거동에 미치는 섬유배향각의 영향에 관한 연구)

  • 이택순;최영근
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.2
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    • pp.391-401
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    • 1995
  • Several tests of the Double Cantilever Beam(DCB) were carried out for influence of the fiber orientation on the Mode I of the interlaminar fracture behavior in the Carbon/Epoxy composites. The interlaminar fracture toughness of Mode I was estimated based on the energy release rate of Mode I, $G_{I}$. The fracture toughness at crack initiation, $G_{IC}$, increases from type A to type E. The fracture toughness, $G_{IR}$ , is almost constant macroscopically for type A and type E when crack propagates. $G_{IR}$ for types B, C, D increases rapidly at the beginning of the crack growth then it decreases gradually. The fracture surface observation by SEM was also obtained the same results. Consequently the influence of the fiber orientation on the Mode I Interlaminar fracture behavior was made clear.ear.

Finite Element Analysis for Fracture Resistance of Fiber-reinforced Asphalt Concrete (유한요소해석을 통한 섬유보강 아스팔트의 파괴거동특성 분석)

  • Baek, Jongeun;Yoo, Pyeong Jun
    • International Journal of Highway Engineering
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    • v.17 no.3
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    • pp.77-83
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    • 2015
  • PURPOSES : In this study, a fracture-based finite element (FE) model is proposed to evaluate the fracture behavior of fiber-reinforced asphalt (FRA) concrete under various interface conditions. METHODS : A fracture-based FE model was developed to simulate a double-edge notched tension (DENT) test. A cohesive zone model (CZM) and linear viscoelastic model were implemented to model the fracture behavior and viscous behavior of the FRA concrete, respectively. Three models were developed to characterize the behavior of interfacial bonding between the fiber reinforcement and surrounding materials. In the first model, the fracture property of the asphalt concrete was modified to study the effect of fiber reinforcement. In the second model, spring elements were used to simulated the fiber reinforcement. In the third method, bar and spring elements, based on a nonlinear bond-slip model, were used to simulate the fiber reinforcement and interfacial bonding conditions. The performance of the FRA in resisting crack development under various interfacial conditions was evaluated. RESULTS : The elastic modulus of the fibers was not sensitive to the behavior of the FRA in the DENT test before crack initiation. After crack development, the fracture resistance of the FRA was found to have enhanced considerably as the elastic modulus of the fibers increased from 450 MPa to 900 MPa. When the adhesion between the fibers and asphalt concrete was sufficiently high, the fiber reinforcement was effective. It means that the interfacial bonding conditions affect the fracture resistance of the FRA significantly. CONCLUSIONS : The bar/spring element models were more effective in representing the local behavior of the fibers and interfacial bonding than the fracture energy approach. The reinforcement effect is more significant after crack initiation, as the fibers can be pulled out sufficiently. Both the elastic modulus of the fiber reinforcement and the interfacial bonding were significant in controlling crack development in the FRA.

Mechanical Behavior and Numerical Estimation of Fracture Resistance of a SCS6 Fiber Reinforced Reaction Bonded Si$_3$N$_4$ Continuous Fiber Ceramic Composite

  • Kwon, Oh-Heon;Michael G. Jenkins
    • Journal of Mechanical Science and Technology
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    • v.16 no.9
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    • pp.1093-1101
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    • 2002
  • Continuous fiber ceramic composites (CFCCs) have advantages over monolithic ceramics : Silicon Nitride composites are not well used for application because of their low fracture toughness and fracture strength, but CFCCs exhibit increased toughness for damage tolerance, and relatively high stiffness in spite of low specific weight. Thus it is important to characterize the fracture resistance and properties of new CFCCs materials. Tensile and flexural tests were carried out for mechanical properties and the fracture resistance behavior of a SCS6 fiber reinforced Si$_3$N$_4$ matrix CFCC was evaluated. The results indicated that CFCC composite exhibit a rising R curve behavior in flexural test. The fracture toughness was about 4.8 MPa$.$m$\^$1/2 , which resulted in a higher value of the fracture toughness because of fiber bridging. Mechanical properties as like the elastic modulus, proportional limit and the ultimate strength in a flexural test are greater than those in a tensile test. Also a numerical modeling of failure process was accomplished for a flexural test. This numerical results provided a good simulation of the cumulative fracture process of the fiber and matrix in CFCCs.

Tensile Behavior and Fracture Properties of Ductile Hybrid FRP Reinforcing Bar for Concrete Reinforcement (콘크리트 보강용 고연성 하이브리드 FRP 보강근의 인장 및 파괴 특성)

  • Park, Chan-Gi;Won, Jong-Pil
    • Journal of The Korean Society of Agricultural Engineers
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    • v.46 no.1
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    • pp.41-51
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    • 2004
  • FRP re-bar in concrete structures could be used as a substitute of steel re-bars for that cases in which aggressive environment produce high steel corrosion, or lightweight is an important design factor, or transportation cost increase significantly with the weight of the materials. But FRP fibers have only linearly elastic stress-strain behavior; whereas, steel re-bar has linear elastic behavior up to the yield point followed by large plastic deformation and strain hardening. Thus, the current FRP re-bars are not suitable concrete reinforcement where a large amount of plastic deformation prior to collapse is required. The main objectives of this study in to evaluate the tensile behavior and the fracture mode of hybrid FRP re-bar. Fracture mode of hybrid FRP re-bar is unique. The only feature common to the failure of the hybrid FRP re-bars and the composite is the random fiber fracture and multilevel fracture of sleeve fibers, and the resin laceration behavior in both the sleeve and the core areas. Also, the result of the tensile and interlaminar shear stress test results of hybrid FRP re-bar can provide its excellent tensile strength-strain and interlaminar stress-strain behavior.