• Title/Summary/Keyword: fracture zone

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Acoustic Emission during Crack Propagation Process of Rubber-Modified Epoxy Resin (고무변성 에폭시 수지의 균열진전과정과 음향방출 특성)

  • 이덕보;김현수;최낙삼;남기우;문창권
    • Composites Research
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    • v.16 no.4
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    • pp.44-50
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    • 2003
  • The damage zone around a crack tip occurring before the fracture is a significant domain. which affects the toughening mechanism of materials. In this study. the growth process of damage zone in the vicinity of crack tip for rubber-modified epoxy resin is investigated using an acoustic emission(AE) analysis. The weight fractions of rubber(CTBN 1300$\times$B) in rubber-modified epoxy resin are 5 wt% and 15 wt%. The fracture toughness($K_{IC}$) and the fracture energy($G_{IC}$) were measured using 3 point bending single-edge notched specimens. The damage zone and rubber particles distributed around the crack tip were observed by a polarized optical microscope and an atomic force microscope(AFM). The damage zone around crack tip of rubber-modified epoxy resin was formed at 13 % loading and developed until 57 % loading of the fracture load. The crack initiated at 57 % loading grew repeatedly in the stick-slip propagation behavior. Based on time-frequency analysis, it was confirmed that AE signals with frequency bands of 0.15~0.20 MHz and 0.20~0.30 MHz were generated from cavitation and stable/unstable cracking inside the damage zone.

An efficient algorithm for scaling problem of notched beam specimens with various notch to depth ratios

  • Karamloo, Mohammad;Mazloom, Moosa
    • Computers and Concrete
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    • v.22 no.1
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    • pp.39-51
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    • 2018
  • This study introduces a new algorithm to determine size independent values of fracture energy, fracture toughness, and fracture process zone length in three-point bending specimens with shallow to deep notches. By using the exact beam theory, a concept of equivalent notch length is introduced for specimens with no notches in order to predict the peak loads with acceptable precisions. Moreover, the method considers the variations of fracture process zone length and effects of higher order terms of stress field in each specimen size. In this paper, it was demonstrated that the use of some recently developed size effect laws raises some concerns due to the use of nonlinear regression analysis. By using a comprehensive fracture test data, provided by Hoover and Bazant, the algorithm has been assessed. It could be concluded that the proposed algorithm can facilitate a powerful tool for size effect study of three-point bending specimens with different notch lengths.

An experimental study on the fracture of Nd:YAG laser welded amorphous foils (Nd:YAG 레이저를 이용한 비정질 박판 용접부의 파괴에 대한 실험적 연구)

  • 이건상
    • Laser Solutions
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    • v.3 no.3
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    • pp.31-37
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    • 2000
  • In this paper, the possibilities of the laser overlap spot welding were studied to utilize the advantageous properties of amorphous metal foils. In order to estimate the usage of amorphous metals foils as structural members, the tensile shear strength and the fracture features were investigated. Although the crystalline zone on the surface was formed, it was not the direct cause of the fracture of the weld. The fracture of the weld resulted from the geometry discontinuity between the workpiece and the protrusion zone, which was formed during the weld process. The vein pattern - the typical feature of the fracture of the amorphous metal - was formed on the fracture surface. The tensile shear stress was reached to 1200 N/㎟ (2-foils overlap welding) and 900 N/㎟ (10-foils overlap welding), whereas the tensile strength of the workpiece was 1500-2000 N/㎟.

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Crack Analysis of Concrete Gravity Dam Using Surface Integral Method (표면적분법을 이용한 콘크리트 댐의 균열 해석)

  • 진치섭;이영호;손기석
    • Journal of the Korea Concrete Institute
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    • v.12 no.3
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    • pp.31-37
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    • 2000
  • When a crack is produced in a concrete structure, a micro crack zone of fracture process zone (FPZ) appears at the crack tip. To investigate the behaviour of this the micro crack zone, nonlinear fracture mechanics (NLFM) must be applied. However, when a massive concrete structure such as a concrete gravity dam is considered, the micro crack zone can be neglected and the structure can be assumed to have linear elastic fracture mechanics (LEFM) behaviour. This study is divided into two main topics : (1) Calculating stress intensity factor (SIF) at the crack tip by surface integral method and (2) Investigating the propagation of the initial crack. If the initial crack propagates, the angle of the propagation is calculated by using maximum circumferential tensile strength theory. This study, also, contains the effects of body forces and water pressures on the crack face.

Effect of initial coating crack on the mechanical performance of surface-coated zircaloy cladding

  • Xu, Ze;Liu, Yulan;Wang, Biao
    • Nuclear Engineering and Technology
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    • v.53 no.4
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    • pp.1250-1258
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    • 2021
  • In this paper, the mechanical performance of cracked surface-coated Zircaloy cladding, which has different coating materials, coating thicknesses and initial crack lengths, has been investigated. By analyzing the stress field near the crack tip, the safety zone range of initial crack length has been decided. In order to determine whether the crack can propagate along the radial (r) or axial (z) directions, the energy release rate has been calculated. By comparing the energy release rate with fracture toughness of materials, we can divide the initial crack lengths into three zones: safety zone, discussion zone and danger zone. The results show that Cr is suitable coating material for the cladding with a thin coating while Fe-Cr-Al have a better fracture mechanical performance in the cladding with thick coating. The Si-coated and SiC-coated claddings are suitable for reactors with low power fuel elements. Conclusions in this paper can provide reference and guidance for the cladding design of nuclear fuel elements.

A Modeling Study on the AVO and Complex Trace Analyses of the Fracture Bone Reflection (파쇄대 반사에너지의 AVO 및 복소트레이스 분석에 관한 모형연구)

  • Han Soo-Hyung;Kim Ji-Soo;Ha Hee-Sang;Min Dong-Joo
    • Geophysics and Geophysical Exploration
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    • v.2 no.1
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    • pp.33-42
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    • 1999
  • AVO and complex trace analyses mainly used to characterize natural gas reservoir were tested in this paper for a possible application to detection of major geological discontinuities such as fracture zones. The test data used in this study were calculated by utilizing a viscoelastic numerical program which was based on the generalized Maxwell body for a horizontal fracture model. In AVO analysis of a horizontal fracture zone, p-wave reflection appears to be variant depending upon the acoustic-impedence contrast and the offset distance. The fracture zone is also effectively clarified both in gradient stack and range-limited stack in which fracture zone reflection is attenuated with the increasing offset distance. In complex attribute plots (instantaneous amplitude, frequency, and phase), the top and bottom of the fracture Tone are characterized by a zone of strong amplitudes and an event of the same phase. Low frequency characteristics appear at the fracture zone and the underneath. Amplitude attenuation and waveform dispersion are dependent on Q-contrast between the fracture zone and the surrounding media. They were properly compensated by optimum inverse Q-filtering.

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Change in Fracture Toughness within Heat-Affected Zone of SA-Welded 9% Ni Steel (LNG 저장탱크 내조용 9% Ni강의 SAW 용접열영향부내 파괴인성 변화 평가)

  • Jang, Jae-Il;Lee, Jeong-Seok;Lee, Baek-U;Ju, Jang-Bok;Gwon, Dong-Il;Kim, U-Sik
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.3
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    • pp.528-536
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    • 2002
  • As one step for the safety performance of LNG storage tank, the change in fracture toughness within the X-grooved weld heat-affected zone (HAZ) of newly developed 9% Ni steel, which was submerged arc (SA)-welded, was investigated. Both crack initiation fracture toughness and crack arrest fracture toughness were evaluated by the crack tip opening displacement (CTOD) tests and compact crack arrest (CCA) tests. As the evaluated region approached the fusion line, each test result shorted different tendency, that is, crack initiation toughness decreased while crack arrest toughness increased. The results were discussed through the observation of the microstructural change.

Fracture properties and crack tip constraint quantification of 321/690 dissimilar metal girth welded joints by using miniature SENB specimens

  • Bao, Chen;Sun, Yongduo;Wu, Yuanjun;Wang, Kaiqing;Wang, Li;He, Guangwei
    • Nuclear Engineering and Technology
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    • v.53 no.6
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    • pp.1924-1930
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    • 2021
  • By using miniature SENB specimens, the fracture properties of the materials in the region of welded metal, 321 stainless steel heat affected zone, 690 alloy heat affected zone of 321/690 dissimilar metal girth welded joints were tested. Both the J-resistance curves and critical fracture toughness of the three different materials are affected by the crack size because of the effect of crack tip constraint. Groups of constraint corrected J-resistance curves of the three materials are obtained according to J-Q-M approach. The welded metals exhibit the best fracture resistance but the worst fracture resistance is observed in the material of 690 alloy heat affected zone.

Effects of Crack Velocity on Fracture Properties of Modified S-FPZ Model (수정 특이-파괴진행대이론의 파괴특성에 대한 균열속도의 영향)

  • Yon Jung-Heum
    • Journal of the Korea Concrete Institute
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    • v.16 no.4 s.82
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    • pp.511-520
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    • 2004
  • The fracture energy evaluated from the previous experimental results can be simulated by using the modified singular fracture process zone (S-FPZ) model. The fracture model has two fracture properties of strain energy release rate for crack extension and crack close stress versus crack width relationship $f_{ccs}$ ( w ) for fracture process zone (FPZ) development. The $f_{ccs}$( w ) relationship is not sensitive to specimen geometry and crack velocity. The fracture energy rate in the FPZ increases linearly with crack extension until the FPZ is fully developed. The fracture criterion of the strain energy release rate depends on specimen geometry and crack velocity as a function of crack extension. The variation of strain energy release rate with crack extension can explain theoretically the micro-cracking, micro-crack localization and full development of the FPZ in concrete.

A Study on Fracture Behavior in Shear Band during Micro Hole Punching Process (미세 홀 펀칭시 전단 파괴 거동 연구)

  • 유준환;임성한;주병윤;오수익
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2003.05a
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    • pp.230-235
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    • 2003
  • In the micro hole punching, the size and shape of burr and burnish zone are very important factors to evaluate quality of micro holes which depend on punch-die clearance, stain rate, workpiece material and etc. To get micro holes with small burr and wide burnish zone for industrial demands, not only the parametric study but also a study on fracture behavior in shear band are necessary. In this study, 100 $\mu\textrm{m}$, 25 $\mu\textrm{m}$ micro holes in diameter were fabricated on brass (Cu63/Zn37) and SUS 316 foils as aspect ratio 1:1, and the characteristics of micro holes was investigated comparing with man holes over several mm by scanning electron microscopic views and section views. Like macro hole, micro hole is also composed of 4 portions, rollover, burnish zone, fracture zone and it shows similar fracture behavior in shear band, but? by high strain rate (10$^2$∼ 10$^3$s$\^$-1/) unlike macro hole fabrication and increment of relative grain size several different results are shown.

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