• Title/Summary/Keyword: tensile damage

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Influence of explosives distribution on coal fragmentation in top-coal caving mining

  • Liu, Fei;Silva, Jhon;Yang, Shengli;Lv, Huayong;Zhang, Jinwang
    • Geomechanics and Engineering
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    • v.18 no.2
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    • pp.111-119
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    • 2019
  • Due to certain geological characteristics (high thickness, rocky properties), some underground coal mines require the use of explosives. This paper explores the effects of fragmentation of different decks detonated simultaneously in a single borehole with the use of numerical analysis. ANSYS/LS-DYNA code was used for the implementation of the models. The models include an erosion criterion to simulate the cracks generated by the explosion. As expected, the near-borehole area was damaged by compression stresses, while far zones and the free surface of the boundary were subjected to tensile damage. With the increase of the number of decks in the borehole, different changes in the fracture pattern were observed, and the superposition effects of the stress wave became evident, affecting the fragmentation results. The superposition effect is more evident in close distances to the borehole, and its effect attenuates when the distance to the borehole increase.

Viscoelastic constitutive modeling of asphalt concrete with growing damage

  • Lee, Hyun-Jong;Kim, Y. Richard;Kim, Sun-Hoon
    • Structural Engineering and Mechanics
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    • v.7 no.2
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    • pp.225-240
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    • 1999
  • This paper presents a mechanistic approach to uniaxial viscoelastic constitutive modeling of asphalt concrete that accounts for damage evolution under cyclic loading conditions. An elasticviscoelastic correspondence principle in terms of pseudo variables is applied to separately evaluate viscoelasticity and time-dependent damage growth in asphalt concrete. The time-dependent damage growth in asphalt concrete is modeled by using a damage parameter based on a generalization of microcrack growth law. Internal state variables that describe the hysteretic behavior of asphalt concrete are determined. A constitutive equation in terms of stress and pseudo strain is first established for controlled-strain mode and then transformed to a controlled-stress constitutive equation by simply replacing physical stress and pseudo strain with pseudo stress and physical strain. Tensile uniaxial fatigue tests are performed under the controlled-strain mode to determine model parameters. The constitutive equations in terms of pseudo strain and pseudo stress satisfactorily predict the constitutive behavior of asphalt concrete all the way up to failure under controlled-strain and -stress modes, respectively.

Damage Detection of Fiber-Metal Laminates Using Optical Fiber Sensors (광섬유 센서를 이용한 섬유-금속 적층판의 손상 감지)

  • 양유창;한경섭
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2002.10a
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    • pp.161-164
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    • 2002
  • Optical fiber vibrations sensors (OFVSs) and extrinsic Fabry-Perot interferometer (EFPI) were used in damage monitoring of fiber-metal laminates(FML). The optical fiber vibration sensor and EFPI were applied in order to detect and evaluate the strain, damage and failure of FML. Damages in composites, such as matrix cracks, delamination and fiber breakage may occur as a result of excessive load, fatigue and low-velocity impacts. Tensile test was performed with the measurement of optical signal and acoustic emission (AE). The signals of the optical fiber vibration sensor due to damages were quantitatively evaluated by wavelet transform. EFPI was less sensible to the damage signals compared with the optical fiber vibration sensor. It was found that damage information of comparable in quality to acoustic emission data could be obtained from the optical fiber vibration sensor signals.

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Prediction of Deformation Mechanism and Fracture for an Auto-Part with Advanced High Strength Steel using Solid Element and Damage Theory (연속체요소 및 손상이론을 이용한 고강도강 차량부품의 변형기구와 파단 예측)

  • Kwak, J.H.;Yoon, S.J.;Kim, S.H.;Park, J.K.;Han, H.G.
    • Transactions of Materials Processing
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    • v.26 no.5
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    • pp.293-299
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    • 2017
  • In this paper, finite element stamping analysis was carried out for the front lower arm to examine the applicability of solid element with damage theory to predict shear fracture phenomena induced by sheared edge as well as deformation mechanisms. Mechanical properties related to deformation and damage theory were determined from tensile test. Shear fracture was predicted by normalized Cockcroft-Latham model with initial imposition of the damage value along the sheared edge. Simulation results illustrated that the analysis with solid element and damage theory predicted edge profile, strain distribution, and forming load more accurately than the analysis with shell element. Simulation with solid element can also predict the shear fracture more exactly comparing to analysis with shell element and forming limit curve.

Hydrolysis of Silk Fibroin with Boiling Water, Hydrochloric Acid, and Sodium Hydroxide -On the Quantitative Change in Terminal Amino Group Content- (견피브로인의 비등수 염산 및 수산화나트륨에 의한 가수분해 -말단아미노기의 정양적변화를 중심으로-)

  • Park Chan Hun;Dho Seong Kook
    • Journal of the Korean Society of Clothing and Textiles
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    • v.11 no.1
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    • pp.63-69
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    • 1987
  • Silk fibroin is likely to be hydrolyzed by acids or alkalies at high temperature, and the degree of the hydrolysis has been inferred from the changes in tensile strength and elongation. But, in this experiment, it was intended to infer that from the quantitative changes in terminal aminp group content as well as in tensile strength and elongation. Silk yarn was treated with boiling water, hydrochloric acid, and sodium hydroxide under various conditions. The boiling water somewhat degraded silk fibroin. Silk yarn treated with sodium hydroxide contained more terminal amino group than that treated with hydrochloric acid. This result agreed fairly well with the loss in weight, tensile strength, and elongation: the terminal amino group content increased with the decrease of tensile strength, elongation, and weight. The damage by sodium hydroxide to the silk fibroin was greater than that by hydrochloric acid.

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Tensile Design Criteria Evaluation of Cast-In-Place Anchor by Numerical Analysis (수치해석에 의한 직매형 앵커기초의 인장 설계기준 평가)

  • 장정범;서용표;이종림
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2004.04a
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    • pp.209-216
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    • 2004
  • Numerical analysis is carried out to identify the appropriateness of the design codes that is available for the tensile design of fastening system at Nuclear Power Plant (NPP) in this study. This study is intended for the cast-in-place anchor that is widely used for the fastening of equipment in Korean NPPs. The microplane model and the elastic-perfectly plastic model are employed for the quasi-brittle material like concrete and for the ductile material like anchor bolt as constitutive model for numerical analysis and smeared crack model is employed for the crack and damage phenomena. The developed numerical model is verified on a basis of the various test data of cast-in-place anchor. The appropriateness of both ACI 349 Code and CCD approach of CEB-FIP Code is evaluated for the tensile design of cast-in-place anchor and it is proved that both design codes give a conservative results compared with real tensile capacity of cast-in-place anchor.

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A tensile criterion to minimize FE mesh-dependency in concrete beams under blast loading

  • Gang, HanGul;Kwak, Hyo-Gyoung
    • Computers and Concrete
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    • v.20 no.1
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    • pp.1-10
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    • 2017
  • This paper focuses on the mesh-size dependency in numerical simulations of reinforced concrete (RC) structures subjected to blast loading. A tensile failure criterion that can minimize the mesh-dependency of simulation results is introduced based on the fracture energy theory. In addition, conventional plasticity based damage models for concrete such as the CSC model and the HJC model, which are widely used for blast analyses of concrete structures, are compared with the orthotropic model that adopts the introduced tensile failure criterion in blast tests to verify the proposed criterion. The numerical predictions of the time-displacement relations at the mid-span of RC beams subjected to blast loading are compared with experimental results. The analytical results show that the numerical error according to the change in the finite element mesh size is substantially reduced and the accuracy of the numerical results is improved by applying a unique failure strain value determined by the proposed criterion.

Evaluation on Corrosion of A106 Carbon Steel using AE Technique (음향방출기법을 이용한 A106 탄소강의 부식평가)

  • Lee, Jin-Kyung;Lee, Sang-Pill
    • Journal of Ocean Engineering and Technology
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    • v.22 no.5
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    • pp.100-105
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    • 2008
  • A106 Carbon Steel has recently been used as the material for pipes, nozzles, and tank shells in nuclear power plants. Its corrosion resistance gives the steel many advantages for use in structures under high temperature and high pressure. This steel is also expected to be used as a structural material in the shipbuilding industry for applications involving severe conditions, such as high temperature and pressure. In this study, the mechanical properties of A106 carbon steel were evaluated in regard to its corrosion times. The tensile and yielding strengths decreased as the corrosion time increased. In particular, the tensile strength was influenced by corrosion. In addition, an acoustic emission (AE) technique was used to clarify the microscopic damage to specimens that had undergone corrosion for a certain period. It was found that AE parameters, such as events, energy, duration time, and amplitude were useful for evaluating the degree of damage and remaining life of the corroded specimen. Various properties of the waveform and frequency range were also seen, based on the degree of damage to the specimen from the corrosion time.

Effects of bleaching time and hydrogen peroxide concentration on hair damage (탈색시간과 과산화수소 농도에 의한 모발의 손상)

  • Kim, Chung-Wun;Chun, Hong-Sung
    • Korean Journal of Human Ecology
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    • v.14 no.3
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    • pp.433-439
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    • 2005
  • In this study, we investigated the morphological and physical changes of hair after bleaching treatments with different concentration of hydrogen peroxide in bleaching agent (3, 6, 9, or 12%) and various treatment time (10, 30, or 60 minutes). Tresses of virgin black hair were bleached using a commercial ammonium persulfate-hydrogen peroxide solution. The tensile strength of virgin hair treated with a bleaching agent depended on the concentration of hydrogen peroxide and the treatment time. As the concentration of hydrogen peroxide in bleaching agent went high and the treatment time increased, the tensile strength of the hair increased but the extension degree decreased. The virgin hairs which were not treated by bleaching agent showed morphologically healthy cuticle, whereas the bleached hairs showed swelled and damaged cuticle patterns. The swelling of the hair and the breaks of the cuticles increased positively by the concentration of hydrogen peroxide and the treatment time. These results suggest that exposure to more concentrated hydrogen peroxide with other bleaching components may lead to more severe hair damage.

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Fracture Toughness Improvement of Graphite/Epoxy Composite by Intermittent Interlaminar Bonding (간헐적인 층간접착 을 이용한 Graphite/Epoxy 복합재료 의 파괴인성 개선)

  • 임승규;홍창선
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.8 no.5
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    • pp.425-434
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    • 1984
  • The concept of intermittent interlaminar bonding is investigated as a means of improving the fracture toughness of cross-ply Gr/Ep composites without significant loss of tensile strength and modulus. The concept of linear elastic fracture mechanics(LEFM)is used to study the effects of strong bonded area and bonding composites. The experimental results indicate that the fracture toughness and notch strength of intermittent interlaminar bonded composities are improved and the tensile strength only decreased by 3-8% in comparison to those of the fully bonded composites. Damage zones around the crack tip are detected by the modified X-Ray non-destructive testing technique and the fractography. The improvement of toughness is explained based on the damage zones. The mechanisms of damage zone are shown to be caused by subcrack along the fiber on the 0.deg. ply, matrix cracking along the fiber on the 90.deg. ply, interlaminar delamination, and ply pull-out of the 0.deg. ply.