• Title/Summary/Keyword: Dynamic Fracture Mechanics

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Peridynamic analysis of dynamic fracture behaviors in FGMs with different gradient directions

  • Kou, Miaomiao;Bi, Jing;Yuan, Binhang;Wang, Yunteng
    • Structural Engineering and Mechanics
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    • v.75 no.3
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    • pp.339-356
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    • 2020
  • In this article, a developed bond-based peridynamic model for functionally graded materials (FGMs) is proposed to simulate the dynamic fracture behaviors in FGMs. In the developed bond-based peridynamic model for FGMs, bonds are categorized into three different types, including transverse directionally peridynamic bond, gradient directionally peridynamic bond and arbitrary directionally peridynamic bond, according to the geometrical relationship between directions of peridynamic bonds and gradient bonds in FGMs. The peridynamic micromodulus in the gradient directionally and arbitrary directionally peridynamic bonds can be determined using the weighted projection method. Firstly, the standard bond-based peridynamic simulations of crack propagation and branching in the homogeneous PMMA plate are performed for validations, and the results are in good agreement with the previous experimental observations and the previous phase-field numerical results. Then, the numerical study of crack initiation, propagation and branching in FGMs are conducted using the developed bond-based peridynamic model, and the influence of gradient direction on the dynamic fracture behaviors, such as crack patterns and crack tip propagation speed, in FGMs is systematically studied. Finally, numerical results reveal that crack branching in FGMs under dynamic loading conditions is easier to occur as the gradient angle decreases, which is measured by the gradient direction and direction of the initial crack.

A mathematical model to predict fatigue notch factor of butt joints

  • Nguyen, Ninh T.;Wahab, M.A.
    • Structural Engineering and Mechanics
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    • v.6 no.4
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    • pp.467-471
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    • 1998
  • A mathematical model is developed to predict the fatigue notch factor of butt welds subject to number of parameters such as weld geometry, residual stresses under dynamic combined loading conditions (tensile and bending). Linear elastic fracture mechanics, finite element analysis, dimensional analysis and superposition approaches are used for the modelling. The predicted results are in good agreement with the available experimental data. As a result, scatters of the fatigue data can be significantly reduced by plotting S-N curve as ($S{\cdot}K_f$) vs. N.

Dynamic Behaviors of Metal Matrix Composites in Low Velocity Impact (저속 충격하에서의 금속복합재료의 동적 특성)

  • ;Gamal A. Aggag;K.Takahashi
    • Composites Research
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    • v.12 no.1
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    • pp.68-75
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    • 1999
  • This study has observed that the dynamic behavior of Metal Matrix Composites (MMCs) in low velocity impact varies with impact velocity. MMCs with 15 fiber volume percent were fabricated by using the squeeze casting method. The AC8A was used as the matrix, and the alumina and the carbon were used as reinforcements. The tensile and vibration tests conducted yielded the yielded the tensile stress and elastic modulus of MMCs The low pass filter and instrumented impact test machine was adopted to study dynamic behaviors of MMCs corresponding to impact velocity. Stable impact signals were obtained by using the low pass filter. Impact corresponding to impact velocity. Stable impact signals were obtained by using the low pass filter. Impact energy of unreinforced alloy and MM s increased as the impact velocity increased. The increase of crack propagation energy was especially prominent, but the dynamic toughness of each material did not change much. To show the relation between crack initiation energy and dynamic fracture toughness, a simple model was proposed by using the strain energy and stress distribution at notch. The model revealed that crack initiation energy is proportional to the square of dynamic fracture toughness and inversely proportional to elastic modulus.

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Study on failure behaviors of mixed-mode cracks under static and dynamic loads

  • Zhou, Lei;Chen, Jianxing;Zhou, Changlin;Zhu, Zheming;Dong, Yuqing;Wang, Hanbing
    • Geomechanics and Engineering
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    • v.29 no.5
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    • pp.567-582
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    • 2022
  • In the present study, a series of physical experiments and numerical simulations were conducted to investigate the effects of mode I and mixed-mode I/II cracks on the fracture modes and stability of roadway tunnel models. The experiments and simulations incorporated different inclination angle flaws under both static and dynamic loads. The quasi-static and dynamic testing were conducted by using an electro-hydraulic servo control device and drop weight impact system (DWIS), and the failure process was simulated by using rock failure process analysis (RFPA) and AUTODYN software. The stress intensity factor was also calculated to evaluate the stability of the flawed roadway tunnel models by using ABAQUS software. According to comparisons between the test and numerical results, it is observed that for flawed roadways with a single radical crack and inclination angle of 45°, the static and dynamic stability are the lowest relative to other angles of fractured rock masses. For mixed-mode I/II cracks in flawed roadway tunnel models under dynamic loading, a wing crack is produced and the pre-existing cracks increase the stress concentration factor in the right part of the specimen, but this factor will not be larger than the maximum principal stress region in the roadway tunnel models. Additionally, damage to the sidewalls will be involved in the flawed roadway tunnel models under static loads.

Modeling concrete fracturing using a hybrid finite-discrete element method

  • Elmo, Davide;Mitelman, Amichai
    • Computers and Concrete
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    • v.27 no.4
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    • pp.297-304
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    • 2021
  • The hybrid Finite-Discrete Element (FDEM) approach combines aspects of both finite elements and discrete elements with fracture mechanics principles, and therefore it is well suited for realistic simulation of quasi-brittle materials. Notwithstanding, in the literature its application for the analysis of concrete is rather limited. In this paper, the proprietary FDEM code ELFEN is used to model concrete specimens under uniaxial compression and indirect tension (Brazilian tests) of different sizes. The results show that phenomena such as size effect and influence of strain-rate are captured using this modeling technique. In addition, a preliminary model of a slab subjected to dynamic shear punching due to progressive collapse is presented. The resulting fracturing pattern of the impacted slab is similar to observations from actual collapse.

Influence of Rock Inhomogeneity on the Dynamic Tensile Strength of Rock (암석의 동적 인장강도에 미치는 불균질성의 영향)

  • Cho, Sang-Ho;Yang, Hyung-Sik;Katsuhiko Kaneko
    • Tunnel and Underground Space
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    • v.13 no.3
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    • pp.180-186
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    • 2003
  • The fracture processes under dynamic loading in tension were simulated using a proposed numerical approach and analyzed to determine dynamic tensile strength. The dynamic tensile strength and the scatter of the strength data decreased with increasing uniformity coefficients. The differences of static and dynamic tensile strength were due to the stress concentrations and redistribution mechanisms in the rock specimen. Although there were different mechanisms for the static and dynamic fracture processes, the static and dynamic tensile strengths were close to the mean microscopic tensile strength at high values of the uniformity coefficient. This paper shows that the rock inhomogeneity has an effect on dynamic tensile strength and is a factor that contributes to the different specimen strengths under dynamic and static loading conditions.

Influence of the Initiation Error of the Delay Detonator on the Rock Fracture Process in Smooth Blasting (SB발파에서 지발뇌관의 기폭초시오차가 암반파괴과정에 미치는 영향)

  • 조상호;양형식;금자승비고
    • Tunnel and Underground Space
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    • v.14 no.2
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    • pp.121-132
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    • 2004
  • Dynamic fracture processes of rock were analyzed to investigate the influence of the initiation error of the delay detonator in smooth blasting. The analysis models for the smooth blasting considered two blast geometries with three charge holes, and the simultaneous initiations without initiation error, with the initiation error of electronic delay detonator and with the initiation error of pyrotechnically delay detonator(DS detonator) were applied to the charge holes. In order to examine the effect of electronic and DS initiation detonator on the smooth blasting, the fracture process results were analyzed statistically.

Development of Dynamic Photoelastic Experimental Hybrid Method for Propagating Cracks in Orthotropic Material (직교이방성체내의 진전 균열에 대한 동적 광탄성 실험 Hybrid 법 개발)

  • Shin, Dong-Chul;Hawong, Jai-Sug;Sung, Jong-Hyun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.8
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    • pp.1273-1280
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    • 2003
  • In this paper, transparent dynamic photoelastic experimental hybrid method for propagating cracks in orthotropic material was developed. Using transparent dynamic photoelastic experimental hybrid method, we can obtain stress intensity factor and separate the stress components from only isochromatic fringe patterns without using isoclinics. When crack is propagated with constant velocity, the contours of stress components in the vicinity of crack tip in orthotropic material are similar to those of isotropic material or orthotropic material with stationary crack under the static load. Dynamic stress intensity factors are decreased as crack growths. It was certified that the dynamic photoelastic experimental hybrid method was very useful for the analysis of the dynamic fracture mechanics.

Numerical simulation of reinforced concrete nuclear containment under extreme loads

  • Tamayo, Jorge Luis Palomino;Awruch, Armando Miguel
    • Structural Engineering and Mechanics
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    • v.58 no.5
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    • pp.799-823
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    • 2016
  • A finite element model for the non-linear dynamic analysis of a reinforced concrete (RC) containment shell of a nuclear power plant subjected to extreme loads such as impact and earthquake is presented in this work. The impact is modeled by using an uncoupled approach in which a load function is applied at the impact zone. The earthquake load is modeled by prescribing ground accelerations at the base of the structure. The nuclear containment is discretized spatially by using 20-node brick finite elements. The concrete in compression is modeled by using a modified $Dr{\ddot{u}}cker$-Prager elasto-plastic constitutive law where strain rate effects are considered. Cracking of concrete is modeled by using a smeared cracking approach where the tension-stiffening effect is included via a strain-softening rule. A model based on fracture mechanics, using the concept of constant fracture energy release, is used to relate the strain softening effect to the element size in order to guaranty mesh independency in the numerical prediction. The reinforcing bars are represented by incorporated membrane elements with a von Mises elasto-plastic law. Two benchmarks are used to verify the numerical implementation of the present model. Results are presented graphically in terms of displacement histories and cracking patterns. Finally, the influence of the shear transfer model used for cracked concrete as well as the effect due to a base slab incorporation in the numerical modeling are analyzed.

The Effect of Moving Mass on Dynamic Behavior of Cracked Cantilever Beam on Elastic Foundations (탄성기초 위에 놓인 크랙 외팔보의 동특성에 미치는 이동질량의 영향)

  • Ahn, Sung-Jin;Son, In-Soo;Yoon, Han-Ik
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2005.05a
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    • pp.826-831
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    • 2005
  • In this paper the effect of moving mass on dynamic behavior of cracked cantilever beam on elastic foundations is presented. Based on the Euler-Bernoulli beam theory, the equation of motion can be constructed by using the Lagrange's equation. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments. That is, the crack is modelled as a rotational spring. This flexibility matrix defines the relationship between the displacements and forces across the crack section and is derived by applying fundamental fracture mechanics theory. The crack is assumed to be in the first mode of fracture. As the depth of the crack is increased, the tip displacement of the cantilever beam is increased. When the crack depth is constant the frequency of a cracked beam is proportional to the spring stiffness.

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