• Title/Summary/Keyword: crack density

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Evolution of dynamic mechanical properties of heated granite subjected to rapid cooling

  • Yin, Tubing;Zhang, Shuaishuai;Li, Xibing;Bai, Lv
    • Geomechanics and Engineering
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    • v.16 no.5
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    • pp.483-493
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    • 2018
  • Experimental study of the deterioration of high-temperature rock subjected to rapid cooling is essential for thermal engineering applications. To evaluate the influence of thermal shock on heated granite with different temperatures, laboratory tests were conducted to record the changes in the physical properties of granite specimens and the dynamic mechanical characteristics of granite after rapid cooling were experimentally investigated by using a split Hopkinson pressure bar (SHPB). The results indicate that there are threshold temperatures ($500-600^{\circ}C$) for variations in density, porosity, and P-wave velocity of granite with increasing treatment temperature. The stress-strain curves of $500-1000^{\circ}C$ show the brittle-plastic transition of tested granite specimens. It was also found that in the temperature range of $200-400^{\circ}C$, the through-cracks induced by rapid cooling have a decisive influence on the failure pattern of rock specimens under dynamic load. Moreover, the increase of crack density due to higher treatment temperature will result in the dilution of thermal shock effect for the rocks at temperatures above $500^{\circ}C$. Eventually, a fitting formula was established to relate the dynamic peak strength of pretreated granite to the crack density, which is the exponential function.

Dynamic behavior of cracked ceramic reinforced aluminum composite beam

  • Selmi, Abdellatif
    • Smart Structures and Systems
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    • v.29 no.3
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    • pp.387-393
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    • 2022
  • This paper presents the vibration analysis of cracked ceramic-reinforced aluminum composite beams by using a method based on changes in modal strain energy. The crack is considered to be straight. The effective properties of composite materials of the beams are estimated through Mori-Tanaka micromechanical model. Comparison study and numerical simulations with various parameters; ceramic volume fraction, reinforcement aspect ratio, ratio of the reinforcement Young's modulus to the matrix Young's modulus and ratio of the reinforcement density to the matrix density are taken into investigation. Results demonstrate the pronounced effects of these parameters on intact and cracked ceramic aluminum beams.

Finite Element Model to Simulate Crack Propagation Using Interface Elements and Its Verification in Tensile Test

  • Chu, Shi;Yu, Luo;Zhen, Chen
    • Journal of Advanced Research in Ocean Engineering
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    • v.1 no.1
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    • pp.36-43
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    • 2015
  • Since the crack generation and its propagation caused by welding defects is one of the main hull damage patterns, the simulation of crack propagation process has an important significance for ship safety. Based on interface element method, a finite element model to simulate crack propagation is studied in the paper. A Lennard-Jones type potential function is employed to define potential energy of the interface element. Tensile tests of steel flat plates with initial central crack are carried out. Surface energy density and spring critical stress that are suitable for the simulation of crack propagation are determined by comparing numerical calculation and tests results. Based on a large number of simulation results, the curve of simulation correction parameter plotted against the crack length is calculated.

A Study on Fatigue Crack Propagation of Rail Steel under Constant and Mixed Mode Variable Amplitude Loadings

  • Kim, Chul-Su;Chung, Kwang-Woo
    • International Journal of Railway
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    • v.5 no.2
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    • pp.71-76
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    • 2012
  • Recently, axle load, operating speed and traffic density on railroads have had a tendency to increase and thereby cause additional pressure applied on used track. These operating conditions frequently result in service failure due to wear caused by wheel-rail contact and fatigue damage under cyclic loading. Among rail defects, the transverse crack, which has been the most dangerous type of fatigue damages, is developed from the subsurface crack near the rail running face and grows perpendicular to the rail surface. Therefore, it is necessary to investigate systematically the growth behavior of transverse crack for rail steel under mixed mode. In this study, the fatigue crack growth behavior of the transverse crack in rail steel was experimentally investigated under mixed-mode variable amplitude loadings.

The Effect of the DIC Speckle Patterns for a Microcrack Measurement (미소균열 측정에 대한 DIC 스펙클 형상의 영향)

  • Lee, Jun Hyuk;Kwon, Oh Heon
    • Journal of the Korean Society of Safety
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    • v.34 no.4
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    • pp.15-21
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    • 2019
  • In order to secure the safety of various machinery, it is very important to develop a technique for accurately and quickly measuring the cracks generated in the mechanical equipment and evaluating the mechanical characteristics. The evaluation of the mechanical properties is accompanied by an appropriate strain measurement according to the material and crack occurrence of the target structure. Especially, when micro cracks are generated, the evaluation method is very important. Digital image correlation is an optical full field displacement measuring method which is using currently with speckles in the interested area. However the evaluation method and conditions of image distributions have to be considered carefully to measure the crack occurrence because the images of the speckle patterns affect the quality of displacement results. In this study, the speckle pattern density is characterized to improve the accuracy of the measurement method. And also the micro crack initiation is detected by the measured displacement in the adopted speckle pattern distribution. It is shown that the proposed method is useful to determine the density pattern distribution for the accurate measurement and crack detection.

The growth and defects of GaN film by hydride vapor phase epitaxy (HVPE GaN film의 성장과 결함)

  • 이성국;박성수;한재용
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.9 no.2
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    • pp.168-172
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    • 1999
  • The 9 $\mu\textrm{m}$ GaN films on sapphire substrate were grown by Hydride vapor phase epitaxy. Dislocation density of these GaN films was measured by TEM. GaN film with crack free and mirror surface was directly grown on sapphire substrate. The dislocation density of this GaN film was $2{\times}10^9/cm^2$. The surface of GaN film on patterned GaN layer also presented a smooth mirror. But a part of GaN surface included holes because of incomplete coalescence. The dislocation density of GaN film above the mask region was lower than that in the window region. Especially, the dislocation density in the region between mask center and window region was close to dislocation free. The average dislocation density of ELO GaN was $8{\times}10^7/cm^2$.

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Variations of the stress intensity factors for a planar crack parallel to a bimaterial interface

  • Xu, Chunhui;Qin, Taiyan;Yuan, Li;Noda, Nao-Aki
    • Structural Engineering and Mechanics
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    • v.30 no.3
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    • pp.317-330
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    • 2008
  • Stress intensity factors for a planar crack parallel to a bimaterial interface are considered. The formulation leads to a system of hypersingular integral equations whose unknowns are three modes of crack opening displacements. In the numerical analysis, the unknown displacement discontinuities are approximated by the products of the fundamental density functions and polynomials. The numerical results show that the present method yields smooth variations of stress intensity factors along the crack front accurately. The mixed mode stress intensity factors are indicated in tables and figures with varying the shape of crack, distance from the interface, and elastic constants. It is found that the maximum stress intensity factors normalized by root area are always insensitive to the crack aspect ratio. They are given in a form of formula useful for engineering applications.

A Study on the Dynamic Behavior of a Simply Supported Beam with Moving Masses and Cracks (이동질량과 크랙을 가진 단순지지 보의 동특성에 관한 연구)

  • 윤한익;손인수;조정래
    • Journal of Ocean Engineering and Technology
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    • v.17 no.6
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    • pp.47-52
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    • 2003
  • To determine the effect of transverse open crack on the dynamic behavior of simply-supported Euler-Bernoulli beam with the moving masses, an iterative modal analysis approach is developed. The influence of depth and position of the crack in the beam, on the dynamic behavior of the simply supported beam system, have been studied by numerical method. The cracked section is represented by a local flexibility matrix, connecting two undamaged beam segments that is, the crack is modeled as a rotational spring. This flexibility matrix defines the relationship between the displacements and forces across the crack section, and is derived by applying a fundamental fracture mechanics theory. As the depth of the crack is increased, the mid-span deflection of the simply-supported beam, with the moving mass, is increased. The crack is positioned in the middle point of the pipe, and the mid-span defection of the simply-supported pipe represents maximum deflection.

A Model for Degradation of $\beta$-$Al_2O_3$ Solid Electrolyte ($\beta$-$Al_2O_3$ 고체전해질의 퇴화모델)

  • 송효일;김응수;윤기현
    • Journal of the Korean Ceramic Society
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    • v.22 no.5
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    • pp.23-28
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    • 1985
  • A model for degradation of $eta$-$Al_2O_3$ is derived from sress generated by Poiseuille pressure capillary effect and effulent flux in charging process of Na-S Battery. Critical current density for degradation increase with increasing the crack length and crack tip radius. radius 10-7cm and crack length 10-5cm Dependence of crack growth velocity on crack lengh is seperated two regions that is for a large crack length it is predominated by Poiseuille pressure and effulent fluex but in the case of small crack length it is controlled by capillary effect.

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Determination of $k_1$in Elliptic Crack under General Ioading Conditions (타원균열에 작용하는 일반적인 하중에서의 응력확대계수 계산)

  • An, Deuk-Man
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.2
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    • pp.232-244
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    • 1997
  • In this paper weight function theory is extended to the determination of the stress intensity factors for the mode I in elliptic crack. For the calculation of the fundamental fields Poisson's theorem and Ferrers's method were employed. Fundamental fields are constructed by single layer potentials with surface density of crack harmonic fundamental polynimials. Crack harmonic fundamental polynimials up to order four were given explicitly. As an example of the application of the weight function theory the stress intensity factors along crack tips in nearly penny-shaped elliptic crack are calculated.