• Journal of the Korean Society for Precision Engineering
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• v.27 no.9
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• pp.52-57
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• 2010

The analysis of a crack in a bone-like material is performed numerically. The bone-like material is hierarchically structured and each hierarchy is structured by mineral platelets and protein matrix through staggered arrangement. Mechanical behavior of the composite can be analyzed using tension shear chain model. The Dugdale model is adopted to evaluate the fracture energy of Bone-like material. The fracture energy dissipation is assumed to concentrate within a strip near the crack tip along the prospective crack path. Fracture criterion of the bone-like material is estimated by using J integral. Effects of hierarchical level, ratio of elastic modulus of mineral to protein, aspect ratio of mineral platelet and volume fraction on J integral are investigated. It is found that the J integral decreases as elastic modulus ratio and hierarchy level increase. It is also shown that the J integral increases as the volume fraction and aspect ratio decrease.

• Magazine of the Korea Concrete Institute
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• v.8 no.3
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• pp.167-175
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• 1996

Recently, the mortar crack on floor is very serious in construction field, e.g. the crack due to plastic shrinkage and the crack due to drying shrinkage. To prevent this kind of crack, optimum mix proportions not only satisfying the required workability but also minimizing the unit water content were selected. And the expansion admixtures were used to compensate shrmkage of mortar. The water /cement ratio used in construction field is about 64% by the investigation. Even if the water /cement ratio of mortar is reduced, floor mortar is still able to have the required workability by the appropriate use of the fine aggregate with high fineness mo'dulus and superplastizer. The equations hetween mortar flow and water /cement ratio, sand /cement ratio, fineness modulus of fine aggregate were proposed in this study. And the proposed equation may provide available mix proportions of floor mortar.

• Steel and Composite Structures
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• v.48 no.4
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• pp.385-403
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• 2023

To avoid premature damage to the connection joints of a conventional precast concrete shear wall, a new precast concrete shear wall system (NPSW) based on a plastic damage relocation design concept was proposed. Five specimens, including one monolithic cast-in-place concrete shear wall (MSW) as a reference and four NPSWs with different connection details (TNPSW, INPSW, HNPSW, and TNPSW-N), were designed and tested by lateral low-cyclic loading. To accurately assess the damage relocation effect and quantify the damage and deformation, digital image correlation (DIC) and conventional data acquisition methods were used in the experimental program. The concrete cracking development, crack area ratio, maximum residual crack width, curvature of the wall panel, lateral displacement, and deformed shapes of the specimens were investigated. The results showed that the plastic damage relocation design concept was effective; the initial cracking occurred at the bottom of the precast shear wall panel (middle section) of the proposed NPSWs. The test results indicated that the crack area ratio and the maximum residual crack width of the NPSWs were less than those of the MSW. The NPSWs were deformed continuously; significant distortions did not occur in their connection regions, demonstrating the merits of the proposed NPSWs. The curvatures of the middle sections of the NPSWs were lower than that of the MSW after a drift ratio of 0.5%. Among the NPSWs, HNPSW demonstrated the best performance, as its crack area ratio, concrete damage, and maximum residual crack width were the lowest.

• Nuclear Engineering and Technology
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• v.39 no.1
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• pp.75-84
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• 2007

This paper presents a closed-form model for evaluating the restraint effect of pressure induced bending on the opening of a circumferential through-wall crack, which is considered plastic deformation behavior. Three-dimensional finite element analyses with different crack lengths, restraint conditions, pipe geometries, magnitudes of internal pressure, and tensile properties were used to investigate the influence of each parameter on the pressure-induced bending restraint on the crack opening displacement. From these investigations, an analytical model based on elastic-perfectly plastic material was developed in terms of the crack length, symmetric restraint length, mean radius to thickness ratio, axial stress corresponding to the internal pressure, and normalized crack opening displacement evaluated from a linear-elastic crack opening condition. Finite element analyses results demonstrate that the proposed analytical model reliably estimated the restraint effect of pressure-induced bending on the plastic crack opening of a circumferential through-wall crack and properly reflected the dependence on each parameter within the range over which the analytical expression was derived.

• Proceedings of the Safety Management and Science Conference
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• 2001.05a
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• pp.179-184
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• 2001

The objective of this work is to develop the capability to analyze accurately the mixed-mode propagation of a crack in composite structures with elastic orthotropic material stiffness properties and anisotropic material strength characteristics. We employ the normal stress ratio theory to predict the direction of crack extension. It is shown that the angle of crack extension can be altered by the use of second order term in the series expansion is important for the accurate determination of crack growth direction.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.99-104
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• 2000

In this paper, the crack properties fiber reinforced concrete(SFRC) beams by experimental method is discussed. The major role played by the steel fiber occurs in the post-cracking zone, in which the fibers bridge across the cracked matrix. Because of its improved ability to bridging cracks, SFRC has better crack properties than that of reinforced concrete(RC). Crack properties are influenced by longitudinal reinforcement ratio, volume and type of steel fibers, strength of concrete and the stress level. Crack width and number of cracks in SFRC beams have been evaluated from experimental test data at various levels of stress for the tested beams.

• Journal of Ocean Engineering and Technology
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• v.13 no.3 s.33
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• pp.108-113
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• 1999

In this study, CT specimens were prepared from ASTM A516 Gr. 65 which was used for pressure vessel plates for moderate and lower temperature service. Fatigue crack growth test was carried out in the environment of low temperature of $10^{circ}C, -10^{circ}C, -30${circ}C\;and\;-50^{circ}C$ and in the range of stress ratio of R=0.05 and 0.3 by means of opening mode displacement. Based on these test results, the characteristics from temperature and stress ration were shown as follows. 1) As the stress ratio, R increased da/dN and ${Delta}K$ of 2nd stage gradually decreased. And as R decreased, the effect of temperature became greater and greater. 2) As the temperature descended, da/dN decreased on a certain ${Delta}K$, and ${Delta}K$ did in a same da/dN. And the stress ratio, R exerted greater influence at the lower temperature. 3) The fatigue crack growth constant, m increased at $10^{circ}C$ and $-10^{circ}C$, snd decreased at $-30^{circ}C$ and $-50^{circ}C$ following the increment of stress ratio R. And m increased along with the reduction of temperature greatly decreased at $-30^{circ}C$ to come close to two(2).

• Journal of Biosystems Engineering
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• v.34 no.5
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• pp.351-357
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• 2009

This study was conducted to verify the simulation model through the drying test, and investigate effect of factors, such as temperature of drying air, airflow rate, and velocity of the airflow, on the drying. The low temperature drying simulation model was developed based on the circulation dry simulation model presented by Keum et al. (1987), and by modifying low temperature thin layer drying model, equilibrium moisture content model, latent heat of vaporization model, and crack ratio prediction model. The heat pump and experimental dryer with a capacity of 150kg were used for the test. The RMSE between the predicted and measured value was 0.27% (drying temperature), 0.15% (crack ratio), and 2.08% (relative humidity), so the relevance of the model was verified. In addition, the effect of drying temperature, airflow rate, and velocity of the airflow on the drying was examined. The experimental results showed that the crack ratio at drying temperature of $25{\sim}40^{\circ}C$ was allowable. Moreover, at below $30^{\circ}C$, variation of the crack ratio was slight, but drying time was delayed. Given these results, the drying temperature of over $30^{\circ}C$ was effective. As the airflow rate increased, required energy dramatically increased. Whereas drying rate slowly increased, so loss of drying efficiency was caused. Considering these results, the dryer needed to be designed and adjusted to lower than $30\;m^3/min{\cdot}ton$. As velocity of the airflow increased, required drying energy increased when the velocity of the airflow was over $5\;m^3$/hr, while crack ratio and drying rate showed little variation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.3
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• pp.548-554
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• 1994

The high temperature fatigue crack growth behavior of SUS 304 stainless steel at $550^{\circ}C$ and $650^{\circ}C$ was investigated under various kinds of stress ratio and frequency in sinusoidal waveform on the basis of the non-linear fracture mechanics. The result arranging crack growth rate by modified J-integral J' showed influence of stress ratio and frequency. All the data obtained under the test at $550^{\circ}C$ were plotted within data band of da/dN-${\triangle}J_f$ relationship for cycle-dependent crack growth. On the basis of static creep and cycle-dependent data band; both time- and cycle-dependent crack growth behavior was observed under loading conditions at $650^{\circ}C$, but cycle-dependent crack growth behavior predominantly appeared and time-dependent crack growth behaviour was little observed under loading conditions at $550^{\circ}C$. Fractographic examinations for fracture surface indicated that the fracture mode was generally transgranular. The stripes were found on fracture surface and each stripe was accompanied by a crack tip blunting and an abrupt increase in the load-point displacement. The $J'_{an}$ had a validity in case of $650^{\circ}C, but scarcely had it in case of $550^{\circ}C$.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.10a
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• pp.240-245
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• 2000

Fatigue crack propagation rates and characteristics of the SA516-60 steel which is used for the low temperature pressure vessels, were studied in the room temperature of $25^{\circ}C$ and low temperature ranges of $10^{\circ}C,\; -10^{\circ}C,\; -30^{\circ}C,\; -50^{\circ}C, \;and\; -70^{\circ}C4 with stress ratio of R=0.05. The obtained experimental results are as follows; 1) In the logarithmic relationship between the fatigue crack propagation rate(da/dN) and stress intensity factor K, the linear relationship was obtained up to da/dN 〉$8\times10^{-3}$/mm/cycle in the same of room temperature, but in low temperature case, the relationship was extended to the range of crack propagation rate. 2) The lower limit stress intensity factor of SA516-60 $\DeltaK_{th}$ was 15.8MPa and in the case of low temperature $-50^{\circ}C\; and\; -70^{\circ}C$, the crack propagation rate da/dN which showed a linear relation, reached rapidly to the $\DeltaK_{th}$/. As the results, the crack propagation rates of $-50^{\circ}C\; and\; -70^{\circ}C$ were lower than that of room temperature and according to the testing temperature the rates were decreased rapidly to the $\DeltaK_{th}$/. 3) On the relationship between the stress intensity factor $\DeltaK$ and the crack propagation cycle, the stress intensity factors of low cycle region was rapidly increased at low temperature, but $\DeltaK$ was increased rapidly at room temperature of high cycle. 4) On the relationship between the fatigue crack propagation rate and cycle, the fatigue crack propagation rate showed higher gradient in the room temperature than the low temperature due to the increment in ductility at low temperature.