• Steel and Composite Structures
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• 제47권1호
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• pp.121-134
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• 2023

This paper tested 11 concrete-encased concrete-filled steel tube (CFST) composite columns and one reinforced concrete column under combined axial compression and lateral loads. The primary parameters, including the loading system, axial compression ratio, volume stirrup ratio, diameter-to-thickness ratio of the steel tube, and stirrup form, were varied. The influence of the parameters on the failure mode, strength, ductility, energy dissipation, strength degradation, and damage evolution of the composite columns were revealed. Moreover, a two-parameter nonlinear seismic damage model for composite columns was established, which can reflect the degree and development process of the seismic damage. In addition, the relationships among the inter-story drift ratio, damage index and seismic performance level of composite columns were established to provide a theoretical basis for seismic performance design and damage assessments.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.155-158
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• 2005

Damage and fracture of concrete is characterized as the degradation of strength and stiffness. There can be modeled as the so-called homogenized crack model which can overcome the mesh sensitivity. But the plasticity and damage modeling for damage behavior before the fracture of concrete should be combined with the crack model. In this study, a damage function and an unified hardening-softening function are applied to the homogenized crack model to develope a 3-dimensional FEM program for nonlinear damage and fracture analysis of concrete. The comparison of numerical results and experimental data show that the combined modeling in this study can simulate the damage and fracture of concrete without the mesh-sensitivity. It is also shown that the behavior of the so-called Engineering Cementitious Composite(ECC) characterized by strain-hardening and multiple cracks can be well simulated using the modeling.

• Corrosion Science and Technology
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• 제11권5호
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• pp.205-212
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• 2012

With recent advances in engineering and technology, a damage on industrial machineries performing high-speed and high-power requirements has become a problem. There is an increasing possibility of cavitation damage, especially in pumps, propellers and high-speed vessels in a flowing liquid accordingly. There are several factors affecting cavitation damage on materials, including viscosity, pressure, temperature, amplitude applied. In this study, effects of cavity pressure in seawater on the damage for 5083-O aluminium alloy were evaluated by modulating amplitude. Trend of the damage with respect to time and amplitude was analyzed comparatively, and surface degradation of specimens was investigated by using Scanning Electron Microscope(SEM) and 3D microscope. The result reveals that the amount of the damage increased consistently with the increase in time and amplitude while the plastic deformation zone where no appreciable damage occurred was in less than 30 minutes.

• 대한전자공학회논문지
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• 제15권4호
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• pp.26-32
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• 1978

실리콘 태양전지의 수명을 예측하기 위하여 1 MeV electron radiation으로 인한 실리콘 손상을 조사 연구하였다. 그 결과 흑형 실리콘에 있어서는 거의 안정상태의 손상에 이르렀음을 보았다.

• Structural Engineering and Mechanics
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• 제70권6호
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• pp.781-791
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• 2019

Earthquakes most often induce damage to structures, resulting in the degradation or deterioration of integrity. In this paper, based on the experimental study on 5 RC frames with different span length and different layout of buckling-restrained braces, the seismic damage evaluation law of RC frame with buckling-restrained braces was analyzed, and then the seismic damage for different specimens was calculated using different damage models to study the damage evolution. By analyzing and comparing the observation in test and the calculated results, it could be found that, damage evolution models including Gosain model, Hwang model as well as Ou model could better simulate the development of damage during cyclic loading. Therefore, these 3 models were utilized to analyze the development of damage to better demonstrate the evolution law for structures with different layout of braces and under different axial compression ratios. The results showed that from all layouts of braces studied, the eccentrically braced frame behaved better under larger deformation with the damage growing slowly. It could be deduced that the link beam benefited the seismic performance of structure and alleviated the damage by absorbing high values of energy.

• 한국결정성장학회지
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• 제9권5호
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• pp.527-533
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• 1999

치아용 대체재료로 사용되고 있는 세 가지의 세라믹스, 장석질 자기, 운모를 함유한 유리-세라믹 및 유리침윤 알루미나에 대한 접촉피로을 실제 치아의 접촉상황과 유사한 구형입자를 이용한 헤르지안 압입시험법으로 물에서 수행하였으며, 각 재료에서의 접촉손상이 강도에 미치는 영향을 고찰하였다. 초기의 손상형태는 각 재료가 갖는 미세구조에 의존하여 나타났으며, 장석질 자기는 취성거동을 나타내는 cone 형태의 균열이, 운모를 함유한 유리-세라믹은 준-소성 변형 거동을 나타내는 변형이, 그리고 유리침윤 알루미나는 두 재료의 중간거동을 나타내었다. 그러나 반복하중의 수(n=1~n=$10^6$)가 증가됨에 따라 모든 재료에서 급격한 강도저하를 나타내었으며, 파괴는 접촉피로에 의해 형성된 손상에서 일어났다. 일정하중(200N, 500N 및 1000N)에서 반복하중의 수가 증가됨에 따라 두 번의 강도저하가 일어났으며, 첫 번째의 강도저하는 cone 형태의 균열이 주 요인으로 작용되었으며, 두 번째 강도저하는 반복하중에 따른 radial 형태의 균열에 의해 일어났다. 이러한 radial 형태의 균열발생은 각 재료에서 급격한 강도저하를 가져왔으며, 계속적인 반복하중으로 재료의 파괴를 유발시켰다. 반복하중의 수를 고정시킨 수 압입하중의 변화에 따른 강도저하에 대한 고찰을 통해 장석질 자기가 접촉피로에 대한 손상내구성을 갖음을 알 수 있었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.697-700
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• 2000

Fatigue damage to reinforced concrete bridge decks have been found in many bridges. Failure mode of most reinforced concrete decks is caused by local punching shear rather than flexural moment due to cumulated damage. In this study, mechanical degradation of unstrengthened and strengthened bridge deck specimens is experimentally investigated. The unstrengthened deck specimens were damaged under the pulsating loading condition. After the test, deteriorated deck specimens were strengthened with Carbon Fiber Sheet, then loaded to observe the improvement of the fatigue behavior. It is shown that fatigue damaged specimens are similar to real bridge rather than static damaged specimens.

• Computers and Concrete
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• 제2권3호
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• pp.203-214
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• 2005

In the Part 1 paper (Gawin, et al. 2005) some experimental results concerning micro-structural tests, permeability measurements and stress-strain tests of four types of High Performance Concrete, exposed to elevated temperatures (up to $700^{\circ}C$) are presented and discussed. On the basis of these experimental results parameters of the constitutive relationships describing influence of damage and temperature upon material intrinsic permeability at high temperature were determined. In this paper the effects of various formulations of damage-permeability coupling on results of computer simulations are analysed and compared with the results obtained by means of the previously proposed approach, that does not take into account the thermo-chemical concrete damage directly. Numerical solutions are obtained using the recently developed fully coupled model of hygro-thermal and damage phenomena in concrete at elevated temperatures. High temperature effects are considered by means of temperature and pressure dependence of several material parameters. Based on the mathematical model, the computer code HITECOSP was developed. Material parameters of the model were measured by several European laboratories, which participated in the "HITECO" research project. A model problem, concerning hygro-thermal behaviour and degradation of a HPC structure during fire, is solved. The influence of two different constitutive descriptions of the concrete permeability changes at high temperature, including thermo-chemical and mechanical damage effects, upon the results of computer simulations is analysed and discussed.

• Nuclear Engineering and Technology
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• 제55권3호
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• pp.919-926
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• 2023

To analyze the cause of the destruction of thin, carbon-backed lithium fluoride targets during a measurement of the fusion of ⁷Li and ¹⁷O, we estimate theoretically the lifetimes of carbon and LiF films due to sputtering, thermal evaporation, and lattice damage and compare them with the lifetime observed in the experiment. Sputtering yields and thermal evaporation rates in carbon and LiF films are too low to play significant roles in the destruction of the targets. We estimate the lifetime of the target due to lattice damage of the carbon backing and the LiF film using a previously reported model. In the experiment, elastically scattered target and beam ions were detected by surface silicon barrier (SSB) detectors so that the product of the beam flux and the target density could be monitored during the experiment. The areas of the targets exposed to different beam intensities and fluences were degraded and then perforated, forming holes with a diameter around the beam spot size. Overall, the target thickness tends to decrease linearly as a function of the beam fluence. However, the thickness also exhibits an increasing interval after SSB counts per beam ion decreases linearly, extending the target lifetime. The lifetime of thin LiF film as determined by lattice damage is calculated for the first time using a lattice damage model, and the calculated lifetime agrees well with the observed target lifetime during the experiment. In experiments using a thin LiF target to induce nuclear reactions, this study suggests methods to predict the lifetime of the LiF film and arrange the experimental plan for maximum efficiency.

• Computers and Concrete
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• 제33권3호
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• pp.301-308
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• 2024

This paper proposes a numerically-based methodology to implicitly model irreversible deformations in concrete through a damage model. Plasticity theory is not explicitly employed, although resemblances are still present. A scalar isotropic damage model is adopted and the damage variable is split in two: one contributing for stiffness degradation (cracking) and other contributing for irreversible deformations (plasticity). The proposed methodology is thermodynamically consistent as it consists in a damage model rewritten in different terms. Its Finite Element coding is presented, indicating that minor changes are necessary. It is also demonstrated that nonlinear algorithms are unnecessary to model concrete cracking and plasticity. Experimental data from direct tension and four-point bending tests under cyclic loading are compared to the proposed methodology. A numerical case study of a low-cycle fatigue is also presented. It can be concluded that the model is simple, feasible and capable to capture the essentials concerning cracking and plasticity.