• 제목/요약/키워드: Thermal Damage

검색결과 916건 처리시간 0.025초

Effect of damage on permeability and hygro-thermal behaviour of HPCs at elevated temperatures: Part 2. Numerical analysis

  • Gawin, D.;Majorana, C.E.;Pesavento, F.;Schrelfer, B.A.
    • 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.

Degradation of thin carbon-backed lithium fluoride targets bombarded by 68 MeV 17O beams

  • Y.H. Kim;B. Davids;M. Williams;K.H. Hudson;S. Upadhyayula;M. Alcorta;P. Machule;N.E. Esker;C.J. Griffin;J. Williams;D. Yates;A. Lennarz;C. Angus;G. Hackman;D.G. Kim;J. Son;J. Park;K. Pak;Y.K. Kim
    • 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.

저온하에서 시차열 수축에 의한 WMA 콘크리트의 휨강도 변화 (Variation of Flexural Strength of Warm-mix Asphalt Concretes Due to Differential Thermal Contraction at Low Temperatures)

  • 최정순;김성운;김광우
    • 한국도로학회논문집
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    • 제14권4호
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    • pp.63-72
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    • 2012
  • PURPOSES : Hot-mix asphalt(HMA) concretes show a trend of strength increase at low temperature due to binder stiffness increase, but strength decrease below a ceratin low temperature. This is due to the differential thermal contraction(DTC) which is induced by a significant difference in coefficients of thermal contraction between aggregate and asphalt which is coated around the aggregate. This DTC damage is well known to occur in HMA concrete, but is not yet investigated in warm-mix asphalt(WMA) concretes. METHODS : To evaluate DTC damage on WMA in this study, the flexural strength($S_f$) of WMA concretes, which were produced at $30{\sim}40^{\circ}C$ lower temperature, was evaluated in comparison with that of HMA at -5, -15 and $-25^{\circ}C$. RESULTS : Most of WMA and HMA mixtures showed flexural strength increase down to $-15^{\circ}C$ and decrease below $-15^{\circ}C$. this type of strength reduction below $-15^{\circ}C$ can e explained as the effect of differential thermal contraction that is a consequence of the large difference in coefficients of thermal contraction between aggregate and asphalt. the property reduction of WMA is similar the result of previous works dealt with HMA mixtures. CONCLUSIONS : Even though there is some differences by materials used, the WMA concretes showed a significantly lower DTC damage than HMA concrete at low temperature at ${\alpha}$=0.05 level.

Electro-Micromechanical 시험법을 이용한 탄소섬유 강화 Epoxyacrylate 복합재료의 UV 및 열경화에 따른 비파괴적 손상 감지능 및 경화 Monitoring (Nondestructive Damage Sensing and Cure Monitoring of Carbon Fiber/Epoxyacrylate Composite with UV and Thermal Curing using Electro-Micromechanical Technique)

  • Kong, Jin-Woo;Kim, Dae-Sik;Park, Joung-Man;Lee, Jae-Rock
    • 한국복합재료학회:학술대회논문집
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    • 한국복합재료학회 2002년도 추계학술발표대회 논문집
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    • pp.261-264
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    • 2002
  • Interfacial evaluation, damage sensing and cure monitoring of single carbon fiber/thermosetting composite with different curing processes was investigated using electro-micromechanical test. After curing, residual stress was monitored by measurement of electrical resistance (ER) and then it was compared to correlate with various curing processes. In thermal curing, curing shrinkage appeared significantly by matrix shrinkage and residual stress due to the difference in thermal expansion coefficient (TEC). The change in electrical resistance (ΔR) on thermal curing was higher than that on ultraviolet (UV) curing. For thermal curing, apparent modulus was the highest and reaching time until same strain was faster. So far thermal curing shows strong durability on the IFSS after boiling test.

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Micromechanical 시험법과 AE를 이용한 세라믹 PZT 및 고분자 PVDF 센서에 따른 단섬유 강화 에폭시 복합재료의 비파괴 손상감지능 비교 (Comparison of Nondestructive Damage Sensitivity of Single Fiber/Epoxy Composites Using Ceramic PZT and Polymeric PVDF Sensors By Micromechanical Technique and Acoustic Emission)

  • 정진규;김대식;박종만;윤동진
    • 한국복합재료학회:학술대회논문집
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    • 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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    • pp.135-138
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    • 2004
  • Conventional piezoelectric lead-zirconate-titanate (PZT) senor has high sensitivity, but it is very brittle. Recently polymer films such as polyvinylidene fluoride (PVDF) and poly(vinylidene fluoride­trifluoroethylene) (P(VDF-TrFE)) copolymer have been used as a sensor. The advantages of polymer sensor are the flexibility and mechanical toughness. Simple process and possible several shapes are also additional advantages. Polymer sensor can be directly embedded in a structure. In this study, nondestructive damage sensitivity of single basalt fiber/epoxy composites was investigated with sensor type and thermal damage using AE and oscilloscope. And AE waveform for epoxy matrix with various damage types was compared to each other. The damage sensitivity of two polymer sensors was rather lower than that of PZT sensor. The damage sensitivity of PVDF sensor did not decrease until thermal damage temperature at $80^{\circ}C$ and they decreased significantly at $110^{\circ}C$ However, the damage sensitivity of P(VDF-TrFE) sensor at $110^{\circ}C$ was almost same in no damage sensor. For both top and side impacts, the difference in arrival time increased with increasing internal and surface damage density of epoxy matrix.

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열하중을 받는 복합재료 적층판의 손상에 대한 열-음향방출해석 (Analysis of Thermo-Acoustic Emission from Damage in Composite Laminates under Thermal Cyclic Loading)

  • 김영복;민대홍;이덕보;최낙삼
    • 비파괴검사학회지
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    • 제21권3호
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    • pp.261-268
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    • 2001
  • 열-음향방출(thermo-AE) 기법을 이용하여 두께 3mm, $[+45_6/-45_6]_s$ 복합재료 적층판의 열응력 유기 손상에 대한 비파괴평가의 유효성을 연구하였다. 반복적인 열부하 사이클에 의해서 thermo-AE 사상수가 감소하는 경향이 뚜렷하게 나타나서 열부하에 따른 카이저효과가 관찰되었다. 열부하사이클중의 thermo-AE거동을 분석하여 복합재료의 응력자유온도를 결정할 수 있었다. 초음파 C스캔, 광학현미경, 주사형 전자현미경을 통해 섬유파단과 모재파손이 관찰되었으며, 이들 파손 인자는 thermo-AE 신호의 단시간 퓨리에 변환처리에 의해 생성된 3종류의 서로 다른 시간-주파수 특성과 대응하였나 이 특성을 이용하여 복합재료의 냉각열처리 및 반복 열부하사이클시의 손상발생과정 및 내부 마찰거동 내역을 추적할 수 있었다.

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관형 요도 조직 대상 내시경적 레이저 조사 조건 연구 (Endoscopic Laser Irradiation Condition of Urethra in Tubular Structure)

  • 신화랑;임성희;이예찬;강현욱
    • 대한의용생체공학회:의공학회지
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    • 제44권1호
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    • pp.85-91
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    • 2023
  • Stress urinary incontinence (SUI) occurs when abdominal pressure increases, such as sneezing, exercising, and laughing. Surgical and non-surgical treatments are the common methods of SUI treatment; however, the conventional treatments still require continuous and invasive treatment. Laser have been used to treat SUI, but excessive temperature increase often causes thermal burn on urethra tissue. Therefore, the optimal conditions must be considered to minimize the thermal damage for the laser treatment. The current study investigated the feasibility of the laser irradiation condition for SUI treatment using non-ablative 980 nm laser from a safety perspective through numerical simulations. COMSOL Multiphysics was used to analyze the numerical simulation model. The Pennes bioheat equation with the Beer's law was used to confirm spatio-temporal temperature distributions, and Arrhenius equation defined the thermal damage caused by the laser-induced heat. Ex vivo porcine urethral tissue was tested to validate the extent of both temperature distribution and thermal damage. The temperature distribution was symmetrical and uniformly observed in the urethra tissue. A muscle layer had a higher temperature (28.3 ℃) than mucosal (23.4 ℃) and submucosal layers (25.5 ℃). MT staining revealed no heat-induced collagen and muscle damage. Both control and treated groups showed the equivalent thickness and area of the urethral mucosal layer. Therefore, the proposed numerical simulation can predict the appropriate irradiation condition (20 W for 15 s) for the SUI treatment with minimal temperature-induced tissue.

복합재료의 내부손상 평가 (Evaluation of Composite Material Damage)

  • 이재준;김태우;김찬묵
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 2002년도 추계학술대회 논문집
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    • pp.689-692
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    • 2002
  • Composite materials, when damaged under thermal or mechanical loadings, show property changes. Among many mechanical properties of composite materials. the stiffness tend to be reduced due to micro-cracking, debonding, or delamination caused by external loadings. This research presents results regarding the detecting technique of internal damages within composite that experienced low-velocity impacts. Post-damage evaluations were made experimentally using flexural and compression loadings. Preliminary finite element analysis was made and compared with analytical solutions. The experimental results to determine the degree of damage will be compared with finite element results.

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RC 대형 냉각탑 셀의 손상추정에 관한 연구 (A Study on Damage-Assessment of RC Large Cooling Tower Shells)

  • 노삼영
    • 한국공간정보시스템학회:학술대회논문집
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    • 한국공간정보시스템학회 2004년도 춘계 학술발표회 논문집 제1권1호(통권1호)
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    • pp.279-286
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    • 2004
  • An accumulated crack damage which propagates progressively with time was frequently observed on several engineering structures, This paper numerically demonstrates this damage process on large cooling tower shells under thermal and wind loads. Damage states under varying loads are investigated and the influence of this progressive damage process on the life-cycle of cooling towers discussed. The paper presents briefly some fundamentals of the geometrically and physically non-linear numerical analysis employed for reinforced concrete, especially concerning the models used for concrete, steel reinforcement and the bond between them. As a numerical example an existing cooling tower with noticeable meridian crack damage is analysed. The existing damage state of the cooling tower is determined by quasi-static analyses for temperature, hygric and cyclic wind leading. The change in the dynamical behaviour of the structure as mirrored in its natural frequencies and mode shapes is presented and discussed. Finally, the example shows that such damage processes develop progressively over the life-time of the structures.

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