• 한국세라믹학회지
• /
• 제52권6호
• /
• pp.410-416
• /
• 2015

Recently, a new $Y_2O_3$ coating deposited using the EB-PVD method has been developed for erosion resistant applications in fluorocarbon plasma environments. In this study, surface crack formation in the $Y_2O_3$ coating has been analyzed in terms of residual stress and elastic modulus. The coating, deposited on silicon substrate at temperatures higher than $600^{\circ}C$, showed itself to be sound, without surface cracks. When the residual stress of the coating was measured using the Stoney formula, it was found to be considerably lower than the value calculated using the elastic modulus and thermal expansion coefficient of bulk $Y_2O_3$. In addition, amorphous $SiO_2$ and crystalline $Al_2O_3$ coatings were similarly prepared and their residual stresses were compared to the calculated values. From nano-indentation measurement, the elastic modulus of the $Y_2O_3$ coating in the direction parallel to the coating surface was found to be lower than that in the normal direction. The lower modulus in the parallel direction was confirmed independently using the load-deflection curves of a micro-cantilever made of $Y_2O_3$ coating and from the average residual stress-temperature curve of the coated sample. The elastic modulus in these experiments was around 33 ~ 35 GPa, which is much lower than that of a sintered bulk sample. Thus, this low elastic modulus, which may come from the columnar feather-like structure of the coating, contributed to decreasing the average residual tensile stress. Finally, in terms of toughness and thermal cycling stability, the implications of the lowered elastic modulus are discussed.

• Journal of Information Processing Systems
• /
• 제18권4호
• /
• pp.457-469
• /
• 2022

Hydraulic concrete buildings in the northwest of China are often subject to the combined effects of low-temperature frost damage, during drying and wetting cycles, and salt erosion, so the study of concrete deterioration prediction is of major importance. The prediction model of the relative dynamic elastic modulus (RDEM) of four different kinds of modified concrete under the special environment in the northwest of China was established using Grey residual Markov theory. Based on the available test data, modified values of the dynamic elastic modulus were obtained based on the Grey GM(1,1) model and the residual GM(1,1) model, combined with the Markov sign correction, and the dynamic elastic modulus of concrete was predicted. The computational analysis showed that the maximum relative error of the corrected dynamic elastic modulus was significantly reduced, from 1.599% to 0.270% for the BS2 group. The analysis error showed that the model was more adjusted to the concrete mixed with fly ash and mineral powder, and its calculation error was significantly lower than that of the rest of the groups. The analysis of the data for each group proved that the model could predict the loss of dynamic elastic modulus of the deterioration of the concrete effectively, as well as the number of cycles when the concrete reached the damaged state.

• 한국진공학회지
• /
• 제19권5호
• /
• pp.360-364
• /
• 2010

나노 소재의 물성을 측정하기 위하여 대부분의 연구 그룹에서는 크게 두 가지 분석 기법인 분광학을 이용한 분석과 나노트라이볼로지를 이용한 분석을 사용하고 있다. 분광학을 이용한 분석에는 NMR (Nuclear Magnetic Resonance), IR (Infrared Spectroscopy), Raman 등이 대표적이라 할 수 있고, 나노트라이볼로지를 이용한 분석에는 AFM (Atomic Force Micro-Scope), EFM (Electrostatic Force Microscope), KFM (Kelvin Force Microscope), Nanoindenter 등의 탐침을 이용한 측정 기법이 대표적이다. Nanoindenter는 물질의 탄성 및 경도를 측정 할 수 있으며 이를 통해 물질의 특성을 연구 하는 데에 사용된다. 그러나 이런 Nanoindenter의 압입 실험에서 압입 조건 등의 통제 변수가 다르면 그 결과 값도 바뀌는 것을 볼 수 있는데 본 실험에서는 이런 압입 조건 중 Load - Hold - Unload force의 속도 및 시간을 변화시켜 물질의 탄성계수와 경도가 어떠한 차이를 가지는지 연구하였다.

• Computers and Concrete
• /
• 제20권2호
• /
• pp.177-184
• /
• 2017

The characteristics of lightweight aggregate (LWA) with a low specific gravity and high water absorption will significantly change the properties of lightweight aggregate concrete (LWAC). This study aimed at exploring the effect of presoaking degree of LWA on the strength degeneracy of LWAC and flexural behavior of LWAC members exposed to elevated temperatures. The residual mechanical properties of the LWAC subjected to elevated temperatures were first conducted. Then, the residual load tests of LWAC members (beams and slabs) after exposure to elevated temperatures were carried out. The test results showed that with increasing temperature, the decreasing trend of elastic modulus for LWAC was considerably more serious than the compressive strength. Besides, the presoaking degree of LWA had a significant influence on the residual compressive strength and elastic modulus for LWAC after exposure to $800^{\circ}C$. Moreover, owing to different types of heating, the residual load bearing capacity of the slab specimens were significantly different from those of the beam specimens.

• Computers and Concrete
• /
• 제20권4호
• /
• pp.503-509
• /
• 2017

In this study, fire-damaged concrete was investigated by a nonlinear resonance vibration (NRV) technique, in order to evaluate its residual material properties. For the experiments, five cubic concrete specimens were prepared and four of them were damaged at different temperatures using a furnace. With a thermal insulator wrapped at the sides of specimen, thermal gradation was applied to the samples. According to the peak temperatures and depths of the samples, nonlinearity parameters were calculated with the NRV technique before the tendency of the parameters was evaluated. In addition, compressive strength and dynamic elastic modulus were measured for each sample and a comparison with the nonlinearity parameter was carried out. Through the experimental results, the possibility of the NRV technique as a method for evaluating residual material properties was evaluated.

• Nuclear Engineering and Technology
• /
• 제47권1호
• /
• pp.115-125
• /
• 2015

Background: Residual stress always exists on any kind of welded area. This residual stress can cause the welded material to crack or fracture. For many years, the hole-drilling method has been widely used for measuring residual stress. However, this method is destructive. Nowadays, electronic speckle pattern interferometry (ESPI) can be used to measure residual stress with or without the hole-drilling method. ESPI is an optical nondestructive testing methods that use the speckle effect. Mechanical properties can be measured by calculation of the phase difference by the variation of temperature, pressure, or loading force. Methods: In this paper, the residual stress on the butt-welded area is measured by using ESPI with a suggested numerical calculation. Two types of specimens are prepared. Type I is made of pure base metal part and type II has a welded part at the center. These specimens are tensile tested with a material test system. At the same time, the ESPI system was applied to this test. Results: From the results of ESPI, the elastic modulus and the residual stress around the welded area can be calculated and estimated. Conclusion: With this result, it is confirmed that the residual stress on the welded area can be measured with high precision by ESPI.

• 대한기계학회논문집A
• /
• 제28권5호
• /
• pp.578-585
• /
• 2004

Hardness test is performed for determination of the other properties, such as strength, wear resistance and deformation resistance, as well as hardness itself. And it is performed for prediction of residual lifetime by analysis of hardness reduction or hardness ratio. However, hardness test has limitation that observation of residual indent is needed for determination of hardness value, and that is the reason for not to be widely used in industrial field. Therefore, in this study, we performed researches to obtain Brinell hardness value from quantitative numerical formula by analysing relationship between indentation depths from indentation load-depth curve and mechanical properties such as work hardening exponent, yield strength and elastic modulus.

• 한국정밀공학회지
• /
• 제28권2호
• /
• pp.219-225
• /
• 2011

Silicone resin is recently used as encapsulant for high-power LED module due to its excellent thermal and optical properties. In the present investigation, finite element analysis of cure process was attempted to examine residual stress evolution behavior during silicone resin cure process which is composed of chemical curing and post-cooling. To model chemical curing of silicone, a cure kinetics equation was evaluated based on the measurement by differential scanning calorimeter. The evolutions of elastic modulus and chemical shrinkage during cure process were assumed as a function of the degree of cure to examine their effect on residual stress evolution. Finite element predictions showed how residual stress in cured silicone resin can be affected by elastic modulus and chemical shrinkage behavior. Finite element analysis is supposed to be utilized to select appropriate silicone resin or to design optimum cure process which brings about a minimum residual stress in encapsulant silicone resin.

• 한국세라믹학회지
• /
• 제35권8호
• /
• pp.813-818
• /
• 1998

A simple method to measure the elastic modulus E and Poisson's ratio v of diamod-like carbon (DLC) films deposited on Si wafer was suggested. Using the anisotropic etching technique of Si we could make the edge of DLC overhang free from constraint of Si substrate. DLC film is chemically so inert that we could not on-serve any surface damage after the etching process. The edge of DLC overhang free from constraint of Si substrate exhibited periodic sinusoidal shape. By measuring the amplitude and the wavelength of the sinu-soidal edge we could determine the stain of the film required to adhere to the substrate. Since the residual stress of film can be determine independently by measurement of the curvature of film-substrate com-posite we could calculated the biaxial elastic modulus E/(1-v) using stress-strain relation of thin films. By comparing the biaxial elastic modulus with the plane-strain modulus E/(1-{{{{ { v}^{2 } }}) measured by nano-in-dentation we could further determine the elastic modulus and Poisson's ratio independently. This method was employed to measure the mechanical properties of DLC films deposited by {{{{ { {C }_{6 }H }_{6 } }} rf glow discharge. The was elastic modulus E increased from 94 to 169 GPa as the {{{{ { V}_{ b} / SQRT { P} }} increased from 127 to 221 V/{{{{ {mTorr }^{1/2 } }} Poisson's ratio was estimated to be abou 0.16∼0.22 in this {{{{ { V}_{ b} / SQRT { P} }} range. For the {{{{ { V}_{ b} / SQRT { P} }} less than 127V/{{{{ {mTorr }^{1/2 } }} where the plastic deformation can occur by the substrate etching process however the present method could not be applied.

• 한국지반공학회논문집
• /
• 제28권11호
• /
• pp.87-99
• /
• 2012

국내에서 출토되는 퇴적암, 화성암 및 변성암군중 출토빈도가 높은 9개 암종을 대상으로 함수에 의한 탄성계수의 저감거동을 분석하였다. 일축압축강도 기준으로 20MPa 범위로 5개단계로 분활하여 단계별, Group별로 함수 저감거동을 분석한 결과는 5개 퇴적암 전부와 화성암군인 안산암을 포함한 모집단은 단일 저감거동을 보이며, 화성암군인 화강암, 유문암과 변성암군인 편마암은 또 다른 동일 거동을 보이며, 더욱이 저감속도가 퇴적암군을 포함한 모집단에 비해서 2배이상 빠르며 탄성계수의 잔존값도 매우 낮게 나타났다.