Parametric study for optimal design of an air plasma sprayed thermal barrier coating system with respect to thermal stress

Lim, Jang Gyun,Seo, Sangjae,Koo, Jae Mean,Seok, Chang Sung,Choi, Jae Boong,Kim, Moon Ki Elsevier Sequoia 2017 Surface & coatings technology Vol.315 No.-

<P><B>Abstract</B></P> <P>The use of thermal barrier coatings (TBCs) is expected to become more popular in various gas turbines because these coatings provide excellent thermal insulation and damage protection. However, unexpectedly early failure has often discouraged the full use of TBC, resulting in a shortening of the life span of gas turbines because these substrates are directly exposed to harsh operation conditions. The general mechanics of TBC and its complex inner phenomena, mainly related to failure, have been investigated to prolong the lifetime of TBC. However, our understanding is limited because TBC has various specifications and operating conditions, and complex interplays between many factors. The primary goal of this study is to construct an extensive finite element method (FEM) model to evaluate thermal stress of an air plasma sprayed TBC under its operating conditions by considering various inner phenomena, including thermal grown oxide, undulating topology of coating interface, aluminum depletion, creep effect, and elastoplastic deformation. With the proposed FEM model, a parametric study has been conducted with respect to a variety of material properties, as well as the thickness of bond coat and of top coat. The influence of each design factor on thermal stress and the other parameters is fully discussed. Finally, this work leads to optimal design criteria for minimizing thermal stress across a wide range of TBC systems.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A parametric study was carried out for optimal design of thermal barrier coating. </LI> <LI> Elastic modulus of top coat is the most sensitive design parameter to thermal stress. </LI> <LI> Thermal expansion mismatch between top and bond coat was tuned by coating thickness. </LI> </UL> </P>

보일러 헤더 기동시의 탄성 크리프 해석에 의한 열응력 평가

신규인 ( Kyu In Shin ),윤기봉 ( Kee Bong Yoon ) 한국안전학회 2009 한국안전학회지 Vol.24 No.4

Thermal stress and elastic creeping stress analysis was conducted by finite element method to simulate start-up process of a boiler header of 500MW standard fossil power plant. Start-up temperature and operating pressure history were simplified from the real field data and they were used for the thermal stress analysis. Two kinds of thermal stress analysis were considered. In the first case only temperature increase was considered and in the second case both of temperature and operating pressure histories were considered. In the first analysis peak stress was occurred during the temperature increase from the room temperature. Hence cracking or fracture may occur at the temperature far below the operating maximum temperature. In the results of the second analysis von Mises stress appeared to be higher after the second temperature increase. This is due to internal pressure increase not due to the thermal stress. When the stress components of radial(r), hoop(θ) and longitudinal(z) stress were investigated, compression hoop stress was occurred at inner surface of the stub tube when the temperature increased from room temperature to elevated temperature. Then it was changed to tension hoop stress and increased because of the operating pressure. It was expected that frequent start-up and shut-down operations could cause thermal fatigue damage and cracking at the stub tube hole in the header. Elastic-creeping analysis was also carried out to investigate the stress relaxation due to creep and stabilized stress after considerable elapsed time. The results could be used for assessing the creep damage and the residual life of the boiler header during the long-term service.

A Study of Hull Stress Monitoring System Considering Thermal Effect

심천식,허주호,강중규 한국항해항만학회 2008 한국항해항만학회지 Vol.32 No.2

This paper presents hull stress monitoring system installed in LNGC damaged by a Typhoon. Elongation/contraction of removed areas has been assessed in terms of possible residual stress that will take place in replaced blocks when the applied load is removed. The bending moment of a vessel changes actually in terms of loss of longitudinal members and the change of weight distribution in repair procedure. The change of bending moment affects mainly in hull stress of longitudinal members. Hull stress monitoring system was installed on upper deck to prove LNGC stable in the criteria to be less than 40MPa during the period of repair procedure. A temperature measuring system was also installed to exclude the additional stress due to thermal effect from the measured hull stress. As a result, the hull stress was modified with the data measured by the temperature measuring system. This hull stress considering thermal effect was used as a guide stress to check the safety of LNGC during the period of repair procedure. This paper presents hull stress monitoring system installed in LNGC damaged by a Typhoon. Elongation/contraction of removed areas has been assessed in terms of possible residual stress that will take place in replaced blocks when the applied load is removed. The bending moment of a vessel changes actually in terms of loss of longitudinal members and the change of weight distribution in repair procedure. The change of bending moment affects mainly in hull stress of longitudinal members. Hull stress monitoring system was installed on upper deck to prove LNGC stable in the criteria to be less than 40MPa during the period of repair procedure. A temperature measuring system was also installed to exclude the additional stress due to thermal effect from the measured hull stress. As a result, the hull stress was modified with the data measured by the temperature measuring system. This hull stress considering thermal effect was used as a guide stress to check the safety of LNGC during the period of repair procedure.

Nano-Scale CMOSFET에서 Contact Etch Stop Layer의 Mechanical Film Stress에 대한 소자특성 분석

나민기(Min-Ki Na),한인식(In-Shik Han),최원호(Won-Ho Choi),권혁민(Hyuk-Min Kwon),지희환(Hee-Hwan Ji),박성형(Sung-Hyung Park),이가원(Ga-Won Lee),이희덕(Hi-Deok Lee) 대한전자공학회 2008 電子工學會論文誌-SD (Semiconductor and devices) Vol.45 No.4

본 논문에서는 Contact Etch Stop Layer (CESL)인 nitride film의 mechanical stress에 의해 인가되는 channel stress가 소자특성에 미치는 영향에 대해 분석하였다. 잘 알려진 바와 같이 NMOS는 tensile stress와 PMOS에서는 compressive stress가 인가되었을 경우 drain current가 증가하였으며 그 원인을 체계적으로 분석하였다. NMOS의 경우 tensile stress가 인가됨으로써 back scattering ratio (rsat)의 감소와 thermal injection velocity (Vinj)의 증가로 인해 mobility가 개선됨을 확인하였다. 또한 rsat 의 감소는 온도에 따른 mobility의 감소율이 작고, 그에 따른 mean free path ( λO)의 감소율이 작기 때문인 것으로 확인되었다. 한편 PMOS의 compressive stress 경우에는 tensile stress에 비해 온도에 따른 mobility의 감소율이 크기 때문에 channel back scattering 현상은 심해지지만 source에서의 Vinj가 큰 폭으로 증가함으로써 mobility가 개선됨을 확인 할 수 있었다. 따라서 CES-Layer에 의해 인가된 channel stress에 따른 소자 특성의 변화는 inversion layer에서의 channel back scattering 현상과 source에서의 thermal injection velocity에 매우 의존함을 알 수 있다. In this paper, the dependence of MOSFET performance on the channel stress is characterized in depth. The tensile and compressive stresses are applied to CMOSFET using a nitride film which is used for the contact etch stop layer (CESL). Drain current of NMOS and PMOS is increased by inducing tensile and compressive stress, respectively, due to the increased mobility as well known. In case of NMOS with tensile stress, both decrease of the back scattering ratio (rsat) and increase of the thermal injection velocity (Vinj) contribute the increase of mobility. It is also shown that the decrease of the rsat is due to the decrease of the mean free path (λ?). On the other hand, the mobility improvement of PMOS with compressive stress is analyzed to be only due to the so increased Vinj because the back scattering ratio is increased by the compressive stress. Therefore it was confirmed that the device performance has a strong dependency on the channel back scattering of the inversion layer and thermal injection velocity at the source side and NMOS and PMOS have different dependency on them.

Effects of thermal and mechanical stress on the physical stability of human growth hormone and epidermal growth factor

임준열,김남아,임대곤,김기현,정성훈 대한약학회 2015 Archives of Pharmacal Research Vol.38 No.8

Thermal and mechanical stress conditions were applied to two model proteins, human growth hormone (hGH) and epidermal growth factor (EGF), to evaluate protein stability during the manufacturing process, focusing on protein secondary structure and aggregation. The samples were analyzed with differential scanning calorimetry (DSC), circular dichroism (CD), and size-exclusion chromatography (SEC). The monomer and aggregation contents were obtained by SEC and the proteins’ secondary structure on exposure to thermal stress was evaluated by CD. DSC showed that the transition temperature (Tm) of hGH and EGF was 74.43 and 79.11 C, respectively. The accelerated thermal stress temperature was set at 70 C. The monomer content of hGH decreased from 97.8 to 82.3 % in response to thermal stress. However, the monomer content of EGF decreased significantly from 33.73 to 5.61 %. The hGH and EGF showed an increase in a-helix content and a decrease in b-sheet (antiparallel and parallel b-sheet). Moreover, the contents changed significantly during the first 1 h and then changed slightly for the remaining time. On the other hand, shaking stress showed that hGH was highly affected compared to EGF. The hGH monomer steadily decreased and only the half the monomer content remained at 3 h. It is suspected that the shaking stress induced hGH adsorption to the gas–liquid interface, which may facilitate protein denaturation. The results indicate that protective excipients might be necessary for inevitable stress conditions during the developmental process. The stability of each protein differed with respect to specific stress conditions. Therefore, an arrayof complementary analytical methods might be required to evaluate the protein stability.

Effect of thermal fatigue on mechanical characteristics and contact damage of zirconia-based thermal barrier coatings with HVOF-sprayed bond coat

Kwon, Jae-Young,Lee, Jae-Hyun,Kim, Hyeon-Cheol,Jung, Yeon-Gil,Paik, Ungyu,Lee, Kee-Sung Elsevier 2006 Materials science & engineering. properties, micro Vol.429 No.1

<P><B>Abstract</B></P><P>Mechanical characteristics, such as hardness, elastic modulus and indentation stress–strain curves, and contact damage of a thermal barrier coating (TBC) system with a top coat prepared using an air-plasma spraying (APS) process and a bond coat using a high-velocity oxygen flow (HVOF) process have been investigated using the nanoindentation and Hertzian indentation tests, as a function of the thermal fatigue condition. The bond coat and the top coat deposited on the substrate make the TBC system soft, showing lower stress–strain curves than that of the substrate. Thermal fatigue does not affect the stress–strain curves, except for thermal fatigue for 500h. However, the thermally grown oxide (TGO) layer thickness is dependent on the exposure time under thermal fatigue, showing a nominal thickness of approximately 4μm after thermal fatigue for 500h, independent of the number of thermal fatigue cycles. The values of hardness, <I>H</I>, in each component are not greatly affected by thermal fatigue, except for thermal fatigue for 500h, whereas the value of elastic modulus, <I>E</I>, in the bond coat is dominantly affected by thermal fatigue with a smaller increase for the other components—top coat and substrate. The <I>H</I>/<I>E</I> ratio for the top coat is higher than those for the bond coat and the substrate, indicating that resintering of the top coat occurs during thermal fatigue. The top coat acts as a protection layer for contacts, resulting in reduced damage to the substrate. As the exposure time is increased in the thermal fatigue experiments, the damage to the top coat is inhibited with less crack coalescence. The higher stiffness in the bond coat induces a cracking or delamination at the interface between the bond coat and the substrate, whereas thermal fatigue increases the mechanical properties, especially <I>E</I>, of the bond coat and enhances the damage tolerance of the TBC system.</P>

열처리 방법에 따른 SOI 기판의 스트레스변화

서태윤,이상현,송오성,Seo, Tae-Yune,Lee, Sang-Hyun,Song, Oh-Sung 한국재료학회 2002 한국재료학회지 Vol.12 No.10

It is of importance to know that the bonding strength and interfacial stress of SOI wafer pairs to meet with mechanical and thermal stresses during process. We fabricated Si/2000$\AA$-SiO$_2$ ∥ 2000$\AA$-SiO$_2$/Si SOI wafer pairs with electric furnace annealing, rapid thermal annealing (RTA), and fast linear annealing (FLA), respectively, by varying the annealing temperatures at a given annealing process. Bonding strength and interfacial stress were measured by a razor blade crack opening method and a laser curvature characterization method, respectively. All the annealing process induced the tensile thermal stresses. Electrical furnace annealing achieved the maximum bonding strength at $1000^{\circ}C$-2 hr anneal, while it produced constant thermal tensile stress by $1000^{\circ}C$. RTA showed very small bonding strength due to premating failure during annealing. FLA showed enough bonding strength at $500^{\circ}C$, however large thermal tensile stress were induced. We confirmed that premated wafer pairs should have appropriate compressive interfacial stress to compensate the thermal tensile stress during a given annealing process.

Analysis of Stress Distribution in the Laser Welding Process

Chul-Ku Lee,Woo-Ram Lee 한국도시철도학회 2013 IJAR Vol.1 No.1

Welding is one of the techniques to be widely used in the modern industrial sites, and it has been known that the stress caused by the heat source applied to the parent metal during the welding process greatly influence on the weldability. The nonlinear deformation is occurred according to the heat conduction in the welds, and if such deformation is restricted by external force, the residual stress is left in the welds and it will act as defects. In this study, the temperature and stress that are occurred during the laser welding process by applying SCP1-S, are numerically and experimentally analyzed. The author derived the results on heating and cooling in order to predict the stress generated by conducting of the laser welding process. In addition, the change of the stress according to cooling time was grasped, and the stress predicted by the numerical analysis was compared to the results by Hole-Drilling Stress Technique. Finally, that the direction of the main stress during the welding process is the stress in the width direction of the bead, and the stress of welding progress direction at the point away from beads largely appears was confirmed to be caused by the stress and deformation of parent metal according to the thermal impact. It was confirmed that when welding process is progressed, the change from compression stress to tensile stress significantly appeared, and the point a certain distance away from the weld bead appears the slow change of stress.

Thermal tolerance mechanism of invasive cotton mealybug parasitoid, Aenasius arizonensis Girault (Hemiptera: Encyrtidae)

Thimmegowda MN.,Suresh Suroshe Sachin,Sagar D. 한국응용곤충학회 2024 Journal of Asia-Pacific Entomology Vol.27 No.1

The sustainability and fitness of biocontrol agents depends on the abiotic factors of which temperature is the most critical factor. Thermal stress affects parasitoid behavior owing to change in physiological activities. So, an experiment was conducted to know the effect of thermal stress on the antioxidant enzymes in Aenasius arizonensis (Girault), a specific parasitoid of cotton mealybug, Phenacoccus solenopsis (Tinsley). Enzyme activity in P. solenopsis and A. arizonensis at each thermal stress treatment was noticed. At 3 h of thermal stress, the tem perature dependent increase in the SOD activity was observed. The maximum activity was noticed at 41 ◦ C in both P. solenopsis and A. arizonensis compared to the 27 ◦ C. The SOD activity was found more in four hours exposure compared to the three hours exposure at all the temperature treatments. Catalase activity was also found to increase with the increase in temperature, the effect of thermal stress was found to be significant in A. arizonensis and P. solenopsis for the activity of catalase. The maximum GST activity was found at 41 ◦ C for both P. solenopsis nymphs and A. arizonensis adults exposed to different temperature treatments for 3 h of duration. However, all the temperature treatments for P. solenopsis nymphs were non-significant, whereas, for A. arizonensis, it was found significant for the GST activity. We observed that thermal stress had no effect on the concentration of MDA in both P. solenopsis and A. arizonensis subjected to different durations of temperature regimes. Elevated levels of SOD, CAT and GST might be providing possible protection against reactive oxygen species generated under elevated thermal stress.

일체형 세라믹 열교환기의 전산 열응력 해석에 관한 연구

팽진기(Jin Gi Paeng),김기철(Ki Chul Kim),윤영환(Young Hwan Yoon) 대한설비공학회 2009 설비공학 논문집 Vol.21 No.11

The thermal stresses of a ceramic heat exchanger were analyzed numerically since the ceramic material is good in heat resistance but weak in the thermal stress. The analysis of thermal stress was conducted in the ceramic core with two boundary conditions depending on bolt jointing. The thermal stresses were computed by applying temperature and pressure distributions obtained from the numerical results of conjugate heat transfer to ANSYS WORKRBENCH. When number of bolt joining halls was reduced from 8 × 2 to 4 × 2, the maximum principal stresses decrease by 47.6~50.5% and increase in safety factors by 2.18~2.5 for ultimate tensile strength. Thus, it can be said that bolt joining halls should be minimized in ceramic heat exchanger to be efficient in reducing thermal stress. In addition, the width of particular gas flow passages were revised from 52 mm to 42 mm to reduce maximum thermal stresses since certain passages experienced high thermal stresses. From the revision, safety factors were increased by 13.8~14.1% for the boundary condition of 4 × 2 bolt joining halls, Therefore, it is suggested that thermal stress can be reduced by changing local geometry of a ceramic heat exchanger.