Kunihiro Ichikawa

Mechanical Approach for Predicting Fretting Fatigue Strength

Stress distribution at the contact edge is known to have a dominant influence on fretting fatigue strength. Stresses acting on the contact surface are tangential stress and compressive stress. In the present study, fretting fatigue strengths of 12 Cr steel specimen under two different mean stresses have been predicted based on the generalized tangential stress range - compressive stress range diagram. The generalized tangential stress range - compressive stress range diagram was obtained by carrying out fretting fatigue tests and finite element analysis using various steel specimens with various geometries of contact pad from the previous studies. The predicted fretting fatigue strengths were in good agreement with the experimental results.

304 The Influence of Long Term Operation on Delamination Behavior of Thermal Barrier Coatings under Thermo-mechanical Fatigue.

1 緒 言 燃料価格の上昇および環境問題などから,発電効率の 向上が強く求められている.ガスタービンの高効率化に は高温化が効果的であるものの,クリープ強度に対する 材料の制限から,遠心力が作用するタービン動翼の信頼 性を維持するべく,冷却の強化を図る必要がある. 近年,冷却強化の手法の一つとして,熱伝導率の低い セラミック皮膜を動翼表面に施工することで,内部冷却 翼の温度を低減する熱遮蔽コーティング (TBC, Thermal Barrier Coatings) の適用が主流となりつつある. TBCはすでに運用中の翼に施工することも可能であ り,耐食耐酸化性向上も期待できることから,その適用 範囲は今後さらに拡大することが予想される.しかしな がら,TBCの損傷挙動を定量的に評価するには,まだ不 透明な点も多い.1) 従来 TBCに関する研究は,皮膜の性質に関する内容 とはく離強度に関する内容に大別されてきた.膜質につ いて Fujiiらは,高温曝露に伴う焼結によりセラミック層 の気孔率が減少するとともに熱伝導率が増加する挙動を LMP (Larson-Miller Parameter) を用いて整理する手法を 提案している.2)TomimatsuらはEB-PVD (Electron Beam Enhanced Physical Vapor Deposition) により製膜した TBCを対象として,レーザー光を用いた皮膜内の残留応 力測定手法を提案するとともに,高温曝露に伴い残留応 力の値が増加することを報告している.3)また脇らはセラ ミック層の残留応力を応力開放法により求めるとともに, 繰り返し負荷下での皮膜の変形特性を示している.4), 5) 一方強度については,西野らが TBCの施工により等 温下での低サイクル疲労寿命が低温で短寿命,高温で長 寿命となることを示し,これはボンド層の延性の温度依 存性に起因すると説明している.6)しかしながらガスター ビンの高温部品には,Fig. 1に示すように起動・停止に 熱機械疲労下における熱遮蔽コーティングのはく離挙動 吉 竹 茂 飯 尾 哲 史 船 尾 淳 喜 関 原 傑 有 川 秀 行 市 川 国 弘 Delamination Behavior of Thermal Barrier Coatings under Thermo-Mechanical Fatigue

Experimental Investigation of High Temperature Wear Resistant Coatings for Industrial Gas Turbine

In the contact section of industrial gas turbine parts, wear can be observed after normal operations. Especially, in the contact area of combustors and their fittings, such as a transition piece and a seal plate, the severe wear may occur owing to combustion vibration under high temperature. If such severe wear occurs, some inspections or repair of the combustor parts may be needed. The short cycle of inspection and repair will decrease the performance of the gas turbine. Though combustors and their fittings are subjected to high temperature condition without any lubricant, any relevant prevention has not been developed yet. In this paper, wear resistance of ceramic hard coating materials, i.e. titanium nitride (TiN), titanium aluminum nitride (TiaAIN), chromium nitride (CrN), titanium carbide (TiC), silicon carbide (SiC), aluminum oxide (Al2 O3 ) against various metals was tested under the condition similar to that in a gas turbines. These coatings were deposited by physical vapor deposition (PVD) or chemical vapor deposition (CVD) processes. It was concluded that, the combination of Al2 O3 coating and stellite #6B had excellent high temperature wear resistance.© 2003 ASME

Analytical Method of Fatigue Damage Estimation for Compressor Stator Blades of Gas Turbines Experiencing Rotating Stall

To improve the reliability of compressor stator blades of gas turbines, an analytical method for estimating their fatigue damage has been developed. This method is based on blade-vibratory-stress analysis, stress-peak counting, and use of actual environmental data. The blade-vibratory-stress analysis takes the superposition of multi-peaks of the stress spectrum into account. The numerically simulated stress showed better agreement with measured stress than that from a conventional stress analysis, which is based on frequency-response analysis considering a single peak of the lowest single eigen-vibration-mode. A time-domain stress history was synthesized from the blade-vibratory-stress analysis results. Furthermore, the fatigue damage of the blade under rotating stall was estimated by the linear-damage-rule from the stress-peak counting of the stress and from material data. The estimated fatigue-damage agrees well with the measured results. This agreement means that our new fatigue-damage-estimation method is more accurate than the conventional one.Copyright

Life Prediction Method Under Creep-Fatigue Loading for Gas Turbine Combustion Transition Piece of Ni-Based Superalloy N263

In order to develop the life prediction method under creep-fatigue loading for gas turbine combustion transition piece, creep-fatigue tests were carried out on both as-received and aged Ni-based superalloy Nimonic 263. Crack initiation and propagation behaviors for the smooth specimen were observed. An unique relationship was obtained between life fraction and the maximum surface crack length under triangular wave shape loading tests, except the results for the trapezoidal wave loading tests. The latter results were due to the over estimation of the surface crack length at the crack initiation. These were caused from an oxide film break during straining. In the case of removing the oxide film before the measurement of surface crack, the relationship between life fraction and the maximum surface crack length obtained as unique relationship regardless of triangular and trapezoidal strain wave shapes. Using the life prediction method proposed, which is based on maximum surface crack length, the damage of combustion transition piece materials in service was evaluated.© 1997 ASME

Fracture Toughness at High temperature of Tungsten-Rhenium Alloys.

Fracture toughness tests of tungsten and tungsten-rhenium alloy were carried out at elevated temperatures. The effect of rhenium content on fracture toughness and the temperature dependence of fracture toughness were investigated. Fracture surface were observed in detail. Although the fracture toughnesses of three kinds of materials with rhenium of 0, 5 and 10wt% were almost identical at room temperature, the materials with higher rhenium content had the higher fracture toughness at elevated temperatures. The brittle-ductile transition similar to that of steels and the ductile-brittle transition at which recrystallization occurred, were observed for all three kinds of materials. With an increase of rhenium content, the brittle-ductile transition temperature decreased and the ductile-brittle transition temperature increased. A significant grain growth in the temperature range higher than the recrystallizing temperature, which was observed in the tungsten material without rhenium, was not found in the tungsten-rhenium alloy materials.