자료유형  

 학위논문

Control Number  

0016932676

International Standard Book Number  

9798379836177

Dewey Decimal Classification Number  

600

Main Entry-Personal Name  

Zhang, Jian.

Publication, Distribution, etc. (Imprint  

[S.l.] : Purdue University., 2021

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2021

Physical Description  

1 online resource(186 p.)

General Note  

Source: Dissertations Abstracts International, Volume: 85-01, Section: B.

General Note  

Advisor: Zhang, Jing.

Dissertation Note  

Thesis (Ph.D.)--Purdue University, 2021.

Restrictions on Access Note  

This item must not be sold to any third party vendors.

Summary, Etc.  

요약Thermal barrier coatings (TBCs) made of low thermal conductivity ceramic topcoats have been extensively used in hot sections of gas turbine engines, in aircraft propulsion and power generation applications. TBC damage may occur during gas turbine operations, due to either timeand cycle-dependent degradation phenomena, external foreign object damage, and/or erosion. The damaged TBCs, therefore, need to be removed and repaired during engine maintenance cycles. Although several coating removal practices have been established which are based on the trialand-error approach, a fundamental understanding of coating fracture mechanisms during the removal process is still limited, which hinders further development of the process.The objective of the thesis is to develop a particle-based coating removal modeling framework, using both the smoothed particle hydrodynamics (SPH) and discrete element modeling (DEM) methods. The thesis systematically investigates the processing-property relationships in the TBC removal processes using a modeling approach, thus providing a scientific tool for process design and optimization.To achieve the above-mentioned objective, the following research tasks are identified. First a comprehensive literature review of major coating removal techniques is presented in Chapter 2. Chapter 3 discusses an improved SPH model to simulate the high-velocity particle impact behaviors on TBCs. In Chapter 4, the abrasive water jet (AWJ) removal process is modeled using the SPH method. In Chapter 5, an SPH model of the cutting process with regular electron beam physical vapor deposition (EB-PVD) columnar grains is presented. In Chapter 6, a 3D DEM cutting model with regular EB-PVD column grains is discussed. In Chapter 7, a 2D DEM cutting model based on the realistic coating microstructure is developed. Finally, in Chapter 8, based on the particle-based coating removal modeling framework results and analytical solutions, a new fracture mechanism map is proposed, which correlates the processing parameters and coating fracture modes.The particle-based modeling results show that: (1) for the SPH impact model, the impact hole penetration depth is mainly controlled by the vertical velocity component. (2) The SPH AWJ simulation results demonstrate that the ceramic removal rate increases with incident angle, which is consistent with the fracture mechanics-based analytic solution. (3) The SPH model with regular EB-PVD columnar grains shows that it is capable to examine the stress evolutions in the coating with columnar grain structures, which is not available if a uniform bulk coating model was used. Additional analysis reveals that the fracture of the columnar grains during the cutting process is achieved through deflection and fracture of the grains, followed by pushing against neighboring grains. (4) The 3D DEM model with regular coating columnar grains shows that, during the coating removal process, a ductile-to-brittle transition is identified which depends on the cutting depth. The transition occurs at the critical cutting depth, which is based on the Griffith fracture criterion. At small cutting depths, the ductile failure mode dominates the cutting process, leading to fine cut particles. As the cutting depth exceeds the critical cutting depth, a brittle failure mode is observed with the formation of chunk-like chips. (5) The 2D DEM model with the realistic coating microstructure shows that there are densification and fracture during the foreign object compaction process, which qualitatively agrees with the experimental observations. (6) The newly proposed coating fracture mechanism map provides guidance to predict three fracture modes, i.e., ductile brittle, and mixed ductile-brittle, as a function of processing parameters, including the cutting depth and cutting speed.

Subject Added Entry-Topical Term  

Mechanical properties.

Subject Added Entry-Topical Term  

Airplane engines.

Subject Added Entry-Topical Term  

Protective coatings.

Subject Added Entry-Topical Term  

Cutting tools.

Subject Added Entry-Topical Term  

Cracks.

Subject Added Entry-Topical Term  

Energy consumption.

Subject Added Entry-Topical Term  

Sintering.

Subject Added Entry-Topical Term  

Discrete element method.

Subject Added Entry-Topical Term  

Aircraft.

Subject Added Entry-Topical Term  

Gases.

Subject Added Entry-Topical Term  

Oxidation.

Subject Added Entry-Topical Term  

Insulation.

Subject Added Entry-Topical Term  

Deformation.

Subject Added Entry-Topical Term  

Gas turbine engines.

Subject Added Entry-Topical Term  

Fluid mechanics.

Subject Added Entry-Topical Term  

Fracture mechanics.

Subject Added Entry-Topical Term  

Interfaces.

Subject Added Entry-Topical Term  

Energy.

Subject Added Entry-Topical Term  

Materials science.

Subject Added Entry-Topical Term  

Mechanics.

Added Entry-Corporate Name  

Purdue University.

Host Item Entry  

Dissertations Abstracts International. 85-01B.

Host Item Entry  

Dissertation Abstract International

Electronic Location and Access  

로그인을 한후 보실 수 있는 자료입니다.

Control Number  

joongbu:641514