new analysis and design procedures for ensuring gas turbine blades and adhesive bonded joints

177 Pages·2000·6.25 MB·English

NEW ANALYSIS AND DESIGN PROCEDURES FOR
ENSURING GAS TURBINE BLADES AND ADHESIVE
BONDED JOINTS STRUCTURAL INTEGRITY AND
DURABILITY
By
Hsin-Yi Yen, Ph.D.
The Ohio State University, 2000
M. -H. Herman Shen, Adviser
Most load-carrying structural systems under severe operating conditions such
as gas turbine engines usually demand durability, high reliability, light weight, and
high performance. In turn, as it has been reported, a number of structural failures
haveoccurredinaircraftenginesduringdevelopmenttestingandoperationalservice.
In order to prevent failures of turbine engines, the turbine blade vibration must be
attenuated to an acceptable level. To achieve this goal, the blade has to be provided
with higher damping, either externally or internally. The objective of this study
is to explore the feasibility of using a stress dependent magnetomechanical surface
coatingmaterialforenhancinghighdampingcapacityonturbineblades. Theresults
show that a 2% or 4% of blade thickness free surface magnetomechanical coating
layer has a signi(cid:12)cant contribution to the damping enhancement and the reduction
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of vibratory stresses at variouslowand high frequency vibrationmodes under either
non-rotating or rotating conditions.
Similar to the blade failure, the structural reliability and safety of the adhe-
sive bonded joint, one of the most commonly used structural joint designs in the
aerospace industry, isalsoaseriousconcern oftheaircraftdesigncommunity. Adhe-
sive joints easily become weaker due to environmentaldegradation and/or improper
manufacturing procedures. This often reduces structural durability and reliability
signi(cid:12)cantly. This motivates us to develop a new (cid:12)nite element tool/procedure
for assessing the interfacial disbonding mechanics of the single-lap joint with vari-
ous imperfectly-bonded conditions in order to predict the adhesive bonded joint’s
strength more precisely during its service period. According to these conclusions,
a new three-dimensional graphic mesh has been created to display the maximum
stress variations under di(cid:11)erent amounts and sizes of disbonded area. This new
procedure can be used as a basis for the development of a bonded joint reliability
prediction method and accept/reject inspection criteria.
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NEW ANALYSIS AND DESIGN PROCEDURES FOR ENSURING
GAS TURBINE BLADES AND ADHESIVE BONDED JOINTS
STRUCTURAL INTEGRITY AND DURABILITY
DISSERTATION
Presented in Partial Ful(cid:12)llment of the Requirements for
the Degree Doctor of Philosophy in the
Graduate School of The Ohio State University
By
Hsin-Yi Yen, M.S.
* * * * *
The Ohio State University
2000
Dissertation Committee: Approved by
M. -H. Herman Shen, Adviser
Gerald M. Gregorek
Adviser
Rama K. Yedavalli
Aeronautical and
Astronautical Engineering
Chia-Hsiang Menq
Graduate Program
c Copyright by
(cid:13)
Hsin-Yi Yen
2000
ABSTRACT
Most load-carrying structural systems such as gas turbine engines are usually
under severe operating conditions. This type of structure demands durability, high
reliability, light weight, and high performance. In turn, as it has been reported, a
number of structural failures have occurred in aircraft engines during development
testing and operational service. In order to prevent failures of turbine engines, it
becomes necessary to attenuate the turbine blade vibration to an acceptable level.
To achieve this goal, the blade has to be provided with higher damping, either
externally or internally. The objective of this study is to explore the feasibility of
using a stress dependent magnetomechanicalsurface coating materialfor enhancing
high damping capacity on turbine blades.
In the beginning, an analytical procedure is developed for modeling the dy-
namic behavior of beams and blades coated with a plasma sprayed iron-chromium
based coating. The stress or strain dependent damping capability of the coating
material is evaluated experimentally and further quanti(cid:12)ed with a probabilistic dis-
tribution function. The equations of motion and associated boundary conditions
are derived for uniform coated beams and blades. Later, the resulting equation of
motion is solved for beams and blades with a free surface coating layer by a closed
form procedure and (cid:12)nite element approximation. The results show that a 4% of
blade thickness free surface magnetomechanical coating layer can have a signi(cid:12)cant
ii
contribution to the damping enhancement and the reduction of vibratory stresses
at various low and high frequency vibration modes under either non-rotating or
rotating conditions.
Similar to the blade failure, the structural reliability and safety of the adhe-
sive bonded joint, one of the most commonly used structural joint designs in the
aerospace industry, is also serious concern by its imperfectly-bonded interface. This
imperfectly-bonded interface, caused by the environmental degradation and/or im-
proper manufacturing procedures, has weaker interface strength and often reduces
structural durability and reliability signi(cid:12)cantly. This motivates us to develop a
new (cid:12)nite element tool/procedure for assessing the interfacial disbonding mechan-
ics of the single-lap joint with several imperfectly-bonded conditions under various
impulse loading conditions in order to predict the adhesive bonded joint’s strength
more precisely during its service period.
In this study, a new disbonded interface model and a (cid:12)nite element procedure
have been developed to calculate the stress distributions in the adhesive joints with
perfectly-bonded or imperfectly-bonded interfaces under tensile loading. The (cid:12)-
nite element modeling of the weakened strength of the disbonded interface is ac-
complished through a spring element procedure or a newly developed line element
procedure. Those (cid:12)nite element procedures consist of a new modeling technique
for assessing the e(cid:11)ects of interfaces on the stress (cid:12)elds of adhesive joints dur-
ing the degradation process. The results from these procedures determined the
strengthreductionoftheinterfacedepends ontheamountofdisbondedareaandthe
size of each individual disbonded area. According to these conclusions, new three-
dimensional information has been created to display the maximum stress changes
iii
under di(cid:11)erent amounts and sizes of disbonded area. This new procedure can be
used as a basis for the development of a bonded joint reliability prediction method
and accept/reject inspection criteria.
iv
This is dedicated to my parents.
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ACKNOWLEDGMENTS
Iwouldliketoacknowledgemyadviser, Dr. M.-HHermanShenforhisguidance,
encouragement, support, and care during the course of this dissertation. As my
adviser, his suggestions and observations contributed immensely to the success of
this work.
I would like to acknowledge Dr. Gerald M. Gregorek, Dr. Rama K. Yedavalli,
andDr. Chia-HsiangMenqforservingonmydissertationcommitteeandforvarious
suggestions for this dissertation.
Additionally, I also would like to thank Ms. Sandy Rhoads for helping my
paper works , and thank Mr. Tommy George for his valuable suggestions in this
dissertation.
Finally, I thank my parents for their support and encouragement and all my
friends at The Ohio State University for their assistance during the past four years.
vi
VITA
Feb. 12, 1970 .............................Born - Taipei, Taiwan
1992 ......................................B.S. National Cheng Kung University,
Tainan, Taiwan
1992 ......................................Mechanic Trainee
Far East Air Transportation Co.
1992-1994 .................................Legislative OÆcer
R. O. C. Army
1996 ......................................M. S. The Ohio State University
1996-present ..............................Graduate Research Associate
The Ohio State University
PUBLICATIONS
Research Publications
H. -Y. Yen and M. -H. Herman Shen \Passive Vibration Suppression of Turbine
Blades UsingMagnetomechanicalCoating". Journal of Sound and Vibration, under
revision process.
H. -Y. Yen and M. -H. Herman Shen \Development of a New Modeling Procedures
for the Imperfectly-Bonded Interface in Single-Lap Joints". International Journal
of Adhesion and Adhesives, under review.
H. -Y. Yen and M. -H. Herman Shen \A New Finite Element Modeling Technique
forDisbonded Adhesive Joints". toappearin2000 ASME International Mechanical
Engineering Congress and Exposition, November 2000.
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