249
0.01
0.1
1
10 100 1000 10000 100000
Cycles to Failure
Inelastic Strain Range
LCF Model
HRSC
CHSC
THSC
Creep-Fatigue Model
Creep Fatigue Model
BCCR
Fig. 29. Comparisons of Eq. (62-63) with experimental data for IN 100 (coated) at 1000 oC.
4.4 Fatigue-O
Fig. 9. Diagram of phase transformations in Ni30Co28Cr10AlY coating on IN738LC
superalloy after exposure at 900 C and 950 C
between a metal and a coating depending on the aluminum content in the zone: with the
aluminum content 10% the diffusion processes
damage state presents itself as a macroscopic crack, then fracture mechanics concepts have
to be used to characterize the stress-field ahead of the crack tip and the subsequent crack
growth processes. Macroscopic crack growth is usually the last stage of
prediction, development of EB-PVD thermal barrier coatings for turbine airfoils.
Surface and Coating Technology. Vol. 202, No. 4-7, (December 2007), pp. 658-664.
ISSN 0257-8972.
Suo, Z. (1993). Cracking and debonding of microlaminates. Journal of Vacuum S
For large scale systems, a model is not so simple as the above case. Therefore, the control
theory, signals processing and artificial intelligence communities have proposed diverse
methodologies to supervise the system behavior. The general frameworks are
(57)
For constant amplitude fatigue with a constant holding period, substituting Eq. (57) into (49)
and neglecting cavity formation, the integration of Eq. (49) leads to
2 2 1 22 1 exp( ) 2
16
f
s
N
N
Fb
w
(58)
Equation (58) shows that the fatigue life i
nnnn
C
Step 7. Assign the orientations of the I graphs using the set inv
Cfor each target node
including the cycle graphs (no diagonal submatrix) and constraints of the class d.
Step 8. Bring up the number nGR according the assigned redundant graphs; if n
3. The identification of the unknown Pn(T) model parameters from experiments based on
the IPD solution, which gives the proximity of CM and CE profiles by minimizing the F
value.
4. Long-term prediction of mass transfer processes and coating life with the
da d BK
dt X
(86)
The curve for the creep crack growth rate in air was fitted to the test data by Xu et al. (1999)
using a semi-empirical approach (Xu et al. 1999).
LifePredictionofGasTurbineMaterials
263
5.4 Creep-fatigue interaction in crack growth
Crac
(Twentieth Symposium), ASTM STP 1020, pp. 101-126. American Society for Testing
and Materials, Philadelphia, PA.
Riedel, H. (1990). Creep crack growth under small-scale creep conditions. Int. J. Fract. 42, pp.
173-188.
Robinson, E.L. (1952). Effect of tem
After applying a coating and performing heat-treatments a diffusion zone is formed in the
alloy. The zone width, phase composition and structure depend on coating and basic metal
compositions, coating application technique and subsequent heat-treatment co
combined effects of temperature and stress could just induce one dominant damage mode,
for example, it is generally believed that the IP cycle produces predominantly creep damage,
while the OP cycle induces oxide-scale cracking (Sehitoglu, 1992). However,
Fig. 53, respectively. In both cases, the stress has dropped dramatically with the overall
increment of the creep strain. Except those creep strain concentration regions, the majority
of the airfoil, especially the upper half, practically remains in the e
coating type at hand is conformed by experimental investigations for up to 20000 hours
- the oxide forms on the border x1 only;
- aluminium comes to the interdiffusion zone only from a coating ;
- the diffusion factor Def derived by the IPD solution is an
T T
(9)
When combining eqs. (8a) and (9) along with the condition G< one obtains
f hT2Ef . (10)
The general relation (10) shows that the crack stability can be improved by reducing strain
or residual stresses in the coating, lowering the coating thickness
Eq. (22) basically describes the accumulation of plastic strain via the linear strain-hardening
rule with dislocation glide as the dominant process and limited dislocation climb activities.
It is applicable to high strain rate loading conditions, which ar
ppp
nppnpp
I
pn
da d n AI C t p B K C t
dt n p BI I
(83)
GasTurbines
260
where n and p are power-law index, A and B are power-law constants, I n and Ip are HHR
field parameters associated with the HRR field of intragranular deformation and GBS,
respective
To that end, we proceed with the basic concept of strain decomposition that the total
inelastic strain in a polycrystalline material can be considered to consist of intragranular
strain g and grain boundary sliding gbs, as:
in g gbs (1)
The physics-based
D
kT
(14)
The equivalent stress for GBS, eq
gbs , controls the grain boundary dislocation glide with a
back stress gbs. The other equivalent stress, eq , controls grain boundary dislocation climb,
once it surpass a threshold stress, ic, that arises from t
Engineering Congress and Exposition, pp. 787-796, October 31-November 6, 2008,
Boston, Massachusetts, USA.
Watanabe, M.; Ueno,Y.; Mitani,Y.; Iki,H.; Uriu,Y. & Urano, Y. (2008). Developer of a
dynamical model for customers gas turbine generator in industri
AGV
kT kT
(46)
where A0 is the pre-exponential constant, G is the activation energy, V is the activation
volume, 0 is the back stress, k (=1.3810-23 JK-1) is the Boltzmann constant, and T is the
absolute temperature.
The creep behaviors of CM247LC, a DS
the following form:
2
1
2
p
C C
NE
(25)
LifePredictionofGasTurbineMaterials
225
Fig. 8 shows the prediction of Eq. (25) with C = 0.009 for fully-reversed low cycle fatigue of
IN738 at 400oC, in comparison with the experimental data (Fleury & Ha, 2001). T
S83-S88.
Baik, S. & Raj, R. (1982). Mechanisms of creep-fatigue interaction. Metall. Trans. A, 13A, pp.
1215-1221.
Bain, K.R., Gambone, M.L., Hyzak, J.H. & Thoms, M.C. (1988). Development of damage
tolerant microstructure in Udimet 720. In: Superalloys 19
short cycle repeats. GBS contributes to intergranular fracture.
When GBS operates, the accumulation of grain boundary damage, either in the form of
cavity nucleation and growth or as grain boundary cracks, is proportional to the GBS
displacement, such tha
purpose, many recent results of advanced numerical models based on fracture mechanics
are taken into account. A simple method for an assessment of performance capability of
diffusive coatings is presented as a case study performed on rotor blades of high-
damage due to crack initiation and growth. Structural materials of rotor blades and their
coatings determine a maximal permissible temperature of gases incoming to the high
pressure turbine.
The metallic coatings on blades serve as physical barriers betwe
Fig. 6. Scanning digitiser camera
Fig. 7. 3-dimentional model of blade and related passage channel
GasTurbines
354
Fig. 8. Meshing domain in solution range
4. Computational Fluid Dynamics (CFD) analysis
4.1 Discretization procedure
The domain shown in Fig
(81)
where 0 is a pre-exponential strain rate constant, Gis the activation energy, V is the
activation volume, o is the slip resistance of the lattice, H is the work-hardening coefficient,
is the fracture work factor, k is the Boltzmann constant, T is th