By Valeriy Krutiy A Thesis Report Review Faculty of Rensselaer Polytechnic Institute in Partial...

by Valeriy Krutiy

A Thesis Report Review

Faculty of Rensselaer Polytechnic Institute in Partial Fulfillment of the

Requirements for the degree of MASTER OF SCIENCE

Major Subject: MECHANICAL ENGINEERING

Approved: _________________________________________

Alexander Staroselsky, Thesis AdvisorRensselaer Polytechnic Institute

Hartford, Coneticut

SUB-MODELING OF THERMAL MECHANICAL FATIGUE CRACK PROPAGATION

Las

t Upd

ated

: N

ovem

ber

10, 2

009

2

MA

ST

ER

TH

ES

IS R

EP

OR

TSUB-MODELING OF THERMAL MECHANICAL FATIGUE CRACK PROPAGATION

Objective: Damage Tolerance Design Framework for Turbine Blade

Methodology:

• Analytical Solution for crack nucleation

• CAD and FEM Models Definition

• Thermal and Thermal-Structural Analysis

• Develop a Crack Propagation Model

• Incremental Thermal Structural Fracture Mechanics Analysis

• Predicted Crack Trajectory and Crack Growth Analysis

• Framework of the TMF/LCF Crack Propagation in the Turbine Blade

Abstract

Las

t Upd

ated

: N

ovem

ber

10, 2

009

3

MA

ST

ER

TH

ES

IS R

EP

OR


Turbine blades used in aircraft engines Turbine blades used in aircraft engines the most demanding structural applications

Fatigue cracks nucleate at the blade

Considerable amount of blade failures due to TMF

Las

t Upd

ated

: N

ovem

ber

10, 2

009

4

MA

ST

ER

TH

ES

IS R

EP

OR


Thermal Mechanical Fatigue and Fracture Mechanics

Typical strain and temperature cycle for turbine blade.

Extreme temperature gradients produce thermo mechanical fatigue

Ultimate failure in fatigue is always precipitated by fatigue cracking

Illustration of stable crack propagation

Las

t Upd

ated

: N

ovem

ber

10, 2

009

5

MA

ST

ER

TH

ES

IS R

EP

OR


Analytical elasticity based solution for the crack nucleation

Tensile stresses always around the hole during cooling

2b

2aT0

T1

r

θ

2

2 2 2 2 2 2

1 1

( )

r r r

r

a a a

aE Trdr Trdr Trdr

r b a r b a

2

2 2 2 2 2 2

1 1

( )

r r r

a a a

aE T Trdr Trdr Trdr

r b a r b a

Las

t Upd

ated

: N

ovem

ber

10, 2

009

6

MA

ST

ER

TH

ES

IS R

EP

OR


FEM based solution for the crack nucleation

Tensile stresses always around the hole during cooling

Las

t Upd

ated

: N

ovem

ber

10, 2

009

7

MA

ST

ER

TH

ES

IS R

EP

OR


UG/NX ANSYS Models for thermal and structural analysis

CAD and FEM models defined to simulate blade airfoil geometry

UG/NX 2D and 3D models ANSYS 3D model

Las

t Upd

ated

: N

ovem

ber

10, 2

009

8

MA

ST

ER

TH

ES

IS R

EP

OR


Thermal &Thermal-Structural Analysis

Temperature distribution and loading constrains were reviewed and analyzed

Temperature DistributionThe first rib constrained at two points

Las

t Upd

ated

: N

ovem

ber

10, 2

009

9

MA

ST

ER

TH

ES

IS R

EP

OR


Crack propagation zone were defined based on 3D thermo-structural analysis

Crack propagation zoneThermo-structural analysis Results

Thermal &Thermal-Structural Analysis

Las

t Upd

ated

: N

ovem

ber

10, 2

009

10

MA

ST

ER

TH

ES

IS R

EP

OR


The Frank3D Work Flow for Crack Propagation Analysis

Las

t Upd

ated

: N

ovem

ber

10, 2

009

11

MA

ST

ER

TH

ES

IS R

EP

OR


Franck3D/NG Submodels

Mesh Models created after thermo-structural analysis completed.

Smaller portion for fracture analysisAltered full model

Las

t Upd

ated

: N

ovem

ber

10, 2

009

12

MA

ST

ER

TH

ES

IS R

EP

OR


Initial Cracks Geometry

The initial crack inserted into a blade model.

Establishing an initial flaw shape, orientation, and location of crack

Initial crack inserted in model

Las

t Upd

ated

: N

ovem

ber

10, 2

009

13

MA

ST

ER

TH

ES

IS R

EP

OR


Crack Growth Analysis

Crack growth is a five-step process:• SIF’s are computed for all node points along the crack front• At each such point the direction and extent of growth is determined• A space curve is fit through the new crack-front points and, for the

case of a surface crack, extrapolated to extend outside of the body• New Bézier patches are added to the crack surfaces• The extended crack is inserted into an uncracked mesh

Las

t Upd

ated

: N

ovem

ber

10, 2

009

14

MA

ST

ER

TH

ES

IS R

EP

OR


Crack Growth Results

Crack propagates in the same radial plane, has a tendency to transitions from a corner crack to a part-through crack

Las

t Upd

ated

: N

ovem

ber

10, 2

009

15

MA

ST

ER

TH

ES

IS R

EP

OR



Detailed evaluations of individual crack shapes, displacements, and stress intensity factors for different stages of crack growth.

KI Stress Intensity Factor

Las

t Upd

ated

: N

ovem

ber

10, 2

009

16

MA

ST

ER

TH

ES

IS R

EP

OR


Conclusions

• Developed a framework for TMF crack propagation in the turbine blade

• Predicted crack growth path from thermal gradients

• Can predict the remaining turbine blade life

• Completed incremental thermal structural fracture mechanics analysis

• Implemented initial crack into the model, used a submodeling techniques

• Completed thermal-structural analysis

• Reviewed and analyzed temperature distribution and loading constrains

• Created CAD , FEM, crack propagation models

• Completed Analytical/FEM analysis for crack nucleation

Las

t Upd

ated

: N

ovem

ber

10, 2

009

17

MA

ST

ER

TH

ES

IS R

EP

OR


BACKUPThis paper outlines a framework for damage tolerance assessment using computational mechanics software. The framework is presented through the methodology for simulating the growth of through cracks in the airfoil walls of turbine blade structures. A CAD model of the blade airfoil was created. Geometry derived from this model was used to construct a finite elements model. Crack trajectories are allowed to be arbitrary and are computed as part of the simulation. The analysis was conducted under combined effects of thermal and mechanical loads at steady-state conditions. Data similar to a typical turbine blade were used to run a heat transfer analysis and, subsequently, a thermal structural analysis and incremental thermal structural fracture mechanics analysis. The interaction between the thermal-mechanical loads acting on the superstructure and the local structural response near the crack tips is accounted for by employing a hierarchical submodeling and interpolation strategy. Stress intensity factors are computed using an extension of the M-integral method embedded in Franc3D/NG. Crack trajectories are determined by applying the maximum tangential stress criterion. Crack growth results in localized mesh of local element and the deletion regions are remeshed automatically using a newly developed all-quadrilateral meshing algorithm. The predicted crack trajectory and fatigue life compare well with measurements of these same quantities from a failed blades. The effectiveness of the methodology, and its applicability to performing practical analyses of realistic structures, is demonstrated by simulating curvilinear crack growth in a airfoil wall from cooling hole that is representative of a typical turbine blade configuration. Finally, a damage tolerance design methodology is proposed.

Las

t Upd

ated

: N

ovem

ber

10, 2

009

18

MA

ST

ER

TH

ES

IS R

EP

OR


Damage Tolerance Design Methodology is proposed

Conclusions

Las

t Upd

ated

: N

ovem

ber

10, 2

009

19

MA

ST

ER

TH

ES

IS R

EP

OR


The Crack Propagation Computer Codes Review

FRAN3D/NG The FRacture ANalysis Code 3D / Next Generation (FRANC3D/NG or F3D/NG for short) is designed to simulate crack growth in engineering structures where the component geometry, local loading conditions, and the evolutionary crack geometry can be arbitrarily complex. It is designed to be used as a companion to a general purpose Finite Element (FE) package. Currently, interfaces to the ANSYS, ABAQUS, and NASTRAN commercial programs are supported. F3D/NG is a successor to the original FRANC3D program (now referred to as FRANC3D/Classic), which was developed at Cornell University in the late 1980's. While the two codes share a name, the next generation code benefits from over 20 years of experience developing and using the Classic code. The NG version is a complete rewrite employing different approaches for geometrical modeling and deformation analysis.

NASGRO Fracture Analysis Software NASGRO Fracture Analysis Software is a suite of programs based on fracture mechanics principles. NASGRO can be used to analyze crack growth, perform assessments of structural life, compute stresses, and process and store fatigue crack growth properties. The package includes a large set of crack growth rate and fracture data. The software is comprised of the following three modules: • NASFLA - Life Assessment • NASBEM - 2-D Boundary Element • NASMAT - Database of da/dN & fracture test results

AFGROW Fracture Analysis Software The current multiple crack capability allows AFGROW to analyze two independent cracks in a plate (including hole effects), non-symmetric corner cracked holes under tension, bending, and bearing loading (corner cracks only for now). Finite element based solutions are available for two through or corner cracks at holes, and through cracks in plates1under tension loading. These solutions and more information are available in the open literature [27, 28], allow AFGROW to handle cases with more than one crack growing from a row of fastener holes. The COM capabilities in AFGROW have allowed it to be used with an external K-solver program to communicate with AFGROW to perform real time crack growth analysis for multiple cracks (more than two) and cracks growing in complex and/or unique structure. Additional stress intensity solutions and spectrum load interaction models have been added to AFGROW. Finally, user-defined plug-in modules may now be used by AFGROW to allow users to include proprietary or unique stress intensity solutions.

Las

t Upd

ated

: N

ovem

ber

10, 2

009

20

MA

ST

ER

TH

ES

IS R

EP

OR


Fatigue cracks nucleate at the blade leading edge cooling hole locations

Turbine blades used in aircraft engines Advanced Blade Design, Cooling and Materials were introduced

However we still have considerable amount of blade failures due to TMF

Las

t Upd

ated

: N

ovem

ber

10, 2

009

21

MA

ST

ER

TH

ES

IS R

EP

OR


Fracture Mechanics and Fatigue Crack Growth The ultimate failure in fatigue is always precipitated by fatigue cracking. Fatigue crack growth - foundational area of damage-tolerant design. Damage tolerance is a mechanistic philosophy and methodology whereby the remaining strength and/or life of a component is determined after measurable damage.

Schematic Illustration of the different regimes of stable crack propagation

Las

t Upd

ated

: N

ovem

ber

10, 2

009

22

MA

ST

ER

TH

ES

IS R

EP

OR



Detailed Evaluations of KI stress intensity factor

KII Stress Intensity Factor

Las

t Upd

ated

: N

ovem

ber

10, 2

009

23

MA

ST

ER

TH

ES

IS R

EP

OR



Detailed Evaluations of Kink Angle

Kink Angle

Las

t Upd

ated

: N

ovem

ber

10, 2

009

24

MA

ST

ER

TH

ES

IS R

EP

OR


The numerical simulation results examined here consist of stress intensity factor histories and life predictions


Las

t Upd

ated

: N

ovem

ber

10, 2

009

25

MA

ST

ER

TH

ES

IS R

EP

OR


Thermal-Structural Analysis

The different flight conditions are simulations of a temperature – stress scenario that brings crack propagation. For the 2D model the sensitivity study of loading constrains were reviewed to identify possible crack propagation conditions and eliminate improper displacement restrictions.

The first rib constrained at two points The all ribs constrained

Las

t Upd

ated

: N

ovem

ber

10, 2

009

26

MA

ST

ER

TH

ES

IS R

EP

OR


Las

t Upd

ated

: N

ovem

ber

10, 2

009

27

MA

ST

ER

TH

ES

IS R

EP

OR


Las

t Upd

ated

: N

ovem

ber

10, 2

009

28

MA

ST

ER

TH

ES

IS R

EP

OR


Las

t Upd

ated

: N

ovem

ber

10, 2

009

29

MA

ST

ER

TH

ES

IS R

EP

OR


Maximum “Hoop” Stress Criterion for Crack Turning Prediction

Erdogan and Sih, “On the extension of plates under plane loading and transverse shear,” Journal of Basic Engineering, Vol. 85D, No. 4 (1963), pp. 519-527

dd

0

r 0

KII

KI

sin 3cos 1

r

x

y

The crack-tip will “kink” in the direction where

or, equivalently,

r

r

1

2rcos

2

KI 1 sin2 ( 2) 32 KII sin() 2KII tan( 2)

KI cos2 ( 2) 32 KII sin( )

KI sin() KII 3cos( ) 1

-80

-60

-40

-20

0

20

40

60

80

-90 -60 -30 0 30 60 90

kink

ang

le

arctan(KII/KI)-

Las

t Upd

ated

: N

ovem

ber

10, 2

009

30

MA

ST

ER

TH

ES

IS R

EP

OR


b

n

t

r

crack front

perpendicular plane

predicted new crack-front points

In FRANC3D, new crack-front locations are computed in planes perpendicular to the crack front according to the Paris relation

This is done for a series of points on the old crack front.

The crack extends at the local angle corresponding to the maximum hoop stress unless planar extension is specified.

b

I

I

K

Kaa

maxmax

a

Las

t Upd

ated

: N

ovem

ber

10, 2

009

31

MA

ST

ER

TH

ES

IS R

EP

OR


Date post:	31-Dec-2015
Category:	Documents
Upload:	augustine-caldwell
View:	215 times
Download:	0 times

By Valeriy Krutiy A Thesis Report Review Faculty of Rensselaer Polytechnic Institute in Partial...

Documents