Toward Incorporating Cold Dwell Fatigue

Lifetime Predictions into DARWIN®

Kwai S. Chan, Michael P. Enright, and R. Craig McClung

Southwest Research Institute®

San Antonio, TX 78238

Cold Dwell Fatigue Workshop

Dayton, Ohio

April 18-19, 2016

Outline

• Status of SwRI cold dwell fatigue modeling

NAVAIR Phase II Program, Ray Pickering TPOC

• Status of ICME modeling in DARWIN

AFRL Phase II & IIE Programs, Pat Golden TPOC

• Future needs for incorporating cold dwell

fatigue life prediction into DARWIN

2

Characteristics of Cold Dwell Fatigue

• Beta-transformed

microstructures with

large prior beta grains

• Micro-textured region

(MTR) with hard

alpha grains (basal

planes aligned

normal to stress axis)

• Time-dependent

crack formation and

growth mechanisms

3

Time-Dependent

Degradation

Mechanisms

o Creep

o Hydrogen

Microtexture

o Orientation

o Size

Processing

o Beta

o Alpha + Beta

Highlights of SwRI CDF Modeling

• Treated fracture mechanisms identified in the paper by

Pilchak and Williams (Metall. Mater. Trans. A, Vol. 42A,

2011, 1000-1027)

• Developed a decohesion model for treating hydrogen-

induced time-dependent crack growth

• Applied model to analyze cold dwell fatigue life data of

Ti-6-4 and IMI 685 from the literature

• Delineated various hydrogen degradation modes as a

function of hydrogen content

Chan and Moody, “A Hydrogen-Induced Decohesion Model for Treating Cold Dwell

Fatigue in Ti-based Alloys,” Metall. Mater. Trans. A, published online, 2016

4

SwRI CDF Modeling: Hydrogen-Induced Decohesion Model

Strain

0.00 0.02 0.04 0.06 0.08 0.10 0.12

Str

ess, M

Pa

0

1000

2000

3000

4000

5000

CH = 0 ppm

10 ppm

20 ppm

40 ppm

100 ppm

1 = CH

C-Axis

(0001) Slip Plane

Slip

Plane

Dislo

cation P

ileup

Slip

: Hydrogen Atom

5

C-Axis

(0001) Plane

Slip

Plane

Dislo

cation P

ileup

Slip

: Hydride Habit Plane

: Hydrogen Atom

SwRI CDF Modeling: Hydrogen-Induced Failure Modes

• Slipband

decohesion: strain-

dominated failure

• Facet decohesion

• S-Nf data from Hack

and Leverant (x)

and Evans (y)

Cycles To Failure

100 101 102 103 104 105

Str

ess, M

Pa

1000

2000

500

Ti AlloysRT

1Hz, 300s Dwell

Model Calculation

Strain-dominated Faiure

Facet-dominated Faiure

IMI 685 [y]

Strain-Dominated Failure

Facet-Dominated Fracture

Ti-6-4 [x] IMI 685 [x]

IMI 685 [y]Ti-6-4 [y]

x: MMTA, Vol. 13A, 1982, 1729-1738; y: Scripta Metallurgica, Vol. 21(4), 1987, 469-474.

6

mm

fcr fN

RT

Q

c

E H

o

exp2

Highlights of SwRI CDF Modeling (2)

• Developed a methodology for treating combined cycle-

dependent and time-dependent crack growth in Ti-6-4

• Applied methodology to treat cold dwell fatigue crack

growth in Ti-6-4

• Performed a demonstration probabilistic analysis on a

Ti-6-4 ring disk by hacking into DARWIN

• Identified microtexture most susceptible to cold dwell

fatigue and quantified the conditional risk

7

SwRI CDF Modeling: da/dt Response vs Grain Orientation

• Extracted da/dt data from dwell

fatigue data of textured Ti-6Al-

4V (basal transverse texture)

from Stubbington and Pearson

(z)

K, MPa(m)1/2

1 10 100

da/d

t, m

/s

10-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

Ti-6Al-4V

20oC

TL Orientation

30 ded from TL

70 deg from TL

90 deg from TL

C-Axis

Angle From C-Axis (), Deg

0 20 40 60 80 100

No

rmali

zed

Rate

(N

R)

10-3

10-2

10-1

100

101

log (NR) = - 0.01945

C-Axis

Ti-6Al-4VRT

Basal Transverse Texture

z: Eng. Frac. Mech., Vol. 10, 1978, 723-756

8

mBKFdt

da

SwRI CDF Modeling: da/dN Response vs Frequency

• Strong

dependence on

alpha grain

orientation

• da/dN data from

Stubbington and

Pearson

• Basal

Transverse

Texture

Effective Frequency, Hz

10-4 10-3 10-2 10-1 100 101 102

da/d

N, m

/cycle

10-7

10-6

10-5

10-4

10-3

Ti-6Al-4V

R=0.1, 20oC

K = 20 MPa(m)1/2

Experiment

TL Orientation

30 deg from TL

70 deg from TL

90 deg from TL

Model

C-Axis

9

dt

dat

fdN

da

dN

dad

Ftotal

1

SwRI CDF Modeling: Kth and Kc Properties

• Kc (fracture

toughness) depends

on alpha grain

orientation

• Kth (static threshold)

is assumed to be

independent of grain

orientation

10

o

H

m

thC

CRTtK ln

12

32/1

HV

RT

Q

bC

H

mo

exp

Orientation Angle ( ), Deg

0 20 40 60 80 100

Kth

or

KC

, M

Pa(m

)1/2

0

20

40

60

80

100

120

Ti-6Al-4VRT

Basal Transverse Texture

KC

Kth

C-Axis

Stubbington and Pearson

Model

DARWIN® Overview

Design Assessment of Reliability With INspection

11

Demonstration DARWIN Analysis

• Ti-6Al-4V ring disk in FAA

AC33.14-1 test case

modified with a cold dwell

loading cycle

• The dwell time is two hours

per flight cycle

Time

Sp

eed

6800 rpm

Room Temperature Test Cycle

Basal-Transverse

Basal-Longitudinal

12

Demonstration DARWIN Analysis: Deterministic Life Calculation

• Disk life under

cold dwell

fatigue loading

is strongly

influenced by

orientation of

the alpha

grains

13

Flight Cycles

101 102 103 104

Defe

ct

Are

a,

mm

2

10-2

10-1

100

101

102

103

104

Ti-6Al-4V, RTTL Orientation

Basal Transverse Texture

0oC-Axis

Angle ( ) from C-Axis

30o

45o

70o

90o

Demonstration DARWIN Analysis: Risk of Disk Fracture

• Strong dependence

on microtexture

• Basal transverse is

most susceptible to

cold dwell fatigue

Flight Cycles

0 5000 10000 15000

Ris

k o

f F

ractu

re

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Ti-6Al-4V, RT

Basal Transverse Random Texture

Basal Longitudinal

14

Key Takeaways from

SwRI CDF Modeling

• Cold dwell fatigue occurs in hard alpha grains with c-axis

parallel to the stress axis and is enhanced by hydrogen-

induced decohesion

• Materials with the basal transverse microtexture are

most susceptible to cold dwell fatigue

• Time-dependent fracture response equations for

quantifying the effects of microtexture on cold dwell

fatigue and fracture risk have been developed

• Cold dwell fatigue can be mitigated or even eliminated

by controlling the microtexture to reduce clustering of

hard alpha grains

15

Integrating Life Management with

Manufacturing Process Simulation

Link DEFORM output with DARWIN input

Finite element geometry (nodes and elements)

Finite element stress, temperature, and strain results

Residual stresses at the end of processing / spin test

Location specific microstructure / property data

Tracked location and orientation of material anomalies

16 Copyright 2016 Southwest Research Institute

Status of ICME Modeling in DARWIN: Location-Specific Microstructure

• DARWIN has been integrated with DEFORM to accept

(deterministic or probabilistic) DEFORM calculations of

average grain size, ALA grain size, and volume fractions of

ALA grains at specific locations of a Ni-base superalloy disk.

17

Visualization of DARWIN random

grain size results based on

average grain size training data

from DEFORM:

(a) grain size mean, and

(b) grain size standard deviation.

(a) (b)

Status of ICME Modeling in DARWIN: Supergrain Identification

• DARWIN was enhanced to

import additional microstructure

information (Euler angles, major

and minor axes of grains) from

DEFORM

• Identified supergrains at

selected locations within a

component by computing the

grain mis-orientation angles

between grain neighbors in a

cluster of grains (currently for

Ni-base alloys)

18

Supergrain

Status of ICME Modeling in DARWIN: Location-Specific Crack Growth Properties

19

• da/dt and da/dN prediction based on grain size or

precipitate size scaling for Ni-base superalloys

Visualization of DARWIN da/dt scaling

factor results based on average grain

size training data from DEFORM:

(a) da/dN and da/dt scaling factor

means, and

(b) da/dN and da/dt scaling factor

standard deviations.

(a) (b)

O

m

O

DdN

da

D

DD

dN

da2/

o

p

o

dt

da

dt

da

Vision: DEFORM-DARWIN ICME Platform for

Designing Robust CDF-Resistant Ti Disks

20

◆ Stress

◆ Strain

◆ Temperature

◆ residual stress

◆ anomaly orientat ion

◆ average grain size

Key◆ Current DARWIN

◆ Completed in Phase I

◆ Proposed Phase II

◆ Other DARWIN Funding

Cycle-&Time-basedResults

◆ Fracture risk

◆ Risk contribut ion–Location–Anomalytype–Failuremode–Microstructure–Environment

Forma onModule◆ Mult iple Anomaly Types

◆ Multiple Failure Modes

Propaga onModule◆ Single Failure Mode

◆ Mult iple Failure Modes

◆ Microstructure

◆ Environment

Compe ngFailureModeAnalysis

Fa gue&ReliabilityAnalysis

DARWIN®

◆ Cycle- based life/ risk

◆ Time- based life/ risk

ANSYS

ABAQUS

MARC

FEAnalysis

ManufacturingProcessModeling

DEFORMMicrocode

RawMaterialProduc on

FormingOpera ons

HeatTreatment

MachiningOpera ons

Stochas cParameters

◆ Anomaly size

◆ Anomaly orientat ion

◆ Stress scatter

◆ Life scatter

◆ Residual stress scatter

◆ Grain size scatter

Orientation Distribution Function (ODF), Volume

Fraction, and Size of Alpha Grains

Probabilistic

Life-Prediction,

Fracture Risk

Certification

Improve Design

Glavicic and Venkatesh, JOM, V.66, 2014, pp 1310-1320

DEFORM

New Capabilities Needed From DEFORM

• Orientation and size of alpha grains for the entire disk (not

just at selected locations)

21

• Option 1

• Upgrade DEFORM to provide alpha grain

size and orientation information for the entire

disk

Potential Approaches

• Option 2

• Consider a threshold stress approach for CDF and develop a technique

to use the alpha grain size and orientation information for critical

locations identified by the threshold stress

• Use autozoning to identify and reduce the number of microtexture

regions where grain orientation data are needed

New Capabilities Needed for DARWIN

• New interface to read and visualize alpha grain

orientation and size data from DEFORM

• Enhanced capability for treating microtexture region in

DARWIN

• Need to treat orientation as well as the size of the

microtexture region for the entire disk

• Probability distribution function of alpha grains needs to

include both grain size and grain orientation

• Need to expand da/dt response equation to include both

grain size and grain orientation effects

• Need robust Kth and Kc models for various microtextures

and sizes

22

Demonstration of New Capabilities

• Implement cold dwell fatigue modeling

methodology including hydrogen-

induced time-dependent crack growth

and microtextured regions into

DARWIN

• Perform deterministic analyses on a Ti

engine component using a realistic

mission profile with cold dwell fatigue

loads and actual microtextural data

generated by EBSD measurements

• Perform probabilistic analyses on a

demonstration problem

23

Alpha Grain Orientation

Alpha Grain Size

Multilevel V&V of CDF Design Platform

Individual Models

• V&V of microtextural

predictions from DEFORM

compared with EBSD

measurements

• V&V of da/dt, Kth, and Kc

models compared against

experimental data and

texture measurements by

EBSD or other techniques

• Performed on small number

of laboratory specimens

Combined DEFORM-DARWIN

• V&V of DEFORM-DARWIN

predictions of alpha grain

size and orientation

distributions compared

against experimental data

from multiple disks (from a

previous MAI program)

• V&V of DARWIN predictions

of disk fracture risk under

cold dwell fatigue with

assistance from OEM

partners

24

Summary

• Cold dwell fatigue involves both cycle-dependent and

time-dependent crack growth mechanisms

• Developed da/dt framework for treating microtexture

effects on cold dwell fatigue

• Current DEFORM-DARWIN platform may be extended

to treat cold dwell fatigue in Ti rotors

• Vision of a DEFORM-DARWIN ICME platform for design

of CDF-resistant Ti disks was presented

• New capabilities needed for the DEFORM-DARWIN

ICME Ti disk design platform were identified

25

26

Thank You

Hydrogen Degradation Maps

Hydrogen Content, wt. ppm

10 100 1000

E(C

H)/

E(r

ef)

, c

r(C

H)/

cr(

ref)

or

cr(

CH)/

cr(

ref)

0.01

0.1

1

E(CH)/E(ref) >

cr(C

H)/

cr(ref)

Dislocation Core Effects Dominate

cr(C

H)/

cr(ref) >

E(CH)/E(ref)

DecohesionEffects Dominate

Hydrogen Effects

Hydride Fracture

cr(C

H)/

cr(ref)

E(CH)/E(ref)

cr(C

H)/

cr(ref)

Region I

Region II

Region III

Fracture Mechanism Maps

• Hydrogen-related time-

dependent crack

growth is operative at

temperatures below Td

• Creep and oxidation-

related crack growth is

operative at

temperatures above Td

28

Temperature, K

0 200 400 600 800 1000

da/d

t, m

/s

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Creep + OxidationHydride Embrittment

K = 50 MPa(m)1/2 K = 20 MPa(m)1/2

Ti-6246

Ti-6-4240 wppm H

Ti-6-460 wppm H

Ti-6Al100 wppm H

Ti-6Al-6V-2Sn38 wppm H

Ti-5Al-2.5Sn0.9 atm H

2

Td

Hydrogen in Solid Solution

Fracture Mechanism Map

Demonstration DARWIN Analysis: Orientation Distributions of Alpha Grains

• Three textures are

analyzed

Basal Transverse

Basal Longitudinal

Random Texture

Orientation Angle ( ), Deg

0 20 40 60 80 100

PD

F

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

Ti-6Al-4V

C-Axis

Basal Transverse

Random Texture

Basal Logitudinal

29

Potential Benefits

• Mitigate or reduce the risk of fracture of Ti disks due to

cold dwell fatigue in traditional near-alpha Ti alloys

• Provide a new ICME platform for designing robust Ti

disks for current and future Ti alloys

• Accelerate the certification process for Ti disks made

from new Ti alloys

• Improve the reliability and safety of current and future Ti

disks used in military and commercial aircrafts

30