NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety...

34
NASA Langley Damage Tolerance Experiences by Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium on Composite Damage Tolerance And Maintenance Chicago July 19-21, 2006

Transcript of NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety...

Page 1: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

NASA Langley Damage Tolerance Experiences

by

Ivatury S. RajuNASA Engineering and Safety Center

NASA Langley Research CenterHampton, Virginia

presented at the

FAA Symposium on Composite Damage Tolerance

And MaintenanceChicago

July 19-21, 2006

Page 2: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

NASA Langley’s Composites Programs

SOA Analysis

Emerging Continuum Methods

Future Directions

Outline

Page 3: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Allowable Damage Limit

(ADL)

Increasing Damage Severity

Ultimate

~ Maximum load per fleet lifetime

Design LoadLevel

Continued safe flight

Limit

Critical Damage Threshold (CDT)

1.5 Factor of Safety

Structural durability affects the frequency and cost of inspection, replacement,

repair, or other maintenance

Structural damage tolerance ensures damage will be found by maintenance

practices before becoming a safety threat

Discrete source events (e.g., engine burst, birdstrike) can cause severe damage but it is known to pilot

ResidualStrength(notional)

The structure must always be able to sustain design ultimate loads in the presence of nondectabledamage.

(FAR 25.571 & Mil-17)

Durability and Damage Tolerance Requirements

Page 4: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Textile Materials

Page 5: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Details of Stitched Plates

Load Direction

StitchingSpacedAt 3.2mm

48 ply stitched laminate[+45/0/-45/90]6s

Compression After Impact Strength

0

100

200

300

400

500

600

700

0 20 40 60 80 100 120

Unstitched AS4/3501-6

Stitched AS4/3501-6

Toughened MatrixCompositesComp.

Stress,MPa

Impact Energy, J

Stitching Improves Damage Tolerance

Page 6: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

No damage or permanent deformation at DLLTest Article with repair of simulated damage failed at 97% of DUL

AS4/3501-6 and IM7/3501-6 in textile preform

NASA ACT Program – Full Scale Wing Box Test (2000)

Page 7: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Dislocations

Twinning

Stacking Fault[1 1 0]

[0 0 1]

x

y

[1 1 0]

Void Coalescence

10 nm

Damage ScienceDamage Science

20 20 μμmm

Emerging Continuum MethodsEmerging Continuum Methods

Com

plex

ity, C

ompu

tatio

nal E

xpen

se

Time

1/41/23/4

0

1

G /(G + G )ΙΙ ΙΙ ΙΙΙ

GT

GIc + GIIc − GIc( ) GII +GIII

GT

⎝ ⎜

⎠ ⎟

η

+ GIIIc − GIIc( ) GIII

GII +GIII

GII +GIII

GT

⎝ ⎜

⎠ ⎟

η ≥ 1

t≈0

LaRC Decohesion Element(Technology adopted by ABAQUS)

Mixed-Mode Fracture

Bilinear Traction-Displacement Law

Perfectly plastic (pp)

Linear softening (lin)

Progressive softening (pro)

Regressive softening (reg)

G

σ

pro lin reg

c

σ

Needleman (Ne)

Nepp0

c

CGdF

=∫ δδσδ

0 )(

QuickTime™ and a decompressor

are needed to see this picture.

Wide range of element sizes

Narrow range

Classical

Enhanced

Enhanced formulation allows the useof elements up to three times larger thanwith the classical damage model.

MMB Specimen

Delamination growth

FY05 Advances

Current StateCurrent State--ofof--thethe--ArtArt

0

0.5

1

1.5

2

2.5

3

0 50 100 150 200

G I

in-lb/in 2

Pressure, P (psi)

b=0.750in.b=0.625in.b=0.500in.

Evolution of Damage Tolerance at NASA Langley (1999-)

Page 8: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

The liquid hydrogen composite tank failed during the protoflight ground test.

Hypersonic Experimental Vehicle (X-33 Program)

Page 9: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

The lobes are sandwich construction:The inner face sheet is [45/903/-45/03/-45/903/45]TThe outer face sheet is [65/0/-65/90/-65/0/65]T

The face sheets are IM7/977-2 laminates.The core is a honeycomb Korex 3/16 - 3.0 (1.5 in. thick).The adhesive is AF-191.

X-33 Composite Liquid Hydrogen Tank Failure

Page 10: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

X-33 Composite Liquid Hydrogen Tank Failure

Page 11: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Teflon Tape in CoreInner Skin Microcracking

Weak Core to Face Sheet Bond Strength/Toughness

Causes of the X-33 Composite Tank Failure

Page 12: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

0

0.5

1

1.5

2

2.5

3

0 50 100 150 200

GI

in-lb/in2

Pressure, P (psi)

b=0.750in.b=0.625in.b=0.500in.

mean-Gcr

3σ-Gcr

Lowest measured-Gcr

b

2.625”

R=0.5”

Hig

hest

mea

sure

d -P

3σ -

P

Strain Energy Release Rates for an F.O.D. Debond

Page 13: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Local FE Model

Global FE Model

Lug and Pin

Rear Fuselage and Tail Configuration

Page 14: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Attributes25,931 nodes21,519 elementsContact modeled200 plies in lugGlobal-local coupled analysisDamage monitored as load incremented

x

yz

3D-Shell Finite Element Model

Page 15: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2

Load Factor

Fres

(MN

)

FresMx

11.0

Onset of Damage

Peak Mx

Peak Fres

0.0

7.0

1.0

3.0

2.0

4.0

5.0

6.0

8.0

9.0

10.0

Mx

(kN

-m)

Damage Propagation from PFA

Page 16: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Test Failure Load 907 kNPredicted Failure Load896 kN

Failed Test LugFailed Test Lug

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(c) View through the outer thickness of the lug

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(c) View through the outer thickness of the lug

Elements with predicted damage

Unsymmetricdamage

due to loading

Predicted Failures

Comparison of Predicted and Test Results

Page 17: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(c) View through the outer thickness of the lug

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(b) View through the outer thickness of the lug

Unsymmetric Damage Due to Configuration and

Applied Moments

Elements with Predicted Damage

(a) View normal to the hole

(c) View through the outer thickness of the lug

Elements with Predicted Damage

FWDFWDUnsymmetricDamage Due to

Configuration and Applied Moments

LoadLoad

12

W375 Accident Conditions – Damage

Page 18: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Normalized Failure Load for 1985-Certification Test, 2003-Subcomponent Test and W375 Accident Condition

0.0

0.5

1.0

1.5

2.0

2.5

3.0

1985 Test SC Test W375Accident Case

Nor

mal

ized

Fai

lure

Loa

d,kN

PFA Analysis Failure LoadPFA Analysis Load at Maximum Moment MXTest Failure Load

0.0

0.5

1.0

1.5

2.0

2.5

3.0

1985 Test SC Test W375Accident Case

Nor

mal

ized

Fai

lure

Loa

d,kN

PFA Analysis Failure LoadPFA Analysis Load at Maximum Moment MXTest Failure Load

Page 19: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Dislocations

Twinning

Stacking Fault[1 1 0]

[0 0 1]

x

y

[1 1 0]

Void Coalescence

10 nm

Damage ScienceDamage Science

20 20 μμmm

Emerging Continuum MethodsEmerging Continuum Methods

Com

plex

ity, C

ompu

tatio

nal E

xpen

se

Time

1/41/23/4

0

1

G /(G + G )ΙΙ ΙΙ ΙΙΙ

GT

GIc + GIIc − GIc( ) GII +GIII

GT

⎝ ⎜

⎠ ⎟

η

+ GIIIc − GIIc( ) GIII

GII +GIII

GII +GIII

GT

⎝ ⎜

⎠ ⎟

η ≥ 1

t≈0

LaRC Decohesion Element(Technology adopted by ABAQUS)

Mixed-Mode Fracture

Bilinear Traction-Displacement Law

Perfectly plastic (pp)

Linear softening (lin)

Progressive softening (pro)

Regressive softening (reg)

G

σ

pro lin reg

c

σ

Needleman (Ne)

Nepp0

c

CGdF

=∫ δδσδ

0 )(

QuickTime™ and a decompressor

are needed to see this picture.

Wide range of element sizes

Narrow range

Classical

Enhanced

Enhanced formulation allows the useof elements up to three times larger thanwith the classical damage model.

MMB Specimen

Delamination growth

FY05 Advances

Current StateCurrent State--ofof--thethe--ArtArt

0

0.5

1

1.5

2

2.5

3

0 50 100 150 200

G I

in-lb/in 2

Pressure, P (psi)

b=0.750in.b=0.625in.b=0.500in.

Evolution of Damage Tolerance at NASA Langley (1999-)

Page 20: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Building Block Integration.

Verification of Design Data and Methodology

Development of Design Data

Number of Specimens

Chr

onol

ogic

al S

eque

nce

Spec

imen

Com

plex

ity

Certification Methodology (Mil-Hbk.-17)

Structural Levels of Testing & Analysis

Static/Fatigue

Material Selection and Qualifications Coupons

Design Allowables Coupons

Structural Elements

Sub-components

Components

Full Scale Article

Ana

lysi

sA

naly

sis Reduced Testing

More accurate design tools reduced recurring costs

Reduced reliance on testingFaster design process reduced non-recurring costs

High-Fidelity Progressive Failure Analysis

Building Block Approach

Page 21: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Conceptual Preliminary Detailed

DesignKnowledge,DesignFreedom

Time into Design Process

DesignFreedom

Goal

GoalKnowledge about Design

Design Freedom vs. Knowledge

Page 22: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Building Block Integration.

Verification of Design Data and Methodology

Development of Design Data

Number of Specimens

Chr

onol

ogic

al S

eque

nce

Spec

imen

Com

plex

ity

Certification Methodology (Mil-Hbk.-17)

Structural Levels of Testing & Analysis

Static/Fatigue

Material Selection and Qualifications Coupons

Design Allowables Coupons

Structural Elements

Sub-components

Components

Full Scale Article

Ana

lysi

sA

naly

sis Reduced Testing

More accurate design tools reduced recurring costs

Reduced reliance on testingFaster design process reduced non-recurring costs

High-Fidelity Progressive Failure Analysis

Building Block Approach

Page 23: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

• Failure Criteria are used for predicting damage initiation and final failure

• Composites have multiple damage modes; each requires a different criterion

• Failure Criteria are used for predicting damage initiation and final failure

• Composites have multiple damage modes; each requires a different criterion

σ11σ11

σ22σ22

m

m

-XC-XC

ϕ

2a0

σ22, YT

tτ12, S

Lis is

α=53º

τL

τTσn

σ22

τ12α

Fiber orientation

Matrix Tension & Shear

Fiber Compression

Matrix Compression and Shear

LaRC04 Criteria• In-situ matrix strength

prediction• Advanced fiber kinking

criterion• Prediction of angle of

fracture (mat. compression)• Criteria used as activation

functions within framework of damage mechanics

LaRC04 Criteria• In-situ matrix strength

prediction• Advanced fiber kinking

criterion• Prediction of angle of

fracture (mat. compression)• Criteria used as activation

functions within framework of damage mechanics

Failure Criteria for Laminated Composites

Page 24: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Gibbs Free Energy

Strains:

Lamina Secant Relation

Rate of Damage Growth

fi: LaRC04 failure criteria as activation functions

Softening

Compression Tension

CDM ensures consistent material degradation and mesh-independent solution

LaRC04 in Continuum Damage Model

Page 25: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

DefinitionPultruded graphite rods positioned through-thickness (z-direction) of a composite laminatePins are 0.2-0.5mm diameter rodsTypical range of areal density between 0.5% and 4%Inserted into uncured laminate using ultrasonic hammer

Purposes / DrawbacksImprove composite laminate transverse strengthProhibit delaminationDegrade laminate (in-plane) properties, see micrograph

ApplicationsAreas with significant out-of-plane loads such as bonded stiffener terminationAreas exposed to impact damage threat

Z-Pin preform: Insertion side**Z-Pin preform: Upper side**

*James Ratcliffe, NIA. **Pierre Minguet, Boeing. ***Jeffery Schaff, Sikorsky Aircraft.

Z-Pins protruding from laminate*

Fiber misalignment from z-pins***

z-pins

Z-Pin Technology

Page 26: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

GT

GIc + GIIc − GIc( ) GII

GT

⎝ ⎜

⎠ ⎟

η ≥ 1B-K Criterion

2D Fracture Criterion(only Mode I and Mode II)

3D Problems Contain Mode III

sublaminate buckling problem

Pure Mode III Testing

edge crack torsion test

ECT produces pure mode III data

GIIIc normally higher than GIIc

No mixed-mode test with mode III component

circulardelamination

contours show out-of-plane

displacement

New Delamination Criterion Needed

Page 27: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

1/41/23/4

0

1

G /(G + G )ΙΙ ΙΙ ΙΙΙ

GT

GIc + GIIc − GIc( ) GII +GIII

GT

⎝ ⎜

⎠ ⎟

η

+ GIIIc − GIIc( ) GIII

GII +GIII

GII +GIII

GT

⎝ ⎜

⎠ ⎟

η ≥ 1

Mode I-III interaction similar to the measured mode I-II interactionLinear interpolation between mode III and mode II

Proposed 3D Mixed-Mode Criterion

Page 28: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Dislocations

Twinning

Stacking Fault[1 1 0]

[0 0 1]

x

y

[1 1 0]

Void Coalescence

10 nm

Damage ScienceDamage Science

20 20 μμmm

Emerging Continuum MethodsEmerging Continuum Methods

Com

plex

ity, C

ompu

tatio

nal E

xpen

se

Time

1/41/23/4

0

1

G /(G + G )ΙΙ ΙΙ ΙΙΙ

GT

GIc + GIIc − GIc( ) GII +GIII

GT

⎝ ⎜

⎠ ⎟

η

+ GIIIc − GIIc( ) GIII

GII +GIII

GII +GIII

GT

⎝ ⎜

⎠ ⎟

η ≥ 1

t≈0

LaRC Decohesion Element(Technology adopted by ABAQUS)

Mixed-Mode Fracture

Bilinear Traction-Displacement Law

Perfectly plastic (pp)

Linear softening (lin)

Progressive softening (pro)

Regressive softening (reg)

G

σ

pro lin reg

c

σ

Needleman (Ne)

Nepp0

c

CGdF

=∫ δδσδ

0 )(

QuickTime™ and a decompressor

are needed to see this picture.

Wide range of element sizes

Narrow range

Classical

Enhanced

Enhanced formulation allows the useof elements up to three times larger thanwith the classical damage model.

MMB Specimen

Delamination growth

FY05 Advances

Current StateCurrent State--ofof--thethe--ArtArt

0

0.5

1

1.5

2

2.5

3

0 50 100 150 200

G I

in-lb/in 2

Pressure, P (psi)

b=0.750in.b=0.625in.b=0.500in.

Evolution of Damage Tolerance at NASA Langley (1999-)

Page 29: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

[0 0 1]

Continuum Representation of Atomistic Behavior

Mechanisms of Nano-crack Propagation

Computational Damage Science

KI = 0.36 MPa-m1/2

stress profileσyy(x)

opening profile δn(x)

δ n[n

m]

σsyy

[GP

a] Brittle Tip

Twinning Tip

Dislocations

Twinning

Stacking Fault[1 1 0]

[0 0 1]

x

y

[1 1 0]

Void Coalescence

10 nm

Calculation of Normal Stress and Crack Opening

Develop a fundamental understanding of the underlying damage processes that contribute to fracture initiation and propagation

20 20 μμmm

SEM micrograph of fatigue crack tip

200 200 μμmm

SEM micrograph of fatigue crack emanating

from EDM notch

Micro-Scale Crack Growth

Experimental Damage Science

Materials characterization and in-situ mechanical testing with

environmental capabilities

In-situ loading frame with heater/cooler and specimen tilt for EBSD analysis

Testspecimen

Develop multi-disciplinary Damage Science approach to:1) Characterize material structure and characteristic damage processes, 2) Develop multi-scale models to predict damage, and 3) Validate models through examination of near-tip damage processes.

Damage Science

Page 30: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Damage tolerance of composite wing boxes and full scale wing structures

Textile compositesStitchingEfficient analysis methods

SOA analysis demonstrated onX-33 LH2 tank failureAA587 composite lug analysis

Emerging continuum methodsNew criteria for interlaminar and intralaminar failureContinuum damage models - Mesh independenceZ-pinning

Damage science to understand failure initiation and growth -Damage Tolerance

Summary

Page 31: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Test Article failed at 83% of DUL under combined bending & torsionUnanticipated shear failure mode at out-of-tolerance gap

AS4/1806 and AS4/974

NASA ACT Program – Center Wing Box Test (1991)

Page 32: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Test article failed at 94% of DUL due to nonvisible impact damageCompression after impact (CAI) strength allowable did not account

for damaged elements (skin/stiffener) interaction

Composite stub box

AS4/3501-6 and IM7/3501-6 in textile preform

NASA ACT Program – Wing Stub Box Test (1996)

Page 33: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Upper Cover Compression Panel

Stringer RunoutPanel

Tension

Skin Ply Drop-off

Bulkhead Shear Clip Specimen

Compression

Upper Cover Splice Specimen

Rib Clip Pull-off SpecimenPostbuckling

Specimen

Hi-Load Panels

Spar Cap Longitudinal Shear Panel

Repair Panel

Substructure Shear Specimen

Building Block Approach – Reliance on Extensive Testing

Page 34: NASA Langley Damage Tolerance Experiences - Raju · Ivatury S. Raju NASA Engineering and Safety Center NASA Langley Research Center Hampton, Virginia presented at the FAA Symposium

Modeling ComplexitiesFailure of unidirectional and laminated

composites (in-situ)

Material nonlinearity & material degradation laws

Thermal residual stresses

Effects of stress gradients & notches

Size Effects

Finite Element implementation

Delamination growth: static & fatigue

Damage mode interaction

Stitched composites and textiles

LaRC04 Failure Criteria

LaRC04 Decohesion Elements

FY04 FY05-06

Enhanced Decohesion

Element&

High-Cycle Fatigue Model

Continuum Damage Model

In-Situ Strengths

Progressive Damage Analysis