Aging Effects Evaluation of A Beechcraft Starship and a ... · CRFP 737-200 Horizontal Stabilizer. The Joint Advanced Materials and Structures Center of Excellence 2 Research Team

The Joint Advanced Materials and Structures Center of ExcellenceJune 21st, 2006

Aging Effects Evaluation of A Aging Effects Evaluation of A BeechcraftBeechcraftStarship and a Decommissioned Boeing Starship and a Decommissioned Boeing

CRFP 737CRFP 737--200 Horizontal Stabilizer200 Horizontal Stabilizer

2The Joint Advanced Materials and Structures Center of Excellence

Research Team (Beechcraft Starship)

Principal Investigators & ResearchersDr. John Tomblin, Wichita State UniversityLamia Salah, Wichita State University

FAA Technical MonitorCurtis Davies

Other FAA Personnel InvolvedPeter Sheprykevich, Larry Ilcewicz

Industry ParticipationRic Abbott


Objective/ Methodology

To evaluate the aging effects of a beechcraft starship after 12 years of service (1827 hours)

Non-Destructive Inspection to identify flaws induced during manufacture/ service (delamination, disbonds, impact damage, moisture ingression, etc…)Coupon level static and fatigue testing to investigate any degradation in the mechanical properties of the material.Physical and thermal tests to identify possible changes in the chemical composition of the material


Status to Date

Engineering Report Review (Ongoing)LH wing has been cut and is currently being inspected using Through Transmission ultrasonics for flaws induced during either manufacture or serviceDurability and Damage Tolerance test set-up on the RH wing is in progress

Wiffletrees have been installed on the wing for load applicationWing spectrum has been built to simulate gust, maneuver and taxi loads.

Loads match those used for certification at all wing stations except at the root since the wing is cantilevered.

Strain gage locations have been defined. Strain gages will be installed after completing the baseline NDI inspection

Meeting with the OEM to establish NDI procedures and requirements to conduct the first inspection

Reference standards are being built from LH wing to conduct the baseline NDI on the RH wing


Research Team (B737)

Principal Investigators & ResearchersDr. John Tomblin, Wichita State UniversityLamia Salah, Wichita State University

FAA Technical MonitorCurtis Davies

Other FAA Personnel InvolvedPeter Sheprykevich, Larry Ilcewicz

Industry ParticipationDr. Matthew Miller, The Boeing CompanyDan Hoffman, Jeff kollgaard, Karl Nelson, The Boeing Company


Objective/ Methodology

To evaluate the aging effects of a (RH) graphite-epoxy horizontal stabilizer after 18 years of service

Non-Destructive Inspection to identify flaws induced during manufacture or service

Mechanical testing on coupons extracted from the structure to investigate any degradation in the mechanical properties of the material

Physical and thermal analysis to quantify porosity and moisture levels in the structure and characterize its thermal properties after 18 years of service


Background

The purpose of the NASA ACEE (Aircraft Energy Efficiency) program was to develop new technologies to reduce fuel consumption in aircraft structures

The ACEE program was subdivided into four development areas: laminar flow systems, advanced aerodynamics, flight controls and composite structures

The ACEE Composites program focused on redesigning existing structural components using lighter materials

A building block approach was followed where composite structure development would startwith lightly loaded secondary components followed by medium primary components and finally wing and fuselage development


DC-10 Upper Aft RudderDC-10 Upper Aft Rudder

B 727 ElevatorL1011 Inboard AileronDC-10 Vertical Stabilizer

L1011 Vertical Fin

B-737 Horizontal stabilizer

L1011 Inboard AileronDC-10 Vertical Stabilizer

L1011 Vertical Fin


DC-10 Vertical Stabilizer

L1011 Vertical Fin


DC-10 Vertical Stabilizer

L1011 Vertical Fin


DC-10 Vertical StabilizerDC-10 Vertical Stabilizer

L1011 Vertical FinL1011 Vertical Fin

B-737 Horizontal stabilizerB-737 Horizontal stabilizer

Background

Six aircraft secondary and medium primary components were redesigned using composite materialsACEE program was ended before the implementation of advanced materials in wing and fuselage components


Boeing redesigned, manufactured, certified, & deployed five shipsets of 737-200 horizontal stabilizers using graphite-epoxy compositesCertification was achieved in 1982 and all shipsets were introduced into commercial service in 1984Boeing closely monitored the performance of the stabilizers for 7 years. Outstanding performance was demonstrated with no in-service incidents attributed to aging of the composite structure

Background


Boeing 737 Fleet Status

Shipset / ProductionLine #

Entry into Service

Airline Status as of March, 2006

1 / 1003 2 May 1984 A In service (60000 hours, 45000 flights)2 /1012 21 March 1984 A In service (61000 hours, 46000 flights)3 / 1025 11 May 1984 B Damaged beyond repair 1990; partial teardown

completed in 1991 (17300 hours, 19300 flights)4 / 1036 17 July 1984 B & C Stabilizers removed from service 2002 (approx.

39000 hours, 55000 flights); partial teardown of R/H unit at Boeing

5 / 1042 14 August 1984 B & D Stabilizers removed from service 2002 (approx. 52000 hours, 48000 flights); teardown of L/H unit at Boeing; teardown of R/H unit at NIAR, Wichita State

DSO of 75000 flightsUpper Skin Inboard Delaminations at Stringer Runouts due to maintenance personnel walking on a no-step zone


Horizontal Stabilizer Description

Designed such that maximum commonality is achieved with respect to the existing structureInterchangeable with its metal counterpart 21.6% weight savings/ metal structureMaterial: NARMCO T300/5208Stiffened Skin Structural box arrangement with co-cured I stiffenersHoneycomb ribs for cost efficiencyRoot lugs used titanium platesbonded and bolted to a pre-cured graphite epoxy chord


Corrosion/ Lightning Protection Scheme

Corrosion Protection SchemeCorrosion protection by co-curing a fiberglass ply onto the graphite-epoxy structure or painting the surface with primer and epoxy enamelAll aluminum structure was anodized or alodine treated, primed and enameledFasteners were installed with wet polysulfide sealant

Lightning Protection SchemeBonding Straps connecting the Aluminum leading edge, the aluminum rib cap of the outboard closure rib and the aluminum elevator spar were used to provide an electrical path around the entire perimeter of the structural boxAn Aluminum flame spray was used to protect the stabilizer’s critical strike areaThe outboard skin panels were insulated using a layer of fiberglass co-cured to the parent structure prior to applying the conductive coating


Disassembly

Upper skin assembled using Inconel “Big Foot” blind fastenersLower skin assembled using titanium Hi-Lokfasteners with corrosion resistant steel collars and washersThe upper skin was disassembled first by drilling out the blind fasteners using a Monogram fastener removal kit: the fastener head was drilled out until the shank could be driven out of the structureOnce the upper skin was dismantled, the lower skin’s Hi-Lok fasteners were disassembled


Disassembly/ PreliminaryFindings

Upper Skin (RH)



Lower Skin (RH)



Center Box (RH)

Structure held very wellNo evidence of pitting or corrosion as would be observed in a metal structureNo residual strains compared to the LH


Visual Inspection

Evidence of Shimming


Visual Inspection

A few corroded fasteners due to sealant deterioration


Visual Inspection

Degradation of Tedlar Moisture Barrier film


Non-Destructive Inspection

Pulse-echo and through-transmission non-destructive methods were used to inspect the stabilizer using 2.25 Mhz frequency transducersBoth methods confirmed the large amounts of porosity in the upper skin Pulse-echo results obtained confirmed the existence of delaminated stringers and demonstrated the increased accuracy/ sensitivity of the current inspection methods compared to those used in the 1980’s

1980’s sensitivity Today’s sensitivity



Manual Pulse-echo was performed to inspect the skin/ stringer co-cured bonds and identify areas with delaminated stringers

Upper skin Inboard delaminations at stringer runouts


Destructive Evaluation

Destructive evaluation has been conducted on sections of the stabilizer identified as disbonds from the NDI inspection to verify the existence of these delaminations. Destructive evaluation confirmed the results


Non Destructive Inspection prior to teardown (RH Lower Skin RapidScan, SNL)

A

B

C

D

NDI/ DE

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Grid Reference Suspected flaw

A3 – A4 Disbond of the stringer

B3 – B4 Disbond of the stringer

B8 Possible delamination

C11 Delamination above the stringer

D13 - D14 Scattered porosity

C15 Delamination above the stringer

A16 Disbond of the stringer



NDI pulse echo inspection showed significant levels of porosity in the upper skin compared to the lower skin (tooling and process variability)Porosity levels have been quantified using image analysis/ physical testsVery porous repair between rib stations 2 and 3 (str 5 and 8)


Physical Tests Results

LS Max Void Content = 1.83%

US Max Void Content = 5.38%

( )

0-0.5 0.5-1 1-1.5 1.5-2 2-2.5

2.5-3 3-3.5 3.5-4 4-5 5.0 above

Physical tests were conducted per ASTM D3171 to quantify porosity levels in both skins


Moisture Content Evaluation

Moisture content in the aged structure has been quantified per ASTM D5229: specimens were extracted from different locations in the upper skin and lower skins of the stabilizer and have been dried to evaluate the moisture content of the structure. The results showed that the moisture content in the upper skin is slightly higher than the moisture levels found in the lower skin but overall the percent moisture varied from 0.5 to 0.9% (design moisture level of 1.1%)

CONDITIONING HISTORY - LOWER SKIN

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.00 5 10 15 20 25 30 35 40

Time (days)

% W

eigh

t Gai

n (T

otal

)

Rib7Str1

Rib7Str4

CONDITIONING HISTORY - UPPER SKIN

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.00 5 10 15 20 25 30

Time (days)

% W

eigh

t Gai

n (T

otal

) Rib7Str1

Rib7Str6


Thermal Analysis

DMA technique to determine the glass transition temperature of the aged material for coupons extracted from both the upper and lower skins

Thermal analysis was conducted on coupons with actual in-service moisture content and dried coupons to compare the difference between the in-service Tg with respect to the dry Tg.

Storage Modulus is an indication of the stiffness of the material, tanδ is a measure of the damping of the material

DMA curves with a shallow storage modulus transition and a narrow tanδ indicate a highly cross linked material


Thermal Analysis

Tg values consistent but lower than LH Results (Courtesy the Boeing Co)Average values (174°C/215°C (RH))DMA test parameters vary/ Tg obtained is a “wet” Tg (at least 0.6% moisture content) Dry Tg (205°C/225°C)

Glass Transition Temperature (DMA)

020406080

100120140160180200220240260

Upper Skin

Tg

(deg

-C)

Onset of Storage ModulusPeak of Tan d


Thermal Analysis/ DSC

Non-Reversing heat flow curves reveal exotherms/ chemical reactionsDSC heat of reaction values are extremely small (<6J/g) indicating a highly cross linked material (fully cured)Reversing heat flow curves reveal TgDrying the specimen increased the cure onset (water acts as a plasticizer)Water content does not affect the degree of cure

DSC, Rib 7, as extracted DSC, Rib 7, dry


Microscopy/ Image Analysis

Image analysis was performed to detect porosity/ micro-cracking and any evidence of aging in the structure. Both images show evidence of porosity embedded in the laminate. The flange cross section also shows evidence of microcracking initiating in the void areas.

X-section of stringer 2, rib station 2 at a magnification of 50xstringer web (left image) and flange (right image).


Mechanical Tests

Tested Upper Skin Compression Coupons

Compression Test Set-up

Mechanical Tests were conducted according to the 1980’s requirements/ standards


Mechanical Tests Results

Upper Skin Compression Test Results

0

10

20

30

40

50

60

70

102-1

Bas

eline

102-2

Bas

eline

US_R1_

STR9_

10_C

1US_R

1_STR

9_10

_C2

US_R1_

STR9_

10_C

3US_R

2_STR

4_5_

C1US_R

2_STR

4_5_

C2US_R

2_STR

4_5_

C3US_R

6_STR

0_1_

C1US_R

6_STR

0_1_

C2US_R

6_STR

0_1_

C3

Ulti

mat

e C

ompr

essi

ve S

tres

s (K

si)

Mechanical Data - MeasuredMechanical Data - Normalized



Lower Skin Compression Test Results

0

10

20

30

40

50

60

70

80

102-1

Bas

eline

102-2

Bas

eline

LS_R2_

STR4_5_

C1LS_R

2_STR4_

5_C2

LS_R2_

STR4_5_

C3LS_R

4_STR2_

3_C1

LS_R4_

STR2_3_

C2LS_R

4_STR2_

3_C3

LS_R6_

STR0_1_

C1LS_R

6_STR0_

1_C2

LS_R6_

STR0_1_

C3

Ulti

mat

e C

ompr

essi

ve S

tres

s (K

si)

Mechanical Data - MeasuredMechanical Data - Normalized


Mechanical Tests

Tested Lower SkinTension CouponsTension Coupon Test Set-up

Mechanical Tests were conducted according to the 1980’s requirements/ standards



Lower Skin Tension Test Results

0

10

20

30

40

50

60

101-1

Bas

eline

101-2

Bas

eline

LS_R2_

STR4_5-T

1LS_R

2_STR4_

5-T2

LS_R2_

STR5_6-T

1LS_R

4_STR3_

4-T1

LS_R6_

STR0_1-T

1LS_R

6_STR0_

1-T2

LS_R6_

STR1_2-T

2

Ulti

mat

e Te

nsile

Str

ess

(Ksi

) Mechanical Data-MeasuredMechanical Data-Normalized



Upper Skin Tension Test Results

0

10

20

30

40

50

60

70

101-1

Bas

eline

101-2

Bas

eline

US_R1_

STR8_9-T

1

US_R1_

STR9_10

-T1

US_R2_

STR4_5-T

1

US_R2_

STR5_6-T

1

US_R2_

STR5_6-T

2

US_R3_

STR3_4-T

1

US_R6_

STR0_1-T

1

US_R6_

STR0_1-T

2

US_R6_

STR1_2-T

1

Ulti

mat

e Te

nsile

Str

ess

(Ksi

) Mechanical Data - MeasuredMechanical Data - Normalized


On-Going Efforts

Mechanical test Evaluation to identify possible changes in the static and fatigue properties of the material

Testing of current T300/5208 to evaluate the possible differences between the material 25 years ago and the current material and to establish baseline for mechanical test

Additional physical tests to further quantify porosity in the structure and correlate mechanical test results with physical test data


Conclusions/Value of the results

Structure held extremely well after 18 years of service: no obvious signs of aging to the naked eye such as pitting and corrosion as would a metal structure with a similar service history exhibitPhysical tests showed moisture levels in the structure after 18 years of service as predicted during the design phaseThermal analysis results very consistent with those obtained for the left hand stabilizer Significant improvements in composite manufacturing processes and NDI methodsTeardown provides closure to a very successful NASA program and affirms the viability of composite materials for use in structural components


Conclusions/Value of the results

Understand the aging mechanism of composite structures (current aging studies focused on metal structures)

Producibility large co-cured assemblies reduce part and assembly cost, however other costs should be taken into account, for example, when disposing of non-conforming assemblies Supportability needs to be addressed in design. Composite structures must be designed to be inspectable, maintainable and repairable

most damage to composite structures occurs during assembly or routine aircraft maintenance

SRM’s, engineering information needed for in-service maintenance and repair

Documents

Aging Effects Evaluation of A Beechcraft Starship and a ... · CRFP 737-200 Horizontal Stabilizer. The Joint Advanced Materials and Structures Center of Excellence 2 Research Team