AgingAging ofof CompositeComposite AircraftAircraft StructuresStructures BeechcraftBeechcraft StarshipStarship andand BB--737737 HorizontalHorizontal StabilizerStabilizer
John Tomblin, PhD Executive Director, NIAR
Lamia Salah Sr. Research Engineer, NIAR
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence FAA Sponsored Project Information
¾ Principal Investigators & Researchers ¾ Dr. John Tomblin, Wichita State University ¾ Lamia Salah, Wichita State University ¾ FAA Technical Monitor ¾ Curtis Davies ¾ Other FAA Personnel Involved ¾ Larry Ilcewicz, Peter Sheprykevich ¾ Industry Participation ¾ Mike Mott, Ric Abbott
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 2 Motivation/ Objective
¾ Current market/ economic conditions are requiring the use of aircraft structures beyond their DSO ¾ Industry is relying on existing inspection standards to ensure aging aircraft airworthiness ¾ Most aging studies are focused on metallic structures, need to address composite aging as well
¾ To evaluate the aging effects on a Beechcraft starship (NC-8) main wing after 12 years of service (1827 hours)
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 3 Background
¾ Program was launched in 1982 ¾ Objectives were to produce the most advanced turboprop business airplane feasible at the time and to promote the use of composites in a business aircraft ¾ Benefits: to achieve elaborate contours through composite molding, lower part count, manufacturing simplicity, composite’s resistance to corrosion, good fatigue properties, weight savings. ¾ 70% of the airframe by weight is composite ¾ FAA certification was obtained on June 14th 1988 to FAA part 23 regulations and special conditions ¾ A total of 53 airframes were built but only a handful ever sold. In 2003, the OEM decided to retire the entire Starship fleet except five that were still flying as of Summer of 2007.
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 4 Approach/ Methodology
¾ Non-Destructive Inspection to identify flaws induced during manufacture/ service (delamination, disbonds, impact damage, moisture ingression, etc…) ¾ Coupon level static and fatigue tests to investigate any degradation in the mechanical properties of the material (comparison with OEM tests) ¾ Physical and thermal tests to validate design properties, identify possible changes in the chemical/ physical/ thermal properties of the material ¾ Full scale static, durability and damage tolerance tests to evaluate the structural health/performance of the main wing 19 years since manufacture (12 years in service)
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 5 Test Article Description (Main Wing)
¾ Monococque structure with three spars and five full-chord ribs symmetric wrt about the aircraft centerline ¾ The wing skins are cured in one piece 54 feet tip to tip ¾ The wing skins are secondarily bonded to the spars and ribs using paste adhesive
Root Rib MLG Spar Inboard Flap Rib MLG Rib
FWD Curved Spar Mid Flap Rib
FWD Spar Outboard Flap Rib Mid Elevon Rib
Aft Spar Inboard Center Spar Aft Spar Middle
Aft Spar Outboard
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 6 Test Article Description (Main Wing)
Skin ¾H-Joint: used to join the upper and Paste Adhesive lower skins to the spars ¾A cutout is first routed in the skin prior to bonding the joint to the skin. ¾The joint is then secondarily bonded to the skin using paste and film Film Adhesive adhesive Paste Adhesive ¾ The spars are finally bonded to the assembly using paste adhesive
Spar
BL 199 US H-Joint Cross Section
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 7 Test Article Description (Main Wing)
Skin ¾ V-Joint: used to bond the upper and Paste lower wing skins to sections of the Adhesive forward and aft spars ¾ The pre-cured graphite epoxy joint is secondarily bonded to the wing skin first using paste adhesive ¾ After this process is completed, the assembly is subsequently joined to the Paste spars using paste adhesive Adhesive
BL 78 LS
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 8 Test Article Description (Main Wing)
¾ Lightning Protection achieved through the use of hybrid woven graphite/ aluminum fabric as the surface ply in all exterior surfaces ¾ Materials used was E7K8 12K/ 280 and 145 tape and AS4 E7K8 3K/195 PW fabric. Material qualification was conducted per Military Handbook 17 specifications. ¾ Lamina and Laminate testing was conducted to generate tension, compression, shear strength and strain allowables in various environmental conditions
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 9 Disassembly
¾ Main components disassembled (fuselage, forward wing, main wing, nacelles, fuel tanks) ¾ Main wing cut in two pieces for ease of transportation
Coupon Full Scale Article Destructive Evaluation
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 10 NDI-LH Main Wing
Preliminary TTU Non-Destructive inspection showed no evidence of flaws induced during manufacture or service in the skins. OEM records suggest that porosity levels in the upper skin LE flanges exceed 2.5%
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 11 Thermal Analysis-DMA
¾ Storage Modulus is an indication of the stiffness of the material, tanδ is a measure of the damping of the material ¾ DMA curves with a shallow storage modulus transition and a narrow tanδ indicate a highly cross linked material
Lower Skin LF BL 260 DMA results Storage Modulus 159°C 318°F Tan δ 193°C 379°F
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 12 Thermal Analysis-DSC
Lower Skin UF BL 260 DSC results Very small heat of reaction values indicative of a highly cross linked material
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 13 Full Scale Structural Test
¾ A baseline Non-Destructive Inspection scan has been generated prior to conducting the full scale test in order to identify possible manufacturing flaws or defects induced during service
¾ NDI grid has been drawn on the structure for ease of inspection and flaw growth monitoring
¾ Visual inspection, TTU and tap testing were used for the inspection
¾ A few areas in both the upper and lower skins have been identified as disbonds by the inspectors
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 14 Full Scale Structural Evaluation
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 15 Full Scale Structural Evaluation
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 16 Wet Lay-Up Repair
¾ Wet lay-up repair per BS 24204 and BS23727 using EA 956 resin ¾ Repair Analysis conducted by the OEM and demonstrated positive margins for axial loading ¾ Repair Stacking sequence: PW45/T0/8HS0/T0/8HS90/T0/PW45
Scarfed repair area Ply 1 application Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 17 Wet Lay-Up Repair
Ply 2 application
Cured Repair
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 18 Strain Gage Identification/ NDI Inspection Grid
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 19 Test Article Instrumentation
SG R11 Lower Skin RBL 294.2 FS 477.5 Repair Instrumentation
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 20 Limit Load Test- Upbending Case Cond 4A
¾ Limit Load Cond 4A- (Max Positive Moment) ¾ During certification, wing suffered damage at 122%LL 135%LL and 141%LL before sustaining UL ¾ Shear/ moment/ torque introduced matched the static 4A values from RBL 100 to RBL 360
BENDING MOMENT VS LSTA
3000000
Proposed Test 2500000 FT-575 Test FT-575 Requested Static Up-Bending 4A 2000000 max Env min Env
1500000
1000000
500000
Bending Moment (in-lbs) Moment Bending 0
-500000
-1000000
-1500000 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 LSTA (in)
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 21 Limit Load Test
¾ Wing sustained 100% Up-bending Limit Load Test
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 22 Limit Load Test
¾ Strain vs % LL comparison between current test and wing max upbending certification test (Cond 4A) ¾ No major change in compliance, certification data correlates very well with aged structure limit load test results
Strain vs % LL (Current Test vs Static Max Strain vs % LL (Current Test vs Static Max Up-Bending Test to failure) Up-Bending Test to failure)
3500 0 R6A_test_USRBL174FS424.5 R10_LS_RBL208_FS439.5 3000 R30A_4A_To failure R62A_to_failure -500 2500 -1000 2000 -1500 1500
-2000 1000 Strain (microstrain) Strain Strain (microstrain) -2500 500
-3000 0 020406080100 0 20406080100 %Limit Load % Limit Load
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 23 Ongoing Efforts
¾ Image Analysis and physical tests ¾ Mechanical Testing: flatwise tension C297, flexure C393, core shear C273
Compression V-joint Static/ Cyclic H-joint Static/ Cyclic after impact Tension/ Compression Tension Wichita State University FHT
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 24 Conclusions
¾ Structure held extremely well after 12 years of service: no obvious signs of aging to the naked eye as would a metal structure with a similar service history exhibit ¾ Preliminary Thermal analysis results show no degradation in thermal properties of the material and that the skins are fully cured/ cross-linked ¾ LH NDI showed no major defects/ damage in the skins introduced during manufacture or service ¾ NDI response subject to operator interpretation (full test article inspection) ¾ Full scale test results of the “aged wing” correlated very well with the results obtained for the certification article
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 25 B737-Stabilizer FAA Sponsored Project Information
¾ Principal Investigators & Researchers ¾ Dr. John Tomblin ¾ Lamia Salah ¾ FAA Technical Monitor ¾ Curtis Davies ¾ Other FAA Personnel Involved ¾ Larry Ilcewiz ¾ Industry Participation ¾ Dr. Matthew Miller, The Boeing Company ¾ Dan Hoffman, Jeff Kollgaard, Karl Nelson, The Boeing Company
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 26 Objective/ Methodology
To evaluate the aging effects of a (RH) graphite-epoxy horizontal stabilizer after 18 years of service (48000 flights, 2/3 of DSO)
¾ Non-Destructive Inspection to identify flaws induced during manufacture or service
¾ Mechanical testing on coupons extracted from the structure to investigate any degradation in the mechanical properties of the material
¾ Physical, thermal and image analysis to quantify porosity and moisture levels in the structure, characterize its thermal properties and its state at the micro- structural level (microcracks, etc…)
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 27 Background
¾ The B737-200 CRFP stabilizer was built as part of the NASA ACEE (Aircraft Energy Efficiency) program initiated in late 1975
¾ The purpose was to develop new technologies to reduce fuel consumption in aircraft structures
¾ The ACEE program was subdivided into four development areas: laminar flow systems, advanced aerodynamics, flight controls and composite structures
¾ The ACEE Composites program focused on redesigning existing structural components using lighter materials
¾ A building block approach was followed where composite structure development would start with lightly loaded secondary components followed by medium primary components and finally wing and fuselage development Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 28 Background
¾The OEM redesigned, manufactured, certified, & deployed five shipsets of 737-200 horizontal stabilizers using graphite-epoxy composites
¾Certification was achieved in 1982 and all shipsets were introduced into commercial service in 1984
¾The OEM 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
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 29 Boeing 737 Fleet Status
¾DSO of 75000 flights ¾Upper Skin Inboard delaminations at stringer runouts due to maintenance personnel walking on a no-step zone
Shipset / Production Entry into Carrier Status as of January 1, 2008 Line # Service
1 / 1003 2 May 1984 A & E (60000 hours, 45000 flights)
2 /1012 21 March 1984 A Removed from Service (62000 hours, 47000 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 B & D Stabilizers removed from service 2002 (approx. 1984 52000 hours, 48000 flights); teardown of L/H unit at Boeing; teardown of R/H unit at NIAR, Wichita State Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 30 Horizontal Stabilizer Description
¾ Designed such that it is interchangeable with the metal structure in terms of geometry, aerodynamic shape to meet control effectiveness and flutter requirements ¾ 21.6% weight savings/ metal structure ¾ Material: NARMCO T300/5208 ¾ Stiffened skin structural box arrangement with co-cured I stiffeners ¾ Honeycomb ribs for cost efficiency, fastened to the skins using shear ties ¾ Spars are I beams consisting of two pre-cured C channels and two pre-cured caps subsequently bonded together ¾ Root lugs used steel plates bonded and bolted to a pre-cured graphite epoxy chord
Composite vs. Metal Stabilizer Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 31 Corrosion/ Lightning Protection Scheme
Corrosion Protection Scheme ¾ Corrosion protection by co-curing a fiberglass ply onto the graphite-epoxy structure or painting the surface with primer and epoxy enamel ¾ All aluminum structure was anodized or alodine treated, primed and enameled ¾ Fasteners were installed with wet polysulfide sealant
Lightning Protection Scheme ¾ Lightning protection scheme provided an electrical path around the perimeter of the structure. Bonding straps were used to connect the aluminum leading edge, the aluminum rib cap of the outboard closure rib, the aluminum elevator spar and the spar lugs ¾ An Aluminum flame spray was used on the stabilizer’s critical strike area. The outboard skin panels were insulated using a layer of fiberglass. Mechanical fasteners were used to electrically connect the aluminum flame area to the metal cap of the outboard closure rib
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 32 Disassembly
¾ Upper skin assembled using Inconel “Big Foot” blind fasteners ¾ Lower skin assembled using titanium Hi-Lok fasteners with corrosion resistant steel collars and washers ¾ The 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 structure ¾ Once the upper skin was dismantled, the lower skin’s Hi-Lok fasteners were disassembled
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 33 Disassembly/ Preliminary Findings
Upper Skin (RH)
Lower Skin (RH)
¾Structure held very well ¾No evidence of pitting or corrosion as would be observed in a metal structure ¾No residual strains compared to the LH Center Box (RH) Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 34 Disassembly/ Preliminary Findings
Front (Top) and Rear (Bottom) Spars after disassembly Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 35 Visual Inspection
Degradation of Tedlar Moisture Barrier film
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 36 Visual Inspection
A few corroded fasteners due to sealant deterioration
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 37 Visual Inspection
Phenolic shims used to fill gaps between skin and ribs
Liquid Shims used to fill gaps between the upper skin and the stabilizer ribs Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 38 Non-Destructive Inspection Prior to teardown
S11 S10 S9 S8 S7 S6 S5 S4 S3 S2 S1
S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11
RapidscanTM analysis (pulse echo time of flight data) of the R/H of the B737 stabilizer (Courtesy of Sandia National Laboratories and NDT solutions ltd. UK) Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 39 Non-Destructive Inspection after Teardown
¾ Pulse-echo and through-transmission non-destructive methods were used to inspect the stabilizer using 2.25 Mhz frequency transducers ¾ Both methods confirmed the large amounts of porosity in the upper skin ¾ 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
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 40 Non-Destructive Inspection
¾ NDI pulse echo inspection showed significant levels of porosity in the upper skin compared to the lower skin (tooling and process variability) ¾ Porosity levels have been quantified using image analysis/ physical tests ¾ Very porous repair between rib stations 2 and 3 (str 5 and 8)
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 41 Non-Destructive Inspection
¾ 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
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 42 Destructive Evaluation
¾ 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.
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 43 Moisture Content Evaluation
¾ 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. ¾ The results showed that the moisture content in the upper skin varied from 0.743 to 0.913% (design moisture level of 1.1%)
Moisture Distribution In the Upper Skin
Design Moisture level 1.1% Maximum Moisture content 0.913% Average Moisture Content 0.829% Minimum Moisture Content 0.743% 1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3 Percent Moisture Content (%) 0.2
0.1
0.0 Upper Skin Samples Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 44 Moisture Content Evaluation
Moisture Distribution In the Lower Skin
Design Moisture level 1.1% Maximum Moisture content 0.92% Average Moisture Content 0.77% Minimum Moisture Content 0.69% 1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3 Percent MoistureContent (%) 0.2
0.1
0.0 Lower Skin Samples ¾ The moisture content in the lower skin varied from 0.69 to 0.92% (design moisture level of 1.1%)
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 45 Physical Tests Results-US
¾ Physical tests were conducted per ASTM D3171 to quantify porosity levels in both skins
Upper Skin (Max void Content 7.26%)
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 46 Physical Tests Results-LS
¾ Physical tests were conducted per ASTM D3171 to quantify porosity levels in both skins
Lower Skin (Max void Content 3.82%) Front and Rear Spars (Less than 1.14% and 1.67% void content)
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 47 Thermal Analysis
¾ DMA technique to determine the glass transition temperature of the aged material for coupons extracted from both the upper and lower skins ¾ 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. ¾ Storage Modulus is an indication of the stiffness of the material, tanδ is a measure of the damping of the material ¾ DMA curves with a shallow storage modulus transition and a narrow tanδ indicate a highly cross linked material
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 48 Thermal Analysis
¾ Tg values consistent and comparable to LH Results (Courtesy the Boeing Co) average values for RH (201°C/233°C) ¾ DMA test parameters vary/ Tg obtained is a “wet” Tg (at least 0.69% moisture content) DMA Results for coupons excised from the upper skin of the B-737 Horizontal Stabilizer (Boeing Method)
300 As extracted Storage Modulus Values Baseline TMA Dry Tg 238 °C As Extracted Peak of Tangent Delta Values 250
200
150
Temperature (°C) 100
50
0 Test Samples Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 49 Thermal Analysis- Spar Skin Comparison
¾ Spar Tg is about 18°C higher than the skin Tg. (1 cure cycle for skin, 2 for spars)
DMA Results Comparison for coupons excised from the upper skin and the front and rear spars of the B-737 Horizontal Stabilizer (ASTM Standard)
300
Baseline TMA Dry Tg 238 °C
250
200
150
Temperature (°C) Temperature 100
50
0 REAR SPAR FRONT SPAR UPPER SKIN
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 50 Thermal Analysis/ DSC
¾ Non-Reversing heat flow curves reveal exotherms/ chemical reactions DSC heat of reaction values are extremely small (<6J/g) indicating a highly cross linked material (fully cured) ¾ Reversing heat flow curves reveal Tg ¾ Drying the specimen increased the cure onset (water acts as a plasticizer) ¾ Water content does not affect the degree of cure
DSC, Rib 7, as extracted Wichita State University DSC, Rib 7, dry
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 51 Thermal Analysis/ Comparison with new material
New material DMA correlates very well with Lower “as extracted” Skin Values (Lower moisture and void contents, higher Tg) DMA Results Comparison for coupons excised from the skins and coupons manufactured from the new T300/5208 (ASTM Standard)
300
Baseline TMA Dry Tg 238 °C
250
200
150 Temperature (°C) Temperature 100
50
0 UPPER SKIN NEW MATERIAL LOWER SKIN
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 52 Thermal Analysis/ Comparison with new material
• Spars have reached an almost fully cured status, postcuring occurred during the secondary bonding process (4% cure conversion increase wrt new material) Upper Skin has lower Heat of Reaction values than new material, additional curing has occurred during the life span of the structure (UV exposure), 2% cure conversion increase wrt new material % Cure Comparison Between New Material, Spars and Upper Skin
99% Cure 1.00
0.99 97% Cure
0.98
0.97
0.96 95% Cure
0.95 % CURE % 0.94
0.93
0.92
0.91
0.90 NEW MATERIAL REAR SPAR FRONT SPAR UPPER SKIN
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 53 Microscopy/ Image Analysis
¾ Image analysis was performed to detect porosity/ micro-cracking and any evidence of aging in the structure. ¾ 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 50x stringer web (left image) and flange (right image). Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 54 Mechanical Tests
Mechanical Tests were conducted according to the 1980’s requirements/ standards
Tested Upper Skin Compression Coupons
Compression Test Set-up Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 55 Mechanical Tests Results
Lower Skin Compression Test Results
80 Mechanical Data - Measured 70 Mechanical Data - Normalized 60
50 40 30
20 10
0 Ultimate Compressive Stress (Ksi) Stress Compressive Ultimate e 1 3 2 1 3 in _C _C2 _C _C1 _C _C3 _C _C 5 3 3 asel B R4_5 R4_5 R2_3 R0_1 R0_1 1 ST STR4_ ST STR2_ ST STR2_ ST ST 02- _ _ _ 1 102-2 Baseline _R2_ _R2_ _R4_ _R6_ _R6_ LS LS_R2 LS LS_R4 LS LS_R4 LS LS_R6_STR0_1_C2LS
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 56 Mechanical Tests Results
Lower Skin Compression Test Results, Modulus
7 Mechanical Data - Measured 6 Mechanical Data - Normalized
5
4
3
Modulus (Msi)Modulus 2
1
0
e 1 2 3 1 2 3 1 2 3 C C C C C C C C lin _ _ _ _ 3_ 1_ se _5 _5 _3 _ _1 _ _1_C Ba TR0 2-1 STR4 STR4 STR2 STR0 0 _ _ _ _ _S 1 102-2 Baseline2 2 4 6 6 R R R R R LS_ LS_R2_STR4_5_LS_ LS_R4_STR2_3_LS_ LS_R4_STR2LS_ LS_R6_STR0LS_ Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 57 Mechanical Tests
Mechanical Tests were conducted according to the 1980’s requirements/ standards
Tested Lower SkinTension Coupons Tension Coupon Test Set-up
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 58 Mechanical Tests Results
Lower Skin Tension Test Results 60
Mechanical Data-Measured ) 50 Mechanical Data-Normalized
40
30
20
10 Ultimate Tensile Stress (Ksi Stress Tensile Ultimate
0
e 1 1 2 n T T T eline 6- 4- 2- seli s a a 5_ 3_ 1_ R R 1 B 2 B _ST _ST 1- 1- 2 4 10 10 _R S_R2_STR4_5-T1 S_R S_R6_STR0_1-T1 L LS_R2_STR4_5-T2LS L L LS_R6_STR0_1-T2LS_R6_STR
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 59 Mechanical Tests Results
Lower Skin Tension Test Results, Modulus
7 Mechanical Data-Measured 6 Mechanical Data-Normalized
5
4
3
Modulus (Msi) Modulus 2
1
0
e 2 1 1 2 n ne li -T T -T T e 5-T1 4-T1 2-T2 s _ _5 _ _1 _ aseli 4 0 R R B Ba T T -2 S STR5_6- S STR0_1- 1 _ _ 01-1 2_ 4_STR3 6_ 6_STR1 1 10 R R R R _ _ S S_R2 S S_R6 LS_R2_STR4 L L LS_ L L LS_
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 60 Element Testing-Crippling
Crippling Test Set-Up Failed Specimen
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 61 Element Testing-Crippling
Skin Panel Load vs Strain Readings 35000 Failure Load 30193 lbs 32000 lbs for baseline 30000
25000
20000
15000 Load, lbf
10000 Onset of Buckling (800 micro in/in) 1100 for baseline Skin Panel Load vs Strain Readings 5000 35000 Failure Load 30193 lbs 32000 lbs for baseline 0 30000 0 500 1000 1500 2000 2500 3000 3500 4000 4500 Strain, micro in/in 25000 Strain 2 Strain 7 Strain 4 Strain 9 20000
15000 Load, lbf Load, Failure Strain (5200 micro in/in) 10000 6100 for baseline
5000
0 0 1000 2000 3000 4000 5000 6000 Strain, micro in/in
Strain 6 Strain 7 Strain 8 Strain 9 Strain 10 Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 62 Conclusions Value of the results
¾ 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 exhibit ¾ Physical tests showed moisture levels in the structure after 18 years of service as predicted during the design phase ¾ Thermal analysis results very consistent with those obtained for the left hand stabilizer ¾ Thermal analysis showed that the degree of cure of the spars is close to 100%, that additional curing may have occurred in the upper skin due to UV exposure (overall at least 95% cure was achieved in the structure) ¾ Significant improvements in composite manufacturing processes and NDI methods ¾ New material resin system thermal properties comparable to old material but strength is higher (fiber processing improvement) ¾Teardown provides closure to a very successful NASA program and affirms the viability of composite materials for use in structural components Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 63 A Look Forward Benefits to Aviation
¾ Understand the aging 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 ¾ most damage to composite structures occurs during assembly or routine aircraft maintenance ¾ SRM’s are essential to operating with composite structures, engineering information needed for in-service maintenance and repair
Wichita State University
June 17th, 2008 The Joint Advanced Materials and Structures Center of Excellence 64