Advanced Composite Structural Materials in Business Jets. Michael J. Hoke President, Abaris Training Resources Inc.

Size: px

Start display at page:

Download "Advanced Composite Structural Materials in Business Jets. Michael J. Hoke President, Abaris Training Resources Inc."

Ella Cook
6 years ago
Views:

1 Advanced Composite Structural Materials in Business Jets Michael J. Hoke President, Abaris Training Resources Inc. 1

2 Abaris Training Resources Inc. Advanced Composite Manufacturing and Repair Training since day courses; 8 different courses for degreed engineers, 18 for technicians We train all major airframe manufacturers, military services, NASA, military drone manufacturers, MRO s, airlines, and many others. We also train 160 FAA inspectors per year. Main location in Reno, NV; satellite location in Griffin, GA. 2

3 We conduct on-site one-week classes all over the world; in the last year for example: Two classes for the CAA in London One for EASA in Cologne Two for FedEx in Indy Two for Airbus in Broughton, Wales One for the U.S. Navy in Patuxent River, MD One for Delta Airlines in Atlanta Two for Emirates Airlines in Dubai One for Hickam AFB in Hawaii One for Gulfstream in Savannah One for United Technologies in Mexicali One in two weeks for Tinker AFB One this week for the U.S. Army at Redstone Arsenal 3

4 Honda Jet Thermoset Carbon Fiber Fuselage 4

G-650: Thermoplastic carbon fiber rudder Gulfstream for more than two decades has incorporated increasing levels of composite materials in its aircraft.

5 G-650: Thermoplastic carbon fiber rudder Gulfstream for more than two decades has incorporated increasing levels of composite materials in its aircraft. Pressure bulkheads, the horizontal stabilizer, floor panels, furnishings and fairings are a few of the sections made lighter and stronger by the addition of composites. 5

6 Carbon Fiber vs. Fiberglass which is best? Carbon Fiber (Black): Very high tensile and compressive strength to weight ratio Very high bending stiffness to weight ratio Not very good at impact resistance fibers are brittle Expensive Cannot be used for radomes or antenna covers Fiberglass (White): Significantly heavier than CF; although strong in both tension and compression Lower bending stiffness Better at impact resistance than CF Considerably less expensive Can be used for radomes or antenna covers 6

Carbon Fiber vs. Fiberglass Other Issues Fiberglass is an excellent electrical insulator. Carbon Fiber is an electrical conductor, although not a good one.

7 Carbon Fiber vs. Fiberglass Other Issues Fiberglass is an excellent electrical insulator. Carbon Fiber is an electrical conductor, although not a good one. Carbon fiber in direct contact with aluminum or steel will cause galvanic corrosion in the metals; not an issue with fiberglass. No CF problem with Titanium or Stainless Steels. Corrosion with carbon fiber prop on metallic hub 7

8 Thermosets vs. Thermoplastics Thermoset Curing Process Thermoset plastics contain polymers that cross-link together during the curing process to form an irreversible chemical bond this is a one-time cure only; they cannot be re-heated and re-molded after the initial cure. Thermoplastics Curing Process Thermoplastics pellets soften when heated and become more fluid as additional heat is applied. The curing process is completely reversible as no chemical bonding takes place. This characteristic allows thermoplastics to be reheated, remolded and recycled without negatively affecting the material s physical properties. Important note Bonded repairs are commonly done with thinner thermoset composites, and work well. Bonded repairs cannot be done to most structural thermoplastic composites they must be repaired with mechanically fastened doublers. Adhesives will not adhere well to most thermoplastics. 8

9 Impact level affects damage 9

10 Where can composites be used? 787 example 10

11 We do many scarfed bonded repairs, here s a practice repair on a 787 Courtesy of Boeing 11

12 Simple temporary backside support for thin solid laminate scarfing Courtesy of Boeing 12

13 The individual plies are clearly distinguishable in this scarfed CF panel Typical ½ inch per ply scarf removal shown 13

14 However a bonded scarf repair: Won't transfer very high loads adequately from a thick solid laminate Can get huge quickly think of a 1 hole in a 100-ply solid laminate, scarfed at ½ per ply: The scarf diameter would be 50 inches on each side of the hole, plus the hole diameter itself, for a total diameter of 101 inches or 8.4 feet! 14

15 Goal of Composite Repair Design: Rebuild Fiber Load Path Through Structure Ideal repair would match original properties: Strength Stiffness Weight Trade-offs with actual repairs: To match strength; repair is typically stiffer & heavier To match stiffness; repair is typically weaker & heavier Cannot match all original properties! A repaired part will never be exactly equal to the original structure, at the same finished weight as the original structure. Calculate the knock-down factor with repair design & analysis. 15

16 Bolted doubler repair feasibility Determining when to use a doubler can be tricky. A repair-design analysis may be necessary to determine proper repair approach If the laminate is less than ⅛ inch thick: recommend a tapered-scarf repair If the laminate is greater than ½ inch thick: recommend a doubler repair

17 787 door frame damage Courtesy of Boeing 17

18 Titanium doubler bolted repair: works well on thick solid laminates, but not on thin structures or on sandwich panels Courtesy of Boeing 18

19 Very careful repair design, drilling and close-tolerance holes mandatory Courtesy of Boeing 19

20 Formed metallic internal doubler example Courtesy of Boeing 20

21 A-300 bolted repair? 21

22 A-300 bolted repair from below 22

23 A-300 bolted repair from above 23

24 Delaminations vs. Disbonds A delamination is a separation of two adjacent layers of cloth or tape. A disbond is a separation of a laminate from a different underlying substrate: from honeycomb or foam core, another laminated structure, etc. 24

25 Delaminations or Disbonds can be caused by: Impacts Overheating Overloading Poor surface preparation before bonding fingerprints, etc. Improper cure of adhesive Bondline too thick or thin Wrong adhesive Wrong pressure during cure Etc, etc... 25

26 Visual inspection Remove paint, especially if cracked ( DO NOT use chemical paint strippers!) In fiberglass and Kevlar, whitish areas indicate air (delams and disbonds) and broken fibers. Since carbon fiber is black and opaque, it s much harder to see internal defects visually. 26

27 Cirrus SR-22 general aviation airplane. Wingtip loading on aft attach points causes floor to break here at wing root Fiberglass turns white at the point of fracture 27

28 Why it breaks there: Foam Core The transition area from 2x2 foam core to 4+ plies is the weaker area and will delaminate and/or break first. Strong Weaker Strong 28

29 Transition Area / Weakest Point Strong Area - Reinforced Plies Strong Area Aft Attach Fitting 29

30 Manual inspection In CF, one can often feel soft spots, high spots, and low spots, which may indicate an underlying problem. Tap testing (use a coin?): A good area should tap with a sharp metallic ring. A delam/disbond will have a dull thud. Careful consistent tapping in an organized pattern, using a felt tip pen to mark the outer edges of the tone change, can outline large irregularly shaped areas of damage 30

31 Tension Vs. Compression Failures FORWARD EDGE AFT EDGE 31

32 32

33 Compression Side 40 33

34 NDI Techniques Tap Testing good for near-surface delaminations. Ultrasonic good for somewhat deeper defects. X-Rays good for detecting metallic inclusions, not good at delaminations. Thermography can be good at near-surface defects, and for detecting water in honeycomb. Not good for deep defects in thick solid structures. What CANNOT be detected weak, but still stuck adhesive bonds!! 34

35 So the FAA and EASA say: Bonded repair size limits, on structures critical to flight safety, must be set so that the structure can operate at Limit Load after complete bond failure, up to the limits of any arresting features which may be present. If stiffness is lost due to the loss of the repair, then flutter may be an issue that must be considered as well. 35

36 What is HEWABI? High-Energy Wide-Area Blunt Impact 36

37 HEWABI damage to a composite pressure vessel: May not be clearly visible; May be spread over a large area of the composite structure; May cause considerable structural damage with minimal external indications; for example disbonding of internal bonded stiffeners. 37

38 Special Inspection Procedures for a highload event in a composite structure Identify that a very high-load event has occurred; Assure that indications of structural damage are found in an initial inspection; Involve the OEM, if necessary; Provide a process for additional inspections that are designed to identify all of the structural damage; and Provide a process for approval for return to service. 38

39 Large transport horizontal stabilizer visible damage from outside is minimal but suspicious (courtesy of EASA) 39

40 Visible impact damage from the inside is substantial (courtesy of EASA) 40

41 Another example of hidden damage, which six months later led to not-so-hidden damage! Courtesy of EASA

42 Burn damage on internal fire from ELT battery mounted in roof. CFRP burned inside paint blistered, but CFRP did not burn all the way through, like it may look. Courtesy of EASA 42

43 Repair in progress largest mechanically fastened composite repair ever to a pressure vessel. Courtesy of EASA 43

44 Summary Larger & more complex composite primary structures are today s big new composite repair challenge 787 and A-350 are the big examples, but new heavier helicopter structures such as the 84,700 lb. gross weight CH-53K also have lots of composites, including rotor blades. These large composite structures are rapidly developing in the business jet world as well. Standardized repair materials & methodologies are necessary to support these new structures. Good training is a must! 44

45 Questions? 45

46 Thank you! Michael J. Hoke Abaris Training Resources Inc. 46

FAA Inspection. Federal Aviation Administration Research Activities for Composite Materials

FAA Inspection. Federal Aviation Administration Research Activities for Composite Materials FAA Inspection Research Activities for Composite Materials Presented to: The 2006 Composite Damage Tolerance & Maintenance Workshop By: Dave Galella, ATO-P Date: Outline Inspection Systems Research - Background