Transcript RicCommentsFAAmatlSpec

FAA/NASA Meeting on Industry
Composite Specifications
August 2002
FAA Report on Proposed Industry
Prepreg Specifications
Ric Abbott
Abbott Aerospace Composites
Wichita, Kansas
FAA/NASA Meeting on Industry
Composite Specifications
August 2002
THE “INDUSTRY COMMITTEE”
• The report suggests that the committee will be
approving certification data
• The ACO should be the first point of contact
• Assistance for the ACO may come from the NRS office,
FAA Tech Center, NASA, academia….
FAA/NASA Meeting on Industry
Composite Specifications
August 2002
SINGLE RESIN/FIBER ea SPEC
• The report methodology is founded on a single
resin/fiber combination cover by each specification
• This is not very practical for large scale production
• It is usual to allow the prepreg supplier some flexibility
for fiber supply
• Also, the end user usually needs flexibility in
procurement to a given class of performance, such as
250° F/autoclave cure
FAA/NASA Meeting on Industry
Composite Specifications
August 2002
EQUIVALENCE
• End user required to show equivalence to previous data
base?
• Should say data base generated other than under end
user’s qualification plan
Otherwise: B-767 data need to be re-approved for
B-777?
• The regulations require statistical material properties
“sufficient” to show positive margins with the applied
internal loads (including factor of safety)
FAA/NASA Meeting on Industry
Composite Specifications
August 2002
RECALCULATION AFTER “N BATCHES”
• The recalculation of allowables after n batches is
essentially requiring n batches for qualification
•So, three batch (AGATE) method is only a provisional
approval?
•Test article parts, including flight hardware, were
already fabricated after 10 batches on the Premier
program
•Acceptance testing, today, does not usually include
environmental effects
FAA/NASA Meeting on Industry
Composite Specifications
August 2002
STATISTICAL ANALYSIS
• The AGATE statistical analysis is very desirable to
produce reasonable allowables when reduced
qualification testing of three batches is employed
•Whereas, the report recommends Mil Hnbk-17 analysis
FAA/NASA Meeting on Industry
Composite Specifications
August 2002
FORM/TYPE/GRADE
• End user specs usually include all forms of the prepreg
in one spec, eg., tape, tow, PW fabric, 5HS fabric, etc.
•Tow count is also part of the basic designator
•Resin content is usually defined in the body of the spec
as this may be varied based on fabrication needs
FAA/NASA Meeting on Industry
Composite Specifications
August 2002
OUTER LIMITS OF PROCESS WINDOW
• Laminar properties should not involve deliberate
process variations within the spec window
•Conformity inspection is based on panels built to the test
process requirements
•Manufacturing process is the subject of the next level of
the building block, element testing
• Element testing is the level at which critical lay-ups,
allowable process variations, and QA acceptance
standards are investigated
FAA/NASA Meeting on Industry
Composite Specifications
August 2002
LAMINA and LAMINATE TESTS
• Tables 5a and 5b confuse lamina and laminate tests
•Bearing and CAI (as part of material qualification) are
typically conducted on pseudo-isotropic laminates
fabricated from each material form under consideration
•Bearing test should not specify countersunk fasteners;
this is part of detail joint design
Element test level should deal with detail design: eg.,
local joint laminates maybe built up with
combinations of tape, fabric, adhesive plies, etc.
FAA/NASA Meeting on Industry
Composite Specifications
August 2002
DURABILITY and SERVICE LIFE TESTS, TABLE 7
• Fracture toughness (on all-zero direction plies) can be
useful to compare materials, but has little practical value
in structural design and certification
• Fatigue testing on arbitary lay-ups without damage is
not useful in compliance with damage tolerance
regulations; flaw growth testing is needed and is best
done on critical laminates and joints specific to the
particular project (R = -1 is more severe than most civil
aircraft load cycles)
• Similarly, impact damage is required for certification,
but to detectable damage or applicable threat levels
FAA/NASA Meeting on Industry
Composite Specifications
August 2002
SUMMARY COMMENTS
• The report seems to propose a simplified composite
structural certification approach for emerging airframe
fabricators
In place of the building block approach the
supplier conducts much more testing than usual
for lamina properties
The end user may go straight to full scale
validation using load enhancement factors without
internal load analysis
Therefore much greater assurance is needed of the
exact material used
FAA/NASA Meeting on Industry
Composite Specifications
August 2002
SUMMARY COMMENTS…contd
• The report seems to propose a simplified composite
structural certification approach for emerging airframe
fabricators
Therefore the report should be an AC which
presents acceptable means of compliance with
each applicable regulation in CFR 14 part 23,
27….
FAA/NASA Meeting on Industry
Composite Specifications
August 2002
SUMMARY COMMENTS…concluded
• The report, as it stands, will probably be applied in
future as “FAA Policy” and enforced as the only
acceptable means of compliance with CFR 14, part
25.613
•Therefore the recommendations should be within an
Advisory Circular (or revisions to existing AC’s) with
much wider and more formally documented industry and
public input