Introduction to this NASA M&P Homepage System
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GSFC-752-SPEC-002.x4
Fabrication Engineering Branch
Specification for
High-Modulus Graphite
Filament Prepreg Material
for Space Applications
Draft Revision .x4
June, 1994
SPECIFICATION FOR HIGH-MODULUS GRAPHITE FILAMENT PREPREG MATERIAL
FOR SPACE APPLICATIONS
1 Scope
This specification establishes the requirements for prepreg
materials: aligned high modulus graphite fibers preimpregnated
with B-staged thermoset resin. The prepreg shall have the
ability to be molded using low pressure (15-100 PSI) laminating
methods at to a fully thermoset state. The material is
acceptable for low outgassing applications.
1.1 Material Purchase and Material Control
This specification is meant to assure quality and properties of
prepregs for use in space flight structures. Section 3.3 assures
the utilization only of materials properly stored and correctly
dated. All other requirements apply to the purchasing, shipping,
and inspection of the materials upon manufacture.
1.2 Unique fiber and resin designations.
This specification covers a large set of prepreg materials. Each
unique combination of fiber and resin will have its own set of
mechanical and thermal parameters, which are specified in the
appendices, having one appendix for each material.
a. T50/ERL 1962. Unidirectional prepreg tape, ply thickness
of .005 inches. Required properties listed in Appendix A.
b. P75S/ERL 1962. Unidirectional prepreg tape, ply thickness
of .005 inches. Required properties listed in Appendix B.
c. T50/cyanate ester. Unidirectional prepreg tape, ply
thickness of .005 inches. Required properties listed in
Appendix C.
d. M50J/cyanate ester. Unidirectional prepreg tape, ply
thickness of .005 inches. Required properties listed in
Appendix D.
2 Applicable Documents
2.1 Government Documents
MIL-B-131 Barrier Materials, Water Vapor proof, Grease
proof, Flexible, Heat Sealable.
NASA SP-R-0022 Vacuum Stability Requirements of Polymeric
Material for Spacecraft Application
OSHA Form 20 Material Safety Data Sheet
NFS 18-52.210-75 Packaging and Marking with Alternate II
(Space Flight Use)
MIL-T-29586(AS) Thermosetting Polymer Matrix, Unidirectional
Carbon Fiber Reinforced Prepreg Tape (Widths up
to 60 inches), General Specification For
2.2 Non-Government Documents
ASTM C613 Test Method for Resin Content of Carbon and
Graphite Prepregs by Solvent Extraction
ASTM D790 Flexural KProperties of Unreinforced and
Reinforced Plastics and Electrical Insulating
Materials
ASTM D3410 Compressive Properties of Unidirectional or
Crossply Fiber-Resin Composites
ASTM D3039 Tensile Properties of Fiber-Resin Composites
ASTM D2344 Apparent Interlaminar Shear Strength of Parallel
Fiber Composites by Short Beam Method
ASTM D3418 Transitional Temperature of Polymers by Thermal
Analysis Methods
ASTM D3530 Volatile Content of Carbon Fiber-Epoxy Prepreg
ASTM D3531 Resin Flow of Carbon Fiber-Epoxy Prepreg
ASTM D3532 Test Method for Gel Time of Carbon Fiber Epoxy
Prepreg
ASTM E595 Total Mass Loss and Collected Volatile
Condensable Materials from Outgassing in a
Vacuum Environment
SACMA SRM 4-88 SACMA Recommended Test Method for Tensile
Prioperties of Oriented Fiber-Resin Composites
3 Requirements
3.1 Uncured Product Characteristics:
The uncured characteristics of the B-stage material, as received,
shall conform to the requirements of this section (3.1), and be
certified by manufacturer. All batches of material used in
delivery lots shall be tested and certified to by the
manufacturer (see 4.1.2).
3.1.1 Dimensions
The material shall be supplied to the width specified on the
purchase order. Width tolerances shall be +0.2 in . and -0.0 in
. of the specified dimensions.
3.1.2 Chemical and Physical Properties
The chemical and physical properties of the uncured material
shall be as specified in the appropriate material Appendix listed
in 1.2.
3.1.3 Workmanship
The preimpregnated unidirectional graphite material shall be
uniformly wetted, uniform in appearance; and the edges shall be
straight and parallel. The product shall contain no foreign
matter that would be detrimental to the end use.
NOTE
Any portion of the material not meeting the
workmanship criteria of 3.1.3 shall be tagged
and identified in the roll condition log (see
paragraph 5.1.4). All defects so tagged shall
not be included in the calculation of
quantity delivered. Additional fully
complying material shall be supplied with the
shipment to compensate for any tagged
defective areas.
3.1.3.1 Liners: Liners used shall not alter the physical,
chemical or mechanical properties of the prepreg. In the event
that liner sections are inadvertently included in a layup, the
liner material shall be capable of being detected by ultrasonic
pulse echo C-scan or through transmission techniques at
frequencies commonly used in part production. Liners shall be
easily removed at ambient temperature, shall not tear upon
standard removal techniques, and shall not misalign, distort, or
break fibers after removal. No removal of prepreg resin shall be
permitted and only minimal transfer of liner release agent shall
be allowed. The use of silicone release agents shall be
prohibited. Liners shall be capable of being machine slit, hand
knife cut, die cut or automatic knife cut coincident with the
prepreg. Clear film liners or black liners, which cannot be
readily seen or which may be mistaken for resin, shall not be
used.
3.1.3.2 Collimation: Fiber bundles that are not parallel to
each other or to the edge of the roll due to bundle cross-overs,
poor collimation, severe wrinkles or distortions shall be
identified by tagging.
3.1.3.3 Warp and Fill Alignment: For fabric, the warp and fill
yarns shall be perpendicular to each other and parallel to the
warp and fill direction of the prepreg fabric within 1" maximum
in any 21" of fabric width or length. Filament bundles that are
not parallel to each other or to the edge of the roll due to
bundle cross-overs, poor collimation, severe wrinkles or
distortions shall be identified by tagging.
3.1.3.4 Gaps: Gaps between tows which are greater than 0.03"
in width are unacceptable. Gaps between tows which are between
.01" and .03" in width and greater than 6.0" in length are
unacceptable.
3.1.3.5 Wrinkles: Out of plane wrinkles and prepreg overlap
shall be identified by tagging.
3.1.3.6 Excessive Fish Eyes or missing tows: For
unidirectional tape, tow separation with angular distortion of
adjacent tows shall not exceed 0.060" in separation and/or two
fish eyes per square inch. For fabric, tows which are missing in
the warp or fill directions shall not be acceptable for
manufacturing use.
3.1.3.7 Tow and Filament breaks: A discontinuous tow or damage
in a large number of filaments is reason for rejection and shall
be tagged. Splices in an individual tow shall not exceed one per
square foot. An acceptable tow splice is defined as a tow
overlap of 1.25" ñ 0.50" of the discontinuous tow.
3.1.3.8 Excessive Resin: Areas where resin build-up is 50%
greater than the normal average thickness and greater than or
equal to 0.25" long shall be tagged.
3.1.3.9 Areas lacking sufficient resin impregnation of the
fibers greater than or equal to 0.5 in2 shall be tagged.
3.1.3.10 Waviness: The prepreg tape and carrier-separator film,
when placed on a flat surface at or above 68ø F, shall not form a
wavy pattern (out of plane condition) exceeding ten times the
thickness of the prepreg.
3.1.3.11 Carrier-Separation Ply Adherence: Separation of the
prepreg tape from the carrier-separator ply greater than 0.5"
long and the width of the roll shall be tagged.
3.1.3.12 Defect removal and identification: As specified in the
contract or purchase order, defects as specified in paragraphs
3.1.3.1 through 3.1.3.11 shall be either removed in accordance
with paragraph 3.1.3.13 or identified in accordance with
paragraph 3.1.3.15. If defects are to be identified in accordance
3.1.3.15, the material shall be manufactured by direct
impregnation only.
3.1.3.13 Full width defect removal . Not allowed, unless
specifics of splicing are approved by GSFC technical officer.
3.1.3.14 Splicing. Not allowed, unless specifics of splicing
are approved by GSFC technical officer.
3.1.3.15 Defect identification: Defective areas shall be
identified using a compatible marking ink or flag of contrasting
color to that of the prepreg material and the material
identification marking as specified in 3.1.3.16. The defect
marking ink shall be applied only on the liner and not the
prepreg material. The defect identification markings shall not
cover or mask the defects identified. If the prepreg material has
to be marked itself, flags should be used. The roll condition log
shall indicate the type, location, and longitudinal length of
each defect and shall allow the purchaser to locate all defects
from the start of the roll to an accuracy of ñ 1 foot. Multiple
tow defects closer to each other than 1 foot shall be considered
as a continuous defect length. The cumulative defect lengths
within a roll shall not be included in the net roll length. The
total defect length per roll shall not exceed 10 percent of the
total roll length.
3.1.3.16 Material identification marking: Markings or flags
shall not adversely affect the mechanical properties or mask the
defects in the material or the defect markings, and shall be
legible after unwinding the roll. No identification markings
allowed on the prepreg material. The
identification markings shall be applied to the liner and be of a
contrasting color to the liner, prepreg material, and defect
identification markings.
3.1.4 IR Scan:
The vendor shall provide a reference scan of the impregnating
resin taken over the range, 2.5 through 15.0 microns. An IR
spectrum analysis shall be made from a sample of each resin lot
and compared with the reference spectrum. The sample shall
produce results which have the same peaks as the reference
spectrum.
3.1.5 Fibers:
The fibers shall be treated with a surface finish that will
provide superior mechanical properties and be completely
compatible with the resin system used. Fiber supplier
certifications shall be furnished to GSFC for each roll or
section of roll impregnated. These certifications shall consist
of mean and sample variation for ultimate tensile strength, fiber
modulus, and density. Each certification shall include the
corresponding fiber lot number and yarn batch numbers and the
fiber sizing technique used.
3.1.6 Weight:
Weight (Quantity) shall be as specified on the purchase order.
Variation of ñ10% is allowed.
3.1.7 Stability and Working Life:
The material shall meet the requirement of 3.1.1, 3.1.2, and 3.2
under the following conditions:
3.1.7.1 Stability: The storage life of the material when
stored in a closed container at or below 0ø F shall be a minimum
of 6.0 months from the date of manufacture. The manufacturer can
recommend a later expiration date.
3.1.7.2 Working Life: The minimum ambient working life
of the material shall be a minimum of 7 days when stored at 70ø F
+-10ø F at a maximum of 60 percent relative humidity.
3.1.8 Woven Fabric:
3.1.8.1 Selvage: The woven fabric shall have selvage edges. The
acquisition activity shall state the selvage width.
3.1.8.2 Tracer strands: An X-ray detectable glass or Kevlar
tracer yarn shall be placed on 2.0 inch centers in the warp
direction and 6.0 inch centers in the fill direction in each ply
of material as specified in the purchase order or contract. The
tracer yarns shall not outgas during processing of the prepreg,
or be the cause of thermal microcraking in the composite.
3.2 Performance Characteristics:
When a test laminate has been prepared as described in detail by
the supplier, the performance characteristics of the cured
material shall conform to 3.2.1 and 3.2.2
3.2.1 Mechanical Properties
The mechanical properties of the cured test laminate shall
conform to the listed requirements in Table 2 of the appropriate
material appendix listed in paragraph 1.2 of this specification.
3.2.2 Outgassing
The cured test laminate shall conform to the requirements of NASA
SP-R-002, "Vacuum Stability Requirements of Polymeric Material
for Spacecraft Applications".
3.3 Material Control
This section establishes minimum requirements for material
control. Other specifications may be added to any project,
establishing more detailed requirements.
3.3.1 Handling and Storage of Prepregs
Prepreg material shall be stored in a closed container at or
below 0ø F in a sealed bag meeting the requirements of MIL-B-131.
The materials may be removed from storage occasionally, but the
bag shall not be opened until the temperature of the material is
5øF above the dew point of the room. Storage life and
out-of-storage-condition times will be recorded in a roll
condition log; and the log will always be current.
3.3.2 Recertification:
Lots or portions of lots older than the storage life (3.1.7.1) or
with an out-time in excess of that established for 3.1.7.2
shall not be used without retesting. Retest requirements, final
acceptance, and end use of this retested prepreg material for
NASA flight projects will be determined by the Flight Assurance
Manager.
4 Quality Assurance Provisions
4.1 Certification of Prepreg Material
4.1.1 Fiber Certification
The manufacturer or supplier of the prepreg material shall
certify that the graphite fiber used in the prepreg material
manufactured conforms to the applicable requirements specified in
3.1.5. The supplier shall furnish actual test data that
demonstrate conformance.
4.1.2 Prepreg Certification
The supplier shall certify that the prepreg material supplied
conforms to all the requirements of 3.1, including Table 1 of
the appropriate Appendix, and record the GSFC specification
number and revision to which the material conforms.
4.2 Testing for properties of the cured laminate
4.2.1 Qualification Tests
Materials for the GSFC are pre-qualified, based on prior use in
spaceflight programs and/or on extensive preliminary test data,
with extensive statistical analysis. This information is the
basis for restricting purchase of prepreg materials to those
materials listed paragraph 1.2. If the supplier changes
procedures, formulations or any aspect of the production, the
supplier must notify the GSFC, and must submit test data from a
minimum of six samples from each of the three separate lots for
each mechanical property test conditions.
4.2.2 Supplier Certification Testing
The appropriate material Appendices list those properties which
shall be tested by the supplier or outside vendor for conformance
to these specifications. The supplier shall test each lot of
material for conformance to the properties listed in these
Appendices. The supplier shall furnish actual test data that
demonstrates conformance. Should the material fail to comply with
the above requirements, one retest of the failed property is
allowed. The second failure to comply shall be cause for
rejection of that lot of material.
Note:
For non-flight use, the purchase order can
request the exception of 4.2.2 if
mechanical testing is not required.
4.3 Test Methods:
4.3.1 Volatile Content:
ASTM D3530, unless the resin system contains volatile reactive
ingredients. Method B shall be employed if the resin system
consists of volatile reactive ingredients.
Method B
The piece of prepreg is weighed to the nearest 0.1 mg (Wi). The
specimen is placed in between two Teflon release films 8" x 8"
and then sandwiched between two aluminum plates eight inches
square. Two C-clamps are applied snugly to the sandwich and the
assembly heated to 250 ñ 10ø F for 20ñ 1 minute. After cooling,
the film is carefully removed from the specimen and the specimen
weighed to the nearest 0.1 mg (Wf). The volatile content is then
calculated as follows:
4.3.2 Resin Content and Fiber Areal Weight
Resin content and fiber areal weight of the prepreg shall be
tested per MIL-T-29586, 4.7.1.2; ASTM D3171; or equivalent.
4.3.3 Resin Flow
Resin flow shall be tested per ASTM D3531 or equivalent, if
specified in Table 1.
4.3.4 Tack
Tack shall be tested for conformance to the Tack Table:
a. Cut two 3" x 1" specimens from the prepreg (splice or butt
joint, if necessary). The 0ø direction shall be in the 3"
direction.
b. Attach one piece of test material to a dry aluminum test
panel which has been cleaned to water break-free condition
with chlorine-free scouring powder and then dried. Apply
the test piece with light pressure using a squeegee or
roller over the backing film.
c. Remove the backing and apply the other strip to the first
strip applied. Tack in a similar manner. Remove the
backing from second strip.
d. Position the plate vertically.
e. Maintain specimens in this position for 30 minutes at a
temperature of 70ø F to 80ø F.
f. Record pass or fail and level of tack per the following
TABLE :
TACK LEVEL TABLE
Tack level
I Low Tack
Prepreg is stiff and boardy.
II
Dry but slight drape.
III Slight tack:
Sticks to itself when hand applied but does not stick to a
vertical tool.
IV
Prepreg sticks to itself and vertical tool.
V
Sticks to hands but no resin transfer.
VI High Tack
Wet and sloppy with resin transfer.
4.3.6 Drape
Drape shall be tested as follows for conformance to Table 1.
a. Cut a prepreg sample 1.0" x 3.0", nominal, with the fiber
oriented in the long direction.
b. Drape the 1.0" dimension of the specimen over a rod per the
table below and gently shape it to the rod contour:
Fiber Modulus Range (MSI) Rod Dimension (in)
0-50 0.125 "
50-65 1.0 "
65-80 1.5 "
80-120 2.0 "
c. The sample fibers shall not break or tear with this
treatment under inspection with a 10x magnifier. (The
specimen may be lightly heated with backing removed.)
d. A group of three specimens shall be treated and reported as
pass or fail. Failure of any of the specimens shall
constitute failure of the group.
4.3.7 Gel time:
Gel time shall be measured per ASTM D3532 or using the
Fisher-Johns Resin Gel Time Method. The Fisher-Johns Resin Gel
Time Method is as follows:
a. Specimens should be 0.25 by 0.25 inches and one ply thick.
b. Preheat the Fisher-Johns Platform to the test temperature
specified in the applicable specification sheet.
c. Insert the specimen between two covered glasses and place
on the heated platform. Start the timer.
d. Periodically, at least once every 30 seconds apply moderate
pressure to the top cover glass using a probe and observe
any movement of the resin. As the resin nears its gel
point, probe continuously until no further movement is
observed. Stop the timer and record the time to the nearest
second.
4.4 Inspection and Compliance:
4.4.1 Responsibility for inspection
Unless otherwise specified herein or in the contract or purchase
order, the contractor (material supplier) is responsible for the
performance of all inspection requirements (examinations and
test) as specified herein. The contractor (material supplier) may
use his own or any other facilities suitable for the performance
of the inspection requirements specified herein, unless
disapproved by the Government (GSFC). The Government reserves the
right to perform any of the inspections set forth in the
specification where such inspections are deemed necessary to
assure supplies and services conform to prescribed requirements.
4.4.2 Responsibility for compliance
All items must meet all requirements of sections 3, 4 and 5. The
inspection set forth in this specification shall become a part of
the contractors (material suppliers) overall inspection system or
quality program. The absence of any inspection requirements in
the specification shall not relieve the contractor (material
supplier) of the responsibility of ensuring that all products or
supplies submitted to the Government (GSFC) for acceptance comply
with all requirements of the contract or purchase order. Sampling
inspection, as part of manufacturing operations, is an acceptable
practice to ascertain conformance to requirements, however, this
does not authorize submission of known defective material, either
indicated or actual, nor does it commit the Government (GSFC) to
accept defective material.
5 Delivery:
5.1 Packaging:
5.1.1 Unit Packaging
The epoxy-preimpregnated graphite materials shall be supplied in
continuous lengths on rolls as specified on the purchase order.
Tape or woven goods shall be supplied in continuous lengths wound
on 10 in diameter cardboard cores. Each roll shall be placed into
an evacuated, heat-sealed, MIL-B-131 moistureproof bag and marked
per 5.3. Maximum net weight per roll shall not exceed 30 lb.
5.1.2 Shipping Container
The shipping container used shall be a wood or cardboard box
meeting common carrier regulations. The box shall be sufficiently
braced and packaged to prevent damage to the inside barrier bags.
The core shall be supported in the box such that the graphite
tape does not rest against the side of the box. The box shall
contain sufficient dry ice to maintain the contents at or below a
maximum temperature of 0ø F for a minimum of 72.0 hours following
shipment. Place a device that can accurately and continuously
monitor and record the date, time of day and temperature inside
the shipping container so that any temperature excursion can be
verified along with its duration during shipment. A Ryan seven
day temperature recorder or equivalent can be used. All prepreg
shipped must be delivered to GSFC within the seven day capability
of the Ryan monitoring recorder.
Note:
A high visibility marking, indicating
immediate refrigeration upon receipt, shall
be prominently displayed on the outside
surface of the shipping container.
5.1.4 Roll condition log
For each roll, the roll condition log shall supply the batch and
roll numbers used in the manufacturing of the prepreg roll, roll
width, average roll thickness and roll length. It shall also
indicate all splice locations, defect locations, defect types and
lengths. The roll condition log for each individual prepreg roll
shall be mailed to GSFC before the prepreg roll is shipped. This
log will be used by GSFC to record and track the prepreg rolls
out of proper storage conditioning temperatures, relative
humidity and date of manufacture.
5.2 Safety Data:
The vendor shall supply a Material Safety Data Sheet (OSHA Form
20 or equivalent) either attached to the bill of lading or within
the exterior packaging.
5.3 Identification
The following identification shall be marked directly on the bill
of lading, directly on the exterior package, on the waterproof
barrier bag, and on a label in the cardboard core of each roll:
a. Manufacturer's name
b. Manufacturer's material description and identification
c. Material size: width and nominal thickness
d. Lot identification with the batch number(s) of fiber(s) &
resin(s) used in that lot or provide mechanical and
physical testing data on all delivery lots per paragraph
3.2.1.
e. Date of manufacture
f. Gross weight
g. Net usable and billable weight (excluding any additional
tagged material; see 3.1.3 Note)
h. Linear length of fully conforming prepreg
i. GSFC Purchase Order #; and GSFC specification # and
revision letter
j. Areal weight (g/m2)
5.4 Shipping :
5.4.1
The Supplier shall assure delivery during normal working hours on
non-holiday weekdays. No deliveries will be made on Friday after
3 PM. This requirement normally implies shipment on a Monday or
Tuesday.
5.4.2
The supplier shall notify the technical representative or the
requester listed on the contract when shipment is made and shall
be told the airbill number for each separate package being
shipped.
6 Application Data
Typical Properties are listed below and are not requirements of
this specification:
Typical Properties
a) Coefficient of thermal expansion close to zero, with the
laminate design depending on the type, fiber, and resin of
the prepreg (CTE = 0 ñ 0.1 x 10-6 / ø F)
b) Outgassing of cured laminate, per ASTM E595:
Total Mass Loss (TML) ó 0.4 %
Volatile Condensable Materials (VCM) ó 0.01 %
7 Notes:
7.1 Definitions.
1) Linear Normalization: Linear normalization is defined as:
2) GSFC: Goddard Space Flight Center
3) TBD: To Be Determined
4) Coefficient of Variation : The ratio of the sample
standard deviation to the sample mean expressed as a
percentage.
Appendix C
T50/cyanate ester, 0.005" ply thickness
Table 1. Uncured Material Properties
Note: NOT INCLUDED
Table 2. Cured Laminate Properties
Note: NOT INCLUDED