Significant progress has been made during the past three months on the preparation of carbon fiber composites using advanced polymer resins. The results are set forth in recent reports and publications, and will be presented at forthcoming national and international meetings. Current and ongoing research activities reported herein include: powdered tow ribbonizing; unitape from powdered tow; customized towpreg for textiles and ATP; and textile composite research. During the period ahead research will be directed toward further development of the new powder curtain prepregging method and on ways to customize dry powder towpreg for textile and robotic applications in aircraft part fabrication. Studies of multi-tow powder prepregging and ribbon preparation will be initiated in conjunction with continued development of prepregging technology and the various aspects of composite part fabrication using customized towpreg. Also, a major effort during the coming months will be participating in the analysis of the performance of the new solution prepregger

Marchello, Joseph M.

English

NASA Technical Reports Server

Department of Civil Engineering
College of Engineering and Technology
Old Dominion University
Norfolk, Virginia 23529
POLYMER INFILTRATION STUDIES
By
Joseph M. Marchello, Principal Investigator
Progress Report
For the period October 1, 1992 - December 31, 1992
Prepared for
National Aeronautics and Space Administration
Langley Research Center
Hampton, Virginia 23665
Under
Research Grant NAG-l-1067
Robert M. Baucom, Technical Monitor
MD-Polymeric Materials Branch
Submitted by the
Old Dominion University Research Foundation
P.O. Box 6369
Norfolk, Virginia 23508-0369
December 1992
https://ntrs.nasa.gov/search.jsp?R=19930006242 2020-03-17T08:30:18+00:00Z
POLYMER INFILTERATION STUDIES
SummarY
Significant progress has been made during the past
three months on the preparation of carbon fiber
composities using advanced polymer resins. The results
are set forth in recent reports and publications, and
will be presented at forthcoming national and
international meetings.
Current and ongoing research activities reported
herein include:
_Powdered Tow Ribbonizing
4 Unitape from Powdered Tow
Customized Towpreg for Textiles and ATP
- Textile Composite Research
A
J
During the period ahead research will be directed
toward further development of the new powder curtain
pregregging method and on ways to customize dry powder
towpreg for textile and robotic applications in aircraft
part fabrication. Studies of multi-tow powder prepregging
and ribbon preparation will be intiated in conjunction
with continued development of prepregging technology and
the various aspects of composite part fabrication using
customized towpreg. Also, a major effort during the
coming months will be participating in the analysis of
the performance of the new solution prepregger.
Polymer Infilteration Studies
The goal of the polymer infilteration investigations
is to develop methods by which to produce advanced
composite material for automated part fabrication
utilizing textile and robotic technology in the
manufacture of subsonic and supersonic aircraft. This
object is to achieved through research investigations at
NASA Langley Research Center and by stimulating
technology transfer between contract researchers and the
aircraft industry.
The powder curtain prepregging system, which was
started up successfully last Summer, is currently
undergoing modifications. During the next few weeks, an
automated powder return system will be installed and the
resin monitoring gamma gauge will be connected to the
pull roller of the takeup winder to provide a feedback
quality control loop for the unit. These changes should
provide better opersting control over fugitive powder and
improved towpreg quality control.
Issues in the use of powder coated towpreg for
textile applications have been the subject of significant
effort. Progress to date was presented at the Fiber-Tex
meeting in Philadelphia in October, see attachments. An
outline of planned textile composites research has been
prepared to guide activities during the next two years,
see attachments.
Consideration of the ways to customized towpreg for
use in automated tow /fiber placement has resulted in
several new approaches and will be the subject of a paper
to be presented at the 10th Thermoplastic Matrix and Low
Cost Composite Review in February, see attachments.
Noteworthy among the ideas that have been developed is
the potential benefits from use of non-rectangular
ribbon, and the thermal wave bonding model of tow
placement with on-the-fly-cure. As described in the
attached memoranda, several efforts to produce quality
towpreg ribbon are underway. In addition to die forming
methods, it is planned to investigate making unitape from
powdered tow which can then be slit into the desired
ribbon geometry.
Three papers are schedule for presentation at the
38th International SAMPE Symposium & Exhibition next May.
The first paper deals with the new powder curtain
prepregging method and will be the inital public
disclosure of the new process. The second paper describes
the new NASA solution pregregger, and the third paper
reports on the effect of fiber volume fraction on
composite properties.
Attachments
i. Specialized Prepreg Ribbon for Automated Fiber
Placement, Memorandum dated November 25, 1992.
2. Towpreg Ribbonizing, Memorandum dated December 21,
1992.
3. Outline of Projects for Textile Composite Activities
for FY 93 and FY 94
4. " Issues in the Use of Powder-Coated Towpreg for
textile Applications", M. Hugh, J.Marchello, and
N. Johnston, presented at FIBER-TEX'92.
November 25, 1992
Memorandum
To:
From:
Subject:
N. Johnston, R. Baucom, J. Nelson, D. Sandusky,
M. Hugh, S. Wil_nson, and J. Hinckley
J. M. Sarchello_i_
Specialized Pre_reg Ribbon for Automated Fiber
Placement
As we discussed during our meeting last Thursday,
several approaches are being taken to try to make ATP
ribbon, using advanced resins (thermoplastics and
toughened thermosets), that has special cross-sections
(triangle, trapezoid, parallelogram). Efforts elsewhere
(Scot Taylor and John Muzzy) have not yet produced a good
quality preconsolidated ribbon of uniform width. On
Monday, we made our first run with the "hot shoe" die.
As will be discussed later, the results were encouraging,
but not a complete success. The purpose of this
memorandum is to try to summarize where these efforts
stand and what are their directions during the period
ahead.
ATP ribbon is currently made by slitting unitape
prepreg (epoxy thermoset or APC-2 PEEK thermoplastic).
There are four approaches to making towpreg ribbon from
powdered fiber tow.
- Pultrude towpreg through a die. This is the
approach being investigated by Scot Taylor.
- Pass the towpreg between a set of roller dies.
This has been tried here and by John Muzzy.
- Pull the towpreg over an open "hot shoe" die. We
have just begun this study.
- Pass powdered tows through our prepregger to make
a unitape and slit to desired ribbon shape.
Monday afternoon we pulled powder towpreg made of
12k AS-4 carbon fibers coated with PEEK (40 w%) through
the "hot shoe" ceramic die. This was the first test of
the die which has a 1/4 inch rectangular channel and is
intended for use in making PEEK ribbon for McAir.
During the runs a pulling rate of 6 ft/min was used
which means that towpreg residence time in the die hot
zone was about 2 seconds. At 705°F the ribbon appeared
essientially unchanged. It was 1/4 inch wide and looked
the same as the material on the feed spool. At 750°F the
ribbon had contracted to a 3/8th inch width. It was clear
that resin had flowed with some accumulation at the top
(open) side of the ribbon. A quartz top on the die had
been removed because it caused resin buildup and die
jamming.
Samples of the ribbon from both the 705 and 750°F
pulling runs were taken to obtain micrograph and SEM
photographs. Additional tests with this die will be made
during the next few weeks. These runs will explore
questions such as: Why did the ribbon contract to a width
less than that of the die? How can the accumulation of
resin on the top side of the ribbon be eliminated? What
is the extent of fiber damage? Is the ribbon fully
wetted, or are there dry fibers in the center?
As mentioned during our meeting last Thursday, the
idea of passing powder coated tows through the prepregger
to make unitape should be explored. Ultimately one would
want to powder coat on-line, however, until a reliable
12 inch wide powder curtain feeder has been developed,
it seems best to powder coat off-line. In regard to
making customized ATP tape from slit powder tow unitape
there are several issues that need to be resolved:
- Can unitape be made from tow that has been coated
with powdered thermoplastic resin?
- Can a 12 inch long powder curtain feeder be
developed?
- Can Unitape be slit at angles to obtain the ribbon
shapes needed for customized ATP tow?
When modifications to the powder curtain unit have
been completed, it will be used to make PEEK towpreg for
use in addressing the first question. We have been
thinking of producing 30 spools, each holding 300 feet
of towpreg, as the starting material for the unitape
tests. Once we have purchased 12 inch helix screws for
the two large powder feeders, the development of the
powder Curtain sleeves for the screws and their testing
can begin in the powder booth. During our visit to
American GFM last week we saw ultrasonic cloth and
prepreg cutters that can be set at angles to produce the
various towpreg ribbon architectures. Acquisition of
these type cutters and the develoment of appropriate
mounts for them on the prepregger would begin the
resolution of the third question. One additional concern
is how best to take up the ribbon?
December 21, 1992
Memorandum
To: N. Johnston, R. Baucom, D. Sandusky, M. Hugh,
S. Wilkinson, and J. Hinkley
From: J.M. Marchell__/%
Subject: Towpreg Ribbo_mzing
On December 2, we visited Custom Composites in
Atlanta to observe their powder prepregging system and
to discuss towpreg ATP ribbonizing with John Muzzy and
his students at Georgia Tech. The powder prepregging unit
at Custom Composites was operated at 125 ft/min during
our visit and seemed to do a good job. Significant
amounts of powder are carried over and collected for
reuse. This may result in fiber plugging of the feeder
over time, since some fibers are usually present in
recycled powder. Quality control continues to be an area
of concern and they are working on development of an on-
the-fly tow ribbon weighing guage.
The students at Georgia Tech have given up on using
roller dies for ribbonizing. So have we. They are testing
a 3 inch electrically heated pultrusion die. During the
discussion, it was suggested that they try operating at
higher temperature and consider preheating the entering
towpreg to just below T_ The ribbon, made from a 12k AS4
PEEK tow, that they shoged us appeared similar to ribbon
being made by Scott Taylor. According to McAir, the main
concerns with these ribbons has been dry fibers in the
center and loose fibers on the surface which tend to jam
the ATP ribbon cutter.
As mentioned in the November 25 memorandum, our
current ribbonizing activities deal with using the open
hot shoe die. From the results of the initial runs,
described in the memorandum, it was clear that something
had to be done to keep the ribbon at the 1/4 inch width.
Two changes have been made. First was to use two towpregs
rather than only one. Second was to reduce the drag, or
tension on the tows, by raising the guide bars in front
and back of the die, so that the towpreg is not held
tightly in the die slot, but simply slides through it.
These approaches produce a good appearing ribbon
during short runs on December ii and 14. It has the
desired 1/4 inch width, is about I0 mills thick, and
appears similar to silt APC-2. There are differences. The
towpreg has 40 w% resin so the ribbon has a lower fiber
volume than APC-2, and it is not as nice an appearing
ribbon. SEM photos indicate a resin rich layer in the
middle of the ribbon. Since we made it from two ribbons,
one on top of the other, a boundary region was expected,
but not one with quite as much resin as shown in the SEM
photos. The approach of heating from the top and dragging
the ribbon bottom over the die may result to resin flow
into the ribbon center. This could explain the SEM
photgraphs. The ribbon is of about the same stiffness as
APC-2. It does not appear to have loose fibers on the
surface, so it may not plug the McAir ATP ribbon cutters.
On December 16 the system, using two towpregs, was
continuously operated for a 75 minute interval. The
objective was to determine what problems might arise
during extended operation, and if possible, to make
ribbon for McAir to test. After an initial slow startup
the unit was held at a tow speed of I0 ft/min with a die
temperature of about 1200°F. During the first thirty
minutes the ribbon appeared good, but resin and fibers
were observed accumulating in the die. At first this did
not seem to be a problem and may actually have reduced
die friction, however over time some of the fiber and
resin in the die would release and pass out attached as
a clump on the ribbon, which had to be picked or cut off.
In the middle of the run we came to a cut in the
towpreg on one of the feed spools. Rather than shutdown
we managed to feed the cut towpreg through the die hot
zone on the fly and return to steady operation in a few
minutes. As the one hour mark was approached fiber and
resin accumulation became a major problem resulting in
necking down of the ribbon and excessive clumps on the
ribbon leaving the die. The unit was shutdown after 75
minutes when one of the feed spools ran out of towpreg.
Also, early in the run the reversing mechanism on the
takeup winder failed, requiring that it be manually
reversed at the end of each traverse.
On the basis of the these test runs it is difficult
to say whether the hot shoe die approach can be developed
as a pratical method for producing large quantities of
ATP ribbon. The concerns expressed above will need to be
addressed in designing a new die for additional tests.
Also, as mentioned in the November 25 memorandum, in
parallel with this effort, we shall try to use the
prepregger to make a tape from powdered towpreg which can
then be slit into ATP ribbon.
Outline of Projects for Textile Composite Activities for FY93 and FY94
Framewrapping for Unidirectional Composites
Mechanical Properties - Resin Qualification (AMD0036, AMD0029, LARC-TPI)
SBS
Flexure Strength and Modulus
Compression
Tension
Tape Product from Powder Coated Material
Powder coated product as off-line process
Powder coating on-line with tape production
Determine appropriate degree of consolidation needed in tape product to produce
well-consolidated panels
Thermal tests to verify state (extent of cure, Tg, etc.) of polymer in tape product
Optical microscope tests to verify state (degree of consolidation, % voids,
distribution of polymer, wetting of fibers, etc.) of tape product
Mechanical Properties
Open Hole Tension - quasi-isotropic layup
Open Hole Compression - quasi
Compression after Impact - quasi
Woven 8HS Composites from Powder Coated Towpreg
Produce 8HS fabric from powder coated towpreg yarn
Improve the towpreg yarn for the weaving process
Produce composite panels
Determine appropriate layup for optimal processing
Characterize consolidation of composites with regards to varying Vf
Characterize bulkiness of fabrics
Determine tension and compression strengths and moduli of 8HS composites
Braiding
Establishbraidingprotocolfor biaxial andtriaxial fabrics
Improveyarnfor braidingprocess
Vary tow sizes
Vary resincontent, Vf
Measure tension and compression strengths and moduli as functions of
tow size
resin content, Vf
Characterize bulk factor of 2D fabrics
Debulking and Consolidation of 2D (braided and woven) fabrics
Develop methods for debulking powder-coated preforms
Characterize fiber movement
Identify point of intimate contact
Develop preform debulking tooling
Develop methods for net shape consolidation
Preform stitching
Net shape tooling
Produce three demonstration parts
Select geometry of structure
Machine tooling for structure
Consolidate final part
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Polymer infiltration studies

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