Increased application of polymer matrix composite (PMC) materials in large vehicle structures requires consideration of non-autoclave manufacturing technology. The NASA Composites for Exploration project, and its predecessor, Lightweight Spacecraft Structures and Materials project, were tasked with the development of materials and manufacturing processes for structures that will perform in a heavy-lift-launch vehicle environment. Both autoclave and out of autoclave processable materials were considered. Large PMC structures envisioned for such a vehicle included the payload shroud and the interstage connector. In this study, composite sandwich panels representing 1/16th segments of the barrel section of the Ares V rocket fairing were prepared as 1.8 m x 2.4 m sections of the 10 m diameter arc segment. IM7/977-3 was used as the face-sheet prepreg of the autoclave processed panels and T40-800B/5320-1 for the out of autoclave panels. The core was 49.7 kilograms per square meters (3.1 pounds per cubic feet (pcf)) aluminum honeycomb. Face-sheets were fabricated by automated tape laying 153 mm wide unidirectional tape. This work details analysis of the manufactured panels where face-sheet quality was characterized by optical microscopy, cured ply thickness measurements, acid digestion, and thermal analysis

Lort, Richard D., III

McCorkle, Linda S.

Miller, Sandi G.

Pelham, Larry I.

Scheiman, Daniel A.

Sutter, James K.

Zimmerman, Thomas J.

NASA Technical Reports Server

FACE-SHEET QUALITY ANALYSIS AND THERMO-PHYSICAL 
PROPERTY CHARACTERIZATION OF OOA AND AUTOCLAVE 
PANELS 
Sandi G. Miller
1
, Richard D. Lort III
2
, Thomas J. Zimmerman
2
, James K. Sutter
1
,                  
Larry I. Pelham
3
, Linda S. McCorkle
4
, Daniel A. Scheiman
5
 
 
1
NASA Glenn Research Center, Cleveland, OH. 44135 
2 
BG Smith & Associates, Huntsville, AL 35816 
3
NASA Marshall Space Flight Center, Huntsville, AL 35812 
4
Ohio Aerospace Institute, Cleveland, OH. 44135 
5 
ASRC Aerospace Corp., Cleveland, OH. 44135 
 
 
ABSTRACT 
 
Increased application of polymer matrix composite (PMC) materials in large vehicle structures 
requires consideration of non-autoclave manufacturing technology.  The NASA Composites for 
Exploration project, and its predecessor, Lightweight Spacecraft Structures and Materials 
project, were tasked with the development of materials and manufacturing processes for 
structures that will perform in a heavy-lift-launch vehicle environment.  Both autoclave and out 
of autoclave processable materials were considered.  Large PMC structures envisioned for such a 
vehicle included the payload shroud and the interstage connector.  In this study, composite 
sandwich panels representing 1/16
th
 segments of the barrel section of the  Ares V rocket fairing 
were prepared as 1.8 m x 2.4 m sections of the  10 m diameter arc segment.  IM7/977-3 was used 
as the face-sheet prepreg of the autoclave processed panels and T40-800B/5320-1 for the out of 
autoclave panels.  The core was 49.7 kg/m
2 
(3.1 lb/ft
3
 (pcf)) aluminum honeycomb.  Face-sheets 
were fabricated by automated tape laying 153 mm wide unidirectional tape.  This work details 
analysis of the manufactured panels where face-sheet quality was characterized by optical 
microscopy, cured ply thickness measurements, acid digestion, and thermal analysis. 
 1.  INTRODUCTION 
PMC materials are increasingly utilized in large structures; driving the maturation of advanced 
material and processing technologies.
1
  Efforts from both industry and U.S. Government teams 
have pushed Out of Autoclave (OoA) technology and application forward over the past several 
years; leading to manufacturing demonstrations including the Boeing Wing Spar
2
 and the 
Advanced Composite Cargo Aircraft.
3
 
 
Within NASA, composite structures for heavy-lift launch vehicles are projected to be the largest 
composite structures fabricated for aerospace. Specifically, the interstage of the Ares V Cargo 
Launch Vehicle was planned to be 10 m in diameter and 12 meters in height.
4
  The size 
requirements of these structures have placed considerable emphasis on processing out of the  
 
___________________________________________ 
*
This paper is declared a work of the U.S. Government and is not subject to copyright protection 
in the United States. 
https://ntrs.nasa.gov/search.jsp?R=20120012919 2019-08-30T21:14:12+00:00Z
autoclave.  Manufacturing autoclave quality structures without autoclave pressure places added 
criticality to void removal.  The generation of voids is dependent on a number of factors
5
 
including prepreg chemistry, tack, lay-up, and other considerations.  This paper describes a 
manufacturing feasibility study of 1/16
th
 arc segments of the 10 m Ares V interstage. Two 
material systems were selected; Cytec IM7/977-3 autoclave cure epoxy/ carbon fiber prepreg and 
Cytec T40-800B/5320-1 out of autoclave cure epoxy/ carbon fiber prepreg. This study details 
characterization of sandwich panels prepared from these materials and compares face-sheet 
consolidation in the autoclave and non-autoclave processed materials.  Variation in tool-side and 
bag-side laminate quality is also noted.  The data collected in this paper was used for structural 
analysis and modeling in preparation for larger, 1/6
th
 segment, panel manufacture.  Coupon test 
data on selected panels showed high strength values, indicative of good quality panel 
manufacturing in both the autoclave and out of autoclave systems.
6
   
 
2.  EXPERIMENTAL 
2.1  Panel Fabrication 
The composite tooling was built by Janicki Industries in Sedro-Woolley, WA, using a 
T300/Epoxy substructure with T300/Polyimide topcoat. Tool dimensions are approximately 2.5 
m x 3 m with a curvature following a 5 m  radius concave tool. 
 
IM7/977-3 was selected for autoclave processing and was purchased from Cytec Engineered 
Materials as 145 gsm, 153 mm” wide, uni-tape prepreg.  FM300M 0.08 psf film adhesive, was 
used to co-cure the aluminum core with the IM7/977-3 face-sheet.   
 
T40-800B/5320-1 was also purchased from Cytec Engineered Materials as 145 gsm, 153 mm 
uni-tape prepreg and was used to evaluate the manufacturing feasibility of the panel section via a 
non-autoclave process. FM309-1 M 0.08 psf, film adhesive was used in the vacuum only panel 
fabrication. 
 
Expanded, formed, and perforated aluminum honeycomb core (49.7 kg/m
3
) was purchased from 
Alcore.  A description of panel configuration and core thickness is given in Table 1.  
 
Panels were fabricated at Hitco Carbon Composites, Inc, Gardena, CA, using an Automated 
Tape Laying (ATL) machine (Charger) built by MAG, as depicted in Figure 1. Six inch uni-tape 
was used to allow for fiber steering on the contoured tool.  
 
Figure 1: Automated manufacturing of contoured panel. 
Table 1: Panel Nomenclature and Description 
Panel  Prepreg  Core  Layup  
8000CMDP  IM7/977-3  25.4 mm  [45,90,-45,0]s  
MTP-6001 IM7/977-3  41.3 mm  [60,-60,0]s  
MTP-6003  IM7/977-3  28.6 mm  [60,-60,0]s  
8010CMDP  T40-800/5320-1  25.4 mm  [45,90,-45,0]s  
MTP-6010  T40-800/5320-1  28.6 mm [60,-60,0]s  
MTP-6000  IM7/977-3  28.6 mm [60,-60,0]s  
 
Buildups on the ends of the 8 ply panels consisted of a balanced and symmetrical layup 
intertwined with the original 8 plies for a total of 16 plies.  The buildups were approximately 178 
mm wide and tapered into the acreage.  
2.2  Face-sheet Characterization 
2.2.1 Core and Adhesive Removal  
Sections were removed from the edge of each manufactured panel for characterization of the 
composite skin, as shown in the schematic in Figure 2.  The tool and bag sides were noted.  The 
core was removed from each section and the face-sheets were sectioned for optical microscopy, 
acid digestion, and thermal analysis.  
 
  
2.2.2  Optical Microscopy  
Representative sections of the panel were polished for optical microscopy.  Specimens were 
polished and photographed using an optical microscope.  Thickness measurements were taken by 
a pixel counting method on both tool and bag side face-sheets.  Five thickness measurements 
were taken at each location and averaged.  Ply thicknesses were calculated by dividing the 
measured laminate thickness by the number of plies.   
2.2.3  Void Analysis   
The void volume and fiber content of each laminate panel was calculated following ASTM D 
3171-76, Standard Test Method for Constituent Content of Composite Materials, with six 
samples tested per material.   The matrix material was digested in hot sulfuric acid and hydrogen 
peroxide solutions and the remaining carbon fibers were filtered through a fine mesh screen.  The 
fibers were flushed with water followed by an acetone rinse.  The acetone was evaporated 
overnight in a fume hood and the fibers were then dried in an oven at 100 
o
C prior to weighing.    
2.2.4  Dynamic Mechanical Analysis 
DMA tests followed conditions specified in ASTM D7028-07, Standard Test Method for Glass 
Transition Temperature (DMA Tg) of Polymer Matrix Composites by Dynamic Mechanical 
Analysis.  The test included a 5 
o
C/min ramp from room temperature to 50 
o
C above Tg. The 
frequency was set at 1 Hz, per the ASTM specification and the amplitude set at 20m.  Test 
specimens were dried at 70 
o
C prior to analysis.  A single cantilever fixture was used for all 
DMA testing.   
3.  RESULTS AND DISCUSSION 
3.1 IM7/977-3   
Four panels were fabricated with IM7/977-3 prepreg and cured in an autoclave.  A representative 
panel section image is shown in Figure 3.  Considerable resin bleed-out was noted within the 
sections received for analysis; both along the core and soaked into the peel ply.  Some resin flow 
is not unusual for panels made with this material, as the resin viscosity drops during the initial 
stages of the cure cycle.
7 
 
                          
Figure 3: Resin flow along un-cut edge of IM7/977-3 panel. 
3.1.1 Void Analysis 
Optical microscopy images of IM7/977-3 face-sheet sections are shown in Figure 4, representing 
6 ply and 12 ply regions of panel MTP6000.  Voids are visible within the cross-sections, 
predominately between plies.  Typical dimpling between nodes is called out in Figure 4a.  There 
was not a notable difference in quality between the bag (Figures 4a and 4b) and tool side 
(Figures 4c and 4d) with respect to void content.     
 
a.  b.  
Resin Flow 
Void 
Dimpling 
Peel Ply  
c.  d.  
Figures 4a – 4d: Photomicrographs representing bag (4a and 4b) and tool (4c and 4d) side 
sections of an IM7/977-3 panel. 
 
Several images of the panel cross sections showed areas of face-sheet delamination and 
considerable void content, Figures 5a and 5b.  However, IR thermography of the entire panel 
indicated no significant flaws; and the higher void content may be related to the edge section of 
the larger panel where these pieces were taken.   
 
a.  b.  
Figures 5a – 5b: Photomicrographs show voids within an IM7/977-3 panel. 
 
Acid digestion of these sections resulted in a measured void content below 2%, with no 
significant difference between the tool and bag side of the panel.  Acid digestion results are 
shown in Table 2 for the IM7/977-3 panels.  
 
Table 2: Acid digestion results of the IM7/977-3 skins. 
Panel Face-sheet 
Density (g/cm
3
) 
Average Void 
Content (%) 
Average 
Fiber Vol. 
(%) 
Average Resin 
Wt. (%) 
8000CMDP_Bag 1.59 1.8 65.5 27.0 
8000CMDP_Tool 1.60 1.1 65.2 28.2 
MTP-6001_Bag 1.61 1.0 64.5 28.5 
MTP-6001_Tool 1.61 0.9 64.6 28.5 
MTP-6003_ Bag 1.57 0.7 65.8 27.6 
MTP-6003_Tool 1.58 0.9 65.6 27.6 
MTP-6000_Bag 1.60 1.0 64.4 28.7 
MTP-6000_Tool 1.60 0.9 64.2 28.8 
 
The acid digestion data calls out a higher fiber volume than the expected 60 vol.% and a lower 
resin weight content than anticipated.   
 
The significant visible resin bleed-out shown in Figure 3, and the low resin content reported by 
acid digestion, prompted repeat measurements based on samples taken from within the interior of 
panel MTP-6000.  The resin content of those sections by acid digestion was 28.5 wt. %; 
comparable to that at the edge.  Average fiber volume of the interior samples was 64.0 vol.%.  
3.1.2  Cured Ply Thickness (CPT) 
The manufacturer supplied the average ply thickness as 0.131 mm (5.14 mil).  Cured ply 
thickness (CPT) was measured by optical microscopy and was lower than anticipated; likely due 
to the resin bleed-out and measured low resin content.    
 
Trends in the CPT measurements, Figure 6, were consistent between the four IM7/977-3 panels; 
with the bag-side (BS) skins approximately 2% thinner than the tool-side (TS).  Overall, the 
average face-sheet thickness measured 4.5% thinner than the theoretical CPT.  The range in skin 
CPT varied from 1% to7% lower than theoretical.   
 
  
 
Figure 6:  Average ply thickness for the IM7/977-3 panels. 
8000C
MDP
MTP-6001 MTP-6003 MTP-6000
BS Facesheet 0.125 0.124 0.124 0.122
TS Facsheet 0.129 0.126 0.126 0.122
Theoretical 0.131 0.131 0.131 0.131
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
A
v
er
a
g
e 
P
ly
 T
h
ic
k
n
es
s 
(m
m
) 
IM7/977-3 Average Ply Thicknesses 
BS Facesheet
TS Facsheet
Theoretical
3.1.3  DMA 
The IM7/977-3 face-sheet Tg’s are listed in Table 3.  Tg was determined by the drop in storage 
modulus from a DMA curve. 
 
Table 3:  Tg as determined by DMA 
Panel # Tg (Bag-side)  
(
o
C) 
Tg  (Tool-side) 
 (
o
C) 
8000CMDP 166 179 
MTP6001 173 173 
MTP6003 175 172 
MTP6000 195 (6 ply region) 
  192 (12 ply region) 
196 (6 ply region) 
  207 (12 ply region) 
 
The Tg Cytec lists for the IM7/977-3 neat resin is 178 
o
C.  However, past work with this prepreg 
system has lead to a Tg just over 200 
o
C.
4
  Representative DMA curves are shown in Figure 7.   
 
 
Figure 7:  DMA curves of IM7/977-3 coupons 
 
  
3.2 T40-800B/5320-1 
Two panels were manufactured with T40-800B/5320-1 OoA cure prepreg tape.  The fabricated 
panels did not exhibit the same level of resin bleed-out as was observed in the IM7/977-3 panels.   
3.2.1Void Analysis 
The results of the out of autoclave panel were very similar to those of IM7/977-3.  Optical 
microscopy images showed voids and delamination on both the tool side and bag side of the 
panel.   
 
1000
10000
100000
100 125 150 175 200 225 250 275 300
S
to
ra
g
e 
M
o
d
u
lu
s 
(M
P
a
) 
Temperature (oC) 
8000CMDP_ 8 ply 
MTP6001 and 
MTP6003_ 6 ply 
Average fiber volume, resin content, and void content by acid digestion are listed in Table 4.  
The void content was, in general, greater than that of the autoclave cured panels; however, void 
contents did not exceed 2%.  The fiber volume and resin content in the T40-800B/5320-1 panels 
was representative of manufacturer specifications, likely due to the lower resin flow visible 
during cure.  Optical photomicrographs are shown in Figures 8a – 8d. 
 
 
 
Table 4:  Acid digestion results of the T40-800B/5320-1 panel skins. 
Panel Face-sheet 
Density (g/cm
3
) 
Average Void 
Content (%) 
Average Fiber 
Volume (%) 
Average 
Resin Wt 
8010CMDP_Bag 1.61 1.0 62.0 31.2 
8010CMDP_Tool 1.59 1.8 62.0 30.6 
MTP-6010_Bag 1.60 1.8 60.7 31.6 
MTP-6010_Tool 1.60 1.5 60.9 31.6 
 
a.    b.  
c.  d.  
Figures 8a – 8d: Photomicrographs representing bag (8a and 8b) and tool (8c and 8d) side 
sections of and T40-800b/5320-1 panel. 
3.2.2 Cured Ply Thickness 
Theoretical cured ply thickness (CPT) of the OoA material was 0.136 mm (5.37 mil).  Results of 
optical CPT measurements are given in Figure 9. As with the IM7/977-3 panels, there was a 
tendency for the bag-side skin to be thinner than the tool side skin.  The MTP6010 panel (6 ply) 
face-sheet essentially matched the theoretical CPT.  The 8 ply, 8010CMDP, was almost 10% 
below theoretical CPT on the bag-side, and 5% below CPT on the tool side.   
 
Figure 9: Average ply thickness for the T40-800B/977-3 panels 
 
3.2.3 DMA 
The T40-800B/5320-1 face-sheet Tg’s are listed in Table 5.  Tg was determined by the drop in 
storage modulus from a DMA curve. 
 
Table 5: Tg for T40-800b panels 
Panel # Tg (Bag-side)  
(
o
C) 
Tg  (Tool-side) 
 (
o
C) 
8010CMDP 187 187 
MTP6010 188 189 
 
The Tg measured in this study was on the low end of what would be considered an acceptable Tg 
for this material. 
 
CONCLUSIONS 
As part of a larger manufacturing study, comparison of sandwich panel face-sheets, prepared 
using autoclave cured IM7/977-3 and vacuum bag only processed T40-800b/5320-1, were made 
and included void content, CPT measurement, and thermal analysis.  In general, the measured 
8010C MDP MTP-8001
BS Facesheet 0.123 0.135
TS Facsheet 0.129 0.135
Theoretical 0.136 0.136
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
A
v
er
a
g
e 
P
ly
  
T
h
ic
k
n
es
s 
(m
m
) 
T40-800B/5320-1 Average Ply Thickness 
BS Facesheet
TS Facsheet
Theoretical
CPT ranged from 3% - 5% below theoretical value.  CPT below theoretical values was 
consistently observed in the IM7/977-3 panels and attributed to resin bleed-out during cure.  This 
also led to a greater than anticipated fiber volume, and reduced resin content.  This was observed 
in samples taken from both the panel edge and mid-section. 
While some degree of porosity was observed on all panels, the vacuum only panel resulted in a 
generally higher void content.  There was little difference noted throughout the analysis between 
the tool-side and bag-side skin quality.  
 
REFERENCES 
1. Krzeminski M., Ponsaud P., Coqueret, X.,Defoort, B., Larnac G,Avila R. “Out-of-Autoclave 
Technologies for Competitive High Performance Composites”, SAMPE 2011, Long Beach, 
CA. May 2011. 
2. http://www.compositesworld.com/articles/out-of-autoclave-prepregs-hype-or-revolution 
http://www.sciencedirect.com/science/article/pii/S1359835X11001151 
3. http://www.compositesworld.com/articles/2011-high-performance-resins-highlights 
4. Sutter J. K., Kenner W. S., Pelham L., Miller S. G., Polis D. L., Nailadi C., Hou T. H., Guade 
D. J., Lerch B. D., Lort R. D., Zimmerman T. J., Walker J., Fikes J., and Bowman C., 
“Comparison of Autoclave and Out-of-Autoclave Composites for Heavy Lift Launch 
Vehicles,” Proceedings of SAMPE Fall Technical Conference 2010, Salt Lake City, Utah 
October 11-14, 2010. 
5.  Farhang L., and Fernlund G. “Void Evolution and Gas Transport During Cure In Out- Of-
Autoclave Prepreg Laminates”, SAMPE 2011, Long Beach, CA, May 2011.  
6. Kellas S., Lerch B., and Wilmoth, N., “Mechanical Characterization of In- and Out-of-
Autoclave Cured Composite Panels for Large Launch Vehicles”, SAMPE 2012, Baltimore, 
MD., May 2012. 
7. Miller S.G., Hou T.-H., Sutter J.K., Scheiman D.A., Martin R.E., Maryanski M., Schlea M., 
Gardner J.M., and Schiferl Z.R., “Out-Life Characteristics of IM7/977-3 Composites”, 
SAMPE Fall Technical Conference, Salt Lake City, UT., Oct. 11-14, 2010. 
 


Face-Sheet Quality Analysis and Thermo-Physical Property Characterization of OOA and Autoclave Panels

Increased application of polymer matrix composite (PMC) materials in large vehicle structures requires consideration of non-autoclave manufacturing technology. The NASA Composites for Exploration project, and its predecessor, Lightweight Spacecraft Structures and Materials project, were tasked with the development of materials and manufacturing processes for structures that will perform in a heavy-lift-launch vehicle environment. Both autoclave and out of autoclave processable materials were considered. Large PMC structures envisioned for such a vehicle included the payload shroud and the interstage connector. In this study, composite sandwich panels representing 1/16th segments of the barrel section of the Ares V rocket fairing were prepared as 1.8 m x 2.4 m sections of the 10 m diameter arc segment. IM7/977-3 was used as the face-sheet prepreg of the autoclave processed panels and T40-800B/5320-1 for the out of autoclave panels. The core was 49.7 kg/sq m (3.1 lb/cu ft (pcf)) aluminum honeycomb. Face-sheets were fabricated by automated tape laying 153 mm wide unidirectional tape. This work details analysis of the manufactured panels where face-sheet quality was characterized by optical microscopy, cured ply thickness measurements, acid digestion, and thermal analysis

FACE-SHEET QUALITY ANALYSIS AND THERMO-PHYSICAL 
PROPERTY CHARACTERIZATION OF OOA AND AUTOCLAVE 
PANELS 
Sandi G. Miller
1
, Richard D. Lort III
2
, Thomas J. Zimmerman
2
, James K. Sutter
1
,                  
Larry I. Pelham
3
, Linda S. McCorkle
4
, Daniel A. Scheiman
5
 
 
1
NASA Glenn Research Center, Cleveland, OH. 44135 
2 
BG Smith & Associates, Huntsville, AL 35816 
3
NASA Marshall Space Flight Center, Huntsville, AL 35812 
4
Ohio Aerospace Institute, Cleveland, OH. 44135 
5 
ASRC Aerospace Corp., Cleveland, OH. 44135 
 
 
ABSTRACT 
 
Increased application of polymer matrix composite (PMC) materials in large vehicle structures 
requires consideration of non-autoclave manufacturing technology.  The NASA Composites for 
Exploration project, and its predecessor, Lightweight Spacecraft Structures and Materials 
project, were tasked with the development of materials and manufacturing processes for 
structures that will perform in a heavy-lift-launch vehicle environment.  Both autoclave and out 
of autoclave processable materials were considered.  Large PMC structures envisioned for such a 
vehicle included the payload shroud and the interstage connector.  In this study, composite 
sandwich panels representing 1/16
th
 segments of the barrel section of the  Ares V rocket fairing 
were prepared as 1.8 m x 2.4 m sections of the  10 m diameter arc segment.  IM7/977-3 was used 
as the face-sheet prepreg of the autoclave processed panels and T40-800B/5320-1 for the out of 
autoclave panels.  The core was 49.7 kg/m
2 
(3.1 lb/ft
3
 (pcf)) aluminum honeycomb.  Face-sheets 
were fabricated by automated tape laying 153 mm wide unidirectional tape.  This work details 
analysis of the manufactured panels where face-sheet quality was characterized by optical 
microscopy, cured ply thickness measurements, acid digestion, and thermal analysis. 
 1.  INTRODUCTION 
PMC materials are increasingly utilized in large structures; driving the maturation of advanced 
material and processing technologies.
1
  Efforts from both industry and U.S. Government teams 
have pushed Out of Autoclave (OoA) technology and application forward over the past several 
years; leading to manufacturing demonstrations including the Boeing Wing Spar
2
 and the 
Advanced Composite Cargo Aircraft.
3
 
 
Within NASA, composite structures for heavy-lift launch vehicles are projected to be the largest 
composite structures fabricated for aerospace. Specifically, the interstage of the Ares V Cargo 
Launch Vehicle was planned to be 10 m in diameter and 12 meters in height.
4
  The size 
requirements of these structures have placed considerable emphasis on processing out of the  
 
___________________________________________ 
*
This paper is declared a work of the U.S. Government and is not subject to copyright protection 
in the United States. 
https://ntrs.nasa.gov/search.jsp?R=20150007509 2019-08-31T10:50:45+00:00Z
autoclave.  Manufacturing autoclave quality structures without autoclave pressure places added 
criticality to void removal.  The generation of voids is dependent on a number of factors
5
 
including prepreg chemistry, tack, lay-up, and other considerations.  This paper describes a 
manufacturing feasibility study of 1/16
th
 arc segments of the 10 m Ares V interstage. Two 
material systems were selected; Cytec IM7/977-3 autoclave cure epoxy/ carbon fiber prepreg and 
Cytec T40-800B/5320-1 out of autoclave cure epoxy/ carbon fiber prepreg. This study details 
characterization of sandwich panels prepared from these materials and compares face-sheet 
consolidation in the autoclave and non-autoclave processed materials.  Variation in tool-side and 
bag-side laminate quality is also noted.  The data collected in this paper was used for structural 
analysis and modeling in preparation for larger, 1/6
th
 segment, panel manufacture.  Coupon test 
data on selected panels showed high strength values, indicative of good quality panel 
manufacturing in both the autoclave and out of autoclave systems.
6
   
 
2.  EXPERIMENTAL 
2.1  Panel Fabrication 
The composite tooling was built by Janicki Industries in Sedro-Woolley, WA, using a 
T300/Epoxy substructure with T300/Polyimide topcoat. Tool dimensions are approximately 2.5 
m x 3 m with a curvature following a 5 m  radius concave tool. 
 
IM7/977-3 was selected for autoclave processing and was purchased from Cytec Engineered 
Materials as 145 gsm, 153 mm” wide, uni-tape prepreg.  FM300M 0.08 psf film adhesive, was 
used to co-cure the aluminum core with the IM7/977-3 face-sheet.   
 
T40-800B/5320-1 was also purchased from Cytec Engineered Materials as 145 gsm, 153 mm 
uni-tape prepreg and was used to evaluate the manufacturing feasibility of the panel section via a 
non-autoclave process. FM309-1 M 0.08 psf, film adhesive was used in the vacuum only panel 
fabrication. 
 
Expanded, formed, and perforated aluminum honeycomb core (49.7 kg/m
3
) was purchased from 
Alcore.  A description of panel configuration and core thickness is given in Table 1.  
 
Panels were fabricated at Hitco Carbon Composites, Inc, Gardena, CA, using an Automated 
Tape Laying (ATL) machine (Charger) built by MAG, as depicted in Figure 1. Six inch uni-tape 
was used to allow for fiber steering on the contoured tool.  
 
Figure 1: Automated manufacturing of contoured panel. 
Table 1: Panel Nomenclature and Description 
Panel  Prepreg  Core  Layup  
8000CMDP  IM7/977-3  25.4 mm  [45,90,-45,0]s  
MTP-6001 IM7/977-3  41.3 mm  [60,-60,0]s  
MTP-6003  IM7/977-3  28.6 mm  [60,-60,0]s  
8010CMDP  T40-800/5320-1  25.4 mm  [45,90,-45,0]s  
MTP-6010  T40-800/5320-1  28.6 mm [60,-60,0]s  
MTP-6000  IM7/977-3  28.6 mm [60,-60,0]s  
 
Buildups on the ends of the 8 ply panels consisted of a balanced and symmetrical layup 
intertwined with the original 8 plies for a total of 16 plies.  The buildups were approximately 178 
mm wide and tapered into the acreage.  
2.2  Face-sheet Characterization 
2.2.1 Core and Adhesive Removal  
Sections were removed from the edge of each manufactured panel for characterization of the 
composite skin, as shown in the schematic in Figure 2.  The tool and bag sides were noted.  The 
core was removed from each section and the face-sheets were sectioned for optical microscopy, 
acid digestion, and thermal analysis.  
 
  
2.2.2  Optical Microscopy  
Representative sections of the panel were polished for optical microscopy.  Specimens were 
polished and photographed using an optical microscope.  Thickness measurements were taken by 
a pixel counting method on both tool and bag side face-sheets.  Five thickness measurements 
were taken at each location and averaged.  Ply thicknesses were calculated by dividing the 
measured laminate thickness by the number of plies.   
2.2.3  Void Analysis   
The void volume and fiber content of each laminate panel was calculated following ASTM D 
3171-76, Standard Test Method for Constituent Content of Composite Materials, with six 
samples tested per material.   The matrix material was digested in hot sulfuric acid and hydrogen 
peroxide solutions and the remaining carbon fibers were filtered through a fine mesh screen.  The 
fibers were flushed with water followed by an acetone rinse.  The acetone was evaporated 
overnight in a fume hood and the fibers were then dried in an oven at 100 
o
C prior to weighing.    
2.2.4  Dynamic Mechanical Analysis 
DMA tests followed conditions specified in ASTM D7028-07, Standard Test Method for Glass 
Transition Temperature (DMA Tg) of Polymer Matrix Composites by Dynamic Mechanical 
Analysis.  The test included a 5 
o
C/min ramp from room temperature to 50 
o
C above Tg. The 
frequency was set at 1 Hz, per the ASTM specification and the amplitude set at 20m.  Test 
specimens were dried at 70 
o
C prior to analysis.  A single cantilever fixture was used for all 
DMA testing.   
3.  RESULTS AND DISCUSSION 
3.1 IM7/977-3   
Four panels were fabricated with IM7/977-3 prepreg and cured in an autoclave.  A representative 
panel section image is shown in Figure 3.  Considerable resin bleed-out was noted within the 
sections received for analysis; both along the core and soaked into the peel ply.  Some resin flow 
is not unusual for panels made with this material, as the resin viscosity drops during the initial 
stages of the cure cycle.
7 
 
                          
Figure 3: Resin flow along un-cut edge of IM7/977-3 panel. 
3.1.1 Void Analysis 
Optical microscopy images of IM7/977-3 face-sheet sections are shown in Figure 4, representing 
6 ply and 12 ply regions of panel MTP6000.  Voids are visible within the cross-sections, 
predominately between plies.  Typical dimpling between nodes is called out in Figure 4a.  There 
was not a notable difference in quality between the bag (Figures 4a and 4b) and tool side 
(Figures 4c and 4d) with respect to void content.     
 
a.  b.  
Resin Flow 
Void 
Dimpling 
Peel Ply  
c.  d.  
Figures 4a – 4d: Photomicrographs representing bag (4a and 4b) and tool (4c and 4d) side 
sections of an IM7/977-3 panel. 
 
Several images of the panel cross sections showed areas of face-sheet delamination and 
considerable void content, Figures 5a and 5b.  However, IR thermography of the entire panel 
indicated no significant flaws; and the higher void content may be related to the edge section of 
the larger panel where these pieces were taken.   
 
a.  b.  
Figures 5a – 5b: Photomicrographs show voids within an IM7/977-3 panel. 
 
Acid digestion of these sections resulted in a measured void content below 2%, with no 
significant difference between the tool and bag side of the panel.  Acid digestion results are 
shown in Table 2 for the IM7/977-3 panels.  
 
Table 2: Acid digestion results of the IM7/977-3 skins. 
Panel Face-sheet 
Density (g/cm
3
) 
Average Void 
Content (%) 
Average 
Fiber Vol. 
(%) 
Average Resin 
Wt. (%) 
8000CMDP_Bag 1.59 1.8 65.5 27.0 
8000CMDP_Tool 1.60 1.1 65.2 28.2 
MTP-6001_Bag 1.61 1.0 64.5 28.5 
MTP-6001_Tool 1.61 0.9 64.6 28.5 
MTP-6003_ Bag 1.57 0.7 65.8 27.6 
MTP-6003_Tool 1.58 0.9 65.6 27.6 
MTP-6000_Bag 1.60 1.0 64.4 28.7 
MTP-6000_Tool 1.60 0.9 64.2 28.8 
 
The acid digestion data calls out a higher fiber volume than the expected 60 vol.% and a lower 
resin weight content than anticipated.   
 
The significant visible resin bleed-out shown in Figure 3, and the low resin content reported by 
acid digestion, prompted repeat measurements based on samples taken from within the interior of 
panel MTP-6000.  The resin content of those sections by acid digestion was 28.5 wt. %; 
comparable to that at the edge.  Average fiber volume of the interior samples was 64.0 vol.%.  
3.1.2  Cured Ply Thickness (CPT) 
The manufacturer supplied the average ply thickness as 0.131 mm (5.14 mil).  Cured ply 
thickness (CPT) was measured by optical microscopy and was lower than anticipated; likely due 
to the resin bleed-out and measured low resin content.    
 
Trends in the CPT measurements, Figure 6, were consistent between the four IM7/977-3 panels; 
with the bag-side (BS) skins approximately 2% thinner than the tool-side (TS).  Overall, the 
average face-sheet thickness measured 4.5% thinner than the theoretical CPT.  The range in skin 
CPT varied from 1% to7% lower than theoretical.   
 
  
 
Figure 6:  Average ply thickness for the IM7/977-3 panels. 
8000C 
MDP 
MTP-6001 MTP-6003 MTP-6000 
BS Facesheet 0.125 0.124 0.124 0.122 
TS Facsheet 0.129 0.126 0.126 0.122 
Theoretical 0.131 0.131 0.131 0.131 
0 
0.02 
0.04 
0.06 
0.08 
0.1 
0.12 
0.14 
A
v
er
a
g
e 
P
ly
 T
h
ic
k
n
es
s 
(m
m
) 
IM7/977-3 Average Ply Thicknesses 
BS Facesheet 
TS Facsheet 
Theoretical 
3.1.3  DMA 
The IM7/977-3 face-sheet Tg’s are listed in Table 3.  Tg was determined by the drop in storage 
modulus from a DMA curve. 
 
Table 3:  Tg as determined by DMA 
Panel # Tg (Bag-side)  
(
o
C) 
Tg  (Tool-side) 
 (
o
C) 
8000CMDP 166 179 
MTP6001 173 173 
MTP6003 175 172 
MTP6000 195 (6 ply region) 
  192 (12 ply region) 
196 (6 ply region) 
  207 (12 ply region) 
 
The Tg Cytec lists for the IM7/977-3 neat resin is 178 
o
C.  However, past work with this prepreg 
system has lead to a Tg just over 200 
o
C.
4
  Representative DMA curves are shown in Figure 7.   
 
 
Figure 7:  DMA curves of IM7/977-3 coupons 
 
  
3.2 T40-800B/5320-1 
Two panels were manufactured with T40-800B/5320-1 OoA cure prepreg tape.  The fabricated 
panels did not exhibit the same level of resin bleed-out as was observed in the IM7/977-3 panels.   
3.2.1Void Analysis 
The results of the out of autoclave panel were very similar to those of IM7/977-3.  Optical 
microscopy images showed voids and delamination on both the tool side and bag side of the 
panel.   
 
1000 
10000 
100000 
100 125 150 175 200 225 250 275 300 
S
to
ra
g
e 
M
o
d
u
lu
s 
(M
P
a
) 
Temperature (oC) 
8000CMDP_ 8 ply 
MTP6001 and 
MTP6003_ 6 ply 
Average fiber volume, resin content, and void content by acid digestion are listed in Table 4.  
The void content was, in general, greater than that of the autoclave cured panels; however, void 
contents did not exceed 2%.  The fiber volume and resin content in the T40-800B/5320-1 panels 
was representative of manufacturer specifications, likely due to the lower resin flow visible 
during cure.  Optical photomicrographs are shown in Figures 8a – 8d. 
 
 
 
Table 4:  Acid digestion results of the T40-800B/5320-1 panel skins. 
Panel Face-sheet 
Density (g/cm
3
) 
Average Void 
Content (%) 
Average Fiber 
Volume (%) 
Average 
Resin Wt 
8010CMDP_Bag 1.61 1.0 62.0 31.2 
8010CMDP_Tool 1.59 1.8 62.0 30.6 
MTP-6010_Bag 1.60 1.8 60.7 31.6 
MTP-6010_Tool 1.60 1.5 60.9 31.6 
 
a.    b.  
c.  d.  
Figures 8a – 8d: Photomicrographs representing bag (8a and 8b) and tool (8c and 8d) side 
sections of and T40-800b/5320-1 panel. 
3.2.2 Cured Ply Thickness 
Theoretical cured ply thickness (CPT) of the OoA material was 0.136 mm (5.37 mil).  Results of 
optical CPT measurements are given in Figure 9. As with the IM7/977-3 panels, there was a 
tendency for the bag-side skin to be thinner than the tool side skin.  The MTP6010 panel (6 ply) 
face-sheet essentially matched the theoretical CPT.  The 8 ply, 8010CMDP, was almost 10% 
below theoretical CPT on the bag-side, and 5% below CPT on the tool side.  This variation may 
be due to the use of a rigid caul sheet in the bagging sequence for 8010CMDP.  
 
Figure 9: Average ply thickness for the T40-800B/977-3 panels 
 
3.2.3 DMA 
The T40-800B/5320-1 face-sheet Tg’s are listed in Table 5.  Tg was determined by the drop in 
storage modulus from a DMA curve. 
 
Table 5: Tg for T40-800b panels 
Panel # Tg (Bag-side)  
(
o
C) 
Tg  (Tool-side) 
 (
o
C) 
8010CMDP 187 187 
MTP6010 188 189 
 
The Tg measured in this study was on the low end of what would be considered an acceptable Tg 
for this material. 
 
CONCLUSIONS 
As part of a larger manufacturing study, comparison of sandwich panel face-sheets, prepared 
using autoclave cured IM7/977-3 and vacuum bag only processed T40-800b/5320-1, were made 
8010C MDP MTP-8001 
BS Facesheet 0.123 0.135 
TS Facsheet 0.129 0.135 
Theoretical 0.136 0.136 
0 
0.02 
0.04 
0.06 
0.08 
0.1 
0.12 
0.14 
0.16 
A
v
er
a
g
e 
P
ly
  
T
h
ic
k
n
es
s 
(m
m
) 
T40-800B/5320-1 Average Ply Thickness 
BS Facesheet 
TS Facsheet 
Theoretical 
and included void content, CPT measurement, and thermal analysis.  In general, the measured 
CPT ranged from 3% - 5% below theoretical value.  CPT below theoretical values was 
consistently observed in the IM7/977-3 panels and attributed to resin bleed-out during cure.  This 
also led to a greater than anticipated fiber volume, and reduced resin content.  This was observed 
in samples taken from both the panel edge and mid-section. 
While some degree of porosity was observed on all panels, the vacuum only panel resulted in a 
generally higher void content.  There was little difference noted throughout the analysis between 
the tool-side and bag-side skin quality.  
 
REFERENCES 
1. Krzeminski M., Ponsaud P., Coqueret, X.,Defoort, B., Larnac G,Avila R. “Out-of-Autoclave 
Technologies for Competitive High Performance Composites”, SAMPE 2011, Long Beach, 
CA. May 2011. 
2. http://www.compositesworld.com/articles/out-of-autoclave-prepregs-hype-or-revolution 
http://www.sciencedirect.com/science/article/pii/S1359835X11001151 
3. http://www.compositesworld.com/articles/2011-high-performance-resins-highlights 
4. Sutter J. K., Kenner W. S., Pelham L., Miller S. G., Polis D. L., Nailadi C., Hou T. H., Guade 
D. J., Lerch B. D., Lort R. D., Zimmerman T. J., Walker J., Fikes J., and Bowman C., 
“Comparison of Autoclave and Out-of-Autoclave Composites for Heavy Lift Launch 
Vehicles,” Proceedings of SAMPE Fall Technical Conference 2010, Salt Lake City, Utah 
October 11-14, 2010. 
5.  Farhang L., and Fernlund G. “Void Evolution and Gas Transport During Cure In Out- Of-
Autoclave Prepreg Laminates”, SAMPE 2011, Long Beach, CA, May 2011.  
6. Kellas S., Lerch B., and Wilmoth, N., “Mechanical Characterization of In- and Out-of-
Autoclave Cured Composite Panels for Large Launch Vehicles”, SAMPE 2012, Baltimore, 
MD., May 2012. 
7. Miller S.G., Hou T.-H., Sutter J.K., Scheiman D.A., Martin R.E., Maryanski M., Schlea M., 
Gardner J.M., and Schiferl Z.R., “Out-Life Characteristics of IM7/977-3 Composites”, 
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Face-Sheet Quality Analysis and Thermo-Physical Property Characterization of OOA and Autoclave Panels

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