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Research Papers

In Situ Observations and Pressure Measurements for Autoclave Co-Cure of Honeycomb Core Sandwich Structures

[+] Author and Article Information
Mark Anders

M. C. Gill Composites Center,
Viterbi School of Engineering,
University of Southern California,
Los Angeles, CA 90089
e-mail: anders@usc.edu

Daniel Zebrine

M. C. Gill Composites Center,
Viterbi School of Engineering,
University of Southern California,
Los Angeles, CA 90089
e-mail: zebrine@usc.edu

Timotei Centea

M. C. Gill Composites Center,
Viterbi School of Engineering,
University of Southern California,
Los Angeles, CA 90089
e-mail: centea@usc.edu

Steven Nutt

M. C. Gill Composites Center,
Viterbi School of Engineering,
University of Southern California,
Los Angeles, CA 90089
e-mail: nutt@usc.edu

1Corresponding author.

Manuscript received July 19, 2017; final manuscript received July 26, 2017; published online September 13, 2017. Editor: Y. Lawrence Yao.

J. Manuf. Sci. Eng 139(11), 111012 (Sep 13, 2017) (9 pages) Paper No: MANU-17-1458; doi: 10.1115/1.4037432 History: Received July 19, 2017; Revised July 26, 2017

In this article, we describe an experimental method for investigating the autoclave co-cure of honeycomb core composite sandwich structures. The design and capabilities of a custom-built, lab-scale “in situ co-cure fixture” are presented, including procedures and representative results for three types of experiments. The first type of experiment involves measuring changes in gas pressure on either side of a prepreg laminate to determine the prepreg air permeability. The second type involves co-curing composite samples using regulated, constant pressures, to study material behaviors in controlled conditions. For the final type, “realistic” co-cure, samples are processed in conditions mimicking autoclave cure, where the gas pressure in the honeycomb core evolves naturally due to the competing effects of air evacuation and moisture desorption from the core cell walls. The in situ co-cure fixture contains temperature and pressure sensors, and derives its name from a glass window that enables direct visual observation of the skin/core bond-line during processing, shedding light on physical phenomena that are not observable in a traditional manufacturing setting. The experiments presented here are a first step within a larger research effort, whose long-term goal is to develop a physics-based process model for autoclave co-cure.

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References

Campbell, F. C. , 2003, Manufacturing Processes for Advanced Composites, Elsevier, London, Chap. 8.
Grove, S. M. , Popham, E. , and Miles, M. E. , 2006, “ An Investigation of the Skin/Core Bond in Honeycomb Sandwich Structures Using Statistical Experimentation Techniques,” Composites Part A, 37(5), pp. 804–812. [CrossRef]
Tavares, S. S. , Michaud, V. , and Månson, J.-A. E. , 2009, “ Through Thickness Air Permeability of Prepregs During Cure,” Composites Part A, 40(10), pp. 1587–1596. [CrossRef]
Tavares, S. S. , Michaud, V. , and Månson, J.-A. E. , 2010, “ Assessment of Semi-Impregnated Fabrics in Honeycomb Sandwich Structures,” Composites Part A, 41(1), pp. 8–15. [CrossRef]
Tavares, S. S. , Caillet-Bois, N. , Michaud, V. , and Månson, J.-A. E. , 2010, “ Non-Autoclave Processing of Honeycomb Sandwich Structures: Skin Through Thickness Air Permeability During Cure,” Composites Part A, 41(5), pp. 646–652. [CrossRef]
Tavares, S. S. , Caillet-Bois, N. , Michaud, V. , and Månson, J.-A. E. , 2010, “ Vacuum-Bag Processing of Sandwich Structures: Role of Honeycomb Pressure Level on Skin–Core Adhesion and Skin Quality,” Compos. Sci. Technol., 70(5), pp. 797–803. [CrossRef]
Tavares, S. S. , Roulin, Y. , Michaud, V. , and Månson, J.-A. E. , 2011, “ Hybrid Processing of Thick Skins for Honeycomb Sandwich Structures,” Compos. Sci. Technol., 71(2), pp. 183–189. [CrossRef]
Kratz, J. , and Hubert, P. , 2011, “ Processing Out-of-Autoclave Honeycomb Structures: Internal Core Pressure Measurements,” Composites Part A, 42(8), pp. 1060–1065. [CrossRef]
Kratz, J. , and Hubert, P. , 2013, “ Anisotropic Air Permeability in Out-of-Autoclave Prepregs: Effect on Honeycomb Panel Evacuation Prior to Cure,” Composites Part A, 49, pp. 179–191. [CrossRef]
Kratz, J. , and Hubert, P. , 2015, “ Vacuum Bag Only Co-Bonding Prepreg Skins to Aramid Honeycomb Core—Part I: Model and Material Properties for Core Pressure During Processing,” Composites Part A, 72, pp. 228–238. [CrossRef]
Kratz, J. , and Hubert, P. , 2015, “ Vacuum-Bag-Only Co-Bonding Prepreg Skins to Aramid Honeycomb Core—Part II: In Situ Core Pressure Response Using Embedded Sensors,” Composites Part A, 72, pp. 219–227. [CrossRef]
Centea, T. , Zebrine, D. , Anders, M. , Elkin, C. , and Nutt, S. R. , 2016, “ Manufacturing of Honeycomb Core Sandwich Structures: Film Adhesive Behavior Versus Cure Pressure and Temperature,” Composites and Advanced Materials Expo (CAMX), Anaheim, CA, Sept. 26–29, Paper No. 0096.
Van Ee, D. , and Poursartip, A. , 2009, NCAMP Hexply Material Properties Database for Use With COMPRO CCA and Raven, National Center for Advanced Materials Performance (NCAMP), Wichita, KS.

Figures

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Fig. 1

Section view from a computer-aided design model of the “in situ co-cure fixture”

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Fig. 2

Photographs of the in situ co-cure fixture. (a) Tool plate with core pocket visible, mounted to frame, without lid. (b) Honeycomb core in the pocket, with tape for the vacuum bag around the edges. (c) Tool plate with laminate placed over core.

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Fig. 3

Schematic of the optional side-view visualization configuration (not to scale)

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Fig. 4

Falling core pressure data for an air evacuation test with 5320-1 prepreg and ambient compaction pressure

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Fig. 5

Falling core pressure data split into individual subtests

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Fig. 6

Transverse permeability computed from an air evacuation test with 5320-1 prepreg and ambient compaction pressure

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Fig. 7

Falling core pressure data for an air evacuation test with 5320-1 prepreg and elevated compaction pressure

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Fig. 8

Transverse air permeability for 5320-1 prepreg at room temperature and two autoclave pressures

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Fig. 9

Measured temperatures (solid lines) and modeled material properties (dashed lines) for a controlled pressure experiment

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Fig. 10

In situ images of bond-line formation during controlled pressure tests. Left column: ambient core/bag pressure. Right column: full vacuum on the core and bag. Times t1t4 correspond to those from Fig. 9.

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Fig. 11

Data from a realistic co-cure test. Solid lines indicate measured data and dashed lines indicate modeled properties.

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Fig. 12

Images from a realistic co-cure test, taken at the times indicated on Fig. 11. This test included the “mirror cube” to capture images of fillets from head-on and side-view perspectives simultaneously.

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