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Design Innovation Paper

Additive Manufacturing of Structural Cores and Washout Tooling for Autoclave Curing of Hybrid Composite Structures

[+] Author and Article Information
Daniel-Alexander Türk

Department of Mechanical and Process Engineering,
Product Development Group Zürich,
ETH Zurich,
Zurich 8092, Switzerland
e-mail: dturk@caltech.edu

Andreas Ebnöther, Mirko Meboldt

Department of Mechanical and Process Engineering,
Product Development Group Zürich,
ETH Zurich,
Zurich 8092, Switzerland

Markus Zogg

Inspire AG,
Technoparkstrasse 1,
Zürich 8005, Switzerland

1Corresponding author.

2Present address: Graduate Aerospace Laboratories, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125.

Manuscript received December 20, 2017; final manuscript received May 19, 2018; published online July 9, 2018. Assoc. Editor: Zhijian J. Pei.

J. Manuf. Sci. Eng 140(10), 105001 (Jul 09, 2018) (14 pages) Paper No: MANU-17-1796; doi: 10.1115/1.4040428 History: Received December 20, 2017; Revised May 19, 2018

This paper presents a study combining additive manufactured (AM) elements with carbon fiber-reinforced polymers (CFRP) for the autoclave curing of complex-shaped, lightweight structures. Two approaches were developed: First, structural cores were produced with AM, over-laminated with CFRP, and co-cured in the autoclave. Second, a functional hull is produced with AM, filled with a temperature- and pressure-resistant material, and over-laminated with CFRP. After curing, the filler-material is removed to obtain a hollow lightweight structure. The approaches were applied to hat stiffeners, which were modeled, fabricated, and tested in three-point bending. Results show weight savings by up to 5% compared to a foam core reference. Moreover, the AM element contributes to the mechanical performance of the hat stiffener, which is highlighted by an increase in the specific bending stiffness and the first failure load by up to 18% and 310%. Results indicate that the approaches are appropriate for composite structures with complex geometries.

Copyright © 2018 by ASME
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Figures

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Fig. 1

Schematic processing route for the manufacturing of a hybrid AM-FRP structure using a structural AM core that is over-laminated with FRP and cured

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Fig. 2

Schematic (a) and section view and (b) of telegraphing effect in co-cured honeycombs adapted from Ref. [34,35]

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Fig. 3

Additive manufactured honeycombs with integrated antitelegraphing structure and roof webs for enhanced bonding to the face sheets

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Fig. 4

State-of-the art facing–honeycomb interface using a bonding layer with a difficult filler inspection (a), additive design concept and (b) with horizontal bonding surface for co-cured interface and ideally better shear load introduction

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Fig. 5

Processing route for the manufacturing of a hybrid AM-FRP structure using a functional hull made with AM, and a temperature-resistant filler material

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Fig. 6

Design space (a) and reference hat stiffener consisting of a machined foam core and a CFRP prepreg layup (b)

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Fig. 7

Design concept for a CFRP hat-stiffener beam with AM honeycomb core

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Fig. 8

Relative material density in a longitudinal section of a sandwich core under three-point bending loading. Based on Ref. [38] using a penalty factor p = 1.

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Fig. 9

Design concept for a hat stiffener with CFRP and an AM core using structural lightweight elements

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Fig. 10

Design concept for a CFRP hat-stiffener beam with functional hull made by AM and a temporary filler material

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Fig. 11

Manufacturing impressions: first the honeycomb (a), truss (b), and salt (c) cores are produced with selective laser sintering. Then, CFRP layup is applied (d), the assembly is vacuum bagged (e) and cured in the autoclave (f).

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Fig. 12

Weight comparison

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Fig. 13

Process (a) and three-point bending (b) simulation model

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Fig. 14

Numerical results for (a) reference, (b) honeycomb, (c) truss, and (d) salt core design for relevant load cases. Results show fairly homogenous distributed displacements during processing loading for (b) and (c) and significantly reduced laminate strains and Von Mises stresses for the three-point bending loading in AM core designs.

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Fig. 15

Three-point bending test setup at EMPA

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Fig. 16

Force–displacement diagram of representative samples

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Fig. 17

Section view of tested hat stiffeners. All specimens failed in or next to the load introduction area (encircled).

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Fig. 18

Comparison of failure load (a) and bending stiffness (b). Percentage values compared to the reference.

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Fig. 19

Light-microscope images showing the section view of the truss design (a), a close view of the interface between the laminate (b) and the HST DuraForm composite material and its porosity (c)

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Fig. 20

Comparison of specific stiffness and specific failure load. Percentages compare to reference design.

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