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Research Papers

Consolidation-Driven Defect Generation in Thick Composite Parts

[+] Author and Article Information
J. P.-H. Belnoue

Bristol Composites Institute (ACCIS),
University of Bristol,
Queen's Building, University Walk,
Bristol BS8 1TR, UK
e-mail: jonathan.belnoue@bristol.ac.uk

O. J. Nixon-Pearson, A. J. Thompson, D. S. Ivanov, K. D. Potter, S. R. Hallett

Bristol Composites Institute (ACCIS),
University of Bristol,
Queen's Building, University Walk,
Bristol BS8 1TR, UK

1Corresponding author.

Manuscript received October 30, 2017; final manuscript received January 2, 2018; published online April 6, 2018. Assoc. Editor: Donggang Yao.

J. Manuf. Sci. Eng 140(7), 071006 (Apr 06, 2018) (15 pages) Paper No: MANU-17-1672; doi: 10.1115/1.4039555 History: Received October 30, 2017; Revised January 02, 2018

Fiber waviness is one of the most significant defects that occurs in composites due to the severe knockdown in mechanical properties that it causes. This paper investigates the mechanisms for the generation of fiber path defects during processing of composites prepreg materials and proposes new predictive numerical models. A key focus of the work was on thick sections, where consolidation of the ply stack leads to out of plane ply movement. This deformation can either directly lead to fiber waviness or can cause excess fiber length in a ply that in turn leads to the formation of wrinkles. The novel predictive model, built on extensive characterization of prepregs in small-scale compaction tests, was implemented in the finite element software abaqus as a bespoke user-defined material. A number of industrially relevant case studies were investigated to demonstrate the formation of defects in typical component features. The validated numerical model was used to extend the understanding gained from manufacturing trials to isolate the influence of various material, geometric, and process parameters on defect formation.

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Figures

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Fig. 1

A schematic of the consolidation of prepreg stacks over curved tools: (a) unconstrained ends and interply slip during consolidation give rise to book-end effect and (b) constrained part ends lead to wrinkle formation

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Fig. 2

(a) IMA-M21 pipe sections post cure, (b) micrographs of a typical wrinkle for 4 mm-thick pipe, and (c) micrographs of a typical wrinkle for 6 mm-thick pipe

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Fig. 7

Comparison between a micrograph of the constrained 6-mm-thick sample and the FE model shows good agreement

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Fig. 3

Plot of the bending stiffness of an uncured ply of IMA-M21 in the fiber direction against temperature. The error bars are plot using the standard deviation.

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Fig. 4

Photographs representative of each tested L-bracket configurations

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Fig. 5

Micrograph showing the wrinkle of the 4 mm (a) and 6 mm (b) thick L-bracket under constrained conditions

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Fig. 6

The comparison between a micrograph of the constrained 4-mm-thick sample and the FE model shows excellent agreement. The model is even capable of capturing the in-plane wrinkling observed experimentally.

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Fig. 8

Outcome of the FE simulation of the autoclave curing of a 6-mm-thick C-section with unconstrained ends. The frictional constrains are responsible for wrinkle generation.

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Fig. 9

Influence of temperature on both resin viscosity and wrinkle severity. Resin viscosity measurements refer to those presented in Ref. [36].

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Fig. 10

Influence of the interply friction coefficient on wrinkle severity

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Fig. 11

Influence of uncured plies bending stiffness on wrinkle severity

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Fig. 12

The experimental setup for the manufacturing of the tapered sample

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Fig. 13

(a) Image of the double taper mold into the test machine after curing and (b) CAD model of the mold with a specimen inserted

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Fig. 14

Micrographs of the baseline specimen

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Fig. 15

Micrographs of the t2 + 10% specimen

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Fig. 16

Comparison of the average thickness measured in the (a) thick and (b) thin section of the samples with the model predictions for the three cases studied. The “Targeted” thickness is calculated using the number of plies in the layup and the nominal cured ply thickness as given by the manufacturer.

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Fig. 17

Comparison of the wrinkles observed on the micrographs of the samples with the model predictions

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Fig. 18

Model predictions for the sequence of events leading to the generation of wrinkles in the t2+5% demonstrator. The graph at the top left of the figure displays the displacement of the tool over time.

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Fig. 19

Outcome of the simulation of the autoclave processing of the t2+10%

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