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Research Papers

The Laser Interlaminar Reinforcement of Continuous Glass Fiber Composites

[+] Author and Article Information
Dakai Bian

Department of Mechanical Engineering,
Columbia University,
New York, NY 10025
e-mail: db2875@columbia.edu

Gen Satoh, Y. Lawrence Yao

Department of Mechanical Engineering,
Columbia University,
New York, NY 10025

1Corresponding author.

2Present address: Alcoa Technical Center, New Kensington, PA 15068.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received May 5, 2014; final manuscript received March 30, 2015; published online September 9, 2015. Assoc. Editor: Robert Gao.

J. Manuf. Sci. Eng 137(6), 061001 (Sep 09, 2015) (10 pages) Paper No: MANU-14-1271; doi: 10.1115/1.4030754 History: Received May 05, 2014

Interlaminar crack initiation and propagation are a major mode of failure in laminate fiber reinforced composites. A laser reinforcement process is developed to bond layers of glass fabric prior to the vacuum-assisted transfer molding of laminate composites. Glass fabric layers are bonded by fusing a dense glass bead to fibers within the laser focal volume, forming a 3D reinforcement architecture. Coupled heat transfer and viscous flow modeling is used to capture the temperature and morphology evolution of glass during the reinforcement process under experimentally observed conditions. Mode I double cantilever beam (DCB) testing is performed to quantify the effects of laser interlaminar reinforcements on composite delamination resistance. Postmortem high-resolution imaging of the fracture surface is used to characterize the toughening mechanism of the interlaminar reinforcements. Improved delamination resistance of laser reinforced composites derives from crack arrest and deflection mechanisms, showing a positive correlation to the reinforcement thickness.

Copyright © 2015 by ASME
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References

Figures

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Fig. 1

(a) Sample schematic of a laser joined DCB specimen. (b) An image of a DCB test during displacement controlled loading. Synchronized capture of high-resolution DCB fracture images enables the calculation of fracture energy with high spatial resolution.

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Fig. 2

Interlaminar laser reinforcement process schematic showing (a) the irradiation of a stack of glass fabric resulting in the formation of a void in through the material with a dense ring of glass around the laser spot. (b) The through thickness laser reinforcement process employs a bead of dense glass fill to bond the glass melt, forming a dense reinforcement through the initial stack of glass fabrics.

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Fig. 6

Numerical output of the glass densification process without filler material at 0.2 and 2.4 s. The substrate is shown to form a void in the center of the laser focus with the maximum temperature at the base of the laser penetration depth.

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Fig. 7

Time-dependent melt morphology: temperature depth and diameter obtained from numerical simulation. The melt diameter and the depth are shown to follow the same trend as the experiments observed under optical microscopy.

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Fig. 5

Measurements of the of the melt pool morphology due to laser irradiation on a stack of glass fabrics as a function of time taken from optical microscopy imaging of the fabric after processing. Note that the diameter of the melt ring reaches a steady state and plateaus while the depth of laser penetration is observed to be approximately linear up to the maximum thickness tested.

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Fig. 4

Optical micrograph of the surface fiber morphology after laser irradiation of a single layer of plain woven fabric. A dense ring of glass is formed during the heat-induced compaction of fibers within the fabric.

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Fig. 3

Temperature-dependent glass viscosity from VFT model and densification rates of soda lime and E-glass as obtained from global glass composition calculations [19]

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Fig. 8

Optical micrograph of a through thickness reinforcement formed through four layers of glass fabric using a dense filler glass. Note that the center of the reinforcement is fully dense with little to no porosity, as observed from the greater transparency than the surrounding fabric.

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Fig. 9

Cross section optical micrograph taken of a four layer through thickness joint cross section. Note that the joint is mostly dense with little to no porosity throughout its thickness. The soda lime fill glass is observable in optical images from the contrasting index of refraction from the E-glass fiber melt.

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Fig. 10

Numerical simulation snap shots of fill induced joining at 0.2 and 2.0 s showing the time-dependent evolution of the melt morphology during laser fusion joining. Void formation in the substrate is observed to be suppressed by the addition of the fill material. The temperature and morphology of the joint are otherwise shown to be unchanged from the nonfill simulation.

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Fig. 11

Time-dependent reinforcement morphology output from the numerical simulation, plotting temperature depth and diameter as a function of time. The linear trend of laser penetration observed is consistent with the morphology of the nonjoined simulation.

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Fig. 12

DCB load versus cross head extension output from the Instron output showing higher loading at each characteristic stop in the discontinuous crack propagation corresponding to the reinforcement locations within the sample

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Fig. 13

DCB fracture energy showing significantly higher fracture energy at reinforcement locations due to the increase in load as observed in the load versus extension output. Greater fracture energy is achieved by crack arrest, thereby increasing the load and bending energy required for the crack to propagate around the reinforcement.

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Fig. 14

Compiled data of the average delamination resistance as a function of the number of fabric layers through which the reinforcement is bonded. Note that the average fracture energy follows an approximately linear trend with the joint thickness due to the higher maximum load and peak fracture energies exhibited at the joint locations. Eight samples were tested at each condition. Error bars signify the standard deviation between tests.

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Fig. 15

SEM images of the delamination fracture surface between two layers of plain woven glass fabric composite. The crack front is observed to neatly propagate along the surface of the lamina between fabric layers, choosing the path of least resistance.

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Fig. 16

SEM images of the fracture surfaces around a laser reinforced section showing significant fiber fracture and crack branching behavior due to crack arrest and deflection at joints. The (a) positive and (b) negative imprint of a reinforcement remains on the surface of the DCB sample after the crack has propagated around it. Note that the depth of the fracture surface in the fabric material corresponds to half of the reinforcement thickness. Multiple layers of fabric are exposed on the fracture surface.

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Fig. 17

SEM image of fiber fracture surfaces around a single reinforcement. Fibers from multiple layers are observed from the cross-ply orientations of the fracture surfaces.

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