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Research Papers

Multi-Axial Failure of Ceramic Matrix Composite Fiber Tows

[+] Author and Article Information
M. Blacklock

Department of Mechanical, Aerospace and Civil Engineering, University of Manchester, George Begg Building, Sackville Street, Manchester M13 9PL, UK

D. R. Hayhurst1

Department of Mechanical, Aerospace and Civil Engineering, University of Manchester, George Begg Building, Sackville Street, Manchester M13 9PL, UKd.r.hayhurst@manchester.ac.uk

1

Corresponding author.

J. Appl. Mech 78(3), 031017 (Feb 16, 2011) (10 pages) doi:10.1115/1.4002814 History: Received February 09, 2010; Revised August 18, 2010; Posted October 19, 2010; Published February 16, 2011; Online February 16, 2011

This paper considers the multi-axial stress-strain-failure response of two commercially woven ceramic matrix composites. The different failure mechanisms of uni-axially stressed tows and woven composites are addressed. A model is postulated in which the local transverse and shear stressing, arising from the weave, instantaneously deactivate wake debonding and fiber pullout and initiates dynamic fiber failure; hence, triggering catastrophic failure of the axially stressed region of the tow. The model is shown to predict experimentally measured stress-strain-failure results for the woven composites considered. Simple stress-strain-failure models are also proposed for tows subjected to axial-transverse and axial-shear loadings, but due to the lack of experimental data they have not been validated.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Prediction of woven unit cell behavior by Tang (6) for (a) eight-harness satin weave HITCO C/C (Fig. 2) and (b) plain weave DLR-XT C/C–SiC (Fig. 2)

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Figure 2

Schematic drawing of a unit cell tow arrangement for (a) eight-harness satin weave C/C HITCO material and (b) plain weave C/C–SiC DLR-XT material

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Figure 3

Schematic drawings of (a) a HITCO C/C tow and (b) a DLR-XT C/C–SiC tow

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Figure 4

Tensile stress in 0 deg layer due to high EL of 90 deg layer

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Figure 5

Schematic showing (a) global stress acting on a woven unit cell, (b) local stresses within the circled weave segment, and (c) schematic side section of a finite element model of a weave segment of a tow

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Figure 6

Stress-strain response for HITCO and DLR-XT unidirectional tows (Fig. 3)

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Figure 7

Magnification of the low strain region of the experimental uni-axial stress-strain curves for plain weave DLR-XT composite (Fig. 1) identifying when cracking of the SiC, εmcSiC, and amorphous carbon, εmcAm C, matrices takes place within transverse tows

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Figure 8

Transverse stress-strain curves for unidirectional tows of Nicalon-CAS, HITCO C/C, and DLR-XT C/C–SiC

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Figure 9

Shear stress-shear strain curves for a unidirectional tow of HITCO C/C

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Figure 10

(a) Schematic representation of the division of the composite tow into blocks of length equal to the matrix crack spacing, w; fibers are denoted by solid ellipses; and (b) representation of a single block

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Figure 11

Schematic diagram of a section of a fiber-matrix block of length w extracted from between adjacent matrix cracks. The interface is shown with (a) damage as a result of wake debonding and (b) further interfacial damage due to transverse loading.

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Figure 12

Schematic diagram for an axially loaded tow showing the influence of transverse stresses σ11,σ22 and shear stresses τ23,τ13,τ12 on the Weibull index, g, and on the average critical wake debonding shear stress, τc

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Figure 13

Schematic diagram showing the effect of the Weibull index, g, on the variation of normalized number of wake debonded blocks, N/NT, with composite strain, (ε33)∞

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Figure 14

Schematic diagram of (a) one-half of a representative volume element, half length w/2, showing matrix, fiber, and matrix crack, (b) average fiber stress σf, and (c) average matrix stress, σm. The solid line denotes the instant of wake debonding and the broken line shows stresses after partial propagation of the wake debonded crack.

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Figure 15

Schematic diagram of a representative volume element showing the doubling of the average fiber tensile stress at the wavefront, x, defined by the dark region, following reflection at the element centerline

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Figure 16

(a) Determination of εwd and (b) corresponding failure of woven HITCO C/C composite at εwd

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Figure 17

Predicted stress-strain curve for eight-harness satin weave HITCO C/C (Fig. 2)

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Figure 18

Predicted stress-strain curve for plain weave DLR-XT C/C–SiC (Fig. 2)

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