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Compressive strength of coated rigid-rod polymer fibres

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Abstract

One limitation to the use of high-strength/high-modulus rigid-rod polymer fibres like poly-(p-phenylene benzobisthiazole) (PBZT) and poly-(p-phenylene benzobisoxazole) (PBZO) in composite structures is their low compressive strength. Various theories have been developed to predict compressive strength of rigid-rod fibres. In this study the critical buckling stress for rigid-rod fibres with stiff external coatings has been theoretically modelled assuming that the failure mode in compression is the microbuckling of the fibrils in shear. Our model predicts that significant improvement in fibre compressive strength will occur only when relatively thick coatings, with thickness to diameter (t/D) ratios in excess of > 0.05, are used. Experimentally measured compressive strength of aluminium coated PBZT fibres shows values in good agreement to the theory at t/D ratios of 0.006 and below. Factors related to the selection of suitable coating materials and problems associated with establishing coating performance are identified.

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Abbreviations

P :

axial compressive load

P f :

axial compressive load on the fibre

P c :

axial compressive load on the coating

P icr :

critical buckling load in the ith case

σcr :

critical buckling stress

σco :

compressive strength of the uncoated fibre

σc :

compressive strength of the coated fibre

v(x):

lateral deflection of a buckled fibril or coating

V m :

amplitude of the lateral deflection in the mth mode

m :

number of half-sine waves in the deflection mode

x :

coordinate distance along axial direction

y :

coordinate distance along radial direction

θ:

coordinate distance along circumferential direction

l :

length of the buckling unit

N :

number of fibrils in the fibre

D :

fibre diameter

d :

fibril diameter

t :

coating thickness

I f :

moment of inertia of the fibril

A f :

cross-sectional area of the fibril

E f :

tensile modulus of the fibre

E c :

tensile modulus of the coating material

E :

tensile modulus of the coated fibre

G :

torsional shear modulus of the fibre

vc :

Poisson's ratio of the coating material

ρf :

density of the fibre

ρc :

density of the coating material

ρ:

density of the coated fibre

ΔU f :

strain-energy change in the fibre

ΔU c :

strain-energy change in the coating

ΔT f :

external work done on the fibre

ΔT c :

external work done on the coating

ξ:

d/D

η:

t/D

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Author notes

  1. U. Santhosh

    Present address: Research Applications Inc., 7026 Corporate Way, Suite 211, 45459, Centerville, OH, USA

Authors and Affiliations

  1. AdTech Systems Research Inc., 1342 North Fairfield Road, 45432, Dayton, OH, USA

    U. Santhosh

  2. Central Research and Development, E.I. DuPont De Nemours & Co. Inc., P.O. Box 80304, 19880, Wilmington, DE, USA

    K. E. Newman

  3. AFOSR/NC, Air Force Office of Scientific Research, 20332, Bolling Air Force Base, DC, USA

    C. Y. C. Lee

Authors
  1. U. Santhosh
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  2. K. E. Newman
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  3. C. Y. C. Lee
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Santhosh, U., Newman, K.E. & Lee, C.Y.C. Compressive strength of coated rigid-rod polymer fibres. JOURNAL OF MATERIALS SCIENCE 30, 1894–1901 (1995). https://doi.org/10.1007/BF00351628

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  • DOI: https://doi.org/10.1007/BF00351628

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