Continuous fibers

Continuous fibers ( eng. Continuous fibers ) - structural fibers, the length of which allows you to neglect the end effects when they are loaded in composites and use in continuous technological processes for producing composite products.

Description

The main geometric parameter of the fiber, which determines its effectiveness in the composite structure, is the dimensionless length ${\tilde {l}}$ ${\ displaystyle {\ tilde {l}}}$ equal to the ratio of the fiber length l to its diameter d or to the characteristic cross-sectional size for a fiber of non-circular cross section.

Critical dimensionless length ${\tilde {l}}^{*}$ ${\ displaystyle {\ tilde {l}} ^ {*}}$ - the fiber length l at which the fiber is not destroyed by tensile stresses generated in it through shear stresses at the interface of the fiber and the matrix

${\tilde {l}}^{*}\sim {\frac {{\tilde {\sigma }}_{f}^{*}}{{\tilde {\tau }}_{fm}^{*}}},$ ${\ displaystyle {\ tilde {l}} ^ {*} \ sim {\ frac {{\ tilde {\ sigma}} _ {f} ^ {*}} {{\ tilde {\ tau}} _ {fm} ^ {*}}},}$

Where ${\tilde {\sigma }}_{f}^{*}$ ${\ displaystyle {\ tilde {\ sigma}} _ {f} ^ {*}}$ - the tensile strength of the fiber, which generally depends on its length, and ${\tilde {\tau }}_{fm}^{*}$ ${\ displaystyle {\ tilde {\ tau}} _ {fm} ^ {*}}$ - shear strength of the interface. In the case of an ideal adhesive bond at the interface, the value is equal to the shear strength of the matrix. To neglect end effects, the condition must be met ${\tilde {l}}\gg {\tilde {l}}^{*}$ ${\ displaystyle {\ tilde {l}} \ gg {\ tilde {l}} ^ {*}}$ . For high strength fibers ( ${\tilde {\sigma }}_{f}^{*}$ ${\ displaystyle {\ tilde {\ sigma}} _ {f} ^ {*}}$ > 4000 MPa) in a polymer matrix ( ${\tilde {\tau }}_{fm}^{*}$ ${\ displaystyle {\ tilde {\ tau}} _ {fm} ^ {*}}$ <40MPa) ${\tilde {l}}^{*}$ ${\ displaystyle {\ tilde {l}} ^ {*}}$ ≈ 100. In composites with a metal matrix, the critical dimensionless fiber length can be an order of magnitude smaller.

Fiber continuity in the technological sense means the possibility of its use in continuous technological processes for producing composite products, such as winding, obtaining two- and three-dimensional fabrics, pultrusion, etc. In this case, the continuity criterion is the absolute length of the fiber on the spool, correlated with a specific technological process for the production of composite structural elements.

Literature

Concise Encyclopedia of Composite Materials / Ed. by A. Kelly. - Elsevier Science, 1994 .-- 378 p.
Handbook of Composites. V. 4 / Ed. by A. Kelly, ST Mileiko. - NorthHolland, Amsterdam, 1983.
Composite materials. Reference // Under the general ed. V.V. Vasiliev, Yu. M. Tarnopolsky. - M.: Mechanical Engineering, 1990. - 510 p.

Continuous fibers

Description

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