Page 300 - Engineered Interfaces in Fiber Reinforced Composites

Chapter 7. Improvement of transverse fracture toughness with interface control 28 1

Table 7.1
Comparison of toughening methods for fiber compositesa.

Toughening Composite Modifying Yo increase in % decrease in Test method
method system (Vr) material toughncss strength

Intermittent Boron-epoxy 80% PUV 280 8 Compact tension
bonding (0.25) coating
Boron-epoxy 100% PUV 500 2s Compact tension
(0.25) coating
Kevlar-epoxy 63% Estapol 40 nil Three-point
(0.06) coating bending
Kevlar-epoxy 100% Estapol 340 10-1s Charpy impact
(0.06) coating
Energy Carbon-epoxy Silicon rubber 140 nil4 Izod impact
absorption (0.6) coating
method
Glass-polyester SVF coating 1 so NA Izod impact
(0.06)
Glass-epoxy Latex PBA 600 5 Izod impact
(0.3) coating
Kevlar-epoxy PVAL coating IO0 nil Charpy impact
(0.5)
Delamination Carbon-epoxy Nylon films 270 25 Charpy impact
promoters (NA)
Boron4poxy Perforated Mylar 170 40 Compact tension
(0.2) films
Reduction of Carbon-epoxy Spiro monomer 50 15 Izod impact
shrinkage stress (0.4) additive
"After Kim and Mai (1991a).
Estapol, a blend of polyester/polyether resins; NA, not available; PBA, polybutyl acrylate; PUV,
polyurethane varnish; PVAL, polyvinylalcohol; SVF, silicone vacuum fluid; V, fiber volume fraction.

buckling, unnecessary interfacial debonding, matrix microcracking and warping of
asymmetric laminates consisting of cross-plies, all of which are detrimental to
mechanical/structural performance of the composite.
Further details of the above techniques to improve the transverse fracture
toughness of composites by controlled interfaces of various nature and modifying
materials are discussed in the following sections. The effectiveness of these
toughening methods on transverse fracture toughness and strength in relation to
the controls are summarized in Table 7.1.

7.2. Fiber coating and intermittent bonding concept - experimental studies

Although the criteria and functional requirements for the use of fiber coating are
different between PMCs, MMCs and CMCs, the major common aim of fiber
coatings discussed in this section is to improve the energy absorption characteristics