MODE-I, MODE-II, AND MIXED-MODE-I II INTERLAMINAR FRACTURE-TOUGHNESS OF GFRP INFLUENCED BY FIBER SURFACE-TREATMENT/

The interlaminar fracture behavior of unidirectional glass fiber reinf orced composites with fiber surface treatment has been investigated in modes I and II and for fired mode I to moae II ratio of 1.33. The dat a obtained from these tests have been analyzed by using different anal ytical approaches. The present investigation is focused on the influen ce of the glass fiber surface treatment on the interlaminar fracture t oughness of unidirectional laminates. Glass fibers with two different fiber surface treatments have been investigated. fiber surface treatme nt was carried our by using a polyethylene or silane coupling agent in combination with modifying agents. The glass fibers were embedded in the brittle epoxy matrix. Mode I, mode II, and mixed-mode I/II tests w ere performed in order to determine critical strain energy release rat es. Double cantilever beam (DCB), end-notched flexure (ENF), and mixed -mode flexure (MMF) specimens were used. For both types of fiber surfa ce treatment about the same values of mode I initiation fracture rough ness G(IC)(init) were obtained. It was observed that in mode I interla minar crack growth in the DCB test for the composite sized by polyethy lene, the crack propagation is accompanied by extensive fiber bridging . For both fiber surface treatments interlaminar fracture toughness in creases considerably with increasing of crack length. For the fiber su rface treatment with the silane coupling agent, the value of mode II i nitiation fracture toughness G(IC)(init) was about 2.5-times higher in comparison with that of a composite sized by polyethylene. For both t ypes of fiber surface treatments the mired-mode I/II test has shown a similar behavior to the mode I DCB test.