Rate dependent fracture behavior of highly cross-linked epoxy resin

The fracture behavior of highly cross-linked epoxy resin under plane strain conditions for crack tip strain rates spanning over four orders of magnitude (10(-4) -10(-1) s(-1)) has been examined. The plane strain fracture toughness initially decreases with increasing crack tip strain rate (SMALL ELEMENT OFtip) and saturates at -0.8 MPa-m(-0.5) after is an element of(tip) similar to 0.02 s(-1) is attained. For all the fracture specimens, a fracture process zone (FPZ) forms ahead of the sharp pre-crack prior to catastrophic failure due to the intensified stresses ahead of the crack tip. This FPZ region consists of crazes that govern the micro mechanism of fracture and this was explicitly proved using in-situ testing in a scanning electron microscope. For low strain rates, crazing in the FPZ is expected to be dominated by chain disentanglements, with craze openings more than 200 nm, whereas, chain-scission is expected to dominate at higher strain rates, with lower craze openings of similar to 150 nm.

Automated summary

The fracture behavior of highly cross-linked epoxy resin under different crack tip strain rates was studied. The plane strain fracture toughness initially decreases with increasing strain rate and stabilizes after reaching a certain strain rate. A fracture process zone forms ahead of the sharp pre-crack in all specimens, and the micro mechanism of fracture is governed by crazes. In-situ testing in a scanning electron microscope confirmed the existence of crazes. The size of the craze openings varies with strain rate, with larger openings at lower strain rates and smaller openings at higher strain rates.