title: Effect of Griffith precracks on measurement of composite fracture toughness.
abstract: The objective of this study was to produce true Griffith-type cracks in composite specimens for measuring fracture toughness. A compact test specimen geometry, conforming to the ASTM standard (E-399-84) was chosen for the evaluation. Five methods of precracking were evaluated: 1) placing no precrack (notch in specimen left blunt); 2) placing a sharp notch with a Bard Parker blade under hand pressure; 3) placing a sharp notch with a Bard Parker blade under hand pressure, followed by stressing the sample at 60% of the failure load for 25 cycles; 4) forming a sharp notch by placing a razor blade in the sample during polymerization; and 5) placing a Griffith-type crack. Results indicate that the method of precracking a sample does have a significant effect on the measured value of the fracture toughness.
authors.affiliation: Department of Oral Health Practice, University of Kentucky College of Dentistry, Lexington.
authors.forename: R E
authors.initials: RE
authors.lastname: Kovarik
authors.forename: C W
authors.initials: CW
authors.lastname: Fairhurst
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry*; D003799:Dental Stress Analysis; D006244:Hardness; D008422:Materials Testing / Q000379:methods / Q000592:standards; D014520:Urethane / Q000737:chemistry*
chemical_list: D003188:Composite Resins; C056413:Occlusin; D014520:Urethane