K Ic measurements have been a difficult means to compare materials for a type of fracture toughness related to the material modulus and fracture energy during crack propagation through numerous empirical formulas and standards developed from practice. Also, several fracture toughness mechanisms are discussed especially for fiber-reinforced composites.ġ.1 Problems with K Ic Test Methods and Numerical Answer Further, bulk K Ic accurate experimental values are compared with empirical test results found in literature. Results provided a new correction factor and regression analyses between several numerical integration fracture toughness test methods to support K Ic results. Polymer matrix discontinuous quartz fiber-reinforced composites to accentuate toughness differences were prepared for flexural mechanical testing comprising of 3 mm fibers at different volume percentages from 0-54.0 vol% and at 28.2 vol% with different fiber lengths from 0.0-6.0 mm. Therefore, K Ic is derived from the classical Griffith Crack Theory to include S Ic as a more accurate term for strain energy release rate (□ Ic), along with crack surface energy (γ), crack length (a), modulus (E), applied stress (σ), Y, crack-tip plastic zone defect region (r p) and yield strength (σ ys) that can all be determined from load and deflection data. However, the large body of previous K Ic experimental test results found in the literature offer the opportunity for continued meta analysis with other more practical and accurate fracture toughness results using energy methods and numerical integration. Now that fracture toughness can be calculated accurately by numerical integration from the load/deflection curve as resilience, work of fracture (WOF) and strain energy release (S Ic), K Ic appears to be unnecessary. In fact, over 30 years ago a National Academy of Sciences advisory board stated that empirical K Ic testing was of serious concern and further requested that an accurate bulk fracture toughness method be found. However, artificial man-made cracks several orders of magnitude longer and wider than natural flaws have required a correction factor term (Y) that can be up to about 3 times the recorded experimental value. Critical stress intensity factor (K Ic) has been an approximation for fracture toughness using only load-cell measurements.
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