Simple and accurate fracture toughness testing methods for pyrolytic carbon/graphite composites used in heart‐valve prostheses

Abstract

The fracture toughness is a critical material property for the pyrolytic carbon materials used in mechanical heart-valve prostheses; however, making accurate toughness measurements has traditionally been problematic due to difficulties in fatigue precracking specimens. In this work, a simple, effective, and reliable precracking method is presented where a sharp precrack is "popped in" from a razor micronotch, which allows significant savings of time and materials relative to fatigue precracking methods. It is further shown that equivalent results may be obtained using razor micronotched specimens directly without precracking, provided the notch is sufficiently sharp. Indeed, mean toughness values of 1.46+/-0.13 and 1.35+/-0.09 MPa radicalm were obtained for the pyrolytic carbon-coated graphite materials, using precracked and razor micronotched specimens, respectively. The difference between these mean values proved to be statistically insignificant, and these values are in general agreement with published fracture toughness results obtained using fatigue precracked specimens.

Measurement of the toughness of bone: A tutorial with special reference to small animal studies

“…Slow-speed sawing is recommended through the thickness of the cortical wall in the case of a long bone, and for machining a circumferential through-wall notch. The latter can then be subsequently sharpened by "polishing" with a razor blade irrigated with 1 μm diamond suspension; this razor micronotching technique [35] results in a consistently sharp notch with a root radius of 10 μm. All measurements need to be performed in fluid that simulates in vivo conditions, e.g., Hanks' Balanced Salt Solution (HBSS), at 37 °C.…”

Fracture toughness testing: A discriminatory mechanical testing performance indicator for glass-ionomer restoratives?

“…Sharp notches with crack tip radii of less than 10 m have also been identified to produce comparable results to pre-cracked specimens for dental ceramics [52,53] and pyrolytic carbon/graphite composites [54] which further supports the use of sharp notched SEN bend specimens for K IC testing of brittle materials.…”

Fracture properties of nickel-based anodes for solid oxide fuel cells

“…Several approaches, therefore, have been proposed to precrack brittle materials for bending specimens 16,[22][23][24][25] and compact-tension (CT) or DCB specimens. 26,27 In the present work, two different ways to introduce a sharp crack at the root of the notch were tried. Following Kruzic et al 27 the initial notch was sawed manually with a steel band that had its edge fine ground in the presence of 1 m diamond slurry and simultaneously applying a pressure until a crack had "popped in".…”