Characterizing Brittle Fracture by Modeling Crack Deflection Angles from the Microstructure

Abstract

This study introduces a simple analytical model for fracture toughness to bridge the length scales from grain size to bulk thickness by assembling a virtual crack path from the angles recorded on an unfractured microstructure, which is a great challenge in fracture mechanics due to the high geometrical complexity. Good agreement is found between a crack deflection angle distribution measured from 5764 crack segments and the prediction by the model and the possible influence of residual stress is quasi quantitatively discussed. A total of 7.4% of the crack segments observed acted as crack bridges, while 7.3% was predicted by the model. A quantification of how high an angle needs to be to turn crack deflection into crack bridging is given. The ratio of fracture toughness from grain boundary to grain, G 1c(gb) /G 1c(g) , was measured indirectly from all samples to be between 0.3 and 0.35.

Densification, strengthening and toughening in hafnium carbide with the addition of silicon carbonitride

“…This phenomenon also tends to increase the critical energy for crack propagation and therefore offers a pinning effect at the crack front. 33,36 Thus, the mixed fracture mode may have made a considerable contribution to the higher toughness in the HfC-15 vol% SiCN system. Furthermore, the carbon segregation at triple junctions and the small amount of carbon detected at the grain boundary could alleviate some of the strain energy by facilitating grain boundary sliding as suggested in previous studies.…”

“…It can also be argued that a transgranular cracking always exhibits large crack deflection at the grain boundary if the crack mode is subsequently switched to intergranular. This phenomenon also tends to increase the critical energy for crack propagation and therefore offers a pinning effect at the crack front . Thus, the mixed fracture mode may have made a considerable contribution to the higher toughness in the HfC‐15 vol% SiCN system.…”

Toughened (Ti 0.2Zr 0.2Hf 0.2Nb 0.2Ta 0.2)B 2–SiC composites fabricated by one-step reactive sintering with a unique SiB 6 additive

“…The single transgranular cracking with a straight crack path cannot provide an effective toughening effect in HEBS-1900 composites. Similarly, the crack deflection by the intergranular crack in a homogeneous structure is not very effective way to lead to a crack bridge [54,55]. Some of the micropores were observed to remain in (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 ) B 2 /SiC and (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B 2 /(Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B 2 grain boundaries (Figs.…”

60 years of dislocations in ceramics: A conceptual framework for dislocation mechanics in ceramics

“…In consequence, a better understanding of the crack initiation 221,222 and conditions where stress concentrations can be outmanoeuvred by dislocations 36 needs to be established. As arbitrarily oriented grain boundaries dominate in polycrystals, studies on well-defined bi-crystal interface will not suffice but, instead, the whole complexity and statistics needs to be embraced 223 . While it is widely accepted that an unfulfilled Taylor criterion hinders larger degrees of deformation of polycrystals with randomly oriented grains, this limitation appears not to apply for smaller degrees of deformation as the limitation by necessity of nucleation is the more pressing problem.…”