Authors’ response to “comments on ‘measurement of the microstructural fracture toughness of cortical bone using indentation fracture’”

Mullins, L.P.; Bruzzi, Mark; McHugh, Peter E.

doi:10.1016/j.jbiomech.2008.05.029

Cited by 5 publications

(2 citation statements)

References 21 publications

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“…Exaggerated toughness values have been reported from Vickers indentations, in some cases with barely visible or even no radial cracks at all . The use of Vickers indentation testing in bone tissue has aroused similar controversy . In that instance the application of any analysis based on elastic–plastic theory, indentation or otherwise, is problematic because bone exhibits pronounced time dependence and anisotropy in its deformation, important elements missing from the modeling leading to Eqs.…”

Section: Indentation Toughnessmentioning

confidence: 99%

The Compelling Case for Indentation as a Functional Exploratory and Characterization Tool

et al. 2015

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The utility of indentation testing for characterizing a wide range of mechanical properties of brittle materials is highlighted in light of recent articles questioning its validity, specifically in relation to the measurement of toughness. Contrary to assertion by some critics, indentation fracture theory is fundamentally founded in Griffith-Irwin fracture mechanics, based on model crack systems evolving within inhomogeneous but well-documented elastic and elastic-plastic contact stress fields. Notwithstanding some numerical uncertainty in associated stress intensity factor relations, the technique remains an unrivalled quick, convenient and economical means for comparative, site-specific toughness evaluation. Most importantly, indentation patterns are unique fingerprints of mechanical behavior and thereby afford a powerful functional tool for exploring the richness of material diversity. At the same time, it is cautioned that unconditional usage without due attention to the conformation of the indentation patterns can lead to overstated toughness values. Limitations of an alternative, more engineering approach to fracture evaluation, that of propagating a precrack through a "standard" machined specimen, are also outlined. Misconceptions in the critical literature concerning the fundamental nature of crack equilibrium and stability within contact and other inhomogeneous stress fields are discussed.

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Section: Indentation Toughnessmentioning

confidence: 99%

The Compelling Case for Indentation as a Functional Exploratory and Characterization Tool

et al. 2015

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“…, nacre42 , or more recently enamel123 , there remains a paucity of comprehensive K Ic values for many biological materials, which is due to the difficulty in performing reliable fracture mechanics experiments on irregularly shaped and small-scale biological structures123 .This challenge, while recognized, has still not been solved and there remains a lot of room to develop testing procedures at small scales, using sample preparation methods such as Focus Ion Beam (FIB)124 . In many cases, researchers rely on indentation fracture experiments71,76,77 .Although there are controversies125,126 regarding the absolute value of fracture toughness obtained with these experiments, the technique provides valuable and quantitative information, especially regarding initiation of fracture events which is our prime focus for wear and abrasion. The trends that emerge from the map are the following.…”

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confidence: 99%

Toughening, micromechnics, and multi-scale structural analyses of high-performance biotools

Amini¹

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Through millions of years of evolution, living organisms have refined a wide range of biomineralized tissues to meet the key functional requirements that are central to their survival. This includes load-bearing elements and protective armor that must display adequate stiffness and strength or sharp and cutting "biotools" that are key in predation and feeding. These mineralized tissues exhibit multi-scale hierarchical structures to meet their functional requirements, with a precise organization of their building blocks to optimize the combination of their mechanical properties including stiffness, strength, and fracture resistance. A distinctive model system that has gathered recent interest is the dactyl club from stomatopods (mantis shrimps). In comparison to many biomineralized composites that play a passive (defensive) mechanical role, dactyl clubs are dynamically active, hammerlike devices which are used by stomatopods to shatter the hard shells of their prey through repetitive impact loading. The mantis shrimp appendage is one of the most fascinating multifunctional biological material "biotools" in the animal kingdom, which the animal uses for its aggressive predatory strategies. Its hierarchical structure helps to strike and catch its prey 50 times faster than the blink of an eye, while exhibiting exceptional damage tolerance properties. In this research project, the multi-scale hierarchical structure and chemical composition of mantis shrimp appendages was comprehensively probed by various analytical techniques. It is demonstrated that dactyl impact surface consists of a finelytuned mineral gradient, with fluorapatite substituting amorphous apatite towards the outer surface. Raman spectroscopy measurements show that calcium sulphate, previously not reported in mechanically active biotools, is co-localized with fluorapatite. Ab initio computations suggest that fluorapatite/calcium sulphate interfaces provide binding stability and promote the disordered-to-ordered transition of fluorapatite. Hertzian contact partial loading-unloading indentation measurements revealed that the different layers of the club possess distinctive deformation and energy dissipation mechanisms. High-resolution electron microscopic studies show that sliding and rotation of fluorapatite crystallites leads to a quasi-plastic response in the outer, impact layer of Abstract ii the club. On the other hand, the presence of micro-channels along mineralized chitin fibrils in the inner layer of the club results in a distinct contact mechanics response. Under hydrated conditions, densification of these micro-channels under compressive load leads to a strain hardening behavior in the inner layer of the club. The work demonstrates that the macroscopic size of the club is below the critical size above which Hertizan cone fracture could be formed. Instead, the club's response remains in the quasi-plastic regime.

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Wear and abrasion resistance selection maps of biological materials

Amini

Miserez

2013

Acta Biomaterialia

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Authors’ response to “comments on ‘measurement of the microstructural fracture toughness of cortical bone using indentation fracture’”

Cited by 5 publications

References 21 publications

The Compelling Case for Indentation as a Functional Exploratory and Characterization Tool

The Compelling Case for Indentation as a Functional Exploratory and Characterization Tool

Toughening, micromechnics, and multi-scale structural analyses of high-performance biotools

Wear and abrasion resistance selection maps of biological materials

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