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Mechanical behavior of enamel rods under micro-compression
Publikationstyp
Journal Article
Date Issued
2016-06-23
Sprache
English
Author(s)
TORE-URI
Volume
63
Start Page
183
End Page
194
Citation
Journal of the Mechanical Behavior of Biomedical Materials (63): 183-194 (2016-10-01)
Publisher DOI
Scopus ID
Publisher
Elsevier
Exploring the structural strategies behind the optimized mechanical performance of hierarchical materials has been a focal point of extensive research over the past decades. Dental enamel is one such natural material, comprising a complicated hierarchical structure with a high level of mineral content. Bundles of hydroxyapatite nanofibers (level-1) Ø: 50 nm form enamel rods (level-2) Ø: 5 µm, which constitute bands (level-3) Ø: 50 µm. While a number of studies in the last decade using advanced fracture mechanical methods have revealed an increasing trend in the fracture toughness of enamel with each additional level of hierarchy, there is still no general agreement on how hierarchical structuring affects the stiffness and strength of enamel. In this study, we identified the stiffness and strength values of the isolated rods (level-2) via micro-compression. The rods were tested in three different orientations with respect to the loading direction: parallel, perpendicular and oblique. The highest stress level withstood before catastrophic fracture was observed to be ~1500 MPa in perpendicular orientation. In the oblique loading, the specimens failed by shearing and exhibited a damage-tolerant deformation behavior, which was attributed to the conjugation spots identified between the rods and interrod sheets. The elastic modulus was ~60 GPa on average and similar in all orientations. The isotropy in stiffness was attributed to the mineral contacts residing between rods. This was verified by an analytical model derived for level-1 and extended over higher hierarchical levels. The experimental results obtained at level-2 were comparable to the compressive strength and stiffness values reported for level-1 and bulk enamel in the literature. In general, our results suggest that hierarchy has only a minor influence on the compressive properties of enamel.
DDC Class
620: Ingenieurwissenschaften