TY - JOUR
T1 - Anisotropic crack propagation and deformation in dentin observed by four-dimensional X-ray nano-computed tomography
AU - Lu, Xuekun
AU - Peña Fernández, Marta
AU - Bradley, Robert S.
AU - Rawson, Shelley D.
AU - O'Brien, Marie
AU - Hornberger, Benjamin
AU - Leibowitz, Marty
AU - Tozzi, Gianluca
AU - Withers, Philip J.
N1 - Funding Information:
The authors wish to thankfully acknowledge all the staff in Henry Moseley X-ray Imaging Facility based in the University of Manchester within The Royce Institute (GR EP/R00661X/1) where the X-ray CT work was carried out and the Zeiss Global Centre at the University of Portsmouth for image post-processing and DVC analysis. We appreciate the help from Mr. Brian Daber and Prof. David Watts for their contribution to sample preparation. We are also grateful to the Engineering and Physical Science Research Council (EPSRC) grants EP/I02249X, EP/F007906 and EP/F028431 for funding the Henry Moseley X-ray Imaging Facility. The PI is grateful for an Advanced Grant from the European Research Council (CORREL-CT Grant 695638). The first author is grateful for China Scholarship Council and University of Manchester support. The elephant tusk used in present study was obtained legally from UK customs as a seizure against smuggling.
Funding Information:
The authors wish to thankfully acknowledge all the staff in Henry Moseley X-ray Imaging Facility based in the University of Manchester within The Royce Institute ( GR EP/R00661X/1 ) where the X-ray CT work was carried out and the Zeiss Global Centre at the University of Portsmouth for image post-processing and DVC analysis. We appreciate the help from Mr. Brian Daber and Prof. David Watts for their contribution to sample preparation. We are also grateful to the Engineering and Physical Science Research Council (EPSRC) grants EP/I02249X , EP/F007906 and EP/F028431 for funding the Henry Moseley X-ray Imaging Facility. The PI is grateful for an Advanced Grant from the European Research Council (CORREL-CT Grant 695638 ). The first author is grateful for China Scholarship Council and University of Manchester support. The elephant tusk used in present study was obtained legally from UK customs as a seizure against smuggling.
Publisher Copyright:
© 2019 Acta Materialia Inc.
PY - 2019/9/15
Y1 - 2019/9/15
N2 - Understanding the cracking behaviour of biological composite materials is of practical importance. This paper presents the first study to track the interplay between crack initiation, microfracture and plastic deformation in three dimensions (3D) as a function of tubule and collagen fibril arrangement in elephant dentin using in situ X-ray nano-computed tomography (nano-CT). A nano-indenter with a conical tip has been used to incrementally indent three test-pieces oriented at 0°, 45° and 70° to the long axis of the tubules (i.e. radial to the tusk). For the 0° sample two significant cracks formed, one of which linked up with microcracks in the axial-radial plane of the tusk originating from the tubules and the other one occurred as a consequence of shear deformation at the tubules. The 70° test-piece was able to bear the greatest loads despite many small cracks forming around the indenter. These were diverted by the microstructure and did not propagate significantly. The 45° test-piece showed intermediate behaviour. In all cases strains obtained by digital volume correlation were well in excess of the yield strain (0.9%), indeed some plastic deformation could even be seen through bending of the tubules. The hoop strains around the conical indenter were anisotropic with the smallest strains correlating with the primary collagen orientation (axial to the tusk) and the largest strains aligned with the hoop direction of the tusk. Statement of Significance: This paper presents the first comprehensive study of the anisotropic nature of microfracture, crack propagation and deformation in elephant dentin using time-lapse X-ray nano-computed tomography. To unravel the interplay of collagen fibrils and local deformation, digital volume correlation (DVC) has been applied to map the local strain field while the crack initiation and propagation is tracked in real time. Our results highlight the intrinsic and extrinsic shielding mechanisms and correlate the crack growth behavior in nature to the service requirement of dentin to resist catastrophic fracture. This is of wide interest not just in terms of understanding dentin fracture but also can extend beyond dentin to other anisotropic structural composite biomaterials such as bone, antler and chitin.
AB - Understanding the cracking behaviour of biological composite materials is of practical importance. This paper presents the first study to track the interplay between crack initiation, microfracture and plastic deformation in three dimensions (3D) as a function of tubule and collagen fibril arrangement in elephant dentin using in situ X-ray nano-computed tomography (nano-CT). A nano-indenter with a conical tip has been used to incrementally indent three test-pieces oriented at 0°, 45° and 70° to the long axis of the tubules (i.e. radial to the tusk). For the 0° sample two significant cracks formed, one of which linked up with microcracks in the axial-radial plane of the tusk originating from the tubules and the other one occurred as a consequence of shear deformation at the tubules. The 70° test-piece was able to bear the greatest loads despite many small cracks forming around the indenter. These were diverted by the microstructure and did not propagate significantly. The 45° test-piece showed intermediate behaviour. In all cases strains obtained by digital volume correlation were well in excess of the yield strain (0.9%), indeed some plastic deformation could even be seen through bending of the tubules. The hoop strains around the conical indenter were anisotropic with the smallest strains correlating with the primary collagen orientation (axial to the tusk) and the largest strains aligned with the hoop direction of the tusk. Statement of Significance: This paper presents the first comprehensive study of the anisotropic nature of microfracture, crack propagation and deformation in elephant dentin using time-lapse X-ray nano-computed tomography. To unravel the interplay of collagen fibrils and local deformation, digital volume correlation (DVC) has been applied to map the local strain field while the crack initiation and propagation is tracked in real time. Our results highlight the intrinsic and extrinsic shielding mechanisms and correlate the crack growth behavior in nature to the service requirement of dentin to resist catastrophic fracture. This is of wide interest not just in terms of understanding dentin fracture but also can extend beyond dentin to other anisotropic structural composite biomaterials such as bone, antler and chitin.
KW - Crack shielding
KW - Digital image correlation (DIC)
KW - Indentation fracture
KW - Ivory
KW - Time-lapse imaging
UR - http://www.scopus.com/inward/record.url?scp=85068159877&partnerID=8YFLogxK
U2 - 10.1016/j.actbio.2019.06.042
DO - 10.1016/j.actbio.2019.06.042
M3 - Article
C2 - 31254684
AN - SCOPUS:85068159877
SN - 1742-7061
VL - 96
SP - 400
EP - 411
JO - Acta Biomaterialia
JF - Acta Biomaterialia
ER -