P J Tan, Department of Mechanical Engineering, University College London

Crack initiation and Fracture toughness of random Voronoi Honeycombs
When Feb 25, 2013
from 02:00 PM to 03:00 PM
Where LR8
Contact Name
Contact Phone 01865 283302
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The work presented here is motivated by a commonly held belief that architectural variations, in addition to a reduction in bone density, account for the age-related increase in fracture risk in trabecular bones, a class of materials known as cellular solids. However, there are significant uncertainties in the measurements of the mechanical properties of trabecular bones due, in part, to small sample sizes and to the large length scales of inhomogeneities. Since its 3D architecture is not easy to quantify, the fracture toughness of elastic-brittle Voronoi honeycombs is studied, instead, to gain insights into the influence of cell topological variations. Just like its 3D counterpart, 2D Voronoi honeycombs have isotropic overall mechanical properties and deform primarily by cell wall bending.
In this work, cell regularity in the Voronoi lattices is controlled using a global non-dimensional parameter that places a constraint on the minimum cell size and its distribution. Using a well-known scaling law, the resistance of the lattices to pure mode I and mode II loadings are evaluated and the effects of cell regularity on the global toughness of the lattices compared. The knock-down/enhancement in toughness due to imperfections is found to be different from existing studies that employed a node perturbation technique to introduce imperfections. Fracture loci for the lattices will be shown in combined mode I and II stress intensity factor (SIF) space and their critical effective SIF will be compared under different competing influences of cell-regularity, relative density and mode-mixity. The effects of T –stress (the non-singular stress parallel to the crack plane) upon the effective toughness of the lattices will also be presented. Fracture maps showing the location of initial cell wall fracture will be shown for lattices with different relative density under various mode-mixity conditions. The clustering of the wall fracture locations around the crack-tip in the random lattices is reminiscent of the plastic zone shapes in the linear elastic fracture mechanics of fully dense solids. 

Brief Biography:

PJ Tan obtained his first degree in Mechanical Engineering from the National University of Singapore and his PhD from UMIST/The University of Manchester. He worked as a post-doc in Manchester and Aberdeen before joining UCL as a lecturer in 2007. His research exploits theoretical, computational and experimental methods to characterise the structural and functional performance of engineering materials and structures. His research is multi-disciplinary and covers a number of fields including, but not exclusively, dynamic mechanical response and fracture of cellular solids; constitutive modeling of polycrystalline materials; designing protective functionality (against blast and impact loading) into lightweight sandwich systems; and, impact dynamics.