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Unit Cell Orientation and Batch Variation Effect on the Mechanical Behaviour of Simple Cubic Ti-6Al-4V Lattice Made by Electron Beam Powder Bed Fusion

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Thesis(26.68 MB)

Date

2024

Authors

Supervisor

Chen, Zhan
Singamneni, Sarat

Item type

Thesis

Degree name

Master of Philosophy

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Publisher

Auckland University of Technology

Abstract

Electron beam powder bed fusion (EB-PBF) can make Ti-6Al-4V biomedical bone implants with porous lattice structures that are fully customised and patient-specific, potentially improving osseointegration and preventing stress shielding of Ti-6Al-4V bone implants. However, the mechanical strength of simple Ti-6Al-4V porous lattice structures with geometrical lattice parameters that are favourable for osseointegration and osteoconduction with consideration for the factors of the ease of powder removal, unit cell orientation and batch variation between builds for small lattices in an industrial production setting for EB-PBF have yet to be examined and understood. The mechanical strength of lattice with simple cubic unit cells of features desired for biomedical bone implants was investigated. This study examined the effect of unit cell orientation and batch variation on the mechanical strength of simple cubic Ti-6Al-4V lattice made with EB-PBF for quasi-static compressive and compressive-compressive fatigue loading. Four unit cell orientations of [001], [011], [111] and [√½√½1] made from six batches of the simple cubic lattice were tested for in the quasi-static compressive test and two unit cell orientations of [011] and [√½√½1] made from four batches of the simple cubic lattice were tested in the compressive-compressive fatigue test. Two net themes were used to print the specimens. Four batches were printed with net theme A and two with net theme B. The unit cell orientation affected the mechanical behaviour of the simple cubic Ti-6Al-4V lattice structure under compressive load. The [001] orientation still behaves with a stretching-dominated deformation, even with a small strut diameter and pore diameter that follows the osteoconductive requirement. The [001] orientation is significantly stronger than the [011], [111], and [√½√½1] orientations with bending-dominated deformation, which are in agreement with the quasi-static compressive simulation results. The [001] orientation has the highest compressive strength with σUCS -L of 2.0 to 2.5 times higher, σy-L of 1.8 to 2.1 times higher and EL of 1.6 to 2.1 times higher than other orientations. The [011] and [√½√½1] orientations were also found to affect the fatigue strength of the simple cubic Ti-6Al-4V lattice structure under cyclic compressive-compressive loading. The fatigue strength generally follows the compressive strength trend of the lattice structure. The batch variation factor affected the compressive strength behaviour of the simple cubic Ti-6Al-4V lattice structure. The specimens that were printed using both of the net themes A and B showed that they had been affected by the batch variation of either increasing the spread of the σUCS -L, σy-L and EL values or decreasing their mean values. The batch variation in net theme A were more significant in affecting the compressive strength of the printed lattice specimens. The batch variation factor also affected the fatigue strength of the simple cubic Ti-6Al-4V lattice structure with bending-dominated deformation under compressive-compressive cyclic loading. The fatigue strength generally follows the compressive strength of the lattice structure with the effect of the batch variation factor, but only in LCF regions. The fatigue strength of all the specimen batches seems to converge at 10.5 MPa past 10⁶ cycles to failure.

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http://hdl.handle.net/10292/17915

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