Page 138 - IJB-8-1

Compression Failure of Trabecular Tantalum Scaffolds
experimental specimens. The compressive strain during failure mechanism of the scaffolds were investigated by
FEA simulation was set within the range of elastic compression testing and FEA. The main conclusions are
deformation, comparable to the FEA of porous structures summarized as follows:
in other studies [52-55] . The results (Figure 15) revealed 1) The fabricated Ta scaffolds exhibited favorable pore
that the stress on the struts of trabecular Ta scaffolds structure characteristics for bone tissue ingrowth,
gradually decreases with the increase in porosity under which match well with those of the designed models.
the same compressive strain since the length of the struts Porosity has a significant effect on compressive
of trabecular Ta scaffolds is positively correlated with mechanical properties. As the porosity decreased
porosity. Stress on the struts gradually decreases from from 85% to 65%, the compressive yield strength
the conjunction to the middle [46] . The stress on the struts and elastic modulus increased from 11.9 MPa to
of the trabecular Ta scaffold with porosity of 65% is the 35.7 MPa and from 1.1 GPa to 3.0 GPa, respectively,
largest as a result of the shortest struts. Correspondingly, which lie in the range of those of the cancellous
the trabecular Ta scaffold with porosity of 85% exhibits bone.
the minimum stress distribution on the struts owing to 2) AM-fabricated trabecular Ta scaffolds showed
the longest struts. The stress of trabecular Ta scaffolds excellent ductility and mechanical reliability.
primarily concentrates on the conjunctions of struts They exhibited plastic failure resulting from
and vertical struts, where fractures occurred during the deformation and fracture of Ta struts during
uniaxial static compression testing. Similar FEA results compression testing. No macroscopic cracks were
can be found in other studies [56-59] . Consequently, FEA- found when the scaffolds were subjected to strain up
generated compressive stress distribution and material to 50%. Most microcracks occurred at conjunctions,
deformation are in good agreement with those found and the remaining ones appeared on the struts.
experimentally. However, it should be noted that the 3) FEA simulations revealed that the stress on the struts
stiffness and strength obtained by FEA simulation are of trabecular Ta scaffolds gradually decreased with
higher than those obtained in the compression tests. the increase in porosity under the same compressive
Some of the reasons for this fact could be the surface strain. The stress concentration primarily appeared
roughness or irregularities in the strut area randomly on the conjunctions of struts and vertical struts
produced during laser fusion process. The process under compressive loading. The FEA results are in
imperfections on the struts can reduce the mechanical good agreement with the experimental compressive
properties of porous Ta scaffolds and result in the stress results. Model optimization can be performed by
concentrations which provides opportunities for the introducing an optimized radius at the nodes to
collapse of the structures under compressive loads. In release the stress concentration and strengthen the
addition, the sharp angles at the conjunctions of struts deformation resistance of trabecular Ta scaffolds.
easily result in stress concentration during compression
testing. An effective solution for this problem is to Acknowledgments
introduce the optimized radius at the nodes. Li et al. The authors are grateful to the National Key
[46]
studied the influence of different optimized radius at the
nodes on the mechanical behavior and failure modes of Research and Development Program of China (grant
the diamond lattice structure. They concluded that the No. 2020YFC1107500) for financial support. Xia Jin
introduction of an optimized radius releases the stress would like to thank the Key Lab of Industrial Fluid Energy
concentration at the nodes and improves the mechanical Conservation and Pollution Control (Qingdao University of
reliability of porous structures. Moreover, the stress Technology), Ministry of Education, PR China. Xiaopeng
distribution gradually shifts from the node to the middle Li would like to acknowledge the financial support from
of the struts as the optimized radius increases. Therefore, Australian Research Council (ARC) Discovery Early
based on the results of FEA, model optimization of Career Researcher Award (DECRA) DE190101495.
trabecular Ta scaffolds can be performed to strengthen Conflict of interest
the vertical struts and make the connection of struts
smoother, resulting in a more uniform stress distribution The authors declare that they have no known competing
over the whole structure. financial interests or personal relationships that could
have appeared to influence the work reported in this paper.
5. Conclusions

Trabecular Ta scaffolds with porosities of 65%, 75%, and Author’s contributions
85% were designed and fabricated by LPBF-based AM, J.Y. wrote the manuscript, conceptualized the idea, and
and their porous architectures and microstructures were supervised this research. H.G. and D.Z. conducted the
characterized. The compressive mechanical behavior and experiments. X.J. and X.L. revised the manuscript and

124 International Journal of Bioprinting (2022)–Volume 8, Issue 1