Conclusion
The study focuses on the effect of various topologies on the compressive
quasi-static and fatigue properties of Ti6Al4V cellular materials.
Different structure topologies including trabecular based cellular
material and six different lattice based cellular materials were
experimentally studied. The following conclusion can be drawn from the
conducted study:
- Despite similar imposed target strut thickness and pore sizes, the
fabricated specimens showed light differences in the actual porosity.
Two structures possessed a porosity around 71-72%, the other five
showed porosity of 76-80%. It is known that porosity influences the
performances of cellular materials, however the large differences seen
later in the mechanical properties can be mainly attributed to the
differences in topology, rather than the small differences in
porosity.
- The difference between the monotonic and cyclic Young’s modulus
indicates that specimens undergo stabilization and local
plasticization during the initial loading of the structures.
- The Young’s modulus of the cellular materials has been found to be in
the range of 0.3-20 GPa, which is desirable for biomedical
applications.
- Cubic structures represented the highest stiffness and strength values
due to the presence of vertical struts. They have also shown excellent
fatigue properties experiencing infinite fatigue lives
(>107) for loads below
0.8σy due to the absence of bending in the struts.
However, the failure appeared suddenly on a whole cross-section of the
sample, much earlier with respect to the other structures
- The presence of irregularity (misalignment of nodes) has a significant
effect on the quasi-static and fatigue properties of topologies with
vertical struts. While the effect is quite minimal on cross shaped
structures. Trabecular structures which has a fewer number of struts
per node has displayed good quasi-static and fatigue properties due to
the presence of struts in random directions. The random orientation of
struts appears to induce a deceleration of crack propagation, avoiding
the collapse of many cells at once.
- The normalized S-N curves clearly show the different behavior of the
various studied structures. All the structures with irregular
configuration, and trabecular were been characterized by pure a
bending dominated behavior similar to cross shaped structures. The
fatigue behavior of star regular structures were exactly between the
stiffer, stretching dominated cubic regular structure and the other
bending dominated structures due to the presence of vertical struts as
well as oblique struts.
- The fatigue failure mechanism was found to be highly dependent on the
cell topology. The fatigue cracks have been found to initiate at the
surface irregularities such as voids, textures and dimples from the
LPBF process.