The measured porosity values was calculated as described in section
2.2.1. Star and cross based specimens had the highest porosity values,
while the trabecular structures had the lowest porosity.The variation in
porosity is related to the thickness variation in the struts oriented in
different directions. This clearly indicates the effect of strut
orientation on the overall porosity of the investigated structures. The
thickness variation in struts with different orientations are explained
below.
The strut thickness was measured as described in the section 2.2.2. The
average strut thickness is as shown in Fig.4a. The horizontal struts
have the lowest thickness (~370 µm) while random
structures have the highest measured thickness (~600
µm). The probability distribution curve shown in Fig.4b displayed a
normal distribution. During the printing process, the laser penetrates
into a layer below to induce perfect fusion of metal. But in the case of
horizontal struts, due to absence of support, the laser also melts the
powder from a layer below the first layer. This induces irregularity and
sagging in the struts. Due to this, the thickness of horizontal struts
varied from 280 μm to 450 μm. However, when comparing vertical and
oblique struts, the average thickness is close to each other, however
the distribution indicates that the vertical struts were uniform when
compared to oblique struts. The presence of complete support in vertical
struts layer during the melting process made the strut uniform.
Irregular struts had a similar distribution compared to oblique struts
but with a shift in the average thickness by 20 μm. Random struts in
trabecular specimens are thicker due to overlapping of struts,
especially at the junctions which reduce the porosity of the samples.