Aveneu Park, Starling, Australia

There layer bonding and mechanical behavior. He considered the

There are several studies in the literature about the
mechanical behaviors of the AM fabricated parts. As a recent work, Vicente et
al. 1
examined the effects of the two controllable parameters such as infill pattern
and infill density on strength of the 3D printed parts by using ABS material.
In their work, they used standard infill patterns like honeycomb, rectilinear,
etc. They also compared the behaviors of the parts which are produced by using
the 20%, 50% and 100% densities for each infill types on a loading condition.
They concluded that the dominant effect is due to the density variations.
According to their work, although the infill pattern changes the strength less
than 5%, the density changes the strength more than infill pattern. They came
up with the result that the rectilinear infill pattern with 100% density has
the highest tensile strength. Moreover, Johansson 2,
in his master thesis, argued that the most common failure scenario of a part
produced with FFF 3D printer is the layer bonding. He worked on the parameters
which affect the layer bonding and mechanical behavior. He considered the
software settings and the material as the fabrication parameters. He used
polyethylene terephthalate, ABS and PLA materials. He also considered the
printing orientation, temperature, flow rate, layer height and printing speed
as parameters. He concluded that the ABS has the highest tensile strength and
the major factors which affect the layer bonding are extruder temperature,
printing speed and layer height. He stated that the parts manufactured with an
extruder temperature of 250 oC are seven times stronger than the
ones fabricated with 190 oC. He further added that manufacturing the
part with 0.1 mm layer height increases the load capacity by 91% when compared
with the 0.4 mm layer height. The parts fabricated with a printing speed of 10
mm/sec has 95% better layer bonding performance than the parts with 130 mm/sec
printing speed. Lu et al. 27
worked on a method to reduce the material cost and weight while keeping the
parts as durable as possible. They proposed a hollowing optimization algorithm
based on honeycomb shaped cell structures. They used Voronoi patterns to
construct the interior structure. As a result of their work, they reached an
easily controllable, adaptive optimization methodology. They suggested their
method creates light-weight parts while keeping their durability under the same
loading conditions by using a density function defined by a stress analysis
result. Similarly, Stauben et al. 4
worked on improving the strength of the 3D printed parts using the results of a
stress analysis as a function of modification of interior structure. They
introduced a new implicit slicing methodology. The developed algorithm, which
uses data from FEA software as an input, constructs the tool-path for the
interior structure according to the stress values. In this work, the infill
patterns are not standard patterns. The constructed pattern can be considered
as a kind of random pattern which depends on the stress field. The stress field
data was examined by considering the mathematical curves to get the infill
pattern. As a result of their work, they reached an improvement on tensile
strength about 45%. They also manufactured a part whose elastic modulus was
increased by 57% when the developed algorithm was employed. Adams and Turner 28
worked on the improvement of the strength of the parts by eliminating voids and
gaps by modifying the interior structure. They tried to develop an implicit
slicing algorithm. They considered an infill structure constructed by
considering the finite element analysis results and mathematical curves
modifying the FEA results as mentioned in Stauben’s work. They considered the
same infill structures. However, they examine the effects of this infill
structures on gaps and voids. They used standard dog-bone shape specimens for
their tensile testing performance. They compared the test results of the
specimens with modified interior structures with the ones which have diagonal,
eggcrate, honeycomb and Hilbert shape lines as interior structure. They
obtained these interior structure types from the mathematical equations. They
concluded that the appropriate selection of the modified infill structures
allows the designer to modify the strength, stiffness, yielding behavior, and
the failure behavior of 3D printed parts. 
Tam and Muller 29
studied also on the structural performance of the parts manufactured by AM.
They considered the issue in two cases: 2D planar parts manufactured by using
traditional 3-axis 3D printers and 2.5D surface geometries manufactured by
using a multi-axis robot arm enabled manufacturing method. In 2D case, they
considered the topology and toolpath planning. They also studied the effects of
the printing orientation. They used FEA to obtain the stress lines which were
used to construct the infill structure of the parts. They tried to optimize the
interior structure by considering the volume/mass ratio. They concluded that
the method which uses stress lines resulting from the FEA produces more durable
parts. They also concluded that the strength of the part is higher where the
parts are oriented to preserve the continuity of the infill lines. In 2.5D
case, they used a multi-axis robot arm to preserve the continuity of the stress
lines result from the finite element analysis on curvatures. They concluded
that the parts manufactured by using the multi-axis robot arm shows higher
strength characteristics due to the continuous infill lines derived from stress
results. Baikerikar and Turner 30
studied on the effects of the different infill structures on the strengths of
the specimens. They also performed FEA and compared the results of analyses
with experimental tensile tests. They used standard dog-bone shaped specimens
with hexagonal and circular infill structures. They modified only the infill
structure of specified region on gage section. They constructed infill
structures by using the hexagonal and circular shapes. Besides, for comparison,
they construct specimens with fully filled interior. However, for specimens
with fully filled interior, the thickness of the specified region was decreased
to provide the same weight for comparison. They concluded that the FEA results
are not always reliable means of predicting FDM part behaviors.

In the following chapter, the method developed
throughout this thesis work is described.

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