Figure 5 . Horizontally printed beam used to create a 3D printed
functional structure. (a) 3D printing of the horizontal beam. (b) The deflection-sensing horizontal beam with DIW deposited
conductive path, scale bar = 10 mm. (c) Normalized resistance
response to 0.4, 0.8, 1.2, 1.6, and 2.0 mm deflections over time. (d) Average peak height versus deflection cycling condition.
The plotted resistance shows peaks of increasing amplitude in the sensor
signal corresponding to prescribed deformation. Indeed, the percent
increase from peak to trough of the signal versus deflection shown in Figure 5d indicates a positive trend wherein Δ peak increases
from 9.63% to 29.12% for δ = 0.4 and 0.8 mm, respectively. The trend
continues finally to 52.74% at δ = 2.0 mm; thereby demonstrating the
printed sensor’s potential to represent mechanical deformations in the
structure. Based on these trends, this printed sensor has the potential
to monitor deformations in a pre-existing structure in-situ, which could
be invaluable in structural health monitoring applications.
4. Conclusions
In this work, we developed a
versatile, reconfigurable DIW manufacturing method in tandem with a
two-stage hybrid ink designed to facilitate fabrication of
high-strength, self-supporting parts in unconventional printing spaces,
such as underneath the build surface or horizontally. Our two-stage
hybrid DIW ink combines a photopolymer and tough epoxy resin which is
capable of autonomous curing under ambient temperature conditions,
thereby creating complex, high-strength geometries without removal of
the structure from the printing surface. The photopolymer component can
be cured rapidly to enable layer-by-layer fabrication of complex
structures. The photocured resin also possesses adequate adhesion to
allow the fabrication of large volume structures on a diversity of
substrates including acrylic, wood, glass, aluminum, and concrete.
Moreover, the epoxy component cured after 72 hours in ambient,
room-temperature conditions with increased adhesion strengths. We
demonstrated the capabilities of the reconfigurable DIW extrusion nozzle
method coupled with our developed ink by fabricating complex structures
free of support structures in inverted and horizontal environments. In
addition, via the addition of DIW-deposited conductive paths, we created
a functional 3D printed structure capable of in-situ deformation
monitoring. This work has the potential to be used for applications such
as appending new parts to existing structures for increasing
functionality, repair, and structure health monitoring.