<p>Naturally-occurring biological
materials with stiff mineralized reinforcement embedded in a ductile matrix are
commonly known to achieve excellent balance between stiffness, strength and
ductility. Interestingly, nature offers a broad diversity of architectural
motifs, exemplify the multitude of ways in which exceptional mechanical
properties can be achieved. Such diversity is the source of bio-inspiration and
its translation to synthetic material systems. In particular, the helicoid and the
“brick and mortar” architectured materials are two key architectural motifs we
are going to study and to synthesize new bio-inspired materials. </p>
<p>Due to geometry mismatch(misorientation)
and incompatibilities of mechanical properties between fiber and matrix
materials, it is acknowledged that misoriented stiff fibers would rotate in
compliant matrix beneath uniaxial deformation. However, the role of fiber reorientation inside the flexible
matrix of helicoid composites on their mechanical behaviors have not yet been
extensively investigated. In the present project, fiber reorientation values
of single misoriented laminae, mono-balanced laminates and helicoid architectures
under uniaxial tensile are calculated and compared. In the present work, we introduce a Discontinuous Fiber
Helicoid (DFH) composite inspired by both the helicoid microstructure in the
cuticle of mantis shrimp and the nacreous architecture of the red abalone
shell. We employ 3D printed specimens, analytical models and finite
element models to analyze and quantify in-plane fiber reorientation in helicoid
architectures with different geometrical features. We also introduce additional architectures, i.e.,
single unidirectional lamina and mono-balanced architectures, for comparison
purposes. Compared with
associated mono-balanced architectures, helicoid architectures exhibit less
fiber reorientation values and lower values of strain stiffening. The
explanation for this difference is addressed in terms of the measured in-plane
deformation, due to uniaxial tensile of the laminae, correlated to lamina
misorientation with respect to the loading direction and lay-up sequence.</p>
<p>In addition to fiber, rod-like,
reinforced laminate, platelet reinforced composite materials, “brick and
mortar” architectures, are going to be discussed as well, since it can provide in-plane
isotropic behavior on elastic modulus that helicoid architecture can offer as
well, but with different geometries of reinforcement. Previous “brick and mortar” models available in the
literature have provided insightful information on how these structures promote
certain mechanisms that lead to significant improvement in toughness without
sacrificing strength. In this work, we present a detailed comparative analysis that
looks at the three-dimensional geometries of the platelet-like and rod-like
structures. However, most of these previous analyses have been focused on
two-dimensional representations. We 3D print and test rod-like and tablet-like
architectures and analyze the results employing a computational and analytical
micromechanical model under a dimensional analysis framework. In particular, we
focus on the stiffness, strength and toughness of the resulting structures. It
is revealed that besides volume fraction and aspect ratio of reinforcement, the
effective shear and tension area in the matrix governs the mechanical behavior
as well. In turns, this
leads to the conclusion that rod-like microstructures exhibit better
performance than tablet-like microstructures when the architecture is subjected
to uniaxial load. However, rod-like microstructures tend to be much weaker and
brittle in the transverse direction. On the other hand, tablet-like
architectures tend to be a much better choice for situations where biaxial load
is expected.</p>
<p>Through varying the geometry of
reinforcement and changing the orientation of reinforcement, different
architectural motifs can promote in-plane mechanical properties, such as strain
stiffening under uniaxial tensile, strength and toughness under biaxial tensile
loading. On the other hand, the various out-of-plane orientation of the
reinforcement leads to functionally graded effective indentation stiffness. The
external layer of nacre shell is composed of calcite prisms with graded orientation
from surface to interior. This orientation gradient leads to functionally
graded Young’s modulus, which is confirmed to have higher fracture resistance
than homogenous materials under mode I fracture loading act.</p>
<p>Similar as graded prism
orientation in calcite layer of nacre, the helicoid architecture found in
nature exhibits gradients on geometrical parameters as well. The pitch distance
of helicoid architecture is found to be functionally graded through the thickness
of biological materials, including the dactyl club of mantis shrimp and the
fish scale of coelacanth. This can be partially explained by the long-term evolution
and selection of living organisms to create high performance biological
materials from limited physical, chemical and geometrical elements. This
naturally “design” procedure can provide us a spectrum of design motifs on
architectural materials. </p>
<p>In the present work, linear
gradient on pitch distance of helicoid architectures, denoted by functionally
graded helicoid (FGH), is chose to be the initial pathway to understand the
functionality of graded pitch distance, associated with changing pitch angle.
Three-point bending on short beam and low-velocity impact tests are employed in
FEA to analyze the mechanical properties of composite materials simultaneously.
Both static(three-point bending) and dynamic(low-velocity impact) tests reveal
that FGH with pitch angle increasing from surface to interior can provide multiple
superior properties at the same time, such as peak load and toughness, while
the helicoid architectures with constant pitch angle can only provide one
competitive property at one time. Specifically, helicoid architectures with
smaller pitch angle, such as 15-degree, show higher values on toughness, but
less competitive peak load under static three-point bending loading condition,
while helicoid architectures with middle pitch angle, larger than or equal to
22.5-degree and smaller than 45-degree, exhibit less value of toughness, but
higher peak load. The explanation on this trend and the benefits of FGH is
addressed by analyzing the transverse shear stresses distribution through the
thickness in FEA, combined with analytical prediction. In low-velocity impact
tests, the projected delamination area of helicoid architectures is observed to
increase when the pitch angle is decreasing. Besides, laminates with specific pitch angles, such as 45-degree,
classical quasi-isotropic laminate, 60-degree, specific angle ply, and 90-degree,
cross-ply, are designed to compare with helicoid architectures and FGH.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12229517 |
| Date | 01 May 2020 |
| Creators | Di Wang (8782580) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Mechanical_behaviors_of_bio-inspired_composite_materials_with_functionally_graded_reinforcement_orientation_and_architectural_motifs/12229517 |
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