Abstract:The crumpling of precursor materials to form dense three dimensional geometries offers an attractive route towards the utilisation of minor-value waste materials. Crumple-forming results in a mesostructured system in which mechanical properties of the material are governed by complex cross-scale deformation mechanisms. Here we investigate the physical and mechanical properties of dense compacted structures fabricated by the confined uniaxial compression of a cellulose tissue to yield crumpled mesostructuring. … Show more
“…True stress-true strain curves from high strain-rate compression tests showed that both yield strength and peak stress levels are higher than those observed in the quasi static test; however, the endocarp becomes less ductile. This is the typical strength-ductility trade-off mechanism observed in other materials deformed at high strain rates 53 . These results clearly show a strain-rate dependence of the fruit shell, which may be explained by the strain rate sensitivity of cell material due to viscosity and by localized deformation resulting in subsequent hardening and less ductility.…”
Fruit and nut shells can exhibit high hardness and toughness. In the peninsula of Yucatan, Mexico, the fruit of the Cocoyol palm tree (Acrocomia mexicana) is well known to be very difficult to break. Its hardness has been documented since the 1500 s, and is even mentioned in the popular Maya legend The Dwarf of Uxmal. However, until now, no scientific studies quantifying the mechanical performance of the Cocoyol endocarp has been found in the literature to prove or disprove that this fruit shell is indeed “very hard”. Here we report the mechanical properties, microstructure and hardness of this material. The mechanical measurements showed compressive strength values of up to ~150 and ~250 MPa under quasi-static and high strain rate loading conditions, respectively, and microhardness of up to ~0.36 GPa. Our findings reveal a complex hierarchical structure showing that the Cocoyol shell is a functionally graded material with distinctive layers along the radial directions. These findings demonstrate that structure-property relationships make this material hard and tough. The mechanical results and the microstructure presented herein encourage designing new types of bioinspired superior synthetic materials.
“…True stress-true strain curves from high strain-rate compression tests showed that both yield strength and peak stress levels are higher than those observed in the quasi static test; however, the endocarp becomes less ductile. This is the typical strength-ductility trade-off mechanism observed in other materials deformed at high strain rates 53 . These results clearly show a strain-rate dependence of the fruit shell, which may be explained by the strain rate sensitivity of cell material due to viscosity and by localized deformation resulting in subsequent hardening and less ductility.…”
Fruit and nut shells can exhibit high hardness and toughness. In the peninsula of Yucatan, Mexico, the fruit of the Cocoyol palm tree (Acrocomia mexicana) is well known to be very difficult to break. Its hardness has been documented since the 1500 s, and is even mentioned in the popular Maya legend The Dwarf of Uxmal. However, until now, no scientific studies quantifying the mechanical performance of the Cocoyol endocarp has been found in the literature to prove or disprove that this fruit shell is indeed “very hard”. Here we report the mechanical properties, microstructure and hardness of this material. The mechanical measurements showed compressive strength values of up to ~150 and ~250 MPa under quasi-static and high strain rate loading conditions, respectively, and microhardness of up to ~0.36 GPa. Our findings reveal a complex hierarchical structure showing that the Cocoyol shell is a functionally graded material with distinctive layers along the radial directions. These findings demonstrate that structure-property relationships make this material hard and tough. The mechanical results and the microstructure presented herein encourage designing new types of bioinspired superior synthetic materials.
“…During processing, the surface under variable angle flushing of the working zone is not often sufficient and the retained debris hampers the processing, reduces the processing speed, and leads to short circuits. Another big challenge for EDM can be cutting a workpiece with an uneven structure such as a set of hollow tubes or foam-like material or material with varying mesostructure even from the known conductive and easy-to-machine (by EDM) material [31, 32]. Fig.…”
The productivity of electrical discharge machining (EDM) is relatively low owing to the natural laws of electrical erosion. Precise EDM demands uninterrupted control of the discharge gap and adjustment of process parameters. It is particularly critical for processing large workpieces with complex linear surfaces and for materials with threshold conductivities such as the new advanced ceramic nanocomposites Al2O3+TiC and Al2O3+SiCw+TiC(30–40%). In these cases, adequate flushing of erosion products is hampered by the geometry of the working space or by the small value of the required discharge gap, which does not exceed 2.2–2.5 μm. The methods of adaptive control in modern computer numerical control systems of EDM equipment based on measuring the electrical parameters in the working zone have been shown to be ineffective in the cases described above. This study aims to investigate the natural phenomena of material sublimation under discharge pulses for conductive ceramics and nanocomposites. The measured conductivities of the samples are higher than the percolation threshold. However, the question of machinability remains open owing to detected processing interruptions and poor quality of machined surfaces. New knowledge on EDM of conductive ceramics and nanocomposites can improve the final quality of the machined surfaces and productivity of the method by the introduction of advanced monitoring and control methods based on acoustic emissions. The manuscript presents an up-to-date overview and current state of the research on the subject area. The obtained morphology of the samples and discussion of the findings complete the experimental part of the study. The scientific basis for a new type of adaptive control system is provided. This can improve the effectiveness of parameter control for machining conductive ceramics and nanocomposites and contribute to an increase in the EDM performance for the most critical cases.
“…The microtextures may mainly impact the subsequent relaxation of film structure at the micro- or macroscale, resulting in the retardation of release. Arc-shaped or corrugated surfaces have been approved to be crack-resistant due to a more efficient energy dissipation and interfacial adhesion. − It is possible that microtextured fragments inside the films also undergo a similar process where the internal expansion is constrained due to enhanced interlocking and adhesion. Overall, the engineering of microtexture provides an additional and independent way to control rates without altering film composition, the intercalated molecular agent, or fluid medium.…”
Solution
co-deposition of two-dimensional (2D) nanosheets with
chemical solutes yields nanosheet–molecular heterostructures.
A feature of these macroscopic layered hybrids is their ability to
release the intercalated molecular agent to express chemical functionality
on their surfaces or in their near surroundings. Systematic design
methods are needed to control this molecular release to match the
demand for rate and lifetime in specific applications. We hypothesize
that release kinetics are controlled by transport processes within
the layered solids, which primarily involve confined molecular diffusion
through nanochannels formed by intersheet van der Waals gaps. Here
a variety of graphene oxide (GO)/molecular hybrids are fabricated
and subject to transient experiments to characterize release kinetics,
locations, and mechanisms. The measured release rate profiles can
be successfully described by a numerical model of internal transport
processes, and the results used to extract effective Z-directional diffusion coefficients for various film types. The diffusion
coefficients are found to be 8 orders of magnitude lower than those
in free solution due to nanochannel confinement and serpentine path
effects, and this retardation underlies the ability of 2D materials
to control and extend release over useful time scales. In-plane texturing
of the heterostructured films by compressive wrinkling or crumpling
is shown to be a useful design tool to control the release rate for
a given film type and molecular intercalant. The potential of this
approach is demonstrated through case studies on the controlled release
of chemical virucidal agents.
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