Shape morphing and the possibility of having control over mechanical properties via designed deformations have attracted a lot of attention in the materials community and led to a variety of ...applications with an emphasis on the space industry. However, current materials normally do not allow to have a full control over the deformation pattern and often fail to replicate such behavior at low scales which is essential in flexible electronics. Thus, in this paper, novel 2D and 3D microscopic hierarchical mechanical metamaterials using mutually‐competing substructures within the system that are capable of exhibiting a broad range of the highly unusual auxetic behavior are proposed. Using experiments (3D microprinted polymers) supported by computer simulations, it is shown that such ability can be controlled through geometric design parameters. Finally it is demonstrated that the considered structure can form a composite capable of shape morphing allowing it to deform to a predefined shape.
This study presents novel 2D and 3D microscopic hierarchical mechanical metamaterials capable of exhibiting a broad range of the highly unusual auxetic behavior that can be fully controlled through design parameters. The proposed hierarchical systems can also form composites capable of shape morphing where the initial structures can assume arbitrary predefined shapes.
The ability to significantly change the mechanical and wave propagation properties of a structure without rebuilding it is currently one of the main challenges in the field of mechanical ...metamaterials. This stems from the enormous appeal that such tunable behavior may offer from the perspective of applications ranging from biomedical to protective devices, particularly in the case of micro‐scale systems. In this work, a novel micro‐scale mechanical metamaterial is proposed that can undergo a transition from one type of configuration to another, with one configuration having a very negative Poisson's ratio, corresponding to strong auxeticity, and the other having a highly positive Poisson's ratio. The formation of phononic band gaps can also be controlled concurrently which can be very useful for the design of vibration dampers and sensors. Finally, it is experimentally shown that the reconfiguration process can be induced and controlled remotely through application of a magnetic field by using appropriately distributed magnetic inclusions.
In this work, a novel micro‐scale mechanical metamaterial is proposed that can undergo a magnetically induced transition from one type of configuration to another, with one configuration being strongly auxetic and the other having a highly positive Poisson's ratio. The system allows to also concurrently control the band gap formation.
Non-Newtonian liquids are characterized by stress and velocity-dependent dynamical response. In elasticity, and in particular, in the field of phononics, reciprocity in the equations acts against ...obtaining a directional response for passive media. Active stimuli-responsive materials have been conceived to overcome it. Significantly, Milton and Willis have shown theoretically in 2007 that quasi-rigid bodies containing masses at resonance can display a very rich dynamical behavior, hence opening a route toward the design of non-reciprocal and non-Newtonian metamaterials. In this paper, we design a solid structure that displays unidirectional shock resistance, thus going beyond Newton's second law in analogy to non-Newtonian fluids. We design the mechanical metamaterial with finite element analysis and fabricate it using three-dimensional printing at the centimetric scale (with fused deposition modeling) and at the micrometric scale (with two-photon lithography). The non-Newtonian elastic response is measured via dynamical velocity-dependent experiments. Reversing the direction of the impact, we further highlight the intrinsic non-reciprocal response.
Stepper motors and actuators are among the main constituents of control motion devices. They are complex multibody systems with rather large overall volume due to their multifunctional parts and ...elaborate technological assembly processes. Miniaturization of individual parts is still posing assembly problems. In this paper, a single‐step lithography process to fabricate a micro‐stepper engine with an accurate micrometric rotation axis and an overall sub‐millimeter size is demonstrated. The device is based on the frictional contacts and chiral metamaterials to get rid of the dependence on the accuracy of parts. The functional aspects of fabricated samples are discussed for many rotation cycles and for different frictional surfaces.
Herein, a single‐step lithography process to fabricate a micro‐stepper engine with an accurate micrometric rotation axis and an overall sub‐millimeter size is demonstrated. The device is based on the frictional contacts and chiral metamaterials to get rid of the dependence on the accuracy of parts. The functional aspects of fabricated samples are discussed for many rotation cycles and for different frictional surfaces.
Herein, a novel hierarchical mechanical metamaterial is proposed that is composed of re‐entrant truss‐lattice elements. It is shown that this system can deform very differently and can exhibit a ...versatile extent of the auxetic behavior depending on a small change in the thickness of its hinges. In addition, depending on which hierarchical level is deforming, the whole structure can exhibit a different type of auxetic behavior that corresponds to a unique deformation mechanism. This results in a dual auxetic structure where the interplay between the two auxetic mechanisms determines the evolution of the system. It is also shown that depending on the specific deformation pattern, it is possible to observe a very different behavior of the structure in terms of frequencies of waves that can be transmitted through the system. In fact, it is demonstrated that even a very small change in the parametric design of the system may result in a significantly different bandgap formation that can be useful in the design of tunable vibration dampers or sensors. The possibility of controlling the extent of the auxeticity also makes the proposed metamaterial to be very appealing from the point of view of protective and biomedical devices.
Herein, a novel hierarchical mechanical metamaterial is proposed that can exhibit versatile auxetic behavior depending on a small change in the thickness of its hinges. It is also shown that the thickness of hinges can be used to control the vibrational properties of the structure with an emphasis on the bandgap formation.
•Quartz cannot be discriminated from the mounting resin under optical microscopy.•A human being seems to be perfectly capable of differentiating quartz from resin.•Deep learning methods can extract ...complex features and make predictions thereon.•CNN can be the definitive solution for this problem of quartz/resin discrimination.
Mineral processing is the process of separating commercially valuable minerals from their ores. The final quality of the iron ore is tied to the efficiency of its beneficiation process, which can be optimized when the composition of the iron ore is known. Reflected Light Optical Microscopy (RLOM) has been traditionally used to analyze the composition of iron ore samples. However, due to a similar reflectance, the commercially available mounting resins tend to get mixed with the quartz phase. Therefore, it is a well-known problem that, while the major mineralogical phases (mainly hematite goethite and magnetite) can be segmented, it is not possible to segment and analyze the quartz phase by RLOM. Convolutional Neural Networks (CNNs) are a branch of machine learning that have been experiencing a considerable development and thus efficient application in the field of image analysis and classification. As CNNs have been matching and sometimes even outperforming humans, it is reasonable to apply them to this problem, for a human operator can easily distinguish between quartz and resin. After building a databank constituting of 1747 images of resin and 1745 images of quartz for the training set and 442 images of each class for the testing set, the Convolutional Neural Network (CNN) achieved, once trained, success rates above 95%. This success rate is a clear indicator that CNNs can indeed be a solution to this classic problem.
Previously, rotons were observed in correlated quantum systems at low temperatures, including superfluid helium and Bose-Einstein condensates. Here, following a recent theoretical proposal, we report ...the direct experimental observation of roton-like dispersion relations in two different three-dimensional metamaterials under ambient conditions. One experiment uses transverse elastic waves in microscale metamaterials at ultrasound frequencies. The other experiment uses longitudinal air-pressure waves in macroscopic channel–based metamaterials at audible frequencies. In both experiments, we identify the roton-like minimum in the dispersion relation that is associated to a triplet of waves at a given frequency. Our work shows that designed interactions in metamaterials beyond the nearest neighbors open unprecedented experimental opportunities to tailor the lowest dispersion branch—while most previous metamaterial studies have concentrated on shaping higher dispersion branches.
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