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Optical Measurement of In-plane Waves in Mechanical Metamaterials Through Digital Image Correlation

View Article: PubMed Central - PubMed

ABSTRACT

We report on a Digital Image Correlation-based technique for the detection of in-plane elastic waves propagating in structural lattices. The experimental characterization of wave motion in lattice structures is currently of great interest due its relevance to the design of novel mechanical metamaterials with unique/unusual properties such as strongly directional behaviour, negative refractive indexes and topologically protected wave motion. Assessment of these functionalities often requires the detection of highly spatially resolved in-plane wavefields, which for reticulated or porous structural assemblies is an open challenge. A Digital Image Correlation approach is implemented that tracks small displacements of the lattice nodes by centring image subsets about the lattice intersections. A high speed camera records the motion of the points by properly interleaving subse- quent frames thus artificially enhancing the available sampling rate. This, along with an imaging stitching procedure, enables the capturing of a field of view that is sufficiently large for subsequent processing. The transient response is recorded in the form of the full wavefields, which are processed to unveil features of wave motion in a hexagonal lattice. Time snapshots and frequency contours in the spatial Fourier domain are compared with numerical predictions to illustrate the accuracy of the recorded wavefields.

No MeSH data available.


Schematic of monitored portion of surface area of the lattice, and subdivision into 4 tiles.The figure also illustrates the point of excitation as well as the location of the LDV measurements.
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f4: Schematic of monitored portion of surface area of the lattice, and subdivision into 4 tiles.The figure also illustrates the point of excitation as well as the location of the LDV measurements.

Mentions: where i ∈ 1, …, n, with n denoting is the number of the recordings. In this work, we used n = 14 delayed recordings to realize an effective fs,eff = 14 × fs, where fs = 5 kHz is the frame rate provided by the video camera utilized. A schematic of the interleaving process is presented in Fig. 3. A second advantage is that it provides a wide effective field of view that allows capturing a sufficiently large portion of the surface area of the lattice. We elected to capture the motion only of half of the lattice, invoking symmetry of geometry and loading configuration. The monitored half surface is further divided into 4 tiles as illustrated in Fig. 4. Recordings are first conducted on each of the tiles. A composite video is then obtained from the combination of the 4 tiles which is obtained by aligning the intersection locations in planned overlapping regions. The composite images are obtained by first rotating each tile’s coordinate system so that the edges of the overlapping area align with the global coordinate axes. Then, each tile is translated so that the centroid of its overlap region matches that of its pairing neighbour.


Optical Measurement of In-plane Waves in Mechanical Metamaterials Through Digital Image Correlation
Schematic of monitored portion of surface area of the lattice, and subdivision into 4 tiles.The figure also illustrates the point of excitation as well as the location of the LDV measurements.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5304329&req=5

f4: Schematic of monitored portion of surface area of the lattice, and subdivision into 4 tiles.The figure also illustrates the point of excitation as well as the location of the LDV measurements.
Mentions: where i ∈ 1, …, n, with n denoting is the number of the recordings. In this work, we used n = 14 delayed recordings to realize an effective fs,eff = 14 × fs, where fs = 5 kHz is the frame rate provided by the video camera utilized. A schematic of the interleaving process is presented in Fig. 3. A second advantage is that it provides a wide effective field of view that allows capturing a sufficiently large portion of the surface area of the lattice. We elected to capture the motion only of half of the lattice, invoking symmetry of geometry and loading configuration. The monitored half surface is further divided into 4 tiles as illustrated in Fig. 4. Recordings are first conducted on each of the tiles. A composite video is then obtained from the combination of the 4 tiles which is obtained by aligning the intersection locations in planned overlapping regions. The composite images are obtained by first rotating each tile’s coordinate system so that the edges of the overlapping area align with the global coordinate axes. Then, each tile is translated so that the centroid of its overlap region matches that of its pairing neighbour.

View Article: PubMed Central - PubMed

ABSTRACT

We report on a Digital Image Correlation-based technique for the detection of in-plane elastic waves propagating in structural lattices. The experimental characterization of wave motion in lattice structures is currently of great interest due its relevance to the design of novel mechanical metamaterials with unique/unusual properties such as strongly directional behaviour, negative refractive indexes and topologically protected wave motion. Assessment of these functionalities often requires the detection of highly spatially resolved in-plane wavefields, which for reticulated or porous structural assemblies is an open challenge. A Digital Image Correlation approach is implemented that tracks small displacements of the lattice nodes by centring image subsets about the lattice intersections. A high speed camera records the motion of the points by properly interleaving subse- quent frames thus artificially enhancing the available sampling rate. This, along with an imaging stitching procedure, enables the capturing of a field of view that is sufficiently large for subsequent processing. The transient response is recorded in the form of the full wavefields, which are processed to unveil features of wave motion in a hexagonal lattice. Time snapshots and frequency contours in the spatial Fourier domain are compared with numerical predictions to illustrate the accuracy of the recorded wavefields.

No MeSH data available.