Characterizing Dissipative Elastic Metamaterials Produced by Additive Manufacturing

My research aims to characterize viscoelastic properties of actively manufactured polymers and to examine the impact on the dynamics of elastic metamaterials. I seek to understand how these properties may inference wave attrition at operational frequencies, which may include precise characterization and potential modifications. Polymer characterization requires expertise in material science, radiology, specialized setups and training, which are often lacked for researchers in metamaterials.

Similarly, ultrasonic analysis of wave attenuation and metamaterials involves techniques unfamiliar to chemical engineers. Consequently, merging these two fields poses significant experimental challenges. Viscoelasticity in polymers is a complex phenomenon and there is limited data for storage and loss moduli at ultrasonic frequencies, particularly for additively manufactured polymers.

The aim is to connect material properties with structure driven dynamics of metamaterials, thus enabling a robust and reliable design for targeted working frequencies. Our protocol combines manufacturing, chemical, ultrasonic, and chemical tests with numerical analysis to enhance our understanding of how our scholastic properties affect the dynamics of polymer metamaterials. This knowledge will improve metamaterial design for applications in acoustic clocking, wave guiding, energy harvesting, and other fields requiring effective wave control.

Our future activities will focus on analyzing how different 3D printing parameters affect the viscoelastic properties of final parts. Also, exploring mechanisms to modify these properties to influence the dynamic behavior of polymer metamaterials. We aim to create more accurate and efficient models to simulate viscoelastic behavior in complex geometries for acoustic and ultrasonic applications.

To begin, fabricate cuboidal test samples based on the dimensions provided in the table shown here. Define the test temperature range, avoiding and staying well below the materials, melting temperature. Select a heating rate between one and three degrees Celsius per minute.

For optimal results, opt for the lowest strain value. Set up the parameters for the frequency sweep and the heating rate. For calibration, use the single cantilever test configuration.

Initiate the calibration process to ensure accuracy. For clamping the sample, loosen the screws of the stationary and adjustable clamps when the park mode is activated. Slide the test sample through one side and rest it on the threads of the clamps.

Then tighten the adjustable clamps followed by the stationary clamps. To reinstall the oven, place it over the test configuration and input the initial temperature manually. Wait at least three minutes after reaching the desired temperature.

Now start the measurements. Once the measurements are completed and the oven temperature returns to ambient, remove the oven and the sample, then export the data and shift the curves to a reference temperature using appropriate shift factors to obtain a master curve at the reference temperature. Begin by using the model wizard to create a new model.

Select the 3D space dimension and add the solid mechanic study. Then choose the frequency domain study for transmission analysis. Under the global definitions tab, define relevant parameters and assign values to them.

Using available tools, create the geometry of a metamaterial model. Now right click on components to access the definitions tab, then select probes and choose boundary probe. Assign a boundary on the model to this boundary probe where the transmission loss is to be calculated.

To define a perfectly matched layer or PML, right click on the definitions tab and assign PML properties to geometric blocks surrounding the metamaterial geometry. Apply periodic boundary conditions at faces perpendicular to the periodicity direction and enable the continuity feature. Then right click on the materials tab and add materials from the library to assign material properties to the geometry.

Under the component tab, right click on the linear elastic materials tab and select the viscoelasticity material model. Enter the deviatoric tensor obtained from the calculation, based on DMA results. Next, right click on the prescribed displacement tab and select a portion of the model to be dynamically excited from the graphics window.

Assign the amplitude of out of plane displacement at the expected position of a piezo element. Then generate a suitable mesh for the analyzed model. Now choose an appropriate shift function from the dropdown menu.

Select none if the temperature effects are already considered in the DMA results to be used. Select an appropriate viscoelastic model and enter the values for the deviatoric tensor based on calculations. From the study library, select the add study option, select frequency domain, and enter the target frequency range.

Then press the compute button to compute the study. Now, right click on the results tab and select the 1D plot group function. Right click on the created 1D plot group and choose global from the options.

In the Y axis data tab of the settings window, input the mathematical expression for transmission loss and plot the data. Numerical results for transmission calculations showed a drop in transmission level exceeding 20 decibels, representing a frequency band gap observed within the frequency range. To begin, choose a suitable excitation source based on numerical predictions for an operational frequency range.

Apply reflective tape to the test specimen at the intended signal acquisition point to improve laser signal detection. Adjust the position and angle of the LDV laser to direct it toward the reflective tape. Connect a computer to a signal generator, followed by an amplifier connected to a piezo to create an electric circuit.

Once a proper connection is established, begin the test. To create two separate projects for signal generation and acquisition, select the proper hardware from the start manager dialogue for a generator and a digitizer. Click start to initiate the process in the input mode tab and choose a recording mode.

Pre-select the standard single mode, allowing adjustment of parameters, like mem size. Then set the desired sampling rate under the clock tab. Configure the triggering mode under the trigger tab.

To initiate a single shot recording, click the right moving green arrow button. Once done, end the recording using the stop button. Use the measurement software's easy generator option to generate simple excitation functions, like sign waves or rectangular pulses.

Alternatively, navigate to the new tab. Choose signal calculations and choose the function generator option. Define the length of the signal and start the signal.

To perform a fast furier transform on the signal, select signal calculations under input channels and choose FFT. Choose an appropriate window function for FFT calculation. Before starting the test, point the LDV laser at the vibration source.

Send a signal and calculate FFT to inspect the configuration to ensure proper operation. In another window of the measurement software, observe the received signal. Match FFT results in both windows before proceeding with the experiment.

To start the experiment, point the LDV laser at the desired acquisition point on the metamaterial sample. The pitch catch transmission test revealed a signal drop within the frequency range, indicating the frequency band gap.