 |
Composite structures are designed to ensure several functions such as stiffness, damping, resistance, thermal or acoustic insulation, etc. To achieve these multiple functionalities, the use of “exotic” materials can be helpful.
Shape memory polymers (SMPs) are “smart” materials which have the remarkable ability to recover their primary shape from a temporary one under an external stimulus. SMPs encounter a growing interest over the past ten years, in particular because of their eventual bio-compatibility. They also present many benefits because of their controllable damping property. The chosen polymer is a chemically cross-linked thermoset. It is synthesized via photo polymerization (UV curing) of the monomer tert-butyl acrylate (tBA) with the crosslinking agent poly-ethylene glycol) dimethacrylate (PEGDMA) and the photoinitiator 2,2-dimethoxy-2-phenylacetophenone (DMPA).
In a previous work, the dynamical mechanical characterization of this SMP has been performed using a Dynamic Mechanical Analyzer (DMA50) from Metravib-ACOEM Company on the 0.1-180 Hz frequency range and 0-90°C temperature range. This first experimental campaign has highlighted promising damping properties controllable by the frequency of the mechanical loadings and the temperature field [1].
In order to design a sandwich structure composed of two aluminum skins and a SMP core, the properties had to be extended to larger frequency and temperature domains. This has been first done thanks to the time-temperature superposition (TTS) assumption.
To validate this hypothesis and to improve our knowledge on the material properties, a high frequency viscoanalyzer (HFV) [2] has been used to measure the shear properties of the SMP on the 200-3000 Hz frequency range and 20-80°C temperature range. The SMP properties are identified from both a simplified model and a FE model of the HFV system thanks to Least Mean Square optimization of the residue between the test and the simulation results.
This allows comparing the results obtained from the DMA50 and the HFV. Since their operating conditions are different, there are only few couples of temperature-frequency values available, thus the TTS is also used to extend the comparison.
To conclude the talk, there will be a discussion on the design improvements that need the HFV for the properties measurement of SMP considering their large variations against frequency and temperature. Some results coming from experimental modal analysis on sandwich plate will also be discussed and correlated with a FE model using frequency dependent complex moduli coming from DMA measurements.
[1] Butaud, P., Ouisse, M., Placet, V., & Foltête, E. (2014, September). Experimental Investigations on Viscoelastic Properties of a Shape Memory Polymer. In ASME 2014 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. American Society of Mechanical Engineers.
[2] Renaud, F., Chevallier, G., Dion, J. L., & Lemaire, R. (2011, January). Viscoelasticity Measurement and Identification of Viscoelastic Parametric Models. In ASME 2011 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference (pp. 701-708). American Society of Mechanical Engineers.
