Damping properties of a SMA/GFRP composite beam

Shape memory alloys (SMA) besides shape memory and superelastic properties, are characterised by significant damping properties, especially during phase transformation and in the martensitic state. Combining these features with mechanical properties and light weight of glass fiber reinforced polymer (GFRP) allows the design of advanced composite materials suitable in many structural applications affected by vibration problems. A SMA sheet, after laser patterning, was introduced in a laminated composite between a thick GFRP core and two thin outer layers, with the aim of enhancing the damping capacity of a GFRP beam through passive vibration suppression. The selected SMA was a CuZnAl alloy sheet, obtained from an induction melted ingot, further hot and cold rolled down to 0.2 mm thickness. In order to enhance the interface adhesion between polymer and SMA and to optimally exploit the damping capacity of the sheets, different patterns of elliptical holes investigated.. Besides, the pattern design also allowed the amount of SMA metal introduced in the composite beam to be varied. A pulsed fiber laser source was used in order to realise the hole patterns on the SMA sheets. After the laser processing, the SMA sheets were heat treated in order to gain the desired shape memory properties. The transformation temperatures were checked by differential scanning calorimetry (DSC). The damping properties at room temperature were determined on full scale sheet, using a universal testing machine, with cyclic tensile tests at different deformation amplitudes. The temperature dependence was obtained on miniature samples (1mm wide, 25mm long) with a dynamical mechanical analyser (DMA). Damping properties, obtained from the described dynamic characterization of the CuZnAl sheets were used in conjunction with finite element method (FEM) analysis and modal strain energy (MSE) approach in order to calculate the laminated composite damping capacity. Beams of the laminated composite (25 mm wide, 5mm thick, 200 mm long), with different patterning schemes, were assembled and cured in autoclave. Experimental decay tests on the prototypes in their first flexural mode were performed and the damping properties of the advanced material as a function of the different patterning schemes were verified