Free vibration analysis of homogeneous and FGM skew plates resting on variable Winkler-Pasternak elastic foundationMohamad Javad Ketabdari, Alireza Allahverdi, Sayad Boreyri and Manouchehr Fadavie ArdestaniMechanics & Industry, 17 1 (2016) 107DOI: https://doi.org/10.1051/meca/2015051