Accepted Manuscript letter A general bi-Helmholtz nonlocal strain-gradient elasticity for wave propagation in nanoporous graded double-nanobeam systems on elastic substrate Mohammad Reza Barati, Ashraf Zenkour PII: S0263-8223(17)30252-0 DOI: http://dx.doi.org/10.1016/j.compstruct.2017.02.090 Reference: COST 8312 To appear in: Composite Structures Received Date: 24 January 2017 Revised Date: 20 February 2017 Accepted Date: 24 February 2017 Please cite this article as: Barati, M.R., Zenkour, A., A general bi-Helmholtz nonlocal strain-gradient elasticity for wave propagation in nanoporous graded double-nanobeam systems on elastic substrate, Composite Structures (2017), doi: http://dx.doi.org/10.1016/j.compstruct.2017.02.090 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.