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Submitted on: 17 November 2015.
Revised on: 25 February 2016.
Accepted on: 22 April 2016.
___________________Journal of Theoretical and Applied Mechanics-Bulgaria
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Submitted on: 02 September 2020.
Revised on: 19 December 2020.
Accepted on: 16 February 2021.
___________________Journal of Theoretical and Applied Mechanics-Bulgaria
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Submitted on: 01 May 2012.
Revised on: 04 June 2012.
Accepted on: 20 July 2012.
___________________Journal of Theoretical and Applied Mechanics-Bulgaria