MTM MTM - Machines, technologies, materials : 15th International Scientific Congress Machines, Technologies, Materials, 14. - 17. 03. 2018, Borovetz, Bulgaria. -- Vol. 12, iss. 3 (2018). -- ISSN : 1313-0226. In: MTM - Machines, technologies, materials. -- ISSN 1313-0226. -- Sofia : Scientific -Technical Union of Mechanical Engineering.