Visokohitrostna karakterizacija mehanskih lastnosti celičnih metamaterialov

doktorska disertacija

Abstract

V doktorski raziskavi so bile karakterizirane visokohitrostne mehanske lastnosti novih celičnih metamaterialov z osnosimetrično avksetično kiralno strukturo, katerih geometrija temelji na tridimenzionalni štiri kiralni kvadratni enotski celici z ukrivljenimi medceličnimi povezavami sinusne oblike in prostorsko gradiranostjo v radialni smeri. Z napredno dodajalno tehnologijo 3D tiskanja so bili izdelani vzorci treh različnih osnosimetričnih geometrijskih struktur z različnimi relativnimi gostotami. Za celovito mehansko karakterizacijo v vseh obremenitvenih režimih (kvazi statičnem, prehodno dinamičnem in visokohitrostnem) so bile uporabljene napredne eksperimentalne in računalniško simulacijske metode, s katerimi so bile zajete vse deformacijske faze celičnih metamaterialov, in sicer: začetna faza, plato faza in faza zgoščevanja. S predhodno študijo odziva kiralnih preizkušancev je bilo ugotovljeno, da klasično SHPB preizkuševališče ne omogoča celovite visokohitrostne karakterizacije celičnih metamaterialov, zato je bila izvedena nadgradnja obstoječega SHPB preizkuševališča v preizkuševališče direktnega udarca DIHB. Ustrezno delovanje DIHB preizkuševališča je bilo potrjeno z mehansko karakterizacijo uveljavljene odprto celične kovinske pene m-pore®. Z vpeljavo optične metode sledenja digitalnih slik (DIC) je bila dosežena višja stopnja natančnosti eksperimentalnih opazovanj, ki je omogočila določitev polj pomikov, specifičnih deformacij in Poissonovih razmerij v vseh obremenitvenih režimih na mezo nivoju. Ustrezno potrjeno DIHB preizkuševališče je bilo uporabljeno za obsežno mehansko karakterizacijo novih osnosimetričnih metamaterialov pri različnih deformacijskih režimih. Dokazan je bil vpliv deformacijske hitrosti na utrjevanje metamateriala zaradi vpliva mikrovztrajnosti. Dokazano je bilo, da je lahko z gradirano notranjo kiralno strukturo osnosimetričnih celičnih metamaterialov dosežen konstanten napetostni plato brez oscilacij in postopoma naraščajoče Poissonovo razmerje. Obenem je bila opredeljena tudi geometrijska struktura z najvišjim avksetičnim odzivom, najvišjo togostjo glede na relativno gostoto strukture in najmanjšimi napetostnimi oscilacijami v plato fazi.

Keywords

celični metamateriali;prostorsko gradirana gostota;SHPB;visokohitrostna deformacija;test direktnega udarca;DIC;računalniške simulacije;doktorske disertacije;

Data

Language:	Slovenian
Year of publishing:	2022
Typology:	2.08 - Doctoral Dissertation
Organization:	UM FS - Faculty of Mechanical Engineering
Publisher:	[A. Mauko]
UDC:	[620.17:539.216]:004.94(043.3)
COBISS:	121877251
Views:	3
Downloads:	2
Average score:	0 (0 votes)
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Other data

Secondary language:	English
Secondary title:	High strain rate characterization of mechanical properties of cellular metamaterials
Secondary abstract:	In the doctoral dissertation, unique cellular metamaterials with an axisymmetric chiral auxetic structure were fabricated and characterized. Structures geometry was based on a 3D tetra chiral square unit cell with sinusoidal struts and was spatially graded in the radial direction. Samples of three axisymmetric geometrical structures with different relative densities were manufactured by advanced 3D printing technology. Due to the strain rate sensitivity, an extensive characterization of axisymmetric metamaterials in all loading regimes (quasi-static, transitional and shock regime) was required. Thus, advanced experimental and computer simulation methods were used for extensive characterization of novel metamaterial. Comprehensive mechanical characterization is achieved when the cellular metamaterial passes all the deformation phases, which are: an initial stage, the stress plateau stage and densification stage. In a preliminary study, chiral metamaterials were experimentally tested at classical SHPB test apparatus. Experimental results reviled inadequacy of SHPB apparatus, which only enables partial characterization of cellular metamaterials. By determination of the SHPB apparatus limits, classical SHPB apparatus was modified to enable direct impact test on improved DIHB apparatus. The performance of DIHB apparatus was validated by mechanical characterization of the well-known open cell metal foam m-pore®. In addition, a DIC optical method was implemented to determine the displacement fields, strain fields, and Poisson’s ratios at higher accuracy on meso-scale. DIHB test apparatus enabled extensive mechanical characterization of novel axisymmetric metamaterials with an auxetic structure. A comprehensive characterization of all tested axisymmetric structures was achieved in all loading regimes. It has been proven that with a graded internal chiral structure of axisymmetric cellular metamaterials, a constant plateau stress without oscillations and a gradually increasing Poisson ratio can be achieved. In addition, the geometric structure with the highest auxetic response, the highest stiffness with respect to the relative density of the structure, and the lowest stress oscillations in the plateau phase was determined.
Secondary keywords:	cellular metamaterials;spatially graded density;SHPB;high strain rate;direct impact test;DIC;computer simulation;Univerzitetna in visokošolska dela;
Type (COBISS):	Doctoral dissertation
Thesis comment:	Univ. v Mariboru, Fak. za strojništvo
Pages:	VIII, 126 str.
ID:	15188548