Characterisation of mechanical parameters of high-performance materials under impact loading for aerospace applications

Določene komponente sodobnih tehnoloških napravah so pogosto izpostavljene udarnim obremenitvam. Če želimo optimirati takšne naprave (npr. turbine letalskih motorjev), moramo poznati mehanske lastnosti materiala pri visokih hitrostih obremenjevanja, saj te za večino kovin niso enake kot pri statičnih obremenitvah. V magistrskem delu smo predstavili metodo za določanje dinamičnih lastnosti materiala in zasnovali napravo za testiranje kovinskih preizkušancev, t.i. Split Hopkinson Pressure Bar (SHPB), ki jo bomo v prihodnosti postavili na Fakulteti za strojništvo v Mariboru. Pripravili smo numerični model SHPB, na podlagi katerega lahko napovemo, kakšne napetostne signale lahko proizvedemo med testiranjem. Konstruirali smo tudi različne nove oblike preizkušancev, ki smo jih prav tako numerično preizkusili, in na podlagi rezultatov simulacij izbrali najbolj primerno obliko dog-bone preizkušanca. Ugotovili smo, da s spremembo geometrije preizkušanca vplivamo na napetostno stanje v njem, z dodanim utorom v preizkušancu ustvarimo namesto enoosnega večosno napetostno stanje. Predstavljen je tudi celotni eksperimentalni postopek in rezultati testiranj za dva različna materiala. Testiranja smo izvedli v Impact Engineering Laboratory na univerzi v Oxfordu.Components of advanced engineering systems for transportation applications are often exposed to impact loading. Commonly, alloys behave differently under the influence of either static or dynamic loading. By knowing the mechanical properties of a material at high strain rates, one can optimise their application for use in, for example, aerospace gas turbine engines. One method of determining the dynamic properties of materials is presented in this thesis together with a Split Hopkinson Pressure Bar (SHPB) design for the Faculty of Mechanical Engineering in Maribor. Numerical modelling was used to predict the loading histories which the newly designed SHPB will be able to generate. New specimen geometries were designed and numerically evaluated. Based on these simulation results the most appropriate dog-bone specimen design was chosen. It was shown that specimen stress condition can be modified from a uniaxial to a multiaxial stress state by changing the gauge section and shoulder geometries with the addition of notches, acting as stress conditions. The complete experiment process and data flow during and after experiments, including stress–strain curves, are presented from tests carried out at the Impact Engineering Laboratory at the University of Oxford in support of this thesis