Three different structures of micro-lattice obtained by Selective Laser Melting (SLM) with AlSi7Mg aluminum powder have been considered in this work. Micro-tensile specimens have been printed and tested to identify the parent material properties and to calibrate the parameter of the material model used for the simulations. Compression tests on micro-lattice specimens have been carried out with the aid of a high-resolution camera and Digital Image Correlation (DIC) analysis has been conducted to get localization of strains and to have an additional measure of the global strain. Particular attention has been paid to the definition of a proper test method that allows to identify correctly the metamaterial properties. Being the geometry of these lattice structures different from the one designed by CAD, analysis on the real geometry reconstructed from computed tomography has been performed; in particular, values of real relative densities have been extracted and the influence of the building direction (or printing angle) on the mean strut diameter has been investigated. Preliminary numerical simulations with elasto-plastic models have been carried out to define the best specimen configuration to proper test the behavior of periodic lattice structures and to identify the lightest and most significant model to represent numerically the mechanical response. The Gurson-Tvergaard-Needleman damage model has been applied to model the rupture; cells with ideal geometry and real geometry extracted from CT scan have been simulated both in monoaxial and biaxial state of stress. Good correlation in terms of characteristic curve and failure prediction has been found between experimental results and simulations on real geometry. Finally, from the numerical analysis, yielding and rupture locus on the biaxial stress plane have been found for one of the three considered structures.
Tre diverse strutture di micro-lattice ottenute da Selective Laser Melting (SLM) con polvere di alluminio AlSi0.7Mg sono state considerate in questo lavoro; le proprietà del materiale base sono state identificate tramite test di micro-trazione che hanno anche concesso l’identificazione dei parametri del materiale per i modelli usati nelle simulazioni numeriche. Test di compressione sono stati effettuati su campioni di struttura trabecolare; tramite una fotocamera ad alta risoluzione, l’analisi di autocorrelazione di immagini digitali è stata utilizzata per individuare le localizzazioni di deformazioni e per avere una ulteriore misura della deformazione globale omogeneizzata. Durante le prove sperimentali, attenzione particolare è stata data alla identificazione di un setup sperimentale in grado di determinare correttamente le proprietà del metamateriale. Essendo la geometria delle strutture ottenute diversa da quella disegnata tramite CAD, la geometria reale e ricostruita da tomografia computerizzata è stata analizzata in dettaglio; in particolare sono stati estratti i valori di densità relativa reale ed è stato studiato l’effetto dell’angolo di stampa o di crescita sul diametro delle travi costituenti il reticolo. Simulazioni numeriche preliminari tramite modelli elasto-plastici sono state effettuate al fine di definire la migliore configurazione di provino in termini di caratteristiche geometriche e dimensioni e di individuare un modello semplice e in grado di rappresentare il comportamento di un mezzo composto da molte celle e sottoposto a diverse condizioni di carico. Il modello di danno Gurson-Tvergaard-Needleman è stato infine applicato per modellare la rottura; il comportamento di celle con geometria ideale e reale estratta da tomografia è stato simulato per condizioni di carico monoassiali e biassiali. Buona correlazione con i test sperimentali è stata riscontrata in termini di curve di compressione; una superficie descrivente lo snervamento e la rottura del metamateriale è stata infine disegnata sul piano di sforzo biassiale per una delle tre celle testate.
Experimental characterization and modeling of failure of micro-lattice structures obtained by SLM
GAVAZZONI, MATTEO
2017/2018
Abstract
Three different structures of micro-lattice obtained by Selective Laser Melting (SLM) with AlSi7Mg aluminum powder have been considered in this work. Micro-tensile specimens have been printed and tested to identify the parent material properties and to calibrate the parameter of the material model used for the simulations. Compression tests on micro-lattice specimens have been carried out with the aid of a high-resolution camera and Digital Image Correlation (DIC) analysis has been conducted to get localization of strains and to have an additional measure of the global strain. Particular attention has been paid to the definition of a proper test method that allows to identify correctly the metamaterial properties. Being the geometry of these lattice structures different from the one designed by CAD, analysis on the real geometry reconstructed from computed tomography has been performed; in particular, values of real relative densities have been extracted and the influence of the building direction (or printing angle) on the mean strut diameter has been investigated. Preliminary numerical simulations with elasto-plastic models have been carried out to define the best specimen configuration to proper test the behavior of periodic lattice structures and to identify the lightest and most significant model to represent numerically the mechanical response. The Gurson-Tvergaard-Needleman damage model has been applied to model the rupture; cells with ideal geometry and real geometry extracted from CT scan have been simulated both in monoaxial and biaxial state of stress. Good correlation in terms of characteristic curve and failure prediction has been found between experimental results and simulations on real geometry. Finally, from the numerical analysis, yielding and rupture locus on the biaxial stress plane have been found for one of the three considered structures.| File | Dimensione | Formato | |
|---|---|---|---|
|
tesi.pdf
non accessibile
Descrizione: tesi_gavazzoni
Dimensione
7.87 MB
Formato
Adobe PDF
|
7.87 MB | Adobe PDF | Visualizza/Apri |
I documenti in POLITesi sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/10589/142861