This thesis work is focused on the modelling of fragmentation in a pure tungsten, blunt projectile during ballistic impact. It presents an innovative approach to the numerical reproduction of the fragmentation, based upon the use of cohesive elements in LS-Dyna®. This solution offers very noticeable improvements over the continuous projectile model used in previous studies. The flow stress of the material is reproduced with the Johnson-Cook material model, which was calibrated on the basis of experimental tests found in technical literature. A procedure for the calibration of the parameters of the cohesive bond was hypothesized on the basis of fracture mechanics; the aforementioned parameters were then found through microscopic analyses carried on with both optical and scanning electron microscopes. The finished model, verified through a comparison with the performed shooting tests and other tests found in technical literature, constitutes a lean tool which is able to forecast and describe the fragmentation, while retaining some ease of implementation thanks to the embedded routines present in most multiphysics software packages.
La presente tesi è incentrata sul problema della modellazione della frammentazione di un proiettile cilindrico in tungsteno puro, che si inserisce nell’ambito delle prove balistiche di impatto. Viene proposto e discusso un metodo innovativo per la modellazione numerica della frattura fragile tramite l’utilizzo di elementi coesivi cosituiti ad hoc in ambiente LS-Dyna®, in contrapposizione con il modello continuo utilizzato nei precedenti studi. La legge viscoplastica del materiale viene espressa tramite il modello viscoplastico di Johnson-Cook, i cui parametri sono stati appositamente ricavati per il presente studio. L’ipotesi di partenza per la calibrazione dei parametri costitutivi del legame coesivo si basa sullo studio della meccanica della frattura, e ha portato a ricercare e ottenere i suddetti parametri con l’ausilio di prove sperimentali effettuate tramite microscopio ottico e microscopio elettronico a scansione (SEM). Il modello completo, verificato tramite il confronto con le prove sperimentali effettuate e altre disponibili in letteratura, costituisce un metodo di previsione e descrizione della frattura snello e facilmente implementabile tramite le routine incluse nei pacchetti software più diffusi.
Numerical modelling of fragmentation in a tungsten projectile
ROMANO, TOMMASO
2013/2014
Abstract
This thesis work is focused on the modelling of fragmentation in a pure tungsten, blunt projectile during ballistic impact. It presents an innovative approach to the numerical reproduction of the fragmentation, based upon the use of cohesive elements in LS-Dyna®. This solution offers very noticeable improvements over the continuous projectile model used in previous studies. The flow stress of the material is reproduced with the Johnson-Cook material model, which was calibrated on the basis of experimental tests found in technical literature. A procedure for the calibration of the parameters of the cohesive bond was hypothesized on the basis of fracture mechanics; the aforementioned parameters were then found through microscopic analyses carried on with both optical and scanning electron microscopes. The finished model, verified through a comparison with the performed shooting tests and other tests found in technical literature, constitutes a lean tool which is able to forecast and describe the fragmentation, while retaining some ease of implementation thanks to the embedded routines present in most multiphysics software packages.File | Dimensione | Formato | |
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Tesi Tommaso Romano.pdf
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https://hdl.handle.net/10589/95545