Thin plates of high-strength steel and aluminium are frequently being used in both civil and military ballistic protection systems and their assessment and optimisation is actually an important research topic within these fields. Starting from experimental ballistic tests results, this master thesis describes an intensive investigation on a numerical method capable to simulate correctly a ballistic phenomenon in all its main parts. Thus, its main task should not be confused with the simple identification of the impact behaviour of the material investigated but it is focused on the research of an univocal numerical model able to describe an impact phenomena independently from the target and projectile materials involved. During the ballistic tests conducted at the Norwegian Research Centre, SIMLab, the APM2 7.62mm ammunition and the corresponding blunt one, having the same mass and diameter of the core of the ogival one have been used. A precision rifle (Mauser gun) with a barrel diameter of 7.62mm and a barrel length of 63mm , is used for obtain impact velocities above and below the ballistic limit velocity of the configurations tested. Measuring the initial and residual velocities of the projectiles, the ballistic limit curves are plotted for each target used using the Recht-Ipson interpolation. In addition, a digital high-speed camera system is used to photograph the penetration event. Afterwards, numerical simulations are carried out using the non-finite element code LS-DYNA; modified Johnson-Cook constitutive material model and Cockcroft-Latham failure criterion have been used to represent the targets behaviour. The results from the numerical simulations are compared and discussed in accordance with the experimental observations. In particular, it has been investigated the effect of different numerical parameters such as: mesh dimension, elements stiffness, etc. on both residual velocity of the projectile and damage morphology. Concluding the numerical models built are capable to describe the perforation physical mechanics with good accuracy and the results obtained are encouraging in terms of predicting the response of the plates examined. Thus, this work wants to be a solid starting point for future researches regarding the design of more effective protection and the assessment of ballistic damage on a mechanical component.
Sottili lastre di acciaio ed alluminio sono frequentemente utilizzate nell’ambito della protezione balistica di sistemi e strutture civili e militari. Nello specifico, in questa tesi, partendo da prove sperimentali di impatto balistico, `e effettuata un’ampia indagine riguardante la ricerca di un univoco metodo numerico in grado di simulare correttamente un fenomeno balistico. L’obbiettivo di questo lavoro non deve essere quindi confuso con l’identificazione del comportamento meccanico dei materiali investigati sotto impatto ma `e focalizzato sulla ricerca di un sofisticato modello numerico in grado di descrivere un fenomeno d’urto indipendentemente dal materiale utilizzato. Durante i test balistici condotti presso il Centro Ricerca norvegese SimLab sono stati utilizzati proiettili APM2 ed i corrispettivi proiettili cilindrici, aventi massa e diametro pari a quelli del cuore del APM2. Per quanto riguarda lo sparo, un fucile di precisione calibro 7.62mm e lunghezza 63mm `e utilizzato per ottenere le velocit`a d’impatto necessarie alla costruzione di accurate curve balistiche. Durante gli esperimenti, velocit`a iniziali e residue dei proiettili sono state accuratamente misurate, tramite un telecamera digitale ad alta velocit`a. In seguito alle prove sperimentali, molteplici simulazioni numeriche sono state effettuate utilizzando il software ad elementi finiti LS-DYNA. Per rappresentare numericamente il comportamento meccanico dei componenti coinvolti in un’impatto `e stato utilizzato il legame costitutivo di tipo Johnson-Cook modificato mentre come criterio di rottura il Cockcroft-Latham. I risultati ottenuti numericamente sono stati continuamente confrontati e discussi in conformit`a con le osservazioni sperimentali. Nello specifico, la campagna numerica si `e focalizzata sull’effetto di diversi parametri quali: dimensione delle mesh, rigidit`a degli elementi, ecc. sulla velocit`a residua del proiettile e sul danno prodotto. Concludendo, `e verificato che i modelli numerici costruiti sono in grado di descrivere un processo d’impatto correttamente ed i risultati ottenuti sono incoraggianti in termini di previsione della risposta da parte di piastre metalliche soggette ad urto. Questo lavoro auspica ad essere un solido punto di partenza per future ricerche riguardanti una pi`u efficace progettazione di strutture soggette ad impatto e la successiva valutazione del danno prodotto.
Computer aided design for lightweight protective structures
ZARDI, OMAR
2011/2012
Abstract
Thin plates of high-strength steel and aluminium are frequently being used in both civil and military ballistic protection systems and their assessment and optimisation is actually an important research topic within these fields. Starting from experimental ballistic tests results, this master thesis describes an intensive investigation on a numerical method capable to simulate correctly a ballistic phenomenon in all its main parts. Thus, its main task should not be confused with the simple identification of the impact behaviour of the material investigated but it is focused on the research of an univocal numerical model able to describe an impact phenomena independently from the target and projectile materials involved. During the ballistic tests conducted at the Norwegian Research Centre, SIMLab, the APM2 7.62mm ammunition and the corresponding blunt one, having the same mass and diameter of the core of the ogival one have been used. A precision rifle (Mauser gun) with a barrel diameter of 7.62mm and a barrel length of 63mm , is used for obtain impact velocities above and below the ballistic limit velocity of the configurations tested. Measuring the initial and residual velocities of the projectiles, the ballistic limit curves are plotted for each target used using the Recht-Ipson interpolation. In addition, a digital high-speed camera system is used to photograph the penetration event. Afterwards, numerical simulations are carried out using the non-finite element code LS-DYNA; modified Johnson-Cook constitutive material model and Cockcroft-Latham failure criterion have been used to represent the targets behaviour. The results from the numerical simulations are compared and discussed in accordance with the experimental observations. In particular, it has been investigated the effect of different numerical parameters such as: mesh dimension, elements stiffness, etc. on both residual velocity of the projectile and damage morphology. Concluding the numerical models built are capable to describe the perforation physical mechanics with good accuracy and the results obtained are encouraging in terms of predicting the response of the plates examined. Thus, this work wants to be a solid starting point for future researches regarding the design of more effective protection and the assessment of ballistic damage on a mechanical component.| File | Dimensione | Formato | |
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2012_12_ZARDI.pdf
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https://hdl.handle.net/10589/71917