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Reliable ballistic armor systems are crucial to ensure the safety of humans and vehicles. Typically, these systems are constructed from various materials like fiber-reinforced polymer composites, which are utilized for a favorable weight to ballistic protection ratio. In particular, there has been a quest for eco-friendly materials that offer both strong mechanical properties and sustainable advantages. The present work conducted a ballistic analysis of epoxy matrix composites using raffia (Raphia vinifera) fibers from the Amazon region as reinforcement. The experiments investigated the limit and residual velocities of composites with 10, 20, and 30 vol% of raffia. The experimental density of the composites was lower than that of the epoxy. Fractured surfaces were examined by scanning electron microscopy (SEM) to reveal the failure mechanism. The results showed that composites with 10 vol% raffia fiber fabric had the highest ballistic energy absorption (168.91 J) and limit velocity (201.43 m/s). The ones with 30 vol% displayed a higher level of physical integrity. The SEM micrographs demonstrated the failure mechanisms were associated with delamination and fiber breakage. There was a small variation in residual velocity between the composites reinforced with 10, 20, and 30 vol% of raffia, with 826.66, 829.75, and 820.44 m/s, respectively. [ABSTRACT FROM AUTHOR]

AbstractTo study the influence of the thickness effect on the impact performance of ZK61m magnesium alloy plate, the influence of ogival projectile on the impact performance of magnesium alloy plate of different thicknesses is analyzed through experiments and numerical simulations, the ballistic limits and failure modes of different thicknesses of the punch target plate are obtained. The velocity of the plug is analyzed by introducing the extruded chisel block velocity model. The experimental results show that the ballistic limit value of the target plate in a specific thickness interval (7 ∼ 11 mm) increases slowly with the increase of its thickness, and the failure mode is dominated by the shear punching failure and accompanied by the tensile failure. The plugs formed in the experimental process are consistent with the extruded chisel block velocity model. Numerical simulation results show that the MJC fracture criterion predictions deviate from the experimental results due to the overestimation of the material ductility, while the Lode parameter dependent MMC fracture criterion, which can better predict the ballistic behavior and failure modes of the target plate. [ABSTRACT FROM AUTHOR]

Multi-layer ceramic/fiber reinforced polymer (FRP) composite, especially Al2O3/carbon-aramid hybrid FRP composite, is a common ceramic composite armor system (CCAS) in the protection field. Aiming at selecting an optimal configuration from several schemes with different discrete structural parameters, including the thickness ratio of carbon fiber (CF) to aramid fiber (AF), the prepreg's number of layers (PNL) of CF and AF, etc., a two-step comprehensive optimization and evaluation method is proposed based on the parametrical study of the ballistic behavior and improved analytical hierarchy process (AHP) conducted by finite element analysis (FEA) and Python programming, respectively. The results demonstrate the effectiveness of this two-step methodology despite the influence of these discrete factors on the ballistic behavior is intricate. Besides, when the PNL is less, the configuration with the PNL of CF is 8, the thickness ratio of CF to AF is 3:7 and the PNL of AF is 14 is the desirable design scheme with the highest comprehensive ballistic behavior. [ABSTRACT FROM AUTHOR]

As one of the most widely used personal protective equipment (PPE), body armors play an important role in protecting the human body from the high-velocity impact of bullets or projectiles. The body torso and critical organs of the wear may suffer severe behind-armor blunt trauma (BABT) even though the impactor is stopped by the body armor. A type of novel composite material through incorporating shear stiffening gel (STG) into ethylene-vinyl acetate (EVA) foam is developed and used as buffer layers to reduce BABT. In this paper, the protective performance of body armors composed of fabric bulletproof layers and a buffer layer made of foam material is investigated both experimentally and numerically. The effectiveness of STG-modified EVA in damage relief is verified by ballistic tests. In parallel with the experimental study, numerical simulations are conducted by LS-DYNA® to investigate the dynamic response of each component and capture the key mechanical parameters, which are hardly obtained from field tests. To fully describe the material behavior under the transient impact, the selected constitutive models take the failure and strain rate effect into consideration. A good agreement between the experimental observations and numerical results is achieved to prove the validity of the modelling method. The tests and simulations show that the impact-induced deformation on the human body is significantly reduced by using STG-modified EVA as the buffering material. The improvement of protective performance is attributed to better dynamic properties and more outstanding energy absorption capability of the composite foam.

Functionally graded materials (FGMs) are promising protective structures for lightweight armor plates because of their features and designability. However, traditional discretely layered FGMs with macroscopic interfaces can generate unfavorable interlaminar stresses under ballistic attacks, eventually leading to delamination or interlayer tearing. Herein, we constructed new B4C/2024Al FGMs without sharp interfaces between layers. The FGM armor systems with varying through-the-thickness distributions were tested against 7.62 mm armor-piercing incendiary projectiles. The effects of compositional gradient exponent on the damage characteristics, stress distribution and energy evolution were numerically and experimentally investigated. The results indicated that the smooth transition within through-the-thickness microstructures effectively avoided the occurrence of interlayer delamination or tearing. The compositional gradient exponent played an essential role in the impact response of the FGM targets. The FGM having a linear composition gradient outperformed other nonlinear types with respect to energy absorption and ballistic properties due to the reduced tensile wave strength and prolonged projectile-target interaction time. Furthermore, the structural optimization problem with the objective of maximizing ballistic efficiency was solved using the conjugate gradient method, and the optimal design of the FGM targets was achieved. The current research provides a promising design guideline for developing and optimizing new advanced lightweight composite armor.

Finite element analysis has been carried out to study the effect of stress triaxiality cut-off value in the fracture criterion on the ballistic behavior of 9.94 mm thick Al2024-T351 plates impacted by rigid blunt-, hemisphere- and ogival-nosed projectiles. The plastic and fracture behavior of plates are described by a modified Johnson-Cook (MJC) model and our recently proposed DF2021 criterion, which are implemented into ABAQUS/Explicit finite element code with VUMAT subroutine. The stress triaxiality cut-off parameter in the DF2021 criterion is varied as 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5 with a larger stress triaxiality cut-off parameter corresponding to a lower stress triaxiality cut-off value. The effect of stress triaxiality cut-off values on the ballistic behavior of the targets against three different nose-shaped projectiles is evaluated and compared in terms of ballistic limit velocities, residual velocities, and failure patterns in the impact process. It is observed that the ballistic limit velocity increases with the stress triaxiality cut-off value under the impact of blunt-nosed projectiles while it first decreases and then increases with the stress triaxiality cut-off value under the impact of the hemisphere- and ogival-nosed projectiles. The formed shear plug or fragments exhibit different profiles with variations of the stress triaxiality cut-off value under the impact of hemisphere- and ogival-nosed projectiles, but uniformly exhibit a cylinder shape under the impact of blunt-nosed projectiles. The numerical results are compared with available experiments. It is found that the predictions from the DF2021 criterion with a cut-off parameter of 0.1 have the best agreement with the experiments. The reason causing the difference in the ballistic behavior due to the change of stress triaxiality cut-off value is discussed by analyzing the stress states of failed elements and the energy dissipation. The objective of the study is to evaluate the necessity of considering the stress triaxiality cut-off value in a fracture criterion in predicting ballistic behavior through finite element simulations.

The search for unexplored natural materials as an alternative to synthetic components has driven the development of novel polymeric composites reinforced with environmentally-friendly materials. Natural lignocellulosic fibers (NLFs) have been highlighted as potential reinforcement in composite materials for engineering applications. In this work, a less known Amazonian fiber, the ubim fiber (Geonoma baculifera), is investigated as a possible reinforcement in epoxy composites and was, for the first time, thermally characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Additionally, its chemical structure was elucidated by Fourier transform infrared spectroscopy (FTIR). Ballistic tests were also performed against the threat of a 7.62 mm high-speed lead projectile. The results were statistically analyzed by the Weibull statistical analysis method. FTIR analysis showed the functional groups normally found for NLFs highly rich in cellulose, hemicellulose, and lignin. The TGA/DTG results showed the onset of thermal degradation for the composites (325~335 °C), which represents better thermal stability than isolated ubim fiber (259 °C), but slightly lower than that of pure epoxy (352 °C). The DSC results of the composites indicate endothermic peaks between 54 and 56 °C, and for the ubim fibers, at 71 °C. Ballistic tests revealed higher energy absorption in composites with lower fiber content due to the more intense action of the brittle fracture mechanisms of the epoxy resin, which tended to dissipate more energy. These failure mechanisms revealed the presence of river marks, cracks, and broken fibers with a detachment interface. These results may contribute to the production of ubim fiber-reinforced composites in engineering applications, such as ballistic armors. [ABSTRACT FROM AUTHOR]

Arapaima scales possess a hierarchical structure capable of absorbing a considerable amount of energy before fracture. These natural dermal armors present significant potential in the sustainable development of cost-effective composites. This work aimed, for the first time, to analyze the impact resistance and ballistic performance of arapaima scale-reinforced epoxy composites and their potential application in multilayered armor systems (MAS). Composite plates were prepared with 20%, 30%, and 40 vol% of arapaima scales. Composite specimens were subjected to notched Izod impact and residual velocity stand-alone tests and their MAS through backface signature (BFS) tests, with their fracture surfaces studied using SEM. The Izod tests confirmed the effect of scales' volume fraction on the energy absorbed by the composites, showing an increase with volume fraction. Residual velocity tests showed that composites with 30 vol% of scales resulted in the most significant improvement in absorbed energy. All MAS formulations presented BFS depths lower than the trauma limit specified by the NIJ standard. Fractographic analysis showed that the scales' toughening mechanisms improved the composites' energy absorption capacity. The experimental results substantiate the potential use of arapaima scales as a reinforcement agent in polymeric composites, with 30 vol% being the optimal volume fraction for energy-absorbing applications. [ABSTRACT FROM AUTHOR]

From the mechanistic point of view, magnesium alloys are lightweight materials and are receiving increasing attention in the past several years in various fields. Prof. Liang Zhen from Harbin Institute of Technology, China and the United State military are showing keen interest in the development of magnesium alloys as ballistic resistant material. However, their use is still limited owing to low ductility, low formability, and average mechanical properties. The magnesium alloys components must withstand the shockwave under hypervelocity ballistic impact. The ballistic testing can produce gradient variations of the strain and stress-energy away from the crater, and useful for the development of these alloys in the military and aerospace industry. Therefore, the present review article shed light on the post deformation analysis of the Mg alloys subjected to the different projectiles under ballistic impact, and the underlying mechanisms were discussed. In the end, some important issues regarding the ballistic impact and further studies in this field were proposed.

From the mechanistic point of view, magnesium alloys are lightweight materials and are receiving increasing attention in the past several years in various fields. Prof. Liang Zhen from Harbin Institute of Technology, China and the United State military are showing keen interest in the development of magnesium alloys as ballistic resistant material. However, their use is still limited owing to low ductility, low formability, and average mechanical properties. The magnesium alloys components must withstand the shockwave under hypervelocity ballistic impact. The ballistic testing can produce gradient variations of the strain and stress-energy away from the crater, and useful for the development of these alloys in the military and aerospace industry. Therefore, the present review article shed light on the post deformation analysis of the Mg alloys subjected to the different projectiles under ballistic impact, and the underlying mechanisms were discussed. In the end, some important issues regarding the ballistic impact and further studies in this field were proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

In this research, the ballistic behavior and microstructure evolution of 45vol% B 4 C/AA2024 composites produced by pressure infiltration method were studied. The ballistic behavior of composites was carried out using 7.62 mm armor-piercing incendiary (API). The results demonstrate that the 45vol% B 4 C/AA2024 composites has excellent ballistic performance and the protection coefficient reaches 3.6. The residual microstructure of composites after impact was mainly investigated by the transmission electron microscope (TEM). The results show that the residual microstructure of B 4 C particles mainly include dislocations, stacking faults, twins and poly-crystallization. For Al matrix, the residual microstructure is mainly the existence of large numbers of dislocations especially in the area near the sharp corner of B 4 C particles. In addition, inhomogeneous precipitates of AA2024 matrix were observed after impact. [ABSTRACT FROM AUTHOR]

In recent years, the interest of the scientific community in perforated plates for ballistic protection has increased. Perforated plates do not represent protection by themselves, rather, they are used in the armour systems of armoured vehicles, in conjunction with base armour, since they are intended to induce bend stresses, where a penetrating core fracture occurs. The fragments are subsequently stopped by base armoured vehicle armour. Although for the first time used several decades ago, perforated plates are found to be attractive even today. The main reason is the combination of very convenient properties. Besides high mass effectiveness, they possess a high multi-impact resistance, since their perforations arrest cracks. Therefore, a relatively wide array of materials is suitable for perforated plate fabrication, ranging from alloy steel to some types of cast iron. Being made of metallic materials, raw material costs are relatively low compared to ceramics or composite materials, making them very attractive for present and future armoured vehicles. Finally, armour system consisting of a perforated plate and base plate at some distance, reduce the effectiveness of both shaped charge jets and act as blast mitigators.

The mechanical behavior of aluminum alloy under impact loading using different configurations is described. Perforation tests are referred in this work at wide ranges of specimen using several projectile shapes to analyse their effect on the ballistic curve VR-V0 (conical, hemispherical and blunt), with a diameter of 6.mm. A wide range of impact velocities from 40 to 100 m/s has been used. Experimental and numerical analysis have been carried out to predict the mechanical behaviour of the studied aluminium alloy. This analysis has been done using a high-pressure gas gun. Specimens were prepared from standard 1.0 mm and 1.5 mm thick aluminum sheets with 13x13 cm plates. The resistance and the energy absorbed by the aluminum sheets under dynamic load were obtained by measuring the initial and residual velocities of the projectiles. The experimental and numerical results are presented and compared in terms of ballistic curve VR-V0, a good correlation was observed.

In this paper, a 2D analytical model is introduced for predicting the ballistic behavior of the thin laminated composite plate based on tsai-hill and maximum strain criterions. At first, by using the determination of the moment deformation function along with the expansion of transverse wave from impact point, the nonlinear strains and stresses in the composite plate are calculated. Then, the energy absorbed due to failure modes and deflection of composite plate such as elastic deformation energy, longitudinal and lateral fracture energy, kinetic energy of local movement, delamination and matrix cracking, energy is calculated. For investigation of the various failed layers Tsai-Hill and maximum strain criterions are used. In addition to the effects of strain rate is applied momentarily on the mechanical properties of the composite layers during Penetration process. Finally, the present analytical model based on Tsai-Hill and maximum strain criterions is compared with experimental results. The results show that maximum strain criterion with respect to Tsai-Hill criterion has good agreement with experimental results in the calculation of ballistic limit velocity. According to the obtained results the share of fracture energy compared to the elastic deformation energy by increasing the thickness becomes more and more. Also, the kinetic energy of the local movement, delamination and matrix cracking energy have lower share with respect to fracture and elastic deformation energies in the process of energy absorption. [ABSTRACT FROM AUTHOR]

Functionally gradient materials (FGMs) primarily composed of a discretely layered structure with relatively sharp macroscopic interfaces are highly susceptible to interlayer failure under impact loading. Nacre is regarded as a model system for lightweight armor with high impact-resistant performance owing to its multiple length-scale and gradient structures. However, the simultaneous translation of both structural features into artificial assemblies remains challenging. Herein, we constructed new B 4 C/2024Al FGMs with eliminated sharp interfaces, which reproduced the hierarchical and gradient architectures of nacre. A combined experimental and numerical approach was employed to investigate the protective mechanisms of nacre-like FGMs subjected to 7.62 mm armor-piercing incendiary bullet, and two homogeneous composites were also tested under the same conditions for comparison purposes. The FGMs exhibited improved performance to resist ballistic attacks and maintain integrity compared with the uniform structures. As the ceramic contents decreased along the thickness, the energy dissipation mechanisms transitioned from eroding projectile to plastic deformation. The toughness gradient and varying energy dissipation modes prevented the formation of crushed cones at the ceramic-rich layers. The nacre-like structure created several extrinsic toughening mechanisms, which led to the increased energy-absorbing capability of the target. Meanwhile, the eliminated abrupt interfaces avoided the occurrence of interlayer tearing by diminishing the tensile wave strength and the sudden change of wave impedance, which prolonged the projectile-target interaction period and strengthened the eroding effect on the projectile. The present study opens new opportunities to design advanced lightweight FGMs armors with high impact-resistant protective performance. [ABSTRACT FROM AUTHOR]

Ballistic gelatin is the simulant of the human body during field tests in forensics and other related fields, due to its physical and mechanical similarities to human trunk and organs. Since the ballistic gelatin used in present has important issues to overcome, an alternative approach is the use of gelatin-polymer composites, where a key factor is the insertion of biocompatible materials, which replicate accurately the human tissues. In order to be able to obtain an improved material in terms of mechanical performances by an easy industrial-scale technology, before the verification of the ballistic parameters by shooting in agreement with military standards, one of the best and cheapest solutions is to perform a thorough check of their rheological properties, in standard conditions. [ABSTRACT FROM AUTHOR]

Os materiais compósitos de matriz polimérica (PMCs) reforçados por fibras são considerados excelentes materiais de engenharia. Em aplicações estruturais, quando uma elevada relação resistência peso é fundamental para o projeto, os PMCs vêm substituindo com sucesso diversos materiais convencionais. Materiais têxteis são utilizados, desde a 2ª Guerra Mundial, como blindagens balísticas. Materiais fabricados com fibra do polietileno de altíssimo peso molecular (UHMWPE) são empregados na produção de blindagens, para proteção pessoal e em carros de combate. Todavia, em virtude de terem sido desenvolvidos e comercializados mais recentemente, não existem informações suficientes sobre o desempenho balístico desses materiais após a sua exposição aos agentes ambientais. No presente trabalho foi estudado o comportamento balístico de placas compósitas fabricadas com fibra de polietileno de altíssimo peso molecular (UHMWPE), após sua exposição à radiação gama. Os resultados dos testes balísticos foram relacionados com as alterações macromoleculares induzidas pela irradiação por meio de ensaios mecânicos (dureza, impacto e flexão) e físico-químicos (espectroscopia no infravermelho, calorimetria diferencial de varredura e análise termogravimétrica). Foi verificado que a irradiação gama provoca modificações nas cadeias macromoleculares do polímero, que alteram as propriedades mecânicas do compósito de UHMWPE, reduzindo, nas doses de radiação mais elevadas, o seu desempenho balístico. Estes resultados são apresentados e discutidos.The fiber reinforced polymer matrix composites (PMCs) are considered excellent engineering materials. In structural applications, when a high strength-to-weight ratio is fundamental for the design, PMCs are successfully replacing many conventional materials. Since World War II textile materials have been used as ballistic armor. Materials manufactured with ultrahigh molecular weight polyethylene (UHMWPE) fibers are used in the production of armor materials, for personnel protection and armored vehicles. As these have been developed and commercialized more recently, there is not enough information about the action of the ionizing radiation in the ballistic performance of this armor material. In the present work the ballistic behavior of composite plates manufactured with ultrahigh molecular weight polyethylene (UHMWPE) fibers were evaluated after exposure to gamma radiation. The ballistic tests results were related to the macromolecular modifications induced by the environmental degradation through mechanical (hardness, impact and flexure) and physicochemical (infrared spectroscopy, differential scanning calorimetry and thermal gravimetric analysis) tests. Our results indicate that gamma irradiation induces modifications in the UHMWPE macromolecular chains, altering the mechanical properties of the composite and decreasing, for higher radiation doses, its ballistic performance. These results are presented and discussed.

This paper presents the experimental study of fiber type, fabric structure, orientation of fabric plies and thickness on the ballistic impact behavior of aramid and ultra-high molecular weight polyethylene (UHMWPE) composite laminates. Aramid composite laminates are reinforced by three kinds of fabric structures and UHMWPE composite laminates are reinforced by two kinds of fabric structures. The laminates are fabricated via autoclave curing process. The ballistic behavior of composite laminates is evaluated by ballistic limit velocity, and energy absorbed at ballistic limit. Through a series of ballistic tests, it is demonstrated that unidirectional composite laminates exhibit higher ballistic limit velocity and energy absorption on unit weight basis compared to other laminates. Interesting results are shown by UD-UHMWPE-H62® and UD-UHMWPE-Endumax® fabric-reinforced laminates. Orientation of fabric plies is found to have insignificant effect on ballistic behavior irrespective of material type. A bi-linear relationship is found between the ballistic limit velocity, energy absorption and specimen thickness. [ABSTRACT FROM AUTHOR]

Highlights: [•] We examine the ballistic impact behavior of single-ply 3D orthogonal woven fabric composites. [•] The failure mechanisms are investigated in term of the geometry sizes of penetration holes in the thickness direction. [•] Plugging and hole friction are the dominant failure modes for thinner composite laminates. [•] Delamination, fiber tension and bulge become the main failure modes for thicker composite laminates. [•] Impact properties will increase if in-plane yarns and Z-yarns of single-ply 3D orthogonal woven fabric are optimized. [Copyright &y& Elsevier]

Abstract: In this article we investigate the ballistic behavior of diffusions in random environment. We introduce conditions in the spirit of and of the discrete setting, cf. [A.-S. Sznitman, On a class of transient random walks in random environment, Ann. Probab. 29 (2) (2001) 723–764; A.-S. Sznitman, An effective criterion for ballistic behavior of random walks in random environment, Probab. Theory Related Fields 122 (4) (2002) 509–544], that imply, when , a law of large numbers with non-vanishing limiting velocity (which we refer to as ‘ballistic behavior’) and a central limit theorem with non-degenerate covariance matrix. As an application of our results, we consider the class of diffusions where the diffusion matrix is the identity, and give a concrete criterion on the drift term under which the diffusion in random environment exhibits ballistic behavior. This criterion provides examples of diffusions in random environment with ballistic behavior, beyond what was previously known. [Copyright &y& Elsevier]

Fiber reinforced polymeric-matrix composites have been extensively applied to various structural components successfully replacing many conventional materials, especially in land, sea, air and aerospace vehicles and in sporting goods. Since World War II, polymeric materials have been used in military applications, especially as ballistic armor. Due to their great capacity for absorbing the kinetic energy of projectiles, ultrahigh molecular weight polyethylene (UHMWPE) fibers are presently used in composite armors for personnel and vehicle protection. However, polymers are liable to degrade when subjected to environmental agents such as sunlight, rain, radiation, etc. The aim of the present work was to use accelerated tests, short exposures to weather and gamma radiation, to study the influence of aging agents on the mechanical and ballistic performance of a UHMWPE composite armor. Composite panels were submitted to ballistic tests using 9mm caliber projectiles. The mechanical and ballistic characteristics of composite were related to macromolecular modifications induced in the polymer by the environment through physicochemical testing. Exposure to environmental agents induces changes in the UHMWPE macromolecular chains, altering the mechanical properties and the ballistic behavior of the composite. The use of accelerated tests may be an adequate way to predict the effects of environmental agents on the performance of ballistic armor. These results are presented and discussed. [Copyright &y& Elsevier]

In recent years, the interest of the scientific community in perforated plates for ballistic protection has increased. Perforated plates do not represent protection by themselves, rather, they are used in the armour systems of armoured vehicles, in conjunction with base armour, since they are intended to induce bend stresses, where a penetrating core fracture occurs. The fragments are subsequently stopped by base armoured vehicle armour. Although for the first time used several decades ago, perforated plates are found to be attractive even today. The main reason is the combination of very convenient properties. Besides high mass effectiveness, they possess a high multi-impact resistance, since their perforations arrest cracks. Therefore, a relatively wide array of materials is suitable for perforated plate fabrication, ranging from alloy steel to some types of cast iron. Being made of metallic materials, raw material costs are relatively low compared to ceramics or composite materials, making them very attractive for present and future armoured vehicles. Finally, armour system consisting of a perforated plate and base plate at some distance, reduce the effectiveness of both shaped charge jets and act as blast mitigators. [ABSTRACT FROM AUTHOR]

• The dominant failure mode of the plates is shear plugging in the tests with impact velocities above or slightly below the ballistic limit velocity. • It is also found that the Lode angle affects the fracture behavior of the AA6061-T651 significantly. • The simulation prediction using the MJC fracture criterion significantly overestimated the ballistic limit velocity about 4.9% while the predictions using the WMJC fracture criterion obtained very well accordance with the test results (in 0.15%). The results also show that the fracture criterion with the incorporation of the Lode angle parameter can accurately predict the residual velocity and ballistic limit of the projectile. • For the ductile metal, in the simulation results based on the Lode angle dependent fracture criterion, the degree of effect of the Lode angle decreases with the increase of the ductility of the metallic materials. To reveal the effect and necessity of introducing the Lode angle into a fracture criterion in ballistic performance simulations of metallic Plates, experimental and numerical work were carried out on 6061-T651 aluminum alloy (AA6061-T651) thick Plates. Firstly, a series of ballistic tests were conducted via a one-stage gas gun test facility that blunt-nosed projectiles of φ 12.68 mm penetrated onto 20 mm thick AA6061-T651 Plates at impact velocities ranging from 280.0 m/s to 400.0 m/s. Subsequently, experimental results in terms of initial versus residual velocities of the projectiles and the failure characteristics of the Plates were reported. Experimental results showed that shear plugging was the dominating failure mode of the perforated Plates. Meanwhile, numerical results corresponding to the ballistic tests were obtained using finite element (FE) simulations via the commercial software ABAQUS/Explicit. Specially, we compared the results between simulations using a Lode dependent fracture criterion and a Lode independent. Finally, the FE simulations indicated that using a Lode dependent fracture criterion better predicts the ballistic behavior of the thick AA6061-T651 Plates under impact of blunt-nosed projectiles. It is also found that the Lode angle affects the fracture behaviour of the AA6061-T651 significantly. And this effect decreases with the increase of the materials' ductility. [ABSTRACT FROM AUTHOR]