Ballistic Limit Research Articles

Ballistic limit and damage assessment of hybrid fibre-reinforced cementitious thin composite plates under impact loading

Impact resistance of reinforced concrete (RC) structures can be significantly improved by strengthening RC members with thin composite layers featuring high damage tolerance. Indeed, to limit the well-known vulnerability of cement-based materials against impact loading, the synergistic effects of short fibres and continuous textile meshes as hybrid reinforcement has been proved to be highly beneficial. This paper addresses the characterisation of novel cement-based hybrid composites through accelerated drop-weight impact tests conducted on rectangular plates at different impact energies. Two distinct matrices are assessed, with particular interest in a newly developed limestone calcined clay cement (LC3)-based formulation. Important parameters quantifying energy dissipation capability, load bearing capacity and damage are cross-checked to compute the ballistic limit and estimate the safety-relevant characteristics of the different composites at hand. Although textiles alone can improve the damage tolerance of fine concrete to some extent, the crack-bridging attitude of short, well-dispersed fibres in hybrid composites imparts a certain ductility to the cement-based matrices, allowing a greater portion of the textile to be activated and significantly reducing the amount of matrix spalling under impact.

Ballistic response of additively manufactured AA6061/AA7075 multistack plate for armor-piercing projectile

The current ballistics research study focuses heavily on substituting heavy metals with lightweight materials to make mobility more accessible and effective for all armor applications. To do so, the researchers found that aluminum alloys are the better alternative to substitute steel armor due to their high strength-to-weight ratio. Therefore, this research conducted ballistic studies on aluminum alloys using the Finite Element Analysis (FEM) methodologies and associated mathematical analysis. This Research primarily focuses on the damage factor, ballistic limit, and residual velocity of the bullet following penetration of target plates. In this investigation, the Johnson-Cook fracture and Recht-Ipson models were implemented on materials AA6061-T6 and AA7075-T6. The main objective of these models is to establish the damage factor and verify whether it is less than unity; if the factor is less than unity, it is eligible to study the residual velocity of the bullet after penetration into the target armor plate. The target plate was impacted with a 7.62 mm armor-piercing projectile with an impact velocity of 500 m/s. Monolithic plates of 18 mm thickness were evaluated initially. After that, the multilayered stack of each 3 mm thick plate was analyzed, and studied the effectiveness of using a multilayered stack armor plate.

Development and ballistic impact study on environment friendly sustainable jute reinforced carbon black/lignin-based elastomeric flexible composites

This study compares the behaviour of jute/elastomer bio-composites based on lignin and carbon black under high-velocity impact using experimental methods. Compared to carbon black, SEM data showed that lignin was more evenly distributed across the yarns. The space between the threads was filled by the good interaction of lignin and rubber. Additionally, the findings of the tensile and dynamic compression tests demonstrate that adding lignin to a matrix enhances the tensile strength of rubber samples and composites. On single-layer and three-layer composites made of lignin and carbon black, experimental tests were conducted utilizing a gas gun apparatus with a flat projectile travelling between 100 and 180 m/s. The damage behaviour of the proposed composites is analyzed. The findings demonstrate that the composites' energy absorption and ballistic velocity have enhanced due to the jute-woven fabric cover and the diluted rubber matrix. The results reveal that single and three-layer lignin-based composites exhibit better ballistic limits with an increase of 12.5% and 23.8% over composites based on single and three-layer carbon black composites. Lignin-based composites outperform carbon black composites in terms of energy absorption with single and three-layered lignin-based composites absorbing 23.5% and 25.86% more energy compared to single and three-layered carbon black-based composites. Additionally, the analysis of energy absorption at the ballistic limit for single-layer and three-layer lignin-based composites reveals an increase of 26.56% and 53.35%, respectively, compared to carbon black-based composites.

An experimental study on ballistic limit: the effect of hole drilling on the mechanical properties of a polymeric composite plate produced by the resin transfer molding method

The high fracture strength and exceptional impact resistance of polymer-based composites are of paramount importance to various industries like aerospace, automotive, and construction. The resin transfer molding (RTM) process is used to produce composite samples of superior quality, minimal porosity, and reduced lamination defects. In the present study, the RTM method was employed to fabricate glass fiber-reinforced composites, aiming to investigate their specific mechanical properties and structural performance. The study initially determined the ballistic limit of the produced samples. Subsequently, experimental investigations were carried out to examine the impact of hole drilling on the tensile strength, flexural strength, and impact resistance of the samples. The results revealed that the produced polymer plate demonstrated a ballistic limit with a pressure of 11 bar and a speed of 104 m/s, leading to ball restriction in the plate. The sample without holes showed the highest fracture force, while samples with three and five holes exhibited reduced fracture forces. Additionally, bending force and impact resistance were lower in samples with multiple holes compared to the sample without holes. The impact resistance of the sample with five holes was the lowest among all configurations. The study revealed that the presence of three holes arranged in a row has a lesser impact on reducing the ultimate tensile force compared to the effect of five holes. Moreover, the bending test results indicated that sample failure occurred on the side under tension, resulting in higher bending forces than tensile forces.

High‐dimensional limit theorems for SGD: Effective dynamics and critical scaling

AbstractWe study the scaling limits of stochastic gradient descent (SGD) with constant step‐size in the high‐dimensional regime. We prove limit theorems for the trajectories of summary statistics (i.e., finite‐dimensional functions) of SGD as the dimension goes to infinity. Our approach allows one to choose the summary statistics that are tracked, the initialization, and the step‐size. It yields both ballistic (ODE) and diffusive (SDE) limits, with the limit depending dramatically on the former choices. We show a critical scaling regime for the step‐size, below which the effective ballistic dynamics matches gradient flow for the population loss, but at which, a new correction term appears which changes the phase diagram. About the fixed points of this effective dynamics, the corresponding diffusive limits can be quite complex and even degenerate. We demonstrate our approach on popular examples including estimation for spiked matrix and tensor models and classification via two‐layer networks for binary and XOR‐type Gaussian mixture models. These examples exhibit surprising phenomena including multimodal timescales to convergence as well as convergence to sub‐optimal solutions with probability bounded away from zero from random (e.g., Gaussian) initializations. At the same time, we demonstrate the benefit of overparametrization by showing that the latter probability goes to zero as the second layer width grows.

Energy dissipation mechanism and ballistic characteristic optimization in foam sandwich panels against spherical projectile impact

This study systematically examines the energy dissipation mechanisms and ballistic characteristics of foam sandwich panels (FSP) under high-velocity impact using the explicit non-linear finite element method. Based on the geometric topology of the FSP system, three FSP configurations with the same areal density are derived, namely multi-layer, gradient core and asymmetric face sheet, and three key structural parameters are identified: core thickness (tc), face sheet thickness (tf) and overlap face/core number (no). The ballistic performance of the FSP system is comprehensively evaluated in terms of the ballistic limit velocity (BLV), deformation modes, energy dissipation mechanism, and specific penetration energy (SPE). The results show that the FSP system exhibits a significant configuration dependence, whose ballistic performance ranking is: asymmetric face sheet > gradient core > multi-layer. The mass distribution of the top and bottom face sheets plays a critical role in the ballistic resistance of the FSP system. Both BLV and SPE increase with tf, while the raising tc or no leads to an increase in BLV but a decrease in SPE. Further, a face-core synchronous enhancement mechanism is discovered by the energy dissipation analysis, based on which the ballistic optimization procedure is also conducted and a design chart is established. This study shed light on the anti-penetration mechanism of the FSP system and might provide a theoretical basis for its engineering application.

Ballistic performance of double-layered plates Q235 and 45 steel subjected to impact by projectiles of middle strength

The ballistic resistance behavior of double-layer steel plates incorporated with different materials is experimentally and numerically investigated by using blunt- and ogive-nosed projectiles of middle strength. These materials are Q235 steel (low strength and high ductility) and 45 steel (high strength and low ductility). Experimental results showed that the ballistic resistance is better for the double-layer plates with the front layer of low ductility and high strength and the back layer of high ductility and low strength material than that of the opposite layer order impacted by ogive-nosed projectiles, but the situation is opposite for blunt-nosed projectiles. The ballistic limit of H + A (753.85 m/s) is increased by 29.5% when compared to that of A + H (582.19 m/s) for ogive-nosed projectiles of 45 steel. In the case of blunt projectiles, a 2.8% decrease in the ballistic limit of middle-strength projectile. Ogive-nosed projectiles are more sensitive than blunt-nosed projectiles when it comes to the effect of the layer order of the double-layer plates. Moreover, the ballistic limit velocities of blunt-nosed projectiles are obviously bigger than that of ogive-nosed projectiles for the double-layer plates of the front layer of low strength, while the situation is opposite for the double-layer plates of the front layer of high strength. Furthermore, the projectiles lose some mass and length after impact. The deformation of projectiles is also concerning the nose shape and velocity of projectiles, as well as the layer order of the double-layer plates. Finally, numerical simulation results are obtained and compared using the ABAQUS subroutine VUMAT-modified Johnson-Cook material model. And these results fairly agree with the experiment.

A novel flexible biocomposite with hemp woven fabric and natural rubber based on lignin green filler: investigation numerical and experimental under high-velocity impact

In this study, the comparison of the behavior of hemp/elastomeric biocomposites based on lignin and carbon black has been investigated experimentally and numerically under the influence of high speed. SEM images confirmed the dispersion and good interaction of lignin in natural rubber with a uniform surface coverage of fibers and the gap of yarns. The results of tensile and dynamic compression tests showed that elastomer with lignin filler improves tensile strength for rubber samples and composites compared to carbon black. The high-velocity impact tests were performed on single-layer and three-layer composites based on lignin and carbon. The penetration resistance and failure mechanism of the composites during impact were validated using a constitutive material model for hemp fabric and a user-defined material model (VUMAT) for the nonlinear behavior of rubber materials with a damage criterion in ABAQUS/Explicit. For one-layer and three-layer flexible composites based on lignin, the ballistic limit is 49 and 96 m s−1, respectively. Compared to carbon-based composites, it has increased by 11.36 and 13% for one-layer and three-layers, respectively. Using the dilute matrix to cover hemp fabric increases the resistance of this type of fabric against high-speed impact. Through tensile failure, the stress is transferred to the surrounding fiber bundles so that more threads can participate in the load-bearing process. As a result, the penetration depth in lignin-based composites is lower, and the protective margin is greater, which increases energy absorption.

Enhancing the ballistic resistance of steel/aluminum bilayer armor plates through explosive welding

This work presents a comprehensive analysis of the ballistic response of Q235 steel/6061-T6 aluminum bilayer plates fabricated via explosive welding, with a special focus placed on elucidating the mechanisms of ballistic resistance enhancement due to the bonded interface. For comparison purposes, unbonded Q235 steel/6061-T6 aluminum bilayer plates (e.g. being stacked together or spaced with an air gap) were also investigated. Ballistic tests were carried out to compare the residual velocities and failure behaviours of the welded and unwelded bilayer plates. Computational models were built in LS/DYNA and validated with the experiment. Experimental results showed that the ballistic limit velocity of the explosively-welded plate is 13.4% and 9.4% higher than those of the in-contact plate and air-gapped plate. Simulation results suggested that the enhanced ballistic resistance was attributed to its welded interface. On the one hand, the welded interface allowed effective stress attenuation within the steel layer leading to a greater damage tolerance and more energy dissipation during the prolonged response time. On the other hand, when deforming together with the steel layer, the welded interface enforced a uniform indentation on the central region of the aluminum substrate leading to greater energy absorption due to compression and thinning of the material.

A comparative study on dynamic deformation and ballistic impact response of Ti–4Al–2.5V–1.5Fe–0.25O and Ti–6Al–4V alloys

Titanium alloys are most suitable for lightweight armour applications due to their superior strength to weight ratio, and α+β Ti alloy Ti–6Al–4V is widely used in armour applications. One of the critical factors limiting the widespread use of Ti alloys in armour application is their high cost. Recently, Allegheny Technologies Incorporated introduced ATI-425® Ti alloy with the chemical composition of Ti–4Al-2.5V-1.5Fe-0.25O as a low-cost alternative to Ti–6Al–4V. Though ATI-425 Ti alloy is primarily intended for armour applications, only limited ballistic results are available in the open literature. In the present work, we compare the quasi-static, dynamic deformation, ballistic impact response and post-deformation microstructure of a low-cost α+β Ti alloy ATI-425 with that of Ti–6Al–4V alloy. Analysis of the results showed that both alloys showed similar yield strength values during quasi-static tension and compression tests, while ATI-425 Ti alloy showed higher tensile ductility, Charpy-V notch impact energy and dynamic flow stress than Ti-6Al-4V. The ATI-425 Ti alloy also exhibited slightly better ballistic performance measured in terms of V50 ballistic limit velocity. Detailed microstructural analysis on quasi-static and dynamic compression-tested samples showed mainly {101–2} tensile twins, whereas {101–2} and {112–1} tensile twins are observed in ballistic-tested samples of both the alloys. Activation of deformation twinning in ATI-425 Ti alloy with higher oxygen is attributed to lower Al content which enhances the twinning activity. Adiabatic shear band (ASB)-induced plugging mechanism is ascertained as the perforation mode in both alloys during the ballistic impact. Analysis of propensity to ASB formation indicated that Ti-6Al-4V has a slightly better resistance to ASB formation than ATI-425 Ti alloy. The improved ballistic performance of ATI-425 Ti alloy in comparison to Ti-6Al-4V is attributed to the higher dynamic flow stress, Charpy-V notch impact energy absorption, and moderate resistance to adiabatic shear band formation.

Effect of incorporating Lode angle into fracture criterion on predicting ballistic resistance of 6061-T651 aluminum alloy plates with different thicknesses struck by blunt projectiles

According to existing research, in addition to the second deviatoric stress invariant, Lode angle parameter (hereinafter abbreviated as Lode angle), which is related to the third deviatoric stress invariant, is also required to be taken into account when studying plastic flow and failure of metal materials. In order to study the effect of incorporating Lode angle into fracture criterion on predicting ballistic resistance of 6061-T651 aluminum alloy plates, a one-stage gas gun system was used to conduct ballistic tests of 6061-T651 aluminum alloy plates with different thicknesses when struck by the blunt projectile with a diameter of 12.66 mm and a mass of 34.0 g. Meanwhile, Abaqus/Explicit finite element software with user-defined material subroutine (VUMAT) was used to establish corresponding finite element models. Under the same constitutive model, numerical simulations were carried out by using Lode independent MJC fracture criterion and Lode dependent WMJC fracture criterion. It is found that when using MJC fracture criterion, not only the ductility of material is overestimated in low stress triaxiality state, resulting in significantly higher predicted ballistic limits; but also the predicted material fracture strain in high stress triaxiality state is negative, sometimes causing irrational predictions. Therefore, some modifications to MJC fracture criterion are needed to reasonably predict the impact process. By contrast, the predicted results of Lode dependent WMJC fracture criterion are more consistent with experiments. Besides, as the thickness of the target increases, the ballistic limit shows an “S” shaped growth trend. Overall, for ballistic tests of targets with different thicknesses, WMJC criterion has a better predictive effect than MJC criterion, indicating the importance of incorporating Lode angle into fracture criteria.

Toward a more generalized ballistic limit equation for multi-shock shields

In this paper we develop a single ballistic limit equation for multi-shock shields that is applicable to materials other than those used in its original development, that is applicable to impact scenarios at impact velocities beyond the testable regime and includes an improved projectile density term. The predictions of this ballistic limit equation regarding whether or not a particular multi-shock shield would be perforated by a specific impact was found to compare favorably with both test results and the results of numerical simulation predictions. In the end, the ballistic limit equation developed herein is seen to be not only more applicable to a wider class of spacecraft designs, but also can be used for trade studies that are typically performed to select and optimize multi-shock shielding designs for future spacecraft.

Ballistic performance and damage behavior of three-dimensional angle-interlock woven fabric under ballistic impact: Numerical investigation

3D woven fabrics possess excellent specific performance and processability, making them highly favorable in the field of protective engineering, particularly in applications such as body armor. It is critical to evaluate their ballistic response under various impact loadings for both material manufacturing and application purposes. This paper presents a full-size mesoscale finite element model to investigate the dynamic damage behavior of 3D angle-interlock woven fabric (3DAWF) under ballistic impact. The effectiveness of the proposed numerical model is verified through a comparison with available experimental data in terms of ballistic performance and damage morphology. The effects of projectile shape, impact angle, and pre-stretching loading on the ballistic performance of 3DAWF are discussed. It is observed that 3DAWF demonstrates different impact resistance with different projectile shapes due to variations in the impact area and damage mechanism. The friction generated by projectile sliding plays a significant role in dissipating projectile kinetic energy under oblique impact. Moreover, pre-stretching is found to enhance the ballistic limit and energy absorption of 3DAWF to a certain extent.

Effect of lamination sequence and warhead shape on impact resistance of fiber‐metal laminates

AbstractIn this work, the failure mode and ballistic protection capability of the carbon fiber aluminum alloy laminated target plate under the impact of high‐speed projectile body were studied by ballistic impact test. The effects of the lamination sequence and warhead shape difference on the impact resistance of the laminated aluminum alloy and carbon fiber laminates were analyzed. Two kinds of projectile bodies, flat and oval head, were used to carry out multiple high‐speed impact experiments on four groups of targets with different stacking sequences. By analyzing the result, it is found that the lamination sequence of the target plate has a significant effect on the anti‐impact performance only when the flat head projectile impacts, while the ovoid projectile has almost no effect. In the fiber‐metal composite configuration, the aluminum plate placed in front of the carbon fiber plate showed the best resistance to flat head bullet impact, the ballistic limit speed reached 135 m/s, and the overall impact resistance improved by up to 26% compared with other configurations. Unlike the shear failure caused by flat head projectile, ovoid projectile impact can cause serious tensile and tear damage. Based on the experimental results, it is clear that the laminated structure has better penetration resistance against the flat head projectile, and the placement of aluminum plate on the impact surface can change the failure mode of carbon fiber laminates and improve the energy absorption level of composite plates.Highlights Unlike traditional fiber‐metal laminates, the target plate used in this experiment does not use adhesive, which makes the deformation of the two materials will not affect each other, which is conducive to the study of its own impact resistance. The mechanical behavior and damage failure mode of the target plate under high speed impact load were studied. The impact of ovoid projectile changes the damage failure mode of the target plate. For the configuration of fiber‐metal laminates, the ballistic limit value is as low as 100 m/s, and the energy absorption value fluctuates in the range of 145–190 J with the change of impact velocity. Compared with ovoid projectile, laminated material has stronger impact resistance to flat head projectile. The metal plate arranged on the impact surface can change the damage mode from shear failure to tensile failure, thus greatly improving the ballistic limit and impact resistance, overall impact resistance can be improved by up to 26%.

Novel method in the modeling of adiabatic shear bands in ballistic impact: An application on Inconel 718 alloy

The failure mechanism for thick metal plates ballistically impacted by blunt projectiles is known as an Adiabatic Shear Band (ASB), which results in a catastrophic failure due to concentrated shear deformation. ASBs are generally considered to be a material or structural instability and as such are not controllable. ASBs are also a thermodynamic phenomenon occurring at high strain rates and are characterized by large deformations, localized in a narrow band consisting of highly sheared material. Due to the extreme localization of the shear band, it is difficult to model ASBs using the Finite Element Method, because the mesh size needed to capture it is often not practical for real applications.Validated numerical two-dimensional simulations revealed that the tabulated Johnson-Cook (J-C) material model is successful in predicting this mode of failure only using meshes composed of elements with a size that is of the same magnitude order of the ASB width. Because the ASB width of some high-performance metal alloys such as Inconel 718 is on the order of 1 µm, this material model cannot be used in practical applications to predict ASB.This paper describes the enhancements made to the tabulated J-C material model that allow simulations of Adiabatic Shear Band development, under the correct loading conditions, in meshes with element size of practical use in current engineering applications. Full scale impact tests were used to validate the accuracy of the enhanced material model by comparing the ballistic limit, projectile residual velocity, and failure morphology. It is shown that this approach provides a robust and efficient method for simulating Inconel 718 structures under impact, with meshes composed of element of size compatible with modern commonly available computational resources even when the failure mode is an ASB.

ZK61m magnesium alloy plate thickness effect on the impact characteristics of blunt projectiles experimental and numerical simulation studies

To study the impact resistance of ZK61m magnesium alloy plate, firstly, impact experiments were conducted on magnesium alloy plates of different thicknesses using a one-stage gas gun system to obtain the ballistic limit velocity (BLV) and failure mode of the target plate. In addition, the velocity of the punch plug was analyzed by the squeeze chisel block velocity model. Finally, the corresponding numerical simulations were carried out using the Lode parameter-independent MJC fracture criterion and the Lode parameter-dependent MMC fracture criterion, and the influence mechanism of the Lode parameter on the numerical simulation results was analyzed. The results show that under the impact of the blunt projectile, different thicknesses of target plates mainly occur shear plug failure, the BLV first tends to flatten and then increases sharply with the increase of its thickness. Besides, in the same velocity interval, the plugging velocity decreases with the increase of the target plate thickness; the Lode parameter has an obvious influence on the simulation results, which the MMC fracture criterion is more consistent with the experimental results. However, with the increase of the target plate thickness, both MMC and MJC fracture criteria show the phenomenon of overestimation of the material ductility.

A comparative study on ballistic impact behaviors of glass/epoxy composites

This paper presents an experimental and numerical study to evaluate the ballistic performance of E-glass/epoxy and S2-glass/epoxy composites. Composite materials were produced by vacuum assisted resin infusion molding method. All the specimens were then subjected to ballistic impact tests by gas-gun system. Residual velocities were measured by high-speed camera for different velocities. Ballistic limits of all composites were obtained by curve fitting residual velocity-impact velocity data. It was found that S2-glass/epoxy composite has a higher ballistic limit than E-glass/epoxy. S2-glass/epoxy has also more specific absorbed energy and absorbed energy density than E-glass/epoxy. Numerical results were in good agreement with experimental results.

An Approach to Predicting the Ballistic Limit of Thin Textile-Reinforced Concrete Plates Based on Experimental Results

In this article, a partial selection of experiments on enhancing the impact resistance of structural components with non-metallic, textile-reinforced concrete is discussed. The focus is on the experimental investigations in which the impact resistance of thin, textile-reinforced concrete plates is characterized. The article discusses the materials, fabrics and test setup used. For the experimental work, a drop tower from the Otto Mohr Laboratory, which belongs to the Technische Universtät Dresden, was used. Furthermore, the experimental results are presented and evaluated using different methods. Based on the collected data, a suitable approach to determining the perforation velocity of an impactor through the investigated thin, textile-reinforced concrete plates is shown.

Finite element analysis of the ballistic performance of monolithic and double-layered plates subjected to deformable projectiles

Impact problems have always been a field of interest for researchers because of their wide application in industries, especially in producing protective structures in defence. In the present study, finite element analysis is used to analyze the ballistic performance of monolithic and double-layered plates against cylindrical projectile with different nose shapes, viz. trapezoidal and flat-nosed, using a dynamic temperature displacement explicit analysis in the commercial finite element software ABAQUS. Further, the study compares the ballistic resistance (BR) of plates with different thicknesses (6, 10, and 12 mm) against the same configuration of projectiles. The Johnson–Cook (JC) constitutive strength and damage model characterizes the target and projectile material behavior. Mie–Grüneisen equation of state describes the material behavior of projectile and target under high pressure. The impact response of the target is compared in terms of plate deformation, ballistic limit velocity, and failure pattern of targets during impact. The monolithic plate has 2.42% higher impact resistance than the double-layered plate for the trapezoidal-nosed projectile, while for a flat-nosed projectile, double-layered plates have 9.42% higher BR than the monolithic plates. Moreover, the BR of plates (6, 10, and 12 mm) for flat-nosed projectiles is found to be 7.94, 5.56, and 4.59% higher than trapezoidal-nosed projectiles.

Improved Ballistic Impact Resistance of Nanofibrillar Cellulose Films with Discontinuous Fibrous Bouligand Architecture.

Natural protective materials offer unparalleled solutions for impact-resistant material designs that are simultaneously lightweight, strong, and tough. Particularly, the Bouligand structure found in the dactyl club of mantis shrimp and the staggered structure in nacre achieve excellent mechanical strength, toughness, and impact resistance. Previous studies have shown that hybrid designs by combining different bioinspired microstructures can lead to enhanced mechanical strength and energy dissipation. Nevertheless, it remains unknown whether combining Bouligand and staggered structures in nanofibrillar cellulose (NFC) films, forming a discontinuous fibrous Bouligand (DFB) architecture, can achieve enhanced impact resistance against projectile penetration. Additionally, the failure mechanisms under such dynamic loading conditions have been minimally understood. In our study, we systematically investigate the dynamic failure mechanisms and quantify the impact resistance of NFC thin films with DFB architecture by leveraging previously developed coarse-grained models and ballistic impact molecular dynamics simulations. We find that when nanofibrils achieve a critical length and form DFB architecture, the impact resistance of NFC films outperforms the counterpart films with continuous fibrils by comparing their specific ballistic limit velocities and penetration energies. We also find that the underlying mechanisms contributing to this improvement include enhanced fibril sliding, intralayer and interlayer crack bridging, and crack twisting in the thickness direction enabled by the DFB architecture. Our results show that by combining Bouligand and staggered structures in NFC films, their potential for protective applications can be further improved. Our findings can provide practical guidelines for the design of protective films made of nanofibrils.