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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Mechanical Engineering".

Deadline for manuscript submissions: closed (31 October 2020) | Viewed by 57031

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Dr. Filipe Teixeira-Dias

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Guest Editor

Institute for Infrastructure and Environment (IIE), School of Engineering, The University of Edinburgh, Edinburgh EH9 3JL, UK
Interests: computational and applied mechanics; impulsive dynamics; structural dynamics; materials, structures and systems for energy absorption; armour and protection systems; sports impact and human bio-dynamics, crashworthiness, numerical and analytical methods
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Dr. Mariana Paulino

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Guest Editor

School of Engineering, Faculty of Science, Engineering and Built Environment, Deakin University, Burwood, VIC 3125, Australia
Interests: impact and dynamics; armour and protection systems; crashworthiness; finite element analysis and simulation; computational mechanics; sheet metal forming processes; material constitutive behavior
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Protective structures and systems – including armour systems, vehicle and personal protection, sports protection gear, energy absorbing devices, etc. – are an integral part of modern life and essential in ensuring the safety and well-being of the world’s population. Due to the constant evolution of possible impact scenarios, research into innovative systems is paramount, albeit often a complex task due to impact-related (threat) unknowns, such as the kinetic energy, the dominant energy dissipation mechanisms, etc. This Special Issue aims at disseminating the latest research achievements and findings related to energy absorbing materials, systems and structures, in the scope of armour and protection materials, structures and systems. Papers are welcome on topics related to the theory, testing, modelling, design and applications of armour and protection systems. This includes, but is not limited to:

Energy absorbing materials and structures
Crashworthiness and passenger protection in transport systems
Blast and shock wave mitigation
Terminal ballistics and impact
Personal protective gear and impact in sports
Multi-scale approaches for energy absorption
Analytical methods
Computational techniques and modelling approaches
Testing and experimental techniques
Innovative applications

Dr. Filipe Teixeira-Dias
Dr. Mariana Paulino
Guest Editors

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Keywords

impulsive dynamics
armour and protection systems
energy absorption
ballistic impact
terminal ballistics
blast and shock waves
crashworthiness
personal protection
sports impact

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Published Papers (13 papers)

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Research

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36 pages, 42588 KiB

Open AccessFeature PaperArticle

Sandwich Panels with Polymeric Foam Cores Exposed to Blast Loading: An Experimental and Numerical Investigation

by Kristoffer Aune Brekken, Aase Reyes, Torodd Berstad, Magnus Langseth and Tore Børvik

Appl. Sci. 2020, 10(24), 9061; https://doi.org/10.3390/app10249061 - 18 Dec 2020

Cited by 15 | Viewed by 3594

Abstract

Sandwich panels have proven to be excellent energy absorbents. Such panels may be used as a protective structure in, for example, façades subjected to explosions. In this study, the dynamic response of sandwich structures subjected to blast loading has been investigated both experimentally and numerically, utilizing a shock tube facility. Sandwich panels made of aluminium skins and a core of extruded polystyrene (XPS) with different densities were subjected to various blast load intensities. Low-velocity impact tests on XPS samples were also conducted for validation and calibration of a viscoplastic extension of the Deshpande-Fleck crushable foam model. The experimental results revealed a significant increase in blast load mitigation for sandwich panels compared to skins without a foam core, and that the back-skin deformation and the core compression correlated with the foam density. Numerical models of the shock tube tests were created using LS-DYNA, incorporating the new viscoplastic formulation of the foam material. The numerical models were able to capture the trends observed in the experimental tests, and good quantitative agreement between the experimental and predicted responses was in general obtained. One aim of this study is to provide high-precision experimental data, combined with a validated numerical modelling strategy, that can be used in simulation-based optimisation of sandwich panels exposed to blast loading. Full article

(This article belongs to the Special Issue Armour and Protection Systems)

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21 pages, 7554 KiB

Open AccessArticle

Energy Absorption of Aluminium Extrusions Filled with Cellular Materials Under Axial Crushing: Study of the Interaction Effect

by Javier Paz, Miguel Costas, Jordi Delgado, Luis Romera and Jacobo Díaz

Appl. Sci. 2020, 10(23), 8510; https://doi.org/10.3390/app10238510 - 28 Nov 2020

Cited by 2 | Viewed by 2790

Abstract

This investigation focuses on the interaction effect during the quasi-static axial crushing of circular and square thin-walled aluminium extrusions filled with polymeric foam or cork. The increment in the absorbed energy due to interactions between materials was assessed using a validated numerical model calibrated with experimental material data. Simulations were run with variable cross-section dimensions, thickness, and foam density. The results were used to adjust the parameters of design formulas to predict the average crush forces of foam- and cork-filled thin-walled tubes. The analysis of the energy dissipation per unit volume revealed that the highest increments due to the interaction between materials appeared in the foam-filled square extrusions. Energy dissipation increased with higher density foams for both cross-sections due to a stronger constraint of the aluminium walls, and thus a reduction of the folding length. Thinner tube walls also delivered a higher improvement in the energy dissipation per unit volume than those with thicker walls. The contribution of friction was also quantified and investigated. Full article

(This article belongs to the Special Issue Armour and Protection Systems)

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20 pages, 5158 KiB

Open AccessArticle

Evaluation of Combat Helmet Behavior under Blunt Impact

by Carlos Moure-Guardiola, Ignacio Rubio, Jacobo Antona-Makoshi, Álvaro Olmedo, José Antonio Loya and Marcos Rodríguez-Millán

Appl. Sci. 2020, 10(23), 8470; https://doi.org/10.3390/app10238470 - 27 Nov 2020

Cited by 14 | Viewed by 5711

Abstract

New threats are a challenge for the design and manufacture of modern combat helmets. These helmets must satisfy a wide range of impact velocities from ballistic impacts to blunt impacts. In this paper, we analyze European Regulation ECE R22.05 using a standard surrogate head and a human head model to evaluate combat helmet performance. Two critical parameters on traumatic brain analysis are studied for different impact locations, i.e., peak linear acceleration value and head injury criterion (HIC). The results obtained are compared with different injury criteria to determine the severity level of damage induced. Furthermore, based on different impact scenarios, analyses of the influence of impact velocity and the geometry impact surface are performed. The results show that the risks associated with a blunt impact can lead to a mild traumatic brain injury at high impact velocities and some impact locations, despite satisfying the different criteria established by the ECE R22.05 standard. The results reveal that the use of a human head for the estimation of brain injuries differs slightly from the results obtained using a surrogate head. Therefore, the current combat helmet configuration must be improved for blunt impacts. Further standards should take this into account and, consequently, combat helmet manufacturers on their design process. Full article

(This article belongs to the Special Issue Armour and Protection Systems)

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14 pages, 4946 KiB

Open AccessArticle

Failure Mechanism of Multilayer Ceramic Capacitors under Transient High Impact

by Da Yu, Keren Dai, Jinming Zhang, Benqiang Yang, He Zhang and Shaojie Ma

Appl. Sci. 2020, 10(23), 8435; https://doi.org/10.3390/app10238435 - 26 Nov 2020

Cited by 10 | Viewed by 6042

Abstract

In recent years, penetrating weapons have been used more and more to attack increasingly hard targets; therefore, the impact of such a penetrating process has increased to an extremely high level. As an important component of a fuze, the reliability of the ceramic capacitor in high-impact environments is key for the normal working of the fuze. In this paper, we found that a high-impact causes parameter drift of the multilayer ceramic capacitor (MLCC), which further causes the fuze to misfire. This paper mainly studies the internal mechanism of the MLCC’s parameter drift during high impact. Firstly, transient physical phenomena, such as capacitance fluctuation and the leakage current increase of the ceramic capacitor under a high acceleration impact, were studied experimentally by a Machete hammer, revealing the relationship between the capacitance change, leakage current change, and acceleration under different working conditions. Secondly, a mechanical model of the ceramic capacitor is established to simulate the change in capacitance value, which shows that the main factor of the capacitance change is the deformation-derived change in the facing area between the electrodes. Lastly, an equivalent circuit model is established to simulate the change in the leakage current, which shows that the main factor of the leakage current change is the piezoelectric resistance of the ceramic dielectric. Full article

(This article belongs to the Special Issue Armour and Protection Systems)

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24 pages, 16092 KiB

Open AccessArticle

Numerical Analysis of EOD Helmet under Blast Load Events Using Human Head Model

by Borja Valverde-Marcos, Ignacio Rubio, Jacobo Antona-Makoshi, Anoop Chawla, José Antonio Loya and Marcos Rodríguez-Millán

Appl. Sci. 2020, 10(22), 8227; https://doi.org/10.3390/app10228227 - 20 Nov 2020

Cited by 9 | Viewed by 4372

Abstract

Brain injury resulting from improved explosives devices (IEDs) is identified as a challenge for force securities to improve protection equipment. This paper focuses on the mechanical response of explosive ordnance disposal (EOD) helmet under different blast loadings. Limited published studies on this type of helmet are available in the scientific literature. The results obtained show the blast performance of the EOD helmet because a decrease in the maximum values in the measured damage parameters is found. Therefore, an EOD helmet minimizes the risks of the severity of injuries on the user showing a low probability of injury. Full article

(This article belongs to the Special Issue Armour and Protection Systems)

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15 pages, 4743 KiB

Open AccessArticle

Optimizing Viscoelastic Properties of Rubber Compounds for Ballistic Applications

by Janis Karl, Franziska Kirsch, Norbert Faderl, Leonhard Perko and Teresa Fras

Appl. Sci. 2020, 10(21), 7840; https://doi.org/10.3390/app10217840 - 5 Nov 2020

Cited by 8 | Viewed by 3024

Abstract

Using interlayers of rubber adds a positive effect to the synergy of disruptor–absorber armors. Emerging from its viscoelasticity the material is able to transform mechanical stress into heat. The dynamic mechanical properties of elastomers depend on both ambient temperature and frequency of an applied mechanical load. The damping shows a maximum in the glass transition area. If the frequency of the glass transition is in the magnitude of the mechanical stress rate applied by ballistic impact, the elastomer will undergo the transition and thus show maximized damping. An ideal material for ballistic protection against small calibers is developed by making use of dynamic mechanical analysis and the time–temperature superposition principle. The material is later analyzed by ballistic experiments and compared to other nonideal rubbers with regard to glass transition temperature, hardness and damping. It is shown that by choosing a material correctly with certain glass transition temperature and hardness, the ballistic properties of a steel–rubber–aluminum armor can be enhanced. The chosen material (butyl rubber) with a hardness of 50 °ShA is able to enhance energy absorption during ballistic impact by around 8%, which is twice as good as other rubber with non-optimized properties. Full article

(This article belongs to the Special Issue Armour and Protection Systems)

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15 pages, 7982 KiB

Open AccessArticle

Factors Contributing to Increased Blast Overpressure Inside Modern Ballistic Helmets

by Maciej Skotak, Jonathan Salib, Anthony Misistia, Arturo Cardenas, Eren Alay, Namas Chandra and Gary H. Kamimori

Appl. Sci. 2020, 10(20), 7193; https://doi.org/10.3390/app10207193 - 15 Oct 2020

Cited by 10 | Viewed by 7375

Abstract

This study demonstrates the orientation and the "shape factor" have pronounced effects on the development of the localized pressure fields inside of the helmet. We used anatomically accurate headform to evaluate four modern combat helmets under blast loading conditions in the shock tube. The Advanced Combat Helmet (ACH) is used to capture the effect of the orientation on pressure under the helmet. The three modern combat helmets: Enhanced Combat Helmet (ECH), Ops-Core, and Airframe, were tested in frontal orientation to determine the effect of helmet geometry. Using the unhelmeted headform data as a reference, we characterized pressure distribution inside each helmet and identified pressure focal points. The nature of these localized “hot spots” is different than the elevated pressure in the parietal region of the headform under the helmet widely recognized as the under-wash effect also observed in our tests. It is the first experimental study which indicates that the helmet presence increased the pressure experienced by the eyes and the forehead (glabella). Pressure fingerprinting using an array of sensors combined with the application of principle component analysis (PCA) helped elucidate the subtle differences between helmets. Full article

(This article belongs to the Special Issue Armour and Protection Systems)

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21 pages, 2479 KiB

Open AccessArticle

Cork Core Sandwich Plates for Blast Protection

by Jesús Pernas-Sánchez, Jose A. Artero-Guerrero, David Varas and Filipe Teixeira-Dias

Appl. Sci. 2020, 10(15), 5180; https://doi.org/10.3390/app10155180 - 28 Jul 2020

Cited by 2 | Viewed by 2498

Abstract

A numerical model is developed and validated to analyse the performance of aluminium skin and agglomerated cork core sandwich plates subjected to blast loads. Two numerical approaches are used and thoroughly compared to generate the blast loading: an Arbitrary-Lagrangian–Eulerian approach and the Load Blast Enhanced method. Both of the models are validated by comparing the numerical results with experimental observations. A detailed analysis of the sandwich behaviour is done for both approaches showing small differences regarding the mechanical response of the sandwich structure. The results obtained from the numerical models uncover the specific energy absorption mechanisms happening within the sandwich plate components. A new core topology is proposed, based on these results, which maximises the energy absorption capacity of the plate, keeping the areal density unchanged. A wavy agglomerated cork core is proposed and the effects of different geometrical parameters on the energy absorption are thoroughly analysed and discussed. The proposed optimised plate configuration shows an increase in the total absorbed energy of close to

40 %

relative to a reference case with the same areal density. The adopted optimisation methodology can be applied to alternative configurations to increase the performance of sandwich structures under blast events. Full article

(This article belongs to the Special Issue Armour and Protection Systems)

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15 pages, 1632 KiB

Open AccessArticle

Dynamic Tensile Testing of Needle-Punched Nonwoven Fabrics

by Francisca Martínez-Hergueta, Antonio Pellegrino, Álvaro Ridruejo, Nik Petrinic, Carlos González and Javier LLorca

Appl. Sci. 2020, 10(15), 5081; https://doi.org/10.3390/app10155081 - 23 Jul 2020

Cited by 4 | Viewed by 3370

Abstract

The tensile testing of a needle-punched nonwoven fabric is presented. A high-sensitivity Split-Hopkinson Tensile Bar device was specifically designed for this purpose. The strain gauge measurements were combined with high-speed photography and Digital Image Correlation to analyse the deformation micromechanisms at high strain rates. The experimental set-up allowed to determine the wave propagation velocity of the as-received nonwove fabric, the evolution of the strain field with deformation and the wave interaction inside the fabric. The deformation was accommodated by the same micromechanisms observed during quasi-static tensile testing and ballistic impact, which comprised fibre straightening, rotation and sliding. Heterogeneous strain fields were developed in the nonwoven fabric as a result of the non-linear pseudoplastic response of the fabric and the internal dissipation due to the frictional deformation micromechanisms, preventing the propagation of high magnitude strain waves into the specimen. Additionally, the output forces were analysed to determine the influence of high-strain rates in the mechanical response of the nonwoven fabric, finding an increment of the stiffness for low applied strains under dynamic loading. These findings provide the basis to develop strain-rate dependent constitutive models to predict wave propagation in needle-punched nonwoven fabrics when subjected to impact loads. Full article

(This article belongs to the Special Issue Armour and Protection Systems)

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17 pages, 4511 KiB

Open AccessFeature PaperArticle

Numerical Analysis of Bicycle Helmet under Blunt Behavior

by David Sepulveda-Lopez, Jacobo Antona-Makoshi, Ignacio Rubio and Marcos Rodríguez-Millán

Appl. Sci. 2020, 10(11), 3692; https://doi.org/10.3390/app10113692 - 26 May 2020

Cited by 4 | Viewed by 5119

Abstract

This study evaluates various safety aspects of standardized impacts that cyclists may suffer while wearing a bicycle helmet, by combining a partially validated finite element model of the cranio-cervical region and a newly developed commercial bicycle helmet model. Under EN 1078 standardized impact conditions, the results of simulated impact tests show that the helmet can absorb 40% to 50% of the total impact energy at impact velocities above 4 m/s. Further, based on a relationship between the head injury criterion and the risk of injury from field data, the results of the simulations suggest that minor injuries may occur at impact velocities of 10 km/h, serious injuries at 15 km/h, and severe injuries at 20 km/h. Fatal injuries will likely occur at impact velocities of 30 km/h and higher. Full article

(This article belongs to the Special Issue Armour and Protection Systems)

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15 pages, 9511 KiB

Open AccessArticle

High-Velocity Impact Performance of Aluminum and B₄C/UHMW-PE Composite Plate for Multi-Wall Shielding

by Yangyu Lu, Qingming Zhang, Yijiang Xue, Wenjin Liu and Renrong Long

Appl. Sci. 2020, 10(2), 721; https://doi.org/10.3390/app10020721 - 20 Jan 2020

Cited by 9 | Viewed by 3774

Abstract

Three types of multi-wall shielding were experimentally investigated for their performances under the high-velocity impact of a cm-size cylindrical projectile by using a two-stage light-gas gun. The three shields contained the same two aluminum bumpers but different rear walls, which were 7075-T651 aluminum (Al) plate, boron carbide (B₄C)/Al 7075-T651/Kevlar composite plate and B₄C/ultra-high molecular weight polyethylene (UHMW-PE) composite plate. The impact test was carried out using a cylindrical shape of 6 g mass 7075-T651 Al projectile in a speed range (1.6 to 1.9 km/s) to achieve an effective shield configuration. A numerical simulation was undertaken by using ANSYS Autodyn-3D and the results of this were in good agreement with the experimental results. Meanwhile, both the experimental and the numerical simulation results indicated that B₄C/UHMW-PE composite plates performed a better interception of the high-velocity projectiles within the specific speed range and could be considered as a good configuration for intercepting large fragments in shielding design. Full article

(This article belongs to the Special Issue Armour and Protection Systems)

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19 pages, 4894 KiB

Open AccessArticle

Improved Energy Absorption Characteristics Based on Elastic Polymer-Modified Porous Material for Multiple Extreme Mechanical Impacts

by Jinming Zhang, Keren Dai, Xiaofeng Wang, Da Yu, Benqiang Yang, He Zhang and Zheng You

Appl. Sci. 2020, 10(1), 110; https://doi.org/10.3390/app10010110 - 21 Dec 2019

Cited by 4 | Viewed by 4475

Abstract

Energy absorbing materials are crucial for the protection of electronic devices in various applications. In particular, the protection of materials from multiple extreme mechanical impacts imposes stringent requirements on the characteristics of energy absorption and recoverability. In this paper, a novel design of composite material, elastic polymer-modified porous carbon, is proposed to meet such urgent requirements. At the micro level, the polymer fibers form an elastic skeleton in which porous carbon particles are enveloped. Due to such microstructure, the composite material exhibits excellent performance of energy absorption and recoverability simultaneously, which are validated via various experiments. Furthermore, the microphysical mechanism of its superior energy absorption characteristics is demonstrated theoretically. Additionally, the optimized mass proportions of the two composite phases are discussed. In general, this novel design of energy absorbing material improves the reliability of electronic devices and systems exposed to multiple extreme mechanical impacts. Full article

(This article belongs to the Special Issue Armour and Protection Systems)

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Review

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28 pages, 1614 KiB

Open AccessReview

Visual Methods to Assess Strain Fields in Armour Materials Subjected to Dynamic Deformation—A Review

by Chris L. Ellis and Paul Hazell

Appl. Sci. 2020, 10(8), 2644; https://doi.org/10.3390/app10082644 - 11 Apr 2020

Cited by 8 | Viewed by 3462

Abstract

When impacted by a projectile, ballistic protection undergoes very large strain rates over very short periods of time. During these impact events, materials will undergo a very short region of elastic deformation, before undergoing significant plastic deformation. Due to the high levels of plastic deformation the samples undergo, strain gauges and other embedded sensors are often ineffective or become damaged before useful data can be obtained. Three-dimensional digital image correlation (3D DIC) is a non-invasive measurement method that uses two high-speed cameras, offset from each other by 15–45° to observe a speckle pattern on the sample material. As the material, and by extension the speckle pattern, deforms, the images taken throughout the deformation can be compared in sequence, to determine the motion and deformation of the sample. Recent advances in camera technology have allowed for frame rates in the hundreds of thousands of frames per-second, allowing for the measurement of very high-strain rate impact events. This paper will describe the premise of 3D DIC and provide a review of the current applications and research into high-speed impact testing using 3D DIC. Full article

(This article belongs to the Special Issue Armour and Protection Systems)

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