Back Face Deformation Research Articles

Effect of Z-binding depths on the ballistic performance of 3D woven through-the-thickness angle-interlock fabrics in a multiply system

Lightweight armor with excellent protection against ballistic impacts are pursued by researchers worldwide. This paper systematically investigates the effect of the Z-binding depths on the ballistic performance and failure mechanisms of para-aramid 3D fabrics. Two types of 3D woven through-the-thickness angle-interlock fabrics were designed and fabricated in comparison to the 2D plain weave fabric. The ballistic tests and finite element simulation analyses were carried out based on a similar areal density of 5.2 kg/m2 by layering up the fabrics. According to the experimental results, the variability and cumulative probability of penetration of the 20-P are higher than that of the 3D fabric systems, resulting in a 2.5% higher ballistic limit V50 of 8-5 TA than 20-P. Fabric plies failed abruptly in the 2D system, while the 3D system showed a progressive failure mode. The Z-warps, configure through the thickness of the fabric, result in the projectile tumbling and deviating from its original direction. A larger binding depth can help to prolong the defending process, which will mobilize more yarns to resist the projectile impact. The back-face deformation is well constrained by the 3D fabrics. Due to the fact that the designed 3D woven fabrics are more moldable than the plain weave, it could be potential candidates for the engineering design of female bullet-proof vest interlining.

An analytical model to predict back face deformation of hybrid soft body armors under ballistic impact

In the design of soft body armors for ballistic protection, the blunt trauma effect has to be taken into account and it is usually evaluated by the back face deformation (BFD). Most of the current research on blunt trauma is based on experiments and simulations, whereas the development of analytical models is still rare. This study develops an analytical model to predict BFD for a hybrid panel composed of modified aramid fabrics and Ultra-high molecular weight polyethylene (UHMWPE) unidirectional sheets, which is based on the two-stage damage evolution: shear plugging and tensile bulge. Firstly, the shear and tensile energy of the hybrid panel as well as the deformation energy of the clay were constructed. Secondly, the characteristic equations were developed according to the law of energy conservation and BFD could be obtained by solving the equations. The results of the analytical model were found to be in good agreement with experiments and FE simulations. With the assistance of the model, the effect of projectile geometry and optimized designs for hybrid panels have been studied.

Numerical investigation of the high-velocity impact performance of body armor panels

The body armor can effectively reduce penetration injuries and save many soldiers’ lives. However, back face deformation (BFD) accompanied by ballistic impacts on body armor can lead to fatal injuries to soldiers on the battlefield. In the study, ballistic tests and finite element models are performed to evaluate the protection of body armor panels. Both soft body armor and ceramic till are validated against the experimental data. Then, the performance of the ultra-high molecular weight polyethylene (UHMWPE) soft armor incorporating the RP #1 clay and foam pad is discussed. The simulation results show that the addition of a foam pad can effectively reduce the maximum clay BFD. At the same time, the performance of the ceramic-UHMWPE panel is studied. The ceramic tile can partly absorb the kinetic energy of the high-velocity projectile and enlarge the contact area between the UHMWPE panel and RP #1 clay, which leads to a lower BFD value. In addition, the effects of the interlaminate strength and the laminate stacking direction of the UHMWPE panel on the BFD are discussed. The current simulation can capture the damage behavior of UHMWPE laminates and ceramic tile well, which can be a guide for the design and improvement of new body armor panels.

Experimental and numerical analyses of ballistic resistance evaluation of combat helmet using Hybrid III headform

Combat helmets are the primary system for protecting the head against ballistic impacts. Generally, combat helmets have been evaluated using a ballistic plasticine head surrogate based on international standards. More realistic human head models have recently been introduced to assess combat helmet performance considering biomechanical requirements. In this work, the Hybrid III dummy head and neck has been introduced to evaluate the performance of the combat helmet against the ballistic impact of live ammunition at different impact locations, considering two different thicknesses of the padding system. A numerical model including a helmet and a Hybrid III head and neck, is developed and validated with our experimental data. The results reveal the influence of the location, where the rear impact leads to the highest risk of brain damage. The effect of pad thickness is closely related to the energy absorbed by the helmet, the backface deformation (BFD), the contact force and the acceleration measured on the head.

Ballistic Performance of Epoxy-Ramie Composite - SiC Layered Body Armor Using Finite Element Analysis

Composite body armor has widely used as bulletproof material combined with hard plates made from ceramic or metals. That replaced the use of full-metals body armor that heavy, rigid, and restricts the user's movement. This study investigates the ballistic performance of SiC-based hard layer body armor on its possible impact position using finite element analysis. The body armor panel consists both of soft and hard layers. The soft layer is made from epoxy-ramie composite which is a natural fiber composite. The hard layer made from hexagonal chip l SiC with 4 mm thickness in an array. There are three possible impact points on the chip which are the center of the chip, between two chips, and between three chips. The soft layer is varied at a range of 6-25 mm depending on its capability to comply with the latest NIJ 0101.07-2019 criteria for RF1. NIJ has several criteria for ballistic performance. This paper discusses panel penetration and Back-face Deformation (BFD) based NIJ. Besides, this paper also discusses the impact of energy absorption and velocity reduction of the bullet by the panel.

Effect of Temperature and Ply Angle on Performance of Ultra High Molecular Weight Polyethylene (UHMWPE) Laminates Under Low Velocity Impact

Low velocity impact tests were conducted on ultra high molecular weight polyethylene (UHMWPE) laminates having different ply angle. The tests were conducted at various temperatures using steel impactor having 16mm diameter and hemi spherical shape. The selected impact energies are in the range of 50 to 250 Joule. The performance of the composites was compared with respect to peak force, maximum displacement and back face deformation. Results indicated that with increase of temperature, the contact duration increased whereas deceleration was reduced. Various failure mechanisms involved in energy absorption were also addressed.

Hybrid numerical modeling of ballistic clay under low-speed impact using artificial neural network

Roma Plastilina No. 1 clay has been widely used as a conservative boundary condition in bulletproof vests, namely to play the role of a human body. Interestingly, the effect of this boundary condition on the ballistic performance of the vests is indiscernible. Moreover, back face deformation should be characterized by measuring the indentation in the deformed clay, which is important for determining the lethality of gunshots. Therefore, several studies have focused on modeling not only bulletproof vests but also the clay backing material. Despite various attempts to develop a suitable numerical model, determining the appropriate physical parameters that can capture the high-strain-rate behavior of clay is still challenging. In this study, we predicted indentation depth in clay using an artificial neural network (ANN) and determined the optimal material parameters required for a finite element method (FEM)-based model using an inverse tracking method. Our ANN-FEM hybrid model successfully optimized high-strain-rate material parameters without the need for any independent mechanical tests. The proposed novel model achieved a high prediction accuracy of over 98% referring impact cases.

Behind Shield Blunt Trauma: Characterizing the Back-Face Deformation of Shields with a Focus on Upper Limb Loading.

Shield back-face deformation (BFD) is the result of composite ballistic shields deflecting or absorbing a projectile's energy and deforming towards the user. BFD can result in localized loading to the upper extremity, where the shield is secured to the user. An augmented anthropomorphic test device upper extremity was used to quantify this applied load. Four locations along the upper extremity were tested-the hand, wrist, forearm, and elbow-for investigating differing boundary conditions and their effect on resultant load. Varying stand-off distances, the distance between the back of the shield and the force sensor, were investigated. Digital image correlation was also conducted to measure the dynamic displacement of the shield. The mean peak back-face velocity of the shield was 208.4 ± 38.8m/s, while the average affected area was 1505 ± 158.3 mm2. Impulse was not significantly affected by anatomical location for the same stand-off distance; however, as stand-off distance decreased, the measured force significantly increased (p < 0.05). Notably, impact duration did not differ significantly for any of the impact scenarios. This is the first step in developing injury criteria for this region resulting from behind shield blunt trauma, and these data will be used for developing injury thresholds in post-mortem human surrogates.

Computational modeling of composite armour and effect of CNT inclusion using orthotropic material model

We report development of indigenous Material Point Method (MPM3D) and Smoothed Particle Hydrodynamics (SPH3D) codes for modeling and design of composite body armour. Typical armour consists of a ceramic backed by a polymer matrix composite. The ceramic plate contributes to blunting of bullet nose, its erosion and reduction in speed. The polymer matrix with high tensile strength arrests the bullet. Mie-Gruneisen EOS, Johnson-Cook strength and failure models were used for projectile. Johnson-Holmquist (JH2) model was used for ceramics. An orthotropic model which accounts for different compression and tensile properties in through-thickness and in-plane directions was implemented and used for Ultrahigh Molecular Weight Polyethylene (henceforth termed as ‘PE’). The codes were validated against published results for impact onto PE targets. Then the codes were used to simulate various published experiments (of coauthors) on ceramic/PE composite targets performed according to NIJ standards. Back Face deformation (BFS) is measured. In all cases, the projectiles do not penetrate through the armour panels, consistent with experiments. Typically, the SPH and MPM codes compute BFS values which only deviate within 10–20 % of measured values. The simulation results are also compared with the commercial FEM code simulations. Experiments and simulations were carried out for PE reinforced with Carbon Nanotube (CNT) inclusions. The mechanical moduli and other strength parameters of PE are adjusted to account for the increase in flexural strength due to inclusion of CNT. The CNT inclusion greatly reduces the BFS. The simulations results qualitatively follow these trends.

Ballistic loading and survivability of optical fiber sensing layers for soft body armor evaluation

The authors previously demonstrated the use of FBG sensors in Kevlar mats behind body armor to measure the transient back face deformation (BFD) during ballistic testing. This paper presents a novel sensor system based on a Fiber Bragg Grating embedded in silicone mats to improve the survivability of the body armor in-situ strain sensing layers. Due to the large amount of deformation, a relative slip between the optical fibers and the supporting structure is needed to maintain the performance of the sensors and determine the relationship between the measured strain and deformation shape. Two silicone materials were tested, Smooth-Sil 950 and Sorta-Clear 40, in both 1 mm and 2 mm thicknesses to evaluate their survivability and impact on BFD. To enhance slipping between the fibers and surrounding silicone a thin layer of petroleum jelly was placed on the fibers prior to being cast in the silicone mats. The 1 mm Sorta-Clear 40 mats performed best in silicone survivability, FBG survivability and minimal impact on the BFD. The new system improves on key deficiencies that were found from inserting the fibers directly into the Kevlar with minimal to no impact on the back face deformation.

Experimental study on the low-velocity impact response of inter-ply S2-glass/aramid woven fabric hybrid laminates

This paper presents an experimental evaluation of the effect of hybridization and stacking sequence on the low-velocity impact response of aramid/S2-glass/epoxy hybrid laminates. Plain-weave Kevlar ®29 and satin S2-glass fabrics were used and the laminates were manufactured by vacuum infusion moulding. Eight laminate configurations were studied, including two single-fibre samples (pure aramid or pure S2-glass) and six interply hybrids. Low-velocity impact tests were performed with three different impact energies (19 J, 37 J, 72 J) and significant variations in impact behaviour were observed among the laminates. Response Surface Methodology (RSM) was employed to investigate the effect of hybridization on impact performance, focusing on greater absorbed energy and smaller back face deformation. Hybridization led to significant changes in failure morphology and the combination of aramid and S2-glass laminates enhanced the impact performance, especially for up to 49.5 J impact energy, while the pure S2-glass laminate performed better for higher impact energies.

Performance evaluation of multilayered ceramic composite armors: New design and advanced predictive method

Novel body armors are designed to protect against ballistic threats in the most vulnerable organs within the thorax and abdomen. Decreasing the armor weight without affecting its total integrity after the impact is one of the most challenging tasks. In this study, we combine advanced numerical simulations and experimental tests to investigate the ballistic performance of multilayered armor systems (MAS) consisting of laminated alumina (Al2O3) ceramic plates with multi-curve form and a hybrid composite backing. The ballistic trauma absorption and ceramic fracturing morphology are considered evaluation criteria. The investigation provides enough data on the measured trauma and the results are compared to advanced monolithic ceramics. The ballistic tests showed that bonding three or two ceramic plates with polymeric interlayer decreases considerably the eroded ceramic mass in comparison to monolithic ceramic tiles. Furthermore, the layup of two thin Al2O3tiles with frontal confinement gives the same trauma-weight index as monolithic silicon carbide and reaction-bonded boron carbide plates. The combination of K129 and KM2 aramid weave fabrics decreases the composite backing weight by 33% and increases its ballistic performance in comparison to homogeneous aramid fabrics. Numerical simulations that involve the use of solid Lagrange and adaptive solid/smooth particles hydrodynamics (SPH) numerical approaches with detailed 3D models of the bullet and the MAS are presented in this work. Based on the statistical analysis, a better prediction of the back face deformation and bullet residual length is obtained by the adaptive solid/SPH method, which is found more suitable for the simulation of multilayered armor impact scenarios.

Quantification of Behind Shield Blunt Impacts Using a Modified Upper Extremity Anthropomorphic Test Device.

Ballistic shields are used by military and police members in dangerous situations to protect the user against threats such as gunfire. When struck, the shield material deforms to absorb the incoming kinetic energy of the projectile. If the rapid back-face deformation contacts the arm, it can potentially impart a large force, leading to injury risk, termed behind armor blunt trauma (BABT). This work characterized the loading profiles due to the contact between the deforming back-face of the shield and the arm using a modified upper extremity anthropomorphic test device (ATD). This ATD measured forces at the hand, wrist, forearm, and elbow to compare the locational effects of the force transfer for future investigations of fracture risk. Two composite ballistic shields, both with the same ballistic protection rating, were investigated and had statistically different responses to the same impact conditions, indicating a further need for shield safety evaluation. Additionally, ballistic force curves were compared among stand-off distances, defined as the distance between the back-face of the shield and the front of the force sensor, where the peak impact force significantly decreased with increased stand-off. This study presents the first highly instrumented ATD upper limb capable of evaluating BABT and characterization of these loading profiles. This work demonstrates the importance of realistic boundary conditions as loading varies by anatomical location. Stand-off distance is an effective method to reduce loading and should be considered in future shield design iterations and standards that are developed using this device.

Numerical investigation on hybridization of woven fabric armour to enhance ballistic protection

The soft ballistic armour design requirement involves maximum ballistic energy absorption with lower backface deformation at minimum possible weight. Yarn mechanical properties play a primary role in influencing the above armour characteristics. The study reported to date has analysed the yarn properties, which will yield maximum ballistic energy absorption. However, finding the optimal combination of yarn mechanical properties that will simultaneously satisfy all the above objectives is still a matter of investigation. In view of this, the study first introduces a new parameter, “Inertial Work” (product of armour mass and backface deformation) which enables categorization of armour backface deformation in a mass normalized manner. Further, Specific Ballistic Energy Absorption (SBEA) parameter is introduced for comparison across the fabrics of different densities. The woven fabrics widely used in the ballistic protection domain Kevlar 29, Zylon AS and Spectra 1000 were extensively analysed numerically to study their ballistic response. FE simulation results showed that a single material armour would prove insufficient to simultaneously attain the above design characteristics. Hence a concept of hybridized multilayer-multimaterial armour was established to address this lacuna. It was found that hybridization significantly influenced the ballistic performance of armour. The arrangement of maximum layers of high toughness, low modulus – high failure strain material (Kevlar 29) in front, followed by a material with similar toughness but higher strength (Zylon AS) and then minimum layers of low toughness and low failure strain material (Spectra 1000) at the back resulted in higher SBEA and lower Inertial work.

Ballistic performance of nanopowder intruded Kevlar polymeric composite targets

The effect of nano-filler addition on the mechanical and impact properties of Carbon Nano Tubes (CNT) reinforced Kevlar Epoxy composites were studied. Three different laminates (one without fillers and two with increasing concentration of fillers) were prepared using the hand layup process. Tensile, Inter Laminar Shear Stress (ILSS) and Low-velocity ballistic impact experiments were done and the fractured samples were investigated for microanalysis. All the three experimental results showed better properties for the laminate which contains nano-fillers. Laminates with 0.5% CNT addition showed better tensile, ILSS and energy-absorbing properties when compared with the 1% CNT filled and reference composite. From the fractographic study, the front side damage was minimum for the KC0.5 sample while the back face deformation was lower for the KC1 sample. This increase is mainly attributed to the nanofillers which act as a resistance layer to the projectile impact and also by increasing the interfacial bonding between the layers and the matrix. The brittle nature of the front face with nanofiller matrix toughening is the main phenomenon that significantly improved the composite properties.

A multi-scale modeling approach for UHMWPE composite laminates with application to low-velocity impact loading

Ultra-high molecular weight polyethylene (UHMWPE) composites are used in a wide array of protective armor systems. Design of these systems is largely performed through empirical studies which can be costly and time consuming. Modeling tools that enable enhanced performance through exploitation of the design of laminated composite architectures are desired. In this effort, we present a multi-scale, finite element-based representative volume element (RVE) approach that uses laminate mechanics to capture the ply-level material nonlinearity and strain-induced fiber reorientation of UHMWPE composite laminates subjected to low-velocity impact (LVI) loading. The effects of strain rate on the ply-level material response and predicted LVI response of UHMWPE composites are explored. An LVI methodology is developed to characterize the impact performance of thick-section UHMWPE composite materials and applied with the RVE finite element model to calibrate material and delamination properties for Honeywell® SpectraShield® II SR-3136 and DSM Dyneema® HB210. The multi-scale RVE approach accurately captures the peak back-face deformation and extent of delamination for laminates of these materials across three impact energies. The LVI methodology provides a means to evaluate and rank the impact performance of various UHMWPE composite materials, laminate architectures, and processing conditions. The LVI methodology coupled with the multi-scale RVE approach produces ply-level behavior and delamination properties linked to materials and processing conditions, ultimately creating a modeling tool that is capable of exploring the design of laminate architectures for UHMWPE composite structures.

Effect of the temperature on ballistic performance of UHMWPE laminate with limited thickness

Ultra-high molecular weight polyethylene (UHMWPE) is widely used as bulletproof material, but it has evident temperature sensitivity, which can lead to the fluctuation of impact resistance. To explore the effect of temperature on the ballistic performance of UHMWPE laminates, ballistic experiments were conducted at different temperatures of −20, 10, 80, and 95 °C, respectively. The ballistic efficiency, back face deformation and opening hole characteristic of the laminates were compared and analyzed. At all considered temperatures, the laminates with a thickness of 10 mm were perforated, while those with thicknesses of 20 and 30 mm were not, and the ballistic response of the 20 mm laminates changed most strongly with the variation of the temperature. The temperatures of 10 and 80 °C had no significant effect on the deformation and failure of UHMWPE laminates, while the laminates hardened evidently at −20 °C and softened evidently at 95 °C, and the temperature treatments at −20 °C and 95 °C generally led to the highest and lowest protection performance, respectively. The bulletproof application of UHMWPE laminates at temperatures above 80 °C need extra attention and further investigated. The results of this study will be useful for the design of more flexible and effective UHMWPE-based protective equipment.

Ballistic performance of ultra-high molecular weight polyethylene laminate with different thickness

To explore the influence of thickness on the protective performance and damage mechanism of ultra-high molecular weight polyethylene (UHMWPE) laminates penetrated by 7.62 × 39 mm steel core bullets, field firing tests were carried out for 10-, 20-, and 30-mm-thick laminates at 10°C. The deformation and failure process, final failure state and deformation degree, and cross-section of the opening holes of different thickness UHMWPE laminates were analyzed and compared to determine the protective capability and failure mechanism of the laminates. The results show that the ballistic responses of the UHMWPE laminates with different thicknesses vary significantly, and that the protective capability of the UHMWPE laminates was improved with the increase in the laminate thickness. The 10-mm-thick UHMWPE laminate was perforated by the bullet, while the 20- and 30-mm-thick laminates were not. The 10-mm-thick laminate shows two-stage failure characteristics, while the 20- and 30-mm-thick laminates exhibit three-stage failure characteristics that are different from each other. The largest back-face deformation depth of 17.50–21.25 mm was obtained for the 20-mm-thick laminate, while the deformation of the 30-mm-thick laminate is negligible. It is suggested that the functions and application scenarios for the UHMWPE laminates with different thicknesses are different due to their different protective properties and failure mechanisms.

FEM model of protection bullet helmet made from composite material.

Damage evolution, mechanical behaviour, energy absorbtion, back-face deformation (BFD) and the perforation performance of Kevlar epoxy woven composite with and without foam (PU foam) were examined for various impact energies based on the drop weight test. The Kevlar woven composite induces different damage and deformation depending on its hybrid patterns. The Kevlar composite with PU foam decreases significantly, and the BFD of shell composite and transform locally deformation become a global nature. In addition, damage type - as fibres break - is primary dominant for Kevlar composite without PU foam. However, the role major damage as delamination, significantly appear for Kevlar composite with PU foam. In order to investigate the damage mechanism, energy absorbtion and BFD, FEM simulation were also performed. The FEM simulation is in very good agreement with the drop weight test. Finally, the FEM study showed that PU foam is able to decrease significantly, the BFD of composite shell, and the contact force on the skull, during ballistic impact.

Blast resistance of metallic double arrowhead honeycomb sandwich panels with different core configurations under the paper tube-guided air blast loading

Auxetic double arrowhead honeycombs (DAHs) featured by negative Poisson's ratio is attracting increasing attention owing to their tailorable mechanical properties and outstanding energy absorption capability. In this paper, the two-dimensional metallic DAHs were produced and used as the sandwich cores to construct the large-size double arrowhead honeycomb sandwich panels (DAHSPs). A comprehensive experimental investigation on their dynamic responses under the paper tube-guided air blasts was conducted. It majorly focused on the influence of core configurations induced by the variation of core wall thickness, horizontal distance, inclined angles, thickness allocations and foam filling on the deformation/failure modes, associated mechanisms and blast resistance of the target panels. Fair comparisons among different design strategies were performed to evaluate their relative performance. Experimental results show that relative to increasing the core wall thickness, the decrease of horizontal distance is more remarkable to reduce the back face deflection upon the similar weight expense, whereas the effect of inclined angles is limited due to the competition between enhanced bending stiffness and deteriorated transmitted load. A more efficient approach to decrease the back face deformation is to enlarge the inclined angles when the core relative density is relatively low but to decrease the horizontal distance at a high level of relative density. A further improvement of blast resistance can be achieved by allocating more mass to the stuffer wall rather than the tendon one, or by introducing a gradient DAH core instead of the homogeneous one. Compared to adjusting the metallic DAH core itself, the lightweight polyurethane (PU) foam filling is a more competitive manner to promote the blast performance. The preliminary numerical simulations confirmed the shock focusing effect of the paper tube support and indicated reasonable agreement with the experimental results. The present study is supposed to shed light on the design, manufacturing and optimization of auxetic sandwich structures for protection applications.