Advanced Combat Helmet Research Articles

Design of Mechanics-Guided Helmet Pad and Its Protection Performance Against the Blast Shock Waves.

The blast shock waves generated by the explosion are severe threat to soldiers on the battlefield, while the helmets currently equipped for the soldiers cannot offer sufficient blast protection. Some helmet pads have been developed to improve the protection performance of the combat helmets against shock waves. However, it remains unclear how to design the helmet pads to protect the head more effectively against blast shock waves. This study aims to design a new mechanics-guided helmet pad and evaluate its protection performance by numerical simulations. The design of the new helmet pad is guided by the oblique reflection theory (ORT), and the advanced combat helmet (ACH) pad is applied for comparison. The protection performance of the pads against blast waves from two directions (frontal and lateral) was investigated. The differences in the distributions of overpressure inside the helmet using two types of pads were analyzed, and the intracranial pressure (ICP) of head was compared. The ORT-guided pads can reduce the overpressure inside the helmet, minimizing the possibility of blast-induced traumatic brain injury. Furthermore, the underwash phenomenon can also be controlled when the new pads are applied. The results in this study provide an important theoretical basis and some guidelines on the design of helmet pads for the protection of human brain from blast shock waves.

Temperature Dependent Dynamic Response of Open-Cell Polyurethane Foams

BackgroundPolyurethane foams have many uses ranging from comfort fitting seats and shoes to protective inserts in helmets and sports equipment. Current military helmet designs employ foam pads of varying densities and bulk material properties to help absorb energy from impacts ranging from quasi-static to ballistic level strain-rates.ObjectiveThis study aims to analyze the thermomechanical uniaxial compression behavior of a high density liner foam pad and a low density liner foam pad used in the Advanced Combat Helmet. These experiments were conducted under strain-rates of 102\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^2$$\\end{document} s-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-1}$$\\end{document} and under temperature conditions ranging from -20 to 40 °C. This temperature range was chosen to simulate desert and arctic conditions, with a strain-rate regime chosen to represent loads that would occur often throughout the life of the helmet, such as drops, bumps from riding in a vehicle, or heavy collisions from falling.MethodMultiple experimental apparatuses were used in this study, including a Shimadzu TCE-N300 thermostatic chamber (used to create the varying temperature environments) and a custom-built drop-test system (used to induce intermediate strain-rates). Every experiment was paired with two accelerometers and a high speed camera used for Digital Image Correlation (DIC) to analyze sample deformation and resultant acceleration. The foam’s mechanical response and energy absorption properties were investigated from the measured stress-strain curves. Additionally, each foam composition was analyzed with X-ray computed micro-tomography (XCT) to investigate microstructure properties pre and post-mortem.ResultsResults show that temperature decreased the energy absorption of the low density composition by 48% ± 5% as temperature changed from -20 °C to 40 °C, while energy absorption increased by 53% ± 16% for the high density composition over the same temperature.ConclusionA comparison between the loading response and the material’s density characteristics revealed that the foam’s mechanical properties are heavily dependent on strain-rate applications, as well as environmental factors including temperature. Several important characteristics surrounding each foam composition’s deformation mechanics and damage tolerance as a result of temperature are discussed.

Mechanical analysis of helmeted headforms under ballistic impact with implications in performance evaluation of ballistic helmets

Behind helmet blunt trauma is a significant health concern in modern warfare. The ballistic response of the human head under ballistic impact is highly sought. Towards this end, we conducted ballistic experiments on three different headforms. The following headforms were considered: a) National Institute of Justice based rigid headform, b) Hybrid-III based flexible headform, and c) head model based headform. Headforms b, c were assembled with the Hybrid-III neck. An advanced combat helmet was fitted to the headforms. Helmet-head assembly was subjected to a 9 mm × 19 mm full metal jacket projectile having velocities of 430 ± 15 m/s. The response of the head surrogate in the front, back, side, and crown orientations was studied. Back face deformation (BFD), head kinematics, and intracranial pressures in headforms were measured. In addition, equivalent stress and maximum principal strain in the brain were obtained using concurrent finite element simulations. Results suggest that both local (i.e., due to the localized crushing of the helmet) and global (i.e., due to the bulk motion of the helmet-head parenchyma) responses were dominant under investigated ballistic impacts. Further, the type of the headform affected the biomechanical response. As compared to the rigid headform, a statistically significant increase in head kinematics was observed with the flexible headforms; changes in BFD were statistically insignificant. The orientation dependent responses have been observed. Overall, these results provide novel insights regarding the ballistic response of the headforms with the combat helmet and underscore critical considerations during the ballistic evaluation of helmets.

Study on craniocerebral dynamics response and helmet protective performance under the blast waves

Blast traumatic brain injury (BTBI) is the major type of injury, existing helmets are mainly designed to resist bullets and fragments, so it is necessary to study the explosion- proof performance of helmets. In this study, the validated finite element models including head, Advanced Combat Helmet (ACH), fully-covered helmet based on the prototype of Iron Man helmet were used to establish the blast wave-helmet-head fluid–solid coupling model, dynamic responses such as blast wave flow field pressure, skull stress, brain tissue pressure, displacement and energy absorption were obtained through simulations.Quantitatively analyzed the protective performance of helmets show that wearing ACH can’t reduce the severity of brain injury, but rather increased about 5% compared to without wearing helmet. Wearing fully-covered helmet with same thickness as ACH can reduces the degree of brain injury by about 5%. Fully-covered helmet with same weight as ACH provides better protection, which can reduce the degree of brain injury to 65% than without wearing helmet. Research show that optimizing the shape and thickness of helmet can greatly reduce the brain injury, lighter fully-covered helmet can provide better protection for the brain under blast wave environment. The results can provide reference for new design of helmets.

Protective Performance of Helmets and Goggles in Mitigating Brain Biomechanical Response to Primary Blast Exposure

The current combat helmets are primarily designed to mitigate blunt impacts and ballistic loadings. Their protection against primary blast wave is not well studied. In this paper, we comprehensively assessed the protective capabilities of the advanced combat helmet and goggles against blast waves with different intensity and directions. Using a high-fidelity human head model, we compared the intracranial pressure (ICP), cerebrospinal fluid (CSF) cavitation, and brain strain and strain rate predicted from bare head, helmet-head and helmet-goggles-head simulations. The helmet was found to be effective in mitigating the positive ICP (24–57%) and strain rate (5–34%) in all blast scenarios. Goggles were found to be effective in mitigating the positive ICP in frontal (6–16%) and lateral (5–7%) blast exposures. However, the helmet and goggles had minimal effects on mitigating CSF cavitation and even increased brain strain. Further investigation showed that wearing a helmet leads to higher risk of cavitation. In addition, their presence increased the head kinetic energy, leading to larger strains in the brain. Our findings can improve our understanding of the protective effects of helmets and goggles and guide the design of helmet pads to mitigate brain responses to blast.

Influence of Friction at the Head-Helmet Interface on Advanced Combat Helmet (ACH) Blunt Impact Kinematic Performance.

The purpose of this study was to compare the rotational blunt impact performance of an anthropomorphic test device (ATD: male 50% Hybrid III head and neck) headform donning an Advanced Combat Helmet (ACH) between conditions in which the coefficient of static friction (μs) at the head-to-helmet pad interface varied. Two ACHs (size large) were used in this study and friction was varied using polytetrafluoroethylene (PTFE), human hair, skullcap, and the native vinyl skin of the ATD. A condition in which hook and loop material adhered the headform to the liner system was also tested, resulting in a total of five conditions: PTFE, Human Hair, Skullcap, Vinyl, and Hook. Blunt impact tests with each helmet in each of the five conditions were conducted on a pneumatic linear impactor at 4.3 m/s. The ATD donning the ACH was impacted in seven locations (Crown, Front, Rear, Left Side, Right Side, Left Nape, and Right Nape). The peak resultant angular acceleration (PAA), velocity (PAV), and the Diffuse Axonal Multi-Axis, General Evaluation (DAMAGE) metric were compared between conditions. No pairwise differences were observed between conditions for PAA. A positive correlation was observed between mean μs and PAA at the Front (τ = 0.28; P = .044) and Rear (τ = 0.31; P = .024) impact locations. The Hook condition had a mean PAV value that was often less than the other conditions (P ≤ .024). A positive correlation was observed between mean μs and PAV at the Front (τ = 0.32; P = .019) and Right Side (τ = 0.57; P < .001) locations. The Hook condition tended to have the lowest DAMAGE value compared to the other conditions (P ≤ .032). A positive correlation was observed between the mean μs and DAMAGE at the Rear (τ = 0.60; P < .001) location. A negative correlation was observed at the Left Side (τ = -0.28; P = .040), Right Side (τ = -0.58; P < .001) and Left Nape (τ = -0.56; P < .001) locations. The results of this study indicate that at some impact locations kinematic responses can vary as a function of the friction at the head-to-helmet pad interface. However, a reduction in the coupling of the head-helmet pad interface did not consistently reduce head angular kinematics or measures of brain strain across impact locations. Thus, for the ACH during collision-type impacts, impact location as opposed to μs seems to have a greater influence on head kinematics and rotational-based measures of brain strain.

Head Impact Modeling to Support a Rotational Combat Helmet Drop Test.

The Advanced Combat Helmet (ACH) military specification (mil-spec) provides blunt impact acceleration criteria that must be met before use by the U.S. warfighter. The specification, which requires a helmeted magnesium Department of Transportation (DOT) headform to be dropped onto a steel hemispherical target, results in a translational headform impact response. Relative to translations, rotations of the head generate higher brain tissue strains. Excessive strain has been implicated as a mechanical stimulus leading to traumatic brain injury (TBI). We hypothesized that the linear constrained drop test method of the ACH specification underreports the potential for TBI. To establish a baseline of translational acceleration time histories, we conducted linear constrained drop tests based on the ACH specification and then performed simulations of the same to verify agreement between experiment and simulation. We then produced a high-fidelity human head digital twin and verified that biological tissue responses matched experimental results. Next, we altered the ACH experimental configuration to use a helmeted Hybrid III headform, a freefall cradle, and an inclined anvil target. This new, modified configuration allowed both a translational and a rotational headform response. We applied this experimental rotation response to the skull of our human digital twin and compared brain deformation relative to the translational baseline. The modified configuration produced brain strains that were 4.3 times the brain strains from the linear constrained configuration. We provide a scientific basis to motivate revision of the ACH mil-spec to include a rotational component, which would enhance the test's relevance to TBI arising from severe head impacts.

Comparing the medical coverage provided by four contemporary military combat helmets against penetrating traumatic brain injury

IntroductionModern military combat helmets vary in their shapes and features, but all are designed to protect the head from traumatic brain injury. Recent recommendations for protection against energised projectiles that...

Factors Contributing to Increased Blast Overpressure Inside Modern Ballistic Helmets

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.

Strain Rate Dependent Compressive Response of Open Cell Polyurethane Foam

Polymeric foams are used for impact protection due to their ability to absorb large amounts of strain energy. In this work, the compressive response of an open cell polyurethane foam currently used as liner in the advanced combat helmet is examined across strain rates. A traditional load frame is used to investigate the quasi-static behavior, and two different modifications of a conventional Kolsky (split-Hopkinson) bar configuration are used to probe the dynamic response. A unique, independent method not relying on strain gage signals is presented that leverages high-speed full-field imaging to track the velocity on each side of the sample-bar interface and used to extract the dynamic stress-strain response; the results are compared against traditional strain gage measurements. X-ray tomography is used to examine the global morphological characteristics of the foam. The foam is found to be strongly rate dependent, where the characteristic properties vary logarithmically with strain rate. An analytical expression is presented to describe the rate dependency that collapses all stress-strain curves on a master curve. Full-field kinematic data from digital image correlation taken during loading is used to extract a nonlinear Poisson’s ratio as a function of strain, which is found to be strain rate insensitive. A tangent Poisson function is used to explore the foam’s auxetic behavior. These findings provide insight on physically-based constitutive modeling of foams, crucial to predictive brain injury simulations, as well as motivate the need to probe local heterogenous behavior across strain rates moving forward.

Development of a Methodology for Simulating Complex Head Impacts With the Advanced Combat Helmet.

Blunt impact assessment of the Advanced Combat Helmet (ACH) is currently based on the linear head response. The current study presents a methodology for testing the ACH under complex loading that generates linear and rotational head motion. Experiments were performed on a guided, free-fall drop tower using an instrumented National Operating Committee for Standards on Athletic Equipment (NOCSAE) head attached to a Hybrid III (HIII) or EuroSID-2 (ES-2) dummy neck and carriage. Rear and lateral impacts occurred at 3.0 m/s with peak linear accelerations (PLA) and peak rotational accelerations (PRA) measured at the NOCSAE head center-of-gravity. Experimental data served as inputs for the Simulated Injury Monitor (SIMon) computational model to estimate brain strain. Rear ACH impacts had 22% and 7% higher PLA and PRA when using the HIII neck versus the ES-2 neck. Lateral ACH impacts had 33% and 35% lower PLA and PRA when using HIII neck versus the ES-2 neck. Computational results showed that total estimated brain strain increased by 25% and 76% under rear and lateral ACH impacts when using the ES-2 neck. This methodology was developed to simulate complex ACH impacts involving the rotational head motion associated with diffuse brain injuries, including concussion, in military environments.

Influence of ATD versus PMHS reference sensor inputs on computational brain response in frontal impacts to advanced combat helmet (ACH)

ABSTRACTObjective: This study analyzed the influence of reference sensor inputs from anthropomorphic test devices (ATDs) versus postmortem human subjects (PMHSs) on simulations of frontal blunt impacts to the advanced combat helmet (ACH).Methods: A rigid-arm pendulum was used to generate frontal impacts to ACHs mounted on ATDs and PMHS. An appropriately sized ACH was selected according to standard fitting guidelines. The National Operating Committee on Standards for Athletic Equipment (NOCSAE) head was selected for ATD tests due to shape features that enabled a realistic helmet fit. A custom procedure was used to mount a reference sensor internally near the center of gravity (CG) of the PMHS. Reference sensor data from the head CG were used as inputs for the Simulated Injury Monitor (SIMon). Brain responses were assessed with the cumulative strain damage measure set at 10%, or CSDM(10).Results: Compared to ATD tests, PMHS tests produced 18.7% higher peak linear accelerations and 5.2% higher peak angular velocities. Average times to peak for linear accelerations were relatively similar between ATDs (5.5 ms) and PMHSs (5.8 ms). However, times to peak for angular velocities were higher by a factor of up to 3.4 for PMHSs compared to ATDs. Values for were also higher by a factor of up to 13.1 when PMHS inputs were used for SIMon.Conclusions: The preliminary findings of this work indicate that small differences in ATD versus PMHS head kinematics could lead to large differences in strain-derived brain injury metrics such as CSDM.

Human Skin-Like Composite Materials for Blast Induced Injury Mitigation

Armors and military grade personal protection equipment (PPE) materials to date are bulky and are not designed to effectively mitigate blast impacts. In the current work, a human skin-like castable simulant material was developed and its blast mitigation characteristics (in terms of induced stress reduction at the bone and muscles) were characterized in the presence of composite reinforcements. The reinforcement employed was Kevlar 129 (commonly used in advanced combat helmets), which was embedded within the novel skin simulant material as the matrix and used to cover a representative extremity based human skin, muscle and bone section finite element (FE) model. The composite variations tested were continuous and short-fiber types, lay-ups (0/0, 90/0, and 45/45 orientations) and different fiber volume fractions. From the analyses, the 0/0 continuous fiber lay-up with a fiber volume fraction close to 0.1 (or 10%) was found to reduce the blast-induced dynamic stresses at the bone and muscle sections by 78% and 70% respectively. These findings indicate that this novel skin simulant material with Kevlar 129 reinforcement, with further experimental testing, may present future opportunities in blast resistant armor padding designing.

Assessment of the Effectiveness of Combat Eyewear Protection Against Blast Overpressure.

It is unclear whether combat eyewear used by U. S. Service members is protective against blast overpressures (BOPs) caused by explosive devices. Here, we investigated the mechanisms by which BOP bypasses eyewear and increases eye surface pressure. We performed experiments and developed three-dimensional (3D) finite element (FE) models of a head form (HF) equipped with an advanced combat helmet (ACH) and with no eyewear, spectacles, or goggles in a shock tube at three BOPs and five head orientations relative to the blast wave. Overall, we observed good agreement between experimental and computational results, with average discrepancies in impulse and peak-pressure values of less than 15% over 90 comparisons. In the absence of eyewear and depending on the head orientation, we identified three mechanisms that contributed to pressure loading on the eyes. Eyewear was most effective at 0 deg orientation, with pressure attenuation ranging from 50 (spectacles) to 80% (goggles) of the peak pressures observed in the no-eyewear configuration. Spectacles and goggles were considerably less effective when we rotated the HF in the counter-clockwise direction around the superior-inferior axis of the head. Surprisingly, at certain orientations, spectacles yielded higher maximum pressures (80%) and goggles yielded larger impulses (150%) than those observed without eyewear. The findings from this study will aid in the design of eyewear that provides better protection against BOP.

Evaluation of Environmental Sensors During Laboratory Direct and Indirect Head Exposures.

With the prevalence of traumatic brain injury (TBI) in the military and athletics, several commercial and military environmental sensors (ES) have been developed to quantify head impact exposures. The performance of five ES in controlled laboratory exposures from direct and indirect loadings, and the effect on impact protection and dynamic retention of the worn Advanced Combat Helmet (ACH) was evaluated. Direct impacts were conducted on a drop tower and indirect impacts used a mini-sled. The ES data were compared with laboratory sensors through cross-correlation and comparison of peak values. The effects of ES on dynamic retention were assessed using a one-way ANOVA with Tukey's post hoc analysis against baseline ACH performance. Two ES provided data during the blunt impact tests: one, attached to the side of the headform, correlated well (φ > 0.92) with the laboratory data; the other, mounted in the helmet crown, calculated peak headform velocity, which predicted laboratory velocity well. During indirect impact tests, one environmental sensor (attached to the side of the headform) provided usable data, which correlated well (φ > 0.92) with laboratory data. The inclusion of the environmental sensors did not introduce any safety hazards during the blunt impact attenuation tests or the dynamic retention tests.

Neck Kinematics and Electromyography While Wearing Head Supported Mass During Running.

Advanced combat helmets (ACH) coupled with night-vision goggles (NVG) are required for tactical athletes during training and service. Head and neck injuries due to head supported mass (HSM) are a common occurrence in military personnel. The current study aimed to investigate the effects of HSM on neck muscle fatigue that may lead to chronic stress and injury of the head and neck. Subjects wore an ACH and were affixed with electromagnetic sensors to obtain kinematic data, as well as EMG electrodes to obtain muscle activations of bilateral sternocleidomastoid, upper trapezius, and paraspinal muscles while running on a treadmill. Subjects performed a 2-min warmup at a walking pace, a 5-min warmup jog, running at a pace equal to 90% maximum heart rate until absolute fatigue, and lastly a 2-min cooldown at a walking pace. Kinematic and EMG data were collected over each 2-min interval. Days later, the same subjects wore the same ACH in addition to the NVG and performed the same protocol as the first session. This study showed significant differences in muscle activation of the right upper trapezius [F(1,31) = 10.100] and both sternocleidomastoid [F(1,31) = 12.280] muscles from pre-fatigue to absolute fatigue. There were no significant differences noted in the kinematic variables. This study suggests that HSM can fatigue bilateral neck flexors and rotators, as well as fatigue the neck extensors and rotators on the contralateral side of the mounted NVG.Hanks MM, Sefton JM, Oliver GD. Neck kinematics and electromyography while wearing head supported mass during running. Aerosp Med Hum Perform. 2018; 89(1):9-13.

Finite element analysis of the Advanced Combat Helmet under various ballistic impacts

In this research, ballistic performance of the Advanced Combat Helmet (ACH), which is currently used by the U.S. military, were numerically and experimentally evaluated. The ACH model was first developed and validated against existing test data in literature, which were obtained per the requirements of NIJ-0106.01 standard and the U.S. Army's V50 ballistic limit. The comparison of simulation results to experimental data showed that the developed ACH model was capable of predicting the ACH responses under ballistic impacts of 9-mm bullet and 1.1 g fragment simulating projectile. It is found that stand-off distances, impact point and curvature of impacted area are the main parameters that affect ballistic performance of the ACH. An open field experiment was also conducted for further investigation of ballistic performance of the ACH under higher caliber .223 rifle impact. Later, validated numerical model was used to compare with experimental data in terms of ballistic responses and damage pattern of the ACH. It is also found that although the ACH provides protection against 9-mm bullet impacts, it is inadequate under impact of .223 rifle impact.

The influence of personal protection equipment, occupant body size, and restraint system on the frontal impact responses of Hybrid III ATDs in tactical vehicles

ABSTRACTObjective: Although advanced restraint systems, such as seat belt pretensioners and load limiters, can provide improved occupant protection in crashes, such technologies are currently not utilized in military vehicles. The design and use of military vehicles presents unique challenges to occupant safety—including differences in compartment geometry and occupant clothing and gear—that make direct application of optimal civilian restraint systems to military vehicles inappropriate. For military vehicle environments, finite element (FE) modeling can be used to assess various configurations of restraint systems and determine the optimal configuration that minimizes injury risk to the occupant. The models must, however, be validated against physical tests before implementation. The objective of this study was therefore to provide the data necessary for FE model validation by conducting sled tests using anthropomorphic test devices (ATDs). A secondary objective of this test series was to examine the influence of occupant body size (5th percentile female, 50th percentile male, and 95th percentile male), military gear (helmet/vest/tactical assault panels), seat belt type (3-point and 5-point), and advanced seat belt technologies (pretensioner and load limiter) on occupant kinematics and injury risk in frontal crashes.Methods: In total, 20 frontal sled tests were conducted using a custom sled buck that was reconfigurable to represent both the driver and passenger compartments of a light tactical military vehicle. Tests were performed at a delta-V of 30 mph and a peak acceleration of 25 g. The sled tests used the Hybrid III 5th percentile female, 50th percentile male, and 95th percentile male ATDs outfitted with standard combat boots and advanced combat helmets. In some tests, the ATDs were outfitted with additional military gear, which included an improved outer tactical vest (IOTV), IOTV and squad automatic weapon (SAW) gunner with a tactical assault panel (TAP), or IOTV and rifleman with TAP. ATD kinematics and injury outcomes were determined for each test.Results: Maximum excursions were generally greater in the 95th percentile male compared to the 50th percentile male ATD and in ATDs wearing TAP compared to ATDs without TAP. Pretensioners and load limiters were effective in decreasing excursions and injury measures, even when the ATD was outfitted in military gear.Conclusions: ATD injury response and kinematics are influenced by the size of the ATD, military gear, and restraint system. This study has provided important data for validating FE models of military occupants, which can be used for design optimization of military vehicle restraint systems.

Improvement in head blast-protection via the use of polyurea-augmented advanced combat helmet

Purpose – The purpose of this paper is to optimize the design of the advanced combat helmet (ACH) currently in use, by its designers in order to attain maximum protection against ballistic impacts (fragments, shrapnel, etc.) and hard-surface/head collisions. Since traumatic brain injury experienced by a significant fraction of the soldiers returning from the recent conflicts is associated with their exposure to blast, the ACH should be redesigned in order to provide the necessary level of protection against blast loads. In the present work, augmentations of the ACH for improved blast protections are considered. These augmentations include the use of a polyurea (a nano-segregated elastomeric copolymer)-based ACH external coating/internal lining. Design/methodology/approach – To demonstrate the efficacy of this approach, instrumented (unprotected, standard-ACH-protected, and augmented-ACH-protected) head-mannequin blast experiments are carried out. These experimental efforts are complemented with the appropriate combined Eulerian/Lagrangian transient non-linear dynamics computational fluid/solid interaction analysis. Findings – The results obtained indicated that: when the extent of peak over-pressure reduction is used as a measure of the blast-mitigation effectiveness, polyurea-based augmentations do not noticeably improve, and sometimes slightly worsen, the performance of the standard ACH; when the extent of specific impulse reduction is used as a measure of the blast-mitigation effectiveness, application of the polyurea external coating to the standard ACH improves the blast-mitigation effectiveness of the helmet, particularly at shorter values of the charge-detonation standoff distance (SOD). At longer SODs, the effects of the polyurea-based ACH augmentations on the blast-mitigation efficacy of the standard ACH are inconclusive; and the use of the standard ACH significantly lowers the accelerations experienced by the skull and the intracranial matter. As far as the polyurea-based augmentations are concerned, only the internal lining at shorter SODs appears to yield additional reductions in the head accelerations. Originality/value – To the authors’ knowledge, the present work contains the first report of a combined experimental/computational study addressing the problem of blast-mitigation by polyurea-based augmentation of ACH.

A study on protective performance of bullet-proof helmet under impact loading

A large number of brain injuries and casualties can be caused by the impact of bullets on the bullet-proof helmets, for which the underlying mechanisms are unclear and are likely to be complex. In the current study, an American advanced combat helmet was scanned to obtain 3-dimensional (3D) geometric information, from which a 3D finite element (FE) model of a ballistic helmet was developed. With this model, FE simulation was conducted and the results were compared with and verified by data from a ballistic test and a FE simulation study previously reported. Furthermore, the protective performance of the ballistic helmet was investigated using the FE model. The verification results show that the FE model of this ballistic helmet is effective, and data from the current study should be useful in providing theoretical guidance in the design of ballistic helmets.