Modelling ballistic impact on military helmets:The relevance of projectile plasticity

The need to develop armour systems to protect against attacks from various sources is increasingly a matter of personal,social and national security.To develop innovative armour systems it is necessary to monitor developments being made on the type,technology and performance of the threats(weapons,projectiles,explosives,etc.) Specifically,the use of high protection level helmets on the battlefield is essential.The development of evaluation methods that can predict injuries and trauma is therefore of major importance.However,the risk of injuries or trauma that can arise from induced accelerations is an additional consideration.To develop new materials and layouts for helmets it is necessary to study the effects caused by ballistic impacts in the human head on various scenarios.The use of numerical simulation is a fundamental tool in this process.The work here presented focuses on the use of numerical simulation(finite elements analysis) to predict the consequences of bullet impacts on military helmets on human injuries.The main objectives are to assess the level and probability of head trauma using the Head Injury Criterion,caused by the impact of a 9 mm NATO projectile on a PASGT helmet and to quantify the relevance of projectile plasticity on the whole modelling process.The accelerations derived from the impact phenomenon and the deformations caused on the helmet are evaluated using fully three-dimensional models of the helmet,head,neck and projectile.Impact studies are done at impact angles ranging from 0 to 75°.Results are presented and discussed in terms of HIC and probability of acceleration induced trauma levels.Thorough comparison analyses are done using a rigid and a deformable projectile and it is observed that plastic deformation of the projectile is a significant energy dissipation mechanism in the whole impact process.

Performance study of jute-epoxy composites/sandwiches under normal ballistic impact

This study is undertaken to explore the use of natural fiber Jute-epoxy(JE),Jute-epoxy-rubber(JRE)sandwich composite for ballistic energy absorption.Energy absorbed and residual velocities for these composites are evaluated analytically and through Finite Element Analysis(FEA).FE analysis of JE plates is carried out for different thicknesses(3,5,10 and 15 mm).JE plates and JRE sandwiches having the same thickness(15 mm) are fabricated and tested to measure residual velocity and energy absorbed.The analytical results are found to agree well with the results of FE analysis with a maximum error of 9%.The study on JE composite plate reveals that thickness influences the energy absorption.Experimental and FE analysis study showed that JRE sandwiches have better energy absorption than JE plates.Energy absorption of a JRE sandwich is about 71% greater than JE plates.Damages obtained from FEA and testing are in good agreement,SEM analysis confirms composites failed by fiber rupture and fragmentation.

Behavior of Aramid Fiber/Ultrahigh Molecular Weight Polyethylene Fiber Hybrid Composites under Charpy Impact and Ballistic Impact

The aramid fiber礥HMWPE (ultrahigh molecular weight polyethylene) fiber hybrid composites (AF礑F) were ma-nufactured. By Charpy impact, the low velocity impact behavior of AF礑F composite was studied. And the high velocity impact behavior under ballistic impact was also investigated. The influence of hybrid ratio on the performances of low and high velocity impact was analyzed, and hybrid structures with good impact properties under low velocity impact and high velocity were optimized. For Charpy impact, the maximal impact load increased with the accretion of the AF layers for AF礑F hybrid composites. The total impact power was reduced with the decrease of DF layers and the delamination can result in the increase of total impact power. For ballistic impact, the DF ballistic performance was better than that of the AF and the hybrid ratio had a crucial influence. The failure morphology of AF礑F hybrid composite under Charpy impact and ballistic impact was analyzed. The AF礑F hybrid composites in suitable hybrid ratio could attain better performance than AF or DF composites.

An experimental study on ballistic impact response of jute reinforced polyethylene glycol and nano silica based shear thickening fluid composite

The present study aims at assessing the ballistic impact behaviour of jute reinforced polyethylene glycol(PEG)and nano silica based shear thickening fluid(STF).Preparation of STF is achieved by dispersing the nano silica particles at different weight percentage loadings of 10%,20%,30%and 40%in PEG and the effect of various weight percentages loading of nano silica particles on ballistic performance of the proposed composites is studied experimentally.Rheological studies of the prepared STF’s showed that at all nanosilica loading shear thickening occurred and also the shear thickening was highest at higher loading of nano silica at lower rate of shear.The study reveals that the ballistic performance of the jute fabric is enhanced with impregnation of STF.The ballistic results indicate that energy absorption of the proposed composites is enhanced with increased loading of nano silica particles and at the same time,the effect of STF was reduced.Specific energy absorption(SEA)of the neat fabric and the proposed composites was made use of for the purpose of comparing the energy absorption capabilities.It is found that the SEA of proposed composites with 10%nano silica loading is lesser than the neat fabric both in case of 3 layers and 6 layers.It was also found that proposed composite with 40%nano silica loading exhibits highest SEA compared to neat fabric and its counterparts with its SEA being 3.21 and 3.76 times highest compared to three and six layers of neat fabrics respectively.

Probabilistic Failure Analysis of Composite Beams for Optimum Ply Arrangements under Ballistic Impact

The probabilistic analysis takes into consideration an effect of scatter in elastic and strength properties of composite beam, and velocity of impactor. The damage model is implemented in the FE （finite element） code by a VUMAT （user-defined subroutine）. The inter ply failure is modeled using cohesive surfaces between the plies. Dynamic response is obtained using explicit time domain integration approach. SFEA （stochastic finite element analysis） is used to study the initiation of fiber failure analysis due to ballistic impact. SFEA provided the critical stress input in the limit state which is computationally solved using reliability software. The random variation in these properties is used for determining statistics of stress in the lamina. These are compared to the random strengths in the limit state function and probability failure surface is obtained by using GPRSM （Gaussian process response surface method）. GPRSM is used to predict the Pf （probability of failure） for different ply lay-ups arrangement. The Pf of Chang-Chang initiation of fiber failure for simply supported composite beams with symmetric cross ply lay-ups are （88.9%, 1.47% and 58.1%） greater than the anti-symmetric cross ply, symmetric angle ply and anti-symmetric angle ply, respectively. Sensitivity analysis is also carried out for symmetric cross ply arrangements.

Ballistic impact response of resistance-spot-welded(RSW) double-layered plates for Q&P980 steel

Ballistic impact response of resistance-spot-welded(RSW)double-layered(2×1.6 mm)plates(190 mm×150 mm)for Q&P980 steel impacted by a round-nosed steel bullet(12 mm diameter and 30 mm length)was investigated by using gas gun and high-speed camera system.The RSW specimens were spot welded using a 6 mm diameter electrode face producing a 7.2 mm diameter fusion zone of the spot weld.The ballistic curve and energy balance for the tests of the spot weld of the RSW specimens at different velocity were analyzed to characterize the ballistic behavior of the RSW specimens under bullet impact.The fracture mechanisms of the RSW specimens under bullet impact were presented.For the tests below the ballistic limit,the cracks initiated from the notch-tip and propagated along the faying surface or obliquely through the thickness depending on the impact velocity.For the tests above the ballistic limit,the plug fracture in the front plate of the RSW specimen could be caused by the thinning-induced necking in the BM near the HAZ,while the plug fracture in the rear plate of the RSW specimens may be consist of the circumferential cracking from the rear surface and the bending fracture of the hinged part of material.The effects of the electrode indentation and the weld interfaces on deformation and fracture of the RSW specimens under bullet impact were revealed.For the tests above the ballistic limit,the circumferential fracture from the rear surface of the RSW specimens was always initiated along the interior periphery of the electrode indentation and the crack paths were along the FZ/CGHAZ or CGHAZ/FGHAZ interface.When the circumferential crack also formed outside the electrode indentation,the fracture on the BM/HAZ interface could be found.On the front plate of the RSW specimens,the shear/bending induced cracking from the notch-tip were observed and the crack paths were along the FZ/CGHAZ or CGHAZ/FGHAZ interface.

On the effect of pitch and yaw angles in oblique impacts of smallcaliber projectiles

A terminal ballistic analysis of the effects of 7.62 mm × 51 AP P80 rounds on inclined high-strength armor steel plates is the focus of the presented study.The findings of an instrumented ballistic testing combined with 3D advanced numerical simulations performed using the IMPETUS Afea? software yielded the conclusions.The experimental verification proved that slight differences in the pitch-andyaw angles of a projectile upon an impact caused different damage types to the projectile’s core.The residual velocities predicted numerically were close to the experimental values and the calculated core deviations were in satisfactory agreement with the experimental results.An extended matrix of the core deviation angles with combinations of pitch-and-yaw upon impact angles was subsequently built on the basis of the numerical study.The presented experimental and numerical investigation examined thoroughly the influence of the initial pitch and yaw angles on the after-perforation projectile’s performance.

Dependence of impact regime boundaries on the initial temperatures of projectiles and targets

Towards higher impact velocities,ballistic events are increasingly determined by the material temperatures.Related effects might range from moderate thermal softening to full phase transition.In particular,it is of great interest to quantify the conditions for incipient or full melting of metals during impact interactions,which result in a transition from still strength-affected to hydrodynamic material behavior.In this work,we investigate to which extent the respective melting thresholds are also dependent on the initial,and generally elevated,temperatures of projectiles and targets before impact.This is studied through the application of a model developed recently by the authors to characterize the transition regime between high-velocity and hypervelocity impact,for which the melting thresholds of materials were used as the defining quantities.The obtained results are expected to be of general interest for ballistic application cases where projectiles or targets are preheated.Such conditions might result,for example,from aerodynamic forces acting onto a projectile during atmospheric flight,explosive shapedcharge-jet formation or armor exposure to environmental conditions.The performed analyses also broaden the scientific understanding of the relevance of temperature in penetration events,generally known since the 1960s,but often not considered thoroughly in impact studies.

Ballistic Penetration Damage of Hybrid Thermoplastic Composites Reinforced with Kevlar and UHMWPE Fabrics

Polymer matrix types of fiber hybrid composites are key factors to improve ballistic impact damage tolerances.Here we report ballistic penetration damages of Kevlar/ultra-high molecular weight polyethylene(UHMWPE)hybrid composites with thermoplastic polyurethane(PU)matrix.The hybrid composites were penetrated by fragment-simulating projectiles(FSPs)using an air gun impact system.The effects of stacking sequences on the ballistic performance of hybrid composites were analyzed.Two types of specific energy absorption(the energy absorption per unit area density and the energy absorption per unit thickness)were investigated.It was found that the main damage modes of PU hybrid composites were fiber breakage,matrix damage,fiber pullout and interlayer delamination.The instantaneous deformation could not be used as a reference index for evaluating the ballistic performance of the target plate.The energy absorption process of the PU hybrid composites showed a nonlinear pattern.The hybrid structure affected the specific energy absorption of the materials.

Fracture mechanism of a laminated aluminum alloy plate during ballistic impact

The multilayered 7XXX series aluminum alloy was impacted by 7.62 mm ogival projectiles at velocities ranging from 787 to 851m·s^（-1）. The deformed microstructure under various impacting velocities and fracture surfaces of different sections were investigated at different physical scales to determine the process of failure.Optical microscopy（OM）,electron back-scattered diffraction（EBSD） and scanning electron microscopy（SEM） were used in the investigation. The results show that crater is constrained in the 7B52 front layer and two types of adiabatic shear bands which are transformed bands and deformed bands and different types of cracks are observed.Spall fracture is the significant failure mode of 7B52 front layer, and the resulting delamination leads to the presence of bending tensile fracture instead of the shear plugging.The ductile 7A01 layer blunts and deflects the spall crack tips, preventing the targets from full spall, and induces a constraint of 7A52 rear layer. The level of the constraint determines different fracture modes of 7A52 layer,accounting for the asymmetry of damage.

Ballistic penetration damages of hybrid plain-woven laminates with carbon,Kevlar and UHMWPE fibers in different stacking sequences

Hybrid composite materials combine different fibers in preform and take advantages of different mechanical behaviors for improving ballistic impact damage tolerances.Here we report ballistic impact damages of plain-woven laminates with different hybrids and stacking sequences.Three kinds of hybrid laminates,i.e.,carbon/Kevlar,carbon/ultra-high molecular weight polyethylene(UHMWPE),and UHMWPE/Kevlar,had been prepared and tested in ballistic penetration with fragment simulating projectiles(FSP).The residual velocities of the projectiles and impact damage morphologies of the laminates have been obtained to show impact energy absorptions for the different hybrid schemes.A microstructural model of the hybrid laminates had also been established to show impact damage mechanisms with finite element analysis(FEA).We found that the UHMWPE/Kevlar hybrid laminates with Kevlar layers as the front face have the highest energy absorption capacity,followed by the carbon/Kevlar hybrid laminates with carbon layers as the front face.The main damage modes are fiber breakages,matrix crack and interlayer delamination.The ballistic damage evolutions from the FEA results show that the major damage is shear failure for front layers,while tension failure for the back layers.We expect that the ballistic impact performance could be improved from the different hybrid schemes.

Fatigue crack propagation in a helicopter component subjected to impact damage

Damage tolerant methodology is increasingly used in aeronautical components,especially due the fact that the Aviation Regulation requires such an assessment in case an accidental damage occurs.At present,there is a strong and actual interest in applying such procedures to helicopter components that are subjected to high frequency cyclic loads.In this paper,an investigation on a damaged transmission shaft for a tail rotor transmission of an actual helicopter has been carried out focusing on the fatigue crack propagation.A complete sequence of experimental tests was performed in order to create an actual ballistic damage and to subsequently check the damage tolerant behaviour.The shaft was damaged by oblique ballistic impact and was subsequently subjected to torsional fatigue loading.During the fatigue cycles several cracks propagated from the ballistic damages.Both of these steps(impact and fatigue loading)were also simulated by a complex modelling approach based on Finite Element Models and fracture mechanics theory.The comparison between the experimental and numerical results shows a good agreement but it underlines the need for a very refined modelling technique capable to replicate all the features associated with the damage in order to reliably simulate the subsequent propagation phase.

Failure investigation on high velocity impact deformation of boron carbide(B_(4)C) reinforced fiber metal laminates of titanium/glass fiber reinforced polymer

High velocity ballistic impact deformation behaviour of Titanium/GFRP Fiber Metal Laminates(FML)has been explored.Both single and multiple projectiles impact conditions were considered.Ti/GFRP FML targets were fabricated with addition of 5%and 10%weight percentage of boron carbide(B_(4)C)particles.Mechanical properties of Ti/GFRP FML targets were determined as per ASTM standards.High velocity ballistic experiments were conducted using Armour Piercing Projectile(APP)of diameter 7.62 mm and velocity ranging between 350 and 450 m/s.Depth of penetration of the projectile into the target was measured.The deformation behaviour of Ti/GFRP targets with and without the presence of ceramic powder(B_(4)C)was investigated.“Ductile hole growth”failure mode was observed for pure GFRP target when subjected to single projectile impact whereas“plugging”failure mode was noted for Ti/GFRP targets.The presence of B_(4)C(5%by weight)particles has significantly improved the ballistic resistance of the Ti/GFRP FML target by offering frictional resistance to the projectile penetration.Further addition(10%by weight)of B_(4)C has reduced the ballistic performance due to agglomeration.None of the targets showed‘brittle cracking’or‘fragmentation’failures.When compared to the published results of Aluminium(Al 1100/GFRP and Al 6061/GFRP)FMLs,Ti/GFRP FML showed lesser DoP which increases its potential application to aerospace industry.

Partial penetration of annular grooved projectiles impacting ductile metal targets

Changing and optimizing the projectile nose shape is an important way to achieve specific ballistic performance.One special ballistic performance is the embedding effect,which can achieve a delayed high-explosive reaction on the target surface.This embedding effect includes a rebound phase that is significantly different from the traditional penetration process.To better study embedment behavior,this study proposed a novel nose shape called an annular grooved projectile and defined its interaction process with the ductile metal plate as partial penetration.Specifically,we conducted a series of lowvelocity-ballistic tests in which these steel projectiles were used to strike 16-mm-thick target plates made with 2024-O aluminum alloy.We observed the dynamic evolution characteristics of this aluminum alloy near the impact craters and analyzed these characteristics by corresponding cross-sectional views and numerical simulations.The results indicated that the penetration resistance had a brief decrease that was influenced by its groove structure,but then it increased significantlydthat is,the fluctuation of penetration resistance was affected by the irregular nose shape.Moreover,we visualized the distribution of the material in the groove and its inflow process through the rheology lines in microscopic tests and the highlighted mesh lines in simulations.The combination of these phenomena revealed the embedment mechanism of the annular grooved projectile and optimized the design of the groove shape to achieve a more firm embedment performance.The embedment was achieved primarily by the target material filled in the groove structure.Therefore,preventing the shear failure that occurred on the filling material was key to achieving this embedding effect.

Dynamic impact protective body armour:A comprehensive appraisal on panel engineering design and its prospective materials

Personal body armour is one of the most important pieces of equipment to protect human beings from various critical and fatal injuries.In today’s modern world,various organizations including law enforcement and security service have made it mandatory for their personnel to wear personal protection system while on field duty.However,the systems should comprise an improved ballistic performance,light-weighted,flexible as well as comfortable panel not only to be accepted with a wider range but also for effective performances of the consumer.Generally,the overall performances of the protective body armour could be affected by various parameters including armour design techniques,type of materials used and finishing of the panels.The current paper aims to critically review state-of-art for armour panel design techniques and the different perspective body armour materials.The paper starts by discussing the different body armour and its category.Later,the different states of technology for armour panel design(mostly for women),its problems and the possible solutions will be cited.Later,the commonly used different polymeric fibrous and the future possible advanced materials including carbon nanotube(CNT),Graphene CNT and shear thickening fluids(STFs)treated materials for developing the reinforced body armour panel will be discussed.The authors believe that this paper will enlighten useful guidelines and procedures about the different panel design techniques and current and promising future materials for researchers,designers,engineers and manufacturers working on the impact resistance body armour field.

Development of cost effective personnel armour through structural hybridization

The objective of the present study is to develop cost effective thermoplastic hybrid laminate using Dyneema®HB50 and Tensylon®HSBD 30A through structural hybridization method.Laminates having 20 mm thickness were fabricated and subjected to 7.62
39 mm mild steel core projectile with an impact velocity of 730±10 ms1.Parameters such as energy absorption,back face deformation and rate of back face deformation were measured as a function of hybridization ratio.It was observed that hybrid laminate with 50:50 ratio(w/w)of Tensylon®and Dyneema®with Tensylon®as front face showed 200%more energy absorption when compared to 100%Tensylon®laminate and showed equal energy absorption as that of expensive 100%Dyneema®laminate.Moreover,hybrid laminate with TD50:50 ratio showed 40%lower in terms of final back face deformation than Dyneema®laminate.Rate of back face deformation was also found to be slow for hybrid laminate as compared to Dyneema®laminate.Dynamic mechanical analysis showed that,Tensylon®laminate has got higher stiffness and lower damping factor than Dyneema®and hybrid laminates.The interface between Tensylon®and Dyneema®layers was found to be separating during the penetration process due to the poor interfacial bonding.Failure behaviour of laminates for different hybridization ratios were studied by sectioning the impacted laminates.It was observed that,the Tensylon®laminate has undergone shear cutting of fibers as major failure mode whereas the hybrid laminate showed shear cutting followed by tensile stretching,fiber pull out and delamination.These inputs are highly useful for body armour applications to design cost effective armour with enhanced performance.

Damage mechanics and energy absorption capabilities of natural fiber reinforced elastomeric based bio composite for sacrificial structural applications

The present study deals with the experimental,finite element(FE)and analytical assessment of low ballistic impact response of proposed flexible‘green’composite make use of naturally available jute and rubber as the constituents of the composite with stacking sequences namely jute/rubber/jute(JRJ),jute/rubber/rubber/jute(JRRJ)and jute/rubber/jute/rubber/jute(JRJRJ).Ballistic impact tests were carried out by firing a conical projectile using a gas gun apparatus at lower range of ballistic impact regime.The ballistic impact response of the proposed flexible composites are assesses based on energy absorption and damage mechanism.Results revealed that inclusion of natural rubber aids in better energy absorption and mitigating the failure of the proposed composite.Among the three different stacking sequences of flexible composites considered,JRJRJ provides better ballistic performance compared to its counterparts.The damage study reveals that the main mechanism of failure involved in flexible composites is matrix tearing as opposed to matrix cracking in stiff composites indicating that the proposed flexible composites are free from catastrophic failure.Results obtained from experimental,FE and analytical approach pertaining to energy absorption and damage mechanism agree well with each other.The proposed flexible composites due to their exhibited energy absorption capabilities and damage mechanism are best suited as claddings for structural application subjected to impact with an aim of protecting the main structural component from being failed catastrophically.

Shock-induced reaction behaviors of functionally graded reactive material

In this paper,the ballistic impact experiments,including impact test chamber and impact double-spaced plates,were conducted to study the reaction behaviors of a novel functionally graded reactive material(FGRM),which was composed of polytetrafluoroethylene/aluminum(PTFE/Al)and PTFE/Al/bismuth trioxide(Bi_(2)O_(3)).The experiments showed that the impact direction of the FGRM had a significant effect on the reaction.With the same impact velocity,when the first impact material was PTFE/Al/Bi_(2)O_(3),compared with first impact material PTFE/Al,the FGRM induced higher overpressure in the test chamber and larger damaged area of double-spaced plates.The theoretical model,which considered the shock wave generation and propagation,the effect of the shock wave on reaction efficiency,and penetration behaviors,was developed to analyze the reaction behaviors of the FGRM.The model predicted first impact material of the FGRM with a higher shock impedance was conducive to the reaction of reactive materials.The conclusion of this study provides significant information about the design and application of reactive materials.

Assessment of Self-healing Efficacy of Thermoplastic Ionomer Films Interleaving Carbon-Fibre Reinforced Epoxy Matrix Laminates

In recent years there has been a strong interest in thermoplastic polymers with self-healing behaviour, which after suffering mechanically-induced damage self-repair via energy-activated macromolecular rearrangements. The use of film-shaped self-regenerating polymers in alternating layers with high-performance continuous fibre-reinforced thermosetting polymer matrix laminates is considered particularly attractive in the mitigation of impact damage in high-demanding components and structures, insofar as the self-healing films may at the same time toughen the base fibrous thermosetting matrix laminate composite while providing immediate or subsequent self-repairing according to the above mentioned mechanisms. In this work, mechanical flexural testing along with infrared thermography inspection is proposed for characterizing low temperature （typical of the altitudes in which modem civil and military aircrafts travel） transverse low-energy ballistic impact damage （commonly occurring under the above cited conditions） in thermoplastic ionomer films interleaving carbon-fibre reinforced epoxy matrix laminates, as well as to assess the degree of success of thermally-activated self-healing process of ionomeric phase by external heating sources. Preliminary mechanical results supported the self-healing hypothesis of impact damaged hybrid laminates, and exploratory thermography imaging of both the as-damaged and as-rejuvenated test coupons suggested that this nondestructive evaluation technique is sensitive enough to detect healing effects.

Microstructure evolution of Mg-Zn-Zr magnesium alloy against soft steel core projectile

The study aimed to shed light on the post deformation and damage behavior of an extruded Mg-Zn-Zr alloy under a ballistic impact.The results revealed that the initial microstructure consisted of both{0001}basal and{1010}prismatic fiber texture.After impact,adiabatic shear bands,pronounce different twinning in big grains,,<c>,and<c+a>types of dislocations,and grain refinement through twinning induce recrystallization accommodated the strain,and absorbed∼65.7%of the energy during impact carried by a soft steel projectile.Interestingly,the deformation behavior at the top broad sides of the crater was entirely different.The weak basal texture was changed to a strong prismatic texture,which was further proved by typical sigmoidal compressive stress-strain curves.A revised model for the development of the ultra-fine grains adjacent to the crater has been proposed.The microhardness and yield strength was∼33%and∼40%higher and chiefly ascribed to strain hardening in ultra-fine grained near the surface of the perforation path.The exit of the perforation path was severely damaged and forms onion-shaped concentric rings which were comprised of melted zones,dimples,and cracks.Based on the all interesting findings,this study can be a clue for the development of the lightweight Mg alloy for military and aerospace applications.