Damage of multi-layer spaced metallic target plates impacted by radial layered PELE

Chun Cheng,Zhong-hua Du,Xi Chen,Li-zhi Xu,Cheng-xin Du,Ji-long Han,Xiao-dong Wang

School of Mechanical Engineering,Nanjing University of Science and Technology,Nanjing,210094,China

Keywords:PELE(the penetrator with lateral efficiency)Multi-layer spaced metal target plates Impact Damage

ABSTRACT Three different kinds of PELE(the penetrator with lateral efficiency)were launched by ballistic artillery to impact the multi-layer spaced metal target plates.The impact velocities of the projectiles were measured by the velocity measuring system.The damage degree and process of each layer of target plate impacted by the three kinds of projectiles were analyzed.The experimental results show that all the three kinds of projectiles have the effect of expanding holes on the multi-layer spaced metal target plates.For the normal structure PELE(without layered)with tungsten alloy jacket and the radial layered PELE with tungsten alloy jacket,the diameters of holes on the second layer of plates are 3.36 times and 3.76 times of the diameter of the projectile,respectively.For radial layered PELE with W/Zr-based amorphous composite jacket,due to the large number of tungsten wires dispersed after the impact,the diameter of the holes on the four-layer spaced plates can reach 2.4 times,3.04 times,5.36 times and 2.68 times of the diameter of the projectile.Besides,the normal structure PELE with tungsten alloy jacket and the radial layered PELE whit tungsten alloy jacket formed a large number of fragments impact marks on the third target plate.Although the number of fragments penetrating the third target plate is not as large as that of the normal structure PELE,the area of dispersion of fragments impact craters on the third target plate is larger by the radial layered PELE.The radial layered PELE with W/Zr-based amorphous composite jacket released a lot of heat energy due to the impact of the matrix material,and formed a large area of ablation marks on the last three target plates.?2020 China Ordnance Society.Production and hosting by Elsevier B.V.on behalf of KeAi Communications Co.This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

1.Introduction

Multi-layer structure armor which has been widely used in the protection of ships,urban buildings and special vehicles attracts increasing attentions[1-3].As typical protective armor,multi-layer spaced metal plates have good anti-ballistic and anti-explosive effects,their combination mode is various and selection of materials is wide[4-6].The study of multi-layer spaced metal plates has always been an important project.Ben-Dor et al.[7]established the penetration model of conical projectile to multi-layer contact plates and multi-layer spaced plates under the assumption that the projectile is a rigid body without deformation,the volume of the target plate is constant in plastic deformation,the velocity vector of the projectile remains unchanged during penetration,and there is only one-dimensional stress in the crater.The anti-projectile performance of various target plates at different velocities was analyzed theoretically.Elek et al.[8]corrected the phenomenological model of projectile penetrating into target plate considering the deformation of projectile,and established the calculation model of projectile penetrating into multi-layer(contact and interval)metal target plates on this basis.How ever,for the penetration analysis of multi-layer spaced plates,the synergistic cumulative damage effect of the fragments behind the front panel on the rear plate is not considered.Projectiles destroying multi-layer spaced target plates are also emerging in an endless stream,such as armor-piercing projectiles,tandem warheads and semi-armor-piercing warheads,etc.These projectiles are mostly combined with fuze and material technology to achieve penetration damage effect,but most of them have the following problems.a)High technical requirements for fuze when penetrating multi-layer target plates.b)The projectile is easy to ricochet when it impacts the target plate at a large impact angle.c)When tandem warhead is used,because the diameter of the hole formed by the front shaped charge is small,the loading coefficient of the rear shaped charge is limited and the damage effect is reduced[9-11].

The normal structure PELE is composed of high density cylindrical jacket and low density filling inside.It is a kind of projectile without fuze and explosive.The jacket is subjected to intense impact load at the moment of impacting the metal target plate.The existence of internal defects and rapid deposition of kinetic energy in the jacket lead to the initiation,propagation and interconnection of micro-cracks or voids.In the process of penetrating the target plate,the inner wall of the jacket is also subjected to the radial force produced by the expansion of filling and the radial binding effect of the target plate.After penetrating the target plate,the radial binding of the target plate to the jacket disappears,and the damaged jacket breaks up and the fragments disperse further under the radial force produced by the expansion of filling.The kind of projectile can be used to attack high-value targets such as light armored vehicles with low protection ability,ground parking aircraft, low-altitude hovering helicopters, command and communication equipment[12-15].The fragmentation of radial layered PELE were analyzed qualitatively and verified by experiment in Ref.[16].In this paper,a kind of radial layered PELE aimed at multi-layer spaced metal target plates was designed on the basis of normal structure PELE,and two different materials were selected as jacket materials of the novel structure PELE.Through the impact damage experiments of radial layered PELE and normal structure PELE on multi-layer spaced metal target plates,the damage effect of the plates by two kinds structure of projectiles was compared,and the damage effect of radial layered PELE with two kinds of jacket materials on multi-layer spaced metal target plates was studied.

2.Experiment

2.1.Experimental configuration

The projectiles were fired by a 25 mm caliber ballistic artillery.The experimental set-up and the target plates are shown in Fig.1.The distance between the muzzle and the first target plate is 6 m to ensure that the projectiles impact the target plates vertically.The paper plates with on and off aluminum foil used for measuring the velocity of the projectile are arranged at 0.5 m in front of the first target plate.The velocity of the projectile is calculated by the velocity meter. The size of each target plate is 400 mm×400 mm×5 mm,and the distance between two adjacent layers is 0.2 m.The target plates are named as I,II,III and IV in turn from the position close to the muzzle.

2.2.Projectile structure

Fig.2 shows the projectiles used in the experiment.Among them,Fig.2(a)is normal structure PELE,which is mainly composed of jacket,filling and sabot.The sabot can reduce the leakage of gunpowder gas during launch.The outer diameter of the projectile jacket is 25 mm,the length is50 mm the diameter and length of the filling are 20 and 40 mm respectively.Fig.2(b)is the newly designed radial layered PELE consists of two metal cylindrical jackets and two fillings.The outer jacket is 25 mm in diameter,50 mm in length,and the inner jacket is 10 mm in diameter and 40 mm in length.The outer filling is a cylindrical shell with a diameter of 20 mm and a length of 40 mm,while the inner filling is a cylinder with a diameter of 5 mm and a length of 36 mm.

2.3.Projectile and target material

In the test,the filling materials of the two kinds of structural projectiles are all nylon with larger Poisson's ratio.The jacket material of normal structure PELE is tungsten alloy with high density and strength.The inner and outer jacket materials of radial layered PELE are the same.Two kinds of materials are used as jacket materials of radial layered PELE.The one is tungsten alloy,which is the same as used as the jacket of normal structure PELE.The other one is W/Zr-based amorphous composite.W/Zr-based amorphous composite is a kind of composite material with tungsten wire as reinforcing phase and Zr-based amorphous alloy as bonding phase.It has the characteristics of high density,good adiabatic shear and self-sharpening effect.It can be used in armor piercing projectile and other military fields[17,18].In this experiment,Zr38Ti17Cu10.5-Co12Be22.5is used as bonding phase,and tungsten wires with a diameter of 0.3 mm are uniformly and parallel distributed in amorphous materials as reinforcing phase.The volume fraction of tungsten wire is 80%,and the density of the composites is 17.3 g/cm3[19].The micro-structure of the composites is shown in Fig.3.The target plates are Q235 steel plates.The mechanical properties of tungsten alloy,Q235 steel,W/Zr-based amorphous composite and nylon are shown in Table 1.

Fig.1.Experimental set-up,target plates used for impact experiment,(a)Experimental set-up;(b)Target plates.

Fig.2.Projectiles used in the experiment,(a)Normal structure projectile;(b)Radial layered projectile.

3.Experimental results and discussion

3.1.Normal structure PELE

Fig.3.Schematic diagram of(a)cross section,(b)longitudinal section of composite(white part represents tungsten fiber,black part represents Zr-based bulk metal glass).

Table 1 Main mechanical property of all materials used in the experiment.

When the impact velocity is 1198 m/s,the damage of three-layer spaced Q235 steel plates by normal structure PELE is shown in Fig.4.Fig.4(a)shows the damage view from the front of the target plates,Fig.4(b)represents the damage view from the back of the target plates.The central perforation diameter of the target plate(the red marked circumferential circle of perforation in the second and third layers)is 30 mm,84 mm and 45 mm respectively,which is 1.2 times,3.36 times and 1.8 times of the diameter of the projectile,respectively.It shows that the normal structure PELE can penetrate three layers of interval Q235 steel plate and form perforations on the target plates which are much larger than the diameter of the projectile.At the same time,it can be seen from the experimental pictures that the perforation on the first target plate is regular circular,and the hole wall is relatively smooth.The damage on the second target plate is a jagged perforation,which indicates that the head of the projectile has been broken after the projectile penetrated the first target plate.When the projectile impacts the first target plate,a huge pressure is generated between the projectile and the target plate.The head of the filling in the projectile is compressed and deformed rapidly.Due to Poisson effect,the filling head expands radially.The pressure produced by the expansion of the filling head exerts on the inner side of the jacket head.On the other hand,the jacket is also subjected to the huge impact pressure of the target plate in the axial direction.Microcrack damage occurs inside the jacket,and when the jacket penetrates through the target plate,it loses the restraint of the target plate.The jacket head expands and breaks radially under the expansion force of the filling head,so the perforated wall on the second target plate is serrated.When the projectile penetrates the second target plate,it will continue to be impacted by the pressure of the target plate,the filling will be compressed and expanded further,and the crushing degree of the jacket will be further aggravated.The fragments produced by jacket fragmentation have a certain radial velocity component,and form a large area of perforation and impact crater on the third layer target plate.How ever,due to the severe fragmentation and dispersion of projectile jacket,the volume of residual jacket decreases and the diameter of perforation decreases in the center of the third target plate.The diameter of fragment perforation and impact crater is 213 mm,which is about 8.52 times of the diameter of the projectile.It shows that the projectile has a good destructive effect on the third target plates.

Fig.4.Damage of three-layer spaced Q235 steel plates by normal structure PELE.

3.2.Radial layered PELE

When the impact velocity is 1205 m/s,the damage of four-layer interval Q235 steel plates caused by radial layered PELE with tungsten alloy jacket is shown in Fig.5.The diameter of the central perforation on the target plates(the red marked outer circle of the perforation in the last three layers of the target plate)is 28 mm,94 mm,44 mm and 33 mm respectively,which is 1.12 times,3.76 times,1.76 times and 1.32 times of the diameter of the projectile.Compared with the perforation damage of normal structure PELE on multi-layer spaced Q235 steel plates,the perforation diameter on the first and third layers of target is basically the same,but the perforation on the second layer of target plate by radial layered PELE is significantly larger than that by normal structure PELE.From the perforation morphology of the second layer target plate,both of them are serrated perforations.The difference is that the perforation teeth spacing on the second target plate by radial layered PELE is smaller than that by normal structure PELE,which indicates that the head fragmentation of radial layered PELE is more severe after penetrating the first target plate.Because of the existence of the inner jacket,the radial expansion velocity and volume of the outer filling under the impact pressure are promoted.The radial velocity of the jacket head increases.According to the Mott's dynamic fracture theory[20],the strain rate of the ring is equal to the ratio of the expansion speed of the ring to the radius of the ring,so the strain rate of the outer jacket head increases.With the increase of strain rate,the number of activated damage nucleation sites increases,which leads to the decrease of fragment size and the increase of number of fragments.Therefore,a perforation with smaller teeth spacing and larger diameter is formed on the second target plate impacted by radial layered PELE,which enhances the damage effect of projectile on the target plate.In addition,the number of impact craters formed on the third target plate is more and the area of dispersion is larger.The diameter of dispersion is about 238 mm,which is about 9.52 times the diameter of the projectile.How ever,due to the high degree of jacket fragmentation,many fragments are small in size and mass,and fail to penetrate the third target plate,which weakens the damage effect on the fourth target plate.The diameter of the fragments impact crater on the fourth target plate is 135 mm.The damage progress of the first three Q235 steel plates by radial layered PELE with tungsten alloy jacket is shown in Fig.6.

Fig.5.Damage of four-layer spaced Q235 steel plates by radial layered PELE with tungsten alloy jacket.

Fig.6.Damage progress of the first three Q235 steel plates by radial layered PELE with tungsten alloy jacket.

When the impact velocity is 1203 m/s,the damage of four-layer interval Q235 steel plates caused by radial layered PELE with W/Zr based amorphous composite jacket is shown in Fig.7.The central perforation diameter on the target plate(the red marked outer circle of perforation in the last three layers of target plate)is 60 mm,76 mm,134 mm and 67 mm respectively,which is 2.4 times,3.04 times,5.36 times and 2.68 times the diameter of the projectile.Obviously,the radial layered PELE with W/Zr-based amorphous composite jacket has very good perforation damage ability.The perforation wall of the first layer target plate is rough,the target plate around the perforation has a large deflection bending,and there are a lot of traces of tungsten filament around the front perforation of the target plate.The local enlargement of the front perforation on the first target plate is shown in Fig.8.In the process of projectile penetrating the first target plate,when the stress wave reaches the outer surface of the jacket,it reflects and generates tensile stress wave.Because of the low tensile strength of the bonding phase,the tungsten wires in the jacket are dispersed under the action of tensile stress,resulting in a large number of tungsten wire segments with high radial velocity.The radial discrete tungsten wires enlarge the perforation diameter of the target plate,roughen the hole wall,and leave a large number of tungsten wire marks around the perforation.Besides,a small amount of tungsten wires breaks,which impacts on the surface of the target plate.After the projectile penetrated the first target plate,under the radial expansion pressure of the filling,a large number of tungsten wires bend discretely and the bonding phase breaks up,forming larger perforations on the second target plate.A large number of pits formed by impact of fragments produced by bonding phase around the perforation,and the diffuse diameter of the pits is about 151 mm.With the continuous movement of the projectile,the discrete tungsten wires open further,and the tungsten wires move forward together with the broken bonding phase.A perforation of about 5.36 times the diameter of the projectile is formed on the third target plate.From the back view of the target plate,it can be seen that the tearing marks of the target plate are obvious.It shows that the penetration ability of the projectile decreases gradually,and the diameter of the perforation on the fourth target plate decreases.The perforation diameter of the projectile on the fourth target plate decreases,but the traces left by the impact of the broken bonding phase around the perforation are distributed in a wide range,and the dispersal diameter is about 182 mm.A large number of ablation marks can be seen around the perforation of the target plate from the front view s of the last three layers of target plate.This is because theamorphous alloy(the bonding phase)has higher energy than the crystalline alloy with the same composition and in a metastable state.There is a large negative enthalpy of mixing between the main components of amorphous alloys[21].Under high temperature or high pressure,the atoms in amorphous alloy will propagate by themselves,resulting in chemical reactions and structural relaxation of phase equilibrium.Afterwards,amorphous alloy will crystallize into crystalline substance,releasing a large amount of heat,causing combustion and explosion.The damage progress of the first three Q235 steel plates by radial layered PELE with tungsten alloy jacket is shown in Fig.9.

Fig.7.Damage of four-layer spaced Q235 steel plates by radial layered PELE with W/Zr-based amorphous composite jacket.

Fig.8.Local enlargement of the front perforation on the first target plate.

Fig.9.Damage progress of the first three Q235 steel plates by radial layered PELE with W/Zr-based amorphous composite jacket.

The size of holes and scattered fragments on the plates by the three kinds of projectiles are shown in Table 2.The kinetic energies of the three kinds of projectiles are similar.When the initial kinetic energy is basically the same,for the first and third target plate,the perforations made by the radial layered projectile with W/Zr-based amorphous composite jacket are the largest when compared with the other two kinds of projectiles;for the second target plate,the perforation made by the radial layered projectile with tungsten alloy jacket is the largest;for the third target plate,the impactcrater area is largest by the fragments produced by radial layered PELE with tungsten alloy jacket.

Table 2 Size of holes and scattered fragments on the plates.

4.Conclusion

The penetration tests of normal structure PELE and radial layered PELE on multi-layer interval Q235 steel plates were carried out.It can be found that the perforation damage of the first target plate by the radial layered PELE tungsten alloy jacket and normal structure PELE with tungsten alloy jacket is basically the same.How ever,the diameter of the second layer target plate perforated by radial layered PELE with tungsten alloy jacket is much larger than that of the second layer target plate perforated by normal structure PELE.The perforation diameter of the third target plate is basically the same for the normal structure PELE and radial layered PELE with tungsten alloy jacket.How ever,the fragments of radial layered PELE with tungsten alloy jacket have larger impact crater area on the third target plate,although the number of fragments penetrating the target plate is not as large as that of normal structure PELE.The most important feature of damage by layered PELE with W/Zr-based amorphous composite jacket to multi-layer spaced Q235 steel plate is that larger perforations can be formed on each layer of target plate,and ablation and impact marks can be formed on the front of the target plates behind the first target plate.

Acknowledgments

The work was supported by National Natural Science Foundation of China(Grant No.11802141)and Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX18_0465).