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### Guest Editorial

J. Appl. Mech. 2010;77(5):050301-050301-3. doi:10.1115/1.4001699.
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The authors would like to acknowledge the significant contribution concerning the early history of the ISB made by Joseph E. Backofen, former chairman of NDIA’s Ballistics Division (1980–1998), who was responsible for organizing and guiding many ISB and chairmen of the International Ballistics Committee 1993–2010.

Topics: Ballistics
Commentary by Dr. Valentin Fuster

### Foreword

J. Appl. Mech. 2010;77(5):050501-050501-1. doi:10.1115/1.4001698.
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This issue of the Journal of Applied Mechanics contains 19 scientific papers presented at the 25th International Symposium on Ballistics, 17-21 May 2010, organized at Beijing, China, by the Nanjing University of Science and Technology (NUST) and the China Ordnance Society, under the auspices of the International Ballistics Committee, and in collaboration with the National Defense Industrial Association, USA. Symposium Chairman: Professor Wang Zhongyuan, NUST Symposium Vice Chairman: Professor Zhang Xiaobing, NUST

Commentary by Dr. Valentin Fuster

### RESEARCH PAPERS: Interior Ballistics

J. Appl. Mech. 2010;77(5):051401-051401-9. doi:10.1115/1.4001558.

This work presents a mathematical model for the two-phase flows in the mortar systems and demonstrates the application of approximate Riemann solver on such model. The mathematical model for the two-phase gas-dynamical processes in the mortar tube consists of a system of first-order, nonlinear coupled partial differential equations with inhomogeneous terms. The model poses an initial value problem with discontinuous initial and boundary conditions that arise due to the design complexity and nonuniformity of granular propellant distribution in the mortar tube. The governing equations in this model possess characteristics of the Riemann problem. Therefore, a high-resolution Godunov-type shock-capturing approach was used to address the formation of flow structure such as shock waves, contact discontinuities, and rarefaction waves. A linearized approximate Riemann solver based on the Roe–Pike method was modified for the two-phase flows to compute fully nonlinear wave interactions and to directly provide upwinding properties in the scheme. An entropy fix based on Harten–Heyman method was used with van Leer flux limiter for total variation diminishing. The three-dimensional effects were simulated by incorporating an unsplit multidimensional wave propagation method, which accounted for discontinuities traveling in both normal and oblique coordinate directions. A mesh generation algorithm was developed to account for the projectile motion and coupled with the approximate Riemann solver. The numerical method was verified by using exact solutions of three test problems. The specific system considered in this work is a 120 mm mortar system, which contains an ignition cartridge that discharges hot gas-phase products and unburned granular propellants into the mortar tube through multiple vent-holes on its surface. The model for the mortar system was coupled with the solution of the transient gas-dynamic behavior in the ignition cartridge. The numerical results were validated with experimental data. Based on the close comparison between the calculated results and test data, it was found that the approximate Riemann solver is a suitable method for studying the two-phase combustion processes in mortar systems.

Commentary by Dr. Valentin Fuster
J. Appl. Mech. 2010;77(5):051402-051402-5. doi:10.1115/1.4001560.

Cased telescoped ammunition (CTA) is a kind of charge structure with projectile embedded in the cartridge case. The advantages of CTA, compared with concepts using conventional ammunition, are: (1) reduced charge/ammunition volume, (2) improved performance, and (3) enhanced power and survivabillity of armament. The projectile is placed in the control tube of the cartridge before shooting. After the primer is struck, propellant product gases, generated by the igniter charge burning in the central igniter tube, drive the projectile to move forward along the control tube, and then causing the main propellants around the igniter tube and control tube to burn. Therefore, in the process of interior ballistics, there is a motion of the projectile in the control tube before the projectile engraves the rifles, in contrast with the traditional ammunition. The consistency of this motion has an important influence on the stability of CTA interior ballistic performance. The experiments on the ignition and combustion of propellants and motion of projectile in the control tube are carried out using a high-speed video recording system in this study. The projectile velocity at the entrance of the rifle is obtained from the recorded images. A two-phase flow model of CTA is also established and simulated by using the two-phase flow method and computational fluid dynamics technology. The calculated projectile velocity is in good agreement with the experimental data. The numerical results show that the developed mathematical model gives the correct trend and can provide useful calculated parameters for the structural design of CTA components.

Commentary by Dr. Valentin Fuster
J. Appl. Mech. 2010;77(5):051403-051403-9. doi:10.1115/1.4001285.

Vented flash tubes have often been used in the ignition train of medium and large caliber weapon systems. Despite their long history of ballistic usage, there are undesirable features associated with uneven venting of the combustion products. Pressure measurements at various locations from the flash tube have shown severe variations with time, which is associated with spatially nonuniform mass discharging rate from the vent holes. Measured pressure profiles in the flash tube show counterintuitive, nonmonotonic pressure distributions with the lowest pressure in the middle of the venting section of the flash tube. A model of the flash tube venting process was developed to explain these phenomena using modern, high-order numerical schemes. Source terms accounting for mass addition from the black powder pellets, mass loss through the vent holes, wall friction, differential area changes, and volume changes from surface regression of black powder pellets were fully coupled in the model. The numerical results of this model reproduced the severe pressure variations and nonmonotonic pressure profiles observed in experiments. In general, they are caused by gas dynamic effects from a slowly moving normal shock wave in the middle portion of the venting section of the flash tube. As the driving pressure from the burning black powder pellets changes, the location of the normal shock wave jumps from one vent hole set to another, producing pressure variations observed in experiments. The physical understanding gained from this model solution has provided guidance for achieving more uniform mass discharging rate by varying the vent hole sizes as a function of distance along the flash tube.

Commentary by Dr. Valentin Fuster
J. Appl. Mech. 2010;77(5):051404-051404-7. doi:10.1115/1.4001288.

The multilevel stepped-wall and rectangular observation chambers are designed to study the multipoint ignition process and the combustion stability control mechanism of the bulk-loaded liquid propellant gun. The expansion process and interaction of high-speed twin combustion-gas jets in liquid are studied by means of a high-speed digital camera system. The influence of the nozzle diameter, dual-orifice interval, jet pressure, and chamber structure on the jet expansion shape is discussed. The results indicate that a larger ratio of diameter-to-length can suppress the jet instability in stepped-wall chambers. Higher axial expansion velocity is found under the larger injection pressure, which it increases the instability of jet expansion process. Compared with a rectangular chamber, the axial expansion velocity is smaller, and the radial expansion velocity is larger in stepped-wall chambers under the same conditions. The theoretical studies of interaction of the gas jet with liquid were developed based on the experiment. Two-dimensional unsteady models are used to get the pressure, density, and velocity contours. The numerical simulation results coincide well with the experiment.

Commentary by Dr. Valentin Fuster
J. Appl. Mech. 2010;77(5):051405-051405-5. doi:10.1115/1.4001561.

The erosion and wear in the gun barrel will get worse with an increase in the number of projectiles fired. Generally speaking, the ballistic performance of the gun, measured through indicators such as the maximum pressure $pm$ and the muzzle velocity $v0$, will decrease gradually due to gun barrel erosion. However, the above analysis does not agree with the firing test data of certain types of guns, especially of some small-caliber guns. The ballistic performance of such guns will exhibit an increase to their peak values followed by a gradual decrease with the number of rounds fired. This is the so-called interior ballistic peak phenomenon, also named as the hump effect. Taking several kinds of guns as examples, such as a 76 mm gun and a 100 mm gun, we calculated the engraving pressure $p0$ of the guns by an approximate method and built a lumped-parameter interior ballistic model of the guns that exhibits the effect, according to the interior ballistics theory of guns with erosion and wear. The results of the modeling of the guns under different wear conditions are close to the test data, showing the existence of the peak values of $pm$ and $v0$. The simulation results of some of the other guns that exhibit this phenomenon also show good agreement. Furthermore, it can explain the double-peak phenomenon for some types of guns with double driving bands. It was proven that the mismatch of the structure and the dimensions of the gun bore with those of the projectile driving band is the fundamental cause of this effect. Due to the mismatch, the engraving pressure will first increase and then decrease with the enlargement of the bore dimensions caused by barrel erosion and wear. The variation in the engraving pressure $p0$ will inevitably lead to the variation in interior ballistic performance in the life cycle of the gun. This observed process appears to explain the interior ballistic peak phenomenon.

Topics: Pressure , Guns , Mechanisms
Commentary by Dr. Valentin Fuster
J. Appl. Mech. 2010;77(5):051406-051406-8. doi:10.1115/1.4001559.

During a gun firing, the flow around a projectile will be developing and changing. In particular, the flow around the projectile is disturbed significantly when the projectile overtakes the muzzle flow. Furthermore, the projectile body pressure will also change substantially. Therefore, the shot ejection process has an important effect on the shot accuracy. The maximum projectile velocity is one of the most important design goals of the interior ballistic process and also is the initial condition for the exterior ballistic process. Most researchers take the muzzle velocity as the maximum projectile velocity; actually, after the projectile exits the muzzle, the projectile velocity will increase further due to the influence of the muzzle flow. Most investigations of the muzzle flow focused on the blowout of the high-pressure jet flow after the projectile exited the muzzle. The interior ballistic process was ignored or simply assumed in most investigations. Also, the mutual influence between the moving projectile and the muzzle flow was often neglected. Actually, a precursor shock flow near the muzzle is formed before the projectile exits. This precursor muzzle flow has an important influence on the trajectory of the projectile, especially, for the prevalent trend of gun systems including large caliber cannon and multiple launch gun systems. For these reasons, the interior ballistic process was coupled with the simulation of the flow near the muzzle. A hybrid structured-unstructured gridding method was used to simulate the process from the projectile engraving to the gas ejection phase, accounting for the moving projectile. The simulation results show that the projectile muzzle velocity was 893.99 m/s but the maximum velocity was 899.28 m/s. The projectile velocity increased rapidly to up to 0.8 ms after muzzle exit; thereafter, the projectile velocity increased slowly before reaching its maximum value. The maximum Mach number of the effluent gas increased to 6.83 and the breech pressure decreased to 21.5 MPa at 1.8 ms after the projectile exited the muzzle. The formation and development of the muzzle flow field was highly complex and transient. The analysis of the projectile velocity was conducted during the interior ballistic after-effect period. The predicted muzzle velocity and maximum barrel pressure are in good agreement with those measured in gun firings. Results of the numerical simulation and analysis are helpful to understand and master the aerodynamic process of gun system launching and provide significant guidance for research into shot accuracy and muzzle brake design.

Commentary by Dr. Valentin Fuster

### RESEARCH PAPERS: Exterior Ballistics

J. Appl. Mech. 2010;77(5):051501-051501-10. doi:10.1115/1.4001562.

The methods of missile formation reconfiguration optimal trajectory generating and control are described. Given a formation of intelligence missiles, an initial configuration, a final configuration, a time for reconfiguration, and a set of inter- and intramissile constraint, reconfiguration trajectory generation and control problems focused on determining and controlling a normal input trajectory for each intelligence missile such that every intelligence missile can fly as the expected optimal trajectory while satisfying all the sets of constraints. In this paper, solving the optimal trajectory generation problem by posing the input as a polynomial form and analyzing the symbolic reachability computation based on the quantifier elimination theory is of interest. A combination of proportion and differential control with the position error is used in the design of the missile formation controller used to track the optimal transfer trajectory. Simulations by the package REGLOG demonstrate that the optimal transfer trajectory generation process is feasible; the controller is capable of tracking the optimal transfer trajectory.

Commentary by Dr. Valentin Fuster
J. Appl. Mech. 2010;77(5):051502-051502-5. doi:10.1115/1.4001284.

A lot of numerical and experimental studies indicate that wrap-around fin configuration exhibits a self-induced rolling moment even at angle of attack zero. It depends on the unequal pressure distributions over both sides of the fin. In this paper, we try to prove this special aerodynamic characteristic with a theoretical method. According to the transonic small perturbation potential theory, as well as the transonic small perturbation potential equation, this paper found the expressions of the wrap-around fin convexity and the concave pressure coefficient at subsonic and supersonic by solving the Laplace equation and the Bessel function of imaginary argument, and analyze the phenomena of wrap-around fin rolling moment generation at angle of attack zero, and discuss the reason. The flow field of a projectile with wrap-around fins is solved by numerical method to check the pressure distributions of the two surfaces of the wing at subsonic and supersonic, respectively. The computational result is accordant to the theoretical analysis results. It is proved that the complicated pressure distribution of the wing surfaces leads to the particular characteristic of rolling moment.

Commentary by Dr. Valentin Fuster
J. Appl. Mech. 2010;77(5):051503-051503-6. doi:10.1115/1.4001693.

The pitch-up trajectory is a high parabolic trajectory. Long range interceptor missiles will be important for future air defense. Research indicates that a high parabolic trajectory can enhance the missile range. A method of generating high parabolic trajectories based on a virtual target guidance law is proposed in this paper. The proposed method is formulated and its effectiveness is demonstrated by two test simulations. The simulation results show that a missile can fly in a high parabolic trajectory with good characteristics using the virtual target guidance law. The proposed method fulfills the current needs and is suited for engineering applications.

Commentary by Dr. Valentin Fuster

### RESEARCH PAPERS: Launch Dynamics

J. Appl. Mech. 2010;77(5):051601-051601-9. doi:10.1115/1.4001289.

Rarefaction wave gun (RAVEN) propulsion has renewed interest in the fundamental limits of recoil reductions attainable by redirecting propellant gases rearward from a gun without compromising the projectile propulsion. Compared with a conventional gun there is a great difference in the launch process and launch structure. This paper is concerned with an analysis of the dynamic characteristics of this high performance weapon system by numerical simulation. Based on its launch mechanism and launch structure, the vibration equation describing the vibration characteristics of RAVEN was established by vibration theory, which considered the actual movement of the projectile and inertial breech by coupling the interior ballistic equations of the rarefaction wave gun. A rigid-flexible dynamic model, which considered the coupling effect between the elastic vibration of the launch barrel and the dynamic behaviors of the other parts of the RAVEN, is established via a subsystem method. The vibration response of RAVEN during the launch is analyzed by numerical simulation. Comparisons are presented based on the conventional gun, as well as the rules of how the different parameters affect the vibration response. During the launching of RAVEN, the launch barrel shows significant vibration due to the effect of the propellant gases, the inertial breech, and the projectile, and there is some reduction in the vibration amplitude compared with that observed in a conventional closed chamber gun. The vibration amplitude and duration of the launch barrel, which increased with a decrease in the loading density, an increase in the mass of the inertial breech and projectile, and a delay of the venting time, is affected in a more significant manner by changes in loading density and the mass of projectile. The coupled effect between the launch barrel and the other parts of RAVEN are most prevalent in the $z$-direction. The vibration amplitude along the $z$-direction is higher than that of the $y$-direction. When the coupled effect is considered, the transverse vibration response of the flexible barrel has some reduction compared with the one that does not exhibit the coupling effect.

Commentary by Dr. Valentin Fuster
J. Appl. Mech. 2010;77(5):051602-051602-6. doi:10.1115/1.4001697.

The U.S. Army uses several types of tests to increase the reliability of gun-fired munitions. Systems, subsystems, and components are gun fired to assess reliability. When failures are found, root-cause investigations are completed and parts may be redesigned. For instance, the 155 mm projectile Excalibur uses several types of tests to find failures and build reliability. Components are tested in a rail gun, a new soft-catch gun, and in soft recovery vehicles. With the rail gun, test projectiles are fired from a worn gun tube into a trough of water. The soft-catch gun, a hybrid system using both air and water, has a standard cannon tube and a series of catch tubes to stop a projectile. The third type of test, a soft recovery vehicle, uses a modified tactical Excalibur with a parachute for a soft landing. All three types of tests have on-board recorders to capture ballistic accelerations. Accelerometer data are used in failure investigations, redesign parts, and to design new projectiles. The purpose of this paper is to compare accelerations from different types of ballistic tests. Comparisons were done to determine if the tests were in the same statistical family. Comparisons are made for a United States MACS 5 charge. The maximum axial forces were the same for the soft-catch gun and the soft recovery vehicle. In the balloting directions, the rail gun and soft recovery vehicle had similar forces. The set forward forces differed in all three cases, reflecting the different catch mechanisms for the projectiles. Comparisons of $g$-forces were also made using shock response spectra. The shock response indicated that the damage potential is greatest for the rail gun tests, consistent with an increase rate of failures for some electronics.

Commentary by Dr. Valentin Fuster

J. Appl. Mech. 2010;77(5):051701-051701-4. doi:10.1115/1.4001914.

The use of the gamma-ray absorption technique as a tool in evaluating the quality of manufactured powder metal liners was investigated. With powder metal liners, it is not only of interest to know whether the liner conforms geometrically to the required specifications but it is also important to know whether there is radial symmetry in the density. Powder metal liners manufactured via compaction methods were subjected to a gamma absorption proof of principle experiment and it was concluded that the technique can serve as an effective quality control method in the manufacturing process of powder metal shaped charge liners.

Commentary by Dr. Valentin Fuster

### RESEARCH PAPERS: Terminal Ballistics

J. Appl. Mech. 2010;77(5):051801-051801-9. doi:10.1115/1.4001692.

The integration of a high-hardness steel armor plate inside the bodywork of a vehicle may result in a decrease in the overall ballistic resistance. This phenomenon is referred to as the bodywork effect. The effect was examined for a $5.56×45 mm$ North Atlantic Treaty Organization (NATO) Ball projectile. Previously reported experimental work has confirmed the numerically based assumption that the bodywork effect was due to the flattening of the tip of the projectile upon perforation of the frontal bodywork plate prior to hitting the integrated armor. The amount of qualitative and quantitative experimental data has now been extended. In order to eliminate the data dispersion observed after perforating the bodywork, an adapted projectile geometry with a truncated nose was fired directly against the armor plate. Ballistic testing also involved firing a soft-core $5.56×45 mm$ projectile for which a similar mechanism was observed. A finite element code was used to simulate the impact process for the different types of projectiles. The parameters of the selected strength and failure models were experimentally determined for the high-hardness armor plate. As to the ballistic limit velocity and plugging morphology there is a good correspondence between the experimental and computed results. Nevertheless, an improved failure model is necessary to get satisfactory computed residual projectile velocities.

Commentary by Dr. Valentin Fuster
J. Appl. Mech. 2010;77(5):051802-051802-10. doi:10.1115/1.4001714.

In this paper we present possibilities of increasing the depth of penetration through a steel plate by using segmented kinetic energy penetrators. Conclusions about the possibilities of increasing the penetration depth were formulated based on the critical review of the literature, simulations, and firing test results. A new concept called “forced segmented penetration,” where applied penetrator is composed of two tungsten alloy pieces connected by a screwed steel muff, is presented in this paper. The axial deformation of the connecting muff during the penetration process results in a decrease in the distance between tungsten segments. For this reason the rear segment can hit the front segment to give it some additional kinetic energy, enhancing the penetration depth. Such type of segmented penetration phenomena was not presented earlier. The numerical analyses of the segmented penetrator of the new design are presented in this paper.

Commentary by Dr. Valentin Fuster
J. Appl. Mech. 2010;77(5):051803-051803-7. doi:10.1115/1.4001287.

Jets that emanate from high density porous liners are most widely used for penetration into Earth materials. These shaped-charges differ from those that contain solid copper liners in three major aspects: the porosity, the usually higher initial density, and the very short standoff in which they typically operate. Because penetration depth is commonly very difficult to increase by means of high density solid liners, it is important to understand the benefit of using porous liners in utilization of high density materials. The models published so far to describe the performance of jets formed by porous liners are based on the modification of the virtual origin model to suit this special case, which limits the accuracy of their predictions. Here we present a more general analysis that does not depend on the virtual origin assumption. Our study employs the SCAN semi-analytical code into which a new model for porous jet behavior is incorporated. It is used to explain the benefit of using this type of liner for oil-well penetration, hence penetration into low density targets, as opposed to penetration into hard steel.

Topics: Density , Steel , Jets , Copper , Soil , Concretes
Commentary by Dr. Valentin Fuster
J. Appl. Mech. 2010;77(5):051804-051804-8. doi:10.1115/1.4001713.

A general methodology for estimating the requirements for defeating an explosive-containing mortar threat by an intercepting array of explosively generated natural and controlled fragments is discussed along with the experimental data supporting quantitative interpretation. The target response of covered TNT impacted by single fragments is predicted through numerically determined shock-to-detonation thresholds as well as empirical penetration equations. Included in the methodology is a comprehensive, deterministic endgame model that consists of an intercept model, a static and dynamic fragment model, and a hit model generating the number of effective hits for arbitrary intercept situations. Experimental data supporting the assumptions of the models are reported. The model is also useful in establishing interceptor requirements.

Commentary by Dr. Valentin Fuster
J. Appl. Mech. 2010;77(5):051805-051805-8. doi:10.1115/1.4001738.

Reactive armor panels have been used for many years as very efficient add-on armor against shaped charge warheads. The main features of the defeat mechanisms of the armor are therefore well known. The origin of the irregular disturbances on the shaped charge jet, which leads to the severe fragmentation and scattering of the jet, is however not described in literature. As this scattering of the jet provides the main protection mechanism of the armor, it is of interest to understand the details of the interaction and the origin of the disturbances. Some experimental observations have been made showing that the backward moving plate often displaces the jet relatively smoothly while it is the interaction with the forward moving plate that causes the disturbances that leads to fragmentation and scattering of the jet. In this work, a mechanism for the interaction is proposed based on the theory of Kelvin–Helmholtz instabilities, which explains the origin of the disturbances on the jet due to the interaction with the forward moving plate. Numerical simulations have been performed to show the difference in the mechanisms of backward and forward moving plates when interacting with the jet. The impact angle of the plate seems to be the dominant parameter for the onset of instabilities. A parametric study has also been performed on how different interaction and material parameters influence the development of instabilities of the interface between the jet and the armor plate. The parametric study shows that low-strength jets promote development of instabilities, a tendency that is amplified by frictional forces between the materials. The influence of the plate strength is more complex due to the influence of the structural stability on the contact forces. The effect of friction and melting of the metals in the boundary layer to the development of the instabilities is discussed. A microscopic study of the edge of the penetration channel has been made, which shows that the materials have been melted during the interaction between the plate and the jet.

Commentary by Dr. Valentin Fuster

### RESEARCH PAPERS: Armor and Personal Protection

J. Appl. Mech. 2010;77(5):051901-051901-9. doi:10.1115/1.4001696.

The use of different explosive reactive armor reactive cassettes is shown. Functioning rules of one- and two-layered reactive cassettes are presented. The paper demonstrates different kinds of tests with explosive reactive armour Wisniewski Adam (ERAWA) cassettes. There are some examples of the simulation of impact of different types armour piercing (AP) and high explosive anti-tank (HEAT) ammunition on these cassettes. Simulation was based on “free points” computer codes. The propagation of the detonative wave in the explosive (PBX 9404 and RDX) has been described with the use of the approximation of the so-called “detonative optics,” in which the front of the detonative wave is a surface of the strong discontinuity of the well-known shape (for the punctual initiation—the front is spherical) of the propagation speed, and the parameters of the medium on this surface are defined by the Chapman–Jouguet’s point. Scattering of products of detonation and their influence on the liner of the RPG-7M projectile are described with the use of equations of the hydrodynamics for the cylindrical symmetry. The results of the simulation process of the impact of AP ammunition of 7.62 mm, 12.7 mm, 14.5 mm, and 125 mm caliber, the type of armour piercing fin stabilized discarting sabot (APFSDS), are illustrated in figures. The changing of the following parameters on the axis, i.e., density, thickness, collapsing velocity, and pressure while penetrating of cassettes in time function, is presented. The next step to test the sensitivity of different types of explosive reactive cassettes containing different explosive layers placed on target, is the observation of their reaction to the impact of kinetic energy ammunition. Explosives contain different percentages of wax. The examples of reaction of the two-layered explosive of different thickness with different contents of wax after projectile impact are illustrated. Computer analysis of the parameters’ changes on the axis of the projectile’s penetration into explosive reactive cassettes, i.e., of density, thickness, pressure, impact velocity for different thicknesses of layers of these cassettes, and the projectile type and velocity 800 m/s and 1800 m/s, enables to know the initiation conditions of these cassettes’ explosive. The use of computer simulation makes possible to know the influence of the quantity of wax on the sensitivity of different thicknesses of explosives of one- and two-layered reactive cassettes.

Commentary by Dr. Valentin Fuster
J. Appl. Mech. 2010;77(5):051902-051902-5. doi:10.1115/1.4001291.

This paper introduces a method to determine the material constants for Johnson–Cook model of an as-extruded Mg–Gd–Y series alloy by quasistatic tests on Instron 1251 and Hopkinson bar experiment at room and elevated temperatures. The results indicate that the thermal softening exponent of the current magnesium alloy is as high as 3.05, which is obviously higher than that of most metal materials, such as steel and tungsten. High thermal softening exponent usually means high energy absorption efficiency, and the comparison of the dynamic stress-strain curves between ZK60 and Mg–Gd–Y series alloy indeed indicates that the energy absorption efficiency of the Mg–Gd–Y series alloy is higher than that of ZK60. Additionally, high energy absorption efficiency makes the Mg–Gd–Y series alloy exhibit more excellent antipenetration performance than that of 7A52 aluminum alloy at equal areal density condition.

Commentary by Dr. Valentin Fuster