**1. Introduction**

Reactive materials (RM) are ignited or detonated in the process of penetrating a target, and their joint destruction via the penetration of kinetic energy and chemical energy release is a cutting-edge development in the field of advanced and efficient destruction technology [1–3]. Compared with traditional standard projectiles, the significant technological and damage efficiency advantages of reactive materials projectile (RMP) are mainly reflected in their high-efficiency destruction, versatility, high safety, long storage lives, simple structures, and low costs [4–7].

At present, many achievements have been made in the field of RM warheads around the world [8–15]. Mock et al. [16] studied the impact detonation threshold of polytetrafluoroethylene/aluminum (PTFE/Al) RMs through crash tests; based on the test results, an empirical formula relating the impact activation response time and impact pressure was proposed. The Beijing Institute of Technology [17] conducted a study on the detonation and energy release caused by the impact of PTFE RMs, and they analyzed the influence of the post-target implosion overpressure effect and impact velocity of the RMs on the implosion overpressure and compared the energy release behaviors of the RMs of different formulations.

Due to requiring a dynamic impact process with a high strain rate of the plastic deformation to provide the initiation energy, in general, their impact-induced initiation mechanism is not well understood, and the initiation properties have not been well characterized. One means by which to investigate their impact initiation behavior is through conducting a Taylor impact test. Studies with the PTFE/Al projectile have shown that it first

**Citation:** Li, X.; Hou, C.; Tong, H.; Yang, L.; Chen, Y. Influential Factors of a Reactive Materials Projectile's Damage Evolution Behavior. *Crystals* **2022**, *12*, 1683. https://doi.org/ 10.3390/cryst12111683

Academic Editors: Yong He, Wenhui Tang, Shuhai Zhang, Yuanfeng Zheng and Chuanting Wang

Received: 24 October 2022 Accepted: 17 November 2022 Published: 21 November 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

passes through a brittle fracture stage, and then, this progresses to ignition. This initiation phenomenon indicates that while the fracture process is likely important to the ignition, it is not sufficient to produce the initiation alone. Thus, an additional amount of energy that is possibly related to the crack propagation properties and fracture surface energies must be deposited into the fractured materials before the initiation takes place. More detailed studies show that the first signs of ignition are visible in the regions of intensive shear during the Taylor impact test, and both the finite element analysis and high-speed videos provide further evidence for the intensive shear-induced ignition mechanism [18].

Moreover, the traditional energy release characterization techniques such as bomb calorimetry only measure the energy release behavior of energetic materials that are ignited in a static configuration. However, the initiation efficiencies of these RMs strongly depend upon the impact conditions, which makes the measurement of their energy release characteristics difficult, and the research methods on the mechanism of this explosion damage behavior are still relatively limited.

In view of this situation, based on the analysis of the mechanical behavior of the projectile target, the damage energy release behavior is transformed into the damage evolution behavior of the MLAT. As part of this effort, our research group carried out work on the target by matching the characteristics and the impact velocity [19,20]. This study began with the construction of the numerical simulation models, combined with a theoretical analysis and an experimental verification. The mechanical behavior of the impact action and the evolution behavior of the MLAT under different target action conditions were studied, and the flight dispersion behavior and the change of the perforation caliber of the after-effect target fragments were studied accordingly.

#### **2. Numerical Models**

On the AUTODYN-3D platform, the projectile penetration of the reactive substance was numerically simulated by the Lagrange algorithm. All of the materials were modeled by an erosion model, in which the reactive substance which was activated by the impact pressure obeyed a two-phase powder combustion equation of state (EOS). Gases and solids in the model existed at the same time, simulating the materials' deflagration reaction, and the relevant parameters were taken from the literature [21]. The unreactive materials were modeled with the state impact equation to simulate the mechanical behavior of the RMs under pressure and expansion [22,23].

#### *2.1. Theoretical Model Building*

The action process of the projectile–target interaction was mainly divided into four stages: the penetration of the target and the RM compression deformation fragmentation stage, the RM pressure relief dispersion and local ignition stage after penetrating the target, the RM debris cloud deflagration propagation and chemical energy release stage, and the stage where the shell fragments form a fragment power field. These are shown in Figure 1. When the RMP collides with the steel target, the shock wave generated by the impact compresses the projectile to produce different degrees of radial expansion of the core and the shells, and the Poisson's ratio of the reactive core is greater than that of the shells materials, so the radial expansion of the core is more significant, resulting in a mechanical radial expansion effect. Once the radial stress in the shells exceeds its fragmentation limit, a large amount of shell fragments are generated, and these fragments have a certain radial velocity. At the same time, high strain rates can cause the core of the RM to partially fragment and form a cloud of reactive debris after the steel target arrived. In a debris cloud, small reactive fragments are activated first due to their high specific surface area and surface ignition energy, and they further trigger intensity deflagration. With the increase in the number of aluminum targets, the length of the reactive core will gradually decrease, the radial expansion of the shells will be weakened, and the damage ability of the after-effect aluminum target will be greatly reduced.

**Figure 1.** The process of action of RMP impacting a MLAT.

To obtain the activation state of the reactive substance during the target penetration process, it was necessary to analyze the first impact, that is, the state of the reactive substance during the impact of the steel target. When the RMP hits the steel target, based on the Ranking–Hugoniot relationship, the conservation of the mass, momentum, and energy can be expressed, respectively as follows:

$$
\rho\_1/\rho\_0 = (\mathcal{U} - \mathfrak{u}\_0)/(\mathcal{U} - \mathfrak{u}\_1),
\tag{1}
$$

$$P\_1 - P\_0 = \rho\_0 (\mu\_1 - \mu\_0) / (\mathcal{U} - \mu\_0) \tag{2}$$

$$
\varepsilon\_1 - \varepsilon\_0 = \left(P\_1 u\_1 - P\_0 u\_0\right) / \rho\_0 (\mathcal{U} - u\_0) + \left(u\_1^2 - u\_0^2\right) / 2\tag{3}
$$

where *ρ* is the density, *U* is the shockwave velocity, *u* is the particle velocity, *P* is the impact pressure, and *e* is the specific internal energy. Subscripts 0 and 1 represent the undisturbed and affected states, respectively. In addition, the linear relationships between the shockwave velocity of the RM and the steel target particle velocity can be expressed as:

$$
\mathcal{U}\_P = \mathcal{c}\_p + s\_p \mathfrak{u}\_p \tag{4}
$$

$$\mathcal{U}\_t = \mathfrak{c}\_t + \mathfrak{s}\_t \mathfrak{u}\_t \tag{5}$$

where *c* and *s* are the speed of sound and the materials coefficient, respectively, and the subscripts p and t represent the RM and the target, respectively. The values of *c* and *s* of the steel target were 4610 <sup>m</sup>·s<sup>−</sup><sup>1</sup> and 1.73 [24], respectively, and the corresponding values for the RM were 1350 <sup>m</sup>·s<sup>−</sup><sup>1</sup> and 2.26 [25,26].

At the impact interface, the shockwave is transmitted to the RM and the steel target, respectively, so the particle velocity and pressure compatibility relationship of the entire target surface can be expressed, respectively, as:

$$w\_0 = u\_p + u\_l \tag{6}$$

$$
\rho \rho\_0 (c\_p + s\_p u\_p) \mu p = \rho\_{\mathbb{H}\_0} (c\_\mathbb{H} + s\_\mathbb{H} \mathfrak{u}\_\mathbb{H}) \mathfrak{u}\_\mathbb{H} \tag{7}
$$

We define *Pc* as the critical detonation pressure. By default, at this pressure, the RM can meet the size of the ignition and detonation fragments, while the fragments below this size could undergo a chemical energy deflagration reaction. Based on the shockwave propagation attenuation characteristics, we can effectively describe the activation behavior of the core. This activation length can be described as:

$$\propto\_1 = -\left(1/a\right)\ln\left(P\_c/P\_0\right) \tag{8}$$

where *P*0 is the maximum stress and α is the correlation coefficient for the properties of the RM. According to a previous study [27,28], its value is 0.036 mm<sup>−</sup>1.

#### *2.2. Numerical Simulation Model Building*

The failure of the materials is closely related to the state under the load. In order to better describe the whole process of the projectile target action of the active materials, the principal

stress failure standard was adopted for all of the materials in the numerical simulation, and when the maximum tensile principal stress and shear stress exceeds the ultimate stress value of the materials, the materials will fail. Tables 1 and 2 list the main model parameters used for numerical simulations [29–31]; the erosion algorithm was used for the relevant materials.

**Table 1.** Main materials model.


**Table 2.** Main materials parameter table.


To facilitate the analysis of the problem, the RMP was simplified into three parts: the high-strength shells (30CrMnSiNi2A), a reactive core (PTFE/Al), and a head metal block (a wolfram alloy). Since the symmetry condition was satisfied under positive penetration conditions, the calculations were performed using a 1/4 model, and the three-dimensional simplified model of the RMP is shown in Figure 2. The caliber of the RMP is 30 mm, the ratio of the inner to the outer diameter is 0.6, and the length is 100 mm. The high-strength shells mainly played the role of restraining the reactive core and penetrating the target. The reactive core mainly underwent impact compression and expansion as well as pressure explosion, deflagration, and destruction. The head metal block mainly played a role in enhancing the penetration ability of the warhead. The target was a rolled homogeneous armor (RHA), and the after-effect target was a spaced aluminum target with a thickness of 3 mm. The penetration analysis model is shown in Figure 3.

**Figure 2.** Schematic diagram of the RMP.

**Figure 3.** Three-dimensional penetration analysis model.

#### **3. MLAT Destruction Law Study**

Based on the construction of the above numerical model, this section illustrated how we carried out the study of the MLAT destruction mechanisms of the RMP under different projectile–target interaction conditions, especially the activation behavior caused by the penetration and the evolution behavior of MLAT destruction, in order to obtain a clearer mechanism of RMP penetration-initiation combined damage effects.

#### *3.1. Steel Target Thickness Impact Analysis*

## 3.1.1. Numerical Models

The internal stress peak analysis was performed on the projectile penetration of the RHA steel target, as shown in Figure 4. When the thickness of the RHA steel target was small, the thickness of the steel target had a significant impact on the internal stress value of the projectile. When the target thickness was greater than 15 mm, the internal stress value of the RM was not much different from the case with a target thickness of 15 mm, but when the target thickness was 10 mm or lower, the internal stress value of the RM decreased significantly.

**Figure 4.** Peak stresses of the projectiles penetrating steel target.

In light of the above, the speed was set to 1000 m/s to impact the 2, 8, 15, and 30 mm RHA steel targets. The RMP activation models for different target thicknesses are shown in Figure 5. The red RM near the head of the metal block in Figure 5 was modeled using the Powder Burn EOS, and the pink region away from this area was modeled using the Shock EOS. Figure 5a indicates that the RM was not effectively activated with the 2 mm RHA steel target.

#### 3.1.2. Results and Discussion

The multi-layer target damage pairs with different target thicknesses are shown in Figure 6. For the 2 and 30 mm RHAs, especially the 2 mm RHA, the multi-layertargeted damage effect was significantly reduced, and the fragment dispersion area and the maximum perforation size were slightly larger than the caliber size, without causing any surface damage effects. For the 8 and 15 mm RHAs, the MLAT damage effect was

significant. For the 15 mm RHA, the fragment dispersion area on target No. 2 reached about 750 cm2, the maximum perforation area was about 64 cm2, and the damage and maximum perforation areas reached 27 and 2.5 times the projectile caliber, respectively. The analysis showed that this was due to the thickening of the RHA steel target, which prolonged the target action time. The reactive core was completely compressed and broken, and due to the instantaneous unloading of the steel target pressure, many reactive debris clouds were generated behind the steel target. This produced a violent chemical energy explosion and deflagration, causing large-scale fragmentation damage and a significant reaming effect on the MLAT. However, if the RHA steel targets had been too thick, this would also cause a large amount of RM energy release reactions to occur inside the steel target so that penetration-initiation combined damage effects would not be able to effectively act on the subsequent multi-layer aluminum target.

**Figure 6.** Comparison of MLAT target damage effects for different thicknesses of the RHA steel target.

*3.2. Analysis of Impact Velocity*

#### 3.2.1. Numerical Models

The activation behavior of the 20 mm RHA target plates damaged by the projectile at different impact velocities as shown in Figure 7. The peak internal stress increases with the increase in the impact velocity. With the increase in the impact velocity, the curvature of the area near the impact point increased significantly, and the internal stress of the reactive core increased significantly. When the impact velocity was at 1000 m/s, the activation length of the reactive core was only about 11.62 mm, and the activation rate was about 15.5%. With the increase in the impact velocity, the activation rate of the reactive substance gradually increased, and when the impact velocity reached 1800 m/s, the activation length of the reactive core reached about 51.94 mm, and the activation rate increased to about 69.3%.

**Figure 7.** Changes in internal stress at different impact velocities(red ball: peak internal stress of the reactive core).

Based on the influence of the impact velocity from 800 to 1800 m/s on the activation behavior of the RMP, Figure 8 shows the numerical simulation results of the projectile at different impact velocities and the fracture state diagrams of the shells. When the velocity was 800–1200 m/s, only the head of the projectile showed a slight radial expansion and valgus deformation. No reactive core fracture was evident, and the projectile body remained long. When the impact velocity was greater than 1400 m/s, the entire shells were destroyed after penetrating the RHA steel target, the radial expansion effect was significant, and the head of the unreactive core was also greatly fragmented, ejecting a cone-shaped cloud of reactive debris at the opening.

**Figure 8.** Warhead deformation and fragment distributions after penetrating RHA steel target at different impact velocities: (**a**) v0 = 800 m/s, (**b**) v0 = 1200 m/s, (**c**) v0 = 1400 m/s, and (**d**) v0 = 1600 m/s.

#### 3.2.2. Results and Discussion

The damage status of the double-layer aluminum target at two typical velocities is shown in Figure 9. The perforation produced by the 1# aluminum target in Figure 8a was relatively flat, and the reaming effect was not evident. Only the 2# aluminum target had evident irregular petal-like perforations, and some pits, small holes, and other debris appeared near the perforation. As shown in Figure 8b, after the impact velocity was greater than 1200 m/s, the 1# aluminum target showed a significant reaming effect. The petal-like perforation diameter and damage area were significantly increased when they compared to how they were before. More target plate fragments formed, and the perforation diameter of the 2# aluminum target also increased. However, the damaged area showed a trend of increasing first, and then decreasing.

The damage effects of the RMP on the target plate at different impact velocities are shown in Figure 10. When the impact velocity was 800 m/s, the damage diameters of the 1# and 2# targets were minimized, and that of the 1# target was slightly less than that of the 2# target. This was because when the impact velocity was small, with the extension of the impact action time, the energy released by the projectile kinetic energy was gradually unloaded; the instantaneous stress value inside the projectile did not reach the activation threshold of the reactive substance, and it was not effectively activated. The slight radial expansion effect of the projectile caused the perforation diameter of the 2# target plate to be slightly greater than that of the 1# target plate, mainly based on kinetic energy destruction. When the impact velocity increased to 1400 m/s, the diameter of the 2# target damage reached the maximum value, and the diameter of the 1# target damage gradually decreased. This occurred because when the impact velocity reached a certain value, the projectile and RHA steel target action time was shorter, the initial stress increased, the degree of squeezing of the RM increased, the shells had a significant radial expansion effect, and the deflagration propagation rate of the RM was slower than the detonation wave of the explosive. When the reactive core hit it to form a debris cloud, a violent deflagration reaction occurred in front of the 1# target, causing a large damage area on the target, while only a small amount of RM acted on the 2# target through the 1# target. When the impact velocity reached 1800 m/s, the growth trend of the damage diameter of the 1# target was greatly slowed. If the velocities were too high, the initial stress would increase significantly, the RM would be activated prematurely, and more RMs would react inside the RHA steel target. This would result in less reactive debris overflowing from the shells port, a smaller dispersion radius of the fragments, and a weakening of the MLAT destruction ability.

(**a**) 

(**b**) 

**Figure 9.** Result of damage caused by warheads to double-layer target plates at different impact velocities: (**a**) *v0* = 800 m/s and (**b**) *v0* = 1400 m/s.

**Figure 10.** Damage area of the double-layer target at different impact velocities.

In summary, under the conditions described in this section, when the impact velocity was at 1400–1600 m/s, it could produce a good joint damage effect on the MLAT and result in efficient damage to the battlefield target.

#### *3.3. Metal Block Thickness Effect Analysis* 3.3.1.Numerical Models

The stress variation distribution along the thickness of a typical head metal block is shown in Figure 11. The presence or absence of the head metal block had a significant impact on the penetration performance of the RMP. Furthermore, the change in the thickness of the head metal block also had a greater impact on the penetration performance of the RMP. When the head metal block was not present, the deflagration reaction length of the warhead RM could reach about 45 mm. When the warhead metal block thickness was increased to 20 mm, the deflagration reaction length of the warhead RM was reduced to less than 20 mm.

**Figure 11.** Changes in internal stress under different metal block thicknesses(red triangles: peak internal stress of the reactive core).

Adding a metal block to the head of the RMP could effectively increase the penetration capacity of the projectile, but it would correspondingly weaken its internal stress value, resulting in a significant reduction in the activation rate. To study the effect of the head metal block thickness on the MLAT damage effect, a corresponding activation model was constructed for the numerical simulation calculations, as shown in Figure 12. The head metal block materials was a tungsten alloy, and for comparative analysis, the thicknesses were set to 0, 10, and 20 mm.

**Figure 12.** Metal block thickness activation model.

#### 3.3.2. Results and Discussion

The pressure cloud of an RHA steel target colliding with head metal blocks of different thicknesses is shown in Figure 13. when the head was not equipped with a metal block, the stress on the steel target was the greatest, the reaming effect was the most significant, and the target produced significant ductile reaming holes. With the increase in the thickness of the metal block, the reaming effect was significantly weakened. The analysis suggests that this was due to the increase in the thickness of the head metal block, resulting in a significant decrease in the activation rate of the reactive substance. The energy released by the chemical energy explosion was also sharply reduced. At the same time, due to the increase in the thickness of the metal block, the projectile penetration ability of the RM was enhanced, the target action time was shortened, and the ductility reaming phenomenon was gradually weakened.

**Figure 13.** Pressure cloud diagrams of different head metal blocks colliding with RHA steel target at 0.1 ms, (**a**) 0 mm, and (**b**) 10 mm.

The MLAT damage state pairs for different head metal block thicknesses are shown in Figure 14. When the head metal block was not installed, the damage effect area of the 1# Al target fragment reached 620 cm2, and the perforation area was about 145 cm2. The damage effect area on the 2# Al target fragment reached 706 cm2, and the perforation area reached about 72 cm2. The damage effect area on the surface of the 2# Al target was significantly greater than that of the head metal block, and the average perforation diameter was significantly smaller than the diameter of the head metal block. The improvement of the damage effect when the head metal block was installed was mainly reflected in the 2# and 3# Al targets, and the improvement of the damage effect when the head metal block was not installed was mainly reflected in the 1# and 2# Al targets. The analysis showed that this was due to the installation of thicker head metal blocks, which could effectively enhance the penetration ability of the RMP, reduce the pressure inside the projectile, and weaken the degree of fragmentation of the reactive nucleus. The size of the fragmentation increased, and the activation process occurred slowly, which could act more effectively on the multi-layer target plate.

**Figure 14.** Damage results of MLAT with different metal block thicknesses.

#### **4. Impact Experiments**

Aiming to solve the problem of the mechanism of intrusion and destruction of the RMP, MLAT destruction effect experiments were carried out, and the evolutionary law of the MLAT damage under different projectile–target interaction conditions and the mechanism of the activation initiation of the RMP were verified. This provides reference data for the improvement of the damage efficiency of subsequent RMPs.

#### *4.1. Experimental Setup*

The schematic diagram of the experimental site layout and the actual site layout are shown in Figure 15. The reactive projectile was prepared by using a PTFE/Al powder with a zero-oxygen ratio by mixing cold-pressed sinter hardening materials. The density after sintering was 2.4 g/cm3, and the multi-layer spacer board was composed of an RHA homogeneous armored steel target and an MLAT. The dimensions of the RHA steel target were 500 mm (length) × 500 mm (width), and the thickness dimensions were 2, 8, 15, 20, and 30 mm, respectively. The dimensions of the AL2024 aluminum target were 1000 mm (length) × 1000 mm (width), and the thickness was 3 mm. The spacing between the steel target and the MLAT was 200 mm, and the spacing between the MLAT was 300 mm. The impact speed was about 1000 m/s, and a Tianmu tachymeter and a velocity radar system which was installed in front of the steel target were used to measure the projectile velocities. Two target holders were used to secure the steel target and the MLAT.

(**a**)

(**b**) 

**Figure 15.** Experimental setup (**a**) Schematic diagram of the experimental layout: 1: 30 caliber artillery; 2, 3: Tianmu tachymeter; 4: RHA steel target; 5: MLAT; 6: target frame. (**b**) On-site layout.

#### *4.2. Experimental Results and Discussion*

4.2.1. Analysis of Influencing Factors of Metal Block Thickness

The effects of three typical metal block (w alloy) thicknesses on the multi-layer metal target are shown in Figure 16. The experimental results are shown in Table 3. The damage comparison experiment was carried out with a 20 mm RHA steel target without the installation of the head metal block, a 10 mm head metal block, and a 20 mm head metal block. Through verification experiments, it was shown that the thickness of the metal block of the head had a significant effect on the activation effect of the RM, and the reactive core also had a strong penetration ability. When the head metal block was not installed, its

damage enhancement effect performed well in the aluminum target, especially in the steel target and the first two layers of the MLAT. Because there was no head metal block, the internal pressure of the projectile was greatly increased, resulting in a sharp increase in the pressure of the RM, and thus, more fragmentation occurred. Most of the fragments broke in the steel target and were activated by the ignition, and the reactive fragment cloud gathered behind the steel target, causing a significant reaming effect and a fragmentation effect on the first and second layers of the aluminum target. After the installation of the head metal block, due to the increase in the thickness of the head metal block, the reactive core was impact compression expansion effect reduced when the projectile collided with the steel target. Thus, fewer reactive fragments reached the ignition size, and most of the activation ignitions occurred in front of the 3# aluminum target, resulting in better fragmentation surface destruction and point penetration. Because the influence of the deflagration reaction of the RM on the activation effect could not be considered in the numerical simulation, the activation ignition behavior was analyzed only by the preliminary impact kinetics behavior. Thus, the damage effect was not significant, but the damage characteristics had a certain reference value. To ensure that the RM could reach the activation threshold, the thickness of the metal block of the head was appropriately reduced, and the length of the reactive core was increased to improve the comprehensive penetration and destruction ability of the RMP intrusion to the multi-layer spacer board.

**Figure 16.** Results of multi-layer spacer board damage with different metal block thicknesses.

4.2.2. Analysis of Influencing Factors of Steel Target Thickness

To study the influence of the steel target thickness on the damage behavior of the RMP endpoint, comparative experiments of RHA steel target of different thicknesses were conducted. The RMP caliber was 30 mm, the ratio of the internal to the external diameters was 0.6, and the RHA steel thicknesses were 2, 8, 15, 20, or 30 mm. Only some of the results were taken for analysis. The high-speed images of the RMP impact multi-layer spacer board at the same time are shown in Figure 17, and the damage is shown in Figure 18.


**Table 3.** Experimental results.

**Figure 17.** Comparison of high-speed images of RMP hitting MLAT: (**a**) hitting a 2 mm RHA steel target at a speed of 936 m/s and (**b**) hitting a 15 mm RHA steel target at a speed of 940 m/s.

The experimental results of the multi-layer aluminum target damage effect are shown in Table 3. As the thickness of the target plate increased to 30 mm, higher requirements were placed on the armor-piercing ability of the RMP. It can be seen from the damage of the MLAT that the RMP could penetrate the 30 mm steel target, but when the 15 mm steel target was reached, the damage effect was the best, especially when the third layer of the aluminum target achieved seven piercings. The dimensions of the fragment distribution area were 280 mm × 310 mm, and the maximum perforation sizes were 190 mm × 220 mm, the number of perforations reached seven, and the damage area and maximum perforation size reached 13.5 times and 6.5 times the caliber of the projectile, respectively. The analysis showed that this was due to the increase in the action time of the projectile–target interaction when the steel target was too thick, resulting in more reactive substances being prematurely ignited and detonated during the penetration of the target. The premature release of energy caused a certain reaming effect on the steel target. At the same time, for a thin target plate with a thickness of 2 mm, it can be seen that the damage effect of the RMP was poor, the number of perforations was small, the fragmentation distribution area was small, and the maximum perforation sizes was only 1–2 times the caliber of the projectile. This was consistent with the numerical simulation results. Combined with high-speed photographs, when the steel target was too thin, the resulting projectile–target interaction time was too short; moreover, the impact pressure did not reach the threshold and the reactive core was not effectively broken. Only kinetic energy penetration occurred, and the chemical action of ignition did not occur in the RM.

**Figure 18.** Damage results of MLAT with different RHA steel target thicknesses.

#### 4.2.3. Comparative Discussion

Based on the above findings, some numerical simulations were compared with the experimental results, as shown in Figure 19. The maximum perforation sizes of the four verified target plates were used to validate the numerical model, and the evolution and mechanism of the multi-layer target plate failure were analyzed.

**Figure 19.** Numerical simulation validation: (**a**) Metal block thickness and (**b**) Steel target thickness.

Without installing the head metal block (that is, the 0 mm head metal block), the numerical simulation result of the No. 1 verification target plate was significantly lower than the experimental result, and the numerical simulation results of other verified target plates had certain deviations from the experimental values. The comprehensive destruction effect of the numerical simulations was slightly lower than that of the experiments. For the thickness of the steel target plate, when the 2 mm RHA steel target plate was impacted, the numerical simulation results of the damage effect of the MLAT were slightly lower

than the experimental results, but when the 30 mm RHA steel target plate was impacted, the numerical simulation results and experimental results had significant differences. The analysis showed that, because a series of chemical energy-releasing reactions—such as explosion and deflagration—were involved in the destruction process, the damage process was more complicated; that is, the activation model built in the numerical simulation of this paper was only based on the one-dimensional shock wave theory. The first step of the projectile–target interaction triggered the deflagration effect of a small amount of active materials, and the subsequent partial activation reaction that occurred due to the local stress wave strength caused by the chemical energy release effect was promoted again. Because the reactive core in the experiment still broke in the process of impacting the MLAT, resulting in a smaller fragmentation size of the reactive core again, when the fragmentation activation size was reached, the activation reaction occurred again, so the experimental effect of the post-layer spacer aluminum target was better than the numerical simulation results; however, the overall error was controlled to be within 20%. Thus, we believe the simulation results were reasonable.
