Disordered alloy is a new kind of reactive material, which breaks through the design concept of traditional alloy and exhibits excellent mechanical properties, impact energy release characteristics and adiabatic shear sensitivity, showing good application prospects in high temperature, high pressure, high strain rates and other application environments. Analyzing the impact energy release characteristics of reactive disordered alloy has an important guiding role for its development in the military field and can provide the basis for the design and application of warheads for ammunition. In this paper, the impact energy release characteristics of reactive disordered alloys are introduced from four aspects, including the energy release phenomenon of chemical reaction, the energy release law induced by impacting, the energy release mechanism and the regulation of the energy release behaviors. The chemical reaction showing energy release phenomenon in static and dynamic mechanical experiments is described. The relationship between impact velocities and the energy release overpressures or the efficiency of energy release of reactive disordered alloys is obtained. The effect between impact velocities and crushing degree of the reactive disordered alloys or characteristics of the target on the energy release mechanism is discussed. At the same time, the regulation effects of preparation process and the kinds of element on energy release effect of disordered alloy materials are summarized. This kind of alloy own good impact energy release characteristics, presented an ideal energetic structural material. Furthermore, the research progress of reactive disordered alloys applied to warheads in military area is summarized from three directions, including fragment, armor-piercing core and shaped charge liner. The macro and micro penetration behavior and mechanism of warheads of reactive disordered alloys are analyzed under high-speed loading conditions. Via the design of the structure, the good penetration and damage performance benefit from the self-sharpening and energy release characteristics of the material. Finally, the further development trend and demands of reactive disordered alloy are prospected.
In order to study the cratering stage in the dynamic penetration process of projectiles into the concrete targets, the cratering stage is further divided into two phases according to the damage of the projectile during penetration. Combined with the shape function of projectile head, streamline field of the Z model and normal expansion theory (NET), an analytical and calculation model of penetration resistance during the cratering stage is established, which considers the influence of concrete ejection process. Reliability of penetration resistance model during the cratering stage is then verified by test data taken from published papers. The advantages of the present model compared with the existing classical model are analyzed, while the influences of initial impact velocity of projectile, the caliber-radius-head and uniaxial compressive strength of concrete on the dynamic process during the cratering stage are analyzed. With the increase of the initial impact velocity of projectile, the diameter and depth of the ejection region gradually increase, the time of the ejection region to reach the maximum size is gradually shortened, and the time of the dynamic process during the cratering stage is also shortened. With the increase of the caliber-radius-head of the projectile, the diameter and depth of the ejection region gradually decrease, the time of the ejection region to reach the maximum size gradually increases, and the time of the dynamic process during the cratering stage increases, too. With the increase of uniaxial compressive strength of concrete, the diameter and depth of the ejection region are gradually reduced, the time of the ejection region to reach the maximum size is gradually shortened, and the time of the dynamic process during the cratering stage is also shortened. The velocity has the greatest influence on the dynamic process during the cratering stage of the projectile penetration into the concrete target, followed by the caliber-radius-head of the projectile and uniaxial compressive strength of concrete.
Aiming at the urgent demand for theoretical research and engineering application of deep super hard targets in the field of damage and protection, the response zone and boundary conditions during the cavity expansding process are optimized in this paper based on the improved Ottosen yield condition. The entire process of cavity expansion is solved, the changes in the response zone of concrete with different strengths are analyzed. According to the relationship between cavity boundary stress and cavity expansion velocity, a calculation model of projectile penetration depth is established, and the penetration depth of projectile penetration into concrete with different strengths are calculated. The mechanism of the influence of target strength on penetration depth is also analyzed. The results show that the elastic and plastic cracking zone of high-strength concrete is larger and the compacted zone is smaller, indicating that high-strength concrete is more brittle and compact. And the addition of plastic cracking zone can better reflect the phenomenon of concrete with different strengths in penetration. By comparing with the experimental data, it can be seen that the cavity expansion theory established in this paper has good applicability for normal concrete and high-strength concrete. The relationship between radial stress and cavity boundary velocity and the penetration depth also can be accurately calculated by this theory. With the increase of concrete strength, the difference in the cavity boundary stress of the concrete becomes smaller, resulting in a smaller increase in the penetration depth of the projectile as the velocity increases, and the penetration depth of the projectile decreases and gradually tends to a certain value at the same speed.
Earth penetration weapon (EPW) is commonly used to attack the underground target. However, the ballistic trajectory deflection, which is essentially caused by the deflection of the penetrator, commonly decreases the penetration efficiency of the penetrator. Thus, both the deflection angle and depth of penetration (DOP) of the projectile demand rapid and precise predictions. Based on the differential-areal-force-law (DAFL) approach, an analytical contact-resistant pressure is applied on the projectile surface in simulation. It represents the resistant force of the target and considers the free-surface effects of all surfaces of a finite concrete target. The simulation model is verified by comparing with the test results of the DOP and rotation angle of projectiles in open references. The influence of structural deformation upon the deflection of the penetrator is investigated by comparing the dynamics and movement of rigid and deformable projectiles. It indicates that the structural deformation drives the deformable projectile to deflect, which changes the total moment and instant angular velocity of the projectile. Under the same impact conditions, the rotation angle of the deformable projectile is usually larger than that of the rigid projectile. With the aspect ratio of projectile and impact velocity of the projectile decreasing, and the oblique angle of the projectile increasing, the rotation angle of the rigid projectile increases. However, for the deformable projectile, with the aspect ratio and oblique angle of the projectile increasing and the thickness of the projectile decreasing, the rotation angle of projectile increases. The rotation angle of deformable projectile does not monotonously increase with the impact velocity of the projectile increasing. It should be analyzed according to its actual structural deformation. When the impact velocity is less than or equal to 800 m/s and the oblique angle of the projectile is larger than or equal to 20°, the higher the impact velocity, the larger the oblique angle and the aspect ratio, the thinner the thickness of the projectile, the structural deformation contributes larger deflection of the projectile. In this way, to promote the accuracy and reasonability of simulation, it is suggested that the projectile should be deformable when the deformation and dynamics of the projectile are demanded for non-ideal penetration of a penetrator.
It is a developing trend of protection engineering to use high resistance materials such as ultra-high performance concrete to construct bullet-shielding structures. The phenomenon of projectile body rebound was found in the tests of projectile body penetrating ultra-high performance concrete. The projectile rebound effect is very important in the study of engineering protection, weapon damage and warhead design. In order to study the rebound velocity of projectile body after penetration and its influencing factors, the stress of projectile body from penetration to rebound was analyzed. Based on the expression of penetration resistance given by the cavity expansion theory, a one-dimensional elastic bar potential energy model was established from the perspective of the accumulation of deformation energy by penetration resistance, and a one-dimensional stress wave model was established from the perspective of stress wave generated by penetration resistance. The analytical solutions of the rebound velocity were derived from the two models respectively, and the physical quantities affecting the rebound velocity were analyzed. Through numerical simulation, the rebound phenomenon of the projectile body after penetrating the ultra-high performance concrete is reproduced, and the numerical results of the rebound velocity agree well with the two analytical solutions. Through numerical calculation of the same penetration model with different material parameters, the relationship between the rebound velocity and the material parameters in the analytical solution is verified, and the reliability of the theoretical model is proved. The results show that the projectile body accumulates deformation potential energy due to penetration resistance, and the projectile body bounces back due to the release of deformation potential energy after penetration. The initial rebound velocity is independent of the target velocity, proportional to the target material, yield strength and warhead shape coefficient, and inversely proportional to the elastic modulus and density of the projectile body. The results can preliminarily predict the rebound velocity and provide a reference for the design of ultra-high performance concrete protective structure and warhead.
With the development of the hypersonic weapon system, the non-circular cross-section projectile with more space utilization has attracted extensive attention. The high-velocity penetration mechanism of the non-circular cross-section projectile is a crucial issue that must be solved. Based on the truncated conical head structure of a typical anti-ship warhead and the elliptical section projectile’s shape, the elliptical section’s resistance characteristics and damage mechanism of thetruncated cone projectile through the metal sheet at high velocity are studied by numerical simulation. The load applied on the projectile is divided into two parts: shear punching resistance and ductile enlargement resistance. Combined with the numerical simulation results, the high-velocity penetration resistance function and the analytical model of residual velocity are proposed, which are suitable for elliptic cross-section flat projectile and ogive projectile. The differential surface force method and rigid body dynamics are used to construct a normal penetration model, and numerical simulation results verify the validity of the theoretical model. The results show that the elliptical cross-section truncated cone projectile penetrating through the metal sheet can be divided into the head penetration stage under load and the body penetration stage without load. In the head invasion stage, the failure mode of the thin sheet due to project penetration is decomposed into the shear plugging caused by the truncated cone platform and the ductility enlargement of the curved surface of the head. Under high-velocity impact, the damage to the sheet caused by elliptic ogive projectile/blunt projectile is different from that caused by low-velocity impact. When the ogive projectile penetrates through the sheet, ductile enlargement failure occurs. When the sheet is impacted by blunt projectile at high velocity, the coupled failure mode of shear punching and ductile enlargement takes place. The resistance of the elliptical cross-section projectile is the same as that of the circular cross-section projectile with the same cross-sectional area. The difference is that the asymmetric structure of the elliptical cross-section projectile leads to non-uniform load distribution.
In order to deeply investigate the trajectory deflection characteristics of a warhead during the non-normal penetration into the multi-layer spaced target, the trajectories under different impact attitudes are analyzed with combined numerical simulation and theoretical analysis, in which finite element method (FEM) simulations on the penetration process under various impact conditions are conducted systemically, and the deformation and failure morphologies of warhead and target as well as the interaction characteristics between them are discussed in detail. Besides some feature parameters, lateral contact force and angular moment, are introduced in the theoretical analysis. Furthermore, the influence rules of oblique angle and attacking angle on the trajectory deflection characteristics are investigated in detail. Related results indicate that during the non-normal penetration into multi-layer spaced target, the warhead behaves as small staged axial velocity decay combined with obvious lateral trajectory deflection, and the trajectory deflection is mainly derived from the lateral contact force as well as the corresponding angular moment, and the lateral contact force mainly makes its effect during three periods, i.e., when the nose, shoulder and tail of warhead pass through the target, respectively. The oblique angle mainly affects the degree of external load asymmetry exerting on the warhead with increase of the oblique angle, the downward lateral contact force as well as the corresponding angular moment exerting on the warhead all increase, thus the trajectory deflection becomes more severe. Comparatively, the attacking angle determines two factors, one is the radial velocity of warhead at the time when its nose passes through the target, and another is the contact position between the warhead and target when the warhead tail passes through the target. These two factors determine the trajectory simultaneously, so different attacking angles make the lateral contact force and the corresponding angular moment differing from each other during the process of the warhead tail passing through the first target, leading to a critical attacking angle at which the evolution trend of trajectory deflection would turn the other way round. Compared to the penetration into a single layer target, a remarkable feature in the penetration of a warhead into the multi-layer spaced target is that the trajectory deflection shows a cumulative effect, and the situation in the penetration into the former target plate significantly affects the interaction condition between the warhead and the latter target plates, and this further results in a coupling effect between the trajectory deflection and the contact force. The present investigation is of good significance in the practical engineering application, e.g., predicting the penetrating ability of a warhead into the multi-layer spaced target, and optimizing the warhead structure and its impact attitude, etc.
In order to investigate the structural response and failure of projectiles obliquely penetrating into a multi-layered steel plate target, oblique penetration tests were conducted, in which three kinds of projectiles with circular, elliptical, and asymmetric elliptical cross-sections were employed while the ballistic trajectory and structural failure of projectiles were recorded. With the photographs captured by high-speed camera, a pixel measuring method was used to obtain the velocity and attitude deflection angle of projectiles. Based on the test results, the ballistic characteristics, dynamic loads and structural response of projectiles are analyzed by using FEM code ABAQUS/explicit, focusing on the oblique penetration at initial speed of 480 m/s and attack angle within 2°. Then, based on the free-free beam theory and the dynamic loads obtained by numerical simulation, the distributions of axial force, shear force and bending moment within projectiles are calculated, and an analytical method for structural strength and dynamic failure of projectiles is developed. The results show that when the projectile horizontally penetrates a multi-layered steel plate target with positive inclined angle, there exists a critical attack angle. If the attack angle is smaller than this critical value, the projectile will head drop and its trajectory turns downwards; when the attack angle is larger than the critical value, the projectile will be raised and its trajectory turns upwards. In addition, the critical attack angle increases as the thickness of the target plate decreases. For the projectiles with high strength and low ductility, the failure mode is brittle fracture and the distances between the fracture position and the projectile nose is 0.72−0.81 times of its length, which is mainly due to the lateral impact load at the rear part of projectile. Moreover, by means of the dynamic model of the projectile based on the free-free beam theory, the fracture position of projectile during oblique penetration process could be well predicted. Also, among the three types of projectiles with the same length and cross-sectional area, the projectile with asymmetric elliptical cross-section is easier to fracture and the position is even closer to the projectile nose.
In order to study the influence of the cross-section shape and caliber radius head on the penetration performance of elliptical cross-section projectiles, the static deep indentation test of the elliptical cross-section conical indenters was carried out, and the force-displacement curves of different cross-section indenter slowly penetrating the material were obtained. Then, by means of a 30-mm-caliber ballistic gun platform, a series of experiments were carried out on 2A12 thick aluminum targets subjected to normal penetration by three kinds of 30CrMnSi2A steel projectiles with different elliptical cross-section shapes in the striking velocity ranging from 400 m/s to 800 m/s. The penetration depth of projectiles and the failure morphology of targets were experimentally obtained. The penetration dynamic model of projectile into thick metal target was established on the basis of the cavity expansion theory and resistance function correction coefficient. The correctness of the theoretical model is validated by the experimental results in this paper, and the influence of the cross-section shape and caliber radius head of the projectile on the penetration performance are systematically analyzed. The results show that the elliptical section indenter with the same cross-sectional area has higher resistance while slowly penetrating into the material. When the major-to-minor axis length ratio of the cross-sectional of indenters increases from 1.00 to 2.00, the material resistance increases by 10.1%. It is found that there is a large difference in the failure morphology of the target under the penetration of circular and elliptical cross-section projectiles, and the shape of the target tunnel area is consistent with the shape of the projectile cross-section. In addition, when the cross-sectional area of the projectile is equivalent and the major-to-minor axis length ratio of each cross-section was constant, the penetration performance of projectile decreases with the increase of the larger the major-to-minor axis length ratio. The penetration performance of projectile with elliptical cross-section decreases with the increase of the major-to-minor axis length ratio and the decrease of the caliber radius head of the projectile.
To study the penetration performance and failure characteristics of ultra-high strength steel targets against high-mass tungsten alloy kinetic projectiles with different impact velocities, a ballistic gun was used to carry out 215 g tungsten alloy kinetic projectiles to impact the ultra-high strength G50 steel and 45 steel targets at velocities in the range of 689−1489 m/s. According to the experimental results, a conic-like crater was observed in the ultra-high strength steel target against a tungsten alloy kinetic projectile, which was different from the column-like crater mode observed in the experiments of 45 steel targets. It was also observed that there were several unique tensile spall cracks on the crater surface and bottom for the ultra-high strength steel. The depth of penetration (DOP) and the crater volume of these two steel targets were further obtained, which showed that the DOP of G50 steel targets is shorter than that of 45 steel at similar penetration velocity, while the corresponding crater volume is greater than that of 45 steel. Based on the interaction mechanism between the projectile and target, the high-mass tungsten alloy kinetic projectiles are considered to undergo local fragmentation under high radial stress during penetration into the G50 steel target, resulting in unloading tensile waves within the target. It is believed the unloading waves within the target lead to the spalling damage of the crater wall, resulting in the fish-scale-like rough walls and spallation cracks. This also explains why the crater volume of G50 steel is greater than that of 45 steel. In addition, the sharpening effect was caused by the local fragmentation of the kinetic projectile head. Therefore, it is considered that this failure mode was mainly caused by both the tensile fracture of the target induced by the local fragmentation of the projectile and the sharpening behavior of the projectile. Numerical simulations of the penetration of high-mass tungsten alloy projectiles into ultra-high strength steel targets were further performed to demonstrate the entire process of deformation, damage, and failure of the target plate and projectile, which further validated the failure mechanism of the targets.
Lightweight ceramic composite armor is widely used for its lightweight and high bullet-resistant performance. To improve the bullet-resistant performance of ceramic composite armor, research has been conducted on the lightweight and performance improvement of different backing plates. The optimization of the structural design of lightweight ceramic composite armor is of great significance. Taking boron carbide ceramic as the front bullet-resistant panel, and different combinations of carbon fiber T300, UHMWPE, and Kevlar high-performance fiber boards as its composite backing plates. Using a 12.7 mm armor-piercing incendiary bullet to conduct ballistic impact experiments on ceramic/composite backing plates of different structures, the distribution law of fragment blocks and bullet-resistant performance of ceramic composite armor corresponding to different backing plates were analyzed by recovering shattered bullets and ceramic fragments and performing multi-stage screening and weighing. The study shows that adding a layer of carbon fiber board between the ceramic and fiber backing plates can significantly improve the bullet-resistant stiffness gradient of the composite armor, increase the structural stiffness of the entire bullet-resistant target board, and improve the stress wave propagation form between the bullet and the entire panel, prolonging the time and the effect of the stress wave propagation inside the entire ceramic panel after the formation of the ceramic cone and detachment from the ceramic panel, thereby reducing the tensile fracture caused by tensile waves inside the ceramic panel and prolonging the phenomenon of bullet retention. The Rosin-Rammler distribution model was used to characterize the fragment forms of ceramics and bullets. The results show that replacing half-thickness UHMWPE fiber board and Kevlar fiber board with carbon fiber backing plate respectively increased the half-cone angle of the ceramic panel by 2.05% and 4.20%, and the overall average characteristic size of the fragmentation zone decreased by 16.92% and 42.96% respectively. After adding a carbon fiber with high bending strength as the intermediate transition layer of the composite armor board, the failure mode of the backing plate changed, fully utilizing the high tensile strength of the fiber backing plate, thereby improving the overall bullet-resistant performance of the composite armor.
In order to study the mechanism of fragmentation and damage characteristics of elliptical cross-section warhead under internal explosive loading, five types of warheads were designed with the same ratio of charge mass to casing mass but different ratio of minor axis to major axis, and static explosion tests were conducted. The detonation process of the warhead was recorded by high-speed camera, and the destruction capability of the warheads were quantified by measuring the cratering parameters of the witness targets, while the radial velocity distribution of the fragments was obtained by the velocity-measuring targets. The test results show that the radial velocity of the fragments of elliptical cross-section warhead logarithmically increases from the major axis direction to the minor axis direction. There is a significant velocity enhancement compared to circular cross-section warhead, when the ratio of minor to major axis is equal to 0.40, the enhancement reaches to an amazing 83%. The fragments near the major axis are subjected to slip detonation as the dominant driving effect, and the circumferential tensile stress inside the casing leads to tensile cracks on the inner surface of the fragments. At the same time, the tensile cracks disappear gradually as the ratio of minor to major axis increases. In the minor axis direction, the scattered detonation always dominated, and the casing is mainly subjected to radial compressive stresses, thus no tensile crack appears. In addition, due to the influence of rarefaction waves on the end face, the maximum destructive power of the warhead axially occurs at 1/4 of the distance from the non-detonation end. And in the radial direction, the damage power of fragment in the direction of minor axis is significantly greater than that in the major axis direction. Especially when the ratio of minor to major axis is equal to 0.40, the destructive power of the minor axis reaches 1.83 times that of the major axis, but the difference decreases with the increase of minor to major axis ratio.
In order to deepen the understanding of the dynamic response of cylindrical shell under near-field/contact underwater explosion, small-scale model of cylindrical shell was designed and then optical and electronical tests were conducted to investigate the dynamic response of the model. The physical images of the interaction of shock wave/bubble with cylindrical shell were obtained using a camera with high frequency and high resolution. At the same time, dynamic strain, overpressure and damage mode were obtained. By analyzing the damage morphology of 3D laser scanning and high-speed optical physical images, the physical process of the interaction between shock waves, bubbles, and cylindrical shell structures as well as final damage mode are presented. Through the analysis of dynamic strains, the transformation of tension and compression strains and the division of response stages of the explosion-facing surface and back surface of cylindrical shell structure during loading are revealed. Through the analysis of overpressure loads, the completeness of charge detonation and the influence of structural energy absorption on overpressure under contact explosion loading are clarified. Research results have shown that changes in detonation distance can significantly affect the damage morphology of cylindrical shell structures. Under close range loading, cylindrical shell structures mainly exhibit large plastic deformation, while under contact loading, cylindrical shell structures mainly exhibit tearing failure. The formation and collapse of the cavitation zone on the explosion facing surface of cylindrical shell structures under close range loading cannot be ignored, and the damage effect caused by secondary loading should be further studied. The research results can provide a reference basis for the damage assessment of cylindrical shell structures under near-field/contact underwater explosion.
In order to lower the collateral damage of warhead in urban warfare, the new material, polyether ether ketone (PEEK) was used as the warhead shell in this work, by which the fragments could be eliminated while the killing range of shock waves was maintained. The comparison between the warhead using PEEK shell and the one with 2A12 shell and identical shell thickness was conducted, in which the overpressure, specific impulse and fragment velocity were analyzed, the acceleration of fragment was recorded by high-speed camera and the fragments were recovered for further investigation. The results show that the warhead using PEEK shell possessed a 54% lower weight than the one using 2A12 shell and an identical overpressure damage radius. By using PEEK shell, the energy converted into shock wave is more than the case using 2A12 shell, thus the specific impulse is also higher as the proportional distance increasing. Few PEEK fragments were recovered since the tiny PEEK fragments formed under the blast loads were completely burned during the acceleration driven by high temperature detonation products. Therefore, the lethality of warhead using PEEK shell was limited to shock wave and was easily controlled to meet the requirement of low collateral damage in urban warfare.