多层差异性气泡帷幕对水下爆破冲击波的衰减效应的试验研究

为评估气泡帷幕产生的气水混合层对冲击波能量的衰减效应,设计了乳化炸药水下延期爆破试验,研究气泡帷幕对水下爆破冲击波的影响。以冲击波斜入射条件下波阻抗差异性为研究对象,设计多层差异性气泡帷幕。以距爆心12 m处帷幕前、后测点处的冲击波衰减率为评价指标,测得多排孔气泡帷幕前测点处的冲击波压力峰值为1.518 MPa和1.493 MPa,帷幕后测点处的冲击波压力峰值为0.026 MPa和0.034 MPa,冲击波综合衰减率为97.72%⁹8.29%。与陆上岩石爆破冲击波传播规律相比,水下爆破冲击波作用时间短,波阵传播速度快,冲击波压力更大,且传递过程中能量损耗少,传递效率高,同等爆破当量的条件下水下爆破对结构的损害更大。采用多层差异性气泡帷幕对水下爆破施工进行防护,可以在完成水下炸礁爆破施工任务的同时,不破坏水下生态环境。     

Molecular-level analysis of shock-wave physics and derivation of the Hugoniot relations for soda-lime glass

Non-equilibrium and equilibrium molecular dynamics simulations are employed to study the mechanical response of soda-lime glass (a material commonly used in transparent armor applications) when subjected to the loading conditions associated with the generation and propagation of planar shock waves. Particular attention is given to the identification and characterization of various (inelastic-deformation and energy-dissipation) molecular-level phenomena and processes taking place at the shock front. The results obtained revealed that the shock loading causes a 2–4% (shock strength-dependent) density increase. In addition, an increase in the average coordination number of the silicon atoms is observed along with the creation of smaller Si–O rings. These processes are associated with significant energy absorption and dissipation and are believed to control the blast/ballistic impact mitigation potential of soda-lime glass. This study was also aimed at the determination (via purely computational means) of the shock Hugoniot (i.e., a set of axial stress vs. density/specific-volume vs. internal energy vs. particle velocity vs. temperature) material states obtained in soda-lime glass after the passage of a shock wave of a given strength and on the comparison of the computed results with their experimental counterparts. The availability of a shock Hugoniot is critical for construction of a high deformation-rate, large-strain, high pressure material model which can be used within a continuum-level computational analysis to capture the response of a soda-lime glass-based laminated transparent armor structure (e.g., a military vehicle windshield, door window, etc.) to blast/ballistic impact loading.     

装甲钢/芳纶复合材料抗爆震性能研究

采用圆形炸药设计了平面波发生器,研究了不同结构的装甲钢/芳纶复合材料对冲击波的衰减效果.试验结果表明,在装甲钢上加装纤维复合材料板可提高其抗爆震性能,当材料按照波阻抗减小的顺序进行排列时,可更有效衰减冲击波,具有多层结构的材料比双层结构材料的衰减效果更优.     

Two-material optimization of plate armour for blast mitigation using hybrid cellular automata

With the increased use of improvised explosive devices in regions at war, the threat to military and civilian life has risen. Cabin penetration and gross acceleration are the primary threats in an explosive event. Cabin penetration crushes occupants, damaging the lower body. Acceleration causes death at high magnitudes. This investigation develops a process of designing armour that simultaneously mitigates cabin penetration and acceleration. The hybrid cellular automaton (HCA) method of topology optimization has proven efficient and robust in problems involving large, plastic deformations such as crash impact. Here HCA is extended to the design of armour under blast loading. The ability to distribute two metallic phases, as opposed to one material and void, is also added. The blast wave energy transforms on impact into internal energy (IE) inside the solid medium. Maximum attenuation occurs with maximized IE. The resulting structures show HCA's potential for designing blast mitigating armour structures.     

Advanced layered personnel armor

Utilizing shock compression physics considerations and explicit numerical techniques a methodology has been developed to design composite personnel armor by optimizing the role each layer plays during projectile defeat. The initial design consists of a very hard 1st layer to deform and fracture the projectile, an orthotropic 2nd layer to slow down the shock wave propagation in the through thickness direction, whilst allowing rapid propagation in the transverse directions, a 3rd porous layer to absorb the shock wave energy through PV-work, and a 4th layer to provide confinement for the porous medium. Based on the above armor protection concept, composite plates comprising of alumina (Al₂O₃) Ceramic, Dyneema^® HB25 and porous polyurethane (PU) foam were constructed to test against baseline armor AISI 4140 steel plate. A hypothetical orthotropic material model closely resembling that of Dyneema HB25 was derived based on fundamental materials relations as well as limited available literature information. Material models for the other materials used in this research were based on existing sources. An integral experiment was conducted to validate this composite armor against numerical simulations. Through this study, the composite armor has been shown experimentally to be more effective in resisting penetration than a steel plate of equivalent (and slightly greater) areal density, and that the material layering sequence is fundamentally correct, while the numerical modeling has provided a general guidance to the behavior of the system. This research was done to explore this kind of approach to armor design to evaluate its merit. We make no claim that this design is ready for field use.     

Interface profile optimization for planar stress wave attenuation in bi-layered plates

Stress waves scatter upon entering a new medium. This occurs due to the reflection and transmission of the waves, which depends on the impedance mismatch between the two materials and the angle of incidence. For a bi-layered structure with finite dimensions and constant impedance ratio, the scattering and intensity of the stress waves may be varied by changing the interface profile between the two layers. In this paper, a methodology is proposed for optimizing the interface profile between the layers of a finite bi-layered plate for the objective of planar stress wave attenuation. The bi-layered plates are subjected at one end to highly impulsive loadings with various durations, and the geometry of the internal interface is optimized for the purpose of minimizing the amplitude of the maximum reaction force at the opposite fixed end. The optimization methodology is based on a genetic algorithm, which is coupled with a finite element method for analyzing the wave propagation behavior of the plates. It is observed that the interface profile and the amount of stress wave attenuation depend on the duration of the applied impulsive loading, with higher amounts of attenuation obtained when the wavelength associated with the impulsive load is small compared to the dimensions of the bi-layered plates.     

A study of composite material damage induced by laser shock waves

A laser shock wave technique has been used to study the damage tolerance of T800/M21 CFRP (Carbon Fiber Reinforced Polymer) composite material with different lay_ups. Different levels of damage have been created according to various laser irradiation conditions. Several characterization methods such as Optical Microscopy, X-ray Radiography, or Interferometric Confocal Microscopy have been used to quantify these defects. The nature of the defects induced by the shock wave propagation has been studied. The sensitivity of the composite material damage to the shock conditions has been shown and quantified. Moreover, the experimental results gathered with each technique have been compared to each other and it leads to a better understanding of the CFRP behavior under high dynamic loading. These original results have enabled the definition of a specific damage criterion for CFRP under dynamic loading.     

爆炸冲击波在不同介质中传播衰减规律的数值模拟

摘要：采用 ANSYS/LS-DYNA软件对冲击波在水、土、混凝土中的衰减规律进行了模拟研究,由计算得到的压力和能量的曲线,通过分析表明波阻抗对冲击波的初始峰值大小有很大的影响;土中冲击波的持续时间最长,混凝土中冲击波衰减较快;验证了冲击波速和波强度有关,波的强度越大,波速越高;能量的大小和介质的可压缩性有关,土中能量最大,水中能量最小。     

Effect of interlayer on stress wave propagation in CMC/RHA multi-layered structure

Due to the significance of the propagation of stress wave in composite armor during projectile–target interaction, the characteristics of stress wave propagation in multi-layered composite structure under impact load were investigated by traditional Split Hopkinson Pressure Bar system in this study. The effect of interlayer characteristic on the stress wave propagation was discussed. The results show that the interlayer properties between CMC and RHA steel play an important role in the propagation of wave. Compared to “CMC/RHA” structure without interlayer, the tungsten carbide interlayer can increase stress level in CMC layer remarkably, while silica gel layer has an opposite effect, and epoxy resin adhesive layer has no distinct effect on the propagation of stress wave. The increased compressive stress level in CMC layer is very useful when the CMC layer served as the face plate of a composite armor. During the impact process of the projectile to the armor, the anti-penetration capability of the face plate of the composite armor can be improved when in the compression stress state. In the comparison ballistic testing conducted with 7.62 mm armor piercing projectiles, the protection efficiency of the “CMC/WC/RHA” composite armor is about 36% higher than that of the “CMC/RHA” structure, which is in good correlation with the stress wave measurement results.     

Attenuation or enhancement—a one-dimensional analysis on shock transmission in the solid phase of a cellular material

The characteristics of compressive shock wave propagation in the solid phase of a cellular material are studied in the present paper using a one-dimensional mass-spring model. The unique compressive stress–strain relation of a cellular material leads to several interesting observations on the characteristic of one-dimensional stress wave transmission in a cellular material, which are important for understanding the blast and impact mitigation and attenuation through a cellular material. Generally, cellular material attenuates impact- or blast-induced loads by cell collapse mechanism at low impact velocities or low pulse pressure intensities when the stress transmission in a cellular material is limited by the plateau stress before the densification stage starts. This feature leads to wide applications of cellular materials in structural crashworthiness design where low speed impact is considered as potential survivable scenarios. However, scattered information has shown that stress enhancement in cellular material may occur when an intensive loading is applied, which, in contrast to the stress attenuation function of a cellular material, could produce more severe damage on the protected structures. This phenomenon is studied qualitatively in the present paper using a one-dimensional spring-mass model.     

防护条件下爆破冲击波衰减规律研究

在广州天河城西塔楼爆破之前,对近在10 m的玻璃幕墙安全性问题进行了论证.在目前还没有准确可行的计算爆破冲击波方法的条件下,从爆破冲击波对附近目标物的破坏机理入手,在室内对爆炸冲击压力进行了测试,模拟了在防护条件下爆破冲击波的衰减变化情况,并与在无防护条件下爆破冲击波衰减变化进行了同步对比,得到了在防护条件下爆破冲击波的衰减规律,指出近体防护材料的强度只要能够高出爆破冲击波的最大峰值,就能够有效地保护防护对象,这一结论在广州天河城西塔楼爆破拆除防护实践中得到了验证.     

Hybrid S2/Carbon Epoxy Composite Armours Under Blast Loads

Civil and military structures, such as helicopters, aircrafts, naval ships, tanks or buildings are susceptible to blast loads as terroristic attacks increases, therefore there is the need to design blast resistant structures. During an explosion the peak pressure produced by shock wave is much greater than the static collapse pressure. Metallic structures usually undergo large plastic deformations absorbing blast energy before reaching equilibrium. Due to their high specific properties, fibre-reinforced polymers are being considered for energy absorption applications in blast resistant armours. A deep insight into the relationship between explosion loads, composite architecture and deformation/fracture behaviour will offer the possibility to design structures with significantly enhanced energy absorption and blast resistance performance. This study presents the results of a numerical investigation aimed at understanding the performance of a hybrid composite (glass/carbon fibre) plate subjected to blast loads using commercial LS-DYNA software. In particular, the paper deals with numerical 3D simulations of damages caused by air blast waves generated by C4 charges on two fully clamped rectangular plates made of steel and hybrid (S2/Carbon) composite, respectively. A Multi Materials Arbitrary Lagrangian Eulerian (MMALE) formulation was used to simulate the shock phenomenon. For the steel plates, the Johnson-Cook material model was employed. For the composite plates both in-plane and out-of-plane failure criteria were employed. In particular, a contact tiebreak formulation with a mixed mode failure criteria was employed to simulate delamination failure. As for the steel plates the results showed that excellent correlation with the experimental data for the two blast load conditions in terms of dynamic and residual deflection for two different C4 charges. For the composite plates the numerical results showed that, as expected, a wider delamination damage was observed for the higher blast loads case. Widespread tensile matrix damage was experienced for both blast load cases, while only for 875?g blast load fiber failure damage was observed. This agrees well with the experimental data showing that the composite panel was not able to resist to the 875?g blast load.     

Dynamic micromechanical modeling of textile composite strength under impact and multi-axial loading

Micromechanical finite element modeling has been employed to define the failure behavior of S2 glass/BMI textile composite materials under impact loading. Dynamic explicit analysis of a representative volume element (RVE) has been performed to explore dynamic behavior and failure modes including strain rate effects, damage localization, and impedance mismatch effects. For accurate reflection of strain rate effects, differences between an applied nominal strain rate across a representative volume element (RVE) and the true realized local strain rates in regions of failure are investigated. To this end, contour plots of strain rate, as well as classical stress contours, are developed during progressive failure. Using a previously developed cohesive element failure model, interfacial failure between tow and matrix phases is considered, as well as classical failure modes such as fiber breakage and matrix microcracking. In-plane compressive and tensile loading have been investigated, including multi-axial loading cases. Highly refined meshes have been employed to ensure convergence and accuracy in such load cases which exhibit large stress gradients across the textile RVE. The effect of strain rate and phase interfacial strength have been included to develop macro-level material failure envelopes for a 2D plain weave and 3D orthogonal microgeometry.     

Aluminum foam integral armor: a new dimension in armor design

Closed-cell aluminum foam offers a unique combination of properties such as low density, high stiffness, strength and energy absorption that can be tailored through design of the microstructure. During ballistic impact, the foam exhibits significant non-linear deformation and stress wave attenuation. Composite structural armor panels containing closed-cell aluminum foam are impacted with 20-mm fragment-simulating projectiles (FSP). One-dimensional plane strain finite element analysis (FEA) of stress wave propagation is performed to understand the dynamic response and deformation mechanisms. The FEA results correlate well with the experimental observation that aluminum foam can delay and attenuate stress waves. It is identified that the aluminum foam transmits an insignificant amount of stress pulse before complete densification. The ballistic performance of aluminum foam-based composite integral armor (CIA) is compared with the baseline integral armor of equivalent areal-density by impacting panels with 20-mm FSP. A comparative damage study reveals that the aluminum foam armor has finer ceramic fracture and less volumetric delamination of the composite backing plate as compared to the baseline. The aluminum foam armors also showed less dynamic deflection of the backing plate than the baseline. These attributes of the aluminum foam in integral armor system add a new dimension in the design of lightweight armor for the future armored vehicles.     

Planar stress wave attenuation in plates with circular voids and inclusions

This paper addresses planar stress wave attenuation in finite rectangular aluminum plates with circular voids and two types of inclusions; namely, high-density polyethylene (HDPE) and steel. The voids and inclusions act as a source of impedance mismatch and scatter the waves within the plates. The plates studied here have multiple numbers of circular voids and inclusions with different dimensions and positions, and are subjected to short duration transient loadings. To find the most efficient layout and dimensions of the circular voids and inclusions within these plates, a heuristic optimization methodology is developed based on Genetic Algorithms (GA). This methodology is coupled with the Finite Element (FE) method to analyze the wave propagation behavior of the plates under elastic response. The developed optimization methodology is capable of updating the FE model of each candidate design during the optimization procedure, as each in general has different geometric characteristics. The results show that the attenuation capacity of the plates with circular voids and inclusions is a complex function of the dimensions of the plates and the wavelength associated with the transient loading, as well as, the type, positions and dimensions of the voids and inclusions. It is observed that significant amounts of planar stress wave attenuation can be achieved, if the dimensions and positions of the circular voids and inclusions are selected appropriately.     

UHM WPE-PUF复合材料结构设计与隔爆实验

采用层状复合工艺,制备了超高分子量聚乙烯(UHMWPE)-聚氨酯泡沫材料(PUF)复合材料;设计了复合材料隔爆实验,运用定制的聚偏氟乙烯(PVDF)压电传感器,直接测量了隔爆实验中材料内部冲击波压力,研究了UHMWPE-PUF复合材料对爆炸冲击波的衰减性能。研究表明,所制备的UHMWPE-PUF复合材料隔爆能力与同厚度的纯聚氨酯材料相比提高了近50%。将UHMWPE材料与PUF材料进行复合,可以充分发挥UHMWPE材料的高强、高模以及PUF材料较高的吸能特点,同时又弥补了PUF材料强度低的缺陷,且材料对爆炸冲击波的衰减性能得到极大提升,在爆炸防护领域有着很好的应用前景。     

Bio-inspired armor protective material systems for ballistic shock mitigation

Severe transient ballistic shocks from projectile impacts, mine blasts, or overhead artillery attacks can incapacitate an occupant at low frequencies, or sensitive equipment at high frequencies, if they are not properly attenuated by armor protective systems. Unique challenges exist in developing armor protective systems for mitigating both low and high frequency ballistic shocks due to the lack of robust design methodology, the severe dynamic loading conditions, and the uncertainties in predicting ballistic shock responses.Nature offers engineers a blueprint of highly effective, efficient, and adaptive material designs to protect certain regions from external threats. This paper presents the modeling, analysis, design, optimization, fabrication, and experimental validation of bone-inspired armor protective material systems for reducing projectile penetrations and alleviating ballistic shocks at both low and high frequencies. The optimized bone-inspired armor protective material system has a soft–stiff–soft–stiff material distribution pattern based on bone-foramen and osteonal-bone material systems. Analysis and experimental results demonstrated that the bone-inspired armor protective material systems have excellent capabilities for drastic ballistic shock mitigation, weight savings, and significant reductions in penetration and load transmission under ballistic loading conditions.     

Indentation of polyethylene laminates by a flat-bottomed cylindrical punch

Cross-ply polymer laminates reinforced by ultra-high molecular weight polyethylene (UHWMPE) fibers and tapes have been subjected to quasi-static indentation by a flat-bottomed, circular cross section punch and their penetration resistance and failure mechanisms investigated. Three fiber- and two tape-reinforced grades progressively failed during indentation via a series of unstable failure events accompanied by substantial load drops. This resulted in a ‘saw-tooth’ load versus indentation depth profile as the load increased with indentation depth after each failure event. The penetration behavior scaled with the ratio of the thickness of the remaining laminate to the diameter of the punch, and the indentation pressure scaled with the through thickness compressive strength. Failure occurred by ply rupture. The results are consistent with penetration governed by an indirect tension failure mechanism, and with experimental reports that tape-reinforced materials have a similar ballistic resistance to the higher tensile strength fiber-reinforced grades in rear-supported test conditions.     

深孔间隔装药爆破对不同孔壁介质的影响

数值模拟研究了岩石、混凝土和土三种不同孔壁介质深孔间隔装药爆破时的扩孔特征、压力场、应力场、速度场和能量分布及传播衰减规律,还分析了间隔介质(空气和水)和起爆方式等对孔壁介质中冲击波传播规律的影响。研究表明:由于岩石、混凝土和土三种孔壁介质的波阻抗和可压缩性不同,导致爆破后分别形成"狼牙棒"型、"纺锤"型和"圆柱"型三种爆腔。与岩石和混凝土相比,在土体中的扩孔宽度分别提高约60%和约45%,土能缓解孔壁压力和等效应力、降低爆破振动效应、减缓爆炸冲击波的衰减速度和提高能量利用率,而在岩石和混凝土介质中,上述效果的差异性不太明显。与水间隔装药相比,在岩石和混凝土孔壁介质中采用空气间隔装药结构能降低约7%的孔壁压力。在岩石和混凝土孔壁介质中,采用底部起爆方式能够提高炸药的能量利用率,中部起爆方式能够减缓爆破振动效应,而在土体中并不明显。     

The shock properties of a La<Subscript>2</Subscript>O<Subscript>3</Subscript> filled silicate glass

A survey of the shock properties of the silicate glass, LACA has been carried out using manganin stress gauges. The principal Hugoniot has been measured and found to have significantly higher values than for other common silicate glasses. Gauges mounted on the rear of the target (supported with a block of polymethylmethacrylate) show reloading signals superimposed on the main compressive shock pulse. This has been interpreted as evidence of dynamic compressive failure (the failure wave or front). Manganin gauges mounted so as to be sensitive to the lateral component of stress support this hypothesis. Finally, failure front velocities, measured using known lateral gauge separations increase with increasing shock stress, tending towards the shear wave speed.