Effect of projectile hardness on deformation and fracture behavior in the Taylor impact test

The ballistic perforation performance of a kinetic energy projectile would be much more influenced by the projectile’s deformation during the impact process. A projectile may suffer from large deformation and even fracture as more and more advanced materials are used as resistant components. A comparison investigation was presented in this study concerning the deformation and fracture behavior of kinetic energy projectiles manufactured from 38CrSi steel of two different hardness values. Flat-nosed projectiles were fired in a two-stage compressed gun test facility against hard steel plates within the velocity range of 200–600 m/s. The impact process was monitored by a high-speed camera. Experimental results showed that, for the soft projectiles there are three deformation and fracture modes, i.e., mushrooming, shear cracking and petalling, and that for the hard projectiles there are also three modes, mushrooming, shearing cracking and fragmentation.     

弹丸超高速撞击半无限厚铝板数值模拟

微流星体及空间碎片的超高速撞击威胁着长寿命、大尺寸航天器的安全运行,导致其严重的损伤和灾难性的失效.撞击损伤特性研究是航天器防护设计的一个重要问题.本文采用AUTODYN软件的Lagrange法对半无限铝板的超高速斜撞击和与其具有相同法向速度的正撞击进行了模拟,给出了不同撞击角和不同法向速度下半无限厚铝板弹坑深度、宽度、长度的变化规律及多弹坑的形成过程,并与经验方程进行了比较分析.结果发现:随撞击角的增加,弹坑的深度和宽度减小,而弹坑的长度增加;随撞击速度的增加弹坑的直径和深度增加;在撞击角大于70度时出现多弹坑.     

Effect of reinforcement type on high velocity impact response of GRP plates using a sharp tip projectile

High velocity impact performance of glass reinforced polyester (GRP) resin composite plates with different type of reinforcement was investigated. The projectile used was a sharp tipped (30°) conical head with total length of 30 mm and shank length of 15 mm with weight of 9.74 g. Five different types of E-glass fiber reinforcement were used, including chopped strand mat (CSM), plain weave, satin weave, unidirectional and cross-ply unidirectional fiber reinforcements. A smooth barrel gas gun was used to conduct high velocity impact tests in the velocity range of 80–160 m/s. Composite plates with size of 15 cm × 15 cm were prepared in 3 and 6 mm thickness. Results showed higher ballistic limit velocity (velocity at which samples fully penetrated the target plates with zero residual velocity) for 3 mm GRP plates with cross-ply unidirectional reinforcement followed by unidirectional reinforcement and plain weave, the plates with satin weave and CSM reinforcements were almost in same level. The thicker specimens (6 mm), plates with plain weave reinforcement showed better ballistic performance towards sharp tipped conical projectile impact, followed by cross-ply unidirectional, satin weave, unidirectional and CSM reinforced plates. Experimentally determined ballistic limit velocity for all specimens correlate well with estimated ballistic limit values obtained in full perforation tests. Damage assessment conducted on all specimens indicated fiber tension and shear failure for thin-walled and sever delamination for the thick-walled specimens as the dominant failure modes.     

Transient hygrothermoelastic analysis of layered plates with one-dimensional temperature and moisture variations through the thickness

Transient heat and moisture diffusion and the resulting hygrothermal stress field are analysed in a layered plate subjected to hygrothermal loadings at the external surfaces. The one-dimensional transient diffusion is formulated as a one-way coupled problem wherein moisture-induced effects on heat diffusion are neglected, but the exact continuity in moisture flux at layer interfaces holds unlike existing analytical studies. An analytical solution to the diffusion problem is obtained by extending a previously derived solution for double-layered plates. Hygrothermal stresses are evaluated by superposition of stresses due to the applied temperature and moisture fields. First, numerical calculations are performed for a double-layered plate to investigate the influence of moisture-flux continuity at the layer interface on hygrothermal stress distribution. Second, the obtained solutions are applied to the hygrothermoelastic problem of a functionally graded material-like (FGM-like) non-homogeneous plate whose physical properties vary along the thickness direction. Numerical results show that the use of inappropriately simplified continuity conditions for moisture flux may cause a significant error in evaluating the transient hygrothermal stresses in a layered body. Moreover, it is demonstrated that a gradual change in the material composition of FGM-like non-homogeneous plates induces considerable hygrothermal stress relaxation.     

Ultra-high-speed deformation by impact of a projectile flying at speeds on the order of km s

An apparatus was developed to facilitate application of an electro-thermo-chemical accelerator to high-speed deformation experiments. The apparatus is designed on the principle of sequential collision of elastic bodies. Speeds ranging from 600 to 780 m s⁻¹ were achieved, and estimated strain rate of deformation is 10⁷ s⁻¹. The newly developed apparatus can be applied to various types of accelerators for attaining deformation speeds as high as several km s⁻¹. Transmission electron microscopy of aluminum deformed at high speed by use of the apparatus revealed the formation of very small stacking fault tetrahedra (SFTs). This observation is quite new for aluminum; previously, SFTs had not been observed in aluminum, although deformation had been carried out at strain rates lower than 10⁶ s⁻¹. Use of the apparatus promises to provide new insight into high-speed deformation.     

分层对TC4钛合金板抗平头弹撞击失效特性的影响

使用Abaqus/Explicit有限元分析软件,开展平头弹撞击不同厚度双层TC4钛合金板数值模拟,研究双层TC4钛合金板撞击失效特性与失效模式随厚度变化规律及机理.通过对比撞击试验与仿真结果,验证数值模型和参数的有效性.在此基础上与等厚度单层TC4钛合金板的抗侵彻性能进行对比,结果表明,对于12.68 mm直径的平头...     

Experimental and numerical investigations of low velocity impact on functionally graded circular plates

This paper addresses low-velocity impact behaviour of functionally graded clamped circular plates. An experimental work was carried out to investigate the impact behaviour of FG circular plates which is composed of ceramic (SiC) and metal (Al) phases varying through the plate thickness by using a drop-weight impact test system. The influence of the compositional gradient exponent and impactor velocity on the contact forces and absorbed energies was concentrated on the tests. The explicit finite element method, in which a volume fraction based elastic–plastic model (the TTO model) was implemented for the functionally graded materials, was used to simulate their drop-weight impact tests. Effective material properties at any point inside FGM plates were determined using Mori–Tanaka scheme. The experimental and numerical results indicated that the compositional gradient exponent and impactor velocity more effective on the elasto-plastic response of the FG circular plates to a low-velocity impact loading. The comparison at the theoretical and experimental results showed that the use of the TTO model in modelling the elasto-plastic behaviour of FG circular plates results in increasing deviations between the numerical and experimental contact forces for ceramic-rich compositions whereas it becomes more successful for metal-rich compositions.     

Finite element simulation of low velocity impact on shape memory alloy composite plates

Delamination of composite materials due to low velocity impacts is one of the major failure types of aerospace composite structures. The low velocity impact may not immediately induce any visible damage on the surface of structures whilst the stiffness and compressive strength of the structures can decrease dramatically.

Shape memory alloy (SMA) materials possess unique mechanical and thermal properties compared with conventional materials. Many studies have shown that shape memory alloy wires can absorb a lot of the energy during the impact due to their superelastic and hysteretic behaviour. The superelastic effect is due to reversible stress induced transformation from austenite to martensite. If a stress is applied to the alloy in the austenitic state, large deformation strains can be obtained and stress induced martensite is formed. Upon removal of the stress, the martensite reverts to its austenitic parent phase and the SMA undergoes a large hysteresis loop and a large recoverable strain is obtained. This large strain energy absorption capability can be used to improve the impact tolerance of composites. By embedding superelastic shape memory alloys into a composite structure, impact damage can be reduced quite significantly.

This article investigates the impact damage behaviour of carbon fiber/epoxy composite plates embedded with superelastic shape memory alloys wires. The results show that for low velocity impact, embedding SMA wires into composites increase the damage resistance of the composites when compared to conventional composites structures.     

Effect of coating thickness on the deformation behaviour of diamond-like carbon-silicon system

The effect of coating thickness on the deformation behaviour of diamond-like carbon (DLC) coatings on silicon substrates was investigated. Following nanoindentation of a 0.6 µm thick DLC coating, the subsurface microstructures were characterized and the data was compared to prior studies on a similar, but thicker coating. Indentation resulted in localized plastic compression in the coating without any through-thickness cracking. It was shown that the discontinuities in the load-displacement curves appeared at lower loads for the thinner coating. Accordingly, the silicon substrate exhibited cracking, plastic deformation and phase transformation at significantly lower loads than in the case of the thicker coating. Further, the widths, parallel to the interface, over which slip and the phase transformation zone are spread out in the substrate, was found to increase with the thickness of the coating. The mechanism responsible for the first pop-in was found to change from phase transformation in uncoated silicon to dislocation nucleation in the presence of the coating.     

形状记忆聚氨酯热力耦合变形行为实验和有限元模拟

在室温下对形状记忆聚氨酯进行不同应变率下的单调拉伸实验,结合红外测温仪对试样表面温度进行同步监测,研究拉伸过程中的热力耦合效应。结果表明:当应力达到屈服峰后,分子链解缠导致了屈服软化,同时分子链之间的摩擦诱发了局部化温升;随着载荷继续增加,分子链在拉伸方向优先取向导致应变硬化发生,响应的应力和温度不断升高。同时发现,屈服峰和局部化温升均随着应变率的增加而显著增加,然而材料耗散生热诱导的应变软化和应变硬化之间存在竞争机制,使得局部化塑性流动过程对应变率的敏感性降低。基于有限元软件ABAQUS建立板状试样拉伸的有限元模型,对形状记忆聚氨酯的拉伸变形进行热力耦合分析。通过比较不同时刻的塑性应变场和温度场云图发现,局部化的塑性流动和温升均从初始缺陷处萌生,并逐渐向中间移动直至扩展到整个试样。进而提取不同加载速率下的平均温升曲线与实验结果进行了对比,发现二者吻合度较高。     

Effect of prior compression treatment on the deformation behavior of Zr based bulk metallic glass

In the present work, the plasticity of Zr_64.2Cu_11.2 Ni_14.6Al₁₀ bulk metallic glass was enhanced through prior compression treatment. A considerably large compressive plastic deformation (over 6.5%) was achieved by pressing Zr_64.2Cu_11.2 Ni_14.6Al₁₀ bulk metallic glass laterally in specially designed tool steel die before compression test. Numerical analysis was also carried out to investigate the stress distribution under same mechanical conditions. It was revealed that the lateral pressing induced structural heterogeneity and high stress gradients facilitate large plastic strains through the generation of dense multiple shear band network.     

Effect of frictional force and nose shape on axisymmetric deformations of a thick thermoviscoplastic target

Summary We study thermomechanical deformations of a thermally softening viscoplastic thick target impacted at normal incidence by a cylindrical rod made of a material considerably harder than the target material. Thus we regard the penetrator to be rigid and analyze the effect of the penetrator nose shape and the frictional force at the target/penetrator interface on target's deformations. In the postulated expression for the frictional force, the coefficient of friction, defined as the ratio of the tangential force at a point to the normal force there, is a function of the relative speed of sliding between the two bodies. The computed depth of penetration is found to match very well with that observed in experiments by Forrestal et al. For each nose shape studied, the consideration of frictional forces reduces significantly the computed penetration depth. For the same kinetic energy of the penetrator, the penetrator with a sharp nose gives higher values of the penetration depth as compared to that obtained with a blunt nose.     

Effects of shape memory alloys on low velocity impact characteristics of composite plate

The effects of shape memory alloy thin films embedded in composite plates for improving damage resistance of composite structures under low velocity impact were investigated numerically. Analysis model for SMA thin film was developed based on Lagoudas’ model and implemented using the user defined material subroutine of the ABAQUS/Explicit finite element program. Composite damage model based on the Chang–Chang failure criteria was also implemented to consider progressive damage behavior. The finite element simulation of low velocity impact behavior of a shape memory alloy hybrid composite plate was performed using the ABAQUS/Explicit program. Parametric studies were performed to investigate the effect of shape memory alloys for improving damage resistance of composite plate.     

Effect of superelastic shape memory alloy wires on the impact behavior of carbon fiber reinforced in situ polymerized poly(butylene terephthalate) composites

Low-velocity impact properties of shape memory alloy (SMA) wires and carbon fiber reinforced poly(butylene terephthalate) obtained by resin transfer molding were characterized. At the subcritical regime the dissipated energy is not affected by the presence of the wires. However SMA has a positive effect on the maximum absorbed energy, since the maximum allowable load is higher. The contribution of the SMA wires to the higher impact performance of the hybrid composite is suggested to be due to their energy absorbing capability, and also to the high reversible force that acts as a healing force.     

On the room-temperature tensile deformation behavior of a cast dual-phase high-entropy alloy CrFeCoNiAl0.7

The microstructure and room-temperature tensile deformation behavior of the cast CrFeCoNiAl0.7 high-entropy alloy (HEA) were studied in details.The cast HEA consisted of a dual-phase structure of 77.3 vol.％ face-centered-cubic (FCC) phase plus 22.7 vol.％ B2 phase,and exhibited excellent room-temperature tensile properties with a high yield strength of 876 MPa,ultimate tensile strength of 1198 MPa and a relatively large elongation to fracture of ～9 ％.Dislocations gliding in the FCC phase governed the plastic deformation at the early stage of room-temperature tensile,and disordered dislocations were to form dislocation walls as the deformation proceeded.With further increase in strain to a high level,the stacking faults were generated through the dissociation of the geometrically necessary dislocations,serving as the potential heterogeneous nucleation sites for the deformation twins.     

Effect of forging temperature on the microstructure,subsequent aging precipitation behavior,and mechanical properties of Mg-Gd-Y-Zr-Ag alloy

The deformation mechanism,microstructure evolution,and precipitation behavior of a Mg-8.9Gd-1.8Y-0.5Zr-0.2Ag(wt.％)alloy multi-directionally forged at three different temperatures were investigated.As the forging temperature increases,the particle-stimulated nucleation(PSN)effect diminishes as the num-ber of dynamic precipitates decreases,pyramidal slip is activated,grain boundary migration accelerates,and continuous dynamic recrystallization(CDRX)dominates.The microstructures varied greatly,although fine-grained structures were formed at all different forging temperatures.Competitive precipitation be-tween dynamic precipitate growth,dislocation-induced precipitation,and homogeneous precipitation was observed after aging treatment.Among them,the medium temperature(748 K)forged and aged alloy ex-hibits the best mechanical performance,with an ultimate tensile strength of 436 MPa,and elongation of 16.3％.The calculation indicates that the mixed precipitation structure containing the β'precipitate band provides a 35％higher strengthening contribution than the typical homogeneously distributed precipi-tates.The formation of precipitation-free zones(PFZs)ensures that aging will not cause a dramatic de-crease in ductility,which provides a reference for the industrial preparation of high-performance wrought Mg-Gd series alloys.     

Effect of stacking sequence and thickness on the interlaminar stresses for quasi-isotropic laminated plates with a hole

This paper discusses the evaluation of interlaminar stresses, in the presence of in-plane stress gradients, for composite laminates by using three-dimensional equilibrium equations. The stress gradients are calculated by means of an improved finite difference scheme. A quasi-isotropic laminated plate with a circular hole subjected to a uniform tension stress is considered. The effects of stacking sequence and the thickness of the laminate on the interlaminar stresses have been studied.     

Effect of interlayer thickness on shear deformation behavior of AA5083 aluminum alloy/SS41 steel plates manufactured by explosive welding

An AA5083 aluminum alloy plate and an SS41 steel plate were cladded by an explosive welding method using an AA1050 aluminum alloy interlayer plate. The effects of the interlayer thickness on the interface morphology and the shear deformation behavior of the cladded plates were studied. The interfacial zone was composed of an intermetallic compound, FeAl₃, formed by the AA1050 interlayer. The intermetallic compound acted as a crack source at the AA1050/SS41 interface, and the thickness and morphology of the interfacial zone were depended on the thickness of the AA1050 interlayer. In a shear deformation test, the crack propagation behavior varied according to the morphologies of the interfacial zone, and the shear strength of the cladded plates decreased with the interlayer thickness.     

An experimental investigation on the impact behavior of hybrid composite plates

In this experimental study, the impact behavior of hybrid composite plates has been investigated. The increasing impact energy was performed on two types of hybrid composite plates (glass–carbon/epoxy) until complete perforation of specimens. An energy profiling method, showing the relationship between impact energy and absorbed energy, was used together with load–deflection curves to determine the penetration and perforation thresholds of hybrid composites. The failure processes of damaged specimens for different impact energies were evaluated by comparing load–deflection curves and images of damaged samples taken from impacted sides and non-impacted sides. Cross-sections of damaged specimens were also inspected visually and discussed to assess the extent of damage, such as fiber fracture in layers, expansion of delaminations between adjacent layers. The perforation threshold of hybrid composite impacted from surface with carbon fibers was found approximately 30% higher than that of surface with glass fibers.