Perforation of AA5083-H116 aluminium plates with conical-nose steel projectiles – Calculations

The use of aluminium alloys in lightweight protective structures is increasing. Even so, the number of experimental and computational investigations that give detailed information on such problems is limited. In an earlier paper by some of the authors, perforation experiments were performed with 15–30 mm thick AA5083-H116 aluminium plates and 20 mm diameter, 98 mm long, HRC 53 conical-nose hardened steel projectiles. In all tests, initial and residual velocities of the projectile were measured and the ballistic limit velocity of each target plate was determined. In the present paper, an analytical perforation model based on the cylindrical cavity-expansion theory has been reformulated and used to calculate the ballistic perforation resistance of the aluminium plates. In addition, non-linear finite element simulations have been carried out. The target material was modeled with the Johnson–Cook constitutive relation using 2D axisymmetric elements with adaptive rezoning. To allow ductile hole growth, a pin-hole was introduced in the target. The analytical and numerical results have been compared to the experimental findings, and good agreement was in general obtained. A parametric study was also carried out to identify the importance of the different terms of the Johnson–Cook constitutive relation on the perforation resistance of the target. The results indicate that thermal softening cannot be neglected, so an alternative procedure for identification of the material constants in the power-law constitutive relation used in the cavity-expansion theory has been proposed.     

The effect of target strength on the perforation of steel plates using three different projectile nose shapes

The effect of target strength on the perforation of steel plates is studied. Three structural steels are considered: Weldox 460 E, Weldox 700 E and Weldox 900 E. The effects of strain hardening, strain rate hardening, temperature softening and stress triaxiality on material strength and ductility are determined for these steel alloys by conducting three types of tensile tests: quasi-static tests with smooth and notched specimens, quasi-static tests at elevated temperatures and dynamic tests over a wide range of strain rates. The test data are used to determine material constants for the three different steels in a slightly modified version of the Johnson–Cook constitutive equation and fracture criterion.Using these three steel alloys, perforation tests are carried out on 12 mm-thick plates with blunt-, conical- and ogival-nosed projectiles. A compressed gas gun was used to launch projectiles within the velocity range from 150 to 350 m/s. The initial and residual velocities of the projectile were measured, while the perforation process was captured using a digital high-speed camera system. Based on the test data the ballistic limit velocity was obtained for the three steels for the different nose shapes. The experimental results indicate that for perforation with blunt projectiles the ballistic limit velocity decreases for increasing strength, while the opposite trend is found in tests with conical and ogival projectiles. The tests on Weldox 700 E and Weldox 900 E targets with conical-nosed projectiles resulted in shattering of the projectile nose tip during penetration.Finally, numerical simulations of some of the experimental tests are carried out using the non-linear finite element code LS-DYNA. It is found that the numerical code is able to describe the physical mechanisms in the perforation events with good accuracy. However, the experimental trend of a decrease in ballistic limit with an increase in target strength for blunt projectiles is not obtained with the numerical models used in this study.     

Perforation of AA5083-H116 aluminium plates with conical-nose steel projectiles—experimental study

The interest regarding use of aluminium alloys in lightweight protective structures is today increasing. Even so, the number of experimental and computational investigations giving detailed information on such problems is still rather limited. In this paper, perforation experiments have been performed on AA5083-H116 aluminium plates with thicknesses varying between 15 and 30 mm impacted by 20 mm diameter, 98 mm long, HRC 53 conical-nose hardened steel projectiles. In all tests, initial and residual velocities of the projectile were measured and a digital high-speed camera system was used to photograph the penetration and perforation process. Based on these measurements, impact versus residual velocity curves of the target plates were constructed and the ballistic limit velocity of each target was obtained. An analytical perforation model from the open literature is then used to predict the ballistic limit velocity, and excellent agreement with the experimental data is found. The experimental results are finally compared to similar experiments on steel and concrete targets, and the capacity of the different materials is evaluated in relation to total weight.     

Tensile fracture of HTPB based propellant specimens

Abstract

Small addition of titanium (～0·01 wt-%) to low carbon (～0·04 wt-%) aluminium killed extra deep drawing quality steel resulted in a decrease in strain aging as well as a decrease in plastic anisotropy after cold rolling and annealing. The extent of decrease in both the strain aging and plastic anisotropy was found to be a function of Ti/N ratio. It was found that at a Ti/N ratio of 2·4, the aluminium killed low carbon steel was completely non-aging after cold rolling and annealing. However, there was also a concomitant decrease in the plastic anisotropy with the increase in Ti/N ratio. The average plastic anisotropy ratio r _avg decreased from a value of 1·8 in steels with no titanium (Ti/N=0), to a value of 1·4 in steels with Ti/N=2·4.     

Measurement of crack volume due to thermal expansion anisotropy in aluminium titanate ceramics

Grain-boundary crack onset and crack volume at room temperature resulting from thermal expansion anisotropy in aluminium titanate ceramics were studied by dilatometry. Investigation revealed that specimens with low bulk density have a smaller temperature difference between sintering and crack-onset temperature than those of the specimens with high density and the same grain size. The fracture surface energy of aluminium titanate on the grain-boundary cracking in the present study was about 22 J m^–2; the grain-boundary crack volume is proportional to (grain size)^0.5.     

An analytical model for composite sandwich panels with honeycomb core subjected to high-velocity impact

In this paper, an analytical model for perforation of composite sandwich panels with honeycomb core subjected to high-velocity impact has been developed. The sandwich panel consists of a aluminium honeycomb core sandwiched between two thin composite skins. The solution involves a three-stage, perforation process including perforation of the front composite skin, honeycomb core, and bottom composite skin. The strain and kinetic energy of the front and back-up composite skins and the absorbed energy of honeycomb core has been estimated. In addition, based on the energy balance and equation of motion the absorbed energy of sandwich panel, residual velocity of projectile, perforation time and projectile velocity have been obtained and compared with the available experimental tests and numerical model. Furthermore, effects of composite skins and aluminium honeycomb core on perforation resistance and ballistic performance of sandwich panels has been investigated.     

Plastic deformation of polyurea coated composite aluminium plates subjected to low velocity impact

The demand for protective measures for structures is on the rise due to the increasing possibility of structural damage due to threats such as natural disasters, collision of vehicles, and blast and ballistic impacts. Application of an elastomer as a composite material with other base materials such as aluminium, steel and concrete has been considered as one of the measures to mitigate such threats. However, very limited work has been conducted in this area, especially on the feasibility of polyurea (elastomer) as a composite material against low velocity impacts. The focus of this research is to investigate the behaviour of polyurea coated composite aluminium plates subjected to rigid blunt-nosed projectile impact. AA5083-H116 aluminium alloy plates with polyurea coatings of 6 mm and 12 mm thickness were investigated. A blunt cylindrical projectile of high strength steel travelling in the velocity range of 5–15 m/s impacted at the centre of the 300 mm × 300 mm square plates. A polyurea coating was used to absorb part of the impact energy and provide protection to the plates as an energy damping material through application on the impact side of the plates. In addition, uncoated aluminium plates of the same thickness were used in the test program. A gas gun mechanism was used to fire a 5 kg projectile, and laser displacement monitoring equipment was used to record the out-of-plane deformation history of the plate during the impact. The complete test setup has been modelled numerically using the advanced finite element (FE) code LS-DYNA. The models were validated with the experimental results. Deformation time histories obtained from both the experimental and numerical studies for the plates were used to compare the ability of polyurea to effectively mitigate the damage resulting from low velocity impact. The polyurea coated plates showed a considerable reduction in out-of-plane deformation when compared to the uncoated plates. These findings indicate that polyurea can be utilised as an efficient energy absorbing/damping material against low velocity impact damage.     

Energy absorption during projectile perforation of thin steel plates and the kinetic energy of ejected fragments

This paper concerns energy absorption in thin (0.4 mm) steel plates during perforation by spherical projectiles of hardened steel, at impact velocities between 200 and 600 m s⁻¹. Absorbed energies have been obtained from measured incident and emergent projectile velocities. These tests were simulated using ABAQUS/Explicit, using the Johnson and Cook plasticity model. A strain rate-dependent, critical plastic strain fracture criterion was employed to model fracture. Good agreement is obtained between simulations and experiment and the model successfully captures the transitions in failure mode as projectile velocity increases. At velocities close to the ballistic limit, the plates fail by dishing and discing. As the incident velocity is increased, there are two transitions in failure mode, firstly to shear plugging and secondly to fragmentation and petalling. The simulations also show that, during the latter mode of failure, the kinetic energy of ejected debris is significant, and failure to include this contribution in the energy balance leads to a substantial over-estimate of the energy absorbed within the sheet. Information is also presented relating to the strain rates at which plastic deformation occurs within the sample under different conditions. These range up to about 10⁵ s⁻¹, with the corresponding strain rate hardening effect being quite substantial (factor of 2–3 increase in stress).     

A numerical model for bird strike of aluminium foam-based sandwich panels

Experimental bird-strike tests have been carried out on double sandwich panels made from AlSi7Mg0.5 aluminium foam core and aluminium AA2024 T3 cover plates. The bird-strike velocity varied from 140 to 190 m/s. The test specimens were instrumented with strain gauges in the impacted area to measure the local strains of the rear sandwich plate. A numerical model of this problem has been developed with the non-linear, finite element program LS-DYNA. A continuum damage-mechanics-based constitutive model was used to describe the behaviour and failure of the aluminium cover plates. The foam core was modelled by a pressure sensitive constitutive model coupled by a failure criterion on maximum volumetric strains. The bird was represented by an idealised geometry and the material model was defined by a linear equation-of-state. A multi-material arbitrary Lagrangian Eulerian (ALE) element formulation was used to represent the motion of the bird, whereas the sandwich panel was described by a Lagrangian reference configuration. A fluid–structure interface ensured proper coupling between the motion of the bird and the solid materials of the sandwich panel. It was found that the model was able to represent failure of both the aluminium cover plates as well as the aluminium foam core.     

Dynamic tensile deformation and fracture of metal cylinders at high strain rates

An experimental study has been presented on the radial deformation of aluminium and copper cylinders of internal diameter 52 mm and wall thickness 1–7 mm, internally loaded with high explosives. High speed photography and flash radiography have been employed to record the distance–time (x–t) history of the cylinder wall, which has been found to expand under strain rates of 10⁴–10⁵ s⁻¹. The rupture of the cylinder is identified by the leakage of detonation gases, through the cracks in the cylinder wall. Rupture strains of 70–160% have been found for commercially pure aluminium. For a fixed wall thickness, the rupture strain increases with the strain rate. However, when the cylinder wall thickness is changed, a maximum is observed in a graph showing the strain and strain rate relationship. Aluminium appears to follow the Ivanov rupture criteria. From the experimental data the macroscopic viscosity coefficient for aluminium has been found to be 0.55–0.87×10³ Pa s. In the deformation of a copper cylinder the cracks initiate at strains of 30–60%, followed by rupture at very high strains up to 300%. The crack propagation velocity through the copper cylinder wall has been found to be 250–300 m/s. Recovered fragments show wall thinning by 50–60% and also exhibit shear fracture which dominates the radial fracture in high velocity deformation of the metal cylinder.     

Effect of post-weld aging treatment on mechanical properties of Tungsten Inert Gas welded low thickness 7075 aluminium alloy joints

This paper reports the influence of post-weld aging treatment on the microstructure, tensile strength, hardness and Charpy impact energy of weld joints low thickness 7075 T6 aluminium alloy welded by Tungsten Inert Gas (TIG). Hot cracking occurs in aluminium welds when high levels of thermal stress and solidification shrinkage are present while the weld is undergoing various degrees of solidification. Weld fusion zones typically exhibit microstructure modifications because of the thermal conditions during weld metal solidification. This often results in low weld mechanical properties and low resistance to hot cracking. It has been observed that the mechanical properties are very sensitive to microstructure of weld metal. Simple post-weld aging treatment at 140 °C applied to the joints is found to be beneficial to enhance the mechanical properties of the welded joints. Correlations between microstructures and mechanical properties were discussed.     

On the influence of constitutive relation in projectile impact of steel plates

In this paper the influence of constitutive relation has been studied in numerical simulations of the perforation of 12-mm thick Weldox 460 E steel plates impacted by blunt-nosed projectiles in the sub-ordinance velocity regime. A modified version of the well-known and much used constitutive relation proposed by Johnson-Cook and both the bcc- and hcp-version of the Zerilli-Armstrong constitutive relation were combined with the Johnson-Cook fracture criterion. These models were implemented as user-defined material models in the non-linear finite element code LS-DYNA. Identification procedures have been proposed, and the different models were calibrated and validated for the target material using available experimental data obtained from tensile tests where the effects of strain rate, temperature and stress triaxiality were taken into account. Perforation tests carried out in a compressed gas gun on 12-mm-thick circular Weldox 460 E steel plates were then used as base in a validation study of plate perforation using LS-DYNA and the proposed constitutive relations. The numerical study indicated that the physical mechanisms during perforation can be qualitatively well predicted by all constitutive relations, but quantitatively more severe differences appear. The reasons for this are discussed in some detail. It was concluded that for practical applications, the Johnson-Cook constitutive relation and fracture criterion seems to be a good choice for this particular problem and excellent agreement with the experimental results of projectile impact on steel plates were obtained under the conditions investigated.     

Effects of microstructure on the strain-controlled fatigue failure behavior of an aluminium-alloy/ceramic-particle composite

A study has been made to understand the cyclic fatigue and cyclic fracture characteristics of a cast aluminium alloy metal matrix discontinuously reinforced with particulate silicon carbide. The Al/SiC_p composite was strained to failure over a range of strain amplitudes giving lives of less than 10⁴ cycles to failure. The specimens were cycled by using tension-compression loading under total strain control. In the as-cast condition, the aluminum-alloy/ceramic composite displayed combinations of cyclic hardening and softening to failure at higher cyclic-strain amplitudes, and progressive softening to failure at low cyclic-strain amplitudes. The spray-atomized and deposited composite exhibited softening to failure at the higher cyclic-strain amplitudes and combinations of softening and hardening behavior at the lower strain amplitudes. The observed hardening and softening behavior is a mechanical effect and attributed to concurrent and competing influences of interactions between cyclic deformation and composite microstructure during cyclic straining. The processed microstructure exhibited better cyclic ductility and cyclic-strain resistance than the as-cast composite microstructure. The cyclic fatigue behavior of the alloy is briefly interpreted in the light of composite microstructural effects, plastic strain amplitude and concomitant response stress.     

Normal impact and perforation of thin plates by hemispherically-tipped projectiles — II. Experimental results

The present investigation is concerned with the measurement of the forces, permanent deflections, strains and plugs produced by rigid projectiles during contact and perforation of thin aluminium and mild steel plates. Tests were generally executed just below and just above the ballistic limit; a few experiments were conducted at much higher velocity. The direct force measurements were performed by means of a special technique using a projectile containing a piezoelectric quartz crystal. Observations were carried out on more than two hundred 2024-0 aluminium plates, 0.51, 1.27 and 3.175 mm thick and 1.22 mm thick mild steel plates. The tests involved the use of hard-steel projectiles of 12.7 and 6.35 mm diameter with three different nose shapes. The residual strains, of the order of 40%, were measured by using a grid method while the strain history in the vicinity of the impact point was determined by a specially designed gage capable of measuring strains up to 100%.     

The impact resistance of polypropylene-based fibre–metal laminates

The high velocity impact response of a range of polypropylene-based fibre–metal laminate (FML) structures has been investigated. Initial tests were conducted on simple FML sandwich structures based on 2024-O and 2024-T3 aluminium alloy skins and a polypropylene fibre reinforced polypropylene (PP/PP) composite core. Here, it was shown that laminates based on the stronger 2024-T3 alloy offered a superior perforation resistance to those based on the 2024-O system. Tests were also conducted on multi-layered materials in which the composite plies were dispersed between more than two aluminium sheets. For a given target thickness, the multi-layered laminates offered a superior perforation resistance to the sandwich laminates. The perforation resistances of the various laminates investigated here were compared by determining the specific perforation energy (s.p.e.) of each system. Here, the sandwich FMLs based on the low density PP/PP core out-performed the multi-layer systems, offering s.p.e.’s roughly double that exhibited by a similar Kevlar-based laminate.A closer examination of the panels highlighted a number of failure mechanisms such as ductile tearing, delamination and fibre failure in the composite plies as well as permanent plastic deformation, thinning and shear fracture in the metal layers. Finally, the perforation threshold of all of the FML structures was predicted using the Reid–Wen perforation model. Here, it was found that the predictions offered by this simple model were in good agreement with the experimental data.     

Analytical and numerical investigation of polyurea layered aluminium plates subjected to high velocity projectile impact

This paper discusses on the penetration of high velocity projectiles through aluminium–polyurea composite layered plate systems. An analytical model has been proposed to predict the residual velocity of aluminium–polyurea composite plates, and validated with both experimental and numerical investigations. Full metal jacket (FMJ) projectiles (5.56 mm × 45 mm), corresponding to NATO standard SS109, were fired at the aluminium–polyurea composite layered plate systems from a distance of 10.0 m at a fixed velocity of 945 m/s. Four different composite plate configurations were used with thicknesses varying from 16 to 34 mm. Each configuration consisted of six specimens. Residual velocities for each individual test were recorded. Numerical simulations of the penetration process have been performed using advanced finite element code LS-DYNA®. The well-established Johnson–Cook and Mooney–Rivlin material models were used to represent the stress–strain behaviour of aluminium and polyurea in the numerical analysis. The analytical and numerical models provided good approximations for the residual velocities measured during the experimental tests. Polyurea layers contributed positively towards the reduction of residual velocity of the projectile in composite plate systems. In addition, ballistic limit curves for different composite systems have been established based on the validated models. As the results showed that polyurea contributes positively towards the reduction of residual velocity of projectiles, the findings of this study can be effectively used for the similar applications in future armour industry.     

Quasi-static perforation of thin aluminium plates

This paper presents an experimental and numerical investigation on the quasi-static perforation of aluminium plates. In the tests, square plates were mounted in a circular frame and penetrated by a cylindrical punch. A full factorial design was used to investigate the effects of varying plate thickness, boundary conditions, punch diameter and nose shape. Based on the results obtained, both the main and interaction effects on the maximum force, displacement at fracture and energy absorption until perforation were determined. The perforation process was then computer analysed using the nonlinear finite element code LS-DYNA. Simulations with axisymmetric elements, brick elements and shell elements were conducted. Quasi-static, isothermal versions of the Johnson–Cook constitutive relation and fracture criterion were used to model the material behaviour. Good qualitative agreement was in general found between the experimental results and the numerical simulations. However, some quantitative differences were observed, and the reasons for these are discussed.     

Thermomechanical treatment of 2014 aluminium alloy

Abstract

The effect of thermomechanical treatment on the flow stress, fracture strain, structure, and precipitation behaviour of commercial grade 2014 aluminium alloy has been investigated. Specimens in the supersaturated and aged conditions were plastically deformed in torsion tests in the temperature range 293–493 k and strain rate range 2·8 ×10^?3?2·5 s^?1. It is stated that the starting condition of the alloy acts dominantly on the flow stress, fracture strain, and thermally activated processes, which take place during aging. An increase in temperature results mainly in a reduction of flow stress in the aged alloy and an increase in flow stress in the supersaturated alloy. The supersaturated alloy exhibits negative strain rate sensitivity over the entire range of applied temperature while for the aged alloy it is exhibited only in the temperature range 293–393 K. The effect of temperature and strain rate on the fracture strain of the supersaturated alloy is negligible, but the fracture strain of the aged alloy increases with temperature and decreases with strain rate. In the supersaturated alloy, the process of strain aging is dominant during deformation at room temperature and at higher temperatures precipitation aging and recovery are dominant. In the aged alloy, strain aging is dominant in the temperature range 293–443 K and recovery is dominant only at the highest test temperature (493 K).

MST/616     

Impact perforation behavior of CFRPs using high-velocity steel sphere

In order to investigate impact perforation behavior of Carbon Fiber Reinforced Plastics (CFRPs), a steel sphere having a velocity of 500–1230 m/s was impacted to several kinds of CFRP laminate specimens consisting of different carbon fibers, interlaminate sequence, configuration; cross-ply or woven cloths, or thickness. The perforation behaviors were evaluated by absorbed energies during perforation, morphological in situ observations using high-speed framing cameras and postmortem observations. Spheres penetrated specimens in a fluid manner on the front surface, and perforated them in an extrusive manner on the rear surface in case of thick specimens. In case of thin specimens, on the contrary, spheres perforated specimens in fluid manner on the rear surface. In the fluid manner energy absorption was independent of the static mechanical properties of the fibers. In extrusion the energy absorption depended on the static tensile fracture energy of the fiber: high fracture energy resulted in large energy-absorption. The boundary velocities in changing failure modes depended on the tensile moduli of the reinforced fibers. Failure modes were significantly affected by the mechanical properties of the fiber: with low strength or fracture strain of reinforced carbon fiber, the specimens showed plugging fractures on the rear surfaces. With high strength and fracture strain, the specimens showed larger delamination on both surfaces.