Institute of Fundamental Technological Research

The paper is related to the material behaviour of additively manufactured samples obtained by the direct metal laser sintering (DMLS) method from the AlSi10Mg powder. The specimens are subjected to a quasi-static and dynamic compressive loading in a wide range of strain rates and temperatures to investigate the influence of the manufacturing process conditions on the material mechanical properties. For completeness, an analysis of their deformed microstructure is also performed. The obtained results prove the complexity of the material behaviour; therefore, a phenomenological model based on the modified Johnson–Cook approach is proposed. The developed model describes the material behaviour with much better accuracy than the classical constitutive function. The resulted experimental testing and its modelling present the potential of the discussed material and the manufacturing technology.

AlSi10Mg aluminium alloy, additive manufacturing, DMLS method, compression, SHPB experiment, constitutive model

The deformation and failure of a Li-ion pouch battery under a high-velocity impact are studied experimentally and numerically. Ballistic tests were performed with 9 × 19 mm small-caliber projectiles travelling at 360 m/s, using state-of-the-art recording equipment and post-mortem examination under CT scan. The experimental observations are followed by a numerical simulation of the detailed multi-layer battery model. The study provides an insight into mechanisms of the progressive delamination and fracture of subsequent layers. The predicted residual velocity is very close to the measured values, but the impact energy absorption of the battery was found to be relatively low. The presented experimental and numerical analysis may contribute to a design of protection systems, in which rechargeable Li-ion batteries are included.

2D and 3D multilayered FE models, CT scan, delamination, high-velocity projectile impact, large format pouch battery, residual velocity

The aim of the paper is to formulate physically well founded yield condition for initially anisotropic solids revealing the asymmetry of elastic range. The initial anisotropy occurs in material primarily due to thermo-mechanical pre-processing and plastic deformation during the manufacturing processes. Therefore, materials in the "as-received" state become usually anisotropic. After short account of the known limit criteria for anisotropic solids and discussion of mathematical preliminaries the energy-based criterion for orthotropic materials was formulated and confronted with experimental data and numerical predictions of other theories. Finally, possible simplifications are discussed and certain model of isotropic material with yield condition accounting for a correction of shear strength due to initial anisotropy is presented. The experimental verification is provided and the comparison with existing approach based on the transformed-tensor method is discussed.

energy-based yield condition, orthotropic solids, initial anisotropy, strength differential effect, numerical simulation

Thin steel plates with an array of holes, i.e. perforated plates, are used as a passive add-on improving protective properties of armours against small-calibre projectiles. A number of holes in such plates increases the probability of asymmetrical contact between the plate and the projectile, due to which small-calibre projectiles may be destabilized or fragmented before they reach the main-armour. The aim of the study is to analyse the defeat mechanisms provided by 4-mm-thick slotted super-bainitic plates (Pavise™ SBS 600P) against hard-core 7.62mm P80 0.30 AP×51 (0.308 Win) projectiles. To show the dependence between the hit-point and projectile failure, moments when projectiles hit the pre-armour plate were recorded by an ultra-high speed camera and their behaviour after the impact was captured by the flash X-ray radiography. The obtained results complemented by the Lagrangian FEM analysis confirm that slotted steel plates have high protection effectiveness against small-calibre projectiles.

Light-weight ballistic protectionPerforated add-on armourSuper-bainitic steelArmour-piercing (AP) projectile

Monolithic, homogenous ballistic shields consisting of a single thick, high-hardness and high-strength steel plate are rarely applied in modern combat vehicles. Currently, a popular armour concept is a multilayered shield since it is expected that the kinetic energy of a threat may be dissipated by transmission through materials with different properties and also by multiple interface reflections. Searching for a maximum ballistic protection at minimum weight inspires applications of various materials which complementary behaviour provides a high protective efficiency without excessive mass. The preliminary experimental investigation presented in the paper aimed to verify behaviour of two prototyped laminated armours under impacts of small-calibre projectiles (cal. 7.62). The main interest lied in impact properties of materials proposed as the intermediate layer. The first tested concept was a laminated steel armour with the 10 mm thick rubber interlayer. In the second armour, the intermediate layer consisted of a magnetorheological fluid.

energy absorption, rubber, magnetorheological fluid, protective properties

The paper describes the ballistic impact test, in which fragment simulating projectiles (FSPs) of a 20-mm-diameter have been used against 40-mmthick plates made of an aluminum alloy AA7020-T651. To perforate plates, the projectiles must have reached a velocity higher than 890 m/s. Based on the performed ballistic test, the plugging failure mode is numerically modeled using the LS-DYNA software package. Results obtained due to the calculations in the Finite Element Method (FEM) are compared with the results from the Smoothed Particle Hydrodynamics (SPH). A condition of geometrical similarity between the target deformed experimentally and its numerical representation is introduced to evaluate the performed simulations.

Ballistic impact test, Fragment simulating projectile (FSP), Plugging failure mode, Smooth Particle Hydrodynamics (SPH), Optical scanning

The biaxial compression test, based on the concept presented in [1] and on the technique of the channel-die test [2] and [3], is discussed as an experimental method allowing evolution of the friction conditions from the dry-film lubrication, by using MoS2 grease, to the dry conditions to be analysed. This article gives an outline of the experimental set-up, its validation and the technique of the test results analysis. The analysis of friction is based on the experimental data coupled with the numerical simulation of the performed tests and on the theoretical approach introduced in [4]. The Oxygen-Free High Conductivity (OFHC) copper in the ‘as-received’ state in contact with the 42CrMo4 steel are chosen as the materials used for the experimental investigation.

Biaxial compression, Friction modelling, OFHC copper

The present work concerns the description of the yield state of biodegradable materials. As examples, biodegradable polymers are chosen – cornpole CRP-M2, starch fatty acid ester, and PLA/PBAT, poly(lactic acid) (PLA) blended with poly(butylene adipate/terephthalate) (PBAT) [1, 2]. These biodegradable, plant-derived bioplastics are a promising alternative to petroleum-based plastics. To describe the onset of plasticity in the bioplastics under discussion, Burzyński ’s hypothesis of material effort has been applied [3, 4]. The applied criteria account for the differential strength effect and for the shear correction resulting from the difference between experimental and theoretical values, obtained as a result of the Huber-Mises approach [5, 6]. In general, these properties of yield state are characteristic for polymers. The description of yield state for bioplastics is an issue that has hardly been investigated, which illustrates the novel nature of this paper in which this topic is discussed

bioplastics, strength differential effect, shear correction, yield surface, Burzyński yield condition

Ultrafine grained (UFG) and nanocrystalline metals (nc-metals) are studied. Experimental investigations of the behaviour of such materials under quasistatic as well as dynamic loading conditions related with microscopic observations show that in many cases the dominant mechanism of plastic strain is a multiscale development of shear deformation modes. The comprehensive discussion of these phenomena in UFG and nc-metals is given in M.A. Meyers, A. Mishra and D.J. Benson [Mechanical properties of nanocrystalline materials, Progr. Mater. Sci. 51 (2006), pp. 427–556], where it has been shown that the deformation mode of nanocrystalline materials changes as the grain size decreases into the ultrafine region. For smaller grain sizes (d < 300 nm) shear band development occurs immediately after the onset of plastic flow. Significant strain-rate dependence of the flow stress, particularly at high strain rates, was also emphasized. Our objective is to identify the parameters of Perzyna constitutive model, a new description of viscoplastic deformation, which accounts for the observed shear banding. The viscoplasticity model proposed earlier by Perzyna [Fundamental problems in viscoplasticity, Adv. Mech. 9 (1966), pp. 243–377] was extended in order to describe the shear banding contribution in Z. Nowak, P. Perzyna, R.B. Pecherski [Description of viscoplastic fow accounting for shear banding, Arch. Metall. Mater. 52 (2007), pp. 217–222]. The shear banding contribution function, which was introduced formerly by Pe¸cherski [Modelling of large plastic deformation produced by micro-shear banding, Arch. Mech. 44 (1992), pp. 563–584] and applied in continuum plasticity accounting for shear banding in R.B. Pecherski [Macroscopic measure of the rate of deformation produced by micro-shear banding, Arch. Mech. 49 (1997), pp. 385–401] plays pivotal role in the viscoplasticity model. The derived constitutive equations were identified and verified with the application of experimental data provided in the article by D. Jia, K.T. Ramesh and E. Ma [Effects of nanocrystalline and ultrafne grain sizes on constitutive behavior and shear bands in iron, Acta Mat. 51 (2003), pp. 3495–3509], where quasistatic and dynamic compression tests with UFG and nanocrystalline iron specimens of a wide range of mean grain size were reported. Numerical simulation of the compression of the prismatic specimen was made by the ABAQUS FEM program with UMAT subroutine. Comparison with experimental results proved the validity of the
identified parameters and the possibilities of the application of the proposed description for other high strength metals.

Ultra fine grained metals, nanocrystalline metals, viscoplastic deformation, shear banding, shear banding contribution function, numerical simulation of compression test, identification of the model parameters

The main idea of energy-based hypothesis of material effort proposed by Burzyński is briefly presented and the resulting failure criteria are discussed. Some examples, based on the own studies, which depict applications of these criteria are discussed and visualisations of limit surfaces in the space of principal stresses are presented.

Burzyński yield condition, yield surface, strength differential effect, energy-based yield criteria

The paper contains a short presentation of main idea of energy-based hypothesis of material effort proposed by Burzyński with discussion of the resulting failure criteria. Some examples illustrating applications of these criteria are discussed and visualisations of limit surfaces in the space of principal stresses are presented.

Burzyński yield condition, yield surface, strength differential effect, energy-based yield criteria

The paper is related to the energy absorptive properties of additively manufactured metallic cellular structures. The samples of Honeycomb, Auxetic, rhomboidal Lattice and a regular Foam are subjected to dynamic compression due to the blast tests. The cuboidal samples are manufactured by the Direct Metal Laser Sintering (DMLS) method using AlSi10Mg aluminium powder. The experimental tests are performed by means of an Explosive Driven Shock Tube (EDST). The measured results of the transmitted forces in relation to the shortening of the samples allow to analyse of the deformation processes of each selected geometry. In addition, the evaluation of the structural responses leads to the identification of the structure properties, such as the equivalent stress over equivalent strain or the energy absorption per a unit of mass. Moreover, the process of compression is modelled numerically using the explicit code LS-DYNA R9.0.1. The obtained simulations provide the complete analysis of the experimentally observed mechanisms.

Protection of combat-vehicles against impacts of small-calibre projectiles may be improved by the application of relatively thin and hard steel plates perforated by a plurality of holes. It is observed that due to the contact with a plate,the core of armour-piercing (AP) projectiles may be shattered, partially eroded or rotated, depending on the hit-position. The contact asymmetry is the strongest when a projectile hits a hole edge, its core undergoes bending and tends to fracture. The presented study discusses two methods of modelling of the contact and interactions between a bullet and a steel target. One of them is the explicit Lagrangian simulation of impacts of a fully represented AP projectile, another one is the semi-analytical model based on the integration of the motion equations of a 6 DOF rigid projectile. The results of numerical and semi-analytical approaches are compared with the ballistic impact experiment, in which the defeat mechanisms provided by 4-mm-thick slotted bainitic plates (Pavise™ SBS 600P) against hard-core 7.62 mm P80 0.30 AP x 51 (.308 Win) projectiles were verified, [1].

The stress–strain behavior of the rolled AA7020 aluminum tempered in T651 conditions is studied at various strain rates and temperatures. Basing on tensile, shear and compression tests, the effects of strain and strain-rate hardening, thermal softening and plastic anisotropy are discussed. The parameters of the thermo-viscoplastic flow and fracture models proposed by Johnson and Cook are identified and validated basing on the numerical modeling.
The obtained constitutive relations may be applied to model more complex states of stresses resulted from different loading conditions.

AA7020-T651, flow and fracture models, metals under dynamic loadings, numerical simulation of metal deformation

The stress–strain behavior of the rolled AA7020 aluminum tempered in T651 conditions is studied at various strain rates and temperatures. Basing on tensile, shear and compression tests, the effects of strain and strain-rate hardening, thermal softening and plastic anisotropy are discussed. The parameters of the thermo-viscoplastic flow and fracture models proposed by Johnson and Cook are identified and validated basing on the numerical modeling.
The obtained constitutive relations may be applied to model more complex states of stresses resulted from different loading conditions.

AA7020-T651, flow and fracture models, metals under dynamic loadings, numerical simulation of metal deformation