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Quasi-static and dynamic characterization of ultrafine-grained 2017A-T4 aluminium alloy processed by accumulative roll bonding PDF

Halimi A., Boudiaf A., Hemmouche L., Medjahed A., Tria D. E., Henniche A., Djeghlal M. E. A., Baudin T.

Archives of Mechanics

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2021

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Vol. 73, nr 4

339--363

EN

In this study, novel composite strips based on 2017A-T4 aluminium alloy (Al-Cu-Mg) produced by accumulative roll bonding (ARB) were developed. The microstructure and mechanical properties of the ultrafine-grained sheets under quasistatic and dynamic loadings were investigated. The initial microstructure characterization with an Optical Microscope and a Scanning Electron Microscope indicated that the ARBed sheets formed a compact material with the homogeneous and identical thickness for the individual bonded layers. Besides, the presence of precipitates was identified in all the processed strips with diverse sizes, quantities and distribution. Moreover, from Electron Back Scatter Diffraction, the microstructure was noticeably refined with increasing theARBcycles to reach 1.7 mof the grain size at the fifth cycle. The microhardness measurement and the tensile test were carried out for both natural ageing and ARBed specimens. Accordingly, the tensile stress acts on the individual layers rather than the entire sample that conduct to a reduction in the overall properties for the ARBed strips. Furthermore, a stabilization in the mechanical properties for the three first ARB cycles was noted, whereas, the domination of the dynamic recrystallization was responsible for a significant drop after the fourth cycle which is considered as the transition state. The characteristics of the compression deformation were examined under dynamic and quasi-static loadings conditions by using the Split–Hopkinson Pressure Bar system and the universal testing machine, respectively. The strain hardening behaviour was investigated using the Hollomon analysis. It was found that the thermal softening played a crucial role when compared to the strain hardening for all the studied strips. Moreover, the strain rate under the dynamic loading has a minor effect on the stress flow of the ARBed sheets compared to the as-received material.

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Laboratory Investigations on Perforation of 30PM Steel Plates

Janiszewski J., Grązka M., Tria D. E., Surma Z., Fikus B.

Problemy Mechatroniki : uzbrojenie, lotnictwo, inżynieria bezpieczeństwa

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2016

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Vol. 7, Nr 2 (24)

19--40

EN

Abstract. In this study, high strength steel plates made of 30PM steel were subjected to 7.62 Armour Piercing projectiles at the ordnance velocity. Several experiments differing considerably in conditions of interaction between projectiles and plates were performed. Selected parameters were measured before, during, and after ballistic tests, and both projectile and plate were subjected to detailed examination. It is foreseen to use the obtained results in two ways. Protection performance of steel plates will be determined and experimental data will be used as a reference for analyzing various models and numerical techniques, accessible in commercially available hydrocodes. The authors present the methodology, the experimental set-up configuration, and the results of laboratory experiments.

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Dynamic Characterization and Constitutive Modelling of ARMSTAL 500 Steel

Tria D. E., Trębiński R.

Problemy Mechatroniki : uzbrojenie, lotnictwo, inżynieria bezpieczeństwa

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2015

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Vol. 6, Nr 3 (21)

19-40

EN

The behaviour of a high strength steel (ARMSTAL 500) has been investigated using a combination of quasistatic and dynamic tests for a wide strain-rate range 1·10⁻⁴ – 3·10³ s⁻¹. A uniaxial testing machine and a Split Hopkinson Pressure Bar (SHPB) have been used under well controlled testing conditions. Next, the effect of the strain hardening, the strain rate hardening, loading history and stress triaxiality on the strength and ductility of the material has been studied. The present work also describes constitutive and damage models and their implementation available in the nonlinear finite element code LS DYNA. Calibration of constitutive model parameters and damage criteria is most often accomplished via regression techniques applied to laboratory data. A 3D numerical simulation of perforation of ARMSTAL 500 plates with 7.62 × 51 mm AP projectile were carried out with detailed models of target and compared with experiment in order to validate the calibrated models. As it will be shown, ARMSTAL 500 steel is a high strength steel with modest strain-rate sensitivity. The study indicates that the penetration depth can be predicted quantitatively and qualitatively with MJC hardening parameters calibrated from compression tests. The Modified Johnson–Cook constitutive model with Cockcroft and Latham failure model can predict the projectile residual speed and the fragmentation process followed very closely by MJC failure criteria.

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On the influence of fracture criterion on perforation of high-strength steel plates subjected to armour piercing projectile

Tria D. E., Trębiński R.

Archive of Mechanical Engineering

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2015

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Vol. LXII, nr 2

157--179

EN

This paper presents a numerical investigation of fracture criterion influence on perforation of high-strength 30PM steel plates subjected to 7.6251 mm Armour Piercing (AP) projectile. An evaluation of four ductile fracture models is performed to identify the most suitable fracture criterion. Included in the paper is the Modified Johnson-Cook (MJC) constitutive model coupled separately with one of these fracture criteria: the MJC fracture model, the Cockcroft-Latham (CL), the maximum shear stress and the constant failure strain models. A 3D explicit Lagrangian algorithm that includes both elements and particles, is used in this study to automatically convert distorted elements into meshless particles during the course of the computation. Numerical simulations are examined by comparing with the experimental results. The MJC fracture model formulated in the space of the stress triaxiality and the equivalent plastic strain to fracture were found capable of predicting the realistic fracture patterns and at the same time the correct projectile residual velocities. However, this study has shown that CL one parameter fracture criterion where only one simple material test is required for calibration is found to give good results as the MJC failure criterion. The maximum shear stress fracture criterion fails to capture the shear plugging failure and material fracture properties cannot be fully characterized with the constant fracture strain.

PL

Artykuł przedstawia numeryczne badania wpływu kryterium pękania materiału na perforację płyt ze stali pancernej 30PM pociskiem przeciwpancernym 7,6251 mm. Dokonano oceny czterech modeli pękania materiałów plastycznych w celu wyboru najbardziej odpowiedniego z nich. W artykule wykorzystano zmodyfikowany model konstytutywny Johnsona-Cooka (MJC) sprzężony z jednym z czterech kryteriów pękania: kryterium MJC, kryterium Cockrofta-Lathama (CL), kryterium maksymalnego naprężenia stycznego i kryterium stałego granicznego odkształcenia. Zastosowano trójwymiarowy algorytm w opisie Lagrange’a, zawierający zarówno skończone elementy jak i cząstki, z automatyczną konwersją zniekształconych elementów w bezsiatkowe cząstki. Wyniki symulacji numerycznej oceniono na postawie porównania z wynikami doświadczeń. Model pękania MJC, sformułowany w przestrzeni trójosiowości naprężenia i równoważnego odkształcenia plastycznego, pozwolił przewidzieć realistycznie obraz pękania materiału i wartości prędkości resztkowych pocisków. Jednakże wyniki badań wykazały, że również jednoparametrowy model CL, dla którego kalibracji wystarczy jeden prosty test materiałowy, daje porównywalne wyniki z kryterium MJC. Stwierdzono, że kryterium maksymalnego naprężenia stycznego niepoprawnie opisuje proces tworzenia się korka. Również kryterium stałej wartości odkształcenia granicznego nie może być użyte do scharakteryzowania procesu niszczenia materiału.