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Protocol to define material behaviour and failure strain level at low and high strain rates based on a compression test

100%

Jankowiak T. , Rusinek A. , Bendarma A.

tom Vol. 56 nr 2

471--481

Compression test is frequently used to define material behaviour. However, this test may be depending on different effects, for example friction, specimen inertia or local stress triaxiality. For this reason, a new design is proposed to analyse the previous effects and to try to minimize it on quantities measured as macroscopic stress and strain. To have a complete understanding, numerical simulations have been performed using finite element method (Abaqus/Standard and Abaqus/Explicit). It allows one to define the macroscopic behaviour and to have an access to the local values not accessible during experiments for a better understanding of the experimental measurements.

Application of two fracture models in impact simulations

88%

Fras T. , Roth C. C. , Mohr D.

Bulletin of the Polish Academy of Sciences. Technical Sciences

2020

tom Vol. 68, nr 2

317--325

The following discussion concerns modelling of fracture in steel plates during an impact test, in which both target and striker are manufactured from the same material, high-strength high-hardness armour steel – Mars® 300. The test conditions (3 mm thick targets, projectiles with different nose shapes at impact velocity lower than 400 m/s) result in severely damaged components, which results in an analysis of stress states showing material failure. Numerical analyses are performed using two material models: the Johnson-Cook approach, as traditionally used in impact simulations, accounting for the effect of stress triaxiality, strain rate and temperature and for comparison, a simulation by means of the stress triaxiality and Lode angle parameter-dependent Hosford-Coulomb model, also incorporating the effect of the strain rate on a fracture initiation. The aim of the study is to analyse the mechanisms of penetration and perforation observed in the armour steel plates and validation of the modelling approaches.

Calibration of constitutive equations under conditions of large strains and stress triaxiality

75%

Neimitz A. , Galkiewicz J. , Dzioba I.

2018

tom Vol. 18, no. 4

1123--1135

Constitutive equations were calibrated to improve their application in assessing a stress field in front of a crack under the conditions of large strains and stress triaxiality. The Bai–Wierzbicki method was adopted, and certain changes and new terms were introduced to incorporate material softening. Five shapes of specimens were tested to cover a wide range of stress triaxiality conditions and Lode factors. Tests were performed at three different temperatures, namely, +20 °C, –20 °C, and –50 °C, and on three different materials obtained by three different heat treatments of S355JR steel.