Locking of the strain rate effect in Hopkinson bar testing of a mild steel

Mirone, Giuseppe; Barbagallo, Raffaele; Giudice, Fabio

doi:10.1016/j.ijimpeng.2019.04.009

Cited by 30 publications

(17 citation statements)

References 17 publications

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“…Then, the sensitivity of the A2-70 steel to the strain rate is remarkably high, as its dynamic amplification of the flow stress varies from 6% to 22% in the investigated dynamic range. These observations further support the previous findings of the authors in [12] for a different steel with very early necking onset and are also confirmed by Zhang et al [14] for a titanium alloy.…”

Section: Strain Rate Amplification Function Rsupporting

confidence: 92%

“…2c just magnifying the vertical axis for making visible the lower rate histories. All tests exhibit the typical surge of the strain rate beginning at the necking onset, already analysed by the authors in previous works [10][11] [12][13] and by Zhang et al [14] and Zhang et al [15], leading to very large strain rates at failure, nearly ten times greater than the strain rate values at the plateau.…”

Section: Dynamic Tests At Initial Room Temperaturesupporting

confidence: 54%

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Modelling the influence of strain and strain rate on the thermal softening during dynamic loading of ductile metals

Mirone

Barbagallo

2021

EPJ Web Conf.

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Although the combined effect of strain rate and temperature on the behaviour of metals is widely recognized, no universally accepted viewpoints are available about the physical phenomena. Experiments on a highly ductile A2-70 steel, performed at moderate dynamic rates (10 s-1) and different initial temperatures (20 to 150 °C), are firstly aimed here at assessing whether the thermal softening previously verified at static rates on the same steel is also suitable for describing now the mixed effect of dynamic rates and consequent variable temperatures, or further contributions to the thermal softening are necessary for describing such mixed effects. A general multiplicative model of the dynamic hardening is proposed, based on a static flow curve at room temperature to be increased by the dynamic amplification and to be decreased by the thermal softening, the latter incorporating the known “static component” depending on both strain and constant temperatures, together with a new “dynamic component” incorporating the dependence on the temperature variation and promoted by fast straining. The dynamic amplification of the stress is then obtained from another series of dynamic tests ran at initial room temperature and four nominal strain rates between 1 and 1800 s-1. The trend obtained is compatible with the seizing of the strain rate effect beyond necking onset, already found for other metals in previous works. All the experiments are based on the acquisition of the current load (by load cells for the testing machine and by strain gauges for the Hopkinson bar) and of the current cross section through optical diameter measurements by a fast camera; then, the effective current values of true stress-true strain-true strain rate are measured on a semi-local basis over the neck section at different instants during the test.

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Section: Strain Rate Amplification Function Rsupporting

confidence: 92%

Section: Dynamic Tests At Initial Room Temperaturesupporting

confidence: 54%

Modelling the influence of strain and strain rate on the thermal softening during dynamic loading of ductile metals

Mirone

Barbagallo

2021

EPJ Web Conf.

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“…It is interesting to draw a parallel between the results presented in Fig. 7 and the locking phenomenon reported in recent experimental studies (Mirone et al, 2019(Mirone et al, , 2020. These authors observed from split Hopkinson bar tensile tests that even if the strain-rate strongly increases after the onset of necking, this steep increase does not cause a significant amplification of the flow stress.…”

Section: Resultssupporting

confidence: 74%

Influence on strain-rate history effects on the development of necking instabilities under dynamic loading conditions

Jacques

Rodríguez-Martínez

2021

International Journal of Solids and Structures

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“…3 Engineering stress-strain relationship at high strain rates and elevated temperatures Fig. 4a shows the local true strain rate in Ti3Al2.5V alloy increases up to approximately 10000 /s [3][4][5][6]. However, for the polycarbonate, the dynamic local strain rate initially increases dramatically to almost 200 % of the nominal strain rate during strain localization, followed by a rapid drop and finally tends to stay at strain rate of 400 /s which is approximately 20 % of the nominal strain rate until fracture.…”

Section: Resultsmentioning

confidence: 99%

Strain rate and temperature dependent strain localization of dynamically stretched lightweight bars: from metal to polymer

et al. 2021

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This work studies the dynamic strain localization and constitutive relationship of a Ti3Al2.5V alloy in jet engine containment system and a transparent polycarbonate conceived for aircraft canopy application by Digital Image Correlation (DIC) technique from quasi-static condition to high strain rates at different temperatures. The responses of two materials show significant strain rate and temperature sensitivities. Observations of Ti3Al2.5V alloy show that the dynamic local strain rate can reach values up to 1000 % of the nominal strain rate in the necking zone. However, dynamic local strain rate of polycarbonate soars up during strain softening then decreases rapidly with necking propagation, and eventually becomes 20 % of the nominal strain rate until fracture. Appropriate viscoplastic constitutive models are determined for both materials, which are incorporated in finite element simulations to reveal the trend of dynamic local strain rate evolution in dynamic tensile tests. The present work shows two different kinds of strain localization in typical lightweight materials, which should be addressed carefully from Split Hopkinson Tension Bar (SHTB) tests.

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Locking of the strain rate effect in Hopkinson bar testing of a mild steel

Cited by 30 publications

References 17 publications

Modelling the influence of strain and strain rate on the thermal softening during dynamic loading of ductile metals

Modelling the influence of strain and strain rate on the thermal softening during dynamic loading of ductile metals

Influence on strain-rate history effects on the development of necking instabilities under dynamic loading conditions

Strain rate and temperature dependent strain localization of dynamically stretched lightweight bars: from metal to polymer

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