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

Jacques, Nicolas; Rodríguez-Martínez, J.A.

doi:10.1016/j.ijsolstr.2021.111152

Cited by 6 publications

(2 citation statements)

References 65 publications

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“…From the true curves at different strain rates, it is possible to evaluate the dynamic stress amplification R, defined as the ratio between the equivalent stress at a certain strain rate σ eq D and the corresponding equivalent stress in static conditions σ eq ST . As shown in previous works by the authors [22,23] and addressed also by other researchers [29], despite the strain rate varies greatly during a single dynamic test, the stress amplification is not directly related to the actual strain rate. In particular, the authors showed that only the pre-necking plateau value of the strain rate determines the actual behavior of the material.…”

Section: Dynamic Experimental Seriesmentioning

confidence: 60%

Study of the Electron Beam Melting Process Parameters’ Influence on the Tensile Behavior of 3D Printed Ti6Al4V ELI Alloy in Static and Dynamic Conditions

et al. 2022

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The Ti6Al4V alloy is widely adopted in many high-end applications in different fields, including the aerospace, biomechanics, and automotive sectors. Additive manufacturing extends its range of possible applications but also introduces variations in its mechanical performance, depending on the whole manufacturing process and the related control parameters. This work focuses on the detailed tensile stress–strain characterization at low and high strain rates of a Grade 23 Ti alloy manufactured by electron beam melting (EBM). In particular, the main aim is to study the effect of the variation of the EBM process parameters on the performance of the material and their consequent optimization in order to obtain the best printed material in terms of ductility and strength. The adopted optical experimental setups allow the semi-local scale analysis of the neck section which makes possible the accurate estimation of stress, strain, and strain rate, all over the post-necking range and up to the very incipient specimen failure. Among the EBM printing process parameters, the speed function was previously identified as the one mainly affecting the material performance at static rates. Therefore, two different parameter sets, corresponding to the standard value and to an optimized value of the speed function parameter, respectively, are tested here at dynamic rates of 1, 15, and 700 s−1, for assessing the effect of the speed function on the dynamic material response. The results show that the optimized parameter set has a better performance compared to the standard one in terms of strength and ductility. In particular, in both static and dynamic conditions, it presents an increase of the true stress–strain curve (about 5% on average) and an increase of the failure strain (about 11% on average). Moreover, in respect to the standard parameter set, the optimized one is also characterized by a huge increase of the amplification due to the strain rate (about 49% on average for the considered strain rates).

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Section: Dynamic Experimental Seriesmentioning

confidence: 60%

Study of the Electron Beam Melting Process Parameters’ Influence on the Tensile Behavior of 3D Printed Ti6Al4V ELI Alloy in Static and Dynamic Conditions

et al. 2022

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“…Moreover, note that, while 10 −3 s −1 is an arbitrary value for the necking condition, we have checked that the necking strain is largely independent of this threshold value, provided that it is small enough so that the sections outside the necks are unloaded (we have checked that the results obtained with 𝑑𝜀 𝑥𝑥 𝑑𝑡 < 10 −4 s −1 , 10 −2 s −1 and 10 −1 s −1 , are virtually the same). Similar criterion and methodology have been used by N'souglo et al (2021) and Jacques and Rodríguez-Martínez (2021) to determine the formation of necks in plates and rings subjected to dynamic stretching. The saturation value of the major strain outside the necks is referred to as the major necking strain 𝜀 𝑐 𝑥𝑥 , and the minor strain measured at the same material point, and at the same loading time, is called the minor necking strain 𝜀 𝑐 𝑦𝑦 (note that 𝜀 𝑐 𝑦𝑦 = 0 for 𝜒 = 0, and that major and minor necking strains will be used in Section 4.4 to construct forming limit diagrams).…”

Section: Salient Featuresmentioning

confidence: 96%

Modeling dynamic formability of porous ductile sheets subjected to biaxial stretching: Actual porosity versus homogenized porosity

Nieto-Fuentes¹,

Jacques²,

N’souglo³

et al. 2022

Preprint

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This paper investigates the effect of porous microstructure on the necking formability of ductile sheets subjected to dynamic in-plane stretching. We have developed an original approach in which finite element calculations which include actual void distributions obtained from additively manufactured materials are compared with simulations in which the specimen is modeled with the Gurson-Tvergaard continuum plasticity theory (Gurson, 1977;Tvergaard, 1982) which considers porosity as an internal state variable. A key point of this work is that in the calculations performed with the continuum model, the initial void volume fraction is spatially varied in the specimen according to the void distributions included in the simulations with the actual porous microstructure. The finite element computations have been carried out for different loading conditions, with biaxial strain ratios ranging from 0 (plane strain) to 0.75 (biaxial tension) and loading rates varying between 10000 s −1 and 60000 s −1 . We have shown that for the specific porous microstructures considered, the necking forming limits obtained with the Gurson-Tvergaard continuum model are in qualitative agreement with the results obtained with the calculations which include the actual void distributions, the quantitative differences for the necking strains being generally less than ≈ 25% (the calculations with actual voids systematically predict greater necking strains). In addition, the spatial distribution of necks formed in the sheets at large strains is very similar for the actual porosity and the homogenized porosity models. The obtained results demonstrate that the voids promote plastic localization, acting as preferential sites for the nucleation of fast growing necks. Moreover, the simulations have provided individualized correlations between void volume fraction, maximum void size and necking formability, and highlighted the influence of the heterogeneity of the spatial distribution of porosity on plastic localization.

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Effects of large strain reverse loading on the strain rate dependence and dynamic strain localization of ductile metallic rods

Zhang

Townsend

2022

Meccanica

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The dynamic necking of ductile metallic rods with large strain reverse loading history has received little attention in the published literature. A novel bespoke real time strain control setup is constructed to apply the reverse loading directly to the specimen gauge section up to a maximum strain level of ± 0.16. 304L stainless steel is used as a model material in this study. The subsequent tensile tests of the reverse loaded specimens are performed from quasi-static to high strain rates of 1000/s, using a Zwick 050 Machine, hydraulic Instron 8854, and a bespoke split Hopkinson tension bar with high speed photography equipment. The initial flow stress of the 304L rods shows similar strain rate dependence, regardless of the reverse loading history. The local strain rate during strain localization increases dramatically and eventually reaches one order of magnitude higher than the nominal strain rate. A higher strain reverse loading significantly influences the development of necking instabilities, with smaller strain to necking inception, higher local stress in the necking zone, and higher local strain rate up to failure. Instead of evaluating the impact energy absorption up to necking, an analysis of the local stress–strain relationship indicates that the reverse loaded 304L shows good impact energy absorption up to failure. This agrees with the ductile fracture surfaces of the 304L materials with reverse loading.

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

Cited by 6 publications

References 65 publications

Study of the Electron Beam Melting Process Parameters’ Influence on the Tensile Behavior of 3D Printed Ti6Al4V ELI Alloy in Static and Dynamic Conditions

Study of the Electron Beam Melting Process Parameters’ Influence on the Tensile Behavior of 3D Printed Ti6Al4V ELI Alloy in Static and Dynamic Conditions

Modeling dynamic formability of porous ductile sheets subjected to biaxial stretching: Actual porosity versus homogenized porosity

Effects of large strain reverse loading on the strain rate dependence and dynamic strain localization of ductile metallic rods

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