Vincent Grolleau

Last Name

Grolleau

First Name

Vincent

ORCID

0000-0001-8957-055X

Organisational unit

09473 - Mohr, Dirk / Mohr, Dirk

Show all metadata

Search Results

Publications1 - 10 of 16

Using miniature experiments to reveal strength gradients in battery casings
Tancogne-Dejean, Thomas; Roth, Christian; Grolleau, Vincent; et al. (2024)
International Journal of Mechanical Sciences
Complex metallic structures are often manufactured through multi-step forming or casting processes that induce severe mechanical property variations within the final part. Instead of using the virgin material properties to predict the final part performance, the local material properties after manufacturing need to be known. A novel comprehensive testing methodology is presented allowing the resolution of spatial gradients in the plasticity and fracture properties in metallic structures. It involves using a recently-developed miniature linear-motion system that probes the material within 2 mm wide gage sections (uniaxial, notched and central hole tension, in-plane shear). Additionally, a novel mini-bulge testing system is presented along with a mini-punch system to provide further insight into the local material response for biaxial loading conditions. A full testing campaign comprising 60 miniature samples is performed on all sides of a prismatic aluminum casing for Li-ion battery cells. The results demonstrate significant property variations with more than 30 % higher yield stresses for the side walls as compared to the bottom section. The miniature specimens allow identifying a location-dependent anisotropy, which would otherwise be missed by standard-sized samples. Furthermore, it is shown that the anisotropic Yld2000 plasticity model and the stress-state dependent Hosford-Coulomb fracture initiation model can be fully identified using results from experiments on miniature specimens only.
Using surround DIC to extract true stress–strain curve from uniaxial tension experiments
Jordan, Benoit; Grolleau, Vincent; Mohr, Dirk (2023)
International Journal of Solids and Structures
The exact stress–strain curve can be directly identified from uniaxial tension experiments up to the point of onset of diffuse necking. To gain insight into the post-necking hardening response of metals, other experimental methods such as the bulge, compression or torsion experiments are typically employed. Here, we introduce the idea of using surround DIC to obtain accurate specimen shape measurements of tensile specimens with rectangular gage section. Based on the results from a series of detailed three-dimensional finite element simulations of ASTM E8 type of uniaxial tension experiments on a wide spectrum of steel and aluminum behaviors, it is proposed to combine the history of the axial strain on the surface at the specimen center with the average axial stress to extract the stress–strain curve for strains of up to axial true strain of 1. The estimation uncertainty of this stress–strain curve estimation procedure is of the same order as that of the associated experimental uncertainties. This result is validated through an additional computational study for more than 100 distinct hardening behaviors. Furthermore, a surround DIC system composed of four stereo DIC systems is built and used to determine the stress–strain curve for a 1.5 mm thick DP780 steel. In addition, bulge experiments are performed on the same material revealing a good agreement of the post-necking hardening behavior determined through uniaxial and bulge testing.
In-plane Torsion Tests, Toward Large Strains Under Monotonic and Cyclic Loading of Sheet Metals
Colon, Xavier; Grolleau, Vincent; Galpin, Bertrand; et al. (2024)
Lecture Notes in Mechanical Engineering ~ Proceedings of the 14th International Conference on the Technology of Plasticity - Current Trends in the Technology of Plasticity, ICTP 2023 - Volume 4
When compared to the simple shear test, the in-plane torsion test allows for large strains to be achieved without edge effects, specimen tearing from the jaws or buckling. The proposed device offers full optical access to the specimen and enables the use of 2D Digital Image Correlation. In this way, we can observe the effects of the material anisotropy on the strain all along the circumference of the specimen up to large strains. A series of radial grooves machined on the specimen’s inner clamped surface enables the transmission of large torques necessary for high-strength steels. The paper illustrates the potential of this test for the study of plasticity with a focus on anisotropy, large deformations, and cyclic testing. Two steel sheets are considered, a deep drawing low carbon steel DC01 and a stainless steel AISI304. The paper aims to establish a direct relation between Hills’ anisotropy model parameters identified from the standard uniaxial tests and the angular evolution of the effective strain along the shear gage section of the in-plane torsion specimen.
Plane strain tension fracture a t high strain rate
Adlafi, Morwan; Galpin, Bertrand; Mahéo, Laurent; et al. (2021)
EPJ Web of Conferences ~ DYMAT 2021 - 13th International Conference on the Mechanical and Physical Behaviour of Materials under Dynamic Loading
Under plane stress conditions, most micromechanical and phenomenological models predict a minimum in ductility for plane strain tension stress state. Therefore, the stress state of plane strain tension plays a crucial role in many forming and crash applications and the reliable measurement of the strain to fracture for plane strain tension is particularly crucial when calibrating modern fracture initiation models. Recently, a new experimental technique has been proposed for measuring the strain to fracture for sheet metal after proportional loading under plane strain conditions. The basic configuration of the new setup includes a dihedral punch which applies out-of-plane loading onto a Nakazima-type of discshaped specimen with two symmetric holes and an outer diameter of 60 mm. In the present work, the applicability of the test is extended to high strain rates. High strain rates of about 100/s to 200/s are obtained using a drop weight tower device with an original sensor for load measurements. Quasi static tests are also performed for comparison, keeping the same specimen geometry, image recording parameters and set-up. The effective strains at fracture are compared from quasi-static to high strain rate loading for three different materials, i.e one aluminium alloy and two steels.
An Engineering Approximation On The Transformation Of Plastic Work Into Heat At Various Strain Rates And Stress States
Li, Xueyang; Roth, Christian; Grolleau, Vincent; et al. (2025)
MATEC Web of Conferences ~ 44th Conference of the International Deep Drawing Research Group (IDDRG 2025)
Accurate estimation of plastic work conversion into heat is crucial for analyzing metals under dynamic deformation. This study investigates DP800 sheet metal specimens across nine strain rates (0.001/s to 150/s) using notched tension (NT) and shear (SH) specimens to explore stress-state effects. Surface strain fields are monitored via digital image correlation (DIC) using a high-speed optical camera, while temperature rise due to plastic dissipation is measured using a high-speed infrared camera. A temperature rise of 170K is observed at 150/s, with minimal rise at 0.001/s. A Hill'48 yield surface combined with a modified Johnson-Cook hardening law accurately predicts force-displacement and strain histories. We compare two methods of treating the conversion of the plastic work into heat: (1) coupled thermo-mechanical simulations, which are accurate but computationally expensive, and (2) treating temperature as an internal state variable, neglecting heat transfer. We then propose a transition function incorporating both strain rate and stress state dependencies, enabling the internal variable method to achieve comparable accuracy to coupled thermo-mechanical simulations with a marginal increase in computational cost over pure mechanical analysis.
Design of in-plane torsion experiment to characterize anisotropic plasticity and fracture under simple shear
Grolleau, Vincent; Roth, Christian C.; Mohr, Dirk (2022)
International Journal of Solids and Structures
A novel experimental set-up is proposed to perform in-plane torsion experiments on grooved disk specimens. As compared to previously proposed systems, an enhanced clamping system is introduced to enable the torsion testing of high strength materials such as dual phase steels. The clamping is achieved without applying the clamping pressure through an axial actuator. Instead a custom-made washer-nut system is used which allows for the monitoring of the entire specimen front surface with cameras. Experiments are performed on three different steels (DC01, DP980, AISI301) to demonstrate the validity of the technique for measuring the stress-strain curve for strains of up to 2, for strain rate jump testing, for cyclic loading and for fracture testing. In particular, the demonstration experiments elucidate the importance of full field strain measurements during in-plane torsion. The strain fields vary along the gage section circumference in a periodic manner that is related to the anisotropy of the tested material. This important observation is confirmed through a finite element study covering a wide range of anisotropic Hill'48 materials with non-associated plastic flow.
Axisymmetric V-Bending of Sheet Metal: Determining the Fracture Strain and the Weakest Material Direction for Plane Strain Tension in One Test
Beerli, Thomas; Grolleau, Vincent; Mohr, Dirk; et al. (2022)
IOP Conference Series: Materials Science and Engineering
Plane strain tension is one of the most critical loading conditions leading to ductile failure in forming and crash applications. Hence knowing the fracture strain and weakest orientation for this stress state is crucial for safe design. A novel axisymmetric V-bending experiment is proposed to identify the strain to fracture and the weakest sheet material orientation for plane strain tension under proportional loading. After clamping its inner and outer boundaries, a disc-shaped specimen with an annular gage section is bent over a tubular knife of diameter 54mm. A single camera takes images of the top surface of the specimen throughout the experiment. It allows for timely crack detection and digital image correlation-based strain measurements. Experiments are performed on a range of modern engineering materials comprising two aluminium alloys (AA7075 and AA6014) as well as two steels (DP1180 and CR4). The experiments are complemented by Finite Element simulations to assess the robustness of the novel experimental approach.
Replacing strain gages by line camera DIC in Hopkinson bar experiments
Roth, Christian; LeGrelle, Foulques; Tancogne-Dejean, Thomas; et al. (2026)
International Journal of Impact Engineering
Strain gages are widely used to acquire the signals in dynamic experiments with Hopkinson bars. Here, we explore the potential of displacement history measurements with line camera based digital image correlation (DIC) to substitute the role of strain gages and directly obtain particle velocity. After outlining the fundamental equations for deriving stress-strain curves, the technique is applied and validated through split-Hopkinson bar compression and tension tests, as well as direct impact experiments. In direct impact tests, the line camera enables simultaneous measurement of input and output forces, facilitating the verification of quasi-static equilibrium. Moreover, in cases where quasi-static equilibrium is clearly satisfied, a single line camera measurement on the striker bar is sufficient to determine the entire stress-strain curve. Compared to laser interferometry and photon Doppler velocimetry, the line camera DIC system demonstrates superior capability in measuring large displacements of Hopkinson bars. It also offers a reliable non-contact measurement alternative to strain gages, which are prone to delamination under high-impact conditions.
Experimental characterization of a polydicyclopentadiene thermoset, study of protective metal-polymer and polymer-metal two-layer structures
Robin, Marie; Adlafi, Morwan; Galpin, Bertrand; et al. (2024)
Materials Letters
Multilayer structures are frequently used for military impact protection applications. For low-velocity impacts, they can be made from a wide variety of materials, including metallic and polymeric materials. One proposes to investigate the impact resistance of two-layer structures composed of polydicyclopentadiene thermosetting resin (P-DCPD) combined with DP450 steel or AA2024-T3 aluminum. Structures are subjected to debris impacts of 125 J at 10 m/s. Polymer stacking order is evaluated, highlighting the importance of P-DCPD to be the first layer impacted. To understand and validate these experimental results, the behaviors of DP450, AA2024-T3 and P-DCPD are studied. Experimental tests (quasi-static tension and compression, dynamic compression and Iosipescu shear tests) are carried out to characterize P-DCPD and validate material behavior laws. Finite element simulations using LS-Dyna software are used to validate and explain experimental impact results.
Using miniature cuboidal specimens to determine compression Stress–strain curve of sheet metal under static and dynamic loading
Girard, Arthur; Grolleau, Vincent; Mohr, Dirk (2025)
International Journal of Solids and Structures
Characterizing the stress–strain response of sheet metal under both tension and compression is important to provide accurate predictions of spring-back in sheet metal forming. Data on compression is scarce as anti-buckling devices typically need to be used to attain large strains in compression experiments on sheet metal. As a technically simpler alternative, we propose upsetting experiments with miniature cuboidal specimens as these can be conveniently extracted from sheet metal. In addition to static experiments, we design a Dropkinson bar system for the dynamic compression testing of miniature specimens. We demonstrate through finite element simulations that upsetting specimens with square cross-section are equally-suitable for measuring the stress–strain curve as traditional cylindrical specimens with circular cross-sections. Even though the local surface strains can be conveniently measured with planar DIC, detailed analysis revealed that using the average strain along the full specimen height yields the most accurate stress–strain curve estimation. Static and dynamic demonstration experiments are performed on miniature cuboidal specimens extracted from DP780, DP980 and DP1180 steel sheets. The comparison with the results from uniaxial tension experiments reveals a systematic strength differential effect with a yield stress for compression that is up to 4% higher than that for tension. The dynamic experiments at strain rates of about 750/s suggest a yield strength increase of up to 25% (as compared to static experiments).

Publications1 - 10 of 16

Vincent Grolleau

Last Name

First Name

ORCID

Organisational unit

Filters

Search Results