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Huluka , Solomon , 1983-....

Abdul-Latif , Akrum

George , Daniel , 19..-....

Ramtani , Salah

Nedjar , Boumédiene

Deiab , Ibrahim

CY Cergy Paris Université , 2020-....

École doctorale Sciences et ingénierie , Cergy-Pontoise, Val d'Oise

Laboratoire Quartz , Saint-Ouen, Seine-Saint-Denis

Biaxial Characterization of Open-cell Aluminum Foam under Quasi-Static and Intermediate Strain Rate conditions , Solomon Huluka ; sous la direction de Akrum Abdul-Latif et de Rachid Baleh

Titre provenant de l'écran-titre

Ecole(s) Doctorale(s) : École doctorale Sciences et ingénierie

Partenaire(s) de recherche : QUARTZ (ECS, L@RIS, LISMMA) (Laboratoire)

Autre(s) contribution(s) : Akrum Abdul-Latif, Rachid Baleh, Daniel George, Salah Ramtani, Boumédiene Nedjar, Ibrahim Deiab (Membre(s) du jury) ; Daniel George, Salah Ramtani (Rapporteur(s))

Thèse de doctorat Mécanique CY Cergy Paris Université 2023

Biaxial characterizations of open-cell aluminum foam (AS7G06) with a very uniform architecture of regular shape with a uniform distribution under quasi-static and intermediate strain rates were performed. Biaxial characterization was performed using a new patented ACTP (Plastic Compression-Torsion Absorption) device incorporating INSTRON-5582 and a drop weight for quasi-static and intermediate strain rates, respectively.The quasi-static tests were carried out on a universal testing machine - the INSTRON 5582, with a maximum load capacity of 100 kN and using a crosshead speed of 5 mm/min, was selected. The load-displacement relationship was recorded simultaneously during the test thanks to the acquisition chain that links the machine to the computer.All intermediate strain rate tests are performed under an initial impact velocity of approximately 8.4 m/s with a total drop mass (47.0 kg) using a dynamic mass bench.In order to ensure the accuracy of the experimental results, each test is repeated five times under the same experimental conditions. If the differences between the test responses exceed 5%, another test is performed.In quasi-static situations, when ACTP is used, it produces different combinations of biaxial loading complexities in compression-torsion. This simultaneously induces different local deformation states on the cell wall and spacers (compression, bending, buckling and shearing). It has been found that the addition of externally induced shear deformation affects the mechanical properties of the foam and the damage mechanism compared to the uniaxial deformation state (compression, bending, and buckling). The mode of failure due to the complexities of loading is the result of two distinct mechanisms of plastic deformation and damage. Based on these mechanisms, it was noted that the higher the complexity of biaxial loading, the higher the shear rate, the higher the yield strength and energy absorption capacity, and the lower the work hardening effect.Under biaxial loading conditions at intermediate strain rate, the property of the foam is affected not only by the parameters given above, but also by the sensitivity of the foam to the strain rate; and the temperature induced at impact.It has been observed that the higher the relative density, the higher the initial fracture and plateau strength, and the higher the energy absorption capacity. Thus, the most available complex loading path (biaxial60) for FP80 foam offered the highest strength in both loading conditions. The work hardening effect decreases with increasing loading complexity due to increased temperature and damage.The inversion of the torsion component during the crushing process leads to a high plating strength, stress hardening effect, and absorption capacity.Higher energy levels. This is due to the prestressed cell walls/spacers (stress hardened when twisting forward) and the higher frictional force induced during the reverse deformation process.For quasi-static loading conditions, as the complexity of the load increases, the percentage of brittle fracture surface increases. However, for dynamic loading conditions, the opposite effect is noted (i.e., the higher the tilt angle or torsion rate, the higher the ductile fracture mode).

The biaxial characterizations of open-cell aluminum foam (AS7G06) having highly uniform architecture of regular shape with uniform distribution under quasi-static and intermediate strain rates were performed. The tested foams were produced by an innovative process known as CastFoam® (i.e., by 3D printing for a sand pre-form and is prepared by the sand-casting replication technique) using a Kelvin cells model to generate the generally spherical shape with a nominal cell diameter of 10.5 mm. The design of these foams (shape, size, and distribution) is always conducted using a numerical simulation to optimize their mechanical behavior. The samples were machined to the required size using water jet machining and their extremities were reinforced by epoxy resin to avoid its deformation inside the holders. The biaxial characterization was performed using a novel patented ACTP (Absorption par Compression-Torsion Plastique) devices incorporating INSTRON-5582 and drop-weight for quasi-static and intermediate strain rate, respectively. The quasi-static tests were carried out on a universal testing machine- the INSTRON 5582, having a maximum load capacity of 100 kN and using a crosshead speed of 5 mm/min was selected. The load-displacement relation was simultaneously recorded during the test using the acquisition chain which forms the link between the machine and the computer. All the intermediate strain rate tests are conducted under an initial impact velocity of about 8.4 m/s with a total drop mass (47.0kg) using a dynamic drop mass bench. In order to ensure the accuracy of experimental results, each test is repeated five times under the same experimental conditions. If the differences between the test responses exceed 5%, then another test was performed.Under quasi-static when ACTP is used, it produced different combinations of biaxial compression-torsion loading complexities. This induces different local strain states simultaneously on the cell wall and struts (compression, bending, buckling, and shear). The addition of externally induced shear strain was found to affect the mechanical properties of the foam and the damage mechanism when compared with the uniaxial (compression, bending, and buckling) strain state. The failure mode due to the loading complexities is the result of two distinct mechanisms of plastic deformation and damage. Based on these mechanisms, it was noted that the higher the biaxial loading complexity, the greater the shear rate, the greater the yield strength and the energy absorption capacity, and the lower the strain hardening effect. In the biaxial intermediate strain rate loading condition, the property of the foam is affected by not only by the above stated parameters but also by the strain rate sensitivity of the foam; and the temperature-induced during impact. It was observed that the relative density, the higher the initial fracture and plateau strength, and the higher the energy absorption capacity. Thus, the most available complex loading path (biaxial60) for the FP80 foam offered the highest strength under both loading conditions. The strain-hardening effect decreases with an increase in the loading complexity due to the increase in temperature, and the damage. Reversing the torsional component during the crushing process leads to a higher plateau strength, strain-hardening effect, and energy absorption capacity. This is due to the pre-strained (strain hardened during the forward torsion) cell walls/struts and the higher frictional force induced during the reverse deformation process. For the quasi-static loading condition as the loading complexity increases, the percentage of brittle fracture surface increases. However, for the dynamic loading condition, the reverse effect is noted (i.e., the higher, the inclination angle or the torsional rate, the higher the ductile mode of fracture).

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