Publication: Elastoplastic solids subjected to dynamic tension: new experimental and computational insights
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2015-09
Defense date
2015-10-05
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Abstract
This Doctoral Thesis provides new insights into the mechanisms which control flow localization in elastoplastic solids subjected to dynamic tension. For that task, we have a developed a methodology which combines experiments and numerical calculations. Dynamic tension tests have been performed in a high-speed testing machine using specimens with six different gauge lengths, ranging from 20 𝑚�𝑚� to 140 𝑚�𝑚�, that have been tested within a wide spectrum of loading velocities from 1 𝑚�/𝑠� to 7.5 𝑚�/𝑠�. The experiments show that variations in the applied velocity and the gauge length of the samples lead to the systematic motion of the fracture location along the specimen. A key outcome is that we have provided experimental evidences of the deterministic nature of the flow localization in dynamic tensile specimens. Finite element calculations have been conducted in ABAQUS/Explicit in order to complement our experimental findings. The finite elements predict, in agreement with the experiments, the interplay between fracture location, impact velocity and gauge length. Moreover, we have explored the role played by initial and boundary conditions in plastic flow localization. A salient feature is that we have demonstrated that the intervention of stress waves within the specimen is a limiting factor for the sample ductility. On the one hand we have observed that the strain to failure, instead of being a material property, is strongly dependent on the specimen size. On the other hand, we have shown that the topology of the localization pattern is closely connected to the post-uniform elongation of the specimen. Finite difference calculations have been conducted in MATLAB in order to rationalize the experimental and finite element outcomes. For that task, we have developed a simple one-dimensional model within a finite deformation framework. The key point of our finite difference computations is that, unlike the finite element calculations, we solved the kinematics, and thus obtained a complete control of the problem. We show that the intervention of wave propagation phenomena within the specimen is responsible for the interplay between flow localization, impact velocity and gauge length. Moreover, we have explored the role of selected material properties in the kinetics of flow localization. A key outcome is that we have shown that material flaws (may) play a secondary role within the mechanisms which govern plastic localization in dynamic tensile specimens. All in all, we have developed a comprehensive and innovative research to establish: (1) the deterministic nature of flow localization and (2) the material properties and the initial and boundary conditions which control the process at hand
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Elastoplastic solids, Dynamic tension, Finite element method