Calibration of a gradient-enhanced damage model for viscoplastic shell structures
Final Report Abstract
The overall interest that we have pursued with this project is a finite element dynamics for thin-walled structures subjected to impulse loading. Besides several phenomena which can happen during the disturbance nonlocal damage leads the structures to rupture. We have established both numerical and experimental methodology to simulate the localization of defects. Starting from recent results obtained from the nonlocal damage approach we have been presented a complete model including the softening behaviour of the copper during the shock waved loading. An approach to identify the gradient or nonlocal parameters was also introduced. Our study has three methodological features that make it distinct from most other research in this area. First, for numerical simulation an anisotropic gradient-damage model for dynamic finite element computation is established and validated by using the global displacement-force curves obtained from shock-tube tests on copper plate specimens. The model is formulated by introducing a gradient-enhanced free energy, which is enhanced phenomenologically in terms of an equivalent non-local damage variable and its gradient on the mid-surface of shell structures. This enhancement gives rise to an introduction of gradient parameters in terms of a substructure-related intrinsic length-scale and a relationship between non-local and local damage variable. Second, we have conducted micro-tensile and -bending tests to identify all of the gradient parameters via the bending curvatures measured by using the image processing. Third, the anisotropic damage now can be included together with isotropic and kinematic hardening. This allows to predict the change of the principal damage parameters as well as the back stresses. Our approach gives a possibility to remove pathological mesh dependence and with numerical difficulties that appeared in existing simulations of softening and damage phenomena. The numerical results show that the proposed approach can be used to analyse anisotropic damage for plates and shells subjected to shock wave loadings. However, it should be noted that the presented experimental methodology requires exact measurements of the bending curvatures and a large amount of specimens to get reliable statistical values and therefore needs future systematical studies. For future development disspative rheological models including crystallographic information in dynamical simulations should be considered.
Publications
- A gradient-damage model for viscoplastic plates under impulsive loadings: experimental and computational aspects, Proceedings of “Advances in computational mechanics”, ISBN: 978-604-908-577-2, Editors: Tong T. Nguyen, Hung X. Nguyen, Trung T. Nguyen, Thanh D. Chau, p. 279-287, 2012
A.D. Nguyen, M. Stoffel and D. Weichert
- A gradient-enhanced damage approach for viscoplastic thin-shell structures subjected to shock waves, Computer Methods in Applied Mechanics and Engineering, Vol. 217–220, p. 236–246, 2012
A.D. Nguyen, M. Stoffel and D. Weichert
(See online at https://doi.org/10.1016/j.cma.2012.01.017) - On dynamic FE analysis of viscoplastic thinwalled structures with anisotropic gradient damage, Proceedings of “Shell Structures – Theory and Application”, Gdanks, Poland, p. 425-428, 2013. ISBN: 978-1-4822-2908-0
A.D. Nguyen, M. Stoffel, and D. Weichert
