673 research outputs found
A consistent interface element formulation for geometrical and material nonlinearities
Decohesion undergoing large displacements takes place in a wide range of
applications. In these problems, interface element formulations for large
displacements should be used to accurately deal with coupled material and
geometrical nonlinearities. The present work proposes a consistent derivation
of a new interface element for large deformation analyses. The resulting
compact derivation leads to a operational formulation that enables the
accommodation of any order of kinematic interpolation and constitutive behavior
of the interface. The derived interface element has been implemented into the
finite element codes FEAP and ABAQUS by means of user-defined routines. The
interplay between geometrical and material nonlinearities is investigated by
considering two different constitutive models for the interface (tension
cut-off and polynomial cohesive zone models) and small or finite deformation
for the continuum. Numerical examples are proposed to assess the mesh
independency of the new interface element and to demonstrate the robustness of
the formulation. A comparison with experimental results for peeling confirms
the predictive capabilities of the formulation.Comment: 14 pages, 11 figure
Modeling complex crack paths in ceramic laminates: A novel variational framework combining the phase field method of fracture and the cohesive zone model
The steady-state Archard adhesive wear problem revisited based on the phase field approach to fracture
Fracture of solar-grade anisotropic polycrystalline Silicon: A combined phase field–cohesive zone model approach
ArtĂculo Open Access en el sitio web del editor. Pago por publicar en abierto. This work presents a novel computational framework to simulate fracture events in brittle anisotropic polycrystalline materials at the microscopical level, with application to solar-grade polycrystalline Silicon. Quasi-static failure is modeled by combining the phase field approach of brittle fracture (for transgranular fracture) with the cohesive zone model for the grain boundaries (for intergranular fracture) through the generalization of the recent FE-based technique published in [M. Paggi, J. Reinoso, Comput. Methods Appl. Mech. Engrg., 31 (2017) 145–172] to deal with anisotropic polycrystalline microstructures. The proposed model, which accounts for any anisotropic constitutive tensor for the grains depending on their preferential orientation, as well as an orientation-dependent fracture toughness, allows to simulate intergranular and transgranular crack growths in an efficient manner, with or without initial defects. One of the advantages of the current variational method is the fact that complex crack patterns in such materials are triggered without any user-intervention, being possible to account for the competition between both dissipative phenomena. In addition, further aspects with regard to the model parameters identification are discussed in reference to solar cells images obtained from transmitted light source. A series of representative numerical simulations is carried out to highlight the interplay between the different types of fracture occurring in solar-grade polycrystalline Silicon, and to assess the role of anisotropy on the crack path and on the apparent tensile strength of the material. UniĂłn Europea FP/2007–2013/ERC 306622 Ministerio de EconomĂa y Competitividad MAT2015–71036-P y MAT2015–71309-P Junta de AndalucĂa P11-TEP-7093 y P12-TEP- 105
Phase field modeling of brittle fracture in large-deformation solid shells with the efficient quasi-Newton solution and global–local approach
National and Regional Impacts of U.S. Agricultural Exports
International Trade, Output, Employment, Exports, International Relations/Trade, Q10, Q11, Q13, Q17,
A phase field approach for damage propagation in periodic microstructured materials
In the present work, the evolution of damage in periodic composite materials is investigated through a novel finite element-based multiscale computational approach. The proposed methodology is developed by means of the original combination of asymptotic homogenization with the phase field approach to nonlocal damage. This last is applied at the macroscale level on the equivalent homogeneous continuum, whose constitutive properties are obtained in closed form via a two-scale asymptotic homogenization scheme. The formulation considers different assumptions on the evolution of damage at the microscale (e.g., damage in the matrix and not in the inclusion/fiber), as well as the role played by the microstructural reinforcement, i.e. its volumetric content and shape. Numerical results show that the proposed formulation leads to an apparent tensile strength and a post-peak branch of unnotched and notched specimens dependent not only on the internal length scale of the phase field approach, as for homogeneous materials, but also on microstructural features. Down-scaling relations provide the full reconstruction of the microscopic fields at any point of the macroscopic model, as a simple post-processing operation
LOFAR observations of 4C+19.44. On the discovery of low frequency spectral curvature in relativistic jet knots
We present the first LOFAR observations of the radio jet in the quasar
4C+19.44 (a.k.a. PKS 1354+19) obtained with the long baselines. The achieved
resolution is very well matched to that of archival Jansky Very Large Array
(JVLA) observations at higher radio frequencies as well as the archival X-ray
images obtained with {\it Chandra}. We found that, for several knots along the
jet, the radio flux densities measured at hundreds of MHz lie well below the
values estimated by extrapolating the GHz spectra. This clearly indicates the
presence of spectral curvature. Radio spectral curvature has been already
observed in different source classes and/or extended radio structures and it
has been often interpreted as due to intrinsic processes, as a curved particle
energy distribution, rather than absorption mechanisms ({ Razin-Tsytovich}
effect, free-free or synchrotron self absorption to name a few). Here we
discuss our results according to the scenario where particles undergo
stochastic acceleration mechanisms also in quasar jet knots.Comment: 13 pages, 4 tables, 4 figures, pre-proof version, published on the
Astrophysical Journal (Harris, et al. 2019 ApJ, 873, 21
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