Node-to-segment and node-to-surface interface finite elements for fracture mechanics

The topologies of existing interface elements used to discretize cohesive cracks are such that they can be used to compute the relative displacements (displacement discontinuities) of two opposing segments (in 2D) or of two opposing facets (in 3D) belonging to the opposite crack faces and enforce the cohesive traction-separation relation. In the present work we propose a novel type of interface element for fracture mechanics sharing some analogies with the node-to-segment (in 2D) and with the node-to-surface (in 3D) contact elements. The displacement gap of a node belonging to the finite element discretization of one crack face with respect to its projected point on the opposite face is used to determine the cohesive tractions, the residual vector and its consistent linearization for an implicit solution scheme. The following advantages with respect to classical interface finite elements are demonstrated: (i) non-matching finite element discretizations of the opposite crack faces is possible; (ii) easy modelling of cohesive cracks with non-propagating crack tips; (iii) the internal rotational equilibrium of the interface element is assured. Detailed examples are provided to show the usefulness of the proposed approach in nonlinear fracture mechanics problems.Comment: 37 pages, 17 figure

Regional Trade Agreements and Implications for US Agriculture: The Case of CAFTA-DR

International Relations/Trade,

Identification of roughness with optimal contact response with respect to real contact area and normal stiffness

Additive manufacturing technologies are a key point of the current era of Industry 4.0, promoting the production of mechanical components via the addition of subsequent layers of material. Then, they may be also used to produce surfaces tailored to achieve a desired mechanical contact response. In this work, we develop a method to prototype profiles optimizing a suitable trade-off between two different target mechanical responses. The mechanical design problem is solved relying on both physical assumptions and optimization methods. An algorithm is proposed, exploiting an analogy between genetics and the multiscale characterization of roughness, where various length-scales are described in terms of rough profiles, named chromosomes. Finally, the proposed algorithm is tested on a representative example, and the topological and spectral features of roughness of the optimized profiles are discussed

UHECR bending, clustering and decaying feeding gamma anisotropy

Ultra High Energy Cosmic Rays (UHECR), made mostly by Helike lightest nuclei might fit the observed spread clustering along Cen-A; He like UHECR nuclei explain also Virgo absence because these light nuclei fragility and opacity above a few Mpc. UHECR He from Cen-A AGN being fragile should partially fragment into secondaries at tens EeV multiplet (D, 3He, p) as it appears in a twin multiplet discovered (AUGER-ICRC-2011), at 20 EeV along the same Cen-A UHECR clustering. We suggest that UHECR are also (possibly mostly) heavy radioactive galactic nuclei as 56Ni, 57Ni and 57Co, 60Co widely bent (tens degree up to ≥ 100◦) by galactic fields. UHECR radioactivity (in β and γ channels) and decay in flight at hundreds keV is boosted (by huge Lorentz factor ΓNi 109–108) leading to PeVs electrons and consequent synchrotron TeVs gamma offering UHECR-TeV correlated wide area sky anisotropy. Additional electron and tau neutrinos secondaries at PeVs might be the first signature of such expected radioactive secondary tail. Being smeared such decayed neutrinos will be hardly clustered in small scale