354 research outputs found
Efficient equilibrium-based stress recovery for isogeometric laminated curved structures
No full textThis work extends the stress recovery for laminated composite solid plates, proposed in [1,2], to curved structures. Based on 3D Isogeometric Analysis (IGA) computations and equilibrium, this procedure uses a single element through the thickness in combination with a calibrated layer-by-layer integration rule or a homogenized approach, allowing for an inexpensive and accurate approximation in terms of in-plane stresses (and their derivatives), while through-the-thickness stress components are poorly approximated. Relying on the highorder continuity properties of IGA shape functions, an accurate out-of-plane stress state can also be recovered by means of direct integration of the equilibrium equations in strong form. The a posteriori step application, which is straightforward in the context of solid plates, is not trivial in the case of curved geometries. In fact, the notion of in-plane and out-of-plane directions is not clear when modeling this kind of structures in the global reference system, while adopting curvilinear coordinates to express the equilibrium gives rise to additional coupled terms that require an iterative process to resolve the balance of momentum equation. Therefore, we propose to apply the recovery locally, which, despite leading to more elaborated stress derivative terms because of the increasing geometry complexity, still allows for a direct reconstruction as the resolvent system is uncoupled. Several numerical results show the good performance of this approach particularly for composite stacks with significant radius-to-thickness ratio and number of plies.MN
A rigorous and efficient explicit algorithm for irreversibility enforcement in phase-field finite element and isogeometric modeling of brittle crack propagation
No full textIn the present work, a computationally efficient and explicit algorithm for the rigorous enforcement of the irreversibility
constraint in the phase-field modeling of brittle fracture is presented. The proposed approach is staggered and relies on the
alternate minimization of the total energy functional. The phase-field evolution turns out to be governed by a complementarity
boundary-value problem, where the complementarity stems from the irreversibility, while the boundary-value problem is
originated by the presence of the gradient term in the phase-field functional. Several different techniques have been proposed in
the literature to account for damage irreversibility in a computationally effective way. Following a similar approach proposed
in the past for a gradient-plasticity problem, a particularly simple and effective solution strategy based on the Projected
Successive Over-Relaxation (PSOR) method for constrained optimization, where an iterative explicit scheme is used for the
solution of symmetric linear complementarity problems, is presented. Even though the proposed method is restricted to linear
complementarity problems, it can be applied to the numerical simulation of a wide range of problems discussed in the literature.
The performance of the suggested solution algorithm on a number of test cases is compared with that of a recently proposed
penalty approach for the approximated enforcement of irreversibility
LA NUOVA TRANSLATIO DINANZI AGLI ARBITRI TRA DEGIURISDIZIONALIZZAZIONE E DEFINIZIONE DELL’ARRETRATO CIVILE
No full textThe author analyzes the institute of the transfer in arbitration of the pending proceedings, introduced by art. 1 of d.l. 132/2014 and converted by L.162/2014, analyzing the main issues of interpretation and application raised by the new rulesL'autrice analizza l'istituto della devoluzione in arbitrato delle cause pendenti, introdotto dall'art . 1 dl di 132/2014 e convertito dalla L.162 / 2014, analizzando le principali questioni interpretative e applicative sollevate dalle nuove disposizioni
L'ACOLTO DEL MINORE NEI PROCEDIMENTI DI SEPARAZIONE E DI DIVORZIO
No full textL’autrice esamina il tema dell’ascolto dei figli minori nei processi di separazione
e divorzio. L’istituto è disciplinato dall’art. 155-sexies, 1° comma, c.p.c.
ed è oggetto di un vivace dibattito dottrinale, alimentato anche di recente dall’introduzione
del nuovo art. 315-bis, 3° comma, c.c., che ha espressamente riconosciuto
il diritto sostanziale del fanciullo a essere ascoltato in tutti i procedimenti
che lo riguardano. La disciplina dell’audizione viene valutata positivamente
per quanto riguarda l’introduzione del dovere del giudice di sentire il
bambino, viceversa è fortemente criticata per gli altri aspetti. In particolare, la
genericità del dettato normativo è fonte di notevoli incertezze che investono
primariamente la natura giuridica dell’istituto, costituendo uno dei profili più
delicati e discussi dell’ascolto. L’autrice critica anche l’assenza di regole sulle
modalità dell’audizione, con conseguenze negative sul piano delle garanzie e
della tutela dei fondamentali diritti dei minori e dei coniugi.
The author examines the theme of hearing of minor children in the legal
process of separation and divorce. The institute is provided by art. 155-sexies,
paragraph 1, of the code of civil procedure and is the subject of a lively doctrinal
debate, also for the recent introduction of the new article 315-bis, paragraph
3, of the civil code, which has recognized the right of the child to be
heard in all procedures involving him. The discipline is positively assessed regarding
the introduction of the duty of the judge to hear the child, while it is
strongly criticized to the other aspects. In particular, the vagueness of the law
creates a lot of uncertainty regarding the juridical nature of institute, which is
one of the most delicate and discussed profiles. The author also criticizes the
absence of specific rules on how to conduct the hearing with negative consequences
for the fundamental rights of the child and spouses
Higher order phase-field modeling of brittle fracture via isogeometric analysis
No full textThe evolution of brittle fracture in a material can be conveniently investigated by means of the phase-field technique introducing a smooth crack density functional. Following Borden et al. (2014), two distinct types of phase-field functional are considered: (i) a second-order model and (ii) a fourth-order one. The latter approach involves the bi-Laplacian of the phase field and therefore the resulting Galerkin form requires continuously differentiable basis functions: a condition we easily fulfill via Isogeometric Analysis. In this work, we provide an extensive comparison of the considered formulations performing several tests that progressively increase the complexity of the crack patterns. To measure the fracture length necessary in our accuracy evaluations, we propose an image-based algorithm that features an automatic skeletonization technique able to track complex fracture patterns. In all numerical results, damage irreversibility is handled in a straightforward and rigorous manner using the Projected Successive Over-Relaxation algorithm that is suitable to be adopted for both phase-field formulations since it can be used in combination with higher continuity isogeometric discretizations. Based on our results, the fourth-order approach provides higher rates of convergence and a greater accuracy. Moreover, we observe that fourth- and second-order models exhibit a comparable accuracy when the former methods employ a mesh-size approximately two times larger, entailing a substantial reduction of the computational effort
Investigation of microscale brittle fracture opening in diamond with olivine inclusion using XFEM and cohesive zone modeling
No full textInclusions trapped in diamonds are a fundamental source of information to probe the Earth's interior, provided that the pressure conditions at which the diamond grew are correctly determined. This study explores the traditional assumptions in geothermobarometry for olivine-in-diamond host-inclusion systems by employing extended finite element methods (XFEM) and cohesive zone models (CZM) to quantify the contributions of brittle fractures to the relaxation of the residual stress of inclusions. Our analysis was performed assuming that the host-inclusion system does not contain fluids and that the unfractured minerals are elastically isotropic. Our models show that the damage initiation is solely dependent on the shape of the inclusion and on the fracture strength of the diamond host, while the fracture nucleation is influenced by both the size of the inclusion and the toughness of the diamond. Our findings indicate that, in dry systems, the amount of relaxation of residual stress of the inclusion due to the opening of brittle fractures is much lower than that due to the elastic interaction between the host and the inclusion. Moreover, the pressure release due to fractures is not substantially affected by the shape of the inclusion. We also show that the total relaxation of the residual pressure due to the combined effect of the elastic interaction and the brittle deformation is lower than what is observed in natural samples, even when assuming fracture strength and toughness lower than those reported from experiments on single crystals of diamond. Such discrepancies suggest that in natural olivine-diamond systems additional mechanisms such as viscous or plastic deformation and/or the presence of preexisting defects and fluids in the host might play a relevant role in the relaxation of the residual stress. These findings underscore the need for advanced numerical tools that consider the complex interplay of the geometry of the host-inclusion system, the fracture properties, and the presence of fluids and defects in order to build more accurate models to constrain the geological history of diamonds
Questioni di esistenza, unicità, regolarità della soluzione per equazioni alle derivate parziali di evoluzione con caratteristiche reali
No full textStudio di equazioni deterministiche lineari di tipo Schrödinger con coefficienti in (t,x) nelle classi di Gelafand-Shilov e studio di equazioni stocastiche iperboliche con coefficienti in (t,x), sia lineari che semilineari,con caratteristiche che possano intersecars
Biostratigraphical characteristics of the Turonian-?Maastrichtian p.p. (Upper Cretaceous) deposits in the Simbruini-Ernici Mts. (central Apennines, Italy)
No full textThe biostratigraphical characteristics of three sequences outcropping in the Simbruini-Ernici Mts. are discussed in order to reconstruct the lithobiofacies evolution of the Central-Western Latium-Abruzzi carbonate platform during the Turonian-? Maastrichtian p.p.. For each section the macro- and microbiofacies are discussed, with the former characterized by the presence of rudists (Hippuritoida). The occurrence in the neighborhood of some fossiliferous beds of particular biostratigraphical value, us to make correlations with other areas. -Author
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