Prediction of ductile fracture in anisotropic steels for pipeline applications

Large diameter steel pipelines for gas transportation may experience extreme overloads due to external actions such as soil sliding, faults movements, third part interactions. In these scenarios the material undergoes severe plastic strains which locally may reach the fracture limits. Due to the manufacturing process, the steels used in such applications have an anisotropic behavior both for plasticity and fracture. In this paper two steel grades have been characterized in view of anisotropic plastic fracture. Fracture tests have been planned to characterize the fracture behavior under different stress states and in different directions to define the anisotropic sensitivity. Finite element modelling, incorporating an anisotropic plasticity formulation, has been used to calculate the local fracture parameters in the specimens and to define the complete ductile fracture locus. An uncoupled damage evolution law has been finally used to evaluate the fracture limits on real pipelines failed in full scale laboratory tests. The strain to fracture prediction has been verified by local strain measurements on the fractured pipes. The model robustness has been also verified on global parameter predictions, such us the burst pressur

Prosthetic abdominal wall hernia repair in emergency surgery: from polypropylene to biological meshes

The use of nonabsorbable prosthetic materials such as polypropylene, polyester, and ePTFE, have expanded and are now widely used in reparative surgery for abdominal wall hernias

Reconstruction of Black Hole Metric Perturbations from Weyl Curvature

Perturbation theory of rotating black holes is usually described in terms of Weyl scalars $\psi_4$ and $\psi_0$, which each satisfy Teukolsky's complex master wave equation and respectively represent outgoing and ingoing radiation. On the other hand metric perturbations of a Kerr hole can be described in terms of (Hertz-like) potentials $\Psi$ in outgoing or ingoing {\it radiation gauges}. In this paper we relate these potentials to what one actually computes in perturbation theory, i.e $\psi_4$ and $\psi_0$. We explicitly construct these relations in the nonrotating limit, preparatory to devising a corresponding approach for building up the perturbed spacetime of a rotating black hole. We discuss the application of our procedure to second order perturbation theory and to the study of radiation reaction effects for a particle orbiting a massive black hole.Comment: 6 Pages, Revtex

Po River Plume Influence on Marine Biochemical Properties along the Western Adriatic Coast

An international research program was devoted to understanding the dynamic properties of the mesoscale circulation in the Adriatic Sea such as fronts, eddies, coastal filaments, river inflow and study the effects of forcing by winds and river run-offs. The present work focuses specifically on the impact of the Po river outflow on the biochemical properties along the western Adriatic coast under different conditions of river discharge and wind stress in winter and spring. In the winter cruise, the satellite images show a strong front in the northern part of the Adriatic extending from the Italian coast to the Istrian Peninsula. In situ measures showed that the northern water mass was characterized by low temperature and salinity, and high nutrient and chlorophyll concentrations due to a strong Bora event which expanded the Po River plume towards the Istrian Peninsula instead of southwards in the West Adriatic Current. During the spring cruise, wind forcing was quite weak and the volume flux from the Po River was about one third of its mean discharge for this period of the year. Off the Po River, the water column was characterized by a surface layer with low salinity and high dissolved inorganic nitrogen and chlorophyll. This water mass did not extend as far eastwards as in winter because the wind forcing was not nearly as important and the alongshore plume extended southward along the Italian Coast

Gravitational-Wave Recoil from the Ringdown Phase of Coalescing Black Hole Binaries

The gravitational recoil or "kick" of a black hole formed from the merger of two orbiting black holes, and caused by the anisotropic emission of gravitational radiation, is an astrophysically important phenomenon. We combine (i) an earlier calculation, using post-Newtonian theory, of the kick velocity accumulated up to the merger of two non-spinning black holes, (ii) a "close-limit approximation" calculation of the radiation emitted during the ringdown phase, and based on a solution of the Regge-Wheeler and Zerilli equations using initial data accurate to second post-Newtonian order. We prove that ringdown radiation produces a significant "anti-kick". Adding the contributions due to inspiral, merger and ringdown phases, our results for the net kick velocity agree with those from numerical relativity to 10-15 percent over a wide range of mass ratios, with a maximum velocity of 180 km/s at a mass ratio of 0.38.Comment: 9 pages, 5 figures; to appear in Class. Quant. Gra

Black hole puncture initial data with realistic gravitational wave content

We present improved post-Newtonian-inspired initial data for non-spinning black-hole binaries, suitable for numerical evolution with punctures. We revisit the work of Tichy et al. [W. Tichy, B. Bruegmann, M. Campanelli, and P. Diener, Phys. Rev. D 67, 064008 (2003)], explicitly calculating the remaining integral terms. These terms improve accuracy in the far zone and, for the first time, include realistic gravitational waves in the initial data. We investigate the behavior of these data both at the center of mass and in the far zone, demonstrating agreement of the transverse-traceless parts of the new metric with quadrupole-approximation waveforms. These data can be used for numerical evolutions, enabling a direct connection between the merger waveforms and the post-Newtonian inspiral waveforms.Comment: 13 pages, 7 figures; replaced with published versio

The Yamabe invariant for axially symmetric two Kerr black holes initial data

An explicit 3-dimensional Riemannian metric is constructed which can be interpreted as the (conformal) sum of two Kerr black holes with aligned angular momentum. When the separation distance between them is large we prove that this metric has positive Ricci scalar and hence positive Yamabe invariant. This metric can be used to construct axially symmetric initial data for two Kerr black holes with large angular momentum.Comment: 14 pages, 2 figure

Comparisons of binary black hole merger waveforms

This a particularly exciting time for gravitational wave physics. Ground-based gravitational wave detectors are now operating at a sensitivity such that gravitational radiation may soon be directly detected, and recently several groups have independently made significant breakthroughs that have finally enabled numerical relativists to solve the Einstein field equations for coalescing black-hole binaries, a key source of gravitational radiation. The numerical relativity community is now in the position to begin providing simulated merger waveforms for use by the data analysis community, and it is therefore very important that we provide ways to validate the results produced by various numerical approaches. Here, we present a simple comparison of the waveforms produced by two very different, but equally successful approaches--the generalized harmonic gauge and the moving puncture methods. We compare waveforms of equal-mass black hole mergers with minimal or vanishing spins. The results show exceptional agreement for the final burst of radiation, with some differences attributable to small spins on the black holes in one case.Comment: Revtex 4, 5 pages. Published versio

Tracce archeologiche di un terremoto tardo-antico nella Piana del Fucino (Italia centrale)

Il tempo di ricorrenza definito dalle indagini paleosismologiche sulle faglie dell’Appennino abruzzese è nell’ordine dei 1500-2500 anni. Pertanto, in caso di terremoto storico, di elevata magnitudo, relativamente recente (es. il terremoto del 1703 nell’Aquilano o quello del 1915 nella Marsica), l’evento sismico precedente potrebbe essere stato causato dalla stessa sorgente sismogenetica in un’epoca per cui si ha carenza di informazione storica ma abbondanza di fonti archeologiche. Per questo motivo, accanto alle ricerche paleosismologiche, tradizionalmente indirizzate alla definizione del comportamento sismogenetico di una faglia, fin dalla metà degli anni 90 furono avviate ricerche archeosismologiche, mirate all’identificazione di tracce di terremoti distruttivi su emergenze archeologiche, prevalentemente di età classica (Galadini e Galli, 1996). Gli studi archeosismologici nella regione abruzzese hanno consentito di acquisire finora informazioni sugli effetti di tre terremoti distruttivi, noti ai cataloghi sismici (es. Boschi et al., 1995), di cui due (II sec. d.C. e 484-508 d.C.) con epicentro nella regione e un altro (346 d.C.) originato in area limitrofa (Galadini e Galli, 2001; 2004). Nel 2004, l’Istituto Nazionale di Geofisica e Vulcanologia ha avviato una collaborazione con la Soprintendenza per i Beni Archeologici dell’Abruzzo su tematiche geoarcheologiche, sia in prospettiva paleoambientale che per una migliore comprensione degli effetti delle catastrofi naturali del passato su siti archeologici dell’area appenninica. In questo ambito, è stato possibile effettuare indagini in prospettiva archeosismologica durante le fasi di scavo in alcuni siti archeologici della Marsica e della Valle Subequana, come l’anfiteatro di San Benedetto dei Marsi, la villa produttiva di Avezzano-Macerine, il tempio di Castel di Ieri, il piazzale antistante il santuario di Ercole, gli edifici prospicienti la via del Miliario e l’area del Foro ad Alba Fucens. Nel caso dell’anfiteatro di San Benedetto dei Marsi, le evidenze della distruzione sismica vengono dal crollo sincrono delle grandi lastre di pietra che delimitavano il balteo, dalla rotazione di blocchi attorno all’asse verticale, dall’espulsione di angolata in uno degli ambienti prossimi all’ingresso nord della struttura, oltre che dai crolli di ampie parti dell’edificio. Nella villa produttiva di Avezzano, ai crolli di muri di costruzione tarda si accompagnano vistose tracce di combustione, su resti pressoché integri delle travature. Le unità di crollo furono rinvenute al di sopra del piano di calpestio che era ancora in uso al momento della distruzione. La subitaneità dell’evento è testimoniata dal reperimento di una notevole quantità di materiali nelle unità di crollo stesse, a testimonianza di un abbandono improvviso, senza asportazione degli oggetti di uso comune. Ad Alba Fucens, le evidenze della distruzione cosismica erano già note grazie alle pubblicazioni relative alle campagne di scavo soprattutto degli anni 50 e 60. Le fotografie di archivio mostrano i pilastri della cosiddetta Via dei Pilastri in posizione di crollo attraverso la strada, la statua dell’Ercole Epitrapezio in giacitura sul piano di calpestio del sacello, colonne in posizione di crollo con capitello ancora giustapposto