Application of the continuum damage mechanics model in the three point bending test of Ti-6Al-4V titanium alloy specimens

One of the most important and challenging activities in the simulation of the mechanical behaviour of materials is the prediction of the failure phenomena. If well calibrated, damage models can simulate and predict the failure of materials in a generalized way allowing the replication of not only the calibration tests themselves but also of different loading cases. Generally damage models can be categorized into three different groups including phenomenological models, porosity models and continuum damage mechanics (CDM) models. Different CDM models have been proposed by researchers and these models have been applied in diverse loading conditions, geometries and materials. However the limitations and advantages of the CDM models are still not completely explored in the application areas. In this paper, a CDM model, (previously calibrated with round smooth specimen) has been applied in a three-point bending test model in order to simulate the correlated experiment. Specifically, the CDM framework has been applied in a finite element model and the obtained results have been compared with the experimental data. The tested material is Ti-6Al-4V titanium alloy, which is a widely used material in the aerospace industry because of its high strength and low density. Load-displacement data in the experiments and numerical simulations are the main results, which have been compared. Therefore, the ability of the CDM model to simulate the three point bending test has been investigated and the results are discussed

Superloop Equations and Two Dimensional Supergravity

We propose a discrete model whose continuum limit reproduces the string susceptibility and the scaling dimensions of $(2,4m)$-minimal superconformal models coupled to $2D$-supergravity. The basic assumption in our presentation is a set of super-Virasoro constraints imposed on the partition function. We recover the Neveu-Schwarz and Ramond sectors of the theory, and we are also able to evaluate all planar loop correlation functions in the continuum limit. We find evidence to identify the integrable hierarchy of non-linear equations describing the double scaling limit as a supersymmetric generalization of KP studied by Rabin.Comment: 34 page

Massless radiation from Strings: quantum spectrum average statistics and cusp-kink configurations

We derive general formulae for computing the average spectrum for Bosonic or Fermionic massless emission from generic or particular sets of closed superstring quantum states, among the many occurring at a given large value of the number operator. In particular we look for states that can produce a Bosonic spectrum resembling the classical spectrum expected for peculiar cusp-like or kink-like classical configurations, and we perform a statistical counting of their average number. The results can be relevant in the framework of possible observations of the radiation emitted by cosmic strings.Comment: 13 pages, 4 figures, improved explanations, an appendix added on rotating folded strin

Valutazione della capacità di rientro alla base di un elicottero in presenza di danno balistico ad un albero di trasmissione della linea rotore di coda

Nella progettazione di un elicottero militare, destinato ad operare a bassa quota e in ambiente ostile, il danneggiamento di componenti critici, conseguente ad impatto balistico, riveste un ruolo primario nella valutazione delle possibilità di sopravvivenza dell’intera macchina. In questo articolo è quindi proposto uno studio sperimentale, suddiviso in diverse fasi, riguardante la verifica della capacità di un elicottero di portare a termine una missione di rientro alla base a potenza ridotta e in presenza di danneggiamento balistico ad un albero di trasmissione della linea rotore di coda. Il lavoro ha richiesto dapprima l’esecuzione, su esemplari del componente in esame, di prove sperimentali di impatto balistico, condotte utilizzando un proiettile calibro 7.62 NATO. Successivamente su ciascun albero danneggiato sono state eseguite prove torsionali statiche ed a fatica, il cui scopo è stato verificare la resistenza residua del componente all’applicazione di opportuni carichi rappresentativi delle sollecitazioni riscontrate durante la missione di rientro

RF and IF mixer optimum matching impedances extracted by large-signal vectorial measurements

This paper introduces a new technique that allows us to measure the admittance conversion matrix of a two-port device,using a Nonlinear Vector Network Analyzer.This method is applied to extract the conversion matrix of a 0.2 µµµµm pHEMT,driven by a 4.8 GHz pump signal,at different power levels,using an intermediate frequency of 600 MHz.The issue on data inconsistency due to phase randomization among different measurements is discussed and a proper pre- processing algorithm is proposed to fix the problem. The output of this work consists of a comprehensive experimental evaluation of up-and down-conversion maximum gain,stability,and optimal RF and IF impedances

Valutazione della capacità di rientro alla base di un elicottero in presenza di danno balistico ad un albero di trasmissione della linea rotore di coda

Nella progettazione di un elicottero militare, destinato ad operare a bassa quota e in ambienteostile, il danneggiamento di componenti critici, conseguente ad impatto balistico, riveste un ruolo primario nellavalutazione delle possibilità di sopravvivenza dell’intera macchina. In questo articolo è quindi proposto unostudio sperimentale, suddiviso in diverse fasi, riguardante la verifica della capacità di un elicottero di portare atermine una missione di rientro alla base a potenza ridotta e in presenza di danneggiamento balistico ad unalbero di trasmissione della linea rotore di coda.Il lavoro ha richiesto dapprima l’esecuzione, su esemplari del componente in esame, di prove sperimentali diimpatto balistico, condotte utilizzando un proiettile calibro 7.62 NATO. Successivamente su ciascun alberodanneggiato sono state eseguite prove torsionali statiche ed a fatica, il cui scopo è stato verificare la resistenzaresidua del componente all’applicazione di opportuni carichi rappresentativi delle sollecitazioni riscontratedurante la missione di rientro

Handbook on string decay

We explain simple semi-classical rules to estimate the lifetime of any given highly-excited quantum state of the string spectrum in flat spacetime. We discuss both the decays by splitting into two massive states and by massless emission. As an application, we study a solution describing a rotating and pulsating ellipse which becomes folded at an instant of time -- the ``squashing ellipse''. This string interpolates between the folded string with maximum angular momentum and the pulsating circular string. We explicitly compute the quantum decay rate for the corresponding quantum state, and verify the basic rules that we propose. Finally, we give a more general (4-parameter) family of closed string solutions representing rotating and pulsating elliptical strings.Comment: 18 pages, 9 figures. Final version appeared in JHE

On coalgebras with internal moves

In the first part of the paper we recall the coalgebraic approach to handling the so-called invisible transitions that appear in different state-based systems semantics. We claim that these transitions are always part of the unit of a certain monad. Hence, coalgebras with internal moves are exactly coalgebras over a monadic type. The rest of the paper is devoted to supporting our claim by studying two important behavioural equivalences for state-based systems with internal moves, namely: weak bisimulation and trace semantics. We continue our research on weak bisimulations for coalgebras over order enriched monads. The key notions used in this paper and proposed by us in our previous work are the notions of an order saturation monad and a saturator. A saturator operator can be intuitively understood as a reflexive, transitive closure operator. There are two approaches towards defining saturators for coalgebras with internal moves. Here, we give necessary conditions for them to yield the same notion of weak bisimulation. Finally, we propose a definition of trace semantics for coalgebras with silent moves via a uniform fixed point operator. We compare strong and weak bisimilation together with trace semantics for coalgebras with internal steps.Comment: Article: 23 pages, Appendix: 3 page

Half-String Approach to Closed String Field Theory

In this letter we present an operator formalism for Closed String Field Theory based on closed half-strings. Our results indicate that the restricted polyhedra of the classical non-polynomial string field theory, can be represented as traces of infinite matrices, with operator insertions that reparametrise the half-strings.Comment: 13 pages, Latex, OUTP 93-10-

Turbulence structure of open channel flows over permeable and impermeable beds : A comparative study

Peer reviewedPublisher PD