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

Functional Imaging Reveals Movement Preparatory Activity in the Vegetative State

The vegetative state (VS) is characterized by the absence of awareness of self or the environment and preserved autonomic functions. The diagnosis relies critically on the lack of consistent signs of purposeful behavior in response to external stimulation. Yet, given that patients with disorders of consciousness often exhibit fragmented movement patterns, voluntary actions may go unnoticed. Here we designed a simple motor paradigm that could potentially detect signs of purposeful behavior in VS patients with mild to severe brain damage by examining the neural correlates of motor preparation in response to verbal commands. Twenty-four patients who met the diagnostic criteria for VS were recruited for this study. Eleven of these patients showing preserved auditory evoked potentials underwent functional magnetic resonance imaging (fMRI) to test for basic speech processing. Five of these patients, who showed word related activity, were included in a second fMRI study aimed at detecting functional changes in premotor cortex elicited by specific verbal instructions to move either their left or their right hand. Despite the lack of overt muscle activity, two patients out of five activated the dorsal premotor cortex contralateral to the instructed hand, consistent with movement preparation. Our results may reflect residual voluntary processing in these two patients. We believe that the identification of positive results with fMRI using this simple task, may complement the clinical assessment by helping attain a more precise diagnosis in patients with disorders of consciousness

the numerical modelling of a middle strength rock material under flexural test by finite element method coupled to sph

Abstract: Proper fracture assessment of the geological materials, which are highly exposed to hydrostatic loading, is a persistent challenge, in particular when aiming to develop an adequate numerical modelling technique. The mechanical response of a middle strength rock, namely Pietra Serena sandstone, under a Flexural (Four-Point Bending) test is investigated numerically in this study. The FEM-coupled to-SPH numerical technique has been approached in conjunction with an advanced material model implemented in LS-DYNA, namely the Karagozian and Case Concrete (KCC) model. The state of stress is investigated in different parts of the specimen in order to determine the strength of the material and the crack initiation area. The numerical results are finally validated by experimental data to show the reliability of the model

A numerical investigation on significant parameters influencing the flatwise compressive behaviour of a NomexTM Honeycomb

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evaluation of the effects of the numerical modelling choices on the simulation of a tensile test on cfrp composite

Abstract The goal of the present work is to define a method to build a FE model which is able to reproduce an experimental tensile test on CFRP specimen with different stacking sequences (UD and balanced). The defined method assesses the material numerical parameters by means of a simulation that replicates, as a virtual test, the experimental tensile one, and in the future, it will be possible to exploit the data obtained to create a reliable model for the simulation of low velocity impacts. Analyses have been performed using the non-linear solver ABAQUS Explicit. The current work further studies how to model damage and the effect of modifications of the numerical parameters on the results. Indeed, the numerical simulation of composite materials is very sensitive to the numerical choices made. Moreover, from the literature and experiments, the mechanical properties of composites are very variable and hence the evaluation of the model response to such modifications is of particular interest

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

Sensor network optimization for damage detection on aluminium stiffened helicopter panels

Health and Usage Monitoring Systems (HUMS) has received considerable attention from the helicopter community in recent years with the declared aim to increase flight safety, increase mission reliability, extend duration of life limited components and of course reduce the maintenance costs. The latter is about 25 per cent of the direct operating cost of the helicopter, thus playing an important role especially in the case of the ageing aircrafts. In particular, with respect to helicopter fuselages, only some attempts were carried out to monitor directly on-line the damage accumulation and propagation during life. In this field, and in particular in the military applications, an integrated and reliable system for monitoring the damage in the fuselage and for evaluating the time inspections and remaining life (prognosis) is missing. However, because of the presence of many vibratory loads, the diagnosis of helicopter structures is very critical. From one hand, a very large number of sensors would be needed for a robust appreciation of the structural health, from the other hand the industrialization of the product brings the need for a low impact over the existing structures, or toward a reduction in the allowed amount of sensors. As a result, comes the importance for an optimization of the sensor network, with the aim to find out the regions inside the structure which are the most sensible to a damage and at the same time robust to noise. The aim of the present work is to define a methodology for optimising the sensors position inside an helicopter fuselage panel in order to obtain the best compromise between the simplicity and the robustness of a sensor network. In particular, a Finite Element (FE) model will be used to create a database of various damages inside the structure, thus consequently optimising the network sensitivity to any damage. The evaluation of the network performances is provided when some realistic noise [1,2] is added to the FE calculation

Damage assessment of CFRP laminate plate subjected to close-range blast loading: hydrocode methodology validation and case study

Blast loading represents a critical damaging event in all structures. Although composite materials have been increasingly adopted in structural application, the effect of such dynamic loading event on composite structures is still to be evaluated in detail. This work defines a reliable numerical methodology to assess the damage occurring in carbon fiber reinforced polymer (CFRP) plate subjected to close-range blast loading. The numerical methodology is validated with a benchmark experiment found in literature and is employed to study in detail the damage mechanisms and eventual Fluid Structure Interaction (FSI) effects. The numerical analyses are carried out through a commercially available software package employing two methods, i.e., the ConWep and the hybrid coupled Eulerian-Lagrangia (CEL)-ConWep approaches, and the results from the simulations are compared with experimental evidence from the original work. The results show that (i) the hybrid approach seems to be a promising solution in terms of efficiency and accuracy in modelling blast events, (ii) the ConWep approach accurately reproduces experimental observations, even though such a method has strong limitations. (C) 2022 The Authors. Published by Elsevier B.V