Gruppo Italiano Frattura (IGF)
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Mechanical characterization of basalt woven fabric composites: numerical and experimental investigation
No full textBasalt fabric composite, with different twill wave reinforcements, i.e. twill 2/2 and twill 1/3, havebeen studied in this work by means of experimental tests and numerical finite element (FE) simulations. Asfabric reinforcements show repeating undulations of warp and fill yarn, simple mixtures law cannot be applied.As a consequence, the mesoscopic scale, lying between the microscopic and the macroscopic one, has to betaken into account to mechanically characterize a fabric reinforced composite. The aim of this work is toevaluate the stiffness of a fabric reinforced composite in warp and fill direction. In particular a numerical FEmodel, assuming elliptical sections and sinusoidal shape of the yarns, has been implemented and experimentaltests have been carried out in order to validate the proposed model. Finally, the strength and the failure modesof the composite material, for each analysed structure and textile orientation, have been experimentallyinvestigated
Fatigue behavior of lubricated Ni-Ti endodontic rotary instruments
No full textThe use of Ni-Ti alloys in the practice of endodontic comes from their important properties such as shape memory and superelasticity phenomena, good corrosion resistance and high compatibility with biological tissues. In the last twenty years a great variety of nickel-titanium rotary instruments, with various sections and taper, have been developed and marketed. Although they have many advantages and despite their increasing popularity, a major concern with the use of Ni-Ti rotary instruments is the possibility of unexpected failure in use due to several reasons: novice operator handling, presence manufacturing defects, fatigue etc. Recently, the use of an aqueous gel during experimental tests showed a longer duration of the instruments. The aim of the present work is to contribute to the study of the fracture behavior of these endodontic rotary instruments particularly assessing whether the use of the aqueous lubricant gel can extend their operative life stating its reasons. A finite element model (FEM) has been developed to support the experimental results. The results were rather contradictory, also because the Perspex (Poly-methyl methacrylate, PMMA) cannot simulate completely the dentin mechanical behavior; however the results highlight some interesting points which are discussed in the paper
Quantitative estimating size of deep defects in multi-layered structures from eddy current NDT signals using improved ant colony algorithm
No full textDetection and quantitative estimation of deep defects in multi-layered structures is an essential task in a range of technological applications, such as maintaining the integrity of structures, enhancing the safety of aging aircraft, and assuring the quality of products. A novel approach to accurately quantify the two-dimensional axisymmetric deep defect size from eddy current nondestructive testing (NDT) signals is presented here. The method uses a finite element forward model to simulate the underlying physical process and an improved ant colony algorithm (IACA) to solve the inverse problem. Experiments are carried out. The performance comparison between the IACA method and the least square method is shown. The comparison results demonstrate the feasibility and validity of the IACA method. Between them, the IACA method gives a better estimation performance than the least square method at present
Experimental measurement and model validation of COD in pipe under bending with off-centered circumferential crack
No full textThe leak area of circumferential through-thickness crack in pipe under bending depends on the position of the crack with respect to the bending plane. In leak-before-break (LBB) analysis, the assumption that the crack is symmetrically placed with respect to the bending plane is not necessarily conservative. In this work, the crack opening of circumferential cracks, off-centered with respect to the bending plane, was investigated experimentally. Here, three pipe geometries and two crack lengths were investigated. For each crack, the centred and two off-centered configuration were examined. The crack opening displacement (COD) distribution along the crack length was measured for two selected bending load levels using digital image correlation (DIC) technique. These measurements have been used for verifying the solution provided by the hodograph cone method (HCM) as proposed by Bonora [1]
A method for calculation of finite fatigue life under multiaxial loading in high-cycle domain
No full textA method for fatigue life assessment in high-cycle domain under multiaxial loading is presented in this paper. This approach allows fatigue assessment under any kind of load history, without limitations. The methodology lies on the construction - at a macroscopic level - of an “indicator” in the form of a set of cycles, representing plasticity that can arise at mesoscopic level throughout fatigue process. During the advancement of the loading history new cycles are created and a continuous evaluation of the damage is made
Numerical analysis of soil bearing capacity by changing soil characteristics
No full textIn this research work by changing different parameters of soil foundation like density, cohesion and foundation depth and width of square foundation at angle of friction of 0° to 50° with increment of 5°, numerically safe bearing capacity of soil foundation is calculated and it is attempted to assess economical dimension of foundation as well as understanding variation range of bearing capacity at different degree. It could help of civil engineering in design of foundations at any situation
Inferenza bayesiana per l'analisi dei dati di prove di fatica
No full textSi prende in esame il problema della caratterizzazione a fatica dei materiali mediante campioni di dati poco numerosi. Se ne prospetta una soluzione che impiega la metodologia bayesiana. Per la vasta famiglia degli acciai al carbonio, laminati a caldo o bonificati che siano, utilizzando dati di letteratura ed alcune consolidate correlazioni tra proprietà di fatica e resistenza statica, è definita una funzione di densità di probabilità a priori in grado di condensare gran parte delle informazioni disponibili. Queste ultime, in uno con quelle fornite dalla sperimentazione diretta, da esaminare mediante il teorema di Bayes, permettono di identificare con grande accuratezza la resistenza a fatica del particolare acciaio provato. L’efficacia del metodo proposto è verificata con una sperimentazione virtuale su un ipotetico acciaio condotta con il metodo Montecarlo
Numerical modelling in non linear fracture mechanics
No full textSome numerical studies of crack propagation are based on using constitutive models that accountfor damage evolution in the material. When a critical damage value has been reached in a materialpoint, it is natural to assume that this point has no more carrying capacity, as is done numerically in the elementvanish technique. In the present review this procedure is illustrated for micromechanically based materialmodels, such as a ductile failure model that accounts for the nucleation and growth of voids to coalescence,and a model for intergranular creep failure with diffusive growth of grain boundary cavities leadingto micro-crack formation. The procedure is also illustrated for low cycle fatigue, based on continuum damagemechanics. In addition, the possibility of crack growth predictions for elastic-plastic solids using cohesivezone models to represent the fracture process is discussed
The healing of damage after the plastic deformation of metals
No full textThe general regularities of damage healing during the annealing after cold deformation of metal materials are presented in this paper. In categories of damage mechanics the kinetic equations of damage healing during recovery and recrystallization are formulated. Diagrams of damage healing for some metal alloys are presented. The example of use of investigation results for optimization of industrial technology of pipes drawing is presented
Analisi del cedimento strutturale del braccio di una gru portuale
No full textNel presente lavoro vengono discusse le cause del cedimento strutturale del braccio di una gruportuale a portata variabile. L’ispezione delle sezioni di rottura ha mostrato in particolare la presenza di unagrossa fessura preesistente al momento del crollo, che si estendeva per circa metà sezione di uno degli elementitubolari principali che costituiscono il traliccio del braccio.Al fine di stabilire le modalità del crollo, nel lavoro vengono presentati un modello per l’analisi dellapropagazione della fessura, che fa uso del metodo delle weight functions ed un modello per l’analisi di collassodella sezione. Le analisi condotte hanno permesso di concludere che il crollo si è verificato per collasso plasticodella sezione ed hanno messo in evidenza come la fessura in esame, per una parte considerevole della vita, siapropagata in condizioni stabili con velocità di avanzamento circa costante