Crack path dependence on inhomogeneities of material microstructure

Crack trajectories under different loading conditions and material microstructural features play animportant role when the conditions of crack initiation and crack growth under fatigue loading have to beevaluated. Unavoidable inhomogeneities in the material microstructure tend to affect the crack propagationpattern, especially in the short crack regime. Several crack extension criteria have been proposed in the pastdecades to describe crack paths under mixed mode loading conditions. In the present paper, both the Sihcriterion (maximum principal stress criterion) and the R-criterion (minimum extension of the core plastic zone)are adopted in order to predict the crack path at the microscopic scale level by taking into account microstressfluctuations due to material inhomogeneities. Even in the simple case of an elastic behaviour under uniaxialremote stress, microstress field is multiaxial and highly non-uniform. It is herein shown a strong dependence ofthe crack path on the material microstructure in the short crack regime, while the microstructure of the materialdoes not influence the crack trajectory for relatively long cracks

Discontinuous FE approach and lattice models to describe cracking behaviour in fibre-reinforced brittle materials

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Effect of fibre arrangement on the multiaxial fatigue of fibrous composites: a micromechanical computational model

Structural components made of fibre-reinforced materials are frequently used in engineering applications. Fibre-reinforced composites are multiphase materials, and complex mechanical phenomena take place at limit conditions but also during normal service situations, especially under fatigue loading, causing a progressive deterioration and damage. Under repeated loading, the degradation mainly occurs in the matrix material and at the fibre-matrix interface, and such a degradation has to be quantified for design structural assessment purposes. To this end, damage mechanics and fracture mechanics theories can be suitably applied to examine such a problem. Damage concepts can be applied to the matrix mechanical characteristics and, by adopting a 3-D mixed mode fracture description of the fibre-matrix detachment, fatigue fracture mechanics concepts can be used to determine the progressive fibre debonding responsible for the loss of load bearing capacity of the reinforcing phase. In the present paper, a micromechanical model is used to evaluate the unixial or multiaxial fatigue behaviour ofstructures with equi-oriented or randomly distributed fibres. The spatial fibre arrangement is taken into account through a statistical description of their orientation angles for which a Gaussian-like distribution is assumed, whereas the mechanical effect of the fibres on the composite is accounted for by a homogenization approach aimed at obtaining the macroscopic elastic constants of the material. The composite material behaves as an isotropic one for randomly distributed fibres, while it is transversally isotropic for unidirectional fibres. The fibre arrangement in the structural component influences the fatigue life with respect to the biaxiality ratio for multiaxial constant amplitude fatigue loading. One representative parametric example is discussed

Implementazione di un Voting System su Blockchain

In questo documento si andranno ad analizzare i sistemi di voto, dai piu` antichi risalenti all’epoca romana, fino ad i più moderni utilizzati nei vari paesi del mondo ai giorni nostri. Parleremo delle varie tecnologie di voto ed innovazioni che si sono avvicendate nel trascorrere del tempo e di tutte le problematiche relative ad esse. Andremo ad analizzare nel dettaglio i più moderni sistemi di voto elettronici e la loro struttura. Si andrà quindi a definire una nuova e recente tecnologia, la blockchain e si andrà a spiegarne in dettaglio il funzionamento ed i maggiori algoritmi di consenso distribuito relativi ad essa. Infine verra` spiegato il progetto realizzato utilizzando la blockchain. Il progetto consiste in un innovativo sistema di voto elettronico decentralizzato, si andranno ad analizzare i vari componenti del sistema, le proprietà di voto mantenute nel sistema e i vari vantaggi e svantaggi che questa tecnologia se applicata potrebbe portare nel mondo moderno

Mechanical behaviour and phase transition mechanisms of a shape memory alloy by means of a novel analytical model

The aim of the present paper is to examine both the fatigue behaviour and the phase transition mechanisms of an equiatomic pseudo-elastic NiTi Shape Memory Alloy through cyclic tests (up to 100 loading cycles). More precisely, miniaturised dog-bone specimens are tested by using a customised testing machine and the contents of both austenite and martensite phase are experimentally measured by means of X-Ray diffraction (XRD) analyses. On the basis of such experimental results in terms of martensite content, an analytical model is here formulated to correlate the stress-strain relationship to the phase transition mechanisms. Finally, a validation of the present model by means of experimental data pertaining the stress-strain relationship is performed

Sample volume length and registration accuracy assessment in quality controls of PW Doppler diagnostic systems: a comparative study

In clinical diagnostics, Pulsed Wave (PW) Doppler is one of the most used spectral Doppler techniques since it provides quantitative information about the severity of several cardiac disorders. Therefore, routine quality control tests should be scheduled to check whether a proper level of performance is maintained over time. Despite continuous research in the field, performance evaluation of Doppler equipment is still an open issue. Therefore, the present study is focused on the comparative investigation based on a test parameter for the automatic analysis of faults in sample volume length and range gate registration accuracy. The Velocity Profile Discrepancy Index (VPDI) provides a quantitative estimation according to the agreement between the theoretical parabolic velocity profile and the measured one. The index was assessed through an automatic method that post-processes PW spectrogram images acquired at six sample volume depths with respect to the vessel radius of a Doppler reference device. Tests were repeated for three brand-new ultrasound diagnostic systems, equipped with convex and phased array probes, in two working conditions. From the analysis of the results, a lower discrepancy between the measured and the theoretical velocity profile was found for the convex array probes as well as a lower uncertainty contribution

A Novel Equivalent Time Sampling-Based Method for Pulse Transit Time Estimation with Applications into the Cardiovascular Disease Diagnosis

The increasing incidence of cardiovascular diseases (CVDs) is reflected in additional costs for healthcare systems all over the world. To date, pulse transit time (PTT) is considered a key index of cardiovascular health status and for diagnosis of CVDs. In this context, the present study focuses on a novel image analysis-based method for PTT estimation through the application of equivalent time sampling. The method, which post-processes color Doppler videos, was tested on two different setups: a Doppler flow phantom set in pulsatile mode and an in-house arterial simulator. In the former, the Doppler shift was due to the echogenic properties of the blood mimicking fluid only, since the phantom vessels are non-compliant. In the latter, the Doppler signal relied on the wall movement of compliant vessels in which a fluid with low echogenic properties was pumped. Therefore, the two setups allowed the measurement of the flow average velocity (FAV) and the pulse wave velocity (PWV), respectively. Data were collected through an ultrasound diagnostic system equipped with a phased array probe. Experimental outcomes confirm that the proposed method can represent an alternative tool for the local measurement of both FAV in non-compliant vessels and PWV in compliant vessels filled with low echogenic fluids

crack path dependence on inhomogeneities of material microstructure

Crack trajectories under different loading conditions and material microstructural features play an important role when the conditions of crack initiation and crack growth under fatigue loading have to be evaluated. Unavoidable inhomogeneities in the material microstructure tend to affect the crack propagation pattern, especially in the short crack regime. Several crack extension criteria have been proposed in the past decades to describe crack paths under mixed mode loading conditions. In the present paper, both the Sih criterion (maximum principal stress criterion) and the R-criterion (minimum extension of the core plastic zone) are adopted in order to predict the crack path at the microscopic scale level by taking into account microstress fluctuations due to material inhomogeneities. Even in the simple case of an elastic behaviour under uniaxial remote stress, microstress field is multiaxial and highly non-uniform. It is herein shown a strong dependence of the crack path on the material microstructure in the short crack regime, while the microstructure of the material does not influence the crack trajectory for relatively long cracks

Improved Zn-based coatings for ipersandelin steel products

The protection of iron-based alloy products against corrosion is fundamental to preserve their mechanical properties in aggressive environments. Hot-dip galvanizing process represents one of the most used techniques to make protective coatings for such products. In order to improve both mechanical and chemical properties of coating, metallic elements may be added to the traditional zinc bath. In the present paper, two types of improved zinc-based coating are proposed: (i) A coating obtained employing a tin addition (3% in weight); (ii) A coating obtained employing aluminium (5% in weight), tin (1% in weight) and copper (0.5% in weight) additions. Firstly, the performance of such two types of coatings is experimentally investigated through bending tests on ipersandelin steel plate specimens, treated through different bath dipping times. The intermetallic phase thicknesses of coatings are measured for each dipping time, in order to evaluate the kinetic formation. Then, a Finite Element (FE) model is proposed in order to simulate the bending behaviour of the above specimens, both employing the measured phase thickness and implementing the loading and boundary conditions of the experimental tests. A numerical non-linear static analysis is performed. A quite satisfactory agreement between experimental and numerical results is observed, especially under plastic behaviour regime