Fatigue life estimation in welded joints under multiaxial loadings

Welded joints are frequently locations for cracks initiation and propagation that may cause fatigue failure of engineering structures. Biaxial or triaxial stress-strain states are present in the vicinity of welded joints, due to local geometrical constraints, welding processes and/or multiaxial external loadings. Fatigue life evaluation of welded joints under multiaxial proportional (in-phase) cyclic loading can be performed by using conventional hypotheses (e.g. see the von Mises criterion or the Tresca criterion) on the basis of local approaches. On the contrary, the fatigue life predictions of welded joints under non-proportional (out-of-phase) cyclic loading are generally unsafe if these conventional hypotheses are used. A criterion initially proposed by the authors for smooth and notched structural components has been extended to the fatigue assessment of welded joints. In more detail, fatigue life of welded joints under multiaxial stress states can be evaluated by considering a nonlinear combination of the shear stress amplitude (acting on the critical plane) and the amplitude and the mean value of the normal stress (acting on the critical plane). In the present paper, fatigue lifetimes predicted through the proposed criterion are compared with experimental fatigue life data available in the literature, related to fatigue biaxial tests

On a kinked crack model to describe the influence of material microstructure on fatigue crack growth

Threshold condition and rate of fatigue crack growth in both short and long crack regime appear tobe significantly affected by the degree of crack deflection. In the present paper, a theoretical model of aperiodically-kinked crack is presented to describe the influence of the degree of crack deflection on the fatiguebehavior. The kinking of the crack is due to a periodic self-balanced microstress field having a length scale, d.By correlating the parameter d with a characteristic material length (e.g. average grain size in metals, maximumaggregate dimension in concrete), the possibility of using the present model to describe some experimentalfindings related to crack size effects in fatigue of materials is explored. Well-known experimental resultsconcerning two different situations (fatigue threshold and fatigue crack growth in the Paris regime) are brieflyanalysed

Interpreting experimental fracture toughness results of quasi-brittle natural materials through multi-parameter approaches

Natural stones like marbles are often employed as facade panels to externally cover buildings. These natural materials tend to exhibit a quasi-brittle nonlinear fracture behaviour which, conversely to concrete counterpart, has much less been studied in the literature. In the present paper, an experimental campaign on the so-called red Verona marble is carried out, and the results are discussed together with some previously published results on the white Carrara marble. The analysis of the two marbles as a whole allows us to discuss size effect and to point out the need for additional parameters in order to describe their fracture behaviour. The study focuses on a two-parameter model which accounts for a characteristic material length. A quantitative correlation between material microstructure features, obtained from thin sections technique, and the characteristic material length is proposed

effectiveness of a lattice discrete element model to simulate mechanical wave shielding by using barriers into the ground

Abstract Several vibration sources can provoke propagation of mechanical waves into the ground. Such waves have to be taken into account both in designing of new buildings and in shielding of strategic structures. The vibration control systems may be either active systems or passive systems such as vertical barriers. One of the main problems encountered in the numerical simulation of wave shielding by using vertical barriers is the ground modeling. To such an aim, the method originally formulated by Riera is here employed to simulate both typical elastic-dynamic problems and a complex problem consisting in the numerical simulation of a vertical barrier wave shielding into a damaged ground where wave propagation occurs

Special Issue on ‘Multiaxial fatigue 2016: Experiments and modeling’: Selected papers from the 11th International Conference on Multiaxial Fatigue and Fracture (ICMFF11), held in Seville, Spain, on 1–3 June 2016

This Special Issue of the International Journal of Fatigue contains selected papers presented at the International Conference on Multiaxial Fatigue and Fracture held in Seville, Spain, on 1–3 June 2016

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

fracture toughness of fibre reinforced concrete determined by means of numerical analysis

Abstract As is well-known, the addition of fibres to concrete mix (Fibre Reinforced Concrete, FRC) produces a positive effect on cracking behaviour. In this work, the results of an experimental campaign on FRC specimens with randomly distributed micro-synthetic polypropylene fibrillated fibres are examined. The tests concern single-notched beams under three-point bending, where the fibre content varies. Such an experimental testing is numerically analysed through a non-linear finite element model, named 2D-PARC, where a proper constitutive law for fibre-reinforced concrete is implemented. The load-crack mouth opening displacement (CMOD) curves numerically obtained are employed to determine the critical stress-intensity factor (fracture toughness) for different values of fibre content, according to the two-parameter model. The comparison between such numerical results and those obtained by applying the two-parameter model to the experimental load-CMOD curves is performed

Mode I fracture toughness of fibre-reinforced concrete by means of a modified version of the two-parameter model

Abstract The present paper proposes a method to calculate Mode I plane-strain fracture toughness of concrete, by taking into account the possible crack deflection (kinked crack), even in the case of a far-field Mode I loading. As a matter of fact, during fracture extension, cracks may deflect as a result of microstructural inhomogeneities inside the material. Concrete is an inhomogeneous mixture due to aggregates embedded in the cementitious matrix, but additional inhomogeneities may be represented by fibres. Firstly, a two-parameter fracture model based on Mode I analytical expressions of the linear elastic fracture mechanics is employed. Then, in order to take into account the possible crack deflection as a result of the above inhomogeneities, a modified version of such a model is here discussed. Three-point bending tests on both plain concrete specimens and concrete specimens reinforced with micro-synthetic polypropylene fibrillated fibres are experimentally performed, and the modified model is applied

Effect of spectral cross-correlation on multiaxial fatigue damage: simulations using the critical plane approach

The present paper aims to discuss a frequency-domain multiaxial fatigue criterion based on the critical plane approach, suitable for fatigue life estimations in the presence of proportional and non-proportional random loading. The criterion consists of the following three steps: definition of the critical plane, Power Spectral Density (PSD) evaluation of an equivalent normal stress, and estimation of fatigue damage. Such a frequency-domain criterion has recently been validated by using experimental data available in the literature, related to combined proportional and non-proportional bending and torsion random loading. The comparison with such experimental data has been quite satisfactory. In order to further validate the above criterion, numerical simulations are herein performed by employing a wide group of combined bending and torsion signals. Each of such signals is described by an ergodic, stationary and Gaussian stochastic process, with zero mean value. The spectrum of each signal is assumed to be represented by a PSD function with rectangular shape. Different values of correlation degree, variance and spectral content are examined