42 research outputs found
Shape of the power spectral density matrix components: Influence on fatigue damage
No full textThe damage estimation for a structure under random loading is a challenge in fatigue assessment, especially when the loading is multiaxial. The comparison of the effect of different spectra on fatigue damage is essential when the structure can be subjected to different types of loadings. Therefore, in the present paper, the expected fatigue damage produced on metallic structures by combined bending and torsion stationary proportional and nonproportional loading is evaluated varying the shape of spectra of the normal and shear stress tensor components
Mode I fracture toughness of fibre-reinforced concrete by means of a modified version of the two-parameter model
No full textAbstractThe 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
Hot-spot localisation according to the critical plane-based approach
No full textThe tubular welded joints in H-shaped structural components of agricultural sprayers are responsible for failure and the localisation of hot-spots is very important in multiaxial fatigue assessment of such components. Therefore, the purpose of the present paper is to develop a novel approach both to localize hot-spots in tubular welded joints and to estimate the initial crack growth direction. Such an approach is based on the application of the hot-spot stress approach together with the multiaxial critical plane-based criterion proposed by Carpinteri et al. Comparison between experimental data and numerical results has shown a satisfactory agreement in terms of both hot-spots localisation and initial crack growth direction evaluation
A stress gradient approach for fretting fatigue assessment of metallic structural components
No full textIn the present paper, the fretting fatigue life assessment of metallic structural components under cylindrical
contacts is performed by applying a critical plane-based multiaxial fatigue criterion. Such a criterion
is formulated by using the so-called critical point method: a material point located at a certain
distance from the hot-spot on the contact surface is assumed to be the critical point where to perform
the above assessment. The above distance, function of the material properties, is measured along three
alternative paths (a normal path, an inclined path and a principal stress oriented path) and, using such
three different paths to determine the critical point location, the effectiveness of the criterion is evaluated
by means of experimental data related to aluminium alloy specimens under cylindrical contacts. Further,
in order to improve the accuracy of the critical plane-based criterion in terms of fretting fatigue lifetime
evaluation, a new approach involving a critical distance also function of the stress gradient in the contact
zone is proposed and experimentally validated
Mode I fracture toughness of fibre reinforced concrete
No full textLow fracture toughness of concrete represents a serious shortcoming. An effective way to improve the concrete toughness is represented by the dispersion (during mixing) of discontinuous fibres into the concrete mix. The principal beneficial effect of fibres is the crack bridging in the cementitious matrix, providing resistance to crack propagation before fibre debonding and/or pulling out or failure. In the present paper, the fracture behaviour of FRC (fibre reinforced concrete) specimens is examined, with micro-synthetic polypropylene fibrillated fibres being randomly distributed in concrete. The modified two-parameter model, proposed by the authors to calculate Mode I plain-strain fracture toughness for quasi-brittle material, is able to take into account the possible crack deflection (kinked crack) during stable crack propagation
Spectral fatigue life estimation for non-proportional multiaxial random loading
No full textA frequency-domain High-Cycle Fatigue (HCF) criterion based on the critical plane approach is here proposed
to estimate fatigue life of smooth metallic structural components under multiaxial random loading.
The procedure consists of the following three steps: (a) definition of the critical plane; (b) PSD
evaluation of an equivalent normal stress; and (c) computation of the fatigue life. A new formulation
to define the critical plane is adopted in order to improve the lifetime estimation. The criterion is validated
through comparison of the obtained numerical results with experimental fatigue data available
in the literature for structural steel specimens subjected to a combination of random non-proportional
bending and torsion
Fretting High-Cycle Fatigue Assessment Through a Multiaxial Critical Plane-Based Criterion in Conjunction with the Taylor’s Point Method
No full textThe critical plane-based multiaxial criterion originally proposed by the authors for plain fatigue is here applied to estimate the crack initiation life of fretting high-cycle fatigued structural components. Although fretting fatigue can be regarded as a case of multiaxial fatigue, the common multiaxial fatigue criteria have to be modified to account for the severe stress gradients in the contact zone. Therefore, the above criterion is used in conjunction with the Taylor’s point method to numerically estimate the fatigue life of Ti-6Al-4V and Al-4Cu specimens under cylindrical contacts
Investigation of Mode I fracture toughness of red Verona marble after thermal treatment
No full textThe present paper aims to assess the effect of freeze/thaw cycles on fracture behaviour of a natural
stone: the red Verona marble. A wide variety of specimen types and methods to determine Mode I fracture
toughness of natural stones are available in the literature and, in this context, the model originally proposed for
plain concrete, i.e. the Two-Parameter Model (TPM), is adopted. Such a method is able to take into account the
slow nonlinear crack growth occurring before the peak load, typical of quasi-brittle materials, with the advantage
of easy specimen preparation and simple test configuration.
In the present paper, the atmospheric ageing is simulated by means of thermal pre-treatments consisting of
freeze/thaw cycles. Experimental tests are carried out using three-point bending Single-Edge Notched (SEN)
specimens, according to the TPM procedure. The effects of thermal treatment on both mechanical and fracture
parameters are examined in terms of elastic modulus and fracture toughness, respectivel
Fatigue lifetime evaluation of notched components: implementation of the control volume concept in a strain-based LCF criterion
No full textThe goal of the present paper is to discuss the reliability of a strain-based multiaxial Low-Cycle Fatigue (LCF) criterion, recently proposed by some of the present authors, in estimating the fatigue lifetime of metallic structural components weakened by sharp notches. Such a criterion, based on the critical plane approach, is formulated according to the control volume concept related to the Strain Energy Density (SED) criterion: a material point located at a certain distance from the notch tip is assumed to be the verification point where to perform the fatigue assessment. The above distance is assumed to be a function of both the biaxiality ratio (applied shear stress amplitude over normal stress amplitude) and the control volume radii under pure Mode I and pure Mode III loading conditions. Once the position of the verification point and the orientation of the critical plane are determined, the fatigue lifetime is theoretically evaluated through an equivalent normal strain amplitude acting on the critical plane, together with the tensile Manson-Coffin curve. Some uniaxial and multiaxial LCF data, recently published in the literature for V-notched round bars made of Ti-6Al-4V titanium alloy, are analysed through the present criterion
Improved Zn-based coatings for ipersandelin steel products
No full textAbstractThe 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
