Papers by Author: Giovanni Meneghetti

Abstract: In previous papers, the energy dissipated to the surroundings as heat in a unit volume of material per cycle, Q, has been successfully applied to correlate experimental data generated from push-pull, stress- or strain-controlled fatigue tests on AISI 304 L stainless steel plain and notched specimens. In this paper the fatigue behaviour of AISI 304 L un-notched bars under fully-reversed axial or torsional loading was investigated. By using the Q parameter it was found that the experimental data collapse into the same energy-based scatter band previously determined with the push-pull tests. The results found in the present contribution are meant to be specific for the material investigated.

Abstract: The fatigue behaviour of materials is usually synthesised in terms of stress-life (S-N) curve or in terms of strain-life (e-N) curve, the latter being described by the so-called Manson-Coffin equation. It is known that the assumption of equality of the plastic and elastic components between the Manson-Coffin and the stabilised stress-strain curves leads to the so-called compatibility conditions which connect the equations theoretically. The material constants of the Manson-Coffin and of the stabilised stress-strain curve are commonly determined by best fitting separately the experimental data obtained from strain-controlled fatigue tests. As a consequence the compatibility conditions may not be fulfilled. In this paper a method for fatigue data analysis that ensures the compatibility conditions is proposed and validated against experimental data.

Abstract: In this paper the fatigue characterization of an austempered ductile iron (ADI) is presented. The aim of the work is to provide design engineers involved in fatigue assessments with an engineering tool suitable to deal with notches of different severity. Classically, U-notches are divided into blunt notches and sharp notches. The former are characterized by large notch tip radii such that the high cycle fatigue strength is controlled by the elastic peak stress, i.e. by the elastic stress concentration factor. The latter are characterized by reduced notch tip radii such that the effective stress which controls the high cycle fatigue strength is significantly lower than the elastic peak stress and their behaviour become similar to that of a crack having the same length. Blunt notches are assessed according to the classical Notch Mechanics principles, while sharp notches are treated with the Linear Elastic Fracture Mechanics approach. After presenting the classical Frost diagram which highlights the different fatigue behaviour of sharp and blunt notches, fatigue test results generated from notches of different severity are presented as well as a synthesis in a diagram able to account for short cracks/notches, long cracks, sharp notches and blunt notches.

Abstract: In this paper the low cycle fatigue behaviour of an AISI 304L stainless steel is analysed on the basis of energy concepts. In particular during the fatigue tests different forms of energy in a unit volume of material per cycle involved in the fatigue process were measured: the mechanical energy expended was evaluated from the area of the hysteresis loops, while the energy released as heat by the specimen to the surroundings was estimated from surface temperature measurements by means of an infrared camera. By subtracting the mechanical input energy and that released as heat, the energy stored in a unit volume of material at fracture was calculated for each tested specimen. The mean value obtained from different specimens is in agreement with the energy absorbed by the material in a static test.

Abstract: The paper presents a simplified version of the Notch Stress Intensity Factor (NSIF) approach useful for fatigue strength assessments of welded joints. The evaluation of the NSIF from a numerical analysis of the local stress field usually needs very refined meshes and then large computational effort. A relationship is proposed here to estimate the Notch Stress Intensity Factor from finite element analyses carried out by using a mesh pattern with a constant element size. The main advantage of the presented relationship is that only the elastic peak stress numerically evaluated at the V-notch tip is necessary to estimate the NSIF instead of the whole stress-distance set of data (that is why the method has been called Peak Stress Method, i.e. PSM). An application of the PSM to fatigue strength assessment of fillet welded joints made of structural steels and aluminium alloys under tensile or bending loads is presented. In those joints, only mode I stress distribution is singular at the weld toe due to the presence of a V-notch angle equal to 135 degrees.

Abstract: The paper presents a simplified version of the Notch Stress Intensity Factor (NSIF) approach useful for fatigue strength assessments of welded joints. The evaluation of the NSIF from a numerical analysis of the local stress field usually needs very refined meshes and then large computational effort. A relationship is proposed here to estimate the Notch Stress Intensity Factor from finite element analyses carried out by using a mesh pattern with a constant element size. The main advantage of the presented relationship is that only the elastic peak stress numerically evaluated at the V-notch tip is necessary to estimate the NSIF instead of the whole stress-distance set of data (that is why the method has been called Peak Stress Method, i.e. PSM). An application of the PSM to fatigue strength assessment of fillet welded joints made of structural steels and aluminium alloys under tensile or bending loads is presented. In those joints, only mode I stress distribution is singular at the weld toe due to the presence of a V-notch angle equal to 135 degrees.