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The reheat cracking phenomenon (also known as stress relief cracking) is today a well known topic; since the first years of the 1950failure that can be brought to this kind of phenomenon appeared. Nevertheless today the causes and the factors that lead to this failure that interests different types of materials, are not totally cleared. This paper gives to the Reader an overview of the phenomenon, focusing the main causes, the materials that are susceptible, the preventive measures and, finally, the main tests for the characterization. [ABSTRACT FROM AUTHOR]

In the construction of welded structures the research, evaluation and acceptability of imperfections in welded joints are fondamental aspects. In the field of metallic constructions, imperfections can be divided into two groups: linear and non-linear imperfections. Imperfection becomes a defect if it does not fall within the acceptance criteria defined by code or designer and from there derives several corrective actions, such as heat treatment, painting, repairing... The different international codes examined show some common points on implementation of non-destructive testing, but very different are their approaches to the acceptance criteria. A designer choice of a particular acceptance criteria can be summarized in a few key points: stress evaluation of the welded joints, in service conditions, mechanical properties of materials, inspection procedures. The purpose of this paper is a comparison of international standards (European, American and Russian Codes) for the acceptance of imperfections in welded joints. [ABSTRACT FROM AUTHOR]

There are many problems in Solid Mechanics, Physics of Solids and Materials Science that can not been solved using conventional approaches. Besides the effective properties of non-homogeneous bodies, there is an increasing need for incorporating more physical information about small-scale mechanisms of deformation and damage into phenomenological models of plasticity and rupture of materials which are usually considered homogeneous. Cavitation, local stress or strain concentrations at small scale are essential to explain nonlinear phenomena, such as fatigue or ductile rupture, which are not understandable from the simple point of view of average stresses or strains. Precise determination or accurate estimation of local fields is the domain of micromechanics. This work treats the basic concepts of the micromechanics in a simple way, with some practical suggestion on the most commonly used modelling techniques and some applications made by the author on various nodular cast iron microstructures. [ABSTRACT FROM AUTHOR]

In this research paper we compare two different methods to estimate the fatigue life of spot welded joints: the method of fiction notch radius and the implicit gradient approach. The first requires a radius of curvature at the weld toe or at the weld root that is different from zero, the second simply considers the weld as a sharp notch. The comparison is made on the ability to predict the reliability of spot welded joints made of steel with a thickness ranging from 0.8 to 1.5 mm. These joints are subjected to shear loading (lap joints) or to tensile loading (circular cup joints). Finally, we discuss the convergence condition of the numerical analysis needed, in both methods, for the calculation of equivalent stress to be used in the fatigue analysis. [ABSTRACT FROM AUTHOR]

High speed MODE I crack growth in elastic-plastic materials, involving large scale plasticity and dynamic effects connected to rapid propagation, is faced through a cohesive model to compute force nodal release. As it is well known, the search of a maximum stress in the crack tip is not worthwhile in the elastic case, only field factors may be used instead. In the elastic-plastic case, hardening and softening due to geometric reasons or due to local damaging have a deep influence on the exponential behaviour of the measured stress field. However, it is possible to introduce a reference value (finite), which is the stress at the beginning of the softening zone. This entity is taken as a scale factor for cohesive force evaluation that is necessary for the accounting of the dissipated energy. In the present work a procedure to compute this reference value by stress-strain field is presented, for a variety of T-stress conditions. [ABSTRACT FROM AUTHOR]

In this paper, a non-local equivalent stress is calculated by solving a second order differential equation of implicit type. The solution is obtained by assuming a linear elastic constitutive behaviour and the maximum principal stress as equivalent stress. Fatigue behaviour of steel welded joints is taken into account and a general fatigue scatter band is proposed. The non local stress is computed, namely the effective stress, by means of a completely numerical solution of local elastic stress field. In complex 3D welded details the critical point turns out from the analysis and it is not assumed a priori. [ABSTRACT FROM AUTHOR]

Following their research, the authors remarked on the importance of the knowledge of the temperature for stressed material (mechanical component). They show as a temperature (third parameter) is an important parameter to characterise dynamically the material. Being that the thermal release is a function of the applied energy that leads to the failure, the knowledge of parameters linked to energy leads to new hypothesis and definitions of fatigue limit and lifespan. A thermal analysis permits one to evaluate parameters related to the amount of energy to failure of tested material. In [4] A. Risitano and Others, had remarked that during a static traction test, the beginning of plastic behaviour (linked to applied stress) was definable by analysing of the correspondent temperature curve. In the same work, they remarked about the low influence of the test velocity. Still working with high level temperature sensors, the authors observed that during static tests, the temperature variation of the surface specimen, permits to associated the lower dynamic fatigue limit σ0 to a "temperature limit" T0 coincident to the end of thermo-elastic phase. In this case a qualitative physical model, able to give and justify the possibility to evaluate the classic fatigue limit by experimental knowledge of thermo-elastic behaviour is discussed. As an example, the results of traction tests performed on two rectangular section specimens notched with one hole each, where the change of linearity was evident, are reported. The corresponding value of stress was coincident with the fatigue limit σ0 for R= - 1, found by traditional method. [ABSTRACT FROM AUTHOR]

This work deals with the prediction of the fatigue crack growth of bonded joints. Traditionally cohesive zone model is used for the simulation of failure of bonded joint under quasi-static and impact conditions. On the other hand fracture mechanics concepts are used for the prediction of fatigue crack growth in bonded joint. In this work a modified cohesive damage model, accounting for the fatigue crack growth, was implemented in the commercial software ABAQUS. The fatigue damage evolution in the cohesive element is related to the number of cycles through the experimental fatigue crack growth behavior. An automated procedure, valid for any from the geometry and load distribution, was also defined to compute the Strain Energy Release Rate, the necessary input to define the instantaneous fatigue crack growth rate. The model is validated by comparing the simulation to fatigue crack growth tests. [ABSTRACT FROM AUTHOR]

In the Strain Energy Density (SED) approach for fatigue strength assessments of welded joints a well-defined control volume is considered. This volume surrounds the weld root or weld toe, both modelled like sharp (zero radius) V-notches with different opening angles. The volume becomes a circular sector under plane strain conditions, with the radius being about 0.3 mm for welded joints made of structural steel. The mean value of the SED mainly depends on the singular stress fields when the main plate thickness is large enough, whereas the influence of the T-stress component cannot be neglected in the case of thin-walled welded joints. Both contributions are directly accounted for by using finite element models, also when the relevant meshes are quite coarse. This fact makes the application of the SED approach easier than any stress-based approach in the case of complex structures. Due to three-dimensional effects, a non conventional out-of-plane singular mode can be present, in addition with respect to modes I and II of the Williams' solution. This out-of-plane mode, analogous to the Mode III, is discussed here with reference to welded (seam) lap joints under tensile-shear loads. [ABSTRACT FROM AUTHOR]

Closed form solutions for the elastic and elastic-plastic stress fields created by circumferential notches in an axisymmetric shaft under torsional loading are developed. The linear elastic boundary value problem has been formulated by an approach using complex potential functions and some curvilinear coordinate systems. The solutions obtained for the shear stresses have a wide range of applicability, both in terms of the size and shape of the notches and the diameter of the shafts. Conversely the elastic-plastic problem has been solved in closed-form by using the hodograph transformation technique, which reduces the non-linear governing equations into a linear equation system. The present paper is a synthesis of some contributions recently published the same authors. [ABSTRACT FROM AUTHOR]

The problem of fatigue characterization of materials by small data samples is here considered and a Bayesian procedure for data analysis is presented. For both hot rolled and quenched and tempered carbon steels, on the basis of some literature data and by well-established correlations between fatigue and tensile properties, a prior probability density function, able to model most of the available information on material fatigue strength, is defined. Prior information, when fused by means of Bayes theorem with information from experimental data, allows to identify with greater accuracy the fatigue properties of the tested steel A Montecarlo study is carded out to verify the effectiveness of the proposed method, generating small samples of fatigue data by virtual testing. [ABSTRACT FROM AUTHOR]