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Predicting the leakage condition is of primary importance when designing metal-to-metal flanges. The gap between flange surfaces is regarded as a partially open crack with a zero stress intensity factor, then a model based on fracture mechanics is proposed for predicting leakage pressure. An analytical solution was found, with weight function, considering the condition of crack front at the most internal point of the bolt hole. Finite element and experimental tests validated the effectiveness of the model. In addition, the dependencies on the main flange dimensions were investigated and discussed, providing useful guidelines for optimal flange design. [ABSTRACT FROM AUTHOR]

The lateral impact between elastic cylinders is studied using two dynamic models. We propose an elementary example to justify the mechanical energy dissipation in a pure elastic contact and to define the parameters needed for its quantification. A finite element model is presented as the theoretical basis for the quantification of the mechanical energy dissipation produced by the propagation of elastic waves in continuous deformable impacting cylinders. The results are exploited to build an accurate and more numerically efficient dynamic lumped parameter model. The models are applied to the lateral impact of identical cylinders with various diameters and different impact speeds. The impact of the cylinders with a different mass and radius is also analyzed. The calculation of the coefficient of dissipation enables the global loss of mechanical energy to be quantified, and an equivalent damping ratio associated with the impact is calculated. The obtained damping values can be used as a reasonable underestimate of the dissipation produced in the engagement of spur gears, thus allowing a conservative prediction of the dynamic overloads of the system in resonant conditions. • The lateral impact of elastic cylinders is studied using two dynamic models. • A novel lumped parameter dynamic model is proposed. • The impact of cylinders with identical and different diameter is considered. • The coefficient of dissipation is obtained to quantify the mechanical energy loss. • A good agreement between the results of the two models is obtained. • The calculated equivalent damping ratio is applied to model engaging spur gears. [ABSTRACT FROM AUTHOR]

ABSTRACT The aim of the paper is at qualifying a methodology for the fatigue life assessment of structural components obtained by die-casting for vehicle applications. Full-scale fatigue tests were conducted on the back suspension arms of mid-size scooters. Two loading conditions, i.e. bending and combined bending plus torsion, were considered as representative of typical operating conditions. Fatigue tests showed that the locations of failure initiation is different for the two loading configurations. Material was characterized by means of small size standard specimens extracted from the components in order to be representative of the effective material conditions, particularly of the surface. Both static (tensile) and fatigue tests were conducted, making use of three different R-ratios. A finite element (FEM) model of the suspension arm, representative of full-scale test conditions was set-up in order to interpret the tests. The sub-modelling approach was adopted in order to get accurate evaluations of the stress-strain fields with reasonable computing resources and elaboration time. Combined elastic and elastic-plastic analyses were necessary to estimate the stress cycles in the regions critical for fatigue damage. Employing the material properties given by small-size specimens and the proposed FE analysis technique, predictions of either the locations of failure initiation and the fatigue strength of the component were obtained, in quite good agreement with full-scale tests. [ABSTRACT FROM AUTHOR]

Abstract: A general method for evaluating the Stress Intensity Factors (SIFs) of an inclined kinked edge crack in a semi-plane is presented. An analytical Weight Function (WF) with a matrix structure was derived by extending a method developed for an inclined edge crack. The effects of the principal geometrical parameters governing the problem were studied through a parametric Finite Element (FE) analysis, carried out for different reference loading conditions. The WF can be used to produce efficient and accurate evaluations of the SIFs for cracks with initial inclination angle in the range −60° to +60° and kinked angle in the range from −90° to +90°. The agreement between the results with those obtained by accurate FE solutions suggests that the proposed WF can be used as a general tool for evaluating the fracture mechanics parameters of an inclined kinked crack. [Copyright &y& Elsevier]

When the blind hole drilling method is used to evaluate high residual stresses in a metallic component, plastic relaxed strain can be produced in the hole region because of the stress concentration that causes the local stresses to reach yielding. By assuming a linear-elastic behaviour of the material, a significant error can result. The present paper analyses the phenomenon of the plasticity locally induced by the introduction of the hole and proposes a procedure to take into account its effects on the residual stress evaluation. The correcting procedure has been developed by elaborating a large database of elastic-plastic finite element analyses performed considering a wide range of material properties and testing parameters, including all the strain gauge rosettes commonly used. As plasticity induces non-linearity in the relationship between residual stress and relaxed strain, the superposition principle cannot be applied, so the correction is limited to uniform in-depth residual stress fields. However, four hole depths were considered and the related correcting procedures were provided. When variable through thickness residual stress is expected, and high residual stress is confined near the surface region, the correction procedure can be applied to an initial limited depth. [ABSTRACT FROM AUTHOR]

The hole-drilling method, coupled with the influence functions method, is a versatile technique for measuring residual stresses. The latter determines a relationship between residual stress and measured relaxed strains for any experimental configuration and material. However, several parameters which describe the functional basis for the residual stress must be defined. This paper presents a procedure, based on the least squares method and genetic algorithms, optimally to choose these parameters to reduce the effects of noise and uncertainty in experimental measurements. The performance of the method was tested against finite element simulations for typical applications such as shot peening, showing that the method is flexible and accurate and allows the reconstruction of residual stress at deeper positions than other techniques. [ABSTRACT FROM AUTHOR]

Abstract: A procedure for evaluating the fracture mechanics parameters of a subsurface two-dimensional crack parallel to the boundary in an elastic half plane is presented. A Weight Function (WF) with a matrix structure is proposed, to account for the coupling effects between modes I and II, typical in non-symmetrical problems. In order to face any loading condition, the WF was formulated by symmetric and anti-symmetric components and the ‘multiple reference loading’ approach was used to derive their analytical expressions. To this purpose, a parametric Finite Element (FE) analysis was set up and the Stress Intensity Factors (SIFs) were determined for several independent loading conditions. The analysis was carried out for different ratios between crack length and in-depth position and, consequently, the dependence of the WF on this parameter was studied. The WF accuracy was assessed by considering different loading and the method applied for evaluating the SIFs produced by a point-like load travelling on the semi-plane surface. The results indicated that the correct fracture mechanics analysis requires crack closure (either complete or partial) to be taken into account. Consequently, the crack opening displacement (COD) components under general loading conditions have to be evaluated. On the basis of the WF, the related Green Function (GF) was also derived by which the COD components can be efficiently evaluated for any applied load including the contact due to crack closure. [Copyright &y& Elsevier]

Abstract: A general method for evaluating the Stress Intensity Factors of an inclined edge crack originated at the tip of a sharp V-notch in a semiplane is presented. An analytical Weight Function with a matrix structure was derived by extending a method developed for an inclined edge crack in an unnotched semi-plane. The effects of the principal geometrical parameters governing the problem were studied through a parametric finite element analysis, carried out for different reference loading conditions. The Weight Function can be used to produce efficient and accurate evaluations of the stress intensity factors for cracks with inclination angle in the range −72°, +72° emanating from V-notches with opening angle in the range from 18° to 144°. For a crack length up to the 10% of the characteristic notch dimension, the maximum estimated error of the Stress Intensity Factor is lower than 2% (typical errors less than 1%) in the whole ranges of the angular parameters. The capability of the proposed method to analyse cracked notches in finite-size bodies was also considered. The agreement between the results with those obtained by accurate Finite Element solutions suggests that the proposed Weight Function can be used as a general tool for evaluating the Fracture Mechanics parameters of a short crack at any V-notch tip. [Copyright &y& Elsevier]

Abstract: A method for deducing the stress–strain uniaxial properties of metallic materials from instrumented spherical indentation is presented along with an experimental verification. An extensive finite element parametric analysis of the spherical indentation was performed in order to generate a database of load vs. depth of penetration curves for classes of materials selected in order to represent the metals commonly employed in structural applications. The stress–strain curves of the materials were represented with three parameters: the Young modulus for the elastic regime, the stress of proportionality limit and the strain-hardening coefficient for the elastic–plastic regime. The indentation curves simulated by the finite element analyses were fitted in order to obtain a continuous function which can produce accurate load vs. depth curves for any combination of the constitutive elastic–plastic parameters. On the basis of this continuous function, an optimization algorithm was then employed to deduce the material elastic–plastic parameters and the related stress–strain curve when the measured load vs. depth curve is available by an instrumented spherical indentation test. The proposed method was verified by comparing the predicted stress–strain curves with those directly measured for several metallic alloys having different mechanical properties. This result confirms the possibility to deduce the complete stress–strain curve of a metal alloy with good accuracy by a properly conducted instrumented spherical indentation test and a suitable interpretation technique of the measured quantities. [Copyright &y& Elsevier]

The present paper deals with the plastic deformation process into metallic materials occurring in the subindenter region during the loading cycle of spherical indentation test. Load-indentation-depth curve and plastic strains field evolution in the region beneath the indenter are examined using finite element analysis (FEA). The FE model was set up and validated by comparison with experimental spherical indentations carried out on two different materials (Al6082-T6, AISI H13) under four different friction conditions, corresponding to friction coefficients equal to 0.0, 0.1, 0.3, and 0.5. It is confirmed that friction effects on load-indentation-depth curves are negligible for the investigated penetration depths, whereas the plastic deformation process is affected by the contact conditions. The investigation shows that, although the L-h curve is not affected by the contact conditions up to medium values of the penetration depth, remarkable effects are produced in the overall plastic core under the indenter. A strong correlation between plastic strains field and friction coefficient is especially observed at low values of this parameter, whereas a saturation of the phenomena is found for medium-high values of the friction coefficient. [ABSTRACT FROM AUTHOR]