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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]

The paper describes a test rig designed to check and assess the accuracy of the incremental hole drilling (IHD) method. An external load produces a controlled linearly through thickness variable uniaxial stress field (reference bending stress), known with good accuracy, that can be applied and removed at each hole increment. After the separation between the bending relaxed strain from the residual stress relaxed strain, it is possible to reproduce the bending stress distribution in order to have complete confidence of the residual stress measurement. The bending verification of the IHD method was already proposed by other investigators before, but residual stress measurements were then performed on independent configurations. The proposed testing procedure gives a 'real time' verification of the residual stress measurement. Any experimental malfunctioning due to the operator inexperience, or any error during the stress calculation from the relaxed strain would produce an evident difference between the expected reference bending stress and the IHD bending stress output. Moreover, the reference bending stress helped for understanding that the not perfect hole cylindrical shape causes an underestimate of the predicted stress near the surface. A zero depth offset correction was proposed. This correction was tested on the reference bending stress, and then applied to the residual stress prediction. Three shot peening residual stresses IHD measurements were successfully validated by means of the bending stress; moreover, they were in good agreement with independent X-ray diffraction measures also proposed in the paper. [ABSTRACT FROM AUTHOR]

Residual stresses play a fundamental role in predicting the resistance of several structural components, in particular when operating under alternating loads or in aggressive environments. Among the measurement techniques, the hole-drilling method is unrivalled in terms of cost and flexibility. The currently available data reduction techniques do not account for some important parameters, in particular the hole eccentricity, and can be directly used only with certain rosettes or require the partial holes to be drilled at fixed depths. This paper presents a general approach for interpreting hole-drilling measurements that includes the hole eccentricity and several other geometric and material parameters. The method is based on analytical influence functions relating the measured relieved strains to the residual stress by means of integral equations. By elaborating the results of accurate finite-element simulations, continuous analytical influence functions are produced, which can be used to reduce the error in the reconstructed residual stress. We focus on the definition of the influence functions, their evaluation and assessment. [ABSTRACT FROM AUTHOR]

This part deals with the applications of the influence functions developed in part I to solve the inverse problem of determining residual stresses from the measured relaxed strains. The effects of the hole eccentricity and the number of strain gauges on the accuracy of the reconstructed residual stresses are considered for typical experimental conditions. Influence functions for eccentric holes reduce the error in the reconstructed residual stress for typical experimental conditions below 1%, instead of 10% which would be obtained neglecting the eccentricity. The analysis was also applied for comparing the performance of three- and six-element rosettes for compensating eccentricities. When the eccentricity is not included in the elaboration, six-element rosettes with couples of opposite strain gauges halve the error committed by using the equivalent three-element rosette. However, if the eccentricity is included in the influence functions, the three element rosette can predict with a smaller error. [ABSTRACT FROM AUTHOR]

The problem of a two-dimensional elastic body, carrying an inclined edge crack and loaded by a cylinder rolling on the surface, is solved by the weight function method. The load induced by the cylinder on the cracked body was represented by the Hertzian pressure distribution, and the nominal stress distribution in the uncracked body was numerically evaluated by the superposition principle. The crack opening displacement components were obtained by an analytical Green's function. The partial crack closure was considered and the influence of the mutual forces between the crack faces included in the analysis, by which the effective stress intensity factorsKI andKII could be evaluated. By considering different friction conditions between the crack surfaces and several crack inclinations, the evolutions of the effectiveKI andKII during typical loading cycles were analysed. [ABSTRACT FROM AUTHOR]

This paper is aimed at evaluating the behaviour of small cracks emanating from notches in the Ti-6Al-4V alloy. Pulsating four point bending tests were performed at a nominal stress ratio of 0.1 and a frequency of 15 Hz on prismatic specimens with a central hole. The conditions of initiation and early propagation of fatigue cracks were investigated at two relatively high nominal stress levels corresponding to 56.6 and 100% of the 0.2% yield stress of the material. Microstructural effects were discussed. To this purpose a specific device based on the ‘in situ’ detection of cracks by photomicroscopy was developed. Corresponding results were analysed quantitatively considering the effect of the yielded region at the notch tip by elastic–plastic finite element modelling. Furthermore, information regarding the sites of fatigue crack initiation and propagation path were discussed on the basis of careful fractographic analysis of the specimens. The importance of the two phase α, β microstructure on the material damage was highlighted and correlated to the observed oscillations in the crack growth rate. Mechanically and microstructurally long cracks were correlated by linear-elastic fracture mechanics. [ABSTRACT FROM AUTHOR]

Background: Ropivacaine is a new local anaesthetic, which compared to bupivacaine is less toxic and shows greater sensory and motor block dissociation. We hypothesised that treatment of postoperative pain with a combined regimen of continuous epidural infusion and Patient-Controlled Epidural Analgesia (PCEA) using ropivacaine could have given better results compared with those we had obtained using bupivacaine.Methods: Patients undergoing total hip replacement were randomly assigned to two groups. They received epidural analgesia for postoperative pain treatment using ropivacaine, 2 mg x ml(-1) or bupivacaine 2 mg x ml(-1). Both drugs were administered as a constant infusion of 6 ml x h(-1) supplemented by PCEA bolus doses of 2 ml. Patients in both groups received morphine intravenously on demand from a patient-controlled analgesia (PCA) device. An independent observer recorded pain scores, intensity of motor block and morphine consumption at regular intervals during the first 24 h after surgery.Results: Fifty-one patients were evaluated. Ropivacaine and bupivacaine, in similar amounts, provided similar results assessed as adequate to very good postoperative analgesia, whereas motor block was significantly more intense in patients treated with bupivacaine.Conclusions: Despite similar analgesic effects, epidural infusion of ropivacaine combined with PCEA provides higher patient satisfaction than equal doses of bupivacaine due to lack of motor block. [ABSTRACT FROM AUTHOR]

Five species of white truffle were classified using PCR-based techniques. RAPD (random amplified polymorphic DNA) fingerprints and specific pairs of primers were used. A RAPD fragment was constant in Tuber borchii Vittad. isolates and polymorphic among the other species. Two molecular markers specific for T. borchii were developed from the sequence of the non-polymorphic RAPD fragment and from regions flanking the 5'-3' ends of a truffle gene. These markers were applied in the identification of T. borchii fruit bodies, mycelia and mycorrhizas, allowing us to monitor the development of this fungus during its entire life cycle. [ABSTRACT FROM AUTHOR]

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