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Anthropogenic climate change footprints in the ocean go beyond the mixed layer depth, with considerable impacts throughout mesopelagic and deep-ocean ecosystems. Yet, little is known about the timing of these environmental changes, their spatial extent, and the associated timescales of recovery in the ocean interior when strong mitigation strategies are involved. Here, we simulate idealized rapid climate change and mitigation scenarios using the Norwegian Earth System Model to investigate timescales of climate change onset and recovery and the extent of change in the North Atlantic (NAtl) interior relative to Pre-industrial (PI) variability across a suite of environmental drivers (Temperature—Temp; pH; Dissolved Oxygen—DO; Apparent Oxygen Utilization—AOU; Export Production—EP; and Calcite saturation state—Ωc). We show that, below the subsurface domains, responses of these drivers are asymmetric and detached from the anthropogenic forcing with large spatial variations. Vast regions of the interior NAtl experience detectable anthropogenic signals significantly earlier and over a longer period than those projected for the near-surface. In contrast to surface domains, the NAtl interior remains largely warmer relative to PI (up to +50%) following the mitigation scenario, with anomalously lower EP, pH, and Ωc (up to −20%) south of 30°N. Oxygen overshoot in the upper mesopelagic of up to +20% is simulated, mainly driven by a decrease in consumption during remineralization. Our study highlights the need for long-term commitment focused on pelagic and deep-water ecosystem monitoring to fully understand the impact of anthropogenic climate change on the North Atlantic biogeochemistry. publishedVersion

Dynamic characterization of vibrating targets represents a critical issue for many industrial fields. In this paper, a stereo-camera system integrated with a Digital Image Correlation (DIC) algorithm is proposed with the aim at performing 3D full-field vibration measurements in the range of kHz. The system exploits two industrial low-speed cameras, and the Nyquist-Shannon frequency limitation is overcome by a down-sampling approach under the hypothesis that the vibration signal is characterized by a single known frequency component. Experimental results obtained from the measurement of vibrational responses of a cantilever plate excited at three high-frequency resonance values (1121 Hz, 2956 Hz and 4010 Hz) are provided. A comparison with numerical analyses evidences the effectiveness of the proposed approach.

Residual stresses play a major role in the fatigue life and static strength of welded components. The high thermal gradient to which the material is subjected to during welding often leads to tensile residual stresses in critical notched regions. Residual stresses evaluation is crucial as they can cause unexpected failures or premature degradation of components, thus shortening the service life. Since determining their magnitude a priori is challenging, the experimental evaluation is fundamental when tensile residual stresses could be degrading for a component. The assessment of residual stresses can be performed through different techniques, all involving indirect measurements based on the detection of elastic deformation or displacement. In this context, a method belonging to the sectioning method category is proposed to calculate relaxed strains in a pipe-to-plate welded joint. The relaxed strains are determined by means of strain gauges placed on the upper surface of the plate nearby the weld bead. The results thus obtained represent strains measurements generated after an incremental hole cutting process performed on the bottom surface of the plate, opposite respect to the surface where the strain gauges were attached. Through this method, the calculated strains are related to the diameter and depth of the performed hole, as well as the location where the strain gauges are placed on the plate surface.

In the present work, the Fatemi-Socie approach is adopted in order to analyze the fatigue endurance of welded joints under multiaxial loads. This critical plane criterion has already been successfully applied to plain or notched components, however, it is not spread in the assessment of welded joints, yet. This work is focused on the practical implementation issues related to this particular application, which has not been discussed in the literature. The described procedure is adopted for the assessment of one hundred experimental tests and some preliminary results are shown. The specimen under investigation is a pipe-to-plate fillet joint made out of structural steel (S355JR). The tests were performed under both uniaxial and multiaxial, i.e. combined in-phase and out-of-phase bending and torsion, load conditions with a constant amplitude at the laboratories of the University of Pisa, Italy.

The Singh's advanced frequency evaluation (SAFE) diagram is a design tool commonly used to find and thus prevent bladed disk resonances, allowing those modal combinations with no match in terms of angular harmonic shape to be neglected. In principle, the SAFE diagram is based on the assumption that the disk structure is perfectly cyclic; hence, any degree of mistuning would prevent its validity. However, each natural mode of a mistuned bladed disk can be expressed as a superimposition of angular harmonic components. The numbers of nodal diameters of these harmonics are extracted as the discrete Fourier transform of the eigenvector. In this paper, a new graphical representation is proposed to account for this complete harmonic content, instead of just a single (main or nominal) number of nodal diameters as in the conventional SAFE diagram. In addition, the relative intensities of the modal components are shown in this generalized SAFE diagram, for an indication of the induced vibrational magnitude of each possible resonance. Numerical and experimental cases are presented, obtaining significant examples of the proposed diagram. Analyzing the signals of an aeromechanical test, unexpected resonances were observed, which were not predicted by the conventional SAFE, but were detected with the proposed diagram.

A deep understanding of the manufacturing process is needed in order to achieve safety and quality requirements for parts and components; to this regard, residual stresses play an important role in welded structures. Residual stresses are mainly caused by the extremely severe thermal cycle to which the welded metal and base material are subjected to during welding process and their knowledge leads to a better static and fatigue assessment of welded joints. This work deals with the study of residual stresses for a tube to plate T-joint, made of S355JR carbon steel. The work was carried out by both numerical simulations and experimental tests. The numerical simulations were performed by Ansys FE code through a structural-thermal full transient analysis to evaluate stress, strain and temperature in each node at each step of the simulation. The “birth and death” method was employed, together with temperature-dependent material properties.A2Danda3D simulation were performed, in order to evaluate possible differences due to the welding process. Numerical results were compared to some preliminary measurements obtained through an incremental cut made on the plate.

This review focuses on the analysis of numerical models aimed at predicting the residual stress-strain field produced by the selective laser melting process. Our first intent is to favor an intuitive understanding of the underlying physics and then to provide an overview of the available simulation strategies specifying their field of application. In fact, given the complexity and the multi-scale nature of the process, various tailored models are needed for the assessment and prediction of defects and manufacturing issues arising during the building phase. Regarding the estimation of residual stresses, the available models were reviewed and classified on the basis of the dimensional scale of the simulated phenomena. Meso-scale models perform the detailed simulation of the scanning process, but the high computational cost currently prevents their application on the whole build volume (the current limit on the scanning volume is approximately 100 mm3 with dynamic mesh coarsening techniques). Macro-scale models have been developed to overcome this limit by introducing deep simplifications of the thermo-structural problem. From our review, it appears that meso-scale modeling has reached a significant maturity, while a widely adopted strategy for macro-scale simulations has not emerged yet.

A deep knowledge of the production process is needed, in order to achieve quality and safety requirements in a component. In this context, residual stresses play an important role, especially in welded structures. The present work deals with the assessment of residual stresses in a S355JR carbon steel pipe-to-plate welded joint. Both numerical simulations and experimental tests were employed in order to gain wide-ranging knowledge. Numerical simulations were performed with the software Ansys © through an uncoupled (one-way coupling) thermal-structural simulation in order to evaluate the stress, strain and temperature at each node of the finite element model for each phase of the simulation. Temperature-dependent elastic-plastic material properties were adopted in combination with the element birth & death method, necessary to simulate the welding process. Two numerical weld seam solidification methods were employed and discussed, in terms of expected results and simulation performances. The obtained numerical results were compared with experimental data of relaxed radial strains measured nearby the weld seam.

Urease is the most efficient enzyme known to date, and catalyzes the hydrolysis of urea using two Ni(II) ions in the active site. Urease is a virulence factor in several human pathogens, while causing severe environmental and agronomic problems. Sporosarcina pasteurii urease has been used extensively in the structural characterization of the enzyme. Sodium sulfite has been widely used as a preservative in urease solutions to prevent oxygen-induced oxidation, but its role as an inhibitor has also been suggested. In the present study, isothermal titration microcalorimetry was used to establish sulfite as a competitive inhibitor for S. pasteurii urease, with an inhibition constant of 0.19 mM at pH 7. The structure of the urease–sulfite complex, determined at 1.65 Å resolution, shows the inhibitor bound to the dinuclear Ni(II) center of urease in a tridentate mode involving bonds between the two Ni(II) ions in the active site and all three oxygen atoms of the inhibitor, supporting the observed competitive inhibition kinetics. This coordination mode of sulfite has never been observed, either in proteins or in small molecule complexes, and could inspire synthetic coordination chemists as well as biochemists to develop urease inhibitors based on this chemical moiety.

The fatigue strength of pipe-to-plate welded joints under pure bending, pure torsion and combined (in-phase and out-of-phase) bending and torsion has been already investigated in previous works by the authors. The specimen consisted of a pipe joined by seam welding to a plate. Both the pipe and the plate were made of S355 steel. The test apparatus, making use of two independent hydraulic actuators, allows to apply any combination of proportional and non-proportional bending and torsion loads to the specimen. For the analyzed specimens failure originated mainly from the weld root, where a severe notch is present, even if some failure from the weld toe was observed in case of pure bending. The crack propagation and fracture surface under bending and under torsion are significantly different. For this reason, in order to highlight any possible influence of the loading order on the fatigue endurance, the effect of different loading sequences was analysed in this work. To the authors’ knowledge, this subject, which is of interest in case of complex loading histories, has not been widely investigated in the technical literature about welded joints. In a first series of tests, specimens were loaded in pure bending for a given fraction of the estimated endurance and, then, were loaded in pure torsion till failure. A similar series of tests was then conducted by varying the loading order: specimens were firstly loaded in pure torsion for a given fraction of the estimated endurance, followed by a sequence of pure bending till failure. The whole test campaign was repeated for two different fractions of the estimated life, i.e. 0.35 and 0.5. The failure was intended as the presence of a through the thickness crack, whose presence was monitored by a drop in the internal pressure of the pipe. Results are discussed in terms of the Miner’s rule based on nominal stresses as well as on equivalent stresses based on some multiaxial criteria.

The vibrational behavior of vehicles is a crucial issue for the comfort, especially for the professional vehicles. This paper presents a simplified modelling approach for studying the vibrational behavior of a lawn tractor. The vibrational response of a real vehicle is analyzed by an extensive experimental modal analysis and Finite Element model (FE) simulating the modal behavior of the whole tractor. The FEM was then validated by the comparison with the experimental results and then used for identifying the components and connections effectively driving the modal response. Based on these results, a simplified Multi-Body (MB) model, able to reproduce the vibrational response of the studied lawn mower, was then setup, showing good correspondences with experimental results. General guidelines for defining effective vehicles Multi-Body modal models were also derived.

A fatigue test series on a drill collar rotary shouldered connection, thread type 5-1/2 FH MOD, was performed with a dedicated alternating bending resonant test rig. Compared to a quasi-static testing approach, the dynamic loading allowed high testing frequency and a relatively light supporting structure. Crack initiation was identified as the onset of a discrepancy between two strain gauge signals which were monitored throughout the test. A through-wall crack condition was assumed as the effective fatigue failure. The stress distribution in the connection was then analysed with a finite element plane harmonic axisymmetric model, taking into account both the initial make-up torque and the alternating bending load during the test. In these simulations, the most critical stress between the pin or box, in terms of fatigue, mainly depended on the preload. The modelled contact behaviour of the incomplete threads of the box played a significant role in predicting the position of the crack initiation thread root, which was then compared with the test results.

This paper presents a comparison between two local methods that can be used for the fatigue life assessment of welded joints: the notch stress approach and the peak stress method. Even if they have been derived starting from entirely different theoretical backgrounds, both methods are based on the evaluation of a local stress acting at the notch tip of the seam weld, which is usually obtained through a finite element simulation. Said methods are applied to a collection of experimental data from three kinds of welded joints, which are characterized by different geometric parameters and, in particular, by a wide range of the element thickness. A total of 177 experimental tests are evaluated in this investigation, 31 of which are taken from literature while the other 152 are published here for the first time. The performance of the two methods is discussed in terms of the statistical dispersion in the analysed data. This is accomplished comparing the scatter bands obtained from a regression procedure in the S-N plot. In addition, some practical aspects related to the implementation of both methods are discussed, with particular attention to the ease of use offered, considering that this may represent a relevant aspect for the method’s diffusion in practical applications.

The shrink-fit connection undergoes fretting fatigue at the edge of the contact, where both stress concentration and micro-slip take place. A fretting test set-up with a round-shaped specimen is proposed that eliminates lateral edge contact and misalignment, and is also appropriate for deep rolling. Comparative experiments showed a notable strength improvement, induced by deep rolling, along with the beneficial effect of friction reduction due to lubrication. Multiple cracks with clear shallow paths were evident after SEM observation, thus the maximum shear stress amplitude was assumed as a correlating parameter, while the crack arrest was inappropriate especially for deep rolled specimens.

The fatigue resistance of a pipe-to-plate welded joint was investigated under combined in-phase and out-of-phase (changing principal directions) bending and torsion. The specimen consisted of a pipe having 64 mm outer diameter and 10 mm thickness, which is joined by fillet welding to a 25 mm thickness plate. The pipe and plate were made of S355 steel and the joint was not subjected to any after welding relieve treatment. This work represent an extension of a previous work by the authors, in which the fatigue resistance of the same joint was investigated under bending, torsion and combined in-phase loading. A new experimental arrangement, making use of two independent hydraulic actuators, was developed to have the possibility of making out of phase tests. Four series of tests were then carried out in the life range 10 5 – 2 · 10 6 , with two bending to torsion ratios (i.e. σ / τ = 3.25 and σ / τ = 0.88 ) and two load ratios (i.e. R = - 1 and R = 0 ). For the examined joint, failures originated from the weld root, where a severe notch is present. The results confirmed a lower fatigue endurance in case of out-of-phase loading, by a factor ranging from 2 to 8 depending on the number of cycles and on the adopted failure hypothesis.

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.

Experimental modal analysis is challenging when the component has a highly three-dimensional shape, since a great number of measurement points are needed with accurate positioning. An anthropomorphic robotic station is proposed to automate this analysis, specifically on bladed wheels. This provides a reliable control of the spot location and of the beam orientation of a Laser Doppler Vibrometer. The modal frequencies were obtained along with the vibrational shapes and their spatial resolution was managed by exploiting the programming flexibility of the robotic station. The SAFE diagram was easily obtained by measuring a single point for each sector, and an extension of this diagram was demonstrated for the splitter blade wheels. The use of multiple measurement points, for each wheel sector, significantly improved the characterization of the modes having the same number of nodal diameters, hence the same shape coordinate on the SAFE diagram.

With the increasing use of renewable energy sources, Gas Turbines (GTs) are currently required to accomplish more flexible operations for supplying the back-up energy. As a result, thermo-mechanical fatigue issues in the GTs components are emphasized. In this paper, the design of a novel rig for assessing the fatigue behavior in the trailing edge of full scale GTs blades is presented. Based on a detailed Finite Element (FE) analysis of the blade response under thermo-mechanical loads, it is demonstrated that the stress and strain cycles arising in this area during a start-up/shut-down transient can be accurately reproduced by clamping the blade in the shank zone and applying a transversal load to the trailing edge. It is also shown that the stress/strain states can be obtained using a Test Article (TA) extracted from the actual blade. In this configuration, the load magnitude and direction, and the distance of the application point from the blade platform are the test control parameters. A FE model simulating the TA test is developed to determine the test parameters. A tooling for clamping and loading the TA is finally proposed along with a rig apparatus consisting of standard equipment used in material testing.

The fatigue strength at a high number of cycles with initial elastic–plastic behavior was experimentally investigated on quenched and tempered 42CrMo4 steel. Fatigue tests on unnotched specimens were performed both under load and strain controls, by imposing various levels of amplitude and with several high load ratios. Different ratcheting and relaxation trends, with significant effects on fatigue, are observed and discussed, and then reported in the Haigh diagram, highlighting a clear correlation with the Smith–Watson–Topper model. High load ratio tests were also conducted on notched specimens with C (blunt) and V (sharp) geometries. A Chaboche model with three parameter couples was proposed by fitting plain specimen cyclic and relaxation tests, and then finite element analyses were performed to simulate the notched specimen test results. A significant stress relaxation at the notch root became clearly evident by reporting the numerical results in the Haigh diagram, thus explaining the low mean stress sensitivity of the notched specimens.

Bladed wheel dynamic characterization is a crucial issue to avoid resonance excitations. The test bench presented in this paper was designed to independently excite the wheel sectors with one electromagnetic shaker each blade. Since a wide frequency range (1–10 kHz) is usually considered for bladed wheels, custom electromagnetic devices were designed, and then a closed-loop control software was also implemented. The global mode shapes of the wheel were then reconstructed through subsequent accelerometer measurements on all sectors to evaluate the harmonic response. The main target of the test rig is the reproduction of any operational condition by experimentally simulating an arbitrary number of stator vanes. In this way the response levels of the differently excited modes are measured and the modal damping is optimally quantified by providing a selective excitation of any number of nodal diameters. Preliminary results showed how the test setup actually allows to excite those modes with a specific number of nodal diameters, however, also exposed some difficulties to avoid small load components with different numbers of nodal diameters.

The residual stress distribution induced by deep rolling depends on several factors: the material elasto-plastic curve, roller shape, indentation force and rolling feed. Among these, the force and the feed are those parameters that can be easily handled without cost or layout modifications. This paper shows an experimental investigation about these two parameters and a comparative analysis on the obtained residual stress profiles. The deep rolling treatment was performed on aluminium alloy 7075-T6 samples and the used tool was a carbide roller with conical and rounded contact. The residual stresses were measured by combining the hole drilling method and the X-ray diffraction technique. A first evident result was the large difference between the two principal residual stress components. The feed direction residual stress was almost a factor of two larger than the rolling direction residual stress. Parameter trends on residual stress distributions were investigated. The depth of the compressive region increased with the rolling force and the maximum stress position also tended to be subsurface, while for lower loads the maxima were at the surface. On the other hand, the feed parameter did not produce any effect at large depth, and just the initial subsurface distribution was slightly influenced. However, the surface hardness was noticeably affected by the feed, while the rolling force had a less predominant role. Finite element simulations were also carried out and reported in the paper, mainly to obtain information on induced work hardening. The plasticity depth was only affected by the load, indeed it was very similar to the compressive residual stress depth, while the maximum accumulated plasticity was significantly increased by the feed.

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.

The offset between the hole and the centre of the strain-gage rosette is unavoidable, although usually small, in the hole-drilling technique for residual stress evaluation. In this article, we revised the integral method described in the ASTM E837 standard and we recalculated the calibration coefficients. The integral method was then extended by taking into account the two eccentricity components, and a more general procedure was proposed including the first-order correction. A numerical validation analysis was used to consolidate the procedure and evaluate the residual error after implementing the correction. The values of this error resulted limited to a few percentage points, even for eccentricities larger than the usual experimental values. The narrow eccentricity limit claimed by the standard, to keep the maximum error lower than 10%, can now be considered extended by approximately a factor of 10, after implementing the proposed correcting procedure, proving that the effect of the eccentricity is mainly linear within a relatively large range.

A series of tests have been carried out using specimens made of a tube, having a thickness of t = 10 mm, joined to a plate by fillet welding. Two different kinds of specimen were employed, differing in the plate geometry (stiffness). Both kinds of specimen were tested under bending (prevalent load) and shear loading in as welded conditions. Different initiation regions for the fatigue cracks were found and significantly different fatigue resistances were obtained for the two geometries in terms of the nominal stress approach (or in terms of applied load vs cycles to failure). Two local methods for the fatigue life assessment were then applied to independently analyse the experimental results: the fictitious notch rounding approach proposed by Radaj, which is also recommended by some international standards and the more recently proposed peak stress method, which is based on the NSIF concept. It is shown that the nominal stress method, which is by far the simplest method among those recommended in standards for analysing the joint under study, fails to explain the observed different endurances. On the other side, the methods based on local stresses account for the different joint stiffness and provide a reduced scatter in the results. However, even if local approaches, accounts for differences in the structural behaviour of the joint, the knowledge of the actual geometry of the weld need to be accounted for, in order to be able to identify the fatigue crack initiation region. For a design purpose, a safe prediction of the fatigue endurance of the joint can be obtained by all the analysed methods, if the corresponding recommended design curve is used.

Fretting tests are usually performed on flat specimens with lateral contacting pads. The shrink-fitted connection, which experiences fretting at the edge of the contact, prompted the alternative use of a round-shaped specimen. This simplified the equipment and provided an accurate alignment between the fretting specimen and the external hub which plays the role of the pad. The deep rolling treatment can also be efficiently applied to a round shape, which would otherwise be difficult on the flat specimen geometry. After introducing this solution for fretting testing, the paper shows an experimental campaign on three shrink-fitted connections with different sizes and material combinations. There was a significant improvement in fretting fatigue strength, induced by the deep rolling, for all three specimen types. Finally, scanning electron microscopic analyses provided insights into the fretting fatigue nucleation mechanisms both for untreated and deep-rolled specimens.

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.

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.

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.

I compressori centrifughi di elevate dimensioni non permettono l’utilizzo di guarnizioni deformabili, per cui le due meta della flangia di connessione sono forzate mediante bullonatura e la tenuta e affidata al contatto completo delle due superfici. La previsione della pressione di perdita e un aspetto di progetto di notevole interesse per questa tecnologia. L’azione della pressione interna sollecita la separazione delle superfici della flangia, che invece e contrastata dall’azione di serraggio dei bulloni. Il presente lavoro propone un modello per prevedere la condizione di perdita, basato sulla meccanica della frattura. Dato che le due superfici della flangia sono semplicemente a contatto, esse costituiscono una vera e propria fessura parzialmente aperta. Come ben noto il fattore di intensificazione di una fessura parzialmente aperta e nullo. Imponendo che le due superfici siano parzialmente separate ad una distanza fino al bordo del foro del bullone (che offre un canale di fuoriuscita per il fluido in pressione), e imponendo la condizione di fattore di intensificazione nullo, e possibile determinare la pressione di perdita, analiticamente, mediante la tecnica delle “weight functions” (o “funzioni peso”). Il presente lavoro riporta una positiva validazione del modello proposto mediante sia simulazione numerica sia risultati sperimentali in piena scala e in scala ridotta. Il modello analitico proposto offre uno strumento di progetto di immediata implementazione per comparare diverse geometrie di flangia bullonata.

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 factors K I and K II could be evaluated. By considering different friction conditions between the crack surfaces and several crack inclinations, the evolutions of the effective K I and K II during typical loading cycles were analysed.

The paper presents two test rigs designed at the University of Pisa to perform bending fatigue tests on full scale drill pipe connections used for oil drilling. Two types of connection required different configurations of test rig. In both cases, specimen resonance was exploited in order to reduce the loads on the structure and the test duration. This allowed a cost reduction in both the experimental apparatus and tests. Results of fatigue tests are reported and discussed.

The effect of notch geometry on the propa- gation of fatigue cracks emanating from sharp V-shaped notches is investigated by means of an exper- imental campaign performed on Al-7075-T651 spec- imens carrying notches with opening angles of 45°, 90°, and 135°. The samples were tested using a servo- hydraulic machine under different loading directions and at several loading levels. The crack deflection in- duced by the variation in loading direction was deter- mined my measuring the kinking angle and by study- ing the crack propagation plane through fractographic analysis. A linear elastic fracture mechanics approach was adopted for the analysis of experimental results. Stress intensity factors were calculated using an ap- propriate weight function set up for studying inclined edge cracks emanating from sharp V-notches. The in- fluence of KII on the crack propagation was discussed on the basis of theoretical and semi empirical models.

The present paper proposes a new test rig to perform fretting fatigue tests on a shrinkfitted shaft assembly. A shrink-fitted shaft is put under rotating bending by means of an eccentric offset at one end. The shaft is driven near to its first resonance condition to significantly reduce the required force to produce bending. Test parameters are the imposed bending stress amplitude, and the hub radial pressure obtained through conical fitting. The proposed apparatus allows for changing bending stress amplitude and hub pressure to generate fretting fatigue tests at different conditions. In particular, the role of slip amplitude in fretting fatigue can be investigated. At the present stage the proposed apparatus is under construction at the Mechanical Department of the University of Pisa.

Large tubesheets are critical components of huge heat exchangers and have to be fabricated by welding together two or more pieces. These parts are previously drilled in order to get reasonable productivity, but are affected by welding-induced residual stress and distortion. The tube holes are important, as several thousand tubes will be fastened to them, so it is crucial to evaluate their welding distortion to properly design the manufacturing process. This paper presents a finite element simulation of multipass welding of large tubesheets in order to compute the induced tube hole distortions. A welding experiment was conducted on a reduced-scale structure, in order to calibrate and validate the numerical model. Good agreement was found between experimental and numerical data.

This study reports the development of a new open external vascular stent: the lock stent device (LSD). It enables a novel end-to-end sleeve anastomotic technique, named locked anastomosis (LA). The LA technique consists of inserting a graft sleeve within an artery, secured in place by an internal stent and an external LSD. The internal stent, graft, vessel wall, and LSD are fastened together with single sutures. The LSD placement does not require a complete transection of the vessel wall as it can be enlarged and then relaxed to clasp the vessel neck. The tensile strength of the LA technique was accurately measured ex vivo and its stability successfully tested in vivo by acute pressure peak tests and mid-term survival studies. Ex vivo, the ratio between the tensile strength of the LA technique with two, three, and six stitches and that of hand-sewn anastomoses was 0.41 +/- 0.02, 0.59 +/- 0.17, and 1.03 +/- 0.04. In vivo, LA anastomoses tolerated marked increases in blood pressure (peak systolic pressure 195-230 mm Hg) for periods of 15-25 min without leakage. Five pigs survived 10 weeks with abdominal aorto-aortic bypass performed according to the LA technique with three stitches. Aortograms showed no narrowing or thromboses, and histological findings confirm uniform flattening of the aortic wall at the anastomosis, with proliferating neointima and uniformly hypotrophic media. Minimal changes were observed in the adventitia.

The aim of the present paper is to propose an innovative hydrogenation method based on metal hydride dissociation. By heating metal hydride, high pressure of molecular hydrogen is generated, which can be used to promote diffusion through the steel, resulting in very high atomic hydrogen concentration. This new hydrogenation method was tested on a F82H steel, a Reduced Activation Ferritic/Martensitic (RAFM) steel developed for nuclear fusion application, where high temperature Hydrogen Embrittlement (HE) is a matter of serious concern. The main goal of this study is to propose a methodology to perform tensile tests on steel at high temperature and high hydrogen contents. The technique is easy and cheap. Furthermore, by using different metal hydrides and tuning temperatures, different hydrogen concentrations can be tested.

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.

This paper shows an automated procedure to experimentally find the eigenmodes of a bladed wheel with highly three-dimensional geometry. The stationary wheel is supported in free-free conditions, neglecting stress-stiffening effects. The single input / multiple output approach was followed. The vibration speed was measured by means of a laser-Doppler vibrometer, and an anthropomorphic robot was used for accurate orientation and positioning of the measuring laser beam, allowing multiple measurements during a limited testing time. The vibration at corresponding points on each blade was measured and the data elaborated in order to find the initial (lower frequency) modes. These modal shapes were then compared to finite element simulations and accurate frequency matching and exact number of nodal diameters obtained. Being the modes cyclically harmonic, the complex formulation could be attractive, being not affected by the angular phase of the mode representation. Nevertheless, stationary modes were experimentally detected, rather than rotating, and then the real representation was necessary. The discrete Fourier transform of the blade displacements easily allowed to find both the angular phase and the correct number of nodal diameters. Successful MAC experimental to analytical comparison was finally obtained with the real representation after introducing the proper angular phase for each mode.

In the present work closed form relationships for the power losses in rubber V-belt CVT are obtained, together with expressions for the axial thrust on both the driving and driven pulleys, starting from simple physical hypotheses. Losses have been grouped into three main contributions: frictional sliding losses, longitudinal and lateral material hysteresis and frictional losses due to the engagement/disengagement of the belt at the entrance and exit from the pulleys. In order to keep the model simple and to obtain a closed form solution, circumferential slip is assumed to take place mainly in the driven pulley and the sliding angle is assumed constant along the sliding portion of the contact arc. The model was validated through comparison with experimental results obtained on a dedicated test bench capable of measuring the transmitted torques and the axial thrusts on both pulleys, the pulleys rotating speeds and the total belt tension. The sliding angle γ and the damping coefficient Ψ, which were introduced in the analytical relationships, were determined by a best fit procedure on the basis of the obtained experimental results. After having obtained those parameters, the model appeared to be capable of reproducing with a fairly satisfactory agreement the power losses, as well as the axial loads on the pulleys, which were obtained in different operating conditions; thus it is proposed as a useful tool for the design of this kind of transmission.