A pre-existing and inherited geostructural setting plays a fundamental role in preparingand developing large-scale slope deformational processes. These structures affect the kinematics ofthe process, the geometrical characteristics, and the geomorphological evolution. In the ApennineBelt, several deep-seated gravitational slope deformations (DSGSDs) that have evolved under aclear structural control have been recognized during the last decades, but none with a continuousand well-defined basal shear zone (BSZ). The structurally-controlled DSGSD of Luco dei Marsirepresents the first case of a DSGSD in the Apennine Belt with a well-defined BSZ. Starting from adetailed study of the process and the reconstruction of a morpho-evolutionary model of the slope, aseries of numerical modelings were performed for the study of the DSGSD. The analyses allowedus to reconstruct: (i) the mechanism of the process, (ii) the rheological behavior of the rock mass,and (iii) the main predisposing factors of the gravitational deformation. Numerical modeling hasdemonstrated the significant role played by the inherited structures on the DSGSD and, in particular,the importance of an intensely jointed stratigraphic level in the development of the BSZ.

Nickel base superalloys are candidates to be used in shafts for S-CO2 turbines for their excellent high temperature mechanical properties and corrosion resistance. In ICMATE-CNR in the framework of European Project H2020 SOLARSCO2OL, grant agreement n° 952953, several nickel-base superalloys are under investigation through creep tests, simulating the operational working conditions of a S-CO2 turbine.

In questo lavoro sono stati messi a confronto ed elaborati i risultati sperimentali di una campagna di prove di creep eseguita su una superlega di nichel policristallina Nimonic 263, dopo trattamento termico convenzionale ed in condizioni di invecchiamento (over-aging) ad alte temperature (fino a 3500h a 800°C). Tale confronto ha mostrato come la crescita dei precipitati, dopo invecchiamento, influenzi principalmente la prima parte delle curve di creep, con un aumento della velocità minima di creep e conseguente riduzione dei tempi a rottura. L'analisi delle curve di creep ha inoltre mostrato come il prodotto sigma*lambda, con sigma la sollecitazione applicata e lambda l'interdistanza tra le particelle gamma primo, risulti essere un buon parametro, nel campo di sforzi e temperature esplorate, per descrivere il lungo stadio terziario accelerante delle curve tipico di questa particolare classe di leghe. Infine, i risultati sperimentali sono stati utilizzati per verificare una equazione costitutiva in grado di stimare e prevedere l'effetto dell'accrescimento della particelle rinforzanti e dell'accumulo del danno correlato al procedere della deformazione.

The ovary is a dynamic mechanoresponsive organ. In vitro, tissue biomechanics was reported to affect follicle activation mainly through the Hippo pathway. Only recently, ovary responsiveness to mechanical signals was exploited for reproductive purposes. Unfortunately, poor characterization of ovarian cortex biomechanics and of the mechanical challenge hampers reproducible and effective treatments, and prevention of tissue damages. In this study the biomechanical response of ovarian cortical tissue from abattoir bovines was characterized for the first time. Ovarian cortical tissue fragments were subjected to uniaxial dynamic testing at frequencies up to 30 Hz, and at increasing average stresses. Tissue structure prior to and after testing was characterized by histology, with established fixation and staining protocols, to assess follicle quality and stage. Tissue properties largely varied with the donor. Bovine ovarian cortical tissue consistently exhibited a nonlinear viscoelastic behavior, with dominant elastic characteristics, in the low range of other reproductive tissues, and significant creep. Strain rate was independent of the applied stress. Histological analysis prior to and after mechanical tests showed that the short-term dynamic mechanical test used for the study did not cause significant tissue tear, nor follicle expulsion or cell damage.

Silicon resonators fabricated with wafer-level vacuum packaging on ultrathin silicon chips (overall thickness around 60 ?m) are utilized for strain measurements on steel slabs. The thinned chips are glued on steel using M-bond 610 and Loctite EA 9461 adhesives and the sensor response during bending tests performed while operating the resonators in closed loop is measured, evaluating possible non-ideal effects such as creep and hysteresis. In the measurements, the results obtained on the ultrathin chips are compared with those achieved on sensors manufactured on the native 500 ?m thick silicon substrates. The results obtained show an astonishing improvement in the measurements realized with the thinned chips, which show creep levels below 0.1%, no appreciable hysteresis phenomena and strain measurement range extended beyond 850 ??, indicating that chip thinning can be a viable way to obtain high-quality strain measurements on a large range by vacuum-packaged silicon MEMS resonators.

Nell'ambito del contratto (Prot. 510 del 28/02/2018) sono richieste frattografie ed analisi di microscopia su campioni di lega SF286 fornita da EXERGY S.p.A., sottoposti a specifiche prove di creep,concordate con lo stesso committente. I campioni sono ricavati da una barra di lega SF286 e hanno le dimensioni riportate in Fig. 1. Su uno dei campioni è stata eseguita anche una prova di trazione.

The EDDI testing program at ENEA RU has been delayed during 2019 by a series of problems. However, it has been resumed now and it will continue with the programmed tests in 2020. Tests already agreed are concerning creep tests in negligible creep domain of EUROFER97/2 alloy. The testing plan for 2020 has been updated with the latest indications.

A constitutive equation, with parameters derived from the interpolation of primary and steady state stages of constant load creep curves, has been utilized to estimate the stress relaxation behavior of the martensitic steel X20Cr13, alloy used in many high temperature applications, including heavy duty gas turbines. Creep and stress relaxation tests have been performed at 350 degrees C, close to the negligible creep temperature of the studied alloy for stresses of interest for engineering applications. The creep tests were carried out at stresses below and above the yield stress, whereas, for the relaxation stress tests, the imposed strain was in the range 0.2% to 1.2% with the purpose to have, at the beginning of the tests, the same initial stresses of the performed creep tests. After a stress relaxation period, lasting between 10 to 1000 hours, each specimen was generally reloaded at the initial stress and a new relaxation test, on the same specimen, was carried out. This "reloading procedure", simulating the re -tightening of bolts, has been repeated several times. The proposed equation has shown to well predict the experimental creep and stress relaxation behavior of the steel under investigation.

A mathematical model for an elastoplastic continuum subject to large strains is presented. The inelastic response is modelled within the frame of rate-dependent gradient plasticity for non-simple materials. Heat diffuses through the continuum by the Fourier law in the actual deformed configuration. Inertia makes the nonlinear problem hyperbolic. The modelling assumption of small elastic Green-Lagrange strains is combined in a thermodynamically consistent way with the possibly large displacements and large plastic strain. The model is amenable to a rigorous mathematical analysis. The existence of suitably defined weak solutions and a convergence result for Galerkin approximations is proved.

Nell'ambito del contratto sono state sviluppate frattografie dei campioni di lega SF286 fornita dal committente, sottoposta a prove di creep per combinazioni di stress e temeprature concordate con il committente stesso.

Risultati di prove di creep condotte tra 650°C e 1000°C su provini di superlega 247 LC

Presentazione e descrizione delle attività di ricerca della sede di Milano dell'Istituto di Chimica della Materia Condensata e di Tecnologie per l'Energia (ICMATE) - CNR

Le superleghe a base nichel monocristalline di interesse industriale mostrano un genere di instabilità microstrutturale che si presenta solo in modo limitato nelle superleghe policristalline. In particolare, le superleghe monocristalline con una elevata frazione volumetrica di particelle di fase indurente gamma' nella fase matrice gamma, se sottoposte a creep lungo le direzioni cristallografiche <001> ad alte temperature, possono sviluppare i cosiddetti "raft", vale a dire una struttura lamellare, gamma/gamma', perpendicolare alla direzione di applicazione del carico. Questo processo di coalescenza della fase gamma' può avvenire solo ad alte temperature: oper T <= 800°C, la tipica forma cuboidale delle particelle della fase gamma', ottenuta con il trattamento termico iniziale, è stabile anche per prove di creep di migliaia di ore; oper T vicino a 900°C, il processo di "raftatura" può essere lento e completarsi dopo una notevole percentuale della vita a creep del campione; oper T >= 1000°C il processo di "raftatura" può essere molto rapido ed avvenire entro 1-3% della vita del campione. L'obiettivo di questo lavoro è di analizzare criticamente l'effetto della evoluzione della morfologia della fase gamma' sul comportamento a creep della superlega TMS 75 [1], superlega di terza generazione, contenente Renio e sviluppata da NIMS (Tsukuba, Giappone), per l'utilizzo in palette di turbina a gas. L'analisi viene incentrata sulle temperature di 900 e 1100°C, temperature di rilievo per il caso di, rispettivamente, turbine a gas di tipo industriale e motori aeronautici ad alte prestazioni.

The creep behaviour of a new TiAl intermetallic alloy with 8 % in atom of Ta has been investigated under constant load and temperature conditions. The specimens have been creep tested in the temperature range of 700-850 °C and for specific applied stresses, in order to result in rupture times up to 3000 h. The alloy has been cast and properly cooled to enhance the massive transformation typical in such alloy. The sequent designed HIP treatments have been carried out to obtain a final convoluted alpha2 + gamma lamellar microstructure that ensures an adequate room temperature ductility, a critical parameter for intermetallic alloy applications. The material microstructure has been investigated through scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS) and X ray diffraction technique (XRD) to quantify the volume fractions of ?2 and ? phases and to link the microstructure evolution with the creep behaviour. To such aims the specimens have been analysed in the as-received conditions, after temperature exposure with no load applied, i.e. in the specimen heads, and in the gauges after ruptures. After depuration of the creep curves from the acceleration because of the true stress increase with strain, as it happens in constant load creep tests, an acceleration regime proper of the material has been put in evidence. Hence, at any temperature investigated, the alloy has not exhibited a real steady state regime, but a minimum in the creep rate with a significant primary and a dominant tertiary: applied stresses and minimum strain rates have been reported to follow a Norton relationships with exponents of about 7.8 and 4.9 in the temperature range boundaries of 700 °C and 850 °C, respectively. The creep alloy curves at different stresses and temperatures have exhibited the same shapes in plots epsilon vs. t/tR with tR equal to the rupture time, suggesting that the material has experienced the same creep strain correlated damage at any load and temperature. Interrupted creep tests at the minimum strain rates at 700 and 850 °C have been performed for microstructure investigations and comparison. Creep tests with load changes have been also run to have an insight on the nature of the deformation mechanism that controls the deformation.

Bolts in gas turbine units are often subjected to severe work conditions at high service temperatures, for which the relaxation of the initial stress, generated by the tightening couples, can become significant. Besides, since in such conditions re-tightening operations become necessary, the stress trend must be accurately calculated and predicted in order to avoid inappropriate value before every maintenance interval of the turbine. A constitutive equation based on the Continuum Damage Mechanics (CDM) formalism, describing the creep and stress relaxation behaviour of a martensitic steel, has been developed and evaluated. Creep tests were performed at 520°C with applied stresses producing a strain ? = 1 % in a time range of 1000-10000 h. The stress relaxation tests were performed at 520°C, with initial stress at 300 MPa corresponding to a strain in the range of 0.2 %. The specimens were reloaded several times in order to simulate the aforesaid service conditions of bolts. In this work it is proposed a set of equations, with parameters obtained by creep tests interpolation, able to accurately reproduce and well predict the experimental relaxation behaviour of the steel under investigation. The model, fitted on creep tests, includes a term accounting for the internal stress, entailing the capability to foresee the changes in stress relaxation during successive reloading of the same specimens (or, alternatively, during successive re-tightening of the same bolt). The advantage of such approach (i.e. calculating relaxation data from creep tests) consists mainly in the possibility to perform evaluations and assessments even without stress relaxation data, which are more expensive to collect experimentally and rarer to find in literature.

The aim of the following investigation is to evaluate the creep and low cycle fatigue (LCF) properties of DD417G, a new low density, Re free, nickel base superalloy for aeronautical gas turbine blades, developed by the Institute of Metals Research (IMR-CAS) Shenyang, PRC. Constant load creep tests have been carried out from 750 up to 1000°C, at stresses between 90 and 750 MPa to produce time to rupture up to 6000 hours. The creep behaviour of DD417G has been analysed in terms of times to rupture and shapes of the creep curves in function of the applied stress/temperature. Time to rupture: the experimental results are compared with competing alloys taking into account the low density of the here presented alloy. Creep curve shape: the experimental creep curves are characterised by a long predominant tertiary/accelerating creep, where the creep strain rate increases linearly with the accumulated strain, while the primary creep is small. The LCF tests, performed at 750°C and 850°C in longitudinal strain controlled conditions, have evidenced a fairly stable cyclic response. Basquin and Coffin-Manson relationships can adequately predict the fatigue life of the alloy. Examination of fracture surfaces revealed that fracture, induced by creep damage, is internal and mainly starts from eutectic island and pore-initiated cracks. However, fatigue damage starts on the external surface and propagates inward in stage II mode.

The nanobubble inflation method is the only experimental technique that can measure the viscoelastic creep compliance of unsupported ultrathin films of polymers over the glassrubber transition zone as well as the dependence of the glass transition temperature (Tg) on film thickness. Sizeable reduction of Tg was observed in polystyrene (PS) and bisphenol A polycarbonate by the shift of the creep compliance to shorter times. The dependence of Tg on film thickness is consistent with the published data of free-standing PS ultrathin films. However, accompanying the shift of the compliance to shorter times, a decrease in the rubbery plateau compliance is observed. The decrease becomes more dramatic in thinner films and at lower temperatures. This anomalous viscoelastic behavior was also observed in poly(vinyl acetate) and poly (n-butyl methacrylate), but with large variation in the change of either the Tg or the plateau compliance. By now, well established in bulk polymers is the presence of three different viscoelastic mechanisms in the glassrubber transition zone, namely, the Rouse modes, the sub-Rouse modes, and the segmental a-relaxation. Based on the thermorheological complexity of the three mechanisms, the viscoelastic anomaly observed in ultrathin polymer films and its dependence on chemical structure are explained in the framework of the Coupling Model. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

For many years several types of adhesives for load bearing structures have been designed and developed, but the admittance of these adhesives has been hindered. The reason for this is a lack of demonstrated long-time performance and the lack of a testing, approval and classification system. Two new European standards on glue laminated timber and cross laminated timber establish the use of phenolic (PF) and aminoplastic (MF) resins, one component polyurethane (PUR) and emulsion polymer isocyanate (EPI) adhesives. According to the standards, the adhesives have to fulfill many requirements, among others they must not unduly reduce strength and stiffness of engineered timber elements. Also the creep properties and performance at elevated temperatures must be taken into account. The purpose of this study is to explain the European assessment of a new structural adhesive and to analyze the bonding performance of a new PUR adhesive focusing on creep test. Creep performance frequently is a weak point for the PUR adhesives and no information is provided in the literature. Creep deformation test is performed as four point bending tests on specimens 50x50x600 mm that are subjected to a constant load of 4 000 N at weekly varying climate conditions. Specimens bonded with the tested adhesive are compared with specimens bonded with a PRF adhesive. Results show the behavior of the adhesive over one year trial and a statistic discussion is presented. The high bonding strength and particularly the good creep performance that can be achieved indicate that one component polyurethane adhesive has great potential in load bearing timber structures.

Nuclear high heat flux components (HHFCs) experience large thermal gradients and high heat flux variations, which induce severe thermal cyclic loadings. The most critical design issue for these components is their endurance strength under the required number of thermal cycles. The aim of this work is to provide procedures to perform the multiaxial creep-fatigue life assessment of HHFCs. Since the existing design codes present limitations due to simplifying assumptions concerning procedures for the multiaxial fatigue verification considering interactive effects of creep-fatigue and local stress and temperature conditions, better accurate verification methods and rules are developed starting from the available scientific literature and experimental data. The new verification methods identify the shape of the most damaging hysteresis loop considering plasticity and creep strains in both tensile and compressive conditions. The developed procedures are used to post-process the thermomechanical results of finite element (FE) analyses. They foresee the calculation of the creep-fatigue damage in each node and for each cyclic loading of the analyzed FE model by using the fatigue curve corresponding to the shape of the local hysteresis loop. Further more, the most fatigued elements are bounded and the causes of damage are identified to improve the local design. The fatigue damage is evaluated considering the effects of local conditions: temperature, multiaxial stressstrain state, strain intensity range, effect of local mean stresses, material shakedown, accumulated damage for multiple cyclic loads, combined effect of creep-fatigue, hold periods, and neutron flux. The developed procedures are successfully verified by comparing the results with experimental data for different levels of mean stress. This paper presents a description of the procedures and design rules focusing on the innovative aspects. The new procedures have been developed in the framework of the activities for the design, manufacturing, and procurement of the ITER neutral beam injector, and they are applied for creep-fatigue verifications of the in-vessel HHFCs.