1,721,013 research outputs found
Constitutive equations to correlate uniaxial creep behaviour vs stress and temperature for inconel 718
Full text linkThe paper presents uniaxial creep tests conducted on Inconel 718 superalloy, reporting and describing the results obtained. The creep strain curves have been examined in different scenarios: by varying the initial applied stress, by varying the initial test temperature, and by considering the orientation of the specimens with respect to the direction of the material processing. Finally, ductility and deformation accumulation rate have been evaluated to highlight the effect of the precipitation anisotropy on the creep behaviour. Given the complexity of the creep phenomenon, each phase of the creep strain curves of Inconel 718 has been analysed independently, using constitutive models taken from the literature that allow to describe the phenomenon in pure metals and in some alloys
The Magnetoelastic Contribution to the Steel Internal Damping
Full text linkIn this paper, the steel internal damping due to both the thermoelastic and the magnetoelastic phenomena has been investigated through a formulation based on thermodynamical potential joints with a hysteretic damping model. With the aim of focusing on the temperature transient in the solid, a first configuration has been considered, which is characterized by a steel rod with an imposed alternating pure shear strain in which only the thermoelastic contribution was studied. The magnetoelastic contribution was then introduced in a further configuration, in which a steel rod in free motion was subjected to torsion on its ends in the presence of a constant magnetic field. A quantitative assessment of the influence of the magnetoelastic dissipation in steel has been computed according to the Sablik-Jiles model by giving a comparison between the thermoelastic and the prevailing magnetoelastic damping coefficients
Cohesive surface model for delamination and dynamic behavior of hybrid composite with SMA-GFRP interface
Full text linkThe interface model between CuZnAl SMA and GFRP, used in a hybrid composite, is proposed using cohesive surfaces. Using this model and derived parameters, mode-II delamination is studied between CuZnAl SMA insert and GFRP and also between laser patterned CuZnAl SMA insert and GFRP. Natural frequency and damping ratio of the hybrid composite specimen, in the shape of slender beam in a cantilever configuration, are evaluated in impulse tests. A numerical model is also presented, to calculate the aforementioned dynamic properties numerically, using Modal Strain Energy (MSE) and Modal Dynamics procedures by considering the derived interfacial parameters
Analysis of the failure of a tramcar pantograph component through combined experimental approaches
No full textTramcar vehicles collect the required electrical power from the overhead contact line by means of a pantograph that carries a pan head with collector strips in sliding contact with the contact wire. Therefore, any failure of pantograph or of its components has a direct effect on the correct tramcar operation. The paper deals with a case of unexpected failures occurred on a connection element of the articulated frame of the pantograph of tramcars, causing the interruption of the service. No evidence of impact with the overhead line was detected, only it was clear that the immediate cause was the fatigue failure of a pin of the articulated connection between the upper and the lower arms of the frame of the pantograph. To clarify the original cause of the fatigue failure, an approach combining field measurements, laboratory tests and data processing to obtain the stresses acting on the pantograph failed components under service condition was adopted. It was found that the pantograph was subjected to high level of vibrations coming from the vehicle carbody, mainly due to the track irregularity. A comparative failure analysis was carried out and a solution to upgrade the component subjected to failure was proposed and implemented
Investigation of shape memory alloy embedded wind turbine blades for the passive control of vibrations
No full textThis paper investigates hybridized architectures of large wind turbine blade material with the aim to passively suppress uncontrolled vibration. The laminate composite layup of the blade was hybridized by embedding shape memory alloy (SMA) layers, in areas which are recognized as having a major role in the dissipation of energy. The embedded SMA thin sheet was laser patterned in order to improve the interface adhesion and to tailor the flexural stiffness requirement. The response of the blade with new architecture has been investigated in the time domain, to find an optimal composite layup in which the smallest amount of SMA is used while system damping is being maximized
Application of SMA Composites in the Collectors of the Railway Pantograph for the Italian High Speed Train
No full textResidual-stress, material characterization in p22 hrsg-pipeline butt joint
Full text linkPrevious study evaluated residual stress in a circumferential “V”-groove butt joint of a heat-recovery steam generator (HRSG) pipeline; the material was ASTM A-335-Grade P22. Aim had been to check on the influence over creep-relaxation previously found out for a tee made of the same material. The butt joint had been operating for the same period of 200,000 hours, same temperature of 528°C at almost a half pressure (0.46 Kg/mm2 vs. 1.06 Kg/mm2). X-ray diffraction (XRD) technique applied close to the weld highlighted anomalously high stress-level on the outer surface for all four butt-joint samples tested. Residual-stress over 400 MPa observed along the cylinder's tangential direction was statically not acceptable. On the inner surface where deposited beads may have tempered adjacent base material, measurement via blind hole-drilling (BHD) technique showed a symmetrical plane-state residual-stress of 199 MPa. It was consistent with that observed via XRD on the outer surface in the cylinder's longitudinal direction. Supposing a case of incomplete post heating planned for the weld may have explained the occurrence of being much higher than 40 MPa, value predicted after 200,000 hours. Similar influence over creep results found out for the tee and the butt joint had validated modeling welding simulation considered for both joints. A comprehensive new series of XRD tests aims now at measuring residual stress across the cylinder's wall, both inner and outer sides. The shallow layer considered has thickness sufficient for building a map of measurements covering different depths and locations on the surface. The experimental plan includes also BHD tests supporting the XRD ones. Comparison with previous measurements roughly shows stress level increasing similarly across the cylinder's wall from the inner side on: Average stress values, however, appear lower than previous measurements, showing better compatibility to the analysis results
Characterization of CuZnAl SMA/ glass fiber composite material for vibration suppression
No full textIn this work the functional characterization of an innovative composite material, suitable for passive suppression of flexural vibration of beams and shells, is presented and studied. Two patterned thin sheets of Cu66Zn24Al10 (at.%) Shape Memory Alloy (SMA) are embedded into a layered beam, made of glass fiber. The proposed composite combines the density and stiffness of the glass fiber with the high damping properties of SMA, in the martensitic state. A patterning of the SMA sheets, designed and optimized in order to improve the adhesion between SMA and glass fiber, is performed by means of laser technology, using a nanosecond fiber laser. The effect of the laser microcutting process on transformation temperatures and internal friction properties of the SMA elements are analyzed, respectively using DSC and DMA. Moreover, measurements of the structural damping of the layered glass fiber/SMA composite are reported and the capability of the produced composite material to suppress the flexural vibrations is shown. The main conclusion of this work is the improvement of the structural damping properties of the discussed composite material, thanks to the high internal friction of SMA sheets in the martensitic state
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