1,721,099 research outputs found
Fatigue crack growth in ECAPed commercially pure UFG copper
No full textAbstractThis work presents the experimental characterization of the fatigue crack growth resistance of an ultrafine-grained (UFG) copper alloy with a purity level equal to 99.90%. The UFG copper has an average grain size of 300 nm obtained by a 8-passes ECAP process throughout route Bc. The crack propagation behavior is investigated by standard fatigue crack propagation tests conducted in air, at load ratio R=Kmin/Kmax varying from 0.1 to 0.7, on Disk Shaped CT specimens. The tests are conducted at stage I and stage II regime of crack growth rate. Results are partially in contrast with the few experimental data available in literature about this material. In fact, the present copper shows a relatively high fatigue crack resistance with respect to the conventional coarse-grained alloy, especially when increases the applied ΔK=Kmax−Kmin. The analysis of some fracture surface morphologies corresponding to different growth rates, is conducted to highlight the propagation mechanism. A diffuse crack deflection and branching is observed at high nominal R-ratio, that could explain the crack retardation. However, a better understanding is needed on the effective role of the grain size, of the dislocations density and of the impurities at the grain boundaries. A micromechanical model based on a statistically equivalent microstructure obtained with a Voronoi tessellation is under study by the author in order to clarify these aspects
Dispositivo per eccitazione forzata
No full textUn dispositivo per eccitazione forzata 10 comprende un
5 telaio 20, adatto ad ospitare gruppi rotanti 100 e
comprendente una base 21 atta ad essere collegata in modo
solido a strutture ed elementi costruttivi; tre gruppi
rotanti 100, applicati a detto telaio in modo che due tra
detti gruppi rotanti abbiano assi di rotazione giacenti su
10 un piano orizzontale e due tra detti gruppi rotanti abbiano
assi di rotazione giacenti su un piano verticale; un motore
400; mezzi di trasmissione 450, atti a trasmettere il moto
tra detto motore 400 e detti gruppi rotanti 100; detti
gruppi rotanti 100 comprendendo un albero 160; un mezzo di
15 trasmissione 110; un mezzo di connessione 140, adatto ad
assemblare detto gruppo rotante 100 su detto telaio 20; due
cuscinetti 130; un albero 170; due masse eccentriche esterne
180, comprendenti un mozzo adatto ad accoppiarsi con detto
albero 170 in modo da impedire tra essi moto rotatorio; una
20 massa eccentrica interna 190, comprendente un mozzo adatto
ad accoppiarsi con detto albero 170 in modo da impedire tra
essi moto rotatorio
A non-destructive, contactless technique for the health monitoring of ancient frescoes.
Full text linkIn this paper an innovative non-destructive, contactless technique applied to the health monitoring of ancient frescoes is presented. The problem of the health monitoring of artistic frescoes without a direct interaction with structures and paintings is of great concern in the field of art restoration and preservation. In artistic frescoes, the partial detachment of plaster portions is a typical and serious problem. Both layer-to-layer detachments and delaminations and surface cracks are usually present in ancient wall paintings. At present, the standard procedure of diagnosis consists of manual inspection, but produces only approximate information. This paper describes an acoustic, non-invasive, experimental technique of diagnosis, based on the acoustic-structural interaction which occurs when a fresco wall is excited by a loudspeaker. The analysis of the acoustic pressure field and of its alterations allows the assessment of detachments, since the acoustic modal parameters are affected by the acoustic system boundary conditions, i.e. the portion of analyzed fresco. The reconstruction of the modal behavior of the analyzed portion of the fresco is made by a scanning laser Doppler which measure the velocity field of the observed surface. It is a non-contact measure technique that provides a great accuracy. Experiments carried out on fresco artificial specimens show the potential of the technique
Fatigue crack growth resistance of ECAPed ultrafine-grained copper
No full textThis work presents the experimental results of fatigue crack growth resistance of ultrafine-grained (UFG) copper. The UFG copper has a commercial purity level (99.90%) and an average grain size of 300 nm obtained by a 8-passes route Bc ECAP process. The fatigue propagation tests are conducted in air, at load ratios R = Kmin/Kmax varying from 0.1 to 0.7, on small Disk Shaped CT specimens. Both stage I and stage II regime of growth rate are explored. Results are partially in contrast with the few experimental data available in the technical literature, that are by the way about high purity UFG copper. In fact, the present material shows a relatively high fatigue crack resistance with respect to the unprocessed coarse-grained alloy, especially at high values of applied stress intensity factor ΔK. At higher R-ratio a smaller threshold intensity factor is found, together with a lower stage II fatigue crack growth rate. The explanation of such crack growth retardation is based on a diffuse branching mechanism observed especially at higher average ΔK
Micromechanical modeling of the elasto-plastic behavior of heterogeneous nodular cast iron
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