Micromechanical investigation of the influence of defects in high cycle fatigue

This study aims to analyse the influence of geometrical defects (notches and holes) on the high cycle fatigue behaviour of an electrolytic copper based on finite element simulations of 2D polycrystalline aggregates. In order to investigate the role of each source of anisotropy on the mechanical response at the grain scale, three different material constitutive models are assigned successively to the grains: isotropic elasticity, cubic elasticity and crystal plasticity in addition to the cubic elasticity. The significant influence of the elastic anisotropy on the mechanical response of the grains is highlighted. When considering smooth microstructures, the crystal plasticity have has a slight effect in comparison with the cubic elasticity influence. However, in the case of notched microstructures, it has been shown that the influence of the plasticity is no more negligible. Finally, the predictions of three fatigue criteria are analysed. Their ability to predict the defect size effect on the fatigue strength is evaluated thanks to a comparison with experimental data from the literature

Effect of defect size and shape on the high-cycle fatigue behavior

This study aims to examine the effects of both material microstructure and voids on the high-cycle fatigue behavior of metals. To deal with this matter, finite element analyses of polycrystalline aggregates are carried out, for different configurations of crystalline orientations, in order to estimate the mechanical state, at the grain scale, in the vicinity of a small elliptical hole. Fatigue criteria are then applied to estimate the average fatigue limit in fully reversed tension, for different defect sizes and ellipse aspect ratios.The constitutive models and the fatigue criteria are calibrated using experimental data obtained from specimens made of 316L austenitic steel. The estimations are then compared with the experimental trends

Perfluorocyclohexene bridges in inverse DiArylEthenes: synthesis through Pd-catalysed C-H bond activation, experimental and theoretical studies on their photoreactivity.

International audienceThe palladium-catalysed direct di-heteroarylation of 1,2-dichloroperfluorocyclohexene with a variety of heteroarenes gives rise in to a new family of 1,2-di(heteroaryl)perfluorocyclohexenes. These derivatives do not exhibit photoreactivity and this unexpected outcome is explained by calculations demonstrating the lack of reactive isomers

Switching of excited states in cyclometalated platinum complexes incorporating pyridyl-acetylide ligands (Pt-C[triple bond, length as m-dash]C-py): a combined experimental and theoretical study

International audienceThis article presents the design of cyclometalated platinum(II) complexes incorporating pyridyl-appended acetylide ligands of the form Pt-C[triple bond, length as m-dash]C-py, acting either as sites for protonation or methylation reactions or as a host receptor for binding metal cations. The complexes studied are Pt(t-Bu2phbpy)(-C[triple bond, length as m-dash]C-py), 2, which can undergo protonation at the pyridyl N; its cationic N-methylated derivative [Pt(t-Bu2phbpy)(-C[triple bond, length as m-dash]C-pyMe)]+, 4, which serves as a model of the N-protonated species; and a derivative in which the pyridyl ring is incorporated into a macrocyclic diamide-crown ether ligand (3). The co-ligand t-Bu2phbpy is a cyclometalated, N[caret]N[caret]C-coordinated phenylbipyridine ligand carrying tert-butyl groups at the 4-positions of the pyridyl rings. The photophysical properties of the neutral compounds 2 and 3 have been compared to those of the pyridinium, methyl-pyridinium or metal-complexed species (namely 2-H+, 4 and 3-Pb2+). Detailed TD-DFT calculations provide a theoretical basis to account for the experimentally-observed changes upon protonation/methylation/complexation. The joint TD-DFT and experimental studies provide evidence for an unprecedented molecular switch in the nature of the excited state (from mixed L′LCT/MLCT to ML′CT) in which the acceptor ligand in the CT process switches from being the N[caret]N[caret]C ligand to the pyridyl acetylide

Cyclometallated platinum(II) complexes containing pyridyl-acetylide ligands: the selective influence of lead binding on luminescence

International audienceThe design, synthesis, photophysical properties, and the ion-binding properties of cyclometallated platinum(II) complexes containing pyridyl-appended alkynyl ligands are described. When the pyridyl group is incorporated into an azamacrocycle, a specific response towards lead(II) cations involves a change in the nature of the excited charge transfer state, resulting in the appearance of a low-energy absorption band and a partial quenching of luminescence

An unprecedented family of luminescent iridium(III) complexes bearing a six-membered chelated tridentate C^N^C ligand

C.H. acknowledges the Région Bretagne, France for funding. EZ-C acknowledges the University of St Andrews and EPSRC (EP/M02105X/1) for financial support. The authors thank the EPSRC UK National Mass Spectrometry Facility at Swansea University for analytical services. T.R. thanks the FEDER funds for financial support helping the acquisition of the D8Venture diffractometer of ISCR. D.J. acknowledges the European Research Council and the Région des Pays de la Loire for financial support in the framework of a Starting Grant (Marches - 278845) and the LUMOMAT RFI project, respectively. This research used computational resources of 1) the GENCI-CINES/IDRIS, 2) the CCIPL (Centre de Calcul Intensif des Pays de Loire), 3) a local Troy cluster.A new family consisting of three luminescent neutral Ir(III) complexes with the unprecedented [Ir(C^N^C)(N^N)Cl] architecture, where C^N^C is a bis(six-membered) chelating tridentate tripod ligand derived from 2-benzhydrylpyridine (bnpy) and N^N is 4,4'-ditert-butyl-2,2'-bipyridine (dtBubpy) is reported. X-ray crystallography reveals an unexpected and unusual double C-H bond activation of the two distal non-conjugated phenyl rings of the bnpy coupled with a very short Ir-Cl bond trans to the pyridine of the bnpy ligand. Depending on the substitution on the bnpy ligand, phosphorescence, ranging from yellow to red, is observed in dichloromethane solution. A combined study of density functional theory (DFT) and time-dependent DFT (TD-DFT) corroborates the mixed charge-transfer nature of the related excited-states.Publisher PDFPeer reviewe

Micromechanical modeling for the probabilistic failure prediction of stents in high-cycle fatigue

The present paper introduces a methodology for the high-cycle fatigue design of balloon-expandable stents. The proposed approach is based on a micromechanical model coupled with a probabilistic methodology for the failure prediction of stents. This allows to account for material heterogeneity and scatter, to introduce a fatigue criterion able to consider stress gradients, and to perform a probabilistic analysis to obtain general predictions from a limited number of realizations of microstructures investigated. Numerical simulations have allowed to highlight the noteworthy characteristics of the mechanical response in the stent as well as the heterogeneity of the mechanical fields due to stress concentrations in the unit cell geometry and to strain incompatibilities between the grains induced by the anisotropy of their mechanical behavior. The predicted survival probability of the stent is in accordance with the experimental data from the literature. Moreover, the influence of the amplitude of the arterial pressure on the fatigue strength of the stent has been evaluated.This work is funded by the French National Research Agency (Project Fast3D-ANR-11-BS09-012-01) and by the Fondazione Cariplo(Grant 2013-1779). The authors would like to acknowledge Dr. Michele Conti for his useful advice and for providing the three- dimensional stent mesh used in the present work

Sequential double second-order nonlinear optical switch by an acido-triggered photochromic cyclometallated platinum(ii) complex.

International audienceAn unprecedented DTE-based Pt(II) complex, 2(o), which stands as the first example of a sequential double nonlinear optical switch, induced first by protonation and next upon irradiation with UV light is presented

Bay-region functionalisation of Ar-BIAN ligands and their use within highly absorptive cationic iridium(III) dyes

E.Z-C thanks EPSRC (EP/M02105X/1) and NSERC for financial support. F.G. and H.S.S. would like to thank A*STAR AME IRG (A1783c0003) for financial support. F.G. also thanks NTU start-up grant (M4080552) and MOE Tier 1 grant (M4011441). H.S.S. is supported by a NTU start-up grant (M4081012), MOE Tier 1 grants (M4011611), and the Nanyang Assistant Professorship (M4081154). C. H. acknowledges the Région Bretagne for funding. H.S.S. also thanks the Solar Fuels Laboratory at NTU and the Singapore-Berkeley Research Initiative for Sustainable Energy (SinBeRISE) CREATE Programme.We report the synthesis, optical absorption, electrochemical characterisation, and DFT studies of five panchromatic, heteroleptic iridium complexes (four of which are new) supported by Ar-BIAN ligands. In particular, the synthesis of an ester-functionalised Ar-BIAN ligand was carried out by a mechanochemical milling approach, which was advantageous over conventional metal templating solution methods in terms of reaction time and product purity. The introduction of ester and carboxylate functionalities at the bay region of the acenaphthene motif increases each ligand’s π- accepting capacity and imparts grafting capabilities to the iridium complexes. These complexes have absorption profiles that surpass the renowned N3 dye [Ru(dcbpy)2(NCS)2] (dcbpy = 4,4’-dicarboxy- 2,2’-bipyridine), making them of interest for solar-energy-harvesting applications.Publisher PDFPeer reviewe

Photoswitching of the second-order nonlinearity of a tetrahedral octupolar multi DTE-based copper(I) complex.

International audienceThe modulation of the quadratic NLO response of an octupolar metal-based chromophore featuring four photochromic dithienylethene units is reported. Quantum mechanical simulations are consistent with a full switching of the DTE units and reproduce the strong enhancement of the NLO response