The Experts below are selected from a list of 1386 Experts worldwide ranked by ideXlab platform
Sylvain Calloch - One of the best experts on this subject based on the ideXlab platform.
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Fatigue performance of superelastic NiTi near stress-induced martensitic transformation
International Journal of Fatigue, 2017Co-Authors: Eduardo Alarcon, Petr Šittner, Ludek Heller, Shabnam Arbab Chirani, Jaromír Kopeček, Luc Saint-sulpice, Sylvain CallochAbstract:The structural fatigue of superelastic NiTi was studied with special attention paid to the drop in fatigue performance commonly observed at the onset of the stress-induced martensitic transformation. We processed the superelastic NiTi wires into an hourglass shape as a result of which the stress induced martensitic transformation in tension is not localized as confirmed by digital image correlation measurements. The hourglass shaped samples were subjected to force controlled pull-pull fatigue tests at two distinct temperatures selected to investigate the fatigue of NiTi with and without the R-phase transformation involved, and to capture the effect of varying critical stress for the onset of B19′ martensitic transformation. Resulting fatigue curves expressed in terms of both the stress and the strain show a first degradation of fatigue performance at stresses more than 200 MPa below the onset of the martensitic transformation. Furthermore, fatigue curves showed a temperature dependence which was successfully implemented into a modified Basquin’s power law model. Notably, the fatigue life drops down to 104 cycles before the nominal loadings reach the B19′ transformation regime. We further found that fatigue life is shorter for the B2-R-phase transformation regime than for the elasticity of the parent B2 austenite phase at low stresses when strains remain below 1%, however at higher strains the B2-R-phase transforming wire is better than the elastic one. Fatigue Crack observations revealed Crack initiation at the surface and its propagation towards the bulk resulting in a reduction of the cross-section and substantial increase in normal stresses. Martensitic transformation was triggered during the Crack Growth in samples nominally loaded in elastic or R-phase transformation regimes as confirmed by in-situ infrared thermography. As the Crack grows with increasing speed, the activity of transformation processes at the tip gradually increases till Unstable Crack Growth and final rupture occurs, as confirmed by in-situ thermography and stress hysteresis observations. The analysis of fracture surfaces revealed five different Crack Growth regimes - from quasi-cleavage at early Crack Growth, through propagation stage evidenced by striations, till the final ductile fracture evidenced by the typical fracture surface morphology.
Eduardo Alarcon - One of the best experts on this subject based on the ideXlab platform.
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Fatigue performance of superelastic NiTi near stress-induced martensitic transformation
International Journal of Fatigue, 2017Co-Authors: Eduardo Alarcon, Petr Šittner, Ludek Heller, Shabnam Arbab Chirani, Jaromír Kopeček, Luc Saint-sulpice, Sylvain CallochAbstract:The structural fatigue of superelastic NiTi was studied with special attention paid to the drop in fatigue performance commonly observed at the onset of the stress-induced martensitic transformation. We processed the superelastic NiTi wires into an hourglass shape as a result of which the stress induced martensitic transformation in tension is not localized as confirmed by digital image correlation measurements. The hourglass shaped samples were subjected to force controlled pull-pull fatigue tests at two distinct temperatures selected to investigate the fatigue of NiTi with and without the R-phase transformation involved, and to capture the effect of varying critical stress for the onset of B19′ martensitic transformation. Resulting fatigue curves expressed in terms of both the stress and the strain show a first degradation of fatigue performance at stresses more than 200 MPa below the onset of the martensitic transformation. Furthermore, fatigue curves showed a temperature dependence which was successfully implemented into a modified Basquin’s power law model. Notably, the fatigue life drops down to 104 cycles before the nominal loadings reach the B19′ transformation regime. We further found that fatigue life is shorter for the B2-R-phase transformation regime than for the elasticity of the parent B2 austenite phase at low stresses when strains remain below 1%, however at higher strains the B2-R-phase transforming wire is better than the elastic one. Fatigue Crack observations revealed Crack initiation at the surface and its propagation towards the bulk resulting in a reduction of the cross-section and substantial increase in normal stresses. Martensitic transformation was triggered during the Crack Growth in samples nominally loaded in elastic or R-phase transformation regimes as confirmed by in-situ infrared thermography. As the Crack grows with increasing speed, the activity of transformation processes at the tip gradually increases till Unstable Crack Growth and final rupture occurs, as confirmed by in-situ thermography and stress hysteresis observations. The analysis of fracture surfaces revealed five different Crack Growth regimes - from quasi-cleavage at early Crack Growth, through propagation stage evidenced by striations, till the final ductile fracture evidenced by the typical fracture surface morphology.
Xinxin Xing - One of the best experts on this subject based on the ideXlab platform.
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Crack initiation and early Growth behavior of TC4 titanium alloy under high cycle fatigue and very high cycle fatigue
Journal of Materials Research, 2018Co-Authors: Ning Gao, Hongqiao Zhao, Xinxin XingAbstract:The Crack initiation and early Growth behaviors of a TC4 titanium alloy under high cycle fatigue and very high cycle fatigue were experimentally investigated. The results show that it exhibits the duplex S–N curve characteristics associated with surface and interior failures at a stress ratio of 0.1, while it represents the similar S–N curve characteristics only related to surface failure at a stress ratio of −1. The interior failure is accompanied with the occurrence of facets, granular bright facets (GBFs), and fisheye. Slip-like patterns are observable on the facets easily formed under positive stress ratio. The interior failure process is characterized as (i) occurrence of slip lines on partial α grains under cyclic loading, (ii) initiation and Growth of microCracks within some α grains, (iii) coalescence of microCracks and formation of GBF, (iv) stable long Crack Growth within fisheye, (v) Unstable Crack Growth outside fisheye, and (vi) final momentary fracture.
Petr Šittner - One of the best experts on this subject based on the ideXlab platform.
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Fatigue performance of superelastic NiTi near stress-induced martensitic transformation
International Journal of Fatigue, 2017Co-Authors: Eduardo Alarcon, Petr Šittner, Ludek Heller, Shabnam Arbab Chirani, Jaromír Kopeček, Luc Saint-sulpice, Sylvain CallochAbstract:The structural fatigue of superelastic NiTi was studied with special attention paid to the drop in fatigue performance commonly observed at the onset of the stress-induced martensitic transformation. We processed the superelastic NiTi wires into an hourglass shape as a result of which the stress induced martensitic transformation in tension is not localized as confirmed by digital image correlation measurements. The hourglass shaped samples were subjected to force controlled pull-pull fatigue tests at two distinct temperatures selected to investigate the fatigue of NiTi with and without the R-phase transformation involved, and to capture the effect of varying critical stress for the onset of B19′ martensitic transformation. Resulting fatigue curves expressed in terms of both the stress and the strain show a first degradation of fatigue performance at stresses more than 200 MPa below the onset of the martensitic transformation. Furthermore, fatigue curves showed a temperature dependence which was successfully implemented into a modified Basquin’s power law model. Notably, the fatigue life drops down to 104 cycles before the nominal loadings reach the B19′ transformation regime. We further found that fatigue life is shorter for the B2-R-phase transformation regime than for the elasticity of the parent B2 austenite phase at low stresses when strains remain below 1%, however at higher strains the B2-R-phase transforming wire is better than the elastic one. Fatigue Crack observations revealed Crack initiation at the surface and its propagation towards the bulk resulting in a reduction of the cross-section and substantial increase in normal stresses. Martensitic transformation was triggered during the Crack Growth in samples nominally loaded in elastic or R-phase transformation regimes as confirmed by in-situ infrared thermography. As the Crack grows with increasing speed, the activity of transformation processes at the tip gradually increases till Unstable Crack Growth and final rupture occurs, as confirmed by in-situ thermography and stress hysteresis observations. The analysis of fracture surfaces revealed five different Crack Growth regimes - from quasi-cleavage at early Crack Growth, through propagation stage evidenced by striations, till the final ductile fracture evidenced by the typical fracture surface morphology.
Ludek Heller - One of the best experts on this subject based on the ideXlab platform.
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Fatigue performance of superelastic NiTi near stress-induced martensitic transformation
International Journal of Fatigue, 2017Co-Authors: Eduardo Alarcon, Petr Šittner, Ludek Heller, Shabnam Arbab Chirani, Jaromír Kopeček, Luc Saint-sulpice, Sylvain CallochAbstract:The structural fatigue of superelastic NiTi was studied with special attention paid to the drop in fatigue performance commonly observed at the onset of the stress-induced martensitic transformation. We processed the superelastic NiTi wires into an hourglass shape as a result of which the stress induced martensitic transformation in tension is not localized as confirmed by digital image correlation measurements. The hourglass shaped samples were subjected to force controlled pull-pull fatigue tests at two distinct temperatures selected to investigate the fatigue of NiTi with and without the R-phase transformation involved, and to capture the effect of varying critical stress for the onset of B19′ martensitic transformation. Resulting fatigue curves expressed in terms of both the stress and the strain show a first degradation of fatigue performance at stresses more than 200 MPa below the onset of the martensitic transformation. Furthermore, fatigue curves showed a temperature dependence which was successfully implemented into a modified Basquin’s power law model. Notably, the fatigue life drops down to 104 cycles before the nominal loadings reach the B19′ transformation regime. We further found that fatigue life is shorter for the B2-R-phase transformation regime than for the elasticity of the parent B2 austenite phase at low stresses when strains remain below 1%, however at higher strains the B2-R-phase transforming wire is better than the elastic one. Fatigue Crack observations revealed Crack initiation at the surface and its propagation towards the bulk resulting in a reduction of the cross-section and substantial increase in normal stresses. Martensitic transformation was triggered during the Crack Growth in samples nominally loaded in elastic or R-phase transformation regimes as confirmed by in-situ infrared thermography. As the Crack grows with increasing speed, the activity of transformation processes at the tip gradually increases till Unstable Crack Growth and final rupture occurs, as confirmed by in-situ thermography and stress hysteresis observations. The analysis of fracture surfaces revealed five different Crack Growth regimes - from quasi-cleavage at early Crack Growth, through propagation stage evidenced by striations, till the final ductile fracture evidenced by the typical fracture surface morphology.
