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Xiao Cheng Zeng - One of the best experts on this subject based on the ideXlab platform.
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Tuning the electronic properties of transition-metal trichalcogenides via Tensile Strain
Nanoscale, 2015Co-Authors: Jun Dai, Xiao Cheng ZengAbstract:A comprehensive study of the effect of Tensile Strain (e = 0% to 8%) on the electronic structures of two-dimensional (2D) transition-metal trichalcogenide (TMTC) monolayers MX3 (M = Ti, Zr, Hf, Nb; X = S, Se Te) is performed on the basis of density functional theory (DFT) computation. The unStrained TiS3, ZrS3, ZrSe3, HfS3, HfSe3 and NbS3 monolayers are predicted to be semiconductors with their bandgap ranging from 0.80 to 1.94 eV. Our DFT computations show that the biaxial and uniaxial Tensile Strains can effectively modify the bandgap of many TMTC monolayers. In particular, we find that ZrS3 and HfS3 monolayers undergo an indirect-to-direct bandgap transition with increasing Tensile Strain. The indirect bandgaps of ZrSe3 and HfSe3 monolayers also increase with the Tensile Strain. Both ZrTe3 and HfTe3 monolayers are predicted to be metals, but can be transformed into indirect bandgap semiconductors at e = 4% and e = 6%, respectively. Importantly, the TiS3 monolayer can retain its direct-bandgap feature over a range of biaxial or uniaxial Tensile Strains (up to 8%). The highly tunable direct bandgaps of MS3 (M = Hf, Ti, and Zr) by Strain and the availability of metallic and semiconducting properties of MTe3 (M = Hf and Zr) provide exciting opportunities for designing artificial layered structures for applications in optoelectronics and flexible electronics.
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tuning electronic and magnetic properties of early transition metal dichalcogenides via Tensile Strain
Journal of Physical Chemistry C, 2014Co-Authors: Ning Lu, Lu Wang, Xiaojun Wu, Xiao Cheng ZengAbstract:We have performed a systematic first-principles study of the effect of Tensile Strains on the electronic properties of early transition-metal dichalcogenide (TMDC) monolayers MX2 (M = Sc, Ti, Zr, Hf, Ta, Cr; X = S, Se, Te). Our density functional theory calculations suggest that the Tensile Strain can significantly affect the electronic properties of many early TMDCs in general and the electronic bandgap in particular. For group IVB TMDCs (TiX2, ZrX2, HfX2), the bandgap increases with the Tensile Strain, but for ZrX2 and HfX2 (X = S, Se), the bandgap starts to decrease at Strain 6–8%. For the group VB TMDCs (TaX2), the Tensile Strain can either induce the ferromagnetism or enhance the existing ferromagnetism. For the group VIB TMDCs (CrX2), the direct-to-indirect bandgap transition is seen upon application of the Tensile Strain, except CrTe2 whose bandgap decreases with the Tensile Strain even though the direct character of its bandgap is retained. Lastly, for the group IIIB TMDCs (ScX2) in the T metallic...
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Tuning Electronic and Magnetic Properties of Early Transition Metal Dichalcogenides via Tensile Strain
The Journal of Physical Chemistry C, 2014Co-Authors: Hongyan Guo, Lu Wang, Xiao Cheng ZengAbstract:We have performed a systematic first-principles study of the effect of Tensile Strains on the electronic properties of early transition-metal dichalcogenide (TMDC) monolayers MX2 (M = Sc, Ti, Zr, Hf, Ta, Cr; X = S, Se, and Te). Our density-functional theory (DFT) calculations suggest that the Tensile Strain can significantly affect the electronic properties of many early TMDCs in general and the electronic bandgap in particular. For group IVB TMDCs (TiX2, ZrX2, HfX2), the bandgap increases with the Tensile Strain, but for ZrX2 and HfX2 (X=S, Se), the bandgap starts to decrease at Strain 6% to 8%. For the group-VB TMDCs (TaX2), the Tensile Strain can either induce the ferromagnetism or enhance the existing ferromagnetism. For the group-VIB TMDCs (CrX2) the direct-to-indirect bandgap transition is seen upon application of the Tensile Strain, except CrTe2 whose bandgap decreases with the Tensile Strain even though the direct character of its bandgap is retained. Lastly, for the group-IIIB TMDCs (ScX2) in the T metallic phase, we find that the Tensile Strain has little effect on their electronic and magnetic properties. Our study suggests that Strain engineering is an effective approach to modify electronic and magnetic properties of most early TMDC monolayers, thereby opening an alternative way for future optoelectronic and spintronic applications.
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mos2 mx2 heterobilayers bandgap engineering via Tensile Strain or external electrical field
Nanoscale, 2014Co-Authors: Ning Lu, Lu Wang, Xiaojun Wu, Xiao Cheng Zeng, Lei LiAbstract:We have performed a comprehensive first-principles study of the electronic and magnetic properties of two-dimensional (2D) transition-metal dichalcogenide (TMD) heterobilayers MX2/MoS2 (M = Mo, Cr, W, Fe, V; X = S, Se). For M = Mo, Cr, W; X = S, Se, all heterobilayers show semiconducting characteristics with an indirect bandgap with the exception of the WSe2/MoS2 heterobilayer which retains the direct-bandgap character of the constituent monolayer. For M = Fe, V; X = S, Se, the MX2/MoS2 heterobilayers exhibit metallic characters. Particular attention of this study has been focused on engineering the bandgap of the TMD heterobilayer materials via application of either a Tensile Strain or an external electric field. We find that with increasing either the biaxial or uniaxial Tensile Strain, the MX2/MoS2 (M = Mo, Cr, W; X = S, Se) heterobilayers can undergo a semiconductor-to-metal transition. For the WSe2/MoS2 heterobilayer, a direct-to-indirect bandgap transition may occur beyond a critical biaxial or uniaxial Strain. For M (=Fe, V) and X (=S, Se), the magnetic moments of both metal and chalcogen atoms are enhanced when the MX2/MoS2 heterobilayers are under a biaxial Tensile Strain. Moreover, the bandgap of MX2/MoS2 (M = Mo, Cr, W; X = S, Se) heterobilayers can be reduced by the vertical electric field. For two heterobilayers MSe2/MoS2 (M = Mo, Cr), PBE calculations suggest that the indirect-to-direct bandgap transition may occur under an external electric field. The transition is attributed to the enhanced spontaneous polarization. The tunable bandgaps in general and possible indirect–direct bandgap transitions due to Tensile Strain or external electric field make the TMD heterobilayer materials a viable candidate for optoelectronic applications.
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mos2 mx2 heterobilayers bandgap engineering via Tensile Strain or external electrical field
arXiv: Mesoscale and Nanoscale Physics, 2013Co-Authors: Ning Lu, Lu Wang, Xiaojun Wu, Xiao Cheng Zeng, Lei LiAbstract:We have performed a comprehensive first-principles study of the electronic and magnetic properties of two-dimensional (2D) transition-metal dichalcogenide (TMD) heterobilayers MX2/MoS2 (M = Mo, Cr, W, Fe, V; X = S, Se). For M = Mo, Cr, W; X=S, Se, all heterobilayers show semiconducting characteristics with an indirect bandgap with the exception of the WSe2/MoS2 heterobilayer which retains the direct-band-gap character of the constituent monolayer. For M = Fe, V; X = S, Se, the MX2/MoS2 heterobilayers exhibit metallic characters. Particular attention of this study has been focused on engineering bandgap of the TMD heterobilayer materials via application of either a Tensile Strain or an external electric field. We find that with increasing either the biaxial or uniaxial Tensile Strain, the MX2/MoS2 (M=Mo, Cr, W; X=S, Se) heterobilayers can undergo a semiconductor-to-metal transition. For the WSe2/MoS2 heterobilayer, a direct-to-indirect bandgap transition may occur beyond a critical biaxial or uniaxial Strain. For M (=Fe, V) and X (=S, Se), the magnetic moments of both metal and chalcogen atoms are enhanced when the MX2/MoS2 heterobilayers are under a biaxial Tensile Strain. Moreover, the bandgap of MX2/MoS2 (M=Mo, Cr, W; X=S, Se) heterobilayers can be reduced by the electric field. For two heterobilayers MSe2/MoS2 (M=Mo, Cr), PBE calculations suggest that the indirect-to-direct bandgap transition may occur under an external electric field. The transition is attributed to the enhanced spontaneous polarization. The tunable bandgaps in general and possible indirect-direct bandgap transitions due to Tensile Strain or external electric field endow the TMD heterobilayer materials a viable candidate for optoelectronic applications.
Yong-yi Wang - One of the best experts on this subject based on the ideXlab platform.
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Enhancing Tensile Strain Capacity Through the Optimization of Weld Profiles
Volume 4: Production Pipelines and Flowlines; Project Management; Facilities Integrity Management; Operations and Maintenance; Pipelining in Northern , 2014Co-Authors: Yong-yi Wang, Yaoshan Chen, Mamdouh M. SalamaAbstract:In order to optimize cost and performance of high pressure gas pipelines by reducing the wall thickness, pipeline companies are considering the use of higher grade (X70 or above) steels or a composite pipe of thin steel liner and fiber wrap. The use of high strength steels and thinner pipes can result in challenges when the pipe is installed in areas imposing high Strain demand such as discontinuous permafrost regions. For high strength steels, the difficulty of ensuring the strength overmatching of the weld metal and the potential softening of the heat affected zone (HAZ) can result in gross Strain concentration in the weld region and thus reduce the Strain capacity of the pipeline in the presence of weld defects. Also, a thinner pipe has lower Strain capacity than a thicker pipe for the weld defect of the same dimensions. One of the economical and effective ways of mitigating the possibility of gross Strain concentration and increasing the Strain capacity of a weld region containing weld defects is through the use of appropriate weld profiles. For instance, adding a smooth and wide layer of weld reinforcement (termed weld overbuild) can increase the effective strength of the weld.The effectiveness of the weld overbuild in improving the Tensile Strain capacity of girth welds is evaluated using the Level 4a approach of the PRCI-CRES Tensile Strain models. The crack-driving force is obtained through finite element analysis (FEA) of welds with planar weld and HAZ flaws of various sizes. It was demonstrated that weld overbuild with appropriate dimensions is an effective method to increase the Tensile Strain capacity (TSC) of girth welds which may have limited TSC without the overbuild. The role of weld profiles in girth weld integrity is discussed from the perspectives of historical evidence and more recent analysis and experimental tests.Copyright © 2014 by ASME
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Multi-Tier Tensile Strain Models for Strain-Based Design: Part 2 — Development and Formulation of Tensile Strain Capacity Models
Volume 4: Pipelining in Northern and Offshore Environments; Strain-Based Design; Risk and Reliability; Standards and Regulations, 2012Co-Authors: Ming Liu, Yong-yi Wang, Yaxin Song, David Horsley, Steve NanneyAbstract:This is the second paper in a three-paper series related to the development of Tensile Strain models. The fundamental basis of the models [1] and evaluation of the models against experiment data [2] are presented in two companion papers. This paper presents the structure and formulation of the models.The philosophy and development of the multi-tier Tensile Strain models are described. The Tensile Strain models are applicable for linepipe grades from X65 to X100 and two welding processes, i.e., mechanized GMAW and FCAW/SMAW. The Tensile Strain capacity (TSC) is given as a function of key material properties and weld and flaw geometric parameters, including pipe wall thickness, girth weld high-low misalignment, pipe Strain hardening (Y/T ratio), weld strength mismatch, girth weld flaw size, toughness, and internal pressure. Two essential parts of the Tensile Strain models are the crack driving force and material’s toughness. This paper covers principally the crack driving force. The significance and determination of material’s toughness are covered in the companion papers [1,2].Copyright © 2012 by ASME
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Multi-Tier Tensile Strain Models for Strain-Based Design: Part 1 — Fundamental Basis
Volume 4: Pipelining in Northern and Offshore Environments; Strain-Based Design; Risk and Reliability; Standards and Regulations, 2012Co-Authors: Yong-yi Wang, Fan Zhang, Ming Liu, David Horsley, Steve NanneyAbstract:This is the first paper in a three-paper series on the Tensile Strain design of pipelines. The formulation of the multi-tier models [1] and evaluation of the models against experiment data [2] are presented in two companion papers. This paper starts with an introduction of general concept of Strain-based design. The central part of the paper is then devoted to the Tensile Strain capacity, including (1) physical process of Tensile Strain failure, (2) limit states of Tensile Strain failure and associated toughness representation, and (3) fundamental basis of Tensile Strain models. The most significant part of the fundamental basis, the limit state of Tensile failure and associated representation of the material’s toughness, is given the greatest amount of attention.Copyright © 2012 by ASME
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Tensile Strain Capacity of X80 and X100 Welds
Volume 6: Materials Technology; Polar and Arctic Sciences and Technology; Petroleum Technology Symposium, 2012Co-Authors: Yong-yi Wang, Fan ZhangAbstract:High-strength pipelines (API 5L grade X70 and above) provide viable economic options for large-diameter and high-pressure transmission of energy products. To facilitate the understanding and potential use of high-strength pipelines, the Tensile Strain capacity (TSC) of X80 and X100 girth welds was evaluated through a series of mechanical tests and analytical/computational modeling. The experimental tests include Tensile, Charpy, SENT, and curved-wide-plate (CWP) tests. The TSC measured from CWP tests is compared with the prediction from TSC models developed at CRES. The TSC of the girth welds is assessed by comparing experimentally measured values with the expected TSC from similar welds. The assessment confirms that this particular set of X80 and X100 girth welds provide very good Tensile Strain capacity.Copyright © 2012 by ASME
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Tensile Strain Models for Strain-Based Design of Pipelines
Volume 6: Materials Technology; Polar and Arctic Sciences and Technology; Petroleum Technology Symposium, 2012Co-Authors: Yong-yi Wang, Ming Liu, Yaxin Song, David HorsleyAbstract:This paper covers the development of Tensile Strain design models using a multidisciplinary approach, including fundamental fracture mechanics, small-scale material characterization tests, and large-scale tests of full-size pipes. The Tensile Strain design models are formulated in a four-level format. The Level 1 procedure provides estimated Tensile Strain capacity (TSC) in a tabular format for quick initial assessment. The initiation toughness alternatively termed apparent toughness is estimated from upper shelf Charpy impact energy. The Level 2 procedure contains a set of parametric equations based on an initiation-control limit state. The Tensile Strain capacity can be computed from these equations with the input of a pipe’s dimensional and material property parameters. The apparent toughness is estimated from either upper shelf Charpy energy or upper shelf toughness of standard CTOD test specimens. The Level 3 procedure uses the same set of equations as in Level 2 and the toughness values are obtained from low-conStraint tests. In the Level 3 procedure, two limit states based on either initiation control or ductile instability can be used. The Level 4 procedure allows the use of direct FEA calculation to develop crack driving force relations. The same limit states as those in Level 3 may be used. The Level 4 procedures should only be used by seasoned experts in special circumstances where lower level procedures are judged inappropriate.The Tensile Strain design models may be used for the following purposes:(1) The determination of Tensile Strain capacity for a given set of material properties and flaw size.(2) The determination of acceptable flaw sizes for a given set of material properties and target Tensile Strain capacity.(3) The selection of material properties to achieve a target Strain capacity for a given flaw size.(4) The optimization of the Tensile Strain capacity by balancing the requirements of material parameters, such as weld strength (thus weld strength mismatch level) versus toughness.The application of the Tensile Strain design models is given in a companion paper.Copyright © 2012 by ASME
Lu Wang - One of the best experts on this subject based on the ideXlab platform.
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tuning electronic and magnetic properties of early transition metal dichalcogenides via Tensile Strain
Journal of Physical Chemistry C, 2014Co-Authors: Ning Lu, Lu Wang, Xiaojun Wu, Xiao Cheng ZengAbstract:We have performed a systematic first-principles study of the effect of Tensile Strains on the electronic properties of early transition-metal dichalcogenide (TMDC) monolayers MX2 (M = Sc, Ti, Zr, Hf, Ta, Cr; X = S, Se, Te). Our density functional theory calculations suggest that the Tensile Strain can significantly affect the electronic properties of many early TMDCs in general and the electronic bandgap in particular. For group IVB TMDCs (TiX2, ZrX2, HfX2), the bandgap increases with the Tensile Strain, but for ZrX2 and HfX2 (X = S, Se), the bandgap starts to decrease at Strain 6–8%. For the group VB TMDCs (TaX2), the Tensile Strain can either induce the ferromagnetism or enhance the existing ferromagnetism. For the group VIB TMDCs (CrX2), the direct-to-indirect bandgap transition is seen upon application of the Tensile Strain, except CrTe2 whose bandgap decreases with the Tensile Strain even though the direct character of its bandgap is retained. Lastly, for the group IIIB TMDCs (ScX2) in the T metallic...
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Tuning Electronic and Magnetic Properties of Early Transition Metal Dichalcogenides via Tensile Strain
The Journal of Physical Chemistry C, 2014Co-Authors: Hongyan Guo, Lu Wang, Xiao Cheng ZengAbstract:We have performed a systematic first-principles study of the effect of Tensile Strains on the electronic properties of early transition-metal dichalcogenide (TMDC) monolayers MX2 (M = Sc, Ti, Zr, Hf, Ta, Cr; X = S, Se, and Te). Our density-functional theory (DFT) calculations suggest that the Tensile Strain can significantly affect the electronic properties of many early TMDCs in general and the electronic bandgap in particular. For group IVB TMDCs (TiX2, ZrX2, HfX2), the bandgap increases with the Tensile Strain, but for ZrX2 and HfX2 (X=S, Se), the bandgap starts to decrease at Strain 6% to 8%. For the group-VB TMDCs (TaX2), the Tensile Strain can either induce the ferromagnetism or enhance the existing ferromagnetism. For the group-VIB TMDCs (CrX2) the direct-to-indirect bandgap transition is seen upon application of the Tensile Strain, except CrTe2 whose bandgap decreases with the Tensile Strain even though the direct character of its bandgap is retained. Lastly, for the group-IIIB TMDCs (ScX2) in the T metallic phase, we find that the Tensile Strain has little effect on their electronic and magnetic properties. Our study suggests that Strain engineering is an effective approach to modify electronic and magnetic properties of most early TMDC monolayers, thereby opening an alternative way for future optoelectronic and spintronic applications.
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mos2 mx2 heterobilayers bandgap engineering via Tensile Strain or external electrical field
Nanoscale, 2014Co-Authors: Ning Lu, Lu Wang, Xiaojun Wu, Xiao Cheng Zeng, Lei LiAbstract:We have performed a comprehensive first-principles study of the electronic and magnetic properties of two-dimensional (2D) transition-metal dichalcogenide (TMD) heterobilayers MX2/MoS2 (M = Mo, Cr, W, Fe, V; X = S, Se). For M = Mo, Cr, W; X = S, Se, all heterobilayers show semiconducting characteristics with an indirect bandgap with the exception of the WSe2/MoS2 heterobilayer which retains the direct-bandgap character of the constituent monolayer. For M = Fe, V; X = S, Se, the MX2/MoS2 heterobilayers exhibit metallic characters. Particular attention of this study has been focused on engineering the bandgap of the TMD heterobilayer materials via application of either a Tensile Strain or an external electric field. We find that with increasing either the biaxial or uniaxial Tensile Strain, the MX2/MoS2 (M = Mo, Cr, W; X = S, Se) heterobilayers can undergo a semiconductor-to-metal transition. For the WSe2/MoS2 heterobilayer, a direct-to-indirect bandgap transition may occur beyond a critical biaxial or uniaxial Strain. For M (=Fe, V) and X (=S, Se), the magnetic moments of both metal and chalcogen atoms are enhanced when the MX2/MoS2 heterobilayers are under a biaxial Tensile Strain. Moreover, the bandgap of MX2/MoS2 (M = Mo, Cr, W; X = S, Se) heterobilayers can be reduced by the vertical electric field. For two heterobilayers MSe2/MoS2 (M = Mo, Cr), PBE calculations suggest that the indirect-to-direct bandgap transition may occur under an external electric field. The transition is attributed to the enhanced spontaneous polarization. The tunable bandgaps in general and possible indirect–direct bandgap transitions due to Tensile Strain or external electric field make the TMD heterobilayer materials a viable candidate for optoelectronic applications.
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mos2 mx2 heterobilayers bandgap engineering via Tensile Strain or external electrical field
arXiv: Mesoscale and Nanoscale Physics, 2013Co-Authors: Ning Lu, Lu Wang, Xiaojun Wu, Xiao Cheng Zeng, Lei LiAbstract:We have performed a comprehensive first-principles study of the electronic and magnetic properties of two-dimensional (2D) transition-metal dichalcogenide (TMD) heterobilayers MX2/MoS2 (M = Mo, Cr, W, Fe, V; X = S, Se). For M = Mo, Cr, W; X=S, Se, all heterobilayers show semiconducting characteristics with an indirect bandgap with the exception of the WSe2/MoS2 heterobilayer which retains the direct-band-gap character of the constituent monolayer. For M = Fe, V; X = S, Se, the MX2/MoS2 heterobilayers exhibit metallic characters. Particular attention of this study has been focused on engineering bandgap of the TMD heterobilayer materials via application of either a Tensile Strain or an external electric field. We find that with increasing either the biaxial or uniaxial Tensile Strain, the MX2/MoS2 (M=Mo, Cr, W; X=S, Se) heterobilayers can undergo a semiconductor-to-metal transition. For the WSe2/MoS2 heterobilayer, a direct-to-indirect bandgap transition may occur beyond a critical biaxial or uniaxial Strain. For M (=Fe, V) and X (=S, Se), the magnetic moments of both metal and chalcogen atoms are enhanced when the MX2/MoS2 heterobilayers are under a biaxial Tensile Strain. Moreover, the bandgap of MX2/MoS2 (M=Mo, Cr, W; X=S, Se) heterobilayers can be reduced by the electric field. For two heterobilayers MSe2/MoS2 (M=Mo, Cr), PBE calculations suggest that the indirect-to-direct bandgap transition may occur under an external electric field. The transition is attributed to the enhanced spontaneous polarization. The tunable bandgaps in general and possible indirect-direct bandgap transitions due to Tensile Strain or external electric field endow the TMD heterobilayer materials a viable candidate for optoelectronic applications.
Kenji Oi - One of the best experts on this subject based on the ideXlab platform.
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buckling and Tensile Strain capacity of girth welded 48 x80 pipeline
ASME 2013 32nd International Conference on Ocean Offshore and Arctic Engineering, 2013Co-Authors: Mitsuru Ohata, Takahiro Sakimoto, Junji Shimamura, Kenji OiAbstract:This paper presents the experimental and analytical results focused on the compressive and Tensile Strain capacity of X80 linepipe. A full-scale bending test of girth welded 48″ OD X80 linepipes was conducted to investigate the compressive Strain limit regarding to the local buckling and Tensile Strain limit regarding to the girth weld fracture. As for the compressive buckling behavior, one large developing wrinkle and some small wrinkles on the pipe surface were captured relatively well from observation and Strain distribution measurement after pipe reaches its endurable maximum bending moment. The Tensile Strain limit is discussed from the viewpoint of competition of two fracture phenomena: ductile crack initiation / propagation from an artificial notch at the HAZ of the girth weld, and Strain concentration and necking / rupture in the base material.The ductile crack growth behavior from the girth weld notch is simulated by FE-analysis based on the proposed damage model, and compared with the experimental results. In this report, it is also demonstrated that the simulation model can be applicable to predicting ductile crack growth behaviors from a circumferentially notched girth welded pipe with internal high pressure subjected to post-buckling loading.Copyright © 2013 by ASME
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Buckling and Tensile Strain Capacity of Girth Welded 48″ X80 Pipeline
Volume 3: Materials Technology; Ocean Space Utilization, 2013Co-Authors: Mitsuru Ohata, Takahiro Sakimoto, Junji Shimamura, Kenji OiAbstract:This paper presents the experimental and analytical results focused on the compressive and Tensile Strain capacity of X80 linepipe. A full-scale bending test of girth welded 48″ OD X80 linepipes was conducted to investigate the compressive Strain limit regarding to the local buckling and Tensile Strain limit regarding to the girth weld fracture. As for the compressive buckling behavior, one large developing wrinkle and some small wrinkles on the pipe surface were captured relatively well from observation and Strain distribution measurement after pipe reaches its endurable maximum bending moment. The Tensile Strain limit is discussed from the viewpoint of competition of two fracture phenomena: ductile crack initiation / propagation from an artificial notch at the HAZ of the girth weld, and Strain concentration and necking / rupture in the base material.The ductile crack growth behavior from the girth weld notch is simulated by FE-analysis based on the proposed damage model, and compared with the experimental results. In this report, it is also demonstrated that the simulation model can be applicable to predicting ductile crack growth behaviors from a circumferentially notched girth welded pipe with internal high pressure subjected to post-buckling loading.Copyright © 2013 by ASME
Ning Lu - One of the best experts on this subject based on the ideXlab platform.
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tuning electronic and magnetic properties of early transition metal dichalcogenides via Tensile Strain
Journal of Physical Chemistry C, 2014Co-Authors: Ning Lu, Lu Wang, Xiaojun Wu, Xiao Cheng ZengAbstract:We have performed a systematic first-principles study of the effect of Tensile Strains on the electronic properties of early transition-metal dichalcogenide (TMDC) monolayers MX2 (M = Sc, Ti, Zr, Hf, Ta, Cr; X = S, Se, Te). Our density functional theory calculations suggest that the Tensile Strain can significantly affect the electronic properties of many early TMDCs in general and the electronic bandgap in particular. For group IVB TMDCs (TiX2, ZrX2, HfX2), the bandgap increases with the Tensile Strain, but for ZrX2 and HfX2 (X = S, Se), the bandgap starts to decrease at Strain 6–8%. For the group VB TMDCs (TaX2), the Tensile Strain can either induce the ferromagnetism or enhance the existing ferromagnetism. For the group VIB TMDCs (CrX2), the direct-to-indirect bandgap transition is seen upon application of the Tensile Strain, except CrTe2 whose bandgap decreases with the Tensile Strain even though the direct character of its bandgap is retained. Lastly, for the group IIIB TMDCs (ScX2) in the T metallic...
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mos2 mx2 heterobilayers bandgap engineering via Tensile Strain or external electrical field
Nanoscale, 2014Co-Authors: Ning Lu, Lu Wang, Xiaojun Wu, Xiao Cheng Zeng, Lei LiAbstract:We have performed a comprehensive first-principles study of the electronic and magnetic properties of two-dimensional (2D) transition-metal dichalcogenide (TMD) heterobilayers MX2/MoS2 (M = Mo, Cr, W, Fe, V; X = S, Se). For M = Mo, Cr, W; X = S, Se, all heterobilayers show semiconducting characteristics with an indirect bandgap with the exception of the WSe2/MoS2 heterobilayer which retains the direct-bandgap character of the constituent monolayer. For M = Fe, V; X = S, Se, the MX2/MoS2 heterobilayers exhibit metallic characters. Particular attention of this study has been focused on engineering the bandgap of the TMD heterobilayer materials via application of either a Tensile Strain or an external electric field. We find that with increasing either the biaxial or uniaxial Tensile Strain, the MX2/MoS2 (M = Mo, Cr, W; X = S, Se) heterobilayers can undergo a semiconductor-to-metal transition. For the WSe2/MoS2 heterobilayer, a direct-to-indirect bandgap transition may occur beyond a critical biaxial or uniaxial Strain. For M (=Fe, V) and X (=S, Se), the magnetic moments of both metal and chalcogen atoms are enhanced when the MX2/MoS2 heterobilayers are under a biaxial Tensile Strain. Moreover, the bandgap of MX2/MoS2 (M = Mo, Cr, W; X = S, Se) heterobilayers can be reduced by the vertical electric field. For two heterobilayers MSe2/MoS2 (M = Mo, Cr), PBE calculations suggest that the indirect-to-direct bandgap transition may occur under an external electric field. The transition is attributed to the enhanced spontaneous polarization. The tunable bandgaps in general and possible indirect–direct bandgap transitions due to Tensile Strain or external electric field make the TMD heterobilayer materials a viable candidate for optoelectronic applications.
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mos2 mx2 heterobilayers bandgap engineering via Tensile Strain or external electrical field
arXiv: Mesoscale and Nanoscale Physics, 2013Co-Authors: Ning Lu, Lu Wang, Xiaojun Wu, Xiao Cheng Zeng, Lei LiAbstract:We have performed a comprehensive first-principles study of the electronic and magnetic properties of two-dimensional (2D) transition-metal dichalcogenide (TMD) heterobilayers MX2/MoS2 (M = Mo, Cr, W, Fe, V; X = S, Se). For M = Mo, Cr, W; X=S, Se, all heterobilayers show semiconducting characteristics with an indirect bandgap with the exception of the WSe2/MoS2 heterobilayer which retains the direct-band-gap character of the constituent monolayer. For M = Fe, V; X = S, Se, the MX2/MoS2 heterobilayers exhibit metallic characters. Particular attention of this study has been focused on engineering bandgap of the TMD heterobilayer materials via application of either a Tensile Strain or an external electric field. We find that with increasing either the biaxial or uniaxial Tensile Strain, the MX2/MoS2 (M=Mo, Cr, W; X=S, Se) heterobilayers can undergo a semiconductor-to-metal transition. For the WSe2/MoS2 heterobilayer, a direct-to-indirect bandgap transition may occur beyond a critical biaxial or uniaxial Strain. For M (=Fe, V) and X (=S, Se), the magnetic moments of both metal and chalcogen atoms are enhanced when the MX2/MoS2 heterobilayers are under a biaxial Tensile Strain. Moreover, the bandgap of MX2/MoS2 (M=Mo, Cr, W; X=S, Se) heterobilayers can be reduced by the electric field. For two heterobilayers MSe2/MoS2 (M=Mo, Cr), PBE calculations suggest that the indirect-to-direct bandgap transition may occur under an external electric field. The transition is attributed to the enhanced spontaneous polarization. The tunable bandgaps in general and possible indirect-direct bandgap transitions due to Tensile Strain or external electric field endow the TMD heterobilayer materials a viable candidate for optoelectronic applications.
