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- 2019
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Journal article (peer-reviewed)
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- Long, Xu, et al.
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Finite Element Analysis to the Constitutive Behavior of Sintered Silver Nanoparticles Under Nanoindentation
- 2018
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In: International Journal of Applied Mechanics. - 1758-8251 .- 1758-826X. ; 10:10
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Journal article (peer-reviewed)abstract
- Finite element (FE) simulation is adopted as a fundamental tool to evaluate the mechanical reliability of packaging structures for electronic devices. Nevertheless, the determination of mechanical properties of sintered silver nanoparticles (AgNP) remains challenging as the traditional tensile test is difficult to be performed at a limited size. In the current study, spherical nanoindentation is utilized to measure the applied load-penetration depth responses of sintered AgNP reinforced by SiC microparticles at various weight ratios (0.0, 0.5, 1.0 and 1.5 wt.%). To describe the elasto-plastic behavior of this heterogeneous material, FE analysis is performed to simulate the indentation behavior and determine the parameters in the modified power-law model by fitting the average applied load-penetration depth responses. To overcome the uniqueness problem, the Young's modulus is directly determined by continuous stiffness measurement technique and the proposed constitutive model can provide a reasonably accurate mechanical estimation of sintered AgNP. The effect of SiC content on sintered AgNP is discussed by correlating the morphology observed by scanning electron microscope (SEM) and the constitutive parameters obtained from the FE simulations.
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- Long, Xu, et al.
(author)
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Mechanical behaviour of sintered silver nanoparticles reinforced by SiC microparticles
- 2019
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In: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093. ; 744, s. 406-414
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Journal article (peer-reviewed)abstract
- SiC microparticles with various weight ratios (0.0, 0.5, 1.0 and 1.5 wt%) are incorporated into sintered silver nanoparticles (AgNP) as one of the promising packaging materials for high-power electronic devices. Mechanical properties and constitutive behaviour of sintered AgNP reinforced by SiC microparticles are investigated based on nanoindentation experiment and analytical approach. Nanoindentations were performed in the manner of continuous stiffness measurement for a maximum penetration depth of 2000 nm at a strain rate of 0.05 s−1. Particularly, a Berkovich indenter is utilized to evaluate the values of Young's modulus and hardness, and a spherical indenter is utilized to describe the constitutive behaviour. For sintered AgNP with 0.5 wt% SiC, the morphology exhibits uniformly compact microstructures to enable optimizing the heat conductivity, the yield strength and hardening capacity of sintered AgNP material is enhanced. To describe the constitutive behaviour, an analytical approach is proposed to simulate the indentation behaviour. The parameters in the modified power-law model are determined by fitting the average indentation responses. The developed correlation between microstructure and macroscopic properties facilitates the design of AgNP paste morphology and improves the mechanical properties of sintered AgNP in electronics packaging.
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- Cheng, Benyuan, et al.
(author)
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Pressure-induced metallization and amorphization in VO2(A) nanorods
- 2016
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 93:18
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Journal article (peer-reviewed)abstract
- A metallic state enabled by the metal-insulator transition (MIT) in single crystal VO2(A) nanorods is demonstrated, which provides important physical foundation in experimental understanding of MIT in VO2. The observed tetragonal metallic state at ∼28 GPa should be interpreted as a distinct metastable state, while increasing pressure to ∼32 GPa, it transforms into a metallic amorphous state completely. The metallization is due to V 3d orbital electrons delocalization, and the amorphization is attributed to the unique variation of V-O-V bond angle. A metallic amorphous VO2 state is found under pressure, which is beneficial to explore the phase diagram of VO2. Furthermore, this work proves the occurrence of both the metallization and amorphization in octahedrally coordinated materials.
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- Khong, Sei Zhen, et al.
(author)
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Robust synchronisation of unstable linear time-invariant systems
- 2015
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Conference paper (peer-reviewed)abstract
- A framework based on the gap metric and integral quadratic constraints (IQCs) is developed for analysing robust synchronisation of heterogenous linear time-invariant networks. Both the agents and the communication channels are allowed to be dynamic and unstable. Structural properties of the uncertainty are described by IQCs and exploited in synchronisation analysis as a means to reduce conservatism. The homotopy employed in IQC analysis is defined with respect to the graph topology as induced by the gap metric, whereby open-loop unstable dynamics are accommodated. The results in this paper extend recent developments, which have been shown to unify several existing synchronisation analysis methods in the literature.
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- Khong, Sei Zhen, et al.
(author)
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Robust Synchronization in Multi-Agent Networks with Unstable Dynamics
- 2018
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In: IEEE Transactions on Control of Network Systems. - : IEEE. - 2325-5870. ; 5:1, s. 205-214
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Journal article (peer-reviewed)abstract
- The problem of synchronization in heterogenous linear time-invariant networks is investigated. An approach blending the theory of integral quadratic constraints (IQCs) with the gap metric is proposed to study the problem within a unifying framework, where both the agents and communication channels can be dynamic, infinite-dimensional, unstable, and uncertain. Structural properties of the uncertainty are described by IQCs and exploited in the analysis to reduce conservatism. The homotopy employed in IQC analysis is defined with respect to the graph topology induced by the gap metric, whereby open-loop unstable dynamics are accommodated. Sufficient conditions for synchronism are provided, extending recent developments which have been shown to unify several existing synchronization analysis results in the literature.
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