20 results found
Xu Y, Xian J, Stoyanov S, et al., 2022, A multi-scale approach to microstructure-sensitive thermal fatigue in solder joints, International Journal of Plasticity, Vol: 155, ISSN: 0749-6419
This paper presents a multi-scale modelling approach to investigate the underpinning mechanisms of microstructure-sensitive damage of single crystal Sn-3Ag-0.5Cu (wt%, SAC305) solder joints of a Ball Grid Array (BGA) board assembly subject to thermal cycling. The multi-scale scheme couples board-scale modelling at the continuum macro-scale and individual solder modelling at the crystal micro-scale. Systematic studies of tin crystal orientation and its role in fatigue damage have been compared to experimental observations. Crystallographic orientation is examined with respect to damage development, providing evidence-based optimal solder microstructural design for in-service thermomechanical fatigue.
Xu Y, Balint D, Greiner C, et al., 2022, On the origin of plasticity-induced microstructure change under sliding contacts, Friction, ISSN: 2223-7704
Discrete dislocation plasticity (DDP) calculations are carried out to investigate the response of a single crystal contacted by a rigid sinusoidal asperity under sliding loading conditions to look for causes of microstructure change in the dislocation structure. The mechanistic driver is identified as the development of lattice rotations and stored energy in the subsurface, which can be quantitatively correlated to recent tribological experimental observations. Maps of surface slip initiation and substrate permanent deformation obtained from DDP calculations for varying contact size and normal load suggest ways of optimally tailoring the interface and microstructural material properties for various frictional loads.
Bergsmo A, Xu Y, Poole B, et al., 2022, Twin boundary fatigue crack nucleation in a polycrystalline Nickel superalloy containing non-metallic inclusions, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, Vol: 160, ISSN: 0022-5096
Li K-S, Cheng L-Y, Xu Y, et al., 2022, A dual-scale modelling approach for creep-fatigue crack initiation life prediction of holed structure in a nickel-based superalloy, INTERNATIONAL JOURNAL OF FATIGUE, Vol: 154, ISSN: 0142-1123
Xu Y, Balint DS, Dini D, 2021, On the Origin of Plastic Deformation and Surface Evolution in Nano-Fretting: A Discrete Dislocation Plasticity Analysis, MATERIALS, Vol: 14
Xu Y, 2021, A non-local methodology for geometrically necessary dislocations and application to crack tips, INTERNATIONAL JOURNAL OF PLASTICITY, Vol: 140, ISSN: 0749-6419
Xu Y, Ruebeling F, Balint D, et al., 2021, On the origin of microstructural discontinuities in sliding contacts: A discrete dislocation plasticity analysis, INTERNATIONAL JOURNAL OF PLASTICITY, Vol: 138, ISSN: 0749-6419
Xu Y, Gu T, Xian J, et al., 2021, Intermetallic size and morphology effects on creep rate of Sn-3Ag-0.5Cu solder, INTERNATIONAL JOURNAL OF PLASTICITY, Vol: 137, ISSN: 0749-6419
Ruebeling F, Xu Y, Richter G, et al., 2021, Normal Load and Counter Body Size Influence the Initiation of Microstructural Discontinuities in Copper during Sliding, ACS APPLIED MATERIALS & INTERFACES, Vol: 13, Pages: 4750-4760, ISSN: 1944-8244
Xu Y, Wan W, Dunne FPE, 2021, Microstructural fracture mechanics: Stored energy density at fatigue cracks, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, Vol: 146, ISSN: 0022-5096
Xu Y, Joseph S, Karamched P, et al., 2020, Predicting dwell fatigue life in titanium alloys using modelling and experiment, NATURE COMMUNICATIONS, Vol: 11, ISSN: 2041-1723
Xu Y, Fox K, Rugg D, et al., 2020, Cyclic plasticity and thermomechanical alleviation in titanium alloys, INTERNATIONAL JOURNAL OF PLASTICITY, Vol: 134, ISSN: 0749-6419
Lu X, Dunne FPE, Xu Y, 2020, A crystal plasticity investigation of slip system interaction, GND density and stored energy in non-proportional fatigue in Nickel-based superalloy, INTERNATIONAL JOURNAL OF FATIGUE, Vol: 139, ISSN: 0142-1123
Xu Y, Dini D, 2020, Capturing the hardness of coating systems across the scales, Surface and Coatings Technology, Vol: 394, ISSN: 0257-8972
A two-dimensional multi-scale modelling approach that concurrently couples discrete dislocation plasticity and crystal plasticity finite element has been applied to study the hardness variation of coating systems across different scales, covering nano- to micro-indentation. The difference in indentation size sensitivity between film and substrate gives rise to three regimes of hardness, one typically dictated by the intrinsic coating indentation size effect, which is regulated by dislocations activity, and the other two linked to the continuum response of the coating and the substrate. We propose a new hardness formula that incorporates physics-based indentation size effects of thin films into established continuum hardness transition formulae. This formula is shown to substantially improve the hardness prediction of coating systems, particularly when relative indentation depth is at the nanometre scale.
Prastiti NG, Xu Y, Balint DS, et al., 2020, Discrete dislocation, crystal plasticity and experimental studies of fatigue crack nucleation in single-crystal nickel, International Journal of Plasticity, Vol: 126, Pages: 1-14, ISSN: 0749-6419
Dislocation configurational energy and stored energy densities are determined in discrete dislocation and crystal plasticity modelling respectively and assessed with respect to experiments on single crystal nickel fatigue crack nucleation. Direct comparisons between the three techniques are provided for two crystal orientation fatigue tests. These provide confirmation that both quantities correctly identify the sites of fatigue crack nucleation and that stored energy density is a reasonable approximation to the more rigorous dislocation configurational energy. GND density is shown to be important in locating crack nucleation sites because of its role in the local configurational energy density.
Gu T, Xu Y, Gourlay CM, et al., 2020, In-situ electron backscatter diffraction of thermal cycling in a single grain Cu/Sn-3Ag-0.5Cu/Cu solder joint, Scripta Materialia, Vol: 175, Pages: 55-60, ISSN: 1359-6462
The heterogeneous evolution of microstructure in a single grain Cu/SAC305/Cu solder joint is investigated using in-situ thermal cycling combined with electron backscatter diffraction (EBSD). Local deformation due to thermal expansion mismatch results in heterogeneous lattice rotation within the joint, localised towards the corners. This deformation is induced by the constraint and the coefficient of thermal expansion (CTE) mismatch between the β-Sn, Cu6Sn5 and Cu at interfaces. The formation of subgrains with continuous increase in misorientation is revealed during deformation, implying the accumulation of plastic slip at the strain-localised regions and the activation of slip systems (110)/2 and (0)/2.
Xu Y, Balint D, Dini D, 2019, A new hardness formula incorporating the effect of source density on indentation response: a discrete dislocation plasticity analysis, Surface and Coatings Technology, Vol: 374, Pages: 763-773, ISSN: 0257-8972
Planar discrete dislocation plasticity (DDP) calculations that simulate thin single crystal films bonded to a rigid substrate indented by a rigid wedge are performed for different values of film thickness and dislocation source density. As in prior studies, an indentation size effect (ISE) is observed when indentation depth is sufficiently small relative to the film thickness. Thedependence of the ISE on dislocation source density is quantified in this study, and a modified form of the scaling law for the dependence of hardness on indentation depth, first derived by Nix and Gao, is proposed, which is valid over the entire range of indentation depths and correlates the length scale parameter with the average dislocation source spacing. Nanoindentation experimental data from the literature are fitted using this formula, which further verifies the proposed scaling of indentation pressure on dislocation source density.
Xu Y, Balint DB, Dini DD, 2016, A method of coupling discrete dislocation plasticity to the crystal plasticity finite element method, Modelling and Simulation in Materials Science and Engineering, Vol: 24, ISSN: 1361-651X
A method of concurrent coupling of planar discrete dislocation plasticity (DDP) and a crystal plasticityfinite element (CPFE) method was devised for simulating plastic deformation in large polycrystals withdiscrete dislocation resolution in a single grain or cluster of grains for computational efficiency;computation time using the coupling method can be reduced by an order of magnitude compared toDDP. The method is based on an iterative scheme initiated by a sub-model calculation, which ensuresdisplacement and traction compatibility at all nodes at the interface between the DDP and CPFEdomains. The proposed coupling approach is demonstrated using two plane strain problems: (i)uniaxial tension of a bi-crystal film and (ii) indentation of a thin film on a substrate. The latter was alsoused to demonstrate that the rigid substrate assumption used in earlier discrete dislocation plasticitystudies is inadequate for indentation depths that are large compared to the film thickness, i.e. theeffect of the plastic substrate modelled using CPFE becomes important. The coupling method can beused to study a wider range of indentation depths than previously possible using DDP alone, withoutsacrificing the indentation size effect regime captured by DDP. The method is general and can beapplied to any problem where finer resolution of dislocation mediated plasticity is required to studythe mechanical response of polycrystalline materials, e.g. to capture size effects locally within a largerelastic/plastic boundary value problem.
Xu Y, Balint DS, Dini D, 2013, Multi-scale modeling of indentation and contact fatigue: A coupled CPFE/DD approach, Pages: 3416-3419
Wang CE, Cui DL, Yan ZY, et al., 2011, Finite element triangle mesh generation in planar area, Jisuanji Jicheng Zhizao Xitong/Computer Integrated Manufacturing Systems, CIMS, Vol: 17, Pages: 256-260, ISSN: 1006-5911
To improve efficiency and quality of finite element method in complicated assembly design, based on studies of several current Computer Aided Engineering (CAE) platforms, a triangle mesh generation system was established. In this system, isomeric mesh data from heterogeneous Ansys and Patran platform could be imported. Size control methods of mesh element were implemented from several aspects to generate size field information. Hybrid application of Advancing Front Technique (AFT) /Delauany/mapping algorithms for multi-area problem was realized. This system was applied in coupled thermo-solid analysis on axisymmetric components of aero-engine. Application results showed that the proposed method was effective.
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