Browsing by Author "Zhang, Rui"
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Item An Efficient Solution Algorithm For Space–Time Finite Element Method(Springer Verlag) Zhang, Rui; Wen, L.; Xiao, J.; Qian, Dong; Qian, DongAn efficient solution algorithm has been developed for space–time finite element method that is derived from time discontinuous Galerkin (TDG) formulation. The proposed algorithm features an iterative solver accelerated by a novel and efficient preconditioner. This preconditioner is constructed based on the block structure of coupled space–time system matrix, which is expressed as addition of Kronecker products of temporal and spatial submatrices. With this unique decomposition, the most computationally intensive operations in the iterative solver, i.e. matrix operations, are subsequently optimized and accelerated employing the inverse property of Kronecker product. Theoretical analysis and numerical examples both demonstrate that the proposed algorithm provides significantly better performance than the already developed implementations for TDG-based space–time FEM. It reduces the computational cost of solving space–time equations to the same order of solving stiffness equations associated with regular FEM, thereby enabling practical implementation of the space–time FEM for engineering applications.Item Mechanical Properties of Atomically Thin Boron Nitride and the Role of Interlayer Interactions(Nature Publishing Group) Falin, Aleksey; Cai, Qiran; Santos, Elton J. G.; Scullion, Declan; Qian, Dong; Zhang, Rui; Yang, Zhi; Huang, Shaoming; Watanabe, Kenji; Taniguchi, Takashi; Barnett, Matthew R.; Chen, Ying; Ruoff, Rodney S.; Li, Lu Hua; 295272933 (Qian, D); Qian, Dong; Zhang, RuiAtomically thin boron nitride (BN) nanosheets are important two-dimensional nanomaterials with many unique properties distinct from those of graphene, but investigation into their mechanical properties remains incomplete. Here we report that high-quality single-crystalline mono-and few-layer BN nanosheets are one of the strongest electrically insulating materials. More intriguingly, few-layer BN shows mechanical behaviours quite different from those of few-layer graphene under indentation. In striking contrast to graphene, whose strength decreases by more than 30% when the number of layers increases from 1 to 8, the mechanical strength of BN nanosheets is not sensitive to increasing thickness. We attribute this difference to the distinct interlayer interactions and hence sliding tendencies in these two materials under indentation. The significantly better interlayer integrity of BN nanosheets makes them a more attractive candidate than graphene for several applications, for example, as mechanical reinforcements.Item Multi-Responsive and Multi-Motion Bimorph Actuator Based on Super-Aligned Carbon Nanotube Sheets(Elsevier Ltd) Li, J.; Mou, L.; Zhang, Rui; Sun, J.; Wang, R.; An, B.; Chen, H.; Inoue, K.; Ovalle-Robles, R.; Liu, Z.; Zhang, RuiMulti-responsive actuators have recently aroused intensive research for the requirements of being used in various environments. However, their actuation performances are generally lower than their single responsive counterparts because of the restriction of material selection and complicated structural design. Here, for the first time, a multi-responsive actuator that can respond to four types of stimuli including electricity, near infrared light, humidity, and organic vapors was designed by attaching superaligned carbon nanotubes sheets and coating an ink layer on the both sides of the PET film. The multi-responsive actuator shows fast and reversible actuation with high displacement-to-length ratio of 0.79 under electrical stimulus, and large bending angle of 212⁰ in 0.55 s at a bending speed of 646⁰/s under near infrared light irradiation. The actuator also shows fast response exposing to moisture and volatile organic vapors. The actuator shows a large bending angle within ∼0.1 s when exposed to different organic solvents and recovered its initial shape when the solvent was removed. These performances are in the same level of the record values of the thermal-based bimorph actuators. We demonstrated this actuator as a smart electric-control frequency switch at relatively high on/off frequency up to 17.5 Hz. ©2019 Elsevier LtdItem Multiscale Methods for Fatigue and Dynamic Fracture Failure and High-performance Computing Implementation(2020-12-01T06:00:00.000Z) Zhang, Rui; Qian, Dong; Makris, Georgios; Lu, Hongbing; Ryu, Ill; Bernal, Rodrigo; Eason, ThomasThis dissertation presents several multiscale methods for material failure and implementations on high-performance computing (HPC) platforms. The work is motivated by the challenges in fully capturing the mechanics of failure using a single scale method. As such, multiscale approaches that incorporate multiple temporal and spatial scales have been established. To address the high computational costs, efficient algorithms and their implementations on the HPC platform featuring many-core architectures have been developed. Based on the topics being addressed, the dissertation is divided into two parts. First, a multiscale computational framework for high cycle fatigue (HCF) life prediction is established by integrating the Extended Space-Time Finite Element Method (XTFEM) with multiscale fatigue damage models. XTFEM is derived based on the time-discontinuous Galerkin approach, which is shown to be A-stable and high-order accurate. While the robustness of XTFEM has been extensively demonstrated, the associated high computational cost remains a critical barrier for its practical applications. A novel hybrid iterative/direct solver is proposed with a unique preconditioner based on Kronecker product decomposition of the space-time stiffness matrix. XTFEM is further accelerated by utilizing HPC platforms featuring a hierarchy of distributed- and shared-memory parallelisms. A two-scale damage model is coupled with XTFEM to capture nonlinear material behaviors under HCF loading and accelerated by parallel computing using both CPUs and GPUs. Furthermore, an efficient data-driven microstructure-based multiscale fatigue damage model is established by employing the Self-consistent Clustering Analysis, which is a reduced-order method derived from Machine Learning. Robustness and efficiency of the framework are demonstrated through benchmark problems. HCF simulations are conducted to quantify key effects due to mean stress, multiaxial load conditions, and material microstructures. In the second part, a concurrent multiscale method to dynamic fracture is established by coupling Peridynamics (PD) with the classical Continuum Mechanics (CCM). PD is a novel nonlocal generalization of CCM. It is governed by an integro-differential equation of motion, which is free of spatial derivatives. This salient feature makes it attractive for problems with spatial discontinuities such as cracks. However, it generally leads to a much higher computational cost due to its nonlocality. There is a continuing interest to couple PD with CCM to improve efficiency while preserving accuracy in critical regions. In this work, Finite Element (FE) simulation is performed over the entire domain and coexists with a local PD region where crack pre-exists or is expected to initiate. The coupling scheme is accomplished by a bridging-scale projection between the two scales and a class of twoway nonlocal matching boundary conditions that eliminates spurious wave reflections at the numerical interface and transmits waves from the FE domain to the PD region. An adaptive scheme is established so that the PD region is dynamically relocated to track propagating crack. Accuracy and efficiency of the proposed method are illustrated by wave propagation examples. Its effectiveness and robustness in material failure simulation are demonstrated by benchmark problems featuring brittle fracture. Finally, conclusions are drawn from the research work presented and prospective future developments of the established multiscale methods are provided.Item Photothermal Bimorph Actuators with In-Built Cooler for Light Mills, Frequency Switches, and Soft Robots(Wiley-VCH Verlag) Li, J.; Zhang, Rui; Mou, L.; Jung de Andrade, Monica; Hu, X.; Yu, K.; Sun, J.; Jia, T.; Dou, Y.; Chen, H.; Fang, Shaoli; Qian, Dong; Liu, Z.; 295272933 (Qian, D); Zhang, Rui; Jung de Andrade, Monica; Fang, Shaoli; Qian, DongPhotothermal bimorph actuators are widely used for smart devices, which are generally operated in a room temperature environment, therefore a low temperature difference for actuation without deteriorating the performance is preferred. The strategy for the actuator is assembling a broadband-light absorption layer for volume expansion and an additional water evaporation layer for cooling and volume shrinkage on a passive layer. The response time and temperature-change-normalized bending speed under NIR, white, and blue light illumination are at the same level of high performance, fast photothermal actuators based on polymer or polymer composites. The classical beam theory and finite element simulations are also conducted to understand the actuation mechanism of the actuator. A new type of light mill is designed based on a wing-flapping mechanism and a light-modulated frequency switch. A fast-walking robot (with a speed of 26 mm s -1 ) and a fast-and-strong mechanical gripper with a large weight-lifting ratio (˜2142), respectively, are also demonstrated. ©2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim