Papers by Author: Chun Hui Yang

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Authors: Chun Hui Yang, Zhong Qing Su, Lin Ye, Li Min Zhou, Peter D. Hodgson
Abstract: A series of digital frequency filters (DFFs) were designed to screen diverse noises and the spectrographic analysis was conducted to isolate complex boundary reflection, which obscures the damage-induced signals. The scale-averaged wavelet power (SAP) technique was applied to enhance the measurement accuracy of Time of Flight (TOF). As an example, the propagation characteristics of elastic wave in a structural beam of square cross-section were analyzed using such an approach and verified experimentally and numerically, with the consideration of the complicated wave scatter caused by the non-ignorable section dimensions.
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Authors: Chun Hui Yang, Ilchat Sabirov, Jonathan Mullins, Peter D. Hodgson
Abstract: Nanostructured and ultra-fine grained metals have higher strength but extremely limited ductility compared to coarse grained metals. However, their ductility can be greatly improved by introducing a specific range of grain sizes in the microstructures. In the paper, multiscale unit cell approach (UCA) is developed and applied to predict the averaged stress-strain relations of the multiscale microstructure metals. The unit cell models are three-phase structured at different scale lengths of 100 nm, 1 μm and 10 μm with different volume fractions and periodic boundary conditions. The contributions of multi-scale microstructures to the macroscopic structural properties of metals are also studied using a analytic approach—two-step mean-field method (TSMF), where three microstructural parameters are introduced and thus mechanical properties such as strength and ductility are presented as a function of these parameters. For verification of these proposed numerical and theoretical algorithms, the structural properties of the pure nickel with three-grain microstructures are studied and the results from FEA and the proposed theory have good agreement.
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Authors: Jeerachai Supasuthakul, Peter D. Hodgson, Matthias Weiss, Chun Hui Yang
Abstract: Analytical modelling of deep drawing process is of value in preliminary process design to illustrate the influence of major variables including friction and strain hardening on punch loads, cup dimensions and process limits. In this study, analytical models including theoretical solution and a series of finite element models are developed to account for the influences of process parameters including friction coefficient, tooling geometry and material properties on deep drawing of metal cups. The accuracy of both the theoretical and finite element solutions is satisfactory compared with those from experimental work.
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Authors: Yang An, Chun Hui Yang, Peter D. Hodgson, Cui E Wen
Abstract: In the study, both experimental work and numerical modeling are performed to investigate the pore size effects on the mechanical properties and deformation behaviours of titanium foams. Cylindrical titanium foam samples with different pore sizes are fabricated through powder metallurgy. Scanning electron microscope (SEM) is used to determine the pore size, pore distribution and the ratios of the length to width of pores. Compressive tests are carried out to determine the mechanical properties of the titanium foams with different pore sizes. Finally, finite element modeling is attempted to simulate the deformation behaviour and the mechanical properties of the titanium foams. Results indicate that titanium foams with different pore sizes have different geometrical characteristics, which lead to different deformation behaviours of cell walls during compression, resulting in different mechanical properties of titanium foams.
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Authors: Chun Hui Yang, Y.X. Zhang, Hoon Huh
Abstract: In the paper, two novel 2-D hybrid special finite elements each containing an interfacial edge crack, which lies along or vertical to the interface between two materials, are developed. These proposed elements can assure the high precision especially in the vicinity of crack tip and provide a better description of its singularity with only one hybrid element surrounding one interfacial crack, thus, the numerical modeling of fracture analysis on bi-material crack can be greatly simplified. Numerical examples are provided to demonstrate the validity and versatility of the proposed method.
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Authors: Yang An, Cui E Wen, Peter D. Hodgson, Chun Hui Yang
Abstract: The effect of foam fillers on the impact behaviour and energy absorption of an aluminium tube is investigated. Both experimental test and computational simulation are employed in current study. For comparison, hollow tubes and foams are also tested, respectively. Foam filler is found to be ineffective in increasing the crushing loads of the composite tubes over the simple superposition of the crushing loads of hollow tube and foam. Also, foam filler increases the tendency for the concertina mode of folding. The foam fillers of tubes additionally result in increasing the SAE values over those of hollow tubes.
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Authors: Yi Xia Zhang, Chun Hui Yang
Abstract: Efficient and accurate finite elements are crucial for finite element analysis to provide adequate prediction of the structural behavior. A large amount of laminated plate elements have been developed for finite element analysis of laminated composite plates based on the various lamination theories. A recent and complete review of the laminated finite elements based on the higher-order shear deformation theories, including the global higher-order theories, zig-zag theories and the global-local higher-order theories is presented in this paper. Finally some points on the development of the laminated plate elements are summarized.
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Authors: Chun Hui Yang, Zhong Qing Su, Lin Ye, Ye Lu, Michael Bannister
Abstract: Stringer-stiffened plate-like structure is a typical engineering structure and its structural integrity is critical. A guided Lamb wave-based damage identification scheme and an online structural health monitoring (SHM) system with an integrated PZT-sensor network were developed. In the previous studies, the specimens were relatively simple. In this paper, the abovementioned method was extended to the stiffened plate-like structure—a flat plate reinforced by stringer. FE dynamic simulation was applied to investigate the Lamb wave propagation characteristics due to the existence of stringer with the consideration of its material and geometric configurations.
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Authors: Jiang Ting Wang, Peter D. Hodgson, Jing De Zhang, Chun Hui Yang
Abstract: To combine the merits of both metals and ceramics into one material, many researchers have been studying the deposition of alumina coating using plasma spray on metal substrates. However, as the coatings are deposited at a high temperature, residual thermal stresses develop due to the mismatch of thermal expansion coefficients of the coating and substrate and these are responsible for the initiation and expansion of cracks, which induce the possible failure of the entire material. In this paper, the residual thermal-structural analysis of a Fe3Al/Al2O3 gradient coating on carbon steel substrate is performed using finite element modelling to simulate the plasma spray. The residual thermal stress fields are obtained and analyzed on the basis of temperature fields in gradient coatings during fabrication. The distribution of residual thermal stresses including radial, axial and shear stresses shows stress concentration at the interface between the coatings and substrate. The mismatch between steel substrate and composite coating is still the dominant factor for the residual stresses.
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Authors: Akif Kaynak, Chun Hui Yang, Abbas Kouzani
Abstract: Electrochemical synthesis of a tri-layer polypyrrole based actuator optimized for performance was reported. The 0.05 M pyrrole and 0.05 M tetrabutylammonium hexaflurophosphate in propylene carbonate (PC) yielded the optimum performance and stability. The force produced ranged from 0.2 to 0.4mN. Cyclic deflection tests on PC based actuators for 3 hours indicated that the displacement decreased by 60%. PC based actuator had a longer operating time, exceeding 3 hours, compared to acetonitrile based actuators. A triple-layer model of the polymer actuator was developed based on the classic bending beam theory by considering strain electrode material. A tri-layer actuator was fabricated [4, 6], by initially sputter coating a PVDF film with approximately 100nm of gold layer, resulting in a conductive film with a surface resistance of 8-10Ω. The PVDF film was about ~145µm thick had an approximate pore size of 45μm. A solution containing 0.05M distilled pyrrole monomer, 0.05M (TBAPF6) and 1% (w/w) distilled water in PC (propylene carbonate) solution was purged with nitrogen for 15 minutes. The continuity between PPy and PVDF. Results predicted by the model were in good agreement with the experimental data.
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