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Journal articleWu C, Wu R, Tam L-H, 2022,
The creep behavior of semicrystalline carbon nanotube/polypropylene nanocomposite: a coarse-grained molecular study
, Polymer Degradation and Stability, Vol: 196, ISSN: 0141-3910Polypropylene (PP) is vulnerable to creep under constant loads, which is a serious problem for PP-based applications. By incorporating carbon nanotubes (CNTs), the CNT/PP composite exhibits improved creep resistance, while the CNT aggregation with high contents could limit the improvement. In order to ensure the long-term durability, the creep response of CNT/PP composite with different CNT contents should be carefully characterized. In this paper, the coarse-grained models of CNT/PP nanocomposite with various CNT contents are constructed, which are subjected to constant loads at various levels. It is found that the threshold stress and energy barrier for the initiation of fracture show an initial increase and a subsequent decrease, with the transition at 3 wt%. The decline of creep properties with high CNT contents is related to the limited CNT restriction effect on the PP chain behaviors, which is resulted from the sliding between CNT chains and the accelerated interfacial sliding between CNT and PP due to increased interfacial voids, as observed from the behaviors and interactions of investigated molecules and chains during creep. This study provides insights into the molecular creep behavior of CNT/PP nanocomposite, which contributes to the understanding of degradation of composite materials under constant loads.
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Conference paperWu C, Mahmoud MM, Wang Y, et al., 2022,
Impact Behavior of High-Strength Engineered Cementitious Composite and Concrete Layered Slabs
, ISSN: 1013-9826High strength Engineered Cementitious Composite (HS-ECC) is a promising material to be used in protective structures. Due to its high manufacturing efforts and cost compared to conventional concrete, nonlinear finite element (FE) simulation is performed to study the influence of replacing HS-ECC layers with concrete under drop weight impact load. Both materials are simulated using the MAT_72R3 material model impeded in LS-DYNA and verified with experimental results. Several FE slab models were developed to compare the impact responses of different configurations. This study as a whole will provide a guideline for researchers to carry out a performance and cost optimization for protective structure elements.
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Conference paperWu C, Wu R, Tam L-H, 2022,
Understanding Degradation of Fiber/Matrix Interface Under Environmental Effects Using Molecular Simulation
, 10th International Conference on Fibre-Reinforced Polymer (FRP) Composites in Civil Engineering (CICE), Publisher: SPRINGER-VERLAG SINGAPORE PTE LTD, Pages: 2096-2108, ISSN: 2366-2557- Author Web Link
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- Citations: 1
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Journal articleWu C, Wu R, Tam L-H, 2021,
Coarse-grained molecular simulation of the effects of carbon nanotube dispersion on the mechanics of semicrystalline polymer nanocomposites
, Nanotechnology, Vol: 32, ISSN: 0957-4484With the incorporation of carbon nanotubes (CNTs), CNT/polypropylene (PP) nanocomposites are found to possess enhanced mechanical properties, but the reinforcing effect is reduced at large added CNT weight percentages due to CNT aggregation. Optimizing the properties of a nanocomposite requires a fundamental understanding of the effects of CNT dispersion on the nanocomposite. In this work, coarse-grained molecular models of CNT/PP nanocomposites are constructed, which consist of randomly dispersed or aggregated CNT bundles. Our simulation results reveal that with randomly dispersed CNT bundles, the nanocomposite shows properties that continuously improve with increasing CNT contents due to the effective CNT/PP interface and the reinforcing effect of CNTs. By comparison, the nanocomposite with aggregated CNT clusters exhibits a decline in yield strength at CNT contents over 3 wt%, which results from a reduced CNT load-carrying capacity due to the formation of structural voids in the interfacial region. This study achieves an in situ observation of the structural void evolution of loaded nanocomposites, provides valuable insights into the effects of CNT dispersion on the mechanics of CNT/PP nanocomposites, and paves the way for optimizing the design of nanocomposites with superior mechanical properties by designing the CNT dispersion in the structure.
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Journal articleWu C, Chen C, Cheeseman C, 2021,
Size Effects on the Mechanical Properties of 3D Printed Plaster and PLA Parts
, JOURNAL OF MATERIALS IN CIVIL ENGINEERING, Vol: 33, ISSN: 0899-1561- Author Web Link
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- Citations: 6
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Journal articleMa H, Yi C, Wu C, 2021,
Review and outlook on durability of engineered cementitious composite (ECC)
, Construction and Building Materials, Vol: 287, ISSN: 0950-0618Durability is important for construction materials especially when they are used for long-term engineering applications. Engineered cementitious composite (ECC) as a relatively new fiber-reinforced cementitious composite material has attracted broad interest from research and construction communities. ECC has strain-hardening behavior and self-healing ability due to its micro-cracking under tensile loading. These advantages make ECC more durable under various environmental conditions comparing to ordinary concrete. This paper presents an up-to-date review on ECC durability studies in the literature, with detailed discussions on ECC high temperature resistance, permeability resistance, frost and salt corrosion resistance, shrinkage resistance, abrasion resistance, fatigue resistance and etc. These durability discussions are closely related to the behaviors of fiber, matrix and fiber-matrix interface of ECC under various environmental conditions. Finally this paper proposes several research directions related to ECC durability based on the research gaps identified from the comprehensive literature review.
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Journal articleFame CM, Correia JR, Ghafoori E, et al., 2021,
Damage tolerance of adhesively bonded pultruded GFRP double-strap joints
, Composite Structures, Vol: 263, ISSN: 0263-8223Compared with mechanical fastening, adhesive bonding offers numerous advantages in the joining of pultruded glass fiber reinforced polymer (GFRP) sections. However, one critical issue associated with bonded joints is the assessment of their mechanical behavior considering bondline defects. This paper presents the results of an experimental investigation of the damage tolerance of adhesively bonded pultruded GFRP joints considering bondline defects. Double-strap specimens with and without bondline defects were prepared and tested in tension until failure. The location (five different locations in the bond length and width directions), size (10%, 20%, and 30% of the total bonded area in both the bond length and width directions), shape (triangular, rectangular, square, circular, and elliptical), and number (between 1 and 8) of defects within the bondline were considered as variable parameters. This paper reports and discusses the observed failure modes, load–displacement curves, and joint capacities, considering the effects of bondline defects. Interface debonding was observed in regions neighboring the bondline defects, and delamination was observed in other bonded areas. All joints exhibited a linear elastic load–displacement response with sudden and brittle failure, regardless of the presence of bondline defects. The observed capacity reduction of up to 33% could be significant if the defects were located at the edges of the bonded area. Defects of different shapes resulted in similar reductions in joint capacity (21%). Furthermore, the joint was found to be more sensitive to irregularly shaped (e.g., triangular) defects, and reducing the number of defects was more effective in mitigating the reduction in joint capacity than reducing the total defect area was.
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Journal articleWu C, Zhang Z, Tam L-H, et al., 2021,
Group effect of GFRP-timber bolted connections in tension
, Composite Structures, Vol: 262, ISSN: 0263-8223Steel plate bolted connections are frequently used in timber structures. However, these connections may incur durability problem due to the corrosion of the steel plates. This paper proposes using GFRP plate to replace steel plate in timber connections to mitigate the corrosion issue. The group effect of the proposed GFRP-timber bolted connection is studied. Tensile tests of GFRP-timber bolted connections were conducted considering a number of variables including bolt diameter, bolt pitch distance, bolt row number, bolt column number. The failure modes and the load–displacement curves of the connections were reported. Experimental results showed that the group effect of the GFRP-timber bolted connection is strongly affected by the bolt diameter and number of bolts, but little affected by bolt pitch distance. The effect of the number of bolt columns on the group effect was also discovered and quantified. The design equation of the timber bolted connection in Eurocode 5 was modified considering the effects of various parameters. The modified equation was then verified using the experimental data in this paper. Finally, detailed recommendations were provided for the design of the proposed GFRP-timber bolted connection.
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Journal articleMa L, He J, Gu Y, et al., 2021,
Structure design of GFRP composite leaf spring: an experimental and finite element analysis
, Polymers, Vol: 13, ISSN: 2073-4360Due to the high load-bearing capacity and light weight, composite leaf spring with variable width and variable thickness has been increasingly used in the automobile industry to replace the conventional steel leaf spring with a heavy weight. The optimum structural design of composite leaf spring is particularly favorable for the weight reduction. In this study, an effective algorithm is developed for structural optimization of composite leaf spring. The mechanical performance of composite leaf spring with designed dimensions is characterized using a combined experimental and computational approach. Specifically, the composite leaf spring with variable width and variable thickness was prepared using the filament winding process, and the three-dimensional finite element (FE) model of the designed composite leaf spring is developed. The experimental sample and FE model of composite leaf spring are tested under the three-point bending method. From experimental and simulation results, it is shown that the bending stiffness of the designed leaf spring meets the design requirement in the automotive industry, while the results of stress calculation along all directions meet the requirements of material strength requirement. The developed algorithm contributes to the design method for optimizing the stiffness and strength performance of the composite leaf spring.
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