Browsing by Author "Wang, Xiaomeng"

Now showing 1 - 10 of 10
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    Degradation of bending properties of flax fiber reinforced polymer after natural aging and accelerated aging
    (Elsevier Ltd, 2020) Wang, Xiaomeng; Petrů, Michal
    In this paper, the effect of natural aging and accelerated aging on the bending properties of flax fiber reinforced polymer (FFRP) is studied. Test results show that the flexural strength decreases by 11.2%, 14.9%, 15.5%, and the flexural modulus decreases by 21.3%, 32.3%, 35.8%, after 60 days, 120 days and 180 days of natural aging, respectively. Then accelerated test is carried out to predict the long-term performance of FFRP. The results show that short-term exposure test (just considering the temperature and humidity) cannot achieve the same effect on mechanical property degradation as natural aging. A modified residual mechanical property model of FFRP is established according to the test results.
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    Effect of Hygrothermal Aging and Surface Treatment on the Dynamic Mechanical Behavior of Flax Fiber Reinforced Composites
    (MDPI, 2019-07-25) Petrů, Michal; Wang, Xiaomeng
    The recent developments of FRP (fiber reinforced polymer) are towards the growth and usage of natural FRP in the field of engineering due to both environmental and economic benefits. Flax fiber is one of the most commonly used natural fibers. One of the critical factors affecting the mechanical behavior of FFRP (flax fiber reinforced polymer) is hygrothermal aging. Some experimental works have been conducted to investigate the effect of hydrothermal aging on static behavior of FFRP. However, fewer efforts have been made to study its damping properties after hydrothermal aging. In this paper, the effect of surface treatment (including alkalization, silanization, acetylation and alkali-silanization) on dynamic mechanical behavior of FFRP under hygrothermal aging is studied. The results show that water resistance and damping properties of FFRP are improved after surface treatment. The acetylation treated FFRP exhibits excellent damping performance among all treated specimens.
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    Freeze-thaw resistance of epoxy/concrete interface evaluated by a novel wedge splitting test
    (2019-06-20) Wang, Xiaomeng; Petrů, Michal
    Externally bonding using epoxy is one of major applying method for FRP strengthening technology. The long-term performance of the epoxy/concrete interface has been proven to be a key for practical application of FRP strengthening, especially when the strengthened structures are exposed to severe environmental conditions. In this study, an experimental program has been carried out to examine the effect of freeze-thaw cycles (soaked in tap water and 5% sodium sulfate solution) on the deterioration of the epoxy/concrete interface through a novel wedge splitting test, which can directly measure the traction-separation law of the interface under mode I loading. The effect of silane treatment on the freeze-thaw resistance of the interface was also examined. A simplified tri-linear constitutive model of the epoxy/concrete interface was obtained according to the test results. Results showed that both the ultimate bond strength and the fracture energy decrease exponentially with the number of freeze-thaw cycles. Under mode I loading, the failure mode of the reference specimen is the tensile failure of the concrete. With the increase of freeze-thaw cycles, the failure mode gradually turns into adhesive failure along the epoxy/concrete interface. Testing results also confirm that the freeze-thaw resistance of the epoxy/concrete interface can be improved by application of silane coupling agent.
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    Mode I fracture evaluation of carbon fiber reinforced polymer/steel interfaces subject to freeze-thaw cycling
    (Elsevier Ltd, 2020-03) Wang, Xiaomeng; Petrů, Michal
    In order to increase the durability database and have a better understanding of the degradation mechanism, the effect of freeze-thaw cycling on the mode I fracture energy release rate of CFRP (Carbon Fiber Reinforced Polymer)/steel interface is studied by using wedge driving test method. Previous studies show that moisture plays an important role in freezing-thawing cycling, therefore the relationship between moisture and mode I fracture energy release rate of CFRP/steel interface is studied. Because the interfacial moisture content cannot be measured directly, a finite element simulation is established to predict the moisture distribution of the interface based on water uptake tests of component materials. The results show that the mode I fracture energy release rate of CFRP/steel interface decreases nonlinearly with apparent relative humidity. The change of failure mode from debonding within the CFRP layer to adhesive failure long the interface is also observed.
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    Mode I fracture evaluation of CFRP-to-concrete interfaces subject toaggressive environments agents: Freeze-thaw cycles, acid and alkalinesolution
    (Elsevier, 2019-07-01) Petrů, Michal; Wang, Xiaomeng
    The long-term durability of the interface between FRP (fiber reinforced polymer) and concrete is crucial to the safety of FRP strengthened concrete structures. Some experimental works have been carried out to investigate the effect of environmental factors on model II fracture behavior of the FRP-to-concrete interface. However, fewer efforts have been made to estimate interfacial durability under mode I loading. This study evaluates the mode I fracture energy release rate of CFRP (carbon fiber reinforced polymer)-to-concrete interface subjected to freeze-thaw cycling, acid attack, and alkali attack. Significant decrease of fracture energy release rate is observed after environmental conditioning. With the increase of freeze-thaw cycles and soaking time, the failure mode of the specimen changes from tensile failure of concrete to adhesive failure along the interface. Test results also confirm that the durability of the CFRP-to-concrete interface can be improved by application of silane coupling agent under freeze-thaw cycling and alkaline condition.
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    Numerical investigation for the fatigue performance of reinforced concrete beams strengthened with external prestressed HFRP sheet
    (ELSEVIER SCI LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND, 2020-03-20) Wang, Xiaomeng; Zhou, Chuwei; Ai, Jun; Petrů, Michal; Liu, Yao
    External FRP (Fiber Reinforced Polymer) strengthening method has been considered to be an effective way to restore or increase the capacity of RC (Reinforced Concrete) beams. This study focuses on numerical simulating the fatigue performance of HFRP (Hybrid Fiber Reinforced Polymer) strengthened RC beam. Beams are pre-cracked first, then strengthened by HFRP, and subjected to fatigue loading. The test variable is the prestress of HFRP. Stress distribution and damage development of pre-cracking, strengthening and fatigue loading process are analyzed. The user-subroutine UMAT in Abaqus is used for implementation of the constitutive models of component materials. The simulation results show good agreements with experimental data. The failure of both reference beam and strengthened beams is found caused by fatigue fracture of the longitudinal steel bar. Therefore, the stress amplitude of the longitudinal steel bar is the dominant factor of the fatigue life of RC beams. Prestressed HFRP can significantly reduce the stress magnitude of longitudinal steel bar and suppress crack propagation, thus improve the fatigue life of the strengthened RC beam. In an appropriate range, elevating prestress level can prolong fatigue life of strengthened RC beam.
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    Parametric Study of Flexural Strengthening of Concrete Beams with Prestressed Hybrid Reinforced Polymer
    (MDPI, 2019-11) Wang, Xiaomeng; Petrů, Michal; Ai, Jun; Ou, Shikun
    The strengthening method of using hybrid fiber reinforced polymer is an effective way to increase the strengthening efficiency and lower the cost. This paper focuses on simulating the flexural behavior of reinforced concrete beam strengthened by prestressed C/GFRP (Carbon-Glass hybrid Fiber Reinforced Polymer) with different hybrid ratios and prestress levels. An elastoplastic damage constitution is used to simulate the mechanical behavior of concrete. A cohesive zone model under mixed mode is adopted to describe the debonding behavior of the FRP-concrete and concrete-steel interface. The results show good agreement with the experiment in the load-deflection curve, load-stress curve of steel, and HFRP. Furthermore, the failure mode of concrete and FRP debonding obtained from numerical simulation is the same as the test. Considering the improvement of the bending capacity, stiffness, and ductility of the strengthened beam in this paper, the best hybrid ratio of carbon to glass fiber is 1:1, and the suitable prestress level is between 30 and 50% of its ultimate strength.
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    The effect of surface treatment on the creep behavior of flax fiber reinforced composites under hygrothermal aging conditions
    (2019-05-30) Wang, Xiaomeng; Petrů, Michal; Yu, Hang
    The application of natural FRP (Fiber Reinforced Polymer) is being targeted in various fields due to both environmental and economic benefits. FFRP (Flax Fiber Reinforced Polymer) is one of the major natural FRPs. The durability and long-term performance of FFRP have been proven a key to its practical engineering application. Some experimental works have been conducted to investigate the creep properties of FFRP. However, fewer efforts have been made to improve its creep performance thus far. In this paper, the effect of surface treatment on the creep behavior of FFRP under hygrothermal aging conditions is studied, and a fractional-order creep model is established to predict its creep behavior.