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A mechanical device specially designed for the application of low-level post-tensioning forces to glass fiber reinforced polymer
(GFRP) bars has been developed at the University of Missouri-Rolla. Some of the advantageous features of this device are that
it is simple to assemble and the low-level post-tensioning forces can be applied manually and safely without the need for
hydraulic jacks or heavy equipment. This device has been conceived with the main objective of retrofitting masonry buildings,
some of which remain in service despite large, open cracks leading to considerable instability and serviceability concerns.
According to the method derived in this paper, GFRP bars are installed in artificially imposed grooves and then post-tensioned
with low-level stresses with the main objective to partially close these cracks, such that the serviceability and in-plane
capacity of un-reinforced masonry (URM) buildings may be regained. In this paper we describe the mechanical components of
this device, along with its advantageous features and potential application for the retrofit of URM walls. 相似文献
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Luv Verma Jefferson Andrew Srinivasan M. Sivakumar Gurusamy Balaganesan Srikanth Vedantam Hom N. Dhakal 《Molecules (Basel, Switzerland)》2021,26(1)
This paper aims to estimate the enhancement in the energy absorption characteristics of the glass fiber reinforced composites (GFRP) by embedding prestrained pseudo-elastic shape memory alloy (SMA) that was used as a secondary reinforcement. The pseudo-elastic SMA (PE-SMA) embedded were in the form of wires and have an equiatomic composition (i.e., 50%–50%) of nickel (Ni) and titanium (Ti). These specimens are fabricated using a vacuum-assisted resin infusion process. The estimation is done for the GFRP and SMA/GFRP specimens at four different impact velocities (65, 75, 85, and 103 m/s) using a gas-gun impact set-up. At all different impact velocities, the failure modes change as we switch from GFRP to SMA/GFRP specimen. In the SMA/GFRP specimen, the failure mode changed from delamination in the primary region to SMA-pull out and SMA deformation. This leads to an increase in the ballistic limit. It is observed that energy absorbed by SMA/GFRP specimens is higher than the GFRP specimens subjected to the same levels of impact energy. To understand the damping capabilities of SMA embedment, vibration signals are captured, and the damping ratio is calculated. SMA dampens the vibrations imparted by the projectile to the specimen. The damping ratio of the SMA/GFRP specimens is higher than the GFRP specimens. The damping effect is more prominent below the ballistic limit when the projectile got rebounded (65 m/s). 相似文献
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《Composite Interfaces》2013,20(4):305-321
Tensile tests are performed on short glass fiber reinforced nylon-6 composite specimens with an open hole. The specimens with four different fiber surface treatments are used. Fiber weight fractions are 10% and 30%. It is found that the dependence of tensile strength on the diameter of hole is different for different fiber weight fractions. To explain the difference in tensile strength, in-situ observation of microscopic failure process around an open hole is conducted. The micro-grids are printed on the specimen surface to observe the microscopic deformation and fracture clearly. The difference in microscopic failure process due to the difference in fiber surface treatment and fiber weight fraction are observed, which explains the difference in tensile strength qualitatively. In addition, micro-grid methods are applied to measure the axial strain distribution in a short fiber in a real composite. The shear-lag prediction is compared with the experimental results. The fiber axial strain distribution obtained by the micro-grid methods is found to agree well with the shear-lag prediction until extensive interfacial debonding occurs. 相似文献
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Xue Feng Yao M. H. Kolstein F. S. K. Bijlaard Wei Xu ManQiong Xu 《Polymer Testing》2003,22(8):955-963
In this paper, tensile strength and fracture of finite glass fiber-reinforced plastic GFRP (glass/polyester) composite materials with a through-the-thickness eccentrically located circular hole are experimentally studied. The strain response histories near the hole boundary for different eccentrically located holes during the whole damage and fracture process of the notched specimen are recorded. The effects of off-center distance and hole diameter on strength and fracture of the notched specimen are analyzed. The tensile fracture strength of the notched specimen with an eccentrically located hole is determined. Also, the initial stress concentrations in the composite laminate due to the presence of the eccentrically located hole are understood. These results play an important role for predicting strength and evaluating lifetime of laminate composite with complex geometrical cutouts. 相似文献
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Zinov'ev P. A. Tsvetkov S. V. Kulish G. G. van den Berg Robert W. van Schepdael Ludo J. M. M. 《Mechanics of Composite Materials》2001,37(4):281-288
The dependence of the strength properties of two unidirectional fibrous composites on high (up to 500 MPa) hydrostatic pressure has been studied experimentally. Ring specimens of epoxy carbon- and glass-fiber-reinforced plastics were tested in tension using half-disk devices. The tensile strength in the reinforcement direction increased with increase in the pressure up to 300 MPa. However, at a further increase in the pressure, this strength decreased. It was found that the failure mode of unidirectional composites depends on the magnitude of hydrostatic pressure. The failure shapes differed in the location of the failure zone and in the relative extent of longitudinal cracks in the specimens. At atmospheric pressure, the failure zone covered practically the whole volume of the specimens. With increased pressure, the failure zone became localized. At the highest pressures investigated, the failure was accompanied by the formation of a single crack across the reinforcement direction. 相似文献
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The present study continues the work described in part I of this paper in evaluating a long-term-experiment, where a rotor blade segment of a wind turbine is exposed to the elements and thereby monitored with passive thermography. First, it is investigated whether subsurface features in rotor blades – mainly made of GFRP – can generally be detected with thermography from greater distances under favorable conditions. The suitability of the sun for acting as a heat source in applying active thermography has been tested in the previous study. In this study, the climatic influence on thermographic measurement is evaluated. It is demonstrated that there are favorable and unfavorable circumstances for imaging thermal contrasts which reflect inner structures and other subsurface features like potential defects. It turns out that solar radiation serves as a very effective heat source, but not at all times of day. Other environmental influences such as diurnal temperature variations also create temperature contrasts that permit conclusions on subsurface features. Particular scenarios are reconstructed with FEM-simulations in order to gain deeper insight into the driving mechanisms that produce the observed thermal contrasts. These investigations may help planning useful outdoor operations for inspecting rotor blades with thermography. 相似文献
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This work deals with the effect that the use of glass fibres has on the morphology developed by a thermoplastic polymer modified epoxy. In particular, three surface modifications of the glass fibres were studied: calcinations desizing, activation with hydrochloric acid and coating with 3-aminopropyltriethoxy silane. As the epoxy polymer, a model system based on the full reaction of DGEBA and 2-methyl-1,5-diaminopentane was used. As the modifiers of the epoxy thermoset, two thermoplastic polymers were used: poly(methylmethacrylate) and polystyrene. The morphologies were examined either in the polymer bulk or at the interfaces by means of scanning electron microscopy and atomic force microscopy. After a thoroughly examination of the samples it was found that the thermoplastic polymers preferentially accumulate at the interfaces of these materials when activated and silanized glass fibres are used. These results might be attributed to a gradual phase separation process due to stoichiometric gradients which, on the other hand, seems to be conditioned by the nature of glass fibres surface. 相似文献