Fiber Reinforced Plastic Plates Research Articles

Simulation of impact response of multi-layered panels composed of bonded and unbonded plies

This paper presents an investigation into low velocity impact response of different configurations of resin bonded and unbonded layups of glass fabric composites for armour application. A numerical simulation was developed using the finite element code LS-Dyna to model the impact response at low velocities. The numerical results have been validated by comparison with results of impact tests on epoxy-bonded glass fibre-reinforced plastic plates with all edges fixed. Further impact testing of composite panels with various lay-up configurations have been performed using two different types of support: all edges fixed and with the panels mounted on clay foundation with all edges free. Experimental results show that a combination of unbonded flexible and adhesively bonded rigid composite lay-ups, which has a lower weight than fully bonded panels, yields comparable levels of energy absorption.

Laser ultrasonic propagation imaging method in the frequency domain based on wavelet transformation

A wavelet-transformed ultrasonic propagation imaging method capable of ultrasonic propagation imaging in the frequency domain was developed and applied as a new structural damage or flaw visualization algorithm. Since the wavelet-transformed ultrasonic propagation imaging method has strong frequency selectivity, it can visualize the propagation of ultrasonic waves of a specific frequency (for example, to isolate ultrasonic mode of interest and a damage-related ultrasonic wave). The strong frequency selectivity of the wavelet-transformed ultrasonic propagation imaging method was demonstrated, isolating only the zeroth-order asymmetrical mode of the fundamental Lamb wave modes in an anisotropic carbon fiber-reinforced plastic plate with a thickness of 5 mm. The wavelet-transformed ultrasonic propagation imaging method can also convert a complex time domain multiple wavefield into a simple frequency domain single wavefield. This feature enables easy interpretation of the results, and facilitates the precise evaluation of the location and size of structural damage or flaws. We demonstrated this capability by detecting a disbond in a sandwich structure made of Al-alloy skins and a foam core. A disbond with a diameter of 20 mm, which is representative of a common manufacturing flaw, was successfully detected, localized, and evaluated. Since a method to determine the allowable maximum pulse repetition frequency depending on target materials and structures was found by investigating the residual wave caused from the previous laser impinging, our laser ultrasonic system can scan rapidly the target with an optimal pulse repetition rate. In addition, the proposed wavelet-transformed ultrasonic propagation imaging method can visualize damage or flaw without the need for reference data from the intact state of the structure. Hence, we propose the wavelet-transformed ultrasonic propagation imaging approach for automatic inspection of in-service engineering structures, or in-process quality inspection in manufacturing.

An improved closed-form solution to interfacial stresses in rc beams strengthened with a composite plate

The strengthening of concrete structures in situ with externally bonded fiber-reinforced plastic (FRP) composite sheets is increasingly being used for the repair and rehabilitation of existing structures. However, debonding along the FRP-concrete interface can lead to premature failure of the structures. The interfacial stresses have played a significant role in understanding this premature debonding failure of such repaired structures. In this paper, an improved theoretical analysis of the interfacial stresses is presented for a simply supported concrete beam bonded with a FRP plate. The shear strains of the adherends have been included in the present theoretical analysis by assuming a parabolic distribution of shear stress across their thickness. Contrary to some existing studies, the assumption that both adherends have the same curvature is not used in the present investigation. The results of this numerical study are beneficial for understanding the mechanical behavior of material interfaces and for the design of hybrid FRP-reinforced concrete structures.

Mechanical characteristics of a thermo-responsive two-way shape change polymeric laminate

A thermo-responsive bimorph actuator consisting of all-polymeric components, primarily a polyvinylchloride (PVC) plate and a carbon fiber-reinforced plastic plate (CFRP), was fabricated. The strain change of the CFRP plate resulting from environmental temperature change was quite small, while that of the PVC plate was quite large. Such a large strain disparity caused the deflection of bimorph actuator. The bimorph actuator exhibited reversible deflection in accordance with the environmental temperature without hysteresis. The reversible deflection was induced even under a load. Deflection of the bimorph actuator in response to the environmental temperature was theoretically calculated and was in good agreement with the experimental result. Further theoretical analysis predicted a fairly large deflection of the bimorph actuator even under a relatively heavy load.

Impact of the Fiber-reinforced Plastic (FRP) and the Thermal Effect for the Interfacial Stresses

In this article, an original survey on the stresses between the structure and the fibers composite (FRP) was finalized, taking into account, the mechanical and thermal load and the effects of the FRP plate fibers orientation. This originality, puts in evidence a new approach theory and the physical and geometric parameters coupled with the thermal model, which is one aspect that has not be taken into account by previous studies.

Approximate analysis of adhesive stresses in the adhesive layer of plated RC beams

A new popular method for retrofitting reinforced concrete beams is to bond fiber reinforced plastic (FRP) plates to the soffit. An important failure mode for such strengthened members is the debonding of the FRP plate from the member due to high interfacial stresses near the plate ends. As a result, previous researchers have developed several analytical methods to predict the interface performance of bonded repairs. In this paper, a theoretical interfacial stress analysis is presented, including creep and shrinkage effect for simply supported RC beams with a thin FRP composite plate. It explicitly considers the interface slip effect on the structural performance. The results agree reasonably well with those from the existing solutions. The influence of creep and shrinkage effect relative to the time of the casting and the time of the loading of the beams is taken into account. A parametric study has been conducted to investigate the sensitivity of interface behaviours to parameters such as the interface layer stiffness.

Prediction of debonding strength of tensile steel/CFRP joints using fracture mechanics and stress based criteria

In this paper, the debonding strength of axially loaded double shear lap specimens between steel plates and carbon fibre reinforced plastic plates is investigated from the analytical, numerical and experimental point of view. Two steel plates were joined together by two carbon fibre reinforced plastic (CFRP) plates and epoxy adhesive in order to realize double shear lap specimens of different length. Failure of the steel–adhesive interface was identified as the dominant failure mode and fracture mechanics and stress based approach are presented in order to estimate the relevant failure load. A good agreement between the analytical–numerical results and experimental data is achieved.

Effect of End Tapering on Crack-Induced FRP Debonding from the Concrete Substrate

The technique of bonding fiber-reinforced plastic (FRP) plates on the tensile side of concrete members has been proved to be an effective method for structural strengthening. For a RC beam strengthened with FRP plates, failure may occur by concrete cover separation near the plate end, or crack-induced debonding initiated by an opening crack away from the plate end. Experimental investigations have shown that tapering of the FRP plate at its ends is effective in reducing the stress concentrations and increasing the loading for plate end failure to occur. However, with reduced averaged thickness of the tapered plate, crack-induced debonding is also easier to occur. To optimize plate tapering in practical designs, an approach to analyze crack-induced debonding of tapered FRP plates is required. In the present investigation, FRP debonding is first studied with the finite-element method. In the analysis, a three-parameter model is employed for the shear slip relation between concrete and the FRP plate. Based on the findings from FEM analysis, simplifying assumptions are derived and an analytical model is developed for calculating the stresses in the FRP plate and along the concrete-to-FRP interface. The analytical stress distributions show good agreement with those from the FEM analysis. Using the analytical model, the effect of FRP tapering is quantitatively assessed. Also, the effects of various parameters on the ultimate failure load are simulated.

169 積層板の振動特性最適化法について : 実験計画法と他手法の比較

It is desirable to optimize the fiber orientation angles to maximize the fundamental frequencies of the fiber reinforced plastic plates. The optimization is studied here by using the experimental design for nonlinear problems, and it turned out that significantly less number of calculations is necessary as compared to other methods, such as a layerwise optimization approach (LOA). The numerical examples show that assumption of appropriate level values is efficient to obtain the optimum frequency in the vibration problem.

Analysis of Adhesion Stresses for the Design of RC Beam Bonded with Thin Composite Plate

Fibre‐reinforced plastic (FRP) materials have been recognised as new innovative materials for concrete rehabilitation and retrofit. Since concrete is poor in tension, a beam without any form of reinforcement will fail when subjected to a relatively small tensile load. Therefore, the bonding of FRP plate to reinforced concrete (RC) structure is an effective solution to increase its overall strength. In such plated beams, tensile forces develop in the bonded plate and these have to be transferred to the original beam via interfacial shear and normal stresses. Consequently, the debonding of FRP plates bonded to reinforced concrete beams is believed to be initiated by the stress concentration in the adhesive layer. Accurate predictions of the interfacial stresses are prerequisite for designing against debonding failures. In the present analysis, a simple theoretical model to estimate shear and normal stresses is proposed, including the variation in FRP plate fibre orientation. The solution shows significant shear and normal stresses concentration at the plates end. A parametrical study is carried out to show the effects of some design variables, e.g., thickness of adhesive layer and FRP plate, and the distance from support to cut ‐ off end of bonded plates.

Performance in Fire of Small-Scale CFRP Strengthened Concrete Beams

When strengthening concrete members with fiber-reinforced plastic (FRP) materials the strengthening is, typically, undertaken to carry live load. This live load is assumed to remove itself from the strengthened member in the event of a fire. Thus, the fire performance of the FRP is not important. However, if the strengthening system was designed such that the FRP took some of the dead load, then the performance in fire would become important. In this series of tests, 24 reinforced concrete beams were cast. They were divided into eight sets of three. The sets were split into fire tested and control. In the control group were an unstrengthened control set, a set strengthened with bonded carbon FRP (CFRP) plates, and a set with bonded CFRP plates with bolted anchorages. In the fire-tested group were an unstrengthened control set, a set strengthened with bonded CFRP plates, a set with bonded CFRP plates with bolted anchorages, a set strengthened with bonded CFRP plates and a cementitous fire protection system...

Energy-Based Modeling Approach for Debonding of FRP Plate from Concrete Substrate

For concrete beams and slabs strengthened with bonded fiber reinforced plastic (FRP) plates, plate debonding from the concrete substrate is a common failure mode. In this paper, the debonding process is modeled as the propagation of a crack along the concrete/adhesive interface, with frictional shear stress acting behind the crack tip. Crack propagation is taken to occur when the net energy release of the system equals the interfacial fracture energy. The analysis is first performed for the special case with constant shear stress along the debonded interface, and then for the general case with slip softening in the debonded zone. From the results, a direct correspondence between energy-based and strength-based analyses can be established for arbitrary softening behavior along the interface. Specifically, through the proper definition of an effective interfacial shear strength, the conventional strength-based approach can be employed to give the same results as the much more complicated energy-based analysis. Also, based on the relation between the effective shear strength and other material parameters, it is possible to explain the very high interfacial shear stresses observed in experimental measurements. As an application example, distribution of plate stress and interfacial shear stress for the linear softening case is derived. The model results are found to be in good agreement with experimental measurements, showing that the simple linear softening model can describe the debonding process in real material systems.

Determination of Nonlinear Softening Behavior at FRP Composite/Concrete Interface

For concrete beams and slabs, the bonding of fiber reinforced plastic (FRP) plates to the bottom surface is an effective and efficient technique for flexural strengthening. Failure of strengthened members often occurs due to stress concentrations at the FRP/concrete interface. For debonding failure initiated at the bottom of shear or shear/flexural cracks in the concrete, experimental results clearly indicate a progressive failure process accompanied by gradual reduction in shear transfer capability at the interface. Several existing models for FRP debonding have taken interfacial shear softening into account. However, the assumed shear stress versus slip relations employed in the models have never been properly measured. In this investigation, a combined experimental/theoretical approach for the extraction of interfacial stress versus slip relation is developed. With loading applied to a bonded FRP plate, strain is measured at various points along its length. Based on the strain measurements, the interfa...

Three-Parameter Model for Debonding of FRP Plate from Concrete Substrate

Concrete beams retrofitted with bonded fiber reinforced plastic (FRP) plates often fail by debonding of the plate from the concrete surface. To predict the failure load in design, a proper debonding model is required. As debonding is a nonlinear process involving material softening, it can be analyzed once the interfacial shear (τ) versus sliding (s) relationship is known. Recent experimental results indicate that the simplest τ-s relationship should involve three parameters: the maximum shear stress for debonding to initiate, the initial residual stress right after debonding occurs, and a parameter governing the reduction of shear stress with sliding. In this paper, a FRP debonding model based on these three parameters is developed. The applicability of the model is verified through comparison with experimental results. Through a systematic parametric study, the effect of various material and geometric properties on the debonding process is investigated. Implications to the design of FRP strengthened mem...

Concrete Beams Strengthened with Externally Bonded Glass Fiber Reinforced Plastic Plates

In this work, the flexural behavior of reinforced concrete beams strengthened by epoxy bonded glass fiber reinforced plastic plates is investigated through the finite element method. The finite element models based on the widely used package ABAQUS are employed in simulating the behavior of reinforced concrete beams strengthened by externally bonded glass fiber reinforced polymer. The numerical results of four-point bending test of reinforced concrete beams strengthened by externally bonded glass fiber reinforced plastic plates in comparing with the experimental results show satisfactory agreement. The results indicate that the flexure strength of reinforced concrete beams can be significantly increased by externally bonded glass fiber reinforced plastic plates. The dynamic behavior of reinforced concrete beams strengthened by epoxy bonded glass fiber reinforced plastic plates is investigated through the differential quadrature method. In this approach, only eleven sample points are required to obtain convergence.

Creep Deformation of Fiber Reinforced Plastics-Plated Reinforced Concrete Tensile Members

The problem of long-term creep deformation of reinforced concrete tensile elements strengthened by external fiber reinforced plastic (FRP) plates is studied. Formation of discrete cracks in concrete under tension is taken into account. A kinematic model is used, where relative slips between concrete, steel bars, and FRP plates are considered, governed by viscous interface shear stress–slip laws. Bazant’ solidification theory and exponential algorithm are used to obtain incremental constitutive equations for concrete as well as for steel-concrete and FRP-concrete interface laws. Moreover, cohesive normal stresses across transverse cracks in concrete are considered. The incremental differential system of equations is transformed into a nonlinear algebraic system by a finite difference discretization with respect to axial coordinate. Several numerical examples are presented, concerning both short-term and long-term loadings. It is shown that reinforcing by means of FRP plates or sheets has significant benefi...

Experimental study on bond behavior between FRP and concrete

In this paper, two kinds of tests were designed to investigate and study the bond behavior between fiber-reinforced-plastic (FRP) and concrete. By newly designed double-shear test setup, the strain development and distribution in FRP plate was acquired. At the same time, the direct shear bond distribution was given and the effective bond length was suggested. Through a bending test on simply supported beam with an extended end, the strain and stress distribution of FRP plate in the negative moment zone were studied. Based on the test results, conclusions including the maximum effective bond length, the mean bond stress and the development length for flexural bond in the negative moment zone were presented. The effective bond length is about 100 mm and the mean bond stress is about 1.287 MPa. The development length for flexural bond in the negative moment zone is about 300 mm.

き裂を有する長繊維強化複合材料のマトリックス相応力分布の3次元有限要素解析(S07-3 複合材料I,S07 メゾスケールにおける先進材料の力学と強度・機能評価)

Three-dimensional meso-mechanical analysis was conducted by the finite element method (FEM) in order to determine the elastic stress distribution around a crack tip in fiber-reinforced plastics (FRP). FRP plates were modeled as a typical 'one-fiber slice' model, represented by the fiber-resin model. The fibers were arranged in a square array with a fiber volume fraction of 0.60 Matrix crack is parallel to the fiber direction and is subjected to model I loading. The stress intensity factor, K_<lm>, and the average energy release rate was calculated for the above inhomogeneous FRP, and compared with those for a homogeneous FRP. For the long crack, the average energy release rate for the inhomogeneous FRP was equal to that obtained for the homogeneous FRP. For long crack, the matrix-stress distribution ahead of delamination can be divided into three regions: Region I, II and III (IIIa, IIIb) in the order of increasing distance from crack tip. The matrix-sterss in Region I had a singularity of 1/√r, but was smaller than that of the homogeneous FRP. Region IIIa has a singularity, too. But stress intensity factor of Region III was not equal to that of Region I. Region II was transitional region from Region I to IIIa.

Shear strengthening of reinforced concrete beams using different configurations of externally bonded carbon fibre reinforced plates

This paper deals with research undertaken at Oxford Brookes University into shear strengthening of reinforced concrete beams using externally bonded carbon fibre reinforced plastic plates (CFRP). Thirty-eight reinforced concrete beams of 1.8 m length were constructed and tested and are described in this paper. The relative performance of a group of sixteen beams with the same steel reinforcement but with different amounts of shear strengthening is discussed. All the beams were designed to fail in shear using a spreadsheet program. The spreadsheets were designed to ensure that the beams' flexural capacity exceeded the shear capacity after strengthening. The variables were: main reinforcement ratio, spacing between links in the shear span and different configurations of CFRP plates on shear spans. The concrete had an average compressive strength of 61.76 N/mm2. The majority of the beams tested showed a significant improvement in shear strength by the addition of CFRP plates, with increases of between 19–122% over the control beams.

Prediction of the first failure energy of circular carbon fibre reinforced plastic plates loaded at the centre

This work was devoted to the prediction of the elastic energy stored at first failure in a circular composite plate statically loaded at the centre. To describe the load‐ deflection curve, a previous model was further developed, to explicitly account for the tup diameter. The first failure load was calculated through a simple formula, available in the literature, which was suitably varied. An original expression was derived for the energy at first failure. The experimental tests were carried out on carbon fibre reinforced plastic laminates of various thicknesses, which were simply supported at the periphery and loaded using different support and indentor diameters. The results obtained show that the elastic model, which takes into account the non-linearity deriving from large displacements and local indentation, is very accurate in shaping the load ‐deflection curve up to the first failure point. In general, also the predicted load and energy at first failure are in good agreement with the corresponding measured values. Both theory and experiments demonstrate that the critical load is independent of the support diameter, whereas it increases with increasing the plate thickness and the indentor diameter. When the support diameter and thickness increase, the energy at first failure increases as well. A particular condition, resulting in the failure of the force model, is achieved when the curvature of the plate at first failure is considerable. In this case, critical forces notably higher than expected from theory are measured. A possible explanation for this behaviour is given. q 2003 Elsevier Science Ltd. All rights reserved.