Glass Fiber Reinforced Plastic Plates Research Articles

Surface waviness of continuous fiber-reinforced thermosets – Experimental and numerical studies considering the viscoelasticity of the resin

This contribution aims to understand surface waviness formation during cooling and post-curing of glass fiber-reinforced plastics (GFRP). GFRP plates were manufactured by resin transfer molding (RTM). Part surface waviness is determined by tactile contour measuring at ambient temperature up to 1008 h after initial cooling. Additionally, the manufactured plates were exposed to elevated post-curing temperatures to study the influence of resins’ viscoelasticity on their surface waviness. In parallel, the curing and post-curing processes were analyzed using a cure- and temperature-dependent viscoelastic simulation model. The experimental results of this work capture the influence of the resin’s viscoelastic behavior on the surface waviness at ambient and temperatures. The numerical results show a satisfactory agreement with experimental values. Surface waviness amplitude increases up to 25 % for the applied post-curing cycle. The results of the present work underline the importance of the resin’s temperature-dependent viscoelasticity on the process-related formation of surface waviness.

The Wrinkles Characterization in GFRP Composites by Infrared Active Thermography.

An experimental study has been carried out to assess the effectiveness of infrared thermography in wrinkle detection in composite GFRP (Glass Fiber Reinforced Plastic) structures by infrared active thermography. Wrinkles in composite GFRP plates with different weave patterns (twill and satin) have been manufactured with the use of the vacuum bagging method. The different localization of defects in laminates has been taken into account. Transmission and reflection measurement techniques of active thermography have been verified and compared. The section of a turbine blade with a vertical axis of rotation containing post-manufacturing wrinkles has been prepared to verify active thermography measurement techniques in the real structure. In the turbine blade section, the influence of a gelcoat surface on the effectiveness of thermography damage detection has also been taken into account. Straightforward thermal parameters applied in structural health monitoring systems allow an effective damage detection method to be built. The transmission IRT setup allows not only for damage detection and localization in composite structures but also for accurate damage identification. The reflection IRT setup is convenient for damage detection systems coupled with nondestructive testing software. In considered cases, the type of fabric weave has negligible influence on the quality of damage detection results.

Study on Mechanical Behavior of Self-tapping Screws Connection Using Washers in Single-Lapped Glass Fiber Reinforced Plastic Plates by Experiment and Finite Element Analysis

In recent years, mechanical characteristics of Glass Fiber Reinforced Plastic (GFRP) connections using bolts/rivet have been researched in detail, and they are used in many GFRP structures. However, the connection lack bearing strength compared with material strength and they need the prepared holes. In this paper, we surveyed the self-tapping screws connection strength and effects of washers on connection strength of single-lapped GFRP plates using self-tapping screws under tensile-shear loading by experiment and finite element analysis (FEA). The strength of self-tapping screws connection in GFRP plates depends on the washer's diameters. When increasing washer's diameter, the bearing strength of connections increased. Hence, increasing washer's diameter at reasonable levels is an effective method to increase the load carrying capability for self-tapping screws connection in GFRP plates. Moreover, FEA was proposed to investigate the bearing strength of connections and there were good agreements between FEA and experimental results.

Shear Resistance of a Biaxial Hollow Composite Floor System with GFRP Plates

AbstractA new composite floor system was developed to reduce floor-to-floor height and to improve structural capacity and fire resistance as compared with existing encased composite floor systems. The proposed system is composed of asymmetric steel beams with web openings, a biaxial hollow concrete slab, and glass fiber-reinforced plastic (GFRP) plates. The shear resistance of the typical composite beams is commonly determined based on the shear strength of the steel web alone. However, for the proposed system, because the steel web has several circular openings, the concrete contribution to the shear resistance should be included in the design equation. In this paper, tests and finite-element analyses were conducted to evaluate the contribution of the shear-resisting components in the proposed system. An asymmetric steel beam with web openings, inner concrete panels, and a biaxial hollow concrete slab within the effective width for shear were considered as shear-resisting components. Each component fully...

Multi Characteristics Optimization During Milling of Friction Stir Processed Glass Fiber Reinforced Plastic Composites

Accurate machining processes like milling, drilling, cutting, grinding etc are essential for the extended applications of glass fiber reinforced plastics (GFRP) in many engineering fields such as aerospace, marine and machinery. In this study, GFRP plates were friction stir processed (FSP) with an aim to enhance their microstructural properties. The friction stir processed plates were then subjected to milling with solid carbide K6 end mill tool. Taguchi's L9 orthogonal array was used for experimental design. The milling process parameters such as spindle speed, feed and depth of cut at three levels (different FSP feed rates of 15mm/min, 20mm/min and 25mm/min) were optimized with multiple performance considerations of surface roughness and delamination. Multi optimization of machining parameters was done through desirability function analysis. The optimum machining parameters have been identified by a composite desirability value obtained from desirability function analysis. The performance index and significant contribution of process parameters were determined by analysis of variance.

고력볼트를 이용한 유리섬유-강판복합판넬의 지압내력 평가

FRP는 최근에 보강재로서 많이 사용되고 있다. 유리섬유-강판 복합 판넬(GSP)는 이러한 FRP의 한 종류로서 기존에 개발되었던 유리섬유 강화 플라스틱(GFRP)에 비하여 연성 능력을 향상시키고자 상, 하부의 유리섬유층 사이에 얇은 강판을 삽입한 것이다. 이러한 GSP는 자중 대비 높은 강도와 연성 능력이 우수하여, 구조물에 적용되는 사례가 늘어나고 있다. 그러나 GSP를 구조물에 적용시에, 부착을 위해 일반적으로 에폭시를 사용하게 되는데, 이 경우 균일한 품질 확보가 어려우며, 에폭시가 경화되기까지 공사 기간이 늘어나게 된다는 단점이 있다. 이에 본 연구에서는 GSP의 시공성을 향상시키고자 고력볼트를 사용하여, GSP를 부착시키기 위해 지압 내력 실험을 실시하였고, GSP의 지압 내력 평가식을 제안하였다. Recently, FRP(Fiber Reinforced Plastics) is being widely used as a reinforcement material. GSP(Glass Fiber-Steel Composite Plate) is a sort of FRP to improve ductility of GFRP(Glass Fiber-Reinforced Plastics) installing steel plate between top and bottom GFRP Plates. Due to very high strength of GSP comparing to the weight of material, applying of this material is increasing for the building structures. As for the attaching of GSP to the structures, epoxy has been generally used. In this case, however, the quality of epoxy does not remain consistently, and it causes long period of work by hardening epoxy. In this study, to increase workability of GSP, the bearing tests of GSP were performed for applying of building structures with high-tension bolt. And the design equation for bearing capacity could be derived by performing the bearing tests.

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.

Evaluation of Internal Charging of PC Board Materials Used for Spacecrafts

This paper deals with charge-up characteristics of printed circuit (PC) board materials due to electrons penetrating inside a spacecraft body. Glass-fiber-reinforced plastic (GFRP) plates, typical PC board material, were irradiated by electron beam with the energy lower than 20keV simulating decelerated high-energy electrons penetrating through the satellite skin. The charge-up characteristics were obtained as parameters of irradiation time, the energy and the current density of the electron beam. The volume resistivities of the GFRP plates were also evaluated by the decay time constants of the surface potential after electron irradiation. The influence of a protective coating on the charging of the GFRP plates was also tested.

Experimental study of sharp‐tipped projectile perforation of GFRP plates containing sand filler under high velocity impact and quasi‐static loadings

AbstractPenetration and perforation behavior of glass fiber reinforced plastic (GFRP) plates containing 20% sand filler have been investigated via high velocity impact tests using sharp tipped (30°) projectile and quasi‐static perforation tests. Two size sand filler (75 and 600 μm) were used in 4‐, 8‐, and 14‐layered laminated composite plates to study sensitivity of filler size toward loading system. Composite plates were examined for perforation load rate at 5 mm/min and high‐velocity impact loading up to 220 m/s. Results indicated higher energy absorption for GFRP plates containing sand filler for both high‐velocity impact and quasi‐static perforation tests. Higher ballistic limits were recorded for specimens containing sand filler. The study showed clear role played by coarse‐sized sand filler as a secondary reinforcement in terms of higher energy absorption as compared with nonfilled and specimens containing fine‐sized fillers. The investigation successfully characterized behavior of quasi‐static test during penetration and perforation of the sharp‐tipped indenter as an aid for impact application studies. Residual frictional load in the specimens containing sand filler constituted considerable portion of load bearing during perforation in quasi‐static tests. Delaminations followed by fiber and matrix fracture were major failure mode in high‐velocity tests and the main energy absorbing mechanism in thick‐walled plates, whereas in quasi‐static tests the failures were more of matrix fracture and fiber sliding. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

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.

Characteristic Analysis of Solid Materials for Electrical Insulation of HTS Magnets

Following the successful development of practical high temperature superconducting (HTS) wires, there have been renewed activities in developing superconducting power equipment. HTS equipment has to be operated in a coolant such as liquid nitrogen (LN/sub 2/), or cooled by conduction-cooling method such as using Gifford-McMahon (G-M) cryocooler to maintain the temperature below critical level. In this paper, the dielectric strength of some insulating materials, such as polyimide film, epoxy, and Teflon tape in LN/sub 2/ were measured. The insulation materials for HTS current lead cooled by cryocooler needs to satisfy two opposing requirements: electrical insulation and heat conduction. To meet the two requirements, a thermal link that consists of oxide free copper (OFC) sheets, polyimide films, glass GFRP plates, and interfacing material was fabricated. Polyimide film was used as an electrical insulator for the current lead. Surface flashover voltage of glass fiber reinforced plastic (GFRP), the basic property of designing HTS solenoid coil, was also analyzed. Epoxy is a good insulating material but fragile at cryogenic temperature. The multi-layer insulating method for current lead has been suggested to compensate for this fragile property. It consists of Teflon tape layer and epoxy layer fixed by fiber material. Based on these measurements, conduction-cooled HTS current lead for 1.2 kV class DC reactor type high temperature superconducting fault current limiter (HTSFCL) and 6.6 kV class HTS magnets for same type HTSFCL cooled by sub-cooled LN/sub 2/ were successfully fabricated and tested.

Modeling impact induced delamination of woven fiber reinforced composites with contact/cohesive laws

The dynamic delamination in woven glass fiber reinforced plastic (GRP) composite is studied with a 3D finite deformation anisotropic viscoplastic model in conjunction with contact/cohesive laws. The large deformation of the material during impact loading is described through an anisotropic plasticity model in total Lagrangian co-ordinates whose coefficients are determined experimentally. The interaction between lamina is analyzed through a contact/interface model. The tensile and shear tractions in zero thickness interface elements, embedded between lamina, are calculated from interface cohesive law. The interface cohesive law describes the evolution of these tractions in terms of normal and tangential displacement jumps and other interface parameters. The compressive traction at the interface is calculated through the impenetrability condition employed in the contact module. Once the effective displacement jump exceeds a specified critical value, the interface elements are assumed to have failed, i.e., delamination is said to have taken place. Three interface cohesive laws are proposed to describe the delamination process. It is assumed that loading of interface takes place reversibly up to a specified value of the displacement jump followed by irreversible loading beyond this value. This feature represents a partial damage of the interface in the event of unloading. Dynamic delamination in the woven GRP composite is studied through analyses of plate-on-plate impact experiments. The heterogeneity of composite materials leading to wave dispersion and scattering is modeled by considering a layered composition of the GRP plate. Each lamina is assumed to be made of three layers of materials. The middle layer of half the thickness of lamina is considered as GRP and the two end layers of equal thicknesses are considered to be of matrix material, i.e., polyester resin. The possible delamination of the composite material under compressive shock loading is shown to occur due to local shear effects. This is modeled by considering waviness of the interface between lamina. Interfaces with flat as well as two types of wavy structures are analyzed. Analyses are carried out to establish the effect of critical displacement jump, mixed mode coupling parameter employed in interface laws, interface waviness and the effect of interface laws. The response of GRP composite during impact is characterized in terms of the free surface velocity, delamination event vs. time and interface normal and shear stresses. The interface normal and shear stresses are obtained directly from the interface cohesive laws, as well as, by extrapolating continuum stresses from integration points of the neighboring triangular elements to the interface. It is shown that the finite element model predicts the response of the material in confirmation with the available experimental results. The wave dispersion and scattering effects are obtained in the form of attenuation of shock stress and free surface velocity. The model predicts partial delamination during compressive shock loading above a certain threshold due to local shear and mode coupling.

Optimizing Structural Response of Beams Strengthened with GFRP Plates

This paper addresses the structural implications of when a glass fiber reinforced plastic (GFRP) plate is bonded externally to a reinforced concrete (RC) beam for flexural strengthening. Full-scale beams were tested in the laboratory to identify the differences in behavior of a GFRP-plated RC beam from that of a steel-plated one, and then \Ispecial design techniques\N were developed to enhance the utilization of the GFRP plate material. The \Idesign technique\N that was adopted improves the ultimate load capacity of the strengthened composite beam and enhances its ductility in terms of deflection at midspan, energy absorption capacity, and curvature in the pure bending region. Preservation of the plate-adhesive-concrete interface bond and strengthening the compression concrete by confinement through the use of bonded plates onto the beam web are two critical features of this design approach. Experimental observations indicate that there is a limiting thickness to the compression plate beyond which premature bond failure may occur. An analytical model to predict the failure load of the strengthened composite beam is presented that shows good agreement with the test results and confirms that plates effectively bonded to confine the compression concrete make an effective contribution to the composite beam strength, stiffness, and ductility.

The use of carrier fringes in shearography for locating and sizing debonds in GRP plates

Debonds in laminated plates when subjected to vacuum stressing are readily revealed using conventional shearography. In estimating the depth of these debonds from the perturbed fringes, difficulty often arises in assigning accurately the maximum fringe order which corre-sponds to the maximum deflection gradient of the surface of the debonded region. By superposing a set of linear reference carrier fringe pattern onto a conventional shearogram, it is shown in this paper that debonds embedded in a glassfibre-reinforced plastic (GRP) plate may be detected easily from the resulting perturbed fringe pattern. The size and depth of debonds may also be estimated with good accuracy, whether the perturbed carrier fringes are overdriven or non-overdriven. Analysis also indicates that it is generally desirable to use a dense set of reference carrier fringe patterns, which results in a non-overdriven fringe pattern, because it enables a more accurate estimation of the maximum fringe order; the accuracy in the determination of the debond depth is thereby improved.

Locating and Sizing Disbonds in Glassfibre-Reinforced Plastic Plates Using Shearography

Shearography is a double-exposure optical method which reveals defects in components from anomalies in interferometric fringe patterns. In this paper, disbonds of known shapes and sizes are deliberately created at different layers of glassfibre-reinforced plastic (GRP) laminates which are subsequently “vacuum-stressed” during the test. Experimental results show that both the shape and size of disbonds can be deduced easily from the boundaries of the anomalous fringe patterns; the depth of disbonds can also be estimated by counting the number of fringes appearing within these boundaries. The results also correlate well with those predicted from thin plate theory, suggesting that the response of disbonds in GRP plates during vacuum-stressing may be modelled with this theory.

Application of shearography in nondestructive testing of composite plates

Shearography is an interferometric method which provides a whole-field observation of isoclines which are related to surface strains. Since defects in structures such as cracks and delamination induce strain concentrations when the structures are loaded, shearography reveals defects from anomalies in the interferometric fringes. This paper illustrates the use of shearography for estimating the size and depth of disbonds in glassfibre reinforced plastic plates. Square flaws of known sizes are deliberately created within the plates and the “vacuum stressing” method is used to load the defective plates. Results show that disbonds in the plates can be easily sized from the boundaries of the anomalous fringe patterns, and their depths can also be estimated from the number of fringes which appear within the defective areas.

Application of shearography in nondestructive testing of composite plates

Shearography is an interferometric method which provides a whole-field observation of isoclines which are related to surface strains. Since defects in structures such as cracks and delamination induce strain concentrations when the structures are loaded, shearography reveals defects from anomalies in the interferometric fringes. This paper illustrates the use of shearography for estimating the size and depth of disbonds in glassfibre reinforced plastic plates. Square flaws of known sizes are deliberately created within the plates and the “vacuum stressing” method is used to load the defective plates. Results show that disbonds in the plates can be easily sized from the boundaries of the anomalous fringe patterns, and their depths can also be estimated from the number of fringes which appear within the defective areas.

Fiber composite plates for strengthening bridge beams

Although the use of Glass Fiber Reinforced Plastics (GFRP) has increased significantly in recent years, its application in civil engineering has been limited at best. The high strength of GFRP and its resistance to corrosion makes it a suitable candidate in many applications where steel has been predominantly used in the past. In this study, five reinforced concrete beams were strengthened by epoxy-bonding GFRP plates along the tension flange of the beams. The load versus deflection curves to failure and the behavior of each specimen under static loading is presented. It is shown that the method presents great potential for solving some of the global problems facing the aging infrastructure.

Comparison of Single and Muilti-Hole Bolted Joints in Glass Fibre Reinforced Plastic

Data is presented on the strength of single and multi-hole joints in laminated glass fiber reinforced plastic plates bolted to a steel fitting. The laminate lay-up was (—45/0/—45/0°)s. The results suggest that the joint strength, expressed as the load/bolt, decreases as the joint geometry be comes increasingly complex.

The Effect of Stacking Sequence on the Pin-Bearing Strength in Glass Fibre Reinforced Plastic

The pin-bearing strength of glass fibre reinforced plastic plates was measured using specimens possessing mid-plane symmetry and composed of eight layers, two each at 0° , 90° , and ±45° . The results suggest that placing the 90° layer (normal to the applied load) at or next to the surface increases the bearing strength. The ultimate failure mode was found to depend on stacking sequence.