Glass Fiber Reinforced Plastic Materials Research Articles

Laser stripping of functional coatings on glass fiber reinforced plastic substrate.

Glass fiber reinforced plastic (GFRP) with functional coatings is applied more and more in aircraft, thanks to its light weight and excellent mechanical properties. However, the outermost coating must be removed duo to discoloration, paint dropping, cracking, pits, or other fatigued phenomena after a certain amount of service time. The outermost torn coating on a GFRP material is successfully stripped with a nanosecond laser source. The influences of key laser parameters such as laser power, pulse overlap, and pulse width are studied. Thereafter, an optimized laser processing window is obtained and further validated with specified characterization methods. The repainting and adhesive bonding tests afterward indicate that a laser stripping process is superior to traditional sandpaper polishing because of the effects of surface roughening and microstructure interlocking. A case study further suggests that laser stripping outperforms sandpaper polishing because of its higher efficiency and better quality.

Dynamic tensile and failure behavior of bi-directional reinforced GFRP materials

In this paper, a series of static/dynamic tensile tests are performed for glass fiber reinforced plastic (GFRP) composites. Using the combination of high-speed photography and digital image correlation (DIC) technology, true stress–strain curves in different directions and strain rates are obtained. We also obtained the dynamic failure strain of the material in different directions, which are used to accurately describe the dynamic tensile and failure behavior of the material. The experimental results show that there is a stiffness change point N in three directions under different strain rate (10−3 s−1, 10 s−1, 100 s−1) tensile conditions. The stiffness before and after N point is recorded as Einitial and Echanged respectively. The values of Echanged in weft direction and warp direction are about 30% to 50% of Einitial, while Echanged in tilt direction is only about 10% of Einitial. The fiber has the highest strength in the weft direction and the tilt direction has the lowest strength. With the combination of high-speed photography and DIC technology, the dynamic failure parameters of different directions under the strain rate of 100 s−1 are obtained. The dynamic failure strains in three directions are 0.245, 0.373 and 0.341, respectively. The parameters are verified by impact three-point bending test. These works can more accurately describe the dynamic mechanical behavior of glass fiber reinforced plastic (GFRP) composites and provide reference for the design of GFRP structures.

Comparison of PZT, PZT Based 1–3 Composite and PMN–PT Acoustic Emission Sensors for Glass Fiber Reinforced Plastics

Glass fiber reinforced plastics (GFRP) have been widely used for wind turbine blades because of the relative ease of manufacturing them into complex shapes, and their excellent fatigue and corrosion resistance. Acoustic emission (AE) testing has become a primary method for monitoring fiber reinforced plastic structures. However, commercial PZT based AE sensors for general usage may not be useful for GFRP wind-turbine blades because of the acoustic mismatching between GFRP and AE sensors. The objective of this study is to develop high sensitive AE sensors for use on GFRP. To accomplish it, PZT based 1–3 composite and PMN–PT single crystal AE sensors were fabricated and their performances were compared with PZT AE sensor. As results, the PZT based 1-3 composite and PMN–PT AE sensors showed better performance than the PZT AE sensor. PZT based 1-3 composite and PMN–PT AE sensors will be promising alternatives to PZT AE sensors for GFRP materials.

Defect Estimation in Non-Destructive Testing of Composites by Ultrasonic Guided Waves and Image Processing

The estimation of the size and location of defects in multi-layered composite structures by ultrasonic non-destructive testing using guided waves has attracted the attention of researchers for the last few decades. Although extensive signal processing techniques are available, there are only a few studies available based on image processing of the ultrasonic B-scan image to extract the size and location of defects via the process of ultrasonic non-destructive testing. This work presents an image processing technique for ultrasonic B-scan images to improve the estimation of the location and size of disbond-type defects in glass fiber-reinforced plastic materials with 25-mm and 51-mm diameters. The sample is a segment of a wind turbine blade with a variable thickness ranging from 3 to 24 mm. The experiment is performed by using a low-frequency ultrasonic system and a pair of contact-type piezoceramic transducers kept apart by a 50-mm distance and embedded on a moving mechanical panel. The B-scan image acquired by the ultrasonic pitch-catch technique is denoised by utilizing features of two-dimensional discrete wavelet transform. Thereafter, the normalized pixel densities are compared along the scanned distance on the region of interest of the image, and a −3 dB threshold is applied to the locations and sizes the defects in the spatial domain.

Evaluation of composite crashworthy device for pier protection against barge impact

Barge impact is a potential hazard to bridge piers located in navigation waterways. Pier protection against barge impact is of vital importance and thus protective structures of different types are currently extensively used in bridge designs. Glass fiber reinforced plastic (GFRP) is a kind of composite that has been widely used in the design of crashworthy devices for many bridges in China. However, many questions regarding the mechanical properties of this composite remain to be answered. In this paper, a series of material property experiments, i.e. tension, compression, bending and shear experiments, are conducted using GFRP samples, based on which the GFRP material parameters are determined. A quasi-static crushing experiment using a scaled composite cylinder is conducted to investigate the failure mechanism of GFRP, epoxy resin and polyurethane foams which comprise the composite section. In addition, a numerical model of the scaled composite cylinder is developed and validated using experimental results. The validated numerical model is then used to evaluate the effectiveness of a full-scale cylindrical crashworthy device with composite section subjected to barge impact.

Design and Analysis of Cooling Structure on Advanced Air-Core Stator for Megawatt-Class HTS Synchronous Motor

A general high-temperature superconducting synchronous motor (HTSSM) is designed and manufactured with an air-core structure, which eliminates the laminated iron core to concentrate the linkage flux in conventional rotor and stator. In an air-core structure, a nonmagnetic material such as glass fiber-reinforced plastic (GFRP) is used as an armature winding supports to avoid saturation of magnetic field density in the stator core and to reduce the weight and harmonics of the motor. However, GFRP air-core supporters make heat dissipation difficult due to the very low thermal conductivity of GFRP, which makes sustainable and stable operation of HTSSMs impossible. Therefore, in this paper, the concept of advanced air-core stator (AACS) is presented to enhance the cooling performance of a conventional GFRP air-core stator. The AACS concept pertains to the introduction of thermal conductive materials on an armature supporter to replace the GFRP material of a conventional air-core stator. The AACS concept structure for a 1.5-MW-class HTSSM was designed and analyzed using three-dimensional electromagnetic and thermal finite element method.

Understanding the discharge activity across GFRP material due to salt deposit under transient voltages by adopting OES and LIBS technique

In the present study, breakdown characteristics of a glass fiber reinforced plastic (GFRP) with different salt deposit densities (SDD) under standard lightning impulse (LI)/ switching impulse (SI) voltages are studied. Optical emission during discharge process and the discharge current are measured simultaneously. It is observed that flashover voltage (FOV) reduces with increase in salt deposit density on GFRP material under LI/SI (irrespective of the polarity of applied voltage) voltages. It is also observed that irrespective of level of SDD, the FOV is less with SIV compared with LIV. FOV under negative SIV is less compared with positive SIV. Optical emission corresponding to Na I emission at 589 nm in discharge plasma follows the discharge current profile and also the lifetime of Na I emission is high under switching impulse compared with lightning impulse voltages. Na I emission in the discharge plasma sustains for a longer period in case of negative switching impulse voltages. Plasma temperature is estimated using emission lines and it is observed that the local temperature during discharge process is high under negative switching impulse voltage. With increase in salt deposit density, the optical emission spectrum of GFRP material in addition of Na I line at 589 nm is observed. Laser induced breakdown spectroscopy (LIBS) technique is proposed and demonstrated for the detection of a salt deposit on a GFRP material from a standoff distance of 1 m. In addition, temporal and spatial profile of laser induced plasma on the polluted GFRP material is used to quantify the salt deposit. Laser fluence less than 5 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is ideally suited to rank the severity of a salt deposit on GFRP material at an incident laser wavelength of 1064 nm.

Numerical optimization of hole making in GFRP composite using abrasive water jet machining process

Machining of composite materials for the production of bolt holes is essential in the assembly of the structural frames in many industrial applications of glass fiber-reinforced plastic (GFRP). Abrasive water jet cutting technology has been used in industry for such purposes. This technology has procured many overlapping applications and as the life of the joint in the assembled structure can be critically affected by the quality of the holes, so it is important for the industry to understand the application of the abrasive water jet cutting process on GFRP composite materials. The aim of the present work is to assess the influence of abrasive water jet machining parameters on the hole making process of woven-laminated GFRP material and to find the optimum values of the process parameters. Statistical approach was used to understand the effects of the predicted variables on the response variables. Analysis of variance was performed to isolate the effects of the parameters affecting the hole making in abrasive water jet cutting. The results show that the optimum values of cutting feed, fiber density, water jet pressure, standoff distance, and abrasive flow rate upon the response variables are 0.3 m/min, 0.82 g/cm3, 150 MPa, 2 mm, and 100 g/min, respectively.

An experimental study on the behavior of Ao mode transduced using misaligned air-coupled transducers in composite laminates

Air-coupled transducers can be employed for generation and reception of Lamb waves in composite laminates. To generate and receive a particular Lamb mode, the transducers are oriented in a particular angle. The orientations of transducers also determine amplitude of a particular Lamb mode of interest. Any deviation (misalignment) from the right orientation results in a reduction in the amplitude. Therefore, an attempt has been made to establish variation in amplitude of the fundamental anti-symmetric Lamb mode (Ao) when misalignments were purposefully introduced in the air-coupled probes. In the present work, three different misalignments – linear, orientation and synchronized orientation were envisaged. Experiments were performed on two laminates – unidirectional ([03]s) and cross-ply ([0/902/0]s) of GFRP (Glass Fiber Reinforced Plastic) material. Curves were fitted on experimental data to characterize variation in amplitude of Ao mode in each misalignment. Moreover, wave splitting and merging was observed when the probe(s) was (were) rotated in a particular direction in orientation and synchronized orientation misalignments.

English

Research activities have been taking on place in many ports of the world to develop or produce new greenhouse construction materials in order to grow more economic agricultural products. One of the new technological materials is the glass fiber reinforced plastic (GFRP) materials. GFRP materials are basically constituted of resin and continuous or chopped fiber and they are manufactured by using various manufacturing methods. The pultrusion process is a proven manufacturing method for obtaining lengths of high quality GFRP and became a competitive alternative to traditional structural materials. Factors in choosing GFRP materials for greenhouse applications are: lightweight, non‑corrosive, chemically resistant, possess good fatigue strength, provide electrical and flame resistance. In this study, the structural behavior of the greenhouse structure, which is constructed using pultruded GFRP structural element, has been investigated. The mechanical properties of the pultruded GFRP sections have been computed using national and international standards. The proposed structures have been modeled using well known finite element program (SAP, 2000) to investigate the structural behavior under the static and dynamic loads. The pultruded GFRP box section and three different connection details have also been developed. The advantages and importance of GFRP profiles used in the greenhouse structure have been demonstrated. &nbsp; Key words:&nbsp;Glass fiber reinforced plastic, greenhouse model, static analysis, dynamic analysis.

A Study of Cutting Temperatures in Turning of Glass Fiber Reinforced Plastics Materials

Nine kinds of chamfered main cutting edge carbide tools were used in turning of high-strength glass-fiber-reinforced plastics (GFRP) materials to study the temperature of tip's surface and the cutting forces. Force data from these tests were used to estimate the empirical constants of the mechanical model and verify its prediction capabilities. The friction forces and frictional heat generated on elementary cutting tools are calculated by using the measured cutting forces and the oblique cutting analysis. The heat partition factors between the tip and chip are solved by using the inverse heat transfer analysis, which utilizes temperature on the carbide tip’s surface measured by infrared as the input. The tip’s surface temperature of the carbide is solved by finite element analysis (FEA) and compared with those obtained from experimental measurements. A good agreement demonstrates the accuracy of the proposed model.

An improved design of apparatus for multi-specimen bending fatigue and fatigue behaviour for laminated composites

A previously designed fatigue apparatus to test bending fatigue behaviours of glass–fiber reinforced plastic materials is improved in the scope of this research. The advantages of the improved test apparatus are as follows: It can teste 16 samples instead of 10. The square section axis was used to connect the samples more rigid by instead of the round section. So, a good balance and less vibration were obtained on the apparatus. More functional infrared sensors were used instead of proximity sensors that are sensitive to repeated cycling. While the load stress ratio is R = 0 or 1 (two alternative), with a developed adjustable support device, it is R = −1, 0 and 1 (three alternatives). The fatigue behaviours of two groups ( A and E) of composite fiber samples which have different directions but the same volumes were tested by this new apparatus. As a result, it was observed that the directions of the fibers have an important effect on the fatigue strength.

An investigation of bending fatigue behavior for glass-fiber reinforced polyester composite materials

To investigate bending fatigue behaviors for glass-fiber reinforced polyester composite material, 800 g/m 2, 500 g/m 2, 300 g/m 2, and 200 g/m 2 glass-fiber woven and 225 g/m 2, 450 g/m 2, and 600 g/m 2 randomly distributed glass-fiber mat samples with polyester resin have been used. The samples have been produced by the RTM (Resin Transfer Molding) method and the samples have been cut down with directions of 0/90°, ±45°. As results of the combinations from the samples, nine different structures has been obtained. Furthermore, a new mold have been designed for the RTM method. To provide a full infiltration (wetting) of fibers, a simple method has been applied in this new mold system. A new computer aided and multiple-specimen test apparatus have been designed and constructed to simulate load and stress behavior of axial fan blades on the wind tribunes. This multiple specimen apparatus has a big advantage to shorten test time and to test 16 specimens at the same time. Firstly, composite specimens have been applied to the three-point bending test. Later, fatigue tests have been carried out. For the bending fatigue test, “fixed stress” fatigue type has been used. To determine the fatigue limit of all the specimens, S–N diagrams (Wöhler plots) have been derived from experimental results. According to the test results, the highest fatigue life has been obtained from 800 g/m 2 fiber glass woven specimens with 0/90° (group E). The property of anisotropy of the GFRP (Glass Fiber Reinforced Plastic) material is dominant on the fatigue strength which has been clearly observed from the experiments. In the test results, the effective parameters are density of fiber distribution on the area, fiber angle, resin permeability of woven fiber, full infiltration (wetting) or without infiltration of fibers.

Turning of glass–fiber reinforced plastics materials with chamfered main cutting edge carbide tools

In this paper, the machinability of high-strength glass–fiber reinforced plastics (GFRP) materials in turning with chamfered main cutting edge of P and K type carbide tools have been investigated experimentally. Chip formation mechanisms have been obtained with respect to tip's geometries and nose radii. Experimental results for cutting forces were also taken with GFRP as the workpiece material. Force data from these tests were used to estimate the empirical constants of the mechanical model and verify its prediction capabilities. The results show good agreement between the predicted and measured forces. In this study, the nose radius R = 0.3 mm induces a decrease of the cutting force and the smallest cutting force values was achieved in the case of C s = 20°, α S1( α S2) = −10°(10°) and R = 0.3 mm. Comparing the different P and K type of tools, K type tool is better than P type of chamfered main cutting edge tools. The theoretical values of cutting forces were calculated and compared with the experimental results; the forces predicted by this model were consistent with the experimental values.

A study of the heat-affected zone in the UV YAG laser drilling of GFRP materials

This paper describes the characteristics of the heat-affected zone (HAZ) of a UV YAG laser-drilled hole in glass fiber reinforced plastic (GFRP) printed circuit boards. The structures of the HAZ produced by different laser parameters were analyzed. When drilled with lower power and repetition rate, a clear hole wall with very little black charred material was obtained. On the other hand, when drilled with high power and repetition rate, matrix recession and fiber protrusion were observed, also a loose coating was found covering the protruded glass fibers. The results also show that for a given repetition rate, the size of the HAZ increases with increase in average laser power. As for the effect of the pulse repetition rate, a peak value of HAZ width is reached at about 7 kHz for each given laser power, and beyond which the HAZ width decreases. A novel evaluation parameter, defined as the quotient of total area of the HAZ and the profile length, is suggested to quantify the size of the laser-induced HAZ in fiber reinforced composites.

Strength and leakage finite element analysis of a GFRP flange joint

The strength and leakage analysis of a glass fiber reinforced plastic (GFRP) modified stub flanged joint is presented. The analysis is carried out using three-dimensional and axisymmetric finite elements. To model the GFRP material, we use an orthotropic material model. To model the loss of contact between the flange and the gasket, we use a contact condition between these mating parts. In the axisymmetric case, we allow fluid to penetrate the area where contact is lost; the three-dimensional contact formulation, however, does not support this fluid penetration option. We use a commercial finite element package ( Abaqus) to perform the analysis. The primary emphasis is on assessing the strength of the flange and the leak tightness of the gasket. Bolt interaction is not considered, therefore we assume a constant bolt load over the history of the analyses.

酸化物超伝導電流リード 伝導冷却方式超電導マグネット用電流リードの開発 酸化物超電導体電流リードの試作と検討

We have designed and tested superconducting current leads using Bi(2223) oxide superconducting bulk material. Bi(2223) leads were supported by a glass fiber-reinforced plastic (GFRP) which was chosen in consideration of thermal conductivity and thermal expansion. The thermal conductivity of GFRP was one order of magnitude less than that of Bi(2223) bulk material. The difference of the thermal expansion between GFRP and Bi(2223) bulk material was less than 0.1% in the temperature range from 293K to 20K. The critical current of the Bi(2223) leads did not change by the heat cycle from room temperature to 77K. The current lead was cooled by a two-stage Gifford-McMahon cycle refrigerator and operated in a conduction-cooled superconducting magnet successfully.

大型ＧＦＲＰデュワーの開発

The large-sized GFRP dewar has been developed for a 1MJ pulsed superconducting magnet. It is highly desired that the dewar for the use with a pulsed superconducting magnet has to be made of insulating materials to prevent the eddy current heating loss. The glass fiber reinforced plastic (GFRP) is one of the most suitable nonmetallic materials as the structural material of the dewar, because it has characteristic properties such as low thermal conductivity, nonmagnetism, high mechanical strength, and low specific weight. There are varieties of GFRP made of different materials and by different manufacturing method. Selecting the GFRP as the dewar material, care has to be paied to the high strength at low temperature, especially, against thermal shock, and the permeability of helium gas of the GFRP.There have been only few papers on the development of the large-sized GFRP dewar. Those dewar were made by the filament winding method and/or the hand-lay-up method in one united body. On the contrary, the GFRP dewars in the present study have been made by the adhesive-bonding method, because this method is accommodating to the dewar design of complex structure.The designing philosophy together with the selecting of GFRP materials have been presented and discussed. Requirments to design the large-sized dewar are (1) the dewar has to bo made strong enough by selecting proper materials and suitable structures which minimize the concentration of the stress and (2) the dewar has to be vacuum-tight by using the materials of low permeability of helium gas. As the materials, the GFRP's made by the vacuum impregnation method and the filament winding method have been used. To avoid the large ripping force at adhesive-bonding part, the dished bottom plate has been used. Because of the mechanical anisotropy of the bottom plate, the stress is apt to be concentrated on the weakest point of the adhesive-bonding part. Therefore, the GFRP with the glass cloths laminated in the uniform directions has been suited to make the bottom plate.The calculation of thickness and the estimation of heat insulating performance have been made. The manufacturing, the inspections, and the performance tests have been actually done. The heat loss has been estimated to be 0.7-3.8W, which agreed with the measured value 0.6-0.8W for the developed dewar. This heat insulating performance is fairly good.The present development of the large-sized GFRP dewar is showing a success of the present bonding methodology.

The Effects of Weathering on Mechanical Properties of Glass Fiber Reinforced Plastics (Grp) Materials

Glass fiber reinforced plastics composite is extensively used as a structural material for pools, oil pipes and tanks because it has good corrosion resistance properties. The effects of weathering on the mechanical properties of glass fiber reinforced plastics (GRP) in the Sultanate of Oman have been studied. The tensile and three point bend specimens were exposed to outdoor conditions (open atmosphere) in sunlight and tested for various intervals of time. It was observed that as the exposure time to sunlight, ultraviolet radiation and dust increases the mechanical properties of GRP materials decrease. The effects of relative humidity (%RH) on the mechanical properties were also studied. It was found that as the relative humidity increased in the atmosphere during the exposure time, the tensile strength, flexural strength and modulus of elasticity are lowered. This work has revealed that the decrease in the mechanical properties of GRP under weathering conditions is subjected to atmospheric conditions such as humidity, temperature, ultraviolet radiation and pollutant.Key Words: Weathering, Glass-Fiber Reinforced Plastics, Degradation

Application of birefringent coatings to glass-fiber-reinforced plastics

The application of birefringent coatings to plane-stress problems associated with orthotropic-glassreinforced plastic materials is treated. The improvement in the sensitivity of the birefringent-coating method due to the high strength and low modulus of the glassfiber-reinforced plastic materials is noted. Next, the effect of a mismatch in Poisson's ratio between the specimen material and coating is examined and a correction factor is developed which permits determination of boundary stresses even when the mismatch is large. Finally, the stress-strain relations for an orthotropic material are reviewed and an example of a nonsymmetric stress distribution associated with a symmetric fringe pattern is covered.