GFRP Laminates Research Articles

Water sorption and blistering of GFRP laminates with varying structures

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Applying Ultrasonic Vibration to Decrease Drilling-Induced Delamination in GFRP Laminates

Delamination is a major problem in drilling of fiber-reinforced composite materials. Thrust force is an important factor leading to propagation of delamination during drilling process. One of effective methods to reduce machining forces is application of ultrasonic vibrations. In this study ultrasonic assisted drilling is applied to reduce thrust force in drilling of GFRP laminates. In order to conduct experiments a setup is designed and fabricated to apply both vibrations and rotation to drill bits. Using Taguchi method, a set of experiments is conducted with feed rate, spindle speed, and ultrasonic vibration amplitude as control factors. The results show that applying ultrasonic vibration reduces the thrust force and therefore the drilling induced delamination dramatically.

Static mechanical properties of GFRP laminates with fly ash and graphite as filler material

Glass fiber reinforced polymer matrix (GFRP) woven fabric composite material was tested to determine tensile, Flexural and Impact strength. In this paper a comparison study is done for Tensile, Flexural and Impact strength taking two different materials such as (i) woven glass fibre Aralide LY 556epoxy matrix laminates and (ii) woven glass fibre Vinyl Ester epoxy matrix laminates. 1% Graphite and 1% Ash clay are used as filler material as the use of fillers in the matrix, gives rise to many combinations that provide increasing load withstanding capability, reduced coefficient of friction, improved wear resistance and improved thermal properties.

W042003 光ファイバセンサによるFRPの成形モニタリング(【W04200】知的材料・構造システムの現状と今後の展開,機械材料・材料加工部門企画,ワークショップ)

It has been proven that fiber-optic refractive-index sensors can be used for monitoring cure process of thermosetting resin. In the present paper, process monitoring of GFRP was conducted by embedded refractive-index sensors. The sensors were embedded in 0° and 90° directions of unidirectional GFRP laminates and in resin of prepregs in order to investigate effect of reinforcing fibers on refractive index of resin. The laminates were manufactured at 140℃ and pressure of 0.5 MPa by a hot-press molding device. The experimental results showed that the effect of reinforcing fibers had remained small until cure process finished, however thermal residual stress caused by reinforcements affected refractive index of prepreg at cooling. Therefore, it was found that cure index of FRP prepregs could be measured by refractive-index sensors. In addition, it appeared that the refractive-index sensors were available to monitor air voids in resin qualitatively during molding.

802 均質化理論に基づく平織積層板の弾一粘塑性トリプルスケール解析手法の開発(OS8 オーガナイズドセッション《複合材料の変形と破壊およびマルチスケール計算技術》)

In this study, an elastic-viscoplastic triple-scale analysis method for plain-woven laminates is developed based on a homogenization theory. For this, triple-scale modeling of plain-woven laminates is performed by considering a plain-woven laminate as a macro structure, plain fabrics and matrix in the laminate as a meso structure, and fiber and matrix in the plain fabrics as a micro structure. Then, boundary value problems for macro/meso and meso/micro scales are derived based on the time-dependent of homogenization theory, and the relationship between these problems are discussed. It is shown that the present method is successful in taking into account the effects of viscoplasticity of a matrix in plain fabrics on the elastic-viscoplastic behavior of plain-woven GFRP laminates.

315 超音波によるGFRP積層板の温水劣化挙動評価

315 超音波によるGFRP積層板の温水劣化挙動評価

J045092 GFRP積層板成形中の硬化度・ボイドおよびひずみ測定(〔J045-09〕知的材料・構造システム(9))

J045092 GFRP積層板成形中の硬化度・ボイドおよびひずみ測定(〔J045-09〕知的材料・構造システム(9))

Experimental study of steel plate shear walls with infill plates strengthened by GFRP laminates

In this paper, the nonlinear behavior of the composite steel plate shear walls, in which steel infill plates was strengthened by the fiber reinforced polymers (FRP), is experimentally investigated. Tests are designed to evaluate the effect of Glass-FRP layers, the number of GFRP layers and the orientation of GFRP layers on the stiffness, shear strength, cumulative dissipated energy and other major seismic parameters in the composite steel plate shear walls. Experimental models are scaled as one-story steel shear panel models with hinge type connections as boundaries at four corners. In the first test, unstiffened steel infill plate is used for the testing as a reference test. However, in the next four tests, strengthened steel infill plates were used with different numbers and orientation of GFRP layers. Each test was performed under fully reversed cyclic quasi-static loading in the elastic and inelastic response zones of the specimens, in compliance with the ATC-24 (1992) test protocol. The experimental results indicated that by strengthening the infill steel plates yield by laminates strength, ultimate shear strength and cumulative dissipated energy can be significantly increased. The paper therefore presents the background, procedure and set-up used as well as the test results.

An Adaptive Neuro-Fuzzy Inference System Based Modeling for Corrosion-Damaged Reinforced HSC Beams Strengthened with External Glass Fibre Reinforced Polymer Laminates

Problem statement: This study presents the results of ANFIS based model proposed for predicting the performance characteristics of reinforced HSC beams subjected to different levels of corrosion damage and strengthened with externally bonded glass fibre reinforced polymer laminates. Approach: A total of 21 beams specimens of size 150, 250´3000 mm were cast and tested. Results: Out of the 21 specimens, 7 specimens were tested without any corrosion damage (R-Series), 7 after inducing 10% corrosion damage (ASeries) and another 7 after inducing 25% corrosion damage (B-Series). Out of the seven specimens in each series, one was tested without any laminate, three specimens were tested after applying 3 mm thick CSM, UDC and WR laminates and another three specimens after applying 5mm thick CSM, UDC and WR laminates. Conclusion/Recommendations: The test results show that the beams strengthened with externally bonded GFRP laminates exhibit increased strength, stiffness, ductility and composite action until failure. An Adaptive Neuro-Fuzzy Inference System (ANFIS) model is developed for predicting the study parameters for input values lying within the range of this experimental study.

Hygrothermal characterization of gfrp laminates subjected to different water conditions

Hygrothermal characterization of gfrp laminates subjected to different water conditions

Evaluation of Tensile Strength on Repaired Composite Adhesive Bonded Joint

The present work is to study the tensile strength behavior of the repaired material on low velocity impact damaged GFRP laminate using various repair techniques and prediction of their strength through the experimental investigation. While the servicing life of aircraft structures were damaged by the impact damages such as foreign objects collision, mishandlings of tools etc. During the Impact event the laminate were going to cause deformations such as matrix cracking, fiber breaking, and delamination within the laminate. Practically, the damages in composites are unpredictable about their growth where it was using to predict through the ultrasonic A-scan technique. The test specimen made of bi-directional glass fiber and epoxy resin had an impact with a low velocity impact facility. The extent of damage is determined using ultrasonic scanning and the damaged layers were removed using grinding technique. The removed damaged region was repaired using single bonded lap and double bonded lap repair techniques were used to restore the structural integrity of the laminate. These repaired specimens were uniaxially loaded in INSTRON universal testing machine and the behaviors of adhesively bonded patches were studied using load versus displacement graph. From the observed experiments, the failure loads were compared with the strength of undamaged specimen. Using the obtained parameters the optimized repair technique was proposed. Ultimately this work can be used to improve the safety of composite structures while extending their period of service.

J044023 光ファイバ屈折率センサを用いたFRP積層板の成形モニタリング

In the present paper, process monitoring of GFRP laminates during a hot-press molding was conducted by fiber-optic index sensors. From the measured optical power, it appeared that the transverse molding pressure of 0.5MPa applied to optical fibers did not affect the sensor outputs. It was also found that resin flow which covered the sensing part was clearly indicated as sudden fall of the reflected optical intensity. The refractive index curves obtained from the sensor outputs showed that large fluctuation existed in the sensor signal due to scattering from air-voids in resin. The fluctuation disappeared within 20 minutes because the voids were vacuumed. The trend of index curve turned from decrease to increase because of proceeding of cure reaction and then became constant when cure reaction finished. From these results, it appeared that the embedded refractive index sensor could detect resin flow and void vacuuming as well as degree of cure.

816 酸および水環境下における高耐食性GFRP積層板の遅れ破壊寿命評価

816 酸および水環境下における高耐食性GFRP積層板の遅れ破壊寿命評価

Adaptive neuro-fuzzy model for performance evaluation of RC T-beams with externally bonded GFRP reinforcement

The effect of GFRP laminates on the performance of reinforced concrete T-Beams having different internal steel reinforcement ratios was investigated. The parameters of investigation included yield load, ultimate load, yield deflection, ultimate deflection, maximum crack width, deflection ductility and energy ductility. An adaptive Neuro-fuzzy based model was generated to predict the performance characteristics taking percentage of steel reinforcement, thickness of GFRP and the type of fiber used in GFRP as parameters.

Experimental study on the effect of stitch arrangement on mechanical performance of GFRP laminates manufactured on a basis of stitched preforms

This article presents the results of interlaminar shear and flexural tests of stitched polyester glass fiber laminates in dependence on stitch density and main geometric stitching parameters: stitch length and stitch spacing. Purpose of the study is to work out guidelines and indications for manufacturers of composite laminates who use or who plan to use stitching technique. It was found that stitching significantly improves interlaminar shear strength which increases with stitch density. However, stitching causes deterioration of in-plane flexural properties – the deterioration progresses when stitch density increases. Obtained results indicate that it is better to achieve increase in stitch density (resulting in improvement of interlaminar shear strength) by reduction of stitch length than by reduction of stitch spacing. Stitched laminate shows higher flexural strength and flexural modulus when bent into direction parallel to the stitch lines than when bent into the transverse direction. The results obtained within the study and their approximation constants may be a base for a new theoretical model simulating behavior of stitched laminate during static bending and enabling prediction of its mechanical performance.

Acoustic Emission Characterization of Failure Modes in GFRP Laminates Under Mode I Delamination

In order to design structural components using composite materials a deep understanding of the material behaviour and its failure mechanisms is necessary. To create a better understanding of the initiation, growth and interaction of the different types of damage, damage monitoring during mechanical loading is very important. To this direction, AE is a powerful non destructive technique for real time monitoring of damage development in materials and structures which has been used successfully for the identification of damage mechanisms in composite structures under quasi static and dynamic-cycle loading. In this present work, pure resin plate and GFRP composite laminates with stacking sequence of [00]6, are fabricated using Hand lay-up method. During the layup a Teflon tape of width 45 mm is kept in the mid plane of the laminate which serves as an initiator for delamination during loading. As per ASTM STD D5528 01 DCB (Double Cantilever Beam) specimens are cut out from the laminates and are subjected to tensile test in the transverse direction along with acoustic emission monitoring. While loading, Markings are made on the sides of the specimen to track the crack front using a magnifying lens. Parametric analysis is performed on the AE data obtained during crack propagation to discriminate the failure modes. Fast Fourier Transform (FFT) enabled the calculation of frequency content of each damage mechanism. Further STFFT analysis is performed on a portion of the waveforms representing the dominant frequency content pertaining to each damage mechanism.

Intermediate velocity bullet impact response of laminated glass fiber reinforced hybrid (HEP) resin carbon nano composite

In this study, five different types of six layered GFRP laminates were prepared from three types of resin systems and compared for their intermediate velocity bullet impact response. The first panel was made of epoxy resin, second one is of hybrid resin (a blend of 60% epoxy and 40% polyester) and the remaining three panels were made of hybrid resin with MWCNT in three different proportions by weight (0.1%, 0.5% and 1.0%). The composite and nano-composite panels were characterized experimentally for the important issues in the field of aerospace engineering, like medium velocity bullet impact response and vibration damping characteristics. The MWCNTs were responsible for greater characteristics improvement in the hybrid resin due to their high tendency to absorb the impact shock. The panels without MWCNT turn out to be lesser shock absorption capability. Additionally, 0.1% MWCNT hybrid panel shows exceptional damping response by damping the impacted vibration within 9.5 ms. There is also a 175.51% increase in the damping ratio of the panel. The higher percentage MWCNTs show lesser response towards damping of vibration. This may be due to the lengthy entangled structure of MWCNTs in the resin. It is also observed that the impacted damage is higher in the epoxy system panel than the nano-composite panel.

Irreversibly absorbed energy and damage in GFRP laminates impacted at low velocity

The scope of this paper was to establish a correlation between the damage occurring in a composite as a consequence of low-velocity impact and the energy dissipated during the impact phenomenon. To this aim, instrumented impact tests were carried out on glass fabric/epoxy laminates of three different thicknesses, using different energy levels. The irreversibly absorbed energy was obtained from the force–displacement curves provided by the impact machine. To assess damage progression as a function of impact energy, ply-by-ply delamination and fibre breakages revealed by destructive tests were measured. A previous model, based on energy balance considerations, was applied to interpret the experimental results, together with an original method of data reduction, allowing for the isolation of the maximum energy portion due to indentation and vibrational effects. From the results obtained, the contribution of fibre breakage and matrix damage to the irreversibly absorbed energy is comparable at low impact energies; with increasing initial energy levels, delamination becomes predominant in determining energy dissipation. However, the critical energy-release rate required to propagate delamination, as calculated from impact data, is considerably higher than the typical values deriving from Mode II delamination tests performed under laboratory conditions.

Sizing of delamination using time-of-flight of the fundamental symmetric Lamb modes

In this study, a procedure is devised, using the fundamental symmetric Lamb mode (So) to estimate the size of an impact-induced delamination at the bottom interface of a composite laminate, which has been subjected to a low-velocity impact. When S o mode incidents at the edge of delamination, it propagates independently in 0° layer and the rest of layers. Based on the propagation of So mode in the delaminated region, an expression is derived, which can estimate the size of interface delamination using measured arrival times or Time-of-Flight (ToF) of So modes. Numerical simulations were carried out on glass/epoxy (GFRP) cross-ply laminates ([0/902] s) to confirm the derived expression and eventually it was validated through experiments carried out on [0/90/0] GFRP laminates. Moreover, the minimum detectable size of delamination through the proposed method was estimated analytically and verified through numerical simulations.

미시역학적 파손이론을 이용한 복합재 적층판의 피로수명 예측

복합재 적층판의 피로수명을 평가하는 것은 여러 가지 재료와 섬유적층각에 따라 수많은 인증실험이 요구된다. 본 논문에서는 미시역학적 파손이론을 이용하여 복합재의 구성재료인 섬유, 기지 및 섬유/기지 경계면의 피로수명 예측를 통해 복합재 적층판의 피로수명 평가를 할 수 있는 방법을 제시하였다. 기지는 다축응력상태을 고려할 수 있는 일반적인 등방성 재료의 등가응력파손식을 이용하였고, 섬유는 이방성 재료이지만 섬유방향의 응력이 주요하므로 섬유방향의 응력만 고려한 최대응력 파손식을 사용하였다. 섬유/기지 경계면에서는 임계단면파손식을 사용하였고, 경계면의 피로강도가 크다고 가정하여 경계면에서의 피로파손는 무시하였다. 인장과 압축강도가 다른 재료의 평균응력효과를 고려할 수 있도록 수정된 Goodman 식을 이용하였다. 순수 기지의 피로실험 데이터를 기반으로 미시역학적 파손이론을 이용하여 단일 플라이와 복합재 적층판인 UDT[<TEX>$90^{\circ}2$</TEX>], BX[<TEX>${\pm}45^{\circ}$</TEX>]S와 TX[<TEX>$0^{\circ}/{\pm}45^{\circ}$</TEX>]S의 피로수명을 예측해 보았고, 실험 데이터와 잘 일치함을 확인하였다. Many tests are required to predict the fatigue life of composite laminates made of various materials and having different layup sequences. Aiming at reducing the number of tests, a methodology was presented in this paper to predict fatigue life of composite laminates based on fatigue life prediction of constituents, i.e. the fiber, matrix and interface, using micromechanics of failure. For matrix, the equivalent stress model which is generally used for isotropic materials was employed to take care of multi-axial fatigue loading. For fiber, a maximum stress model considering only stress along fiber direction was used. The critical plane model was introduced for the interface of the fiber and matrix, but fatigue life prediction was ignored for the interface since the interface fatigue strength was presumed high enough. The modified Goodman equation was utilized to take into account the mean stress effect. To check the validity of the theory, the fatigue life of three different GFRP laminates, UDT[<TEX>$90^{\circ}2$</TEX>], BX[<TEX>${\pm}45^{\circ}$</TEX>]S and TX[<TEX>$0^{\circ}/{\pm}45^{\circ}$</TEX>]S was examined experimentally. The comparison between predictions and test measurements showed good agreement.