Glass Fiber Reinforced Plastic Laminates Research Articles

2.45 GHz Microwave Processing and Its Influence on Glass Fiber Reinforced Plastics.

During the production of fiber-reinforced composite materials, liquid resin is introduced into the fiber material and cured, i.e., hardened. An elevated temperature is needed for this curing. Microwave curing of composites has been investigated for some time, but it has mostly been done using small domestic or laboratory equipment. However, no investigation has been carried out using an industrial-sized chamber-microwave for glass fiber-reinforced plastic (GFRP). Here, we show that microwave curing produces laminates of the same quality as oven-cured ones. The study shows that, if the process is done right, GFRP samples can be produced with an industrial scale microwave. Even if not fully cured, microwave samples show a glass transition temperature measured with DMA (Tg-DMA) that is comparable to the Tg-DMA according to the proposed cure cycle on the data sheet. Specific microwave-cured configurations show better inter-laminar shear strength than oven specimens. The results show that microwave-based heat introduction can be a beneficial curing method for GFRP laminates. A microwave-optimized process is faster and leads to better mechanical properties.

A novel basic cell modeling method for elastic-viscoplastic homogenization analysis of plain-woven laminates with nesting

In this study, a novel basic cell modeling method is developed for the elastic-viscoplastic homogenization analysis of plain-woven laminates with nesting. For this, based on the periodicity and point-symmetry of internal structures of plain-woven laminates with nesting, a hexagonal prism-shaped basic cell and its boundary conditions are proposed. The basic cell and boundary conditions are then introduced into the homogenization theory for nonlinear time-dependent composites developed by the authors. Using the present method, elastic-viscoplastic behavior of a plain-woven glass fiber-reinforced plastic (GFRP) laminate with nesting subjected to on- and off-axis loading is analyzed. In the analysis, the present method is successful in significantly reducing the analysis domain, and in achieving the modeling of a high volume fraction of fiber bundles. It is shown from the analysis results that the present method accurately predicts experimentally observed macroscopic elastic-viscoplastic behavior of the plain-woven GFRP laminate with nesting. In addition, the elastic-viscoplastic analysis of plain-woven GFRP laminates without nesting is also conducted, showing that the nesting affects elastic-viscoplastic behavior of plain-woven GFRP laminates.

Online monitoring of delamination mechanisms in drilling of Mwcnts reinforced Gfrp nanocomposites by acoustic emission

Among various unconventional Non-Destructive testing (NDT) methods, Acoustic Emission (AE) referred as the most suitable NDT method for detection and characterization of material defects during machining on nanocomposites. AE technique can also be applied for dynamic machining operation called drilling for better understanding of different drilling events from start to the end of the process. The present paper mainly focuses on on-line monitoring of drilling-induced delamination of multi-walled carbon nanotubes (MWCNTs) reinforced glass fiber reinforced plastic (GFRP) nanocomposites laminates through AE technique. A 4 mm thickness of 0.3wt% MWCNTs reinforced GFRP laminates were fabricated by 16 layers of glass fabric cloth with modified epoxy resins for drilling experimentation and trails were conducted on these laminates with uncoated, TiCN and TiAlN coated 6mm diameter carbide twist drills. Design of experiments were planned based on Taguchi L9 orthogonal array and speed, feed were considered as input process parameters. The AE output response parameters such as Root Mean Square (RMS) voltage, AE rise, energy, peak amplitude, hits, AE count, duration and counts to peak were helped to analyse the delamination mechanisms as well as cutting force generation during drilling on nanocomposites. From the experimental results, it was concluded that low feed rate (0.02 mm/rev) and high spindle speed (1500 RPM) with TiCN coated carbide drill gives the reduced delamination factor and thrust force values. Additionally, AE parameters were also highly influenced by the cutting parameters as well as delamination mechanisms. Out of all AE parameters AE-RMS voltage designated as the important parameter to analyse the delamination factor and increased RMS voltage observed with higher feed rate and cutting forces. The other AE parameters were very closely associated to the RMS voltage. Finally, it was confirmed that AE is most suitable NDT technique for on-line monitoring of drilling induced delamination for production of defect free holes on GFRP-MWCNTs composites laminates.

Fatigue Delamination Crack Growth in GFRP Composite Laminates: Mathematical Modelling and FE Simulation

Glass fibre-reinforced plastic (GFRP) composite laminates are used in many industries due to their excellent mechanical and thermal properties. However, these materials are prone to the initiation and propagation of delamination crack growth between different plies forming the laminate. The crack propagation may ultimately result in the failure of GFRP laminates as structural parts. In this research, a comprehensive mathematical model is presented to study the delamination crack growth in GFRP composite laminates under fatigue loading. A classical static damage model proposed by Allix and Ladevèze is modified as a fatigue damage model. Subsequently, the model is implemented in commercial finite element software via UMAT subroutine. The results obtained by the finite element simulations verify the experimental findings of Kenane and Benzeggagh for the fatigue crack growth in GFRP composite laminates.

Experimental investigation of high speed drilling of AL/GFRP multi materials

Objectives: Experimental investigation of the influence of machine tool parameterson the drilling multi material Glass Fiber Reinforced Plastic (GFRP) along with Al 2024. Drilling process issues of GFRP such as: fiber pull-out, poor axial straightness, fuzziness and delamination of GFRP demand this investigation towards the fine tuning and refinement of the existing process. Methods/Statistical Analysis: In this work GFRP laminate was prepared by using compression moulding process and Al 2024 purchased from an industrial supplier. GFRP placed over Al 2024 during the drilling process. Makino S33Vertical machining center was used for conducting the experiment. Syscon dynamometer was used to measure the thrust force and metzer profile projector was used to measure the delamination .Response Surface methodology was used to conduct the experiments. ANalysis Of VAriance (ANOVA) was conducted to find the statistical significance of the process parameters on the responses such as thrust force and delamination. Findings: From the analysis of the findings, certain conclusions could be drawn such as feed (mm/rev) as the most statistically significant process parameter compared to the spindle speed (rpm) and drill bit diameter (mm).Lower feed, higher spindle speed and smaller diameter drill bits are favorable conditions for delamination free holes. Application/ Improvements: These multi material systems are replacing mono (single) material as structural members in aerospace and other similar defense application. These findings could be adopted in fabrication and repair works of above such application. Keywords: Delamination factor, Drill Bit Diameter, RSM and Drill Diameter, Spindle Speed, Feed, Thrust Force

Characterizing the off-axis dependence of failure mechanism in notched fiber metal laminates

Fiber metal laminates (FMLs) are usually more complicated in the failure aspect as compared to their constituents, especially when complex load is applied. In this paper, notched FMLs and the constituents, i.e., the aluminum and glass fiber reinforced plastic (GFRP) were subjected to off-axis tensile loading to evaluate the failure mechanism. Initial attention was paid on the off-axis dependence of mechanical responses, especially on its relation to the notch size. As expected, off-axis dependence of notched strength and notch sensitivity were closely related to the notch size, but different for GFRP laminates and FMLs due to their different damage behavior. Finite element model was employed to predict accurately the mechanical responses of FMLs, particularly for elucidating the damage mechanism. Failure of notched FMLs under off-axis loading was a combined transverse fracture and shear-off, while it was shear-dominated in notched GFRP laminates. Transverse fracture in aluminum appeared first, followed by the fiber breakage, which was postponed by the extensive subcritical damage. Thereafter, shear-failure in fiber and aluminum layers were encountered instantaneously at the descending part. Thus, the critical failure of off-axis notched FMLs was still tension-dominated as that in the on-axis case, but aluminum played the critical role.

Collective effect of bending load and hygrothermal aging on glass fibre reinforced plastic

PurposeThis study aimed to investigate the collective effects of bending load and hygrothermal aging on glass fibre-reinforced plastics (GFRP) due to the fact that stress and water absorption is inevitable during GFRP applications.Design/methodology/approachThe water boiling method was used to study the moisture absorption, desorption behaviour and evaluate the performance of GFRP laminates under loading in this article. The moisture diffusion of laminates is characterized in three aging conditions (25°C, 45°C and 65°C water), along with three levels of bending load coefficients (0, 0.3 and 0.6). The moisture diffusion coefficients are determined through the curve fitting method of the experimental data of the initial process, based on the Fickian diffusion model. Moreover, the laminates’ performance is further discussed after adequate environmental aging and loading.FindingsIt was found that moisture absorption is promoted by the presence of bending load and boiling during this study. The absorption diffusion coefficient and moisture equilibrium content of the specimens increased with an increasing loading ratio and temperature. The bending strength of the laminate varied according to a contrary trend. Furthermore, the desorbed moisture content is found to be much higher after higher levels of bending load because it is harder to desorb the moisture in the interfaces and micro cracks.Research limitations/implicationsCollective effects of bending load and hygrothermal aging promote the absorption and result in accelerating property degradation of GFRP. It is significant to focus on these effects on the failure of GFRP.Originality/valueA novel unit was designed to simulate the various loading acted on containers in this work.

High frequency vibration analysis in drilling of GFRP laminates using candlestick drills

The vibration signal contains a lot of information closely related to the tool performance in drilling the composite material. However, due to the limit of the frequency response characteristics of piezoelectric accelerometer, the monitored vibration signals used in researches were usually below 10kHz. Thus, the high frequency vibration signal was ignored. Drilling experiments of Glass Fiber Reinforced Plastic (GFRP) laminates were carried out utilizing candlestick drills in this article. The high frequency vibration signals of ten candlestick drills with different drill tip geometry parameters were analyzed and compared in time domain, frequency domain and in bispectrum. The results revealed that there was high frequency vibration signal above 10kHz in the process of drilling GFRP laminate. These signals were sensitive to the changes of the drill tip geometry parameters. The changes of the bispectrum energies of these signals could reflect the changes of the cutting performances and the delamination factors for the drills.

Mechanical and optical properties of silk fabric/glass fiber mat composites: an artistic application of composites

Currently, hybrid glass fiber-reinforced plastics (GFRPs) have attracted increasing attention as gradually common used materials. Glass/silk fiber hybrid reinforced plastic (GSFRP), a new kind of material, is designed aiming to create a kind of opaque effect of specific use. Three types of silk/glass composites with five layers of glass mats and a single layer of woven silk fabric lamina with small, medium and large crepe are fabricated by using the hand lay-up method to compare with pure GFRP. Optical properties, including the light transmission property and luminance distribution, were examined with regard to the specimens of GSFRP. Results indicate that light was diffused more efficiently by GSFRP than pure GFRP laminates. Moreover, the greater the crepe degree of silk fabric is, the more efficiently light is diffused and the rise of luminance suppressed. Furthermore, mechanical properties, including the flexural as well as the impact property, were examined through three-point bending and Izod tests, respectively. There is little negative influence on the flexural strength of GSFRP when silk inserted in layer 3 and, as the crepe degree of silk fabric increases, a slightly inferior effect on the impact test presented. From the scanning electron microscopy observation, it is found that the existence of silk fabric inserted in layer 3 could prevent further propagation of the crack and alleviate the delamination of the specimens during the bending process, improving resistance to delamination and bending.

Flexural Response of Fibre Reinforced Polymer Laminated Pre-stressed Concrete Beams

Objectives: To examine the effect of Glass Fiber Reinforced Plastic (GFRP) laminated on strength and deformation capacity of pre-stressed concrete beams under static loading condition. Methods/Statistical Analysis: In this study, 7 Pre-Stressed Concrete (PSC) beams were cast and laminated with GFRP. The beams were tested under monotonically increasing loading and manual readings were recorded. Sufficient data was obtained on the strength, deformation and failure characteristics of pre-stressed beams with and without GFRP laminates for beams tested under static loading. Findings: In all the pre-stressed concrete beams, 5mm UDCGFRP strengthened PSC beams showed an improved flexural strength. The test results inferred that strengthened pre-stressed concrete beams showed 93.15% increase in load carrying capacity than that of control specimens. All GFRP laminated pre-stressed concrete beams experience flexural failure. Application/Improvements: The pre-stressed concrete beams laminated with glass fibre reinforced polymer were found to be very effective in load carrying capacity, deflection and ductility. It can be also be suitably adopted for rehabilitation and restoration of corrosion damaged, old infrastructures and seismic affected concrete structures.

The system of carbon fibre-reinforced plastics micro-tubes for self-healing of glass fibre-reinforced plastics laminates

A system of pultruded carbon fibre-reinforced plastics micro-tubes is used for self-healing simulation in laminated polymer composite. The system consists of a package of micro-tubes, placed in the symmetry plane of the GFR/epoxy laminate stack. Healing agent is a mixture of the epoxy resin and hardener. The healing agent releases and penetrates into the cracks after the composite is damaged by the quasi-static indentation. The specimens are healed at 30℃ for 24 h. Rectangular specimens notched under ASTM D2733 have been subjected to tensile test to determine interlaminar shear strength. Shear strength of specimens has been compared in three states (virgin, damaged and healed) for various ways of healing. After the most effective self-healing, the interlaminar shear strength has been recovered to 70 ± 15% of those for virgin specimens that almost twice exceeds the residual strength of the damaged specimens.

A monolithic compliant large-range gravity balancer

A new monolithic fully compliant gravity balancer is designed with help of a design approach based on shape optimization. The balancer consists of one single clamped–clamped complex-shaped beam on which a weight is attached. The beam is modeled as a planar isogeometric Bernoulli beam. The goal function of the optimization consists of an energy based evaluation of the load path of the beam which is compared with a desired response. The best result of the shape optimization has been constructed out of polycarbonate sheet and out of glass-fiber reinforced plastic laminate. Both have been tested on a compression test bench. The theoretical model has good resemblance with the experimental results.

Powder binders used for the manufacturing of wind turbine rotor blades. Part 1. Characterization of resin‐binder interaction and preform properties

Glass fiber reinforced plastics (GFRP) are the predominant materials used for wind turbine rotor blades. To manufacture blades in a vacuum‐assisted resin infusion process (VARI), a binder is needed for fiber fixation and preform stability. Moreover, solubility and mechanical compatibility of the binder and the epoxy resin matrix are important parameters for processability and the mechanical properties of the composite. The present study therefore characterized and evaluated five chemically different binders with regard to their solubility in a rotor‐blade‐proven epoxy resin using microscopy, viscometry, and differential scanning calorimetry (DSC). The solubility tests enabled a binder‐classification into critically soluble (KE‐60, Epikote 05390), strongly soluble (Grilon MS), partially soluble (D 2433E), and nonsoluble (K‐140) binder types. In subsequent mechanical and thermo‐mechanical testing of resin‐binder plates, the strongly soluble binder Grilon MS showed the best performance, followed by the nonsoluble binder K‐140 and the partially soluble binder D 2433E. These results suggest that binders developing no interfaces within the resin should be preferred. Furthermore, interply adhesion for these three binders was investigated in a peeling test using fiber preforms. It was found that differences in peel strength might be controlled predominantly by different kinds of binder layer formations, but also to some extent by the different binder‐fiber interaction (binder and fiber sizing correlation). Best performance was shown by D 2433E, followed by Grilon MS and K‐140. All in all, the soluble binder Grilon MS exhibited the best results in mechanical testing of resin‐binder plates and is therefore expected to also show the best mechanical performance in GFRP laminates. POLYM. COMPOS., 39:708–717, 2018. © 2016 Society of Plastics Engineers

Influence of specimen type and reinforcement on measured tension–tension fatigue life of unidirectional GFRP laminates

It is well known that standardised tension–tension fatigue test specimens of unidirectional (UD) glass-fibre-reinforced plastics (GFRP) laminates tend to fail at end tabs. The true fatigue life is then underestimated. The first objective of this study was to find for UD GFRP laminates a test specimen that fails in the gauge section. The second objective was to compare fatigue performance of two laminates, one having a newly developed UD powder-bound fabric as a reinforcement and the other having a quasi-UD stitched non-crimp fabric as a reinforcement. In the first phase, a rectangular specimen in accordance with the ISO 527-5 standard and two slightly different dog-bone shaped specimens were evaluated by means of finite element modelling. Subsequent comparative fatigue tests were performed for the laminates with the three specimen types. The results showed that the test specimen type has a significant effect on the failure mode and measured fatigue life of the laminates. A significantly higher fatigue life was measured for the laminate with the powder-bound fabric reinforcement when compared to the laminate with the stitched reinforcement.

Effects of curing pressure on mode II fracture toughness of uni-directional GFRP laminates

The purpose of this work is to investigate the effect of curing pressure on the Mode II interlaminar fracture toughness behaviour of uni-directional glass fibre reinforced plastics (GFRP). Investigation was carried out experimentally on uni-directional GFRP specimens using end notched flexure (ENF) tests to find out the changes in the material and geometric properties due to the application of pressure. Stiffness of the different laminates cured under different pressure was studied and it was shown that both material and geometric stiffness accounts for the total stiffness of the laminate, but their contribution to total stiffness varies. It is shown that fracture toughness values, GIIC, remain unaffected by stiffness since it is only related to the new surfaces created due to crack initiation and propagation. It is shown that the thickness of the matrix layer influences all the properties, including the fracture toughness. The laminates cured at 5 Psi, 400 Psi and 800 Psi exhibit different fracture toughness. Optimum thickness of matrix layer offers both adhesive and cohesive resistance to the crack propagation and thus offers high fracture resistance.

Design of composite tank covers

The problem of design and failure analysis of composite tank covers is discussed in the paper. Covering systems consist of segmental parts of tanks, independently on tank structure. Composite covers have several advantages connected with structure, transport and assembly. Additionally, the construction divided into several sections enables repair and inspection improving. However, on the one hand, failure of the tank covers, which are occurred sometimes, and on the other hand new applications, make it necessary to develop design, analysis and optimization of these structures. In this study, the main advantages of the GRP covers are shown against other covers and roofs systems. The construction of the representative rectangular composite tank cover, segments and joints are described. Failure analysis of the covering segment under combined loading is presented. The exemplary cover was built in the sewage treatment plant in Poland. The cover is built of repetitive two-wave segments with flanges overlapping one another. The segments are made of mixed glass-fiber reinforced plastic laminates. The cover is subjected to the following static loads: dead load, technological vacuum, snow and ice and local load (workers with tools). Static analysis of the exemplary cover was conducted using the finite element code MSC.Marc. The considerations include shell geometry of the cover, structural GRP laminates with specified ply sequences, segment connections of rivet nut–bolt and anchor–nut types, friction at the interface between flanges and between flanges and tank walls. Safety coefficients have been analyzed for the different elements of the exemplary composite cover.

Detection and quantitative evaluation of defects in glass fiber reinforced plastic laminates by microwaves

A novel method using microwaves is proposed to detect and evaluate defects in glass fiber reinforced plastic (GFRP) laminates. A thin circular plastic film simulating delamination was inserted in GFRP laminates and was detected using microwave reflectometry. A focusing mirror sensor consisting of a horn antenna and two metal mirrors was used to improve the measurement resolution. In addition, the thickness of the film was calculated using a proposed model based on microwave propagation theory. Measuring the variation in the amplitude of the microwave reflectivity, a 7.5-μm-thick film was successfully detected in a 3-mm-thick GFRP laminate. Moreover, the calculated results of the inserted film thickness had a high degree of accuracy.

PID control of torque during drilling in GFRP laminates

Purpose – Damage induced during drilling of polymer matrix composites depends upon torque during drilling. Modeling of torque with feed rate and its control becomes imminent for damage free drilling of composite laminates. Therefore, the purpose of this paper is to construct a transfer function between drilling torque and feed rate based upon experiments. Thereafter, the torque is controlled by using PID controller. Design/methodology/approach – This paper presents step-by-step procedure to capture complex drilling dynamics of polymer matrix composites in a mathematical model. A glass fiber reinforced plastic (GFRP) composite laminate is drilled at constant feed rate during experimentation. The corresponding time response of torque is recorded. First order, second order and third order transfer functions between torque and feed rate are identified using system identification toolbox of Matlab®. These transfer functions are then converted into state-space models. Experimental verification is performed on GFRP composite laminate. PID controller is designed using Simulink® to track a given reference torque during drilling of polymer matrix composite. The controller is then validated using different reference torque trajectories. Findings – Good match is observed between torque response from state-space models and experiments. Error analysis based on integral absolute error and integral squared error on experimental and simulated response show that third-order system represents the complex drilling dynamics in a better way than first and second-order systems. PID controller effectively tracks given reference trajectories. Originality/value – Third-order model between torque and feed rate for drilling of composites not available in literature has been presented. PID controller has previously been applied successfully for drilling of conventional materials, this paper extends implementation of PID torque control for drilling of composites.

Multi-Criteria Optimization Using Grey Relational Analysis in Drilling of Glass/Epoxy Polymeric Composites

Glass Fibre Reinforced Polymeric (GFRP) composite materials have been used to make several components in engineering field. This is due to their excellent mechanical properties such as high specific strength, specific stiffness, good fatigue resistance, good corrosion resistance and light weight. Drilling is the process required for these composite materials for fitting and assembly with base part which may generate delamination at entrance and exit. In drilling of GFRP composite, delamination is one of the major defect which is more responsible for the rejection of components in the final assembly of engineering parts. An experimental investigation of full factorial design performed on drilling of Glass Fibre Reinforced plastic laminates using Helical flute straight shank drill and “Brad and Spur” drill by varying the process parameters such as cutting speed and feed rate to find the optimum drilling conditions. The main objective of this paper is to optimize the drilling process parameters with consideration of multiple performances such as specific cutting pressure, power, peel-up delamination factor and push-out delamination factor. Analysis of variance (ANOVA) was carried out for estimating the percentage contribution of process parameters on drilling performance. Grey relational analysis was used in this multiple objective optimization to get damage free drilling of GFRP composite. Response table and graph are used for this analysis which shows that feed rate is the most significant factor than the cutting speed and also it indicates that delamintation free drilling can be obtained at low feed rate and low cutting speed. The result shows that drilling performance can be enhanced effectively thorough this approach.

Evaluation of machinability index on milling of GFRP Composites with different fibre orientations using solid carbide endmill with modified helix angles

Nowadays, glass fibre reinforced plastics (GFRP) plays a vital role in many engineering applications as an alternative to various heavy exotic materials. However, the users of FRP are facing difficulties to machine it, because of fibre delamination, fibre pullout, short tool life, matrix debonding, burning and formation of powder like chips. This research work aims to find out the machinability in milling process of GFRP laminates manufactured by hand lay-up. A plan of experiments based on Taguchi was established and the milling was performed with prefixed cutting parameters. An analysis of variance (ANOVA) has been employed to investigate the effect of cutting parameters on specific cutting pressure and surface roughness. The objective is to evaluate the machinability of GFRP laminates in function of fibre orientation (15°,60° and 105°) and solid carbide end mill tools with 25°, 35° and 45° helix angle and to propose a new machinability index.