Continuous Glass Fiber Research Articles

Impacts of thermoplastics content on mechanical properties of continuous fiber-reinforced thermoplastic composites

Continuous fiber reinforcements are widely used to enhance mechanical properties of composite materials, but the impregnation of continuous fiber reinforcements with thermoplastics is a challenge due to high melt viscosity of the thermoplastic matrix. One of promising routes to improve the impregnation is to prepare commingled yarns with continuous matrix filaments and reinforcement fibers. In this study, we investigate mechanical properties of commingled yarns comprising different ratios of continuous glass fibers and polypropylene filaments, and of the composite plates made up of fabrics woven by the commingled yarns with a different polypropylene content. We found that undistributed or bunched glass fibers occur at high PP contents (>50 wt%), inducing an inhomogeneous mixing of the continuous reinforcement fibers and polypropylene filaments, which resultantly leads to abrupt changes in mechanical properties of both commingled yarns and resulting composites. Notably, the inhomogeneous distribution of continuous glass fibers in the commingled yarn at high PP contents gives rise to unexpected viscoelastic characteristics of resulting composites although impregnation of continuous glass fibers with polypropylene matrix is enhanced as the absolute amount of the polymer matrix increases.

Process parameters and mechanical properties of continuous glass fiber reinforced composites-polylactic acid by fused deposition modeling

This article focuses on 3D printing of continuous glass fiber reinforced composites-polylactic acid by fused deposition modeling. An innovative continuous fiber reinforced composite 3D printer and self-made continuous glass fiber reinforced filament-polylactic acid are applied to study the influences of process parameters including printing temperature, speed, layer height, and fiber volume fraction on mechanical properties of continuous glass fiber reinforced composites-polylactic acid printing samples. Tensile and three-point bending tests are carried out to explore the mechanical responses of printed samples. Experimental results show that the mechanical properties of continuous glass fiber reinforced composites-polylactic acid printing samples are better than those of polylactic acid samples. The tensile and flexural strengths of the specimens are increased by 400% and 204% when the fiber volume fractions are about 5.21% and 6.24%, respectively. The microscopic observations of the fracture surfaces of the tensile samples are also conducted to analyze the influences of layer heights on tensile strength and failure mechanism.

Calculating printing speed in order to correctly print PLA/continuous glass fiber composites via fused filament fabrication 3D printer

In this research, an innovative task of printing speed optimization for continuous fiber composites is examined. Employing continuous fibers is a new method to reinforce samples made by fused filament fabrication (FFF) technology. The printing speed is pivotal in the printing process of composites with continuous fibers because of its significant effect on the geometric shape of the samples, especially their corners. In the experimental part of study, continuous glass fiber (CGF) and polylactic acid (PLA) filaments are utilized during optimization as reinforcing phase and matrix, respectively, and are simultaneously fed into the extrusion-based polymer 3D printer to make PLA/CGF composites. Through the optimization, temperature changes of the deposited rasters in the presence and absence of fibers are calculated at the first step, and then the special relationship between the printing speeds and rasters’ temperature changes is determined. Finally, the optimal printing speed is computed based on a hypothesis, which is proved by the results of high-quality printed composites with different geometric shapes.

Mechanical characterization of particulated FRP composite pipes: A comprehensive experimental study

Particulated fiber reinforced polymer (FRP) composite pipes encompass unidirectional continuous glass fibers (hoop glass), resin (thermoset polymer vinylester) matrix, chop glass (discontinuous short fibers), and particulate reinforcement (sand) impregnated into resin. They are categorized based on their nominal diameter, pressure class, and stiffness class. Mechanical characteristics of this class of composite materials have not, to date, been comprehensively studied. As such, this paper presents a systematic approach toward comprehensive experimental investigation into their mechanical characterizations in terms of the axial and hoop tensile strengths. The particulated FRP composite pipes used in the current study have glass fibers reinforced along the hoop direction at approximately 89° angle. To assure the experimental data accuracy and reliability, three batches associated with each pipe category were selected which slightly differ in the composition of their constituents. Three specimens per batch were selected and two types of tests were conducted on each specimen. 18 tests (2 × 3 batches × 3 specimens)) were conducted per pipe category (9 tests for hoop and 9 tests for axial). Therefore, 648 tests were conducted in total on 36 pipe categories. Instron 5569A and Instron 8801 universal testing machines were utilized for the axial tensile tests and a split disc hydraulic testing machine for the hoop tensile tests. The mean tensile and the hoop axial stresses and their associated standard deviations were calculated based on the Population Standard Deviation (PSD) equation and then plotted against the material constituents. The results demonstrated that an increase in the composition of particulate reinforcement results in a decrease in the axial and the hoop tensile strengths. However, increasing the ratio of resin, chop glass, and glass fibers contributes to the enhancement of the axial and the hoop tensile strengths. This study provides comprehensive design guidelines for engineers and manufacturing industries.

Adhesives for increasing the bonding strength of in situ manufactured metal-composite joints

In this present work, the potential of metallic parts, locally reinforced with a continuous glass fibre reinforced thermoset material, pre-impregnated with an epoxy matrix (prepreg), was evaluated by differential scanning calorimetry (DSC), single-lap shear tests and 3-point bending tests of a metal-composite hybrid hat profile. This technology is evaluated regarding an automotive use case, the DSC experiments in combination with moulding trials have proven curing times below 30 s for a moulding temperature of 180°C. A bonding strength of 13.5 MPa was characterized for a co-cured fibre-reinforced plastic (frp) onto a metallic joining partner. By additionally introducing an epoxy glue film as a bonding agent, which is co-cured together with the frp, the bonding strength can be increased significantly up to 25.4 MPa at the expense of the curing time. The mechanical tests on the hybrid hat profile have shown an increase of energy absorption compared with non-reinforced hat profiles. Here, also an additional glue film extends the performance regarding a co-cured plastic reinforcement without glue film. The influence of the storage conditions of the uncured prepreg materials on the mechanical performance was evaluated by a simulated physical ageing at elevated temperatures, followed by a mechanical characterization of the bonding strength and part performance. Also the effect of different testing temperatures and testing velocities on the capability of the metal-composite hybrid part is illustrated.

Improved mode Ⅰ interlaminar fracture toughness of random polypropylene composite laminate via multiscale reinforcing formed by introducing functional nanofibrillated cellulose

Interface engineering and phase engineering of composites offer a promising route to rationally tune the interlaminar toughness of laminates, as high toughness plays an important role in preventing interlaminar failure and ensuring the safety of components. Herein, unlike the previous melt-mixing process, we coated the second reinforcement TONFC (TEMPO-oxidized nanofibrillated cellulose) on the surface of the main reinforcement (continuous glass fiber) by sol impregnation, and successfully prepared the commingled yarn random polypropylene (PPR) composite laminate with high interlaminar fracture toughness. The surface groups of each raw material of the composite system before and after the reaction were characterized and thereby obtaining the interface strengthening mechanism. Besides, the heterogeneous nucleation effect of TONFC and the mechanism of inducing ꞵ-phase formation were revealed by analysis of crystallization behavior and crystal structure. Further, through a double cantilever beam (DCB) test and morphology analysis, the effect mechanism of the addition of TONFC on the interlaminar crack propagation of PPR composite laminate was explored. This work provides a rapid and efficient avenue for the interlaminar modification of commingled yarn composites.

Processing of pre-impregnated thermoplastic towpreg reinforced by continuous glass fibre and recycled PET by pultrusion

Packaging sector generates 40% of the plastics consumption in Europe. Among the most consumed plastics, polyethylene terephthalate (PET) is still the material that undoubtedly continues to grow in the packaging sector. Hence, there is a concern related to the recycling process, which today is only around 56%. Therefore, the objective of this work focuses on the use of this recycled material as a source of raw material for pultrusion processes. This work studies and compares the processability of final composite pultruded parts by using three different pre-impregnated recycled materials different in their viscosity and stream. Those composites were characterized by mechanical testing and microscopy analysis. The obtained results were compared with those of another pultruded thermoplastic (polypropylene) composite. From this study, it was possible to transform a waste into a product with high added value, reducing the carbon footprint.

Axial compression deformability and energy absorption of hierarchical thermoplastic composite honeycomb graded structures

Thermoplastic composites have advantages of high damage tolerance, reprocessing and recycling capacities which are in growing demand in lightweight engineering applications. Structural gradient were introduced to designed continuous woven glass fiber reinforced hierarchical thermoplastic composite honeycomb graded structures (HTCHGS) aim to improve on deformation stability and induce the failure processes. Axial compression tests were conducted to investigate compression behavior, energy absorption capacity and influence of structural gradient distributions. Experimental observation showed that failure of HTCHGS was induced and constrained as expected, stable rising load plateau achieved by presented staggered conical HTCHGS. The staggered conical HTCHGS obtained mean value of 0.64 and 1.56 J/g on crushing force efficiency and specific energy absorption at the densification displacement. FEM simulations were carried out among presented configurations by parameterized modeling, validated the induced deformation processes by structural gradient which matched well with the tests. Stress distributions were compared among six configurations at typical deformation stage, found core components of staggered configurations contribute more to energy absorption than that of regular configurations. Staggered dumbbell HTCHGS provide long and stable deformation plateau till densification, and staggered conical HTCHGS are considered as optimal energy absorbing components among the configurations which give possible guidance for engineering structural designs.

Fracture toughness characterisation of a glass fibre‐reinforced plastic composite

AbstractBy examining the state of the art, it can be realised that few research works have been done on the fracture behaviour of plastic composites reinforced with continuous glass fibres. Therefore, the present paper deals with the fracture toughness of a unidirectional glass fibre‐reinforced plastic (GFRP), such a parameter being analytically determined by means of the modified two‐parameter model (MTPM). The input data of the MTPM are obtained from an experimental campaign related to three‐point bending tests on single edge‐notched specimens characterised by different sizes. The novelty of this research work is that the MTPM, originally proposed for isotropic materials, is here employed to estimate the fracture toughness of GFRPs characterised by orthotropic mechanical properties.

Effects of cutting temperature and process optimization in drilling of GFRP composites

The present work deals with temperature effects and parametric optimization in the drilling of continuous glass fiber reinforced epoxy composite. Drilling ability was examined operating a drilling system with different drill bits, feed rate, and spindle speed parameters. The investigation was performed by changing the tool and composite interface. Drilling experiments were carried out under the dry condition. Thrust force and drilling temperatures were measured using dynamometer and thermal camera. Peel-up and push-out delamination were evaluated using an image analyzing tool. Results show that the tribo-mechanical behavior of the drilling operation is affected at different levels by tool coating. This behavior is related to the intrinsic friction properties of coating nature. Response surface methodology was used in the evaluation of experiment results. The feed rate of 0.13 mm/rev, spindle speed of 2425 rpm and HSS-TiN drill bit are found as an optimum drilling parameters and drill type.

Measurement and prediction of residual strains and stresses during the cooling of a glass fibre reinforced PA66 matrix composite

The forming process of thermoplastic composites inevitably leads to the development of residual stresses. This study proposes a model to predict the residual stresses at the ply scale of a thermoplastic composite laminate. It accounts for the heat transfer, crystallization kinetics and mechanical behaviour of the laminate. The model is applied to the cooling of a polyamide 66 (PA66) matrix reinforced with continuous glass fibres. The Stress Free Temperature is considered as the starting point of stresses accumulation within each ply and its identification is discussed. The curvatures of [904/04] laminates and their evolution with temperature are recorded with a digital image correlation technique. They are compared to the curvatures predicted by the model, which permits to validate it. The predicted stresses distribution is then discussed. Finally, the model is compared to the Classical Lamination Theory, demonstrating the interest of the developed model.

Fabrication of continuous glass fiber-reinforced dual-cure epoxy composites via UV-assisted fused deposition modeling

This paper proposes an ultraviolet (UV)-assisted fused deposition modeling (FDM) method with a dual-curing process for fabricating continuous fiber-reinforced thermosetting polymer composites (CFRTPCs). The entire approach is based on the additive deposition of fused continuous glass fiber (CGF)/epoxy (EP) filaments, which are rapidly cooled upon exiting the printer nozzle to form a solid three-dimensional (3D) object. At the same time, UV irradiation is used to activate the photoinitiator and photosensitizer to pre-cure the extruded material. The final polymerization and crosslinking reactions are achieved using a post heat treatment. Herein, the UV absorption characteristics and post heating process of the dual-cure EP matrix were investigated to demonstrate the feasibility and generality of the proposed technique. Finally, 3D printed CGF/EP samples with a 43 ± 3 wt% fiber content exhibited a tensile strength and tensile modulus of 272.51 ± 5.12 MPa and 8.01 ± 0.45 GPa, respectively; flexural strength and flexural modulus of 299.36 ± 6.16 MPa and 8.35 ± 0.18 GPa, respectively; and interlaminar shear strength of 34.06 ± 0.83 MPa. The combination of UV irradiation and post heat treatment offers a rapid, feasible, and effective dual-cure solution for 3D printing of CFRTPCs, which could be a reliable fabrication method for the development of thermosetting composite systems used in various applications.

On the mechanical properties of continuous fiber reinforced thermoplastic composites realized through vacuum infusion

Continuous glass fiber reinforced thermoplastic composites have been manufactured and their mechanical properties have been evaluated. A catalyzed monomer is infused through a stack of compacted dry reinforcement under vacuum. The monomer undergoes radical polymerization with a peroxide catalyst. Viscosity and reactivity profile have been characterized to determine the catalyst concentration and temperature of infusion. Glass fiber reinforced thermoplastic composites realized through this method have mechanical properties that are comparable with that of epoxy with an added advantage of excellent toughness and repairability. For example, the residual compressive strength of thermoplastic composites after low-velocity impact is found to be over 140% more than that of epoxy-based composites using the same reinforcement and realized under identical manufacturing methods.

The combined effect of impregnated rollers configuration and glass fibers surface modification on the properties of continuous glass fibers reinforced polypropylene prepreg composites

The continuous glass fibers (CGFs) reinforced thermoplastic composites play a crucial role in many applications such as automobile industry and aeronautic industry. However, there are two problems, one is how to regulate the degree of impregnation (M) and fracture rate of fiber bundle (P), and another is how to improve the interfacial properties. In this work, the different impregnated rollers configurations were designed to obtain appropriate M and P value, and the polyethylenimine (PEI) functionalized carboxylic carbon nanotubes (PEI-CNT) were grafted to the CGFs (PEI-CNT-CGFs) surface through dipping method, which is beneficial to the interfacial properties between CGFs and polypropylene (PP). Both theoretical and experimental results indicated that optimal configuration (F) could achieve ultrahigh degree of impregnation of 99.37% at relatively low fracture rate (3.58%) of fiber bundle, so that the tensile strength was improved dramatically (from 329.3 MPa to 461.8 MPa). Furthermore, the PP/PEI-CNT-CGFs composite manufactured in F configuration showed higher tensile strength (486.3 MPa) due to the better interfacial adhesion, it was an obvious consequence from the SEM images of fractured surface in PP/PEI-CNT-CGFs. This study provides a strategy to obtain ultrahigh performance of CGFs reinforced PP composite by improving degree of impregnation as much as possible with limited fiber breakage, and enhancing interfacial adhesion. It is hugely significant to guide the production of CGFs reinforced thermoplastic prepreg composites.

The effect of fibre length and matrix modification on the fire performance of thermoplastic composites: The behaviour of PP as an example of non-charring matrix

The fire performance of fibre-reinforced polypropylene (PP) was investigated with respect to fibre length and modification of the matrix. Fibre lengths of 3 mm, 12 mm, and continuous fibres were used as reinforcements. E-glass continuous fabrics were melt impregnated with PP and consolidated via compression moulding. E-glass fibre-reinforced PP pellets of 3 and 12 mm were compression moulded. Cone calorimetry tests with incident radiant fluxes of 20, 30 and 35 kW m−2 were used to investigate the fire properties of PP glass fibre composites. Results showed that continuous glass fibre reinforced PP exhibits the best fire performance at 20 kW m−2, while 3-mm fibre has the best performance at 35 kW m−2; 12-mm fibre-reinforced PP exhibitedthe lowest performance in comparison with 3-mm and continuous glass fibre reinforcement. Melic-anhydride (MA)-modified PP was found to increase the heat release rate (HRR) by up to 44% and time to ignition by up to 10% depending on the heat flux applied in comparison with unmodified PP. The glass fibre-reinforced composite made with MA-modified PP has 5–12% lower mean HRR and similar time to ignition in comparison with glass fibre composite made by unmodified PP. This suggests improved fibre adhesion plays a role of the fire performance of glass fibre-reinforced PP.

Composites based on polyphtalamides matrices and continuous glass fibers: structure-processing and properties relationships

Continuous Glass Fiber-Reinforced Thermoplastic Composites (GFRTC) were successfully prepared using two different routes: a reactive laboratory-created approach as well as a compression molding method. Two kinds of high-performance polyphtalamides (PPA) were studied: PPA from a chain extension reaction of its parent prepolymer (named R-PPA) in comparison with a virgin non-reactive PPA (NR-PPA). For the former, the chemo-rheological behaviors were investigated by coupling rheology with fast-scan and high temperature Fourier Transform InfraRed (FTIR) measurements. Interestingly, it was demonstrated that a maximum chain extension conversion could be obtained in a few minutes. Moreover, elevated molar masses could be reached with broad polydispersities. For thermo-compression forming process, and despite the moderate NR-PPA viscosity, it was therefore possible to obtain a good impregnation of the GFRTC with improved mechanical properties. By a subsequent thermal post-treatment, a correlation between the obtained highest glass transition temperatures (Tg), molar masses and induced crystallinities on thermomechanical properties could be emphasized. The present study thus highlights some interesting results to obtain structural heat-resistant GFRTC materials typically used in the field of aerospace and automotive parts intended especially for high service temperature applications.

Synergistic effect of intumescent flame retardant and attapulgite on mechanical properties and flame retardancy of glass fibre reinforced polyethylene composites

The synergistic flame retardant system consisted of intumescent flame retardant (IFR) and organic modified attapulgite (OATP) synergist was used to improve the mechanical properties and flame retardancy of continuous glass fibre reinforced polyethylene composites (GFPE). The IFR was composed of ammonium polyphosphate (APP) as acid source and poly(1,3-diaminopropane-1,3,5-triazine-o-bicyclic pentaerythritol phosphate) (PDTBP) as carbon source. The mechanical properties (tensile strength) of GFPE/IFR/OATP were improved by 35%–43% after adding OATP synergist with rod-like fiber structure due to its strengthening and toughening effect on the resin matrix, and the flame retardancy increased first and then decreased with the increase of OATP synergist loading. When 4 wt% OATP synergist was added into GFPE/IFR, the LOI value increased from 29.5% to 31.3% and the flame spread rate significantly reduced. The synergistic flame retardant system of IFR/OATP could form a stable and dense char layer on the surface of glass fibre and weaken the wicking actions of glass fibre. The synergistic flame retardant system of 26 wt% IFR/4 wt% OATP could endow GFPE with best comprehensive performance.

Physico‐chemical, thermal, and mechanical properties of PLA‐nHA nanocomposites: Effect of glass fiber reinforcement

AbstractIn this study, tri‐layered composites were prepared by reinforcing poly‐lactic acid (PLA) nano‐hydroxyapatite (n‐HA) (1 and 5 wt%) and 20 mol% continuous phosphate glass fibers (PGF). Initially, the effect of addition of 1 and 5% n‐HA on the structural, thermal, mechanical, and thermo‐mechanical properties of 100% PLA was investigated. With 5 wt% n‐HA addition the tensile modulus (TM), flexural modulus (FM), tensile strength (TS), and flexural strength (FS) of 100% PLA was improve by 14.9, 47.4, 6, and 32.9%, respectively. Whereas, the un‐notched impact strength of the nanocomposites suffer 2% deterioration. However, T g decreased by 0.3°C and T c increased by 10°C as 5 wt% n‐HA was added to 100% PLA. Afterwards, the 5% n‐HA/PLA composite were reinforced with 20 mol% continuous PGF and the TM, FM, TS, and FS of the tri‐layered composites were 162.6, 412.5, 28.4, and 157.4% higher as compared to 100%PLA. Furthermore, the storage modulus of the 1% n‐HA‐filled composites was 500 MPa lower than 100%PLA, while 5 wt% n‐HA‐filled composites showed similar storage modulus as 100% PLA. 5 wt% n‐HA‐filled composite showed the highest peak of loss modulus which may be attribute to the chain segment of PLA matrix after the incorporation of HA. Thus, n‐HA and PGF reinforcement resulted in improved mechanical properties of the composites and have great potential as biodegradable bone fixation device with enhanced load‐bearing ability.

Investigation of joining of continuous glass fibre reinforced polypropylene laminates via fusion bonding and hotmelt adhesive film

As the demand for the lightweight and recyclability in automobile industry increases, continuous fiber reinforced thermoplastics (FRTP) have received extensive attention due to their excellent mechanical properties and fully recoverability. One of the ongoing challenges is to achieve sufficient joint strength in spite of the inertness (i.e. lack of functional groups) of some thermoplastics. In this current work, two joining techniques, including fusion bonding and hotmelt film were applied to bond continuously glass fiber reinforced polypropylene (PP/GF) composites. Firstly, operating procedures during the fusion bonding process of PP/GF laminates were focused and assessed. Tests were carried out to investigate the effects of fusion temperature, ply sequence of PP/GF substrates and fusion depth on lap-shear joint strength. The cross-section microstructure and fracture surface were observed by optical and scanning electron microscopy. Then, the adhesion of bonded PP/GF specimens using thermoplastic adhesive film was further investigated. The lap-joint strength and failure mode was compared with fusion-bonded counterparts. The results suggested that fusion-bonded of PP/GF exhibited higher joint strength while joining with hotmelt adhesive film experienced shorten processing period and lower molding pressure. Therefore, fusion bonding and hotmelt adhesive film provide low-cost, feasibility and recyclable adhesion methods, which are promising for joining of continuous fiber-reinforced thermoplastic composites.

Resistance welding of glass fiber reinforced thermoplastic composite: Experimental investigation and process parameter optimization

The utilization of fiber reinforced thermoplastics (FRTP) is expected to fulfill lightweight demand in mass-produced aerospace products. Facing the unavoidable assembly of FRTP parts, fusion bonding methods such as resistance welding are promising compared with mechanical joint and adhesive bonding. In this paper, a procedure has been brought out to understand the relationship between processing conditions and performance of the FRTP welding joints. The adherends were continuous glass fiber reinforced polypropylene (GF/PP) laminates fabricated by hot-pressing method. The influences of time, current and pressure on the bending strength of the resistance welding joints were investigated. A processing window was drawn based on the optical observation of welded surfaces. The quantitative relationship between process parameters and mechanical property of GF/PP welding joint was established by Response Surface Method (RSM) with high accuracy. It was found that bending strength of GF/PP welding joint was improved by 31% compared with hot-pressing benchmark.