Unidirectional Glass Fiber Research Articles

Modeling and failure mechanism study of unidirectional GFRP corrugated sandwich sheet piles based on discrete element method

In this paper, a DEM model of a unidirectional glass fiber reinforced polymer composite sandwich sheet pile (UGFRP-CSSP) is developed to elucidate the damage mechanisms under longitudinal bending and axial compression at the mesoscale, in order to bridge the gap between existing knowledge and its potential applications as sheet pile walls. A series of four-point bending and axial compression tests are performed on UGFRP-CSSP to validate the DEM model, which is calibrated through a sensitivity analysis of the mesoscopic parameters. The failure behavior, crack progress, and initial crack formation of the UGFRP-CSSP are investigated by correlating the results from physical experiments and numerical simulations. The research reveals that the DEM model accurately depicts the failure behavior under bending and compression of unidirectional (UD) composite elements, offering a mesoscopic perspective on the failure origins. It is identified that the tensile shear strength of the resin is the weak point leading to initial failure, as it is lower than that of the glass fibers. Longitudinal bending failure typically initiates at the skin-core interface and around the central axis of core, with cracks propagating longitudinally due to compression shear failure between fibers. Axial compression failure also occurs predominantly at the skin-core interface, with similar longitudinal cracking attributed to tensile shear failure at the acute angle fiber connections in the long span side. Finally, a new viewpoint was proposed that the fiber modulus may have a decisive impact on the failure behavior of UD composite materials.

Development of the forming limit diagram for fiber-reinforced thermoplastic composites and its temperature effect

The aim of this study is to investigate the formability properties of thermoplastic composite sheets and to develop a forming limit diagram (FLD) for them under ambient and elevated temperatures. Polypropylene thermoplastic composite sheets reinforced with unidirectional continuous glass fibers in a four-layer 0–90 layup were used in this research. Experimental findings demonstrate that the failure of samples at room temperature is more similar to brittle failure and occurs suddenly, whereas at elevated temperatures, the failure resembles ductile failure and occurs gradually. Employing the Nakajima method, a forming limit diagram for the composite material was successfully established at both ambient and elevated temperatures. The resultant forming limit diagrams illustrate an augmented strain tolerance of the material at elevated temperatures. Notably, despite the increased depth of stretch observed at elevated temperatures in comparison to ambient conditions, a concomitant reduction in the force requisite to induce deformation is evident.

Evaluation of mode-I delamination toughness of composites for automotive applications

Abstract With the increasing need for energy efficiency, fiber-reinforced composites are being widely used in the automotive industry. This study investigates the inter-laminar fracture behavior of fiber-reinforced composite double cantilever beam specimens considering a non-zero slope at the root. Experiments were conducted on unidirectional and cross-ply glass fiber reinforced epoxy composite specimens and the critical delamination toughness G I C has been evaluated by the proposed weighted residual equation. The proposed mathematical model requires crack length and the load versus displacement data to evaluate delamination fracture energy. This method accounts the measurement scatter and the rotation at the crack tip. For a particular specimen, the proposed model gives a unique value of critical delamination toughness value. The critical interface failure load estimates utilizing the evaluated delamination toughness agrees well with literature and in-house test results of double cantilever beam specimens.

Translaminar fracture toughness characterisation for a glass fibre/polyamide 6 laminated composite by a novel approach based on fictitious material concept

This paper proposes a novel approach for the characterisation of the material fracture toughness associated with translaminar tensile failure, consisting in the application of the Fictitious Material Concept (FMC) by using the testing configuration of the Modified Two Parameter Model (MTPM). The main advantage of such an approach is to avoid the use of nonlinear fracture mechanics for material fracture toughness characterisation. The novel approach is applied to compute the translaminar fracture toughness of a unidirectional glass fibre (GF)/polyamide 6 (PA6) laminated composite. Moreover, the experimental campaign carried out is numerically simulated by means of a micromechanical finite element model, and the fracture toughness is computed by employing two different approaches, that is, the novel one and the MTPM. The present study proves, for the first time, that the Fictitious Material Concept can be applied by considering both experimental and numerical structural responses since it provides, in both cases, quite satisfactory accuracy in term of laminated composite fracture toughness. Therefore, the great advantage is that, when a validated numerical model is available, experimental campaigns may be avoided, saving time and money. Moreover, it is proved that the FMC can be used to investigate specimen size effect on fracture toughness.

Micro-buckling resistant unidirectional glass fiber composites with excellent transverse and longitudinal flexural properties from cross-linking by nano-/micro-aramid fibers

This study aims at obtaining an effective structural design strategy for stronger and more reliable Unidirectional glass fiber (UD-GF) composites by in-situ formed cross-linking from randomly distributed nano-/micro- Aramid pulp (AP) fibers. The flexural strength and stiffness have shown substantial improvements in both the transverse and longitudinal directions due to the AP cross-linking and the “brick-slurry” structure. With AP of 8 g/m2, up to 60–70 % improvement in flexural strengths (both transverse and longitudinal directions) and up to 20–37 % improvement in “effective modulus” have been observed. The noticeable longitudinal improvements have been attributed to the resin reinforcement and interlayer cross-linking provided by ultra-thin AP interlayers, and the resultant improvement in micro-buckling resistance under compression. Since sparsely distributed nano-/micro-AP can be readily incorporated in pultrusion and pre-preg manufacturing processes, this study is not only important for micro-mechanism study, but also provides a plausible improvement in manufacturing.

Experimental investigation and micromechanical analysis of glass fiber reinforced polyamide 6

Achieving process stability in the thermoforming of fiber reinforced polymer materials (FRPs) for aerospace or automotive manufacturing is usually associated with a costly trial-and-error process, where experimental boundary conditions and other influencing factors, such as, for example, material composition, need to be adjusted over time. This is especially true when material phenomena on the microlevel, such as the crystallization kinetics of the polymer matrix or resulting stresses from temperature gradients, are the cause of the process instability. To reduce the experimental effort and reliably predict the material behavior during thermoforming, finite element simulation tools on multiple scales are a useful solution. Hereby, incorporating micromechanical phenomena into the model approaches is crucial for an accurate prediction by further reducing the deviation between simulation and experiment, in particular with regard to the underlying nonlinear material behavior. In this work, unit cell simulations on the microscale of a unidirectional glass fiber reinforced polymer (UD GFRP) are conducted to predict effective thermomechanical properties of a single material ply and ascertain the effect of individual ply constituents on the homogenized material behavior. The polymeric matrix material model used was identified in a prior publication with experimental data at various temperatures for polyamide 6 blends with varying degrees of crystallinities. Various randomization methods are tested to generate the unit cells and replicate the composites’ random fiber distribution, with a focus on process automation. The simulative results are successfully compared to an experimental study on glass fiber reinforced polyamide 6 tested at various temperatures, demonstrating the potential of the approach to reduce both time and cost required for material characterization. Finally, the unit cells are used to generate a database to predict untested load cases that will be used in future work to characterize a homogenized macroscopic material model.

Effect of the Glass Fiber Orientation on Mechanical Performance of Epoxy based Composites

Composites are one of the most advanced and adaptable engineering materials. The strength of any composite depends upon volume/weight fraction of reinforcement, orientation angle and other factors. The present work focuses on the determination of the mechanical properties of pure epoxy and unidirectional glass fiber reinforced epoxy. Nowadays, glass fibers are being used in several engineering applications like electronics, aviation, automobile, sport industry etc. Glass fibers are having excellent properties like high strength, flexibility, stiffness, and resistance to chemical attack. With an increase in the content of unidirectional glass fiber volume the properties of unidirectional glass Fiber Reinforcement Polymer (GFRP) composite were improved. It may be used in different forms like chopped, woven mat, short fibers and long fibers etc. Each type of glass fiber has unique properties and is used for different applications. The mechanical and thermal properties of various polymer composites reinforced with glass fibers when subjected to mechanical loading have been studied and reported.

The Effect of Stacking Sequence and Ply Orientation with Central Hole on Tensile Behavior of Glass Fiber-polyester Composite

An experimental investigation was carried out to study the effect of circular cross-holes on the failure behavior of unidirectional glass fiber reinforced with unsaturated polyester resin composites, varying cross-ply laminates that were subjected to axial tensile load. This paper deals with the effects of the circular notch and the number of plies on nominal tensile and net tensile strengths. Tensile strengths were investigated for composites with cross-ply([0/90]. [90°/0°/90°] and [0°/90°/0°].90°), orientation and varying the laminate layers with a central hole, and effects of volume fraction and number of ply on mechanical properties for un-notched (smooth) and notched specimens were also studied. The results showed that increasing the number of plies has a marginal effect on tensile strength values. The fraction of volume has significant effects and for increasing the number of plies about 9% decreases in nominal tensile strength and about 11% decrease in the net tensile strength was observed. The same results were obtained with finite element analysis.

Birefringent optical fibers to decouple thermo-mechanical effects on FBG sensors

Optical fiber Bragg (FBG) sensors are gaining importance in structural health monitoring (SHM) systems due to their compact size and ability to be embedded into the lamination sequences of composite material elements. A significant challenge, widely discussed in the literature, concerns the decoupling of thermomechanical measurements made through these sensors. This work aims to solve this problem using birefringent optical fibers instead of conventional ones. The distinctive characteristics of birefringent fibers allow an FBG sensor, written in such fibers, to present not a single peak but two distinct peaks, each with different responses to changes in strain and temperature. This is due to the different refractive index distribution in the fiber core section, which allows for two axes on which the light signal propagates at different speeds. This property offers a significant advantage: by having two independent equations associated with the two peaks, it is possible to decouple the thermomechanical measurements using only the fiber itself, without the need to introduce additional components to achieve mechanical decoupling (capillaries with through or interrupted fiber). This would ensure that strain and temperature are measured at the same point. In the first phase of the work, an FBG sensor on a birefringent fiber was characterized and subsequently calibrated. Therefore, a dedicated experimental set-up was created to conduct thermal, mechanical, and thermomechanical characterization tests, in order to verify the feasibility and effectiveness of decoupling. In a second step, such sensor was embedded within a sample of composite material (unidirectional glass fibers), which was subsequently subjected to the same characterization tests conducted on the single fiber. The results highlight the ability of this new transducer to decouple the thermal effect from the mechanical effect, allowing this new technology to overcome the problems of FBG sensors made of standard fibers.

Glass fibre hybridization to improve the durability of circular flax fibre reinforced composites with off-the-shelf recyclable polymer matrix systems for large scale structural applications

Natural fibre composites (NFCs) are not durable in the long run because of the susceptibility of natural fibres to environmental conditions and specifically moisture. Hybridizing NFC laminates externally, with synthetic fibre reinforcements, may improve durability, due to their inherent environmental resistance. This work aims to investigate the effects of glass hybridization, on flax fibre composites, studied via accelerated ageing. In specific, the durability of hybrid flax/glass fibre reinforced polymer composites, with two recyclable polymer matrices was investigated. Unidirectional (UD) flax and UD glass fibre reinforcements were employed to fabricate laminates, with two fully-recyclable off-the-shelf resin systems, as matrix: (i) a bio-based epoxy resin and (ii) an acrylic liquid thermoplastic (Elium®). In addition, a standard petroleum-based epoxy polymer matrix was for reference purposes. Weathering and hygrothermal ageing were used to test the durability of coupons, exposed to UV radiation/condensation/water spray environment (weathering ageing), and full-immersion in distilled water at 23, 40, and 60°C (hygrothermal ageing). In all cases, ageing was performed for a total duration of 56 days. The performance of the unaged and aged composite coupons was assessed and compared in terms of flexural and viscoelastic performance as well as SEM (Scanning Electron Microscopy) analysis. It was revealed that the addition of glass fibres with flax fibres in the hybrid composites improves the performance and better resistance against ageing environments than their neat flax fibre composites.

A Study of the Moisture Absorption Characteristics of Vinyl Ester Polymer and Unidirectional Glass Fibre Vinyl Ester Laminates

A Study of the Moisture Absorption Characteristics of Vinyl Ester Polymer and Unidirectional Glass Fibre Vinyl Ester Laminates

Investigation and calculation of the longitudinal compressive strength of unidirectional glass fiber reinforced polymer considering the fiber orientation distribution

In this study, undulations and their influence on the longitudinal compressive strength of a unidirectional glass fiber reinforced polymer (GFRP) composite are investigated theoretically and experimentally. The objective of this research is to explore the failure mechanisms in FRP and to characterize the mechanical properties of FRP as a function of fiber orientation. For this purpose, a multiscale material model is developed that considers a stochastic fiber orientation distribution (FOD) and models matrix fracture-initiated failure. The relationship between compressive strength and undulation is investigated experimentally on standardized specimens made of unidirectional GFRP. The fiber orientations are measured using X-ray computed tomography and ImageJ image analysis, resulting in a binormal distribution of fiber orientations in the series of samples tested. To examine the failure process in detail, the compression tests are simulated using finite element analysis (FEA). Both the FEA results and the measured compressive strengths confirm the model assumption of matrix fracture-initiated failure under longitudinal compressive loading. The presented analytical model realistically represents the correlation of compressive strength with the FOD.

Role of stacking sequence, metal sheets, and nano particle on strength and toughness of FMLs

The effect of nano particle inclusion and the stacking sequence/metal volume fraction on the tensile strength and energy absorption properties of Fiber Metal Laminates (FML) is investigated. The FML structure is composed of lightweight thin sheets of aerospace grade aluminum alloy 7075 and unidirectional glass fiber composite sheets with Araldite LY5052 thermoset epoxy system as the matrix. The volume fraction of aluminum sheets in the FML structure was varied by increasing the number of aluminum sheets from 2 to maximum 4. In the second batch, the epoxy matrix is reinforced with of multi-walled carbon nano tubes and nano diamond particles together, each with 0.15 wt%. The purpose is to enhance the properties of the epoxy matrix to facilitate higher inter-laminate adhesion (FRP and aluminum). The results of the tensile testing show that with the increase of the metal volume fraction, the tensile strength as well energy absorbing capability (toughness) both are increased. The inclusion of the nano-reinforcements has increased the tensile strength and the toughness of the FML structure as compared to that of the FMLs without nano particles. The strength-to-weight ratio of FML structures is also increased after the inclusion of nano reinforced as desired for aerospace applications.

Hybridization of woven kenaf and unidirectional glass fibre roving for unsaturated polyester composite

This is a study on the mechanical properties of kenaf/glass-reinforced polyester composites intended for use in structural profiles with a wall thickness by max. 6 mm. Mechanical properties such as tensile, compression, bending and interlaminar shear stress were investigated by comparing the hybrid variants with the pure fibreglass variant. According to the study, woven kenaf/unidirectional glass roving (WK/UG) alternate recorded the highest tensile properties among hybrid samples. It demonstrated a decrement of about 8.2% of the tensile strength (404.54 MPa) and 10.7% of tensile modulus (24.54 GPa) compared to conventional fibreglass samples. Alternating WK/UG samples demonstrated higher compressive strength (417.15 MPa) compared to other hybrid specimens, recording a slight decrease at 6.09% compared to pure fibreglass composites. The highest bending properties were also observed in hybrid alternate WK/UG samples among other hybrid laminates with only a decrement of 4.13% in modulus of rupture (456.33 MPa) and 1.9% in modulus of elasticity (14.49 GPa) when compared to the control specimen. The ILSS of hybrid composites 2WK/3UG/2WK (30.97 MPa) and WK/UG alternate (34.90 MPa) showed good agreement with the pure fibreglass (42.33 MPa) composites. Using SEM images, tensile fractured specimens were examined to comprehend composites’ failure mechanism and interfacial adhesion. Overall, woven kenaf/unidirectional glass roving alternate sequence is chosen as a potential alternative in developing structural profiles for moderate load-bearing structural applications. In contrast, 3WK/UG/3WK with a higher kenaf to glass ratio demonstrate potential in low load-bearing structural profile applications.Graphical abstract

Effect of Long Glass Fiber Orientations or a Short-Fiber-Reinforced Composite on the Fracture Resistance of Endodontically Treated Premolars.

This study aimed to evaluate the effect of direct restorations using unidirectional glass fiber orientations and a short-fiber-reinforced composite (SFRC) on the fracture resistance of endodontically treated premolars with mesio-occluso-distal cavities. Ninety double-rooted premolars were selected. Fifteen teeth were left intact/as a control group. The endodontic treatment and cavity preparations of seventy-five teeth were performed and divided into five experimental groups: Resin composite (RC), modified transfixed technique + RC, circumferential technique + RC, cavity floor technique + RC, and SFRC + RC. All teeth were fractured under oblique static loading at a 30° angle using a universal testing machine. The fracture patterns were observed and classified. Data were analyzed with one-way analysis of variance, Pearson chi-square, and Tukey HSD post hoc tests (p = 0.05). The highest fracture strength values were obtained in intact teeth (599.336 N), followed by modified transfixed + RC treated teeth (496.58 N), SFRC + RC treated teeth (469.62 N), RC (443.51 N), circumferential + RC treated teeth (442.835 N), and cavity floor + RC treated teeth (404.623 N) (p < 0.05). There was no significant difference between the RC and the circumferential technique + RC (p > 0.05). Unrepairable fractures were observed at low rates (20%) in the modified transfixed + RC and SFRC + RC teeth, and at higher rates in RC (73.3%), cavity floor + RC (60%), and circumferential + RC (80%) teeth. The application of an SFRC or the modified transfixed technique yielded an improved fracture strength and the fracture pattern of ETPs being restored with a universal injectable composite.

Experimental free vibration and tensile test results of a five-layer sandwich plate by comparing various carbon nanostructure reinforcements with SMA

Considering to need for the sensitive and destructive industries for high stiffness and low weight, an experimental free vibration and tensile test results of a five-layer sandwich plate by comparing various carbon nano structures reinforcements with SMA is discussed. The effect of various reinforcements, including carbon nanostructures (carbon nanotubes (CNT), carbon nanorods (CNRs), Graphene platelets (GPLs)) and nitinol shape memory alloy (SMA) wire on the vibration behavior of a five-layer sandwich plate with a foam core is investigated. The purpose and novelty of this work are to compare the effect of different reinforcements on the vibrations of a five-layer plate so that by using this comparison, one can choose the best reinforcements according to the needs of the desired industry and more suitable economic conditions. Considering a 1 % weight fraction of epoxy resin, GPLs, CNTs, and CNRs increase Young's modulus of face sheets by 30 %, 25 %, and 5.8 %, respectively. In this work, a five-layer sandwich structure model can be suggested, and numerically analyzed. The special advantage novelty of this research compared to previous research is the construction of this five-layer model. This is a simple modeling structure for the construction and preliminary examination of structures with five layers experimentally. Also, the composite structure is made by the vacuum pump method, which does not have the disadvantages of the manual method, and the method is completely optimal. At first, the Young's and shear moduli of unidirectional glass fiber (UGF) are calculated by performing a tensile test. To examine all aspects of the construction of five-layer structures during construction, in this article first, the face sheets are made separately using resin, UGF, and various reinforcements, and then the layers of face sheets and the cores are connected using glue. In the following, the equations of motion for the sandwich plate are derived using refined first-order shear deformation theory (RFSDT) by employing Hamilton's principle. Using the Halpin-Tsai equation and the extended rule of mixture, the mechanical properties of the reinforced composite face sheets are obtained. According to the Brinson model, the constitutive equations of the SMA are presented. The influence of various parameters such as side ratio, thickness ratio, weight fraction of CNRs, CNTs, GPLs and SMA wire, fiber angle, and temperature changes on dimensionless fundamental frequency is also represented. Also, the natural frequency of orthotropic plates by considering reinforcements is higher than that without considering reinforcements. By increasing the aspect ratio (a/h), the dimensionless natural frequency increases, while the natural frequency decreases. For two-layer square angular asymmetric laminated sheets (-θ/θ), the minimum dimensionless natural frequency occurred at the fiber placement angle approximately equal to 26 and 64°. The highest frequency is related to the sandwich plate in that its face sheets have higher strength and stiffness because it is placed further from the middle plane. Also, the highest frequency is related to the sandwich plate, whose face sheets are reinforced with GPLs.

Experimental and computational investigation into the damage mechanisms in composite metal hybrid panels subjected to high pressure blast loading

In this work, a free piston shock tube is utilized to conduct blast experiments on unidirectional glass fiber reinforced thermoplastic composite-metal hybrid panels. Damage and deflection characteristics are obtained in real time during the blast test using fringe projection methods, and post blast damage is assessed by nondestructive evaluation methods. Finite element models are developed in LS Dyna for the blast apparatus and hybrid composite panel and the results are compared to the experimental blast tests. The delamination in the computational model matched both size and shape to the delamination of the composite C-Scan. Furthermore, both dynamic deflection and permanent deflection of the hybrid panel correlated well between the experimental blast test and the LS Dyna blast simulation.

Study on projectile impact resistance of carbon-glass hybrid bioinspired helical composite laminate

Mantis shrimp dactyl clubs have excellent impact resistance due to their special helical structure. Meanwhile, hybrid fibre has become increasingly popular to improve the mechanical properties of composite materials. Based on the helical structure of the periodic region of mantis shrimp dactyl clubs and hybrid fibres, in this study, a hybrid fibre helical lay-up laminate (HHL) is designed. The laminates are prepared using unidirectional carbon fibre prepregs and unidirectional glass fibre prepregs. To study the protective performance and damage process of HHL, a light gas gun impact test and numerical simulation calculations were carried out on the specimens. The harvested protective capability of the HHL specimen was then compared with those of carbon fibre unidirectional lay-up laminate (CUL), carbon fibre helical lay-up laminate (CHL), and hybrid fibre unidirectional lay-up laminate (HUL) specimens. The ballistic protection capability of HHL at different helical lay-up angles was also explored. The testing results show that HHL has the best ballistic protection performance. HHL’s ballistic limiting velocity is 228.5 m/s, which is 49.5%, 30.8%, and 19.9% higher than those of CUL (152.8 m/s), CHL (174.7 m/s), and HUL (190.5 m/s), respectively. Finally, hybrid fibres with a 90° interlaminar helix angle were found to have the highest ballistic limiting velocity. The reason is that the larger interlaminar angle allowed more fibres to be involved in the protection, increasing the energy loss of the projectile and enhancing the protection of the laminate.

Designed and Analysed of Three Distinct Composite Material-Based Mano Leaf Spring using ANSYS

The leaf spring is an important component in vehicles because it provides a comfortable ride and stability to the vehicle. The need to replace leaf springs with stronger and more lasting leaf springs is a key challenge in the transportation and automotive industries. In addition to offering ride comfort and stability, traditional steel leaf springs have a significant impact on the weight of the car. Fibre reinforced polymeric composites, therefore, are appropriate materials for various applications due to their many exceptional properties, including high wear resistance, high strength, long fatigue life, corrosion resistance, and low density. Fiber-reinforced polymeric composites find extensive application in several technical sectors, such as automotive, aviation, military, and marine industries. The utilization of composite materials has become imperative in the automotive industry to attain weight reduction without compromising material strength, as fuel consumption and CO2 emissions have to be reduced. In this paper, three different types of composite-based mono leaf springs were designed and examined. The results of the investigations showed that the 0° unidirectional glass fiber system was unable to correctly produce the required spring rate. Consequently, many combinations of carbon and glass hybrid systems were studied. The analysis showed that the desired spring rate was produced by the material configuration of [0°6G / 0°2C / 0°22G] S. When the final results were contrasted with the FEA findings, it was found that they concurred.

Fabrication and Characterization of Unidirectional Fiberglass Mat/CSM Hybrid Composites Using a Vacuum Infusion Process

Fabrication and Characterization of Unidirectional Fiberglass Mat/CSM Hybrid Composites Using a Vacuum Infusion Process