Glass Fiber Epoxy Laminates Research Articles

Mechanical properties and damage development in glass-fiber epoxy laminates subjected to tensile loading at sub-zero temperatures

In various structural applications polymer composites are exposed to sub-zero and even cryogenic temperatures which may initiate of microstructural damage. To anticipate these events, one needs to understand the behavior of composites in a sub-zero environment. This study focuses on damage initiation and accumulation, and its influence on the properties of cross-ply glass fibers epoxy composites at sub-zero temperatures. The effect of bromine modification of epoxy, and the dissolution in an organic solvent on the mechanical performance of the produced composite is also investigated. To evaluate the influence of a sub-zero environment on the mechanical performance of glass fiber epoxy laminates, tensile tests in a sub-zero environment of unconditioned specimens were carried out. The quasi-static tensile tests were performed to measure the elastic modulus of the composites while loading-unloading experiments were performed to monitor the initiation (and accumulation) of microstructural damage and its influence on the stiffness of glass fiber epoxy laminates. The results of cryogenic damage and fracture in the laminates are discussed with a focus on the degradation of properties of glass fiber crucial for their use in structural applications: strength and stiffness.

Effect of Thermomechanical Loading at Low Temperatures on Damage Development in Glass Fiber Epoxy Laminates.

Due to the high interest in the use of glass/epoxy laminates in aerospace applications, aviation, and as cryogenic tanks, it is crucial to understand the behavior of composites under challenging environmental conditions. Polymer composites are exposed to low temperatures, including cryogenic temperatures, which can lead to the initiation of microdamage. This paper investigates damage initiation/accumulation and its influence on the properties of cross-ply woven glass fiber epoxy composites at low temperatures compared to room temperature conditions. To evaluate the influence of a low-temperature environment on the mechanical performance of glass fiber reinforced epoxy composite (GFRP) laminates, three types of test campaigns were carried out: quasi-static tensile tests and stepwise increasing loading/unloading cyclic tensile tests at room temperature and in a low-temperature environment (-50 °C). We demonstrated that the initial stiffness of the laminates increased at low temperatures. On the other hand, there were no observed changes in the type or mechanism of developed damage in the two test conditions. However, the reduction in stiffness due to the accumulated damage was more significant for the laminates tested at low temperatures (~17% vs. ~11%). Exceptions were noted in a few formulations where the extent of damage at low temperatures was insignificant (<1%) compared to that at room temperature. Since some of the studied laminates exhibited a relatively minor decrease in stiffness (~2-3%), we can also conclude that the formulation of matrix material plays an important role in delaying the initiation and formation of damage.

Quasi-static puncture shear loading behaviour MWCNT/glass fibre epoxy laminates with various indenters

Investigation was performed to evaluate the puncture resistance of multi-walled carbon nanotubes (MWCNTs)/glass fibre epoxy laminate composites using different indenters (conical, elliptical, flat, and hemispherical). For the puncture tests, MWCNT weight percentage and indenter type were varied. Furthermore, the impact of MWCNT on tensile, flexural, and interlaminar shear strength was evaluated. Ultrasonic C-scan provided insights into the damage evolution and failure mechanisms of the laminates under puncture. The results indicate that the flat indenter exhibits prolonged indentation time and enhanced energy absorption, resulting in a disc-shaped failure pattern. On the other hand, the conical indenter demonstrates rapid penetration due to its smaller contact surface area. The elliptical indenter generates higher frictional energy, leading to bulging damage. The hemispherical indenter showed an even distribution of force across the impacted surface, minimizing force concentration and reducing the extent of damage. These findings shed light on the puncture mechanisms of MWCNT/Glass fibre epoxy laminate composites, paving the way for more precise glass fibre laminate composite design and optimisation in practical applications such as aerospace, automotive, and sporting goods, where puncture loading is a critical consideration.

Evaluation of Tensile and Flexural Properties of Unidirectional Glass-Epoxy Laminate with Aluminium Oxide and Magnesium Hydroxide as Filler Materials

Low weight is one of the most important factors in the design process of road and flight vehicles. The design engineers are careful with regards to the weight decrease without thinking twice about the primary strength. The composite is a lightweight material that has decent underlying properties and it is generally utilized. Fiber-supported polymer composites assumed a prevailing part for quite a while in an assortment of uses for their high explicit strength. The current work portrays the turn of events and the portrayal of another arrangement of GFRP. Experiments are carried out to study the effect of the addition of fillers by varying their percentages. The present work focus on the effect of the fillers on properties of Glass fiber epoxy laminates with aluminum oxide and magnesium hydroxide powders as the fillers. In the present work, fabrication and experimental investigation on unidirectional glass epoxy composites are carried out. Initially, glass fiber reinforced polymer laminate fabricated without filler material, hand layup followed by vacuum bagging methods are used . Then, by adding Aluminium oxide and Magnesium hydroxide as a filler material with different percentages like 5%, 10%, and 15% by weights and laminates are fabricated and experimental investigation is conducted to study their mechanical behavior. The comparative studies on the laminates are carried out and the obtained results are analyzed and those are quite interesting.

Thermal cycling of strained nickel‐coated glass‐epoxy composite laminates: Effects on macro mechanical and fiber‐matrix interface properties

AbstractNickel coating of reinforcing fibers via electroless plating can provide superior properties to polymer composites, particularly for radar stealth, although its effect on thermomechanical properties and thermal cycling response are relatively unverified. Thermal cycling of strained nickel‐coated glass fiber epoxy laminates was performed to evaluate its effect through in‐plane shear mechanical testing and fiber‐matrix interface region microscopic observations. Laminates were subjected to 4000 cycles of thermal conditioning (regular and strained). Subsequent in‐plane shear tensile tests revealed a ~10% increase in their ultimate shear strength, which was credited to polymer relaxation and increased plastic energy storage capacity. Atomic force microscopy in force modulation mode showed the most significant fiber‐matrix interface region changes for strained thermal cycled specimens, which we attribute to their higher stress during conditioning and plastic deformation. A relatively short fiber‐matrix interface region length was observed, which we attribute to the lower surface energy of Ni‐glass fiber. Thermomechanical analysis (TMA) revealed a glass‐transition temperature range of 71–110°C, and coefficients of thermal expansion (CTE) were evaluated for several laminate configurations.

Enhancing low velocity impact characteristics of glass fiber laminates by short fiber reinforcement—Failure evolution and damage mechanisms

AbstractFor enhancing impact characteristics, woven glass fiber epoxy laminates are reinforced with short fibers. The 6‐mm‐long slender fillers, when added up to 4% in the matrix, exhibit no influence on the flexural modulus, but at 2% they maximize the laminate's flexural strength. While the dissipation energy continues to increase up to 30 J of impact, the laminates' post‐impact load bearing capacity gets significantly affected beyond 20 J. The reinforced laminates exhibit better elastic response and enhanced damage resistance with as high as 50% reduction in the visible damage area as well as up to 35% increase in the damage initiation force. The degree of damage shows excellent correlation with the visible damage area. The distinct through thickness conical region, diverging from the impact site, is attributed to the presence of microcracks oriented along the fiber directions. The cone boundary, from where the interlaminar failure initiates, is largely the manifestation of transverse matrix cracks. While the damage cone with greater divergence indicates reduced impact resistance of the laminate, the orientation of transverse matrix cracks remains unaffected by the impact energy or the filler content. At low impact energies, the failure initiated from the fiber/matrix interfaces, coalesce to form the matrix cracks, which act as a precursor to the interlaminar failure. However, at high energy levels, several failure mechanisms simultaneously develop with no clear indication of the order of damage evolution. The short fibers enhance the laminate's impact resistance either by arresting the cracks or by developing tortuous crack path with high energy dissipation.

Hygrothermal degradation of mechanical properties of nanoclay based stainless steel and glass fibre-epoxy laminate

Fibre metal laminates (FML’s) are the multilayer composite laminates of metallic sheets and fibre reinforced plastic (FRP) composites. The stacking sequence of metallic sheets and FRP prepregs in FML’s vary as per the type of fibre metal laminate and its application. FML’s are the most suitable materials for shipbuilding, aerospace and aeronautical structural use due to better mechanical properties over traditional materials. In the present research, the mechanical properties of nanoclay based stainless steel and glass fibre-epoxy laminate (SS FML) have been investigated. Hygrothermal conditioning of specimens was performed in two aqueous environments at 40 °C and 70 °C for three months. After hygrothermal conditioning, tensile, flexural, compression and Izod impact tests were performed as per ASTM standards. It is concluded that the nanoclay addition in the epoxy matrix of SS FML improves its mechanical properties drastically. It is due to the fact that the nanoclay in the epoxy matrix improves the interfacial bonding between the composite layers. It is observed that the mechanical properties were reduced more in distilled water due to the salts available in seawater that reduces the moisture absorption in epoxy matrix of SS FML. It is also noticed that the temperature has the considerable effect on the degradation of mechanical properties. Higher temperature of water softens the epoxy, results in highest degradation in distilled water at 70°C.

Effect of long-term thermal cycling and moisture on heated Fibre Metal Laminates and glass-fibre epoxy composites

Heated GLARE, a Fibre Metal Laminate with an integrated heater element, has a promising potential as de- or anti-icing system in aircraft structures. To investigate the long-term durability of heated GLARE previously reported thermal cycling tests up to 12,000 cycles are extended up to 144,000 cycles and moisture conditioning is included. Similar testing up to 72,000 cycles is performed on FM906 glass-fibre epoxy laminates with an integrated heater element to study the influence of the aluminium layers in GLARE.In all test results the initial decrease in interlaminar shear values from 0 to about 10,000 thermal cycles is followed by a recovery phase and a resumed decline after roughly 60,000 cycles. The decrease in ILSS is expected to be caused by internal stress relief which is counteracted by the positive effect of physical ageing due to elevated temperature exposure. Thermal cycling of conditioned samples generally resulted in slightly larger decreases in interlaminar shear strength for both heated GLARE and heated FM906 glass-fibre epoxy laminates.

Enhanced Shear Performance of Hybrid Glass Fiber–Epoxy Laminates Modified with Boron Nitride Nanotubes

Matrix enhancement using nanotubes is one method to produce hybrid, multiscale fiber reinforced polymer (FRP) composites with improved interlaminar performance and added functional properties. Carbon nanotubes (CNTs) have been shown to be promising, and recent advances in the manufacturing of boron nitride nanotubes (BNNTs), which are largely unexplored for structural reinforcement of hybrid composites with microscale fibers, offer new opportunities to employ BNNTs in reinforced hybrid composite structures. This study investigates the shear and impact properties of BNNT hybrid composites, specifically glass fiber–epoxy/BNNT composite laminates. Two manufacturing techniques were used to fabricate the specimens: wet layup and vacuum-assisted resin transfer molding (VARTM). Shear punch, short beam shear, and modified Charpy tests were selected for their relevance to complex loading systems that involve shear, such as ballistic or other impact loading. The addition of 1 wt % BNNTs to the epoxy resin was found...

Characteristic properties of glass fiber reinforced sugarcane bagasse medium density fiber board

Medium density fiberboard (MDF) is one of the wood composites which are used widely in the furniture industry. Therefore, its strengthening is required. Sandwiched material is manufactured by inserting sugarcane bagasse medium density fiberboard between the glass fiber reinforced laminates in just the same fashion as a sandwich. A hand lay-up technique is used to prepare the sandwiched specimen, in which the medium density fiberboard plate is put in between two woven layers of glass fiber epoxy laminates. Tensile and bending tests are done to investigate efficiently the tensile and flexural behaviors for the MDF strengthening process. In addition, compact tension and center notch specimen tests are carried out to obtain the effect of the modification performed for the MDF main material on fracture toughness. Moreover, a water soaking test is held out, and fungal bioassay resistance is investigated to obtain some of the novel material environments. The results illustrate that both tensile and flexural strength are extremely modified and increased. Besides, the results show compatibility and bonding between layered material and medium density fiberboard plate. The fracture toughness is greatly increased, and both tests can be met as regards fracture toughness tests for such novel composite material. The novel material has high resistance to fungal creation, which helps it to be utilized in medical furniture. Finally, it is found that only a very little percentage of absorption is established for the novel produced material.

Assessing glass-fiber modification developments by comparison of glass-fiber epoxy composites with reference materials: Some thoughts on relevance

Any approach for designing composites with improved mechanical properties finally has to be assessed for respective improvements achieved. Glass-fiber reinforced epoxy matrix laminates consist of several constituents. Pretreatment of the constituents, the processes combining the matrix with the reinforcing fibers as well as the curing of the laminate may all have an effect on the resulting mechanical or fracture properties of the composites. In this contribution, the authors present selected cases from recent materials developments, dealing with glass-fiber epoxy laminates for which a thermal fiber treatment for desizing was compared with chemical solvent desizing. While desizing with a solvent and resizing with another type of sizing yielded tensile and interlaminar shear properties comparable to those of laminates prepared from as-received fibers, but lower for desized fibers, resizing after thermal desizing treatment exceeding +500 ℃ yielded lower properties for laminates from desized and resized fibers, but roughly in the same percentage difference as chemically desized and resized fiber laminates. This raises the question of how material or interface modifications in glass-fiber epoxy composites can best be compared for an assessment of the improvements achieved by the fiber treatments or the fiber–matrix interface modifications.

High-Speed Surfactant-Free Fabrication of Large Carbon Nanotube Membranes for Multifunctional Composites

AbstractA high-speed manufacturing process for multiwalled carbon nanotube (MWNT) buckypaper is presented, and its application as an embedded strain sensor for composite materials is demonstrated. This manufacturing method enables the production of sizable carbon nanotube (CNT) membranes with significantly reduced processing time and less manufacturing complexity than other contemporary techniques. The use of surfactants and chemical functionalization of MWNTs was completely avoided in this method because functionality of carbon nanotubes can be hampered by such surface treatments. Microstructure, mechanical properties, and piezoresistive response of the fabricated buckypaper were characterized, and its sensitivity as a strain sensor was analyzed. Stable piezoresistive response could be achieved at low strains, and a high sensitivity to strain was observed when buckypaper was embedded in glass fiber epoxy laminates for strain sensing.

Interlaminar toughening of resin transfer moulded glass fibre epoxy laminates by polycaprolactone electrospun nanofibres

Abstract Delamination and brittle matrix fracture has since long been a problem of fibre reinforced composites. This paper investigates if polycaprolactone (PCL) nanofibre nonwovens can increase the interlaminar fracture toughness of resin transfer moulded glass fibre/epoxy laminates, without causing problems during impregnation and without negatively affecting other (mechanical) properties. The mode I fracture toughness was shown to be dependent on both the nanofibre content as well as on how the nanofibres were introduced into the laminates. Almost 100% improvement in fracture toughness could be achieved by electrospinning the PCL nanofibres on both sides of the glass fibre mats prior to impregnation. This led to a mode I fracture toughness of over 1200 J/m 2 . Tensile and dynamic mechanical properties of the toughened laminates were not affected by the PCL nanofibres. It could be concluded that even state of the art infusion resins with a high intrinsic fracture toughness can benefit significantly from nanofibre toughening.

A multiaxial fatigue damage model for fibre reinforced polymer composites

A multiaxial fatigue damage model for fibre reinforced polymer composite materials is presented. The model combines (i) fatigue-induced fibre strength and modulus degradation, (ii) irrecoverable cyclic strain effects and (iii) inter-fibre fatigue. The inter-fibre fatigue aspect is based on a fatigue-modified version of the Puck multiaxial failure criterion for static failure. The model is implemented in a user material finite element subroutine and calibrated against fatigue test data for unidirectional glass fibre epoxy. A programme of uniaxial fatigue tests on quasi-isotropic glass fibre epoxy laminates is presented for validation of the novel fatigue damage methodology. The latter is successfully validated across a range of stress levels.

Mode-I Fracture and Impact Analysis on Stitched and Unstitched Glass/Epoxy Composite Laminate

A number of approaches have been used to improve the impact damage resistance and tolerance of composite materials. These include control of fibre/matrix interfacial adhesion, laminate design and through the thickness reinforcement. One of the techniques of arresting delamination is providing through-the-thickness reinforcement like stitching. The objective of this work is to understand the influence of fibre orientation and stitching on the mechanical response of the laminate. In this paper, the drop weight impact properties and mode I interlaminar fracture toughness of stitched and unstitched glass fibre epoxy laminate are were studied experimentally. The ultrasonic C-Scan image of the damaged impact specimen is used to find the damage area. A detailed comparison between the stitched and unstitched laminates experimentally confirmed that the stitching effectively suppressed the out of plane impact damage and increased the interlaminar fracture toughness.

Experimental And Finite Element Analysis Of Mechanical Response On Unidirectional Glass Fibre Epoxy Laminate

Research in low velocity impact loading of composites is aimed at reducing the degree of damage in order to improve the damage tolerance. A number of approaches have been used to improve the impact damage resistance and tolerance of composite materials. These include control of fiber/matrix interfacial adhesion, laminate design and through the thickness reinforcement. One of the techniques of arresting delamination is providing through-the-thickness reinforcement like stitching. The objective of this work is to understand the influence of stitching on the impact of the laminate. In this paper, the drop weight impact properties of stitched and unstitched glass fibre epoxy laminate are compared experimentally and the damaged specimen are assessed using back lighting photographic technique. A detailed comparison between the stitched and unstitched laminates experimentally confirmed that the stitching effectively suppressed the out of plane impact damage.

Mixed mode fracture toughness: An empirical formulation for [formula omitted] determination in asymmetric DCB specimens

Asymmetric DCB specimens (ADCB), in which the crack plane is out of the laminate midplane, are simple and useful test configurations to produce a mixed mode load state at the crack tip of the samples. This test configuration is as simple as pure mode I tests. However, the analytical procedures developed in the ASTM D5528-01 standard to calculate G I are no longer valid to analyze the ADCB specimen. In this test configuration, the position of the crack plane controls the mode I and mode II load levels at the crack tip. In this work an empirical formulation, based on Finite Element Modelling (FEM), has been developed in order to calculate G I / G and G II / G (where G = G I + G II ) in ADCB specimens. On the other hand, the Modified Beam Theory (MBT) has been adapted by means of experimental calibration to allow the calculation of G for this test configuration. These formulations have been validated by means of FE modelling for different crack plane positions. Finally, the formulations developed in this paper were used to calculate G I and G II in experimental results on glass fibre epoxy laminates and the obtained results were compared with formulations developed by other authors. A good agreement was found among the different analytical, empirical, and numerical methods studied in this paper.

Failure processes in composite materials: getting physical

This paper describes crack growth processes in carbon fibre and glass fibre-epoxy laminates under stress and quantifies by physical modelling the accumulation of damage with load cycling. Cracking mechanisms are observed directly and identified by in-situ dynamic scanning electron microscopy. Armed with this information, particular attention is given to the differences between these cracking processes and the way they interact, their growth-rate, and their effect on the damage-state of the structure with variations in laminate geometry, with changes in magnitude of applied stress, and with fatigue cycles. Particular attention is given to the internal damage state variable approach to physical modelling.

Dispersion of Waves in Composite Laminates With Transverse Matrix Cracks, Finite Element and Plate Theory Computations

Dispersion relations for laminated composite plates with transverse matrix cracks have been computed using two methods. In the first approach it is assumed that the matrix cracks appear periodically and hence it is possible to consider a periodic cell of the structure using Bloch-type boundary conditions. This problem was formulated in complex notation and solved in a standard finite element program (ABAQUS) using two identical finite element meshes, one for the real part and one for the imaginary part of the displacements. The two meshes were coupled by the boundary conditions on the cell. The code then computed the eigenfrequeneies of the system for a given wave vector. It was then possible to compute the phase velocities. The second approach used may be viewed as a two step homogenization. First the cracked layers are homogenized and replaced by weaker uncracked layers and then the standard first-order shear-deformation laminate theory is used to compute dispersion relations. Dispersion relations were computed using both methods for three glass-fiberepoxy laminates ([0/90]2,[0/90]sand[0/45/-45]s with cracks in the 90 and ±45 deg plies). For the lowestflexural mode the difference in phase velocity between the methods was less then five percent for wavelengths longer than two times the plate thickness. For the extensional mode a wavelength often plate thicknesses gave a five percent difference.

Fatigue crack growth with fiber failure in metal-matrix composites : Begley, M.R. and McMeeking, R.M. Compos. Sci. Technol. (1995) 53 (4), 365–382

Fatigue crack propagation is examined using single overload in cyclic condensation environment. Using this environment the growing crack is exposed cyclically to environments with high and low humidity. These environmental changes cause the formation of a periodic pattern on the fracture surface called beach marks when the crack growth is low. A single overload can also cause the formation of beach marks in the overload affected zone when cyclic condensation environment is used. The markings are being formed due to the retardation of the crack growth subsequent to the overload. The markings are also formed close to the stretch zone and the spacing increases with increasing distance from the overload zone; subsequently they stop forming. The microscopic crack growth rate after the overload obtained from measurement of beach mark spacing is compared with the macroscopic one calculated from crack length measurement. The mechanism of beach mark formation after the overload is the same as in the initiation zone of short cracks and near-threshold propagation of the long one.The materials used are centre-cracked-tension (CCT) specimens of 7075-T6, 2024-T3 and 7075 aluminium glass fibre epoxy laminate (GLARE I).