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The present study investigates the flexural failure properties of a hybrid laminate beam subjected to three-point bending. A symmetrically laminated hybrid beam is constructed using high-strain and inexpensive glass fibre on the top layers and low-strain and expensive carbon fiber on the middle layers. Classical lamination plate theory is used to find the stress and strain distribution that occurs due to the bending moment on the compressive side. The theoretical failure limits of the laminated hybrid beam are analyzed considering the targeted span-to-depth ratios, volume fractions of the fibers and hybrid ratios using the Tsai-Wu failure criterion and Matlab codes. Using the graph of failure index versus hybrid ratios, the minimum thickness of carbon fiber needed for the delay of failure and cost efficiency of the laminated hybrid beam is identified by applying the linear interpolation method. The numerical results indicate that the failure index increases with the increasing loading span and decreases when the volume fraction of fiber increases. In particular, the placement of glass fiber on the top layer of the laminated hybrid beam might have contributed to obtaining higher strains and curvatures before the catastrophic failure properties of carbon fiber. The flexural stiffness of the laminates is found to increase when the hybrid ratio increases. Overall, it is noted that the theoretical analysis is one method that is less time-consuming and cost-effective than other alternative approaches, such as finite element methods and experimental tests to estimate the minimum thickness of high-stiffness and the expensive material needed to maintain the strength and stiffness of the hybrid composite structures over long periods. [ABSTRACT FROM AUTHOR]

Glass fibers (GFs)/epoxy laminated composites always present weak interlaminar shear strength (ILSS) and low cross-plane thermal conductivity coefficient (λ⊥). In this work, silica-sol, synthesized from tetraethyl orthosilicate (TEOS) and KH-560 via sol-gel method, was employed to functionalize the surface of GFs (Si-GFs). Together with a spherical boron nitride (BNN-30), the thermally conductive BNN-30/Si-GFs/epoxy laminated composites were then fabricated. Results demonstrate that Si-sol is beneficial to the improvement of mechanical properties for epoxy laminated composites (especially for ILSS). The BNN-30/Si-GFs/epoxy laminated composites with 15 wt% BNN-30 fillers display the optimal comprehensive properties. In-plane λ(λ//) and λ⊥ reach the maximum of 2.37 and 1.07 W·m−1·K−1, 146.9% and 132.6% higher than those of Si-GFs/epoxy laminated composites (λ// = 0.96 W·m−1·K−1 and λ⊥ = 0.46 W·m−1·K−1), respectively, and also about 10.8 and 4.9 times those of pure epoxy resin (λ// = λ⊥ 0.22 W·m−1·K−1). And the heat-resistance index (THRI), dielectric constant (ε), dielectric loss (tanδ), breakdown strength (E0), surface resistivity (ρs) as well as volume resistivity (ρv) are 197.3 °C, 4.95, 0.0046, 22.3 kV·mm−1, 1.8 × 1014Ω, and 2.1 × 1014Ω·cm, respectively. [ABSTRACT FROM AUTHOR]

The advantages of carbon nanotubes (CNTs) in fortifying the glass fiber reinforced polymeric (GFRP) composites are discussed in this paper. Bolted steel straps are utilized at the edges of composite plate to establish clamped conditions in the test setup. To minimize uncertainties caused by bolt attachments, a genetic algorithm-based model updating approach has been implemented by introducing artificial linear springs at the margins to achieve a better balance between theory and reality. The accuracy of the plate's results (natural frequencies and mode shapes) is verified, and the mechanical properties of randomly dispersed CNTs are incorporated in the formulations of folded plates. Remarkably, the motion equations are brought forward by the first order shear deformation theory (FSDT). Thereafter, two-directional generalized differential quadrature (2D-GDQ) technique is employed to determine natural frequencies from available motion, continuity, and boundary equations. The results of the folded plate are validated first by an experimental modal testing and finally some effective parameters such as folding angle, CNT weight ratio, boundary condition and flange-shape length are examined. [ABSTRACT FROM AUTHOR]

A systematic evaluation of the interlayer crack resistance in the modes I and II loadings of a glass fiber epoxy laminated composite by experimental and computational methods using the cohesive zone model was carried out. The local properties (the ultimate stress σC, the maximum displacement δmax, and the specific work of fracture γF) of the cohesive zone were determined experimentally by the methods of separation and shear of the layer contact zone; the critical intensities of elastic energy release (GIC and GIIC) were found by the method of linear elastic fracture mechanics. Based on the experimental data obtained, the critical length of the cohesive zone was calculated by the Barenblatt micromechanical theory. A numerical evaluation of the crack resistance of a laminated composite under conditions of static loading in the modes I and II was carried out using 3D finite-element models of a double-cantilever beam and end-notched flexure specimens with an implemented cohesive zone obeying the exponential law. The optimal number of interface elements in the finite-element mesh was determined for the cohesive zone calculated based on experimental data, which ensured a sufficient accuracy of numerical calculating the ultimate load of the onset of crack growth and the stress distribution along the length of the cohesive zone with a minimum number of calculations. The approach proposed and the results obtained showed a good agreement between the calculated and experimentally determined characteristics of standard specimens of glass fiber epoxy composite and can be used to calculate the interlayer strength and crack resistance of structural members with a complex geometry made of layered polymer composites. [ABSTRACT FROM AUTHOR]

The leaf spring is an important component that provides suspension and plays a vital role in automotive applications. As a vehicle travels, a tremendous force, mostly in terms of a fatigue load, is applied to the leaf spring assembly, particularly to the eye point of the rear axle. In a vehicle with rear-wheel drive, the leaf spring is subject to twisting forces that are opposite in direction and magnitude during the acceleration of drive wheels. A multileaf spring provides an additional strength, but lacks the flexibility and increases the overall weight of the vehicle. Considering the loading conditions, the availability of space in a vehicle, and geometrical considerations, a composite monoleaf spring is designed. In due consideration of the tensile behavior, fatigue resistance, chipping resistance, and base part resistance, a hybrid laminated spring is constructed for the purpose. The present study focuses on an analysis and behavior of a monoleaf spring made of hybrid composite materials, i.e., carbon and E-glass fibers. It is observed that the natural frequency of a hybrid composite leaf spring is twice the frequency of a conventional leaf spring, particularly in the vertical direction, which means that the occurrences of resonance will be less. Also, it is observed that the stress produced in it is lower than that in a conventional leaf spring. The hybrid composite monoleaf spring proved to have better impact and tensile behavior than a steel one. [ABSTRACT FROM AUTHOR]

GLARE laminates are multi-layered metal-composite materials created from bonding sheets of metallic alloys with carbon or glass fibre layers. The application of hybrid-conventional machining processes such as ultrasonic-assisted drilling (UAD) is becoming of great interest to the aerospace industry due to its capability in reducing the cutting forces and tool wear which are directly responsible for drilling-induced delamination. There is rich literature on the conventional drilling (CD) of GLARE, but no work reported using UAD process. This study will fill this gap and investigate the UAD of GLARE laminates using an indigenously developed UAD system. The influence of spindle speed and feed rate on thrust force and surface roughness metrics (Ra and Rz) were investigated under CD and UAD regimes. The quality of the borehole and damage mechanisms in the laminate constituents was examined using scanning electron microscopy (SEM). The contribution of the drilling parameters on the measured outputs was further evaluated using the analysis of variance (ANOVA) statistical analysis. It was found that UAD resulted in a significant reduction in thrust force by up to 65% while surface roughness metrics Ra and Rz were unaffected by the type of drilling process used. SEM analysis showed irregular and fuzzier surfaces in glass fibre layers in holes machined using UAD due to the longitudinal vibration of the tool. [ABSTRACT FROM AUTHOR]

The incorporation of inorganic nanoparticles with thermosetting epoxy polymer is an emerging field of research over the past few years. It is well analyzed that epoxy matrix is brittle in nature that shows rapid crack initiation and rapid propagation without increasing applied stress value. Therefore, researchers are showing their interest in nanoparticles embedded epoxy composites to improve their fracture resistance (brittleness and toughness). In this investigation, the dispersion of TiO2 nanoparticles at different weight fractions (0-2 %) with glass fiber reinforced epoxy composites is performed to enhance structural and thermo-mechanical properties. The TiO2 nanoparticles are prepared by sol-gel method and structural analysis of TiO2 nanoparticles shows greater interfacial bond with epoxy matrix and glass fibers due to fine dispersion of nanoparticles. From obtained results, a significant enhancement in their tensile strength (38.56 %), flexural strength (30.52 %), inter-laminar shear stress (25.22 %), impact strength (327.10 %), micro-hardness (48.53 %) and fracture energy (40.19 %) with a minimal detrimental effect on toughness was revealed for GFRP-T1.0 compare to GFRP-T0.0 composite laminates. The stiffness and rigidity also improved up to 52.72 % and 34.13 % respectively for GFRP-T1.5 compare to GFRP-T0.0 composite laminates. The effects of nanoparticles contents and clustering size on thermal stability and glass transition temperature of developed composites are observed by thermo-gravimetric analysis. The surface morphology of TiO2 nanoparticles is characterized by transmission electron microscope (TEM) while the dispersion of nanoparticles and failure of developed composites were analyzed by scanning electron microscopy (SEM). [ABSTRACT FROM AUTHOR]

As material age, the durability, strength, and other mechanical properties are impacted. The lifespan of a material generally decreases when exposed to weathering conditions such as wind, temperature, humidity, and light. It is important to have knowledge of how materials age and how the material properties are affected. Regarding materials´ fire behaviour and the effect of ageing on these properties, the knowledge is limited. The research questions of the current work are: Are the fire properties of composite materials affected by ageing? And if so, how is it affected? The study is on material at Technology Readiness Level 9 (TRL). In this study, three composite fibre laminates developed for marine applications were exposed to accelerated ageing. Two different ageing conditions were selected, thermal ageing with an increased temperature of 90°C and moisture ageing in a moderately increased temperature of 40°C and a relative humidity of 90%. Samples were collected after one, two and four weeks of ageing. The reaction-to-fire properties after ageing was evaluated using the ISO 5660–1 cone calorimeter and the EN ISO 5659–2 smoke chamber with FTIR gas analysis. The test results showed that the fire behaviour was affected. Two of the composite laminates, both phenolic/basalt composites, showed a deteriorated fire behaviour from the thermal ageing and the third composite laminate, a PFA/glass fibre composite, showed an improved fire behaviour both for thermal and moisture ageing. The smoke toxicity was affected by the accelerated ageing, especially for the PFA/glass fibre composite that showed a higher production of CO and HCN, both for the thermal aged and the moisture aged samples. [ABSTRACT FROM AUTHOR]

Matrix cracks in composite laminates are almost invariably the first damage mechanisms in composite laminates and are the precursor to more serious forms of damage. The results presented in this paper include experimental investigations into the occurrence of these cracks in a wide range of laminates containing various angle-plies. Ultrasonic detection of these cracks using polar backscattering is found to be successful and shows promise as a method which could be applied outside the laboratory. Further work includes finite element simulations which lead to an understanding of aspects of the accumulation of damage in composite laminates. [ABSTRACT FROM AUTHOR]

Laminated composites with complex structures, such as L, C, or T-shaped geometries, are used at junction parts in the automotive and aerospace industries. Due to delamination failure in the curved or angled region, these structures are relatively weak in the through-thickness direction when subjected to complex loading. To overcome the issue of weak delamination resistance, this study is aimed at investigating the effect of various reinforcements on the strength properties and delamination resistance of glass/epoxy curved laminates under a four-point bending test. Experimental research was carried out on glass/epoxy curved laminates strengthened by combining three different types and geometries of reinforcement. These included chopped short fibers and glass fiber patches between each ply at the corner region of curvature, and stitching of aramid filament at the corner region of 90-degree bending. A 4 mm pitch interval was observed to enhance curved beam strength, interlaminar tensile strength and delamination resistance. The obtained findings show that glass/epoxy curved laminates reinforced with chopped kenaf short fiber, 45° glass fiber and a single stitch at the corner show greater enhancement in curved beam strength by 52.7, 34.3, and 5.6%, respectively, compared to the baseline sample. Similarly, interlaminar tensile strength improved by 69.3, 40, and 78.5% compared to the baseline sample. On the other hand, curved laminates needled with a single stitch at the corner show higher delamination resistance than other reinforcements. The experimental results correlate well with the damage morphology indicated in SEM fractographic images. [ABSTRACT FROM AUTHOR]

As a non-destructive technique, Acoustic emission (AE) can be employed to detect the damage inside the material passively and then locate the damage source. However, fatigue loading poses challenges to AE signal acquisition and processing. In this paper, AE monitoring is performed on glass fiber/epoxy composite laminates under fatigue loads. Due to the intrinsic noise, wavelet packet decomposition is used for noise elimination. Results show that the noise components in original AE signals can be effectively eliminated by the wavelet analysis. Based on the difference of the arrival times, the line positioning method is shown to locate AE sources appearing in the laminates successfully. The peak frequency characteristic of each AE signal is utilized for damage mode classification. The fracture of the laminate is governed by delamination and fiber/breakage, followed by fiber/matrix interface debonding. [ABSTRACT FROM AUTHOR]

This paper describes an experimental study on strain and fracture of plane samples made of glass-fiber laminate and fabric-based laminate with surface and inner aluminum layers. It is shown that the presence of these layers reduces the strength of glass-fiber laminate under static and low-cycle loading. This can be explained by the fact that the stretching of a hybrid composite along the layers is accompanied by the formation of localized tensile regions of glass-fiber laminate across the layers. As a result, both the hybrid composite and its glass-fiber laminate component are stratified. [ABSTRACT FROM AUTHOR]

In this study, the formability of the FML (fiber metal laminate) sheets has been investigated by experimental and numerical methods. The sheets consist of an aluminum skin and a glass fiber reinforced core. Uniaxial tensile and stretch forming tests were performed to extract the forming limit diagram (FLD), experimentally. M-K (Marciniak-Kuczynski) method was implemented to extracting the FLD of the FMLs, numerically. The effect of skin and core thicknesses on formability was studied in variable and constant total thickness by numerical method. Finally, it has been cleared that the numerical model predicts the necking strains with less than 9% error. Also, it has been concluded that with doubling of core thickness in constant and variable total thickness, the average formability improves 15 and 23%, respectively, and with tripling core thickness, these values reach to 26 and 53%. In addition, with twofold increase of skin thickness in constant core thickness, the average formability enhances up to 76%. [ABSTRACT FROM AUTHOR]

Working properties during production, structure, and physicomechanical properties of alloy 1441 sheets of the system Al-Cu-Mg-Li are described, making it possible to prepare thin sheets up to 0.3 mm thick by a coiled cold rolling method. Medium-strength (σ = 450 MPa) alloy 1441 sheet is distinguished by lower density (2.6 g/cm), increased stiffness (E = 79 GPa), and it is used effectively in promising layered aluminum-polymer materials of the FML class for aviation structures. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced polymer composites (GFRP) were prepared and reinforced with two types of multiwalled carbon nanotubes, i.e., amino-functionalized (ACNT) and pristine nanotubes (PCNT). Incorporation of ACNT leads to a significant decrease in equilibrium water content and diffusion coefficient vis-à-vis GFRP composites when immersed in seawater (SW) and distilled water (DW). The experimental results illustrate that the material degradation of the composites is significantly more on immersion in SW as compared to DW. Interestingly, a decrease in mechanical properties was observed initially; however, at a later stage the trend reversed and a recovery in the mechanical properties was seen. This recovery in mechanical properties is ascribed to the possible secondary crosslinking network between excess sodium ions in seawater with the hydroxyl groups of cured epoxy and also to the unreacted silanols on the glass fiber surface. On the contrary, PCNT composites revealed a continuous decreasing trend in mechanical behavior versus aging duration. The present study suggests that it may be advantageous and safer to re-condition (for 15-20 days) FRP nanocomposite parts before being installed in naval vessels. [ABSTRACT FROM AUTHOR]

Non-laminate composites find their paramountcy in large structures, ballistic applications, etc. However, literature about the hole making process in thick composites, non-laminate composites and that under different cooling methods (dry, external and internal) is scarce. Hence the present study examines how the different methods of cooling influence the quality characteristics (drill flank temperature and damage factor) during drilling 20 mm thick Glass Fibre Reinforced Epoxy (GFRE) pultruded composite rods having 80% fibre weight fraction and 0° fibre orientations with reverence to the feed direction. Response Surface Methodology (RSM) was used to design the drilling experiments and the latter was executed utilizing 10 mm diameter twist drills made of cemented carbide. Response surface models utilizing Design-Expert software were developed, which empirically relates the process parameters with the obtained experimental values of quality characteristics. The effects caused by process parameters on quality characteristics were analyzed by utilizing response surface graphs. The process parameters (spindle speed, feed per revolution and coolant pressure) have been optimized within the selected range. The optimal parameter levels are attested by validation test. The contribution of this investigation is to make understand that the use of twist drill with internal cooling is critical to get damage tolerance holes. [ABSTRACT FROM AUTHOR]

Non-laminated composites find application in construction of bridges, ballistic applications, etc. However, literature on the drilling of non-laminated composite materials and literature on the drilling of thick composite materials under different cooling methods (dry, external and internal) is scarce. Hence the present study is aimed to investigate the influence of different cooling methods on quality characteristics (drill temperature and damage factor) while drilling glass fibre reinforced epoxy (GFRE) non-laminated 20 mm thick pultruded composite rods having 80% fibre weight fraction and 0° fibre orientations with respect to the drill. The drilling experiments using TiN/TiAlN coated tungsten carbide twist drills of diameter 10 mm were conducted using response surface methodology (RSM). The experimental values obtained for quality characteristics are empirically related to process parameters by developing a response surface model using Design-Expert software. The effects of process parameters on quality characteristics were analysed by using response surface graphs. The process parameters (feed, spindle speed and coolant pressure) are also optimized within the selected range. The optimal parameter levels are confirmed by validation test. From this investigation, it is evident that the internal cooling method is significant for obtaining high hole quality. [ABSTRACT FROM AUTHOR]

The fiber-metal composites made of aluminum sheets and glass fibers reinforced with a polyester resin as the matrix were studied. The composites were prepared by hand lay-up method. Some aspects of manufacturing affecting the composite behavior were considered. In particular, the influences of the arrangement of layers and their number on the mechanical and physical properties of composites with ten different compositions were investigated. In addition two different densities of glass fibers were considered. The tensile modulus, tensile and impact strengths were determined following ASTM D3039 and ASTM D6110 standards. The results obtained show that the arrangement of the laminate layers influences Young's modulus and the tensile strength of the composite. The impact test results of the laminated structure reinforced with glass fibers illustrate a significant increase in the impact strength owing to adding the glass fibers compared to the control specimens. The simulations of tests using ABAQUS-based FEA were performed. [ABSTRACT FROM AUTHOR]

Residual strength and damage characterization of glass fiber, basalt fiber and its hybrid reinforced in epoxy laminates were studied under compression after impact loading. It involves the exploitation of certain characteristics of basalt fiber, in order to ascertain basalt as a suitable alternative to glass fiber. Basalt fiber, extracted from basalt stone, is economically feasible over conventional fibers such as glass or carbon and has relative advantages, both physically and chemically. Low-velocity impact tests under impact energy of 2.17 J and compression test were conducted on each set of laminates, and along with that, the non-impacted specimens were also compared. The results obtained from compression after impact test revealed that glass laminate possessed the highest resistance to impact damage, and this particular hybrid configuration did not prove superior over plain glass or basalt in both impact and compression tests. Therefore, for compression after impact scenarios, basalt does not serve as a viable alternative for glass fiber, especially in this hybrid configuration. [ABSTRACT FROM AUTHOR]

Since their initial development, fibre metal laminates (FMLs) have slowly started to be used by industry, particularly the aerospace sector. One of the reasons for the relatively slow adoption of FMLs is due to the difficulties faced in shaping them to the desired geometry. Whilst traditional processes such as roll forming are effective in shaping monolithic materials, these processes could potentially destroy the mechanical properties of the composite layer. The approached investigated here uses thermal or laser forming (LF) to shape flat panels of thermosetting glass fibre based FMLs into 2D geometries. This initial empirical investigation covers the effectiveness of the various LF processes and the effects of various parameters have on the forming process. These include laser parameters such as power and velocity and material parameters such as FML lay-up strategy, fibre orientation and comparison with monolithic materials. [ABSTRACT FROM AUTHOR]

We describe the effect of the stacking sequence on the distribution of the deformation and stress fields through the thickness of the laminate. The laminates are made of epoxy resin and glass fibres, having the ratio of 0 to 90° plies equal to 1. This stacking sequence is applied to obtain composite laminates with different thicknesses. The study presented in this paper is focused on the linear static behavior of the cross-ply laminates by means of finite-element models developed using the commercial codes ANSYS 6.1 and LUSAS 15.3. The numerical models represent three-point bending loading cases. A viscoelastic analysis of the laminates based on the correspondence principle is also performed. The results from the finite-element models show good agreement with those obtained using the classical laminate theory, while the viscoelastic storage modulus and loss factors’ distribution indicate the optimal stacking sequences for structural dynamics applications, such as spring leaves for novel car suspension systems. [ABSTRACT FROM AUTHOR]

Fiber metal laminates are an advanced hybrid materials system being evaluated as a damage tolerance and light weight solution for future aircraft primary structures. This paper investigates the impact properties and damage tolerance of glass fiber reinforced aluminum laminates with cross-ply glass prepreg layers. A systematic low velocity impact testing program based on instrumented drop weight was conducted, and the characteristic impact energies, the damage area, and the permanent deflection of laminates are used to evaluate the impact performance and damage resistance. The post-impact residual tensile strength under various damage states ranging from the plastic dent, barely visible impact damage (BVID), clearly visible impact damage (CVID) up to the complete perforation was also measured and compared. Additionally, the post-impact fatigue behavior with different damage states was also explored. The results showed that both GLARE 4 and GLARE 5 laminates have better impact properties than those of 2024-T3 monolithic aluminum alloy. GLARE laminates had a longer service life than aluminum under fatigue loading after impact, and they did not show a sudden and catastrophic failure after the fatigue crack was initiated. The damage initiation, damage progression and failure modes under impact and fatigue loading were characterized and identified with microscopy, X-ray radiography, and by deply technique. [ABSTRACT FROM AUTHOR]

Measurements have been carried out on the in-plane and through the thickness thermal expansion coefficients of glass polypropylene fibre composites of 50% volume fraction between room temperature and 120°C. Only in the temperature range 20° to 75°C are reproducible results obtained. It is confirmed that in-plane negative values may be obtained in specific directions. The physical reason for this and its connection with the necessary appearance of a large Poisson ratio is pointed out. The expansivity of the matrix material depends strongly on temperature. Very good agreement between the experimental values and those predicted from the properties of the two constituents is found provided that the value for the expansivity of the polyoropylene is that within the temperature range considered. It is shown that the polypropylene matrix does not provide a matrix which is stable enough in its properties to enable the system to yield consistent negative values of expansivity. An alternative system is proposed and a single experiment confirms that a negative value of the thermal expansivity of as large as -50 × 10-6 K-1 may be obtained. [ABSTRACT FROM AUTHOR]

Degradation of polymer composites is a significant problem in many engineering aspects. Due to the interaction of various degradation factors during the exploitation of composites, a synergistic effect of destruction is observed. The article describes the phenomena occurring in glass fiber reinforced polyester laminates under the influence of ultraviolet radiation (UV) in an aquatic environment. The laminates were exposed to UV-A, UV-B and UV-C radiation for 1000 h in free-air and underwater conditions. During the test, the materials were immersed at stable depth of 1 mm and 10 mm, respectively. The three-point bending tests performed on the samples after being exposed to UV showed an increase in the flexural strength of the composites. Simultaneously, degradation of the outer surface layer was observed. The degradation removed the thin resin film from the surface which resulted in a direct exposure of the reinforcing fibers to the environment. The transformations taking place in the deeper layers of the composite increased the mechanical strength due to the additional cross-linking reactions excited by the energy arising from the radiation. Moreover, the formation of polymer structures from free styrene remaining after the technological process and the occurrence of free radical reactions as a result of the cage effect was also observed. [ABSTRACT FROM AUTHOR]

The reduction of weight elements is considered as a major objective of several manufacturing companies. This objective will help in growing application sections of the used fiber composites for important structural elements. Modern fiber metal laminate (FML) having lightweight properties is established to be used instead of other substances in different applications including those related to the aerospace industrial sector. Fiber metal laminate is being deemed as an alternative significant substance that is being extensively explored due to its operation, unlike other current materials. There are different profitable FML such as GLARE (glass-reinforced aluminum laminate), established on elevated intensity ARALL glass fibers (aramid-reinforced aluminum laminate), built on fibers of aramid, in addition to CARALL (carbon-reinforced aluminum laminate), centered on fibers of carbon. This paper analyzes important information that contributes to the mechanical characteristics of FMLs under tensile, flexure, impact, etc. conditions. [ABSTRACT FROM AUTHOR]

The nominal strength of structures made of quasibrittle materials shows a noticeable decrease or increase in brittleness with respect to the increase in structure dimension; this is the well-known size effect on strength. The present study aims to analyze and experimentally validate the size effect on laminate composite glass fibers using cohesive laws. This work not only correlates the nominal strength with the size of the failure processing zone but also relates the size of the failure processing zone at failure load to the specimen dimension and geometry. Our study provides a useful tool that enables engineers to obtain a set of design charts that relate the nominal strength of the structure to the size and shape of the specimen. Moreover, it aims to apply a new method to study the effect of structure size on the tensile strength of fiber polymer composite. The results of nominal strength are validated using a matrix of experimental work, and they agree very well with the experimental data. The other fracture properties are compared using an extended finite element method. The output of the analysis is a valuable graph that gives the nominal strength of the open-hole specimen. [ABSTRACT FROM AUTHOR]

Woven composites can offer mechanical improvements over more traditional engineering materials, yet understanding the complex interplay between the fiber-matrix architecture during loading remains a challenge. This paper investigates the evolution of shear failure behavior during the compression of high performance fiberglass composites with varying resin binders at both quasi-static and dynamic strain rates. All samples are comprised of commercially available woven glass cloth with approximately 56 % fiber volume fraction. Laminates with thermosetting resin binders of silicone, melamine, and epoxy were examined. High-speed imaging reveals that failure occurs within a localized shear band region through multiple fiber-weave matrix interface failure with a characteristic macroscopic angle. The shear evolution was spatially mapped using grayscale histograms of the light intensity in the shear regions, and the resulting characteristic angles were measured and analyzed in the context of a Mohr-Coulomb failure criterion. Optical microscopy and high-speed imaging of the shear formation shows initiation appears due to local instabilities from kinking and microbuckling, influenced by the stacking and interlacing regions of tows. [ABSTRACT FROM AUTHOR]

The low-velocity impact behavior of thick and thin unidirectional E-glass fiber-reinforced laminated composite plates with three different stacking sequences subjected to three different impact energies have been investigated. The test specimens were produced by the Vacuum Assisted Resin Injection (VARI) method in a laboratory environment. The thick specimens contained 50 layers of unidirectional E-glass fibers and the thin ones — 16 layers of unidirectional E-glass fibers. The low-velocity impact tests were carried out using a CEAST Fractovis drop-weight impact test device. The contact force–time and energy–time graphics were plotted and the experimental results were interpreted in detail. [ABSTRACT FROM AUTHOR]

The structure, composition and set of properties of specimens and components, and some parameters of the process of production of a promising FML class of metallic polymers based on sheets of high-modulus ( E ~ 79 GPa) alloy 1441 with reduced density ( d ~2.6 g/cm) and an optimized glued prepreg reinforced with fibers of high-strength high-modulus VMPglass are described. Results of fire and fatigue tests of a promising 1441-SIAL structural laminate are presented. [ABSTRACT FROM AUTHOR]

This study presents the tensile properties and cost-property efficiency analyses of a novel composite material type composed of expanded polystyrene as filler, chopped glass fibers as reinforcement agent and epoxy resin as matrix material. Composite specimens were fabricated via expanded polystyrene beads with two different densities, two different length of chopped glass fibers and three levels of fiber/filler weight ratios. Specimens were subjected to tensile tests and cost property analyses were carried out. Experimental studies revealed that novel composite specimens had significantly low density and high specific modulus. Cost-property efficiency analyses revealed that the novel composite is relatively highly efficient material and could be utilized instead of its more expensive counterparts such as conventional plastics or laminated composites especially for non-load bearing applications. [ABSTRACT FROM AUTHOR]

Fatigue life of GFRP (glass-fiber reinforced plastic) composites used in wind turbine rotor blades has been evaluated considering the glass fiber orientations. Three different laminate composites with the respective laminating orientation of 0°, ±45°, and 0°±45° were prepared using vacuum infusion method. Tensile properties and S-N curves for these composites were experimentally determined at room temperature. From the tensile tests, it was found that tensile properties were greatly dependent upon the fiber orientation and the tensile strength of unidirectional composite was the largest and bidirectional (45°) composite was the weakest among three composites. The fatigue properties were determined under constant amplitude load control at different stress ratios, R, of 0.5, 0.1 and −0.2. The properties also show the dependency of stress ratios and fiber orientation. The fatigue life diagrams of these three composite were relatively well presented with the double logarithmic S-N curve. The linear slopes of the respective S-N curves for three composite were not greatly different. The fatigue limits for the composites were evaluated and predicted with linear Goodman and Gerber diagrams. [ABSTRACT FROM AUTHOR]

An analysis of the mechanical and acoustic responses of a laminate composed of 12 layers of glass fiber fabric/epoxy resin and conditioned in environments with relative humidities of 0, 60, and 96% RH at 60°C is presented. The first part of the study consists in following the weight gain according to the duration of hygrothermal conditioning, and the second part—in test ing 45°-oriented specimens in uniaxial tension up to failure at constant imposed displacement rates, with registrating the acoustic emission to track the damage process. The influence of moisture content in the material showed up as a significant decrease in its shear modulus, shear stress, and acoustic emission with growing quantity of absorbed water. An exponential function is proposed for describing the relationship between the varying shear modulus and the shear strain. [ABSTRACT FROM AUTHOR]

The use of plants fibre reinforced composites has continuously increased during recent years. Their low density, higher environmental friendliness, and reduced cost proved particularly attractive for low-tech applications e.g., in building, automotive and leisure time industry. However, a major limitation to the use of these materials in structural components is unsatisfactory impact performance. An intermediate approach, the production of glass/plant fibre hybrid laminates, has also been explored, trying to obtain materials with sufficient impact properties, whilst retaining a reduced cost and a substantial environmental gain. A survey is given on some aspects, crucial for the use of glass/plant fibre hybrid laminates in structural components: performance of hybrids when subjected to impact testing; the effect of laminate configuration, manufacturing procedure and fibre treatment on impact properties of the composite. Finally, indications are provided for a suitable selection of plant fibres with minimal extraction damage and sufficient toughness, for introduction in an impact-resistant glass/plant fibre hybrid laminate. [ABSTRACT FROM AUTHOR]

Three different fiber-reinforced composite test laminates were laid up using carbon-, glass-, and Kevlar-reinforced epoxy prepregs, and then four different hydrophobic barrier films were placed as the out-of-most ply (last ply) on top of the test laminates. The prepared samples were co-cured through an autoclave per recommended cure cycles. These hydrophobic barrier films included polyether ether ketone or PEEK (12.7- and 25.4-μm thicknesses), polytetrafluoroethylene or Teflon (25.4 μm), and polyvinyl fluoride (PVF) or Tedlar (25.4 μm). Tedlar films have been the only source used for moisture prevention in Aerospace composites, so the purpose of the present study was to determine other alternatives and their moisture ingression prevention characteristics. The tape adhesion tests conducted on the barrier films of the composite panels indicated that PEEK and Tedlar films were well bonded on the composite surfaces, while Teflon films failed the tape adhesion tests. The laminate composites that were co-bonded with barrier films were immersed in water up to 29 days, and then 3-point bend tests were conducted on each sample before and after immersion. Test results show that 25.4-μm thick PEEK and Tedlar films on the carbon, glass, and Kevlar laminate composites provided similar mechanical properties. Also, the laminates incorporated with barrier films exhibited significantly higher mechanical properties when compared to the same laminates without any barrier films. This study indicated that these barrier films considerably reduced moisture ingression into the laminate composite structures, which may be useful for applications in composite aircraft and wind turbines. [ABSTRACT FROM AUTHOR]

An evaluation of the interlaminar fracture toughness of polyamide/glass fiber laminates with various layups is reported. Due to large differences in thermal expansion coefficients of fiber and binder the laminates with layups where single layers are swapped exhibit high warping. A technique for avoiding this is proposed, allowing evaluating interlaminar fracture toughness of various angle interfaces. Two different layups for evaluating the Mode I and II interlaminar fracture toughness are tested. The differences of delamination behavior of a number of different-angle fiber interfaces are shown and analyzed. The applicability of the proposed testing technique is discussed. [ABSTRACT FROM AUTHOR]

In this research, the curvature of three-phase unsymmetrical composite laminates was determined based on the Rayleigh–Ritz energy method. Three-phase composite laminate consists of glass fiber, epoxy resin and multi-walled carbon nanotubes (MWCNTs). Micromechanical models including Halpin–Tsai, modified Schapery, bridging and Schapery models have been employed to determine mechanical and thermal properties of nanocomposite plates. The influence of the thickness, curing temperature and weight fraction of MWCNTs were studied analytically. Then, some cross-ply composite specimens were fabricated and the analytical results were certified by experimental ones. Additionally, the results were compared with the Hyer model. It was observed that the proposed model can predict the curvature behavior better than the Hyer model. Study of the effects of mentioned parameters on the curvature of the cross-ply laminates revealed that addition of MWCNTs leads to increase in the elastic modulus and decrease in the CTE. So, the curvature of unsymmetrical cross-ply laminates decreases by addition of appropriate amount of nanoparticles. [ABSTRACT FROM AUTHOR]

A technique of numerical analysis of the influence of reinforcement structure on the nature of the dynamic response and the process of layer-by-layer destruction of layered fiberglass cylindrical shells under an axisymmetric internal explosive loading is elaborated. The kinematic model of deformation of the laminate package is based on a nonclassical theory of shells. The geometric dependences are based on simple quadratic relations of the nonlinear theory of elasticity. The relationship between the stress and strain tensors are established by using Hooke's law for orthotropic bodies with account of degradation of stiffness characteristics of the multilayer composite due to the local destruction of some its elementary layers. An energetically consistent system of dynamic equations for composite cylindrical shells is obtained by minimizing the functional of total energy of the shell as a three-dimensional body. The numerical method for solving the formulated initial boundary-value problem is based on an explicit variational-difference scheme. Results confirming the reliability of the method used to analyze the influence of reinforcement structure on the character of destruction and the bearing capacity of pulse-loaded cylindrical shells are presented. [ABSTRACT FROM AUTHOR]

The development of autonomous finishing operations in manufacturing process has the potential to decrease the costs and increase the quality of the operations. In this context, robotic manipulators have been introduced in sanding and polishing applications. Inspired by the recent development in machine learning and robotics, this paper is focused on designing a system capable of estimating the surface roughness using only a force torque sensor integrated with a robotic manipulator that performs the sanding of fiberglass panels. We present an investigation into the usage of convolution neural networks on the force-torque data to produce a quantitative estimation of surface roughness. To validate the results obtained a profilometer is used to gather pre- and post-operation data. The establishment of a relationship between measured force data and post-operation surface roughness will be used to develop a prediction of the surface quality for sanding operation using robotic manipulators. This project intents to act as proof-of-concept that traditional robotic sensors, can be used beyond their original scope, minimize the complexity of robotic systems integrated into manufacturing processes. [ABSTRACT FROM AUTHOR]

Fiber metal laminates (FMLs) are one of the most applicable composite sheets that consist of metal layers and fiber-reinforced polymers. These layers are jointed to each other with epoxy or polyurethane resins. In the present study, the experimental and numerical investigations of springback in hat-shaped channel bending have been performed. At first, FMLs were produced with aluminum 2024-T3 sheets, unidirectional E-glass fibers and polyurethane resin by using a hot press with the capability of adjusting both the squeezing pressure and temperature. The specimens were produced according to the lay-up in 0° and 90° directions of metal sheets and fiber-reinforced core, then the hat-shaped channel bending was performed. Furthermore, the effect of parameters such as FML lay-up, channel depth, and core thickness on the springback angle in the flange and wall zones was studied. In the numerical section, the parameters such as plastic equivalent strain in metallic layers as well as the springback of FML with different lay-ups were investigated. The results showed that in asymmetric lay-ups where the fiber was in the longitudinal direction, the replacement of lower and upper sheets affected the springback significantly; however, where the fiber is in the transverse direction, the springback was unaffected by the same replacement. Also, due to the low elastic modulus of composite core versus metal skin, the core thickness had little effect on springback. The comparison between numerical and experimental observations showed a desirable agreement of FML geometry after unloading. [ABSTRACT FROM AUTHOR]

The mechanisms of in-plane shear deformation in a cross-ply glass fiber-epoxy laminate were studied through a combination of experiments and simulations. Shear deformation parallel and perpendicular to the fibers led to very different deformation and fracture patterns. Deformation was localized in a matrix shear band parallel to the fibers in the former, while fiber rotation and widespread plastic deformation in the matrix were dominant in the latter. The differences in the mechanical response between both orientations increased with the applied strain and it was shown that the cross-ply laminate response was given by the averaged contribution of both. The relevance of this behavior for the development of continuum damage mechanics models is noted. [ABSTRACT FROM AUTHOR]

To celebrate the 40th anniversary of our journal I would like to pen an account of the state, as I see it, of Fibre Composite Materials. My personal involvement in this field started in the very early 1960s. And I remember being asked to join the Honorary Advisory Board of a journal to be entitled Journal of Materials Science, a few years after that, namely in 1965/66. I thought it a very good idea of Robert Cahn at the time and have been pleased to remain associated with the journal ever since. Since those days the field of composite science has expanded enormously and lately with Carl Zweben I edited, as General Editor, a six volume work on the science and technology of composites entitled Comprehensive Composite Materials. In what follows I have set down a summary of the field of composites engendered by my editing of that comprehensive work adding some history of how the field arose and including some pointers to the future. [ABSTRACT FROM AUTHOR]

Fiber-reinforced composites have a wide range of industrial applications owing to their light weight, high modulus, and good specific strength. Trimming using a mechanical punching tool is the fastest way to post process fiber-reinforced composites. However, quantitative analyses of the defects and process parameters are required to analyze the damage mechanisms and achieve high-quality cut surfaces. In this study, we quantitively investigated the defects on the sheared edge of woven glass epoxy laminates subjected to mechanical punching and explored the correlations between these defects and key process parameters, including punch-die clearance, weave alignment angle, and laminate thickness. The results demonstrate the necessity of considering glass fiber burr length and the dimensions of the cracked area simultaneously to evaluate the quality of the sheared surface. This study provides qualitative data on the interfacial damage mechanisms that occur during mechanical punching, which will help to tailor the process parameters of mechanical punching for fiber-reinforced polymers to obtain smooth cut surfaces. [ABSTRACT FROM AUTHOR]

Fiber-metal laminates (FMLs) composed of metal lamina and reinforcing fibers exhibit an improved crack growth resistance as compared to conventional aircraft materials. The crack resistance of a hybrid FML composite consisting of LY12M aluminum alloy lamina and prepreg layers of HS2 glass fibers and T700 carbon fibers has been experimentally investigated on tensile specimens at stress ratios R = - 1, 0.1, and 0.5. The crack growth rate data at positive stress ratios demonstrate a significant scatter and a large difference between specimen's back and front surfaces formed by 1-mm thick outer aluminum layers. This violation of the test standard requirements for metal materials in the performed FML tests presents a problem of determining a proper failure criterion for the engineering applications of FMLs. Based on the comparative analysis of FML crack resistance results obtained, some qualitative conclusions are drawn on solving this problem. [ABSTRACT FROM AUTHOR]

The delamination produced during drilling CFRP will affect its structural strength seriously. Delamination is closely related to the thrust force during drilling, which is closely related to the tool, so it is particularly important to choose the tools with appropriate geometric structure. Many scholars used tools with different geometric structure to drill CFRP, and then conducted the drilling damage analyses and drilling mechanism researches. It finally came to a conclusion that a drill with a special structure had certain advantages compared with a common twist drill in the drilling process. A new type of plane rake–faced twist drill was used to drill the CFRP laminate with a thin-woven glass fiber surface layer. Experimental results showed that the plane rake–faced twist drill along cutting edge had a constant reference rake angle value, which caused the plane rake–faced twist drill generated smaller thrust force and less drilling damage than the common twist drill. As the reference rake angle of the plane rake–faced twist drill increased, the thrust force and drilling damage decreased. It was revealed the inhibition of the thin-woven glass fiber surface layer on the drilling damage at entrance and exit. Finally, it was proposed that when the plane rake–faced twist drill was used to drill CFRP laminate with a thin-woven glass fiber surface, 46° reference rake angle should be selected. [ABSTRACT FROM AUTHOR]

In this paper, the influence of E-glass fiber volume fraction and laying angle on the damping and strength of composite laminates was comprehensively analyzed. By increasing the fiber laying angle and reducing the glass fiber volume fraction, the damping capacity of the composite laminate was increased, but the tensile strength of the laminate was reduced; By reducing the fiber laying angle and increasing the glass fiber volume fraction, the tensile strength of the composite laminate was increased, but the damping characteristics of the laminate was reduced. In addition, in the damping experiment of composite laminates, in order to avoid the influence of external damping sources, the vacuum non-contact damping test method was adopted in this paper, and the influence of air damping on the damping experiment results of composite laminates was comparatively analyzed. The results of comparative experiments showed that air damping had a very obvious influence on the damping of composite laminates, especially when the damping of composite laminates was small, the influence of air damping would be greater. [ABSTRACT FROM AUTHOR]

The ability to predict the structural response of composites offers a significant advantage to design engineers and provides the possibility of identifying structurally efficient composite assemblies. Various analytical and numerical models are possible, but care has to be taken to ensure that the appropriate structural performance and failure criteria are used. In particular, modeling the progressive failure of composite laminas requires robust and validated failure algorithms that are not only computationally efficient, but are also able to predict the load-deformation characteristics and to ultimately establish the failure load appropriately. This study looks into different progressive failure macromechanical algorithms applied to e-glass-fiber-reinforced composite plates subject to out-of-plane bending. The influence of different boundary conditions of the plates, ranging from fully clamped to simply supported ones, on their ultimate failure load is also investigated. The results are validated by experimental data found in the literature and show that boundary conditions have a significant influence on the predicted ultimate failure load. The study also shows that, in this case, the predominant failure mechanism is the failure of matrix, and after the redistribution of stresses, no consecutive failure due to fiber or fiber-matrix failure occurs in the lamina, therefore a sudden-degradation progressive ply failure algorithm based on the failure mode is sufficient to model the structural performance of composite plates subject to out-of-plane bending. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effects of seawater on the failure mode, first failure load and bearing strength behaviour of the pinned joint of fibreglass-reinforced woven epoxy composite prepregs. The specimens were kept in seawater for 3- and 6-month periods. After each period, their mechanical properties were examined. The edge distance-to-upper hole diameter (E/D), the two hole-tohole centre diameter (K/D), the distance from the upper or the lower edge of the specimen to the centre of the hole-to-hole diameter (M/D), and the width of the specimen-to-hole diameter (W/D) ratios were selected as parameters. Moreover, the finite element models of the specimens were developed using ANSYS software, and the Tsai-Wu criterion was used to obtain the first failure load. The numerical and experimental results were compared and were found to be in good agreement for the first failure load. [ABSTRACT FROM AUTHOR]

Cold expansion has proven to be an effective technique for extending the fatigue life of monolithic materials. Although fiber metal laminate materials show improved fatigue performance compared to their monolithic counterparts, the nucleation and growth of small cracks tends to occur early on in the fatigue life of the material, making acceptance of fiber metal laminates in aerospace more difficult. This work examined whether cold expansion could delay this process in fiber metal laminates and increase the fatigue life of these materials at the same time. The results showed that significant differences existed in the residual strain field between the mandrel exit and entry faces resulting in slower fatigue crack growth on the exit face, which also had higher residual strains in the region surrounding the cold expanded hole. Overall, cold expansion is effective at increasing the fatigue life of fiber metal laminate materials, but is less effective at delaying nucleation and growth of small cracks on the entry face. [ABSTRACT FROM AUTHOR]

In the present paper 3D rate sensitive constitutive model for modeling of laminate composites is presented. The model is formulated within the framework of continuum mechanics based on the principles of irreversible thermodynamics. The matrix (polyester resin) is modeled by employing a 3D rate sensitive microplane model. For modeling of fibers (glass) a uni-axial constitutive law is used. The fibers are assumed to be uniformly smeared-out over the matrix. The formulation is based on the assumption of strain compatibility between matrix and fibers. Total stress tensor is additively decomposed into the contribution of matrix and fibers, respectively. To model de-lamination of fibers, the matrix is represented by periodically distributed initial imperfection over the pre-defined bands, which are parallel to fibers. Physically, this assumption accounts for the matrix-fiber interface in a smeared way. The input parameters of the model are defined by the mechanical properties of matrix and fibers (elastic properties, strength and fracture energy), the volume fraction of fibers and by their spatial orientation. The model is implemented into a 3D finite element code. To assure mesh objective results crack band method is employed. The model is first calibrated using a few basic test results. Subsequently, the model is validated with several numerical examples for specimens loaded in uni-axial tension, uni-axial compression and shear. Comparison between numerical and test results shows that the proposed model is able to predict the resistance and failure mode of complex fiber-reinforced composite for different orientation of fibers and different loading conditions with sufficient accuracy. Finally, based on the qualitative type of the finite element analysis, it is demonstrated that the strain rate dependency becomes more important when the angle between the fiber and load direction increases. [ABSTRACT FROM AUTHOR]

The interest in fibre-reinforced polymer composites is growing rapidly due to its high performance in terms of mechanical properties, significant processing advantages, excellent chemical resistance, low cost, and low density. The development of composite materials based on the reinforcement of two or more fibre types in a matrix leads to the production of hybrid composites. In the present work, woven coir-glass hybrid polyester composites were developed and their mechanical properties were evaluated for different stacking sequences. Scanning electron micrographs of fractured surfaces were used for a qualitative evaluation of interfacial properties of woven coir-glass hybrid polyester composites. These results indicated that coir-glass hybrid composites offered the merits of both natural and synthetic fibres. [ABSTRACT FROM AUTHOR]