Thin Glass Fiber Research Articles

Damage Assessment of Low-Velocity Impacted Sandwich Composite Structures Using X-Ray Micro-Computed Tomography

Sandwich composite structures offer significant versatility in structural system design but are susceptible to low-velocity impact damage, impacting their structural robustness. This study focused on nondestructive testing, particularly using X-ray micro-computed tomography, to assess damage on these structures, comprised of thin glass fibre reinforced polymer face sheets and a polyvinyl chloride foam core, under low-velocity impacts. Impacts were induced by a constant mass of 5.61 kg, dropped from various heights, generating impact energies between 2 and 22 J. This resulted in varied damage levels, from indentations to full perforations. The X-ray micro-computed tomography technique was chosen for its ability to detect internal damage. However, the system’s efficacy in accurately assessing damage depends on numerous factors like focus-to-detector distance, focus-to-object distance, and spatial resolution of the detector, among others. The system yielded an approximated resolution range of 10–25 μm for a focal spot size of 4 μm and the resolution range of 11–26 μm for a spot size of 7 μm. To this end, the system was able to reveal damage inflicted across the specimen through captured and reconstructed images. The quality of the reconstructed images was validated using ImageJ2 software by comparing with the processed images. The median filter was found to deliver images that closely resembled the original ones, albeit with a slight reduction in quality. Damage types varied based on impact energies. Low-level impacts caused matrix cracking and delamination at the foam interface. Medium-level impacts led to intralaminar and interlaminar damage, fibre fractures, and significant damage to the foam core through shearing and crushing. High-level impacts resulted in near or full perforations, with more pronounced delamination at the bottom interface, and fibre fractures in the impact zone, displaying a distinctive diamond-like damage pattern. These findings can be instrumental in developing a predictive impact damage model.

Analysis of surface roughness, temperature, short aging, and residual notched and bearing strengths in supported drilling of thin GFRP composites

This study aimed to analysis open‐hole tensile strength, pin-bearing strength, cutting temperature, and surface roughness of drilled thin glass fiber reinforced polymer composites. The specimens were clamped from both sides during drilling operations. The cutting temperature was measured using high resolution infrared camera. Surface roughness was evaluated by seven parameters to identify the most suitable ones. Multiple regression models were developed to predict critical thrust force (CTF), critical feed, and cutting temperature in drilling operations. The measurements indicate that the cutting temperature is higher than the matrix's glass transition temperature and hence, the surface roughness paramaters Ra, Rq and Ry are increased at the maximum cutting conditions by 57%, 51%, and 36% respectively. In contrast, the bearing strength improved by 13%. This peculiar phenomenon was deeply analyzed with the aid of short ageing effects on the post curing, which increase the crosslinking density within the composites and improve the matrix's capacity to efficiently transmit the loads to the reinforcing fibers. For the first time, the optimum cutting conditions were determined based on the optimum short ageing parameters (temperature and time). Supported drilling increases CTF by 23%, which can reduce machining time and manufacturing costs with fewer delamination concerns.

In-Bulk Temperature Profile Mapping Using Fiber Bragg Grating in Fluids.

The capabilities of Fiber Bragg Grating (FBG) sensors to measure temperature variations in the bulk of liquid flows were considered. In the first step of our research project, reported in this paper, we investigated to what extent the use of thin glass fibers without encapsulation, which only minimally disturb a flow, can fulfill the requirements for robustness and measurement accuracy. Experimental tests were performed in a benchmark setup containing 24 FBG measuring positions, which were instrumented in parallel with thermocouples for validation. We suggest a special assembly procedure in which the fiber is placed under a defined tension to improve its stiffness and immobility for certain flow conditions. This approach uses a single FBG sensor as a reference that measures the strain effect in real time, allowing accurate relative temperature measurements to be made at the other FBG sensor points, taking into account an appropriate correction term. Absolute temperature readings can be obtained by installing another well-calibrated, strain-independent thermometer on the reference FBG. We demonstrated this method in two test cases: (i) a temperature gradient with stable density stratification in the liquid metal GaInSn and (ii) the heating of a water column using a local heat source. In these measurements, we succeeded in recording both spatial and temporal changes in the linear temperature distribution along the fiber. We present the corresponding results from the tests and, against this background, we discuss the capabilities and limitations of this measurement technique with respect to the detection of temperature fields in liquid flows.

Flexural and sinking stiffnesses investigation of metal, glass fiber reinforced plastic and hybrid laminates through a semi‐experimental method

AbstractThe hybrid metal/GFRP laminate is a kind of typical hybrid structure consisting of thin metal sheets and glass fiber reinforced plastic laminates, which combines the benefits of low cost, high strength, excellent impact resistance, and good corrosion resistance. In this work, a semi‐experimental method based on a nondestructive test and the analytic solution of the thin plate's deflection for the flexural and sinking stiffnesses identification of hybrid metal/GFRP laminates was proposed and validated by corresponding numerical simulations. Then, in total 17 different specimens (including metal, GFRP and hybrid metal/GFRP) were prepared and tested by the proposed semi‐experimental method to investigate their flexural and sinking stiffness performances in multiple perspectives (including stiffness per unit mass/volume/price/surface density). The analytic solutions show that the flexural and sinking stiffnesses are proportional to macro equivalent moduli of laminate specimens and proportional to the third power of thicknesses of specimens. The test results show that the stiffnesses per unit mass/density of the 7‐ply GFRP laminate can be comparable to those of the variable‐thickness rolled blank (VRB) made of steels, but the stiffnesses per volume/price of the 7‐ply GFRP laminate are only one fifth to one quarter of those of VRB. It is also found that though the hybrid metal/GFRP laminate with the combination sequence of aluminum plate/5‐ply GFRP/aluminum plate has the lowest GFRP layers' volume fraction, but has the best performances of stiffnesses per unit mass/density. Besides, the VRB part can significantly improve the stiffnesses per unit volume of hybrid metal/GFRP laminates.

In situ construction of a stable composite solid electrolyte interphase for dendrite-free Zn batteries

Building a stable solid electrolyte interphase (SEI) has been regarded to be highly effective for mitigating the dendrite growth and parasitic side reactions of Zn anodes. Herein, a robust inorganic composite SEI layer is in situ constructed by introducing an organic cysteine additive to achieve long lifetime Zn metal batteries. The chemisorbed cysteine derivatives are electrochemically reduced to trigger a local alkaline environment for generating a gradient layered zinc hydroxide based multicomponent interphase. Such a unique interphase is of significant advantage as a corrosion inhibitor and Zn2+ modulator to enable reversible plating/stripping chemistry with a reduced desolvation energy barrier. Accordingly, the cells with a thin glass fiber separator (260 μm) deliver a prolonged lifespan beyond 2000 h and enhanced Coulombic efficiency of 99.5% over 450 cycles. This work will rationally elaborate in situ construction of a desirable SEI by implanting reductive additives for dendrite-free Zn anodes.

Preliminary study on defect detection for sandwich composites using Impact-Echo method

The sandwich composites in this study are laminated structures with two outer thin glass fiber reinforced panels and one or more thick lightweight foam panels as the core material. Such sandwich composites are often used in wind turbine blade. The Impact-Echo method using a microphone as a receiver was used to test the sandwich composite panel specimens. The signals were analysed in the frequency domain and normalized by the Rayleigh wave amplitude. Preliminary results show that thicker plates generally have a lower maximum peak frequency (MPF) for specimens without defects, but MPFs are more unstable due to the higher number of layers of the inner foam plate. Internal defects generated by excavating the core material, with lateral dimensions as small as 20 mm, can be identified from lower MPF and higher maximum peak amplitude in the normalized amplitude spectrum.

An experimental study on alkali resistant glass fiber reinforced concrete

Typical concrete has high compressive strength, low tensile strength, low resistance to cracks, and low elasticity. For tensile strength, concrete is strengthened by steel, but the tensile strength of concrete in itself does not improve. Alkaliresistant CEM-FIL glass fiber, a high tensile strength thin glass fiber material, is blended with a concrete mixture at a weight ratio of 0 to 3%. Specimen sample of concrete grade of M20, was developed and cast for post-testing. After seven and twenty-eight days, compression and flexural experiments were performed after the concrete was reinforced. Compared with the control specimen, we found a substantial improvement in compressive and flexural strength in the glass fiber reinforced sections after seven and twenty- eight days. By adding 3.0 percent glass fiber to the concrete, optimum results were achieved. Our analysis proposes reinforcing concrete with glass fiber with the ability to optimize concrete properties.

Research on drilling CFRP laminate with a thin woven glass fiber surface layer using plane rake–faced twist drill

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.

An Inorganic–Organic Hybrid Polymer Cocatalyst for Photoelectrochemical Water Oxidation with Dual Functions of Accelerating Kinetics and Improving Charge Transfer

Oxygen evolution cocatalysts (OECs) play important roles in improving the efficiency of photocatalysts in solar water splitting. Inorganic–organic hybrid polymers (IOHPs), which have good electroly...

Wetting Dynamics of a Lipid Monolayer.

Direct measurement and control of the dynamic wetting properties of a lipid-coated water-air interface over a wide range of surface tension variations have many important applications. However, the wetting dynamics of the interface near its partial-to-complete wetting transition has not been fully understood. Here, we report a systematic study of the wetting dynamics of a lipid-coated water-air interface around a thin glass fiber of diameter 1-5 μm and length 100-300 μm. The glass fiber is glued onto the front end of a rectangular cantilever to form a "long-needle" atomic-force-microscope probe. Three surface modifications are applied to the glass fiber to change its wetting properties from hydrophilic to hydrophobic. A monolayer of phospholipid dipalmitoylphosphatidylcholine (DPPC) is deposited on the water-air interface in a homemade Langmuir-Blodgett trough, and the surface tension γL of the DPPC-coated water-air interface is varied in the range of 2.5 ≲ γL ≲ 72 mN/m. From the measured hysteresis loop of the capillary force for the three coated fiber surfaces with varying γL, we observe a sharp transition from partial to complete wetting when γL is reduced to a critical value (γL)c. The obtained values of (γL)c are 27 ± 1 mN/m for a DPPC-coated fiber surface and 23 ± 1 mN/m for an trichloro(1H,1H,2H,2H-perfluorooctyl) silane (FTS)-coated surface. Below (γL)c, the contact angle θ0 of the liquid interface is found to be zero for both hydrophobic fiber surfaces and the corresponding spreading parameter S becomes positive. For the FTS-coated fiber surface, the height of capillary rise exhibits a jump when γL is reduced to (γL)c, which indicates that a rapidly advancing liquid film is formed on the fiber surface when the partial-to-complete wetting transition takes place. Our experiment thus establishes a quantitative method by which many other liquid interfaces coated with polymers, surfactants, and biomolecules (such as proteins and lipids) may be characterized dynamically.

Mass Transfer in a Layer of Aluminized Glass-Fiber Material in the Treatment of Chrome-Containing Wastewater

It is possible to use column-type devices with the loading of composite material - thin glass fibres partially coated with an aluminium layer (AGFM) to purify low-concentrated wastewater on plating plant containing chromium compounds. The main physical characteristics of this material are given. For the mass transfer research, current-potential curves obtained by reducing the chromium forms Cr(VI) to trivalent on a thin copper yarn placed in a layer of aluminum-removed fiberglass were studied. Dependence of effective mass-transfer coefficient on solution flow rate is obtained. Taking into account the ionic strength of the solution, the diffusion coefficient of the reducing anion Cr(VI) was calculated, which allowed to move to the criterion equations of the form Nu = f (Pr, Re). Coefficients are found in the criteria mass-transfer equation at different degrees of filling of the filter volume with a AGFM material.

About a Membrane with Microfluidic Porous-Wall Channels of Cylindrical Shape for Droplet Formation.

A low-energy emulsification process is hollow-fiber emulsification. In this process, the lumen diameter of the membrane mostly determines the droplet size. To gain smaller droplets, approaches for downsizing the inner diameter of membranes have to be carried out. In this work, we describe a new method for the fabrication of parallel microfluidic porous-wall channels of a homogeneous cylindrical shape with lumen diameters down to 7 μm. Parallel and symmetric porous-wall channels are induced into polyvinylidene fluoride membranes during the casting process. The technique comprises liquid-induced phase separation and phase-separation micromolding using thin glass and carbon fibers as molds and an in-house designed tool to position the fibers. The channel positioning and alignment are verified within this work. We show and investigate the droplet formation in these porous-wall channels via hollow-fiber emulsification. The formed droplets are very small in diameter and size distribution. The droplet formation at varying flow rates and channel diameters is examined in detail. Moreover, an area of sufficient operating conditions is given using Weber and capillary numbers. As a numbering-up approach, we show the simultaneous formation of spherical droplets in two parallel channels. With the proposed membrane fabrication using micromolding, we push the downscaling approach of hollow-fiber emulsification to lower micron ranges of the channel diameter. With these small channels, droplets with a diameter down to 25 μm were produced, which are more attractive for most applications.

Influence of temperature dependent matrix properties on the high-rate impact performance of thin glass fiber reinforced composites

The influence of measurement temperature on the high velocity (>100 m/s) impact performance was investigated for three thermosetting epoxy resin S-2 glass composite systems. These three model resins were chemically similar but have different glass transition temperatures (Tg) and molecular weights between crosslinks (Mc) through the use of different diamine curing agents (Jeffamine® D230, D400, and D2000). Impact performance was quantified by the projectile kinetic energy absorbed (KE50) as calculated from the characteristic ballistic velocity (V50) of the composites during high velocity impact. Among the resin systems, the KE50 remained essentially constant over a broad range of temperatures for each composite set and modestly increased with decreasing Mc. The superficial damage area associated with delamination showed remarkable sigmoidal behavior as a function of the testing temperature relative to the Tg (T-Tg). Damage was high for low T-Tg values (glassy resin) and decreased as the resin traversed its Tg into the rubbery region. These damage area trends were found to depend on the resin Mc, with higher Mc values resulting in lower overall damage area and a lower inflection point temperature. High speed videography of the back surface of the samples showed that lower damage areas correlated with an increased back face deflection, which enabled energy absorption with relatively less delamination. Composite mechanical tests were performed to validate the impact performance and explain the deformation mechanisms observed during impact energy dissipation. Our results illustrate the critical importance of the resin architecture and temperature-dependent viscoelastic behavior on the impact properties of composites for impact-resistance applications.

Quasi-Static Indentation Response of Galvanized Iron Toughened Glass Fiber/Epoxy Laminates

This paper is aimed to study the quasi-static indentation response of fiber metal laminates (FMLs) that are made of various arrangement of galvanized iron (GI) alloy thin sheet, glass fibre and epoxy polymer. Unidirectional and woven types of glass fiber/epoxy pre-impregnated laminates and three different thickness of GI thin sheet, i.e. 0.5, 1.0 and 2.0 mm, were used to produce FML systems using combination of hand layup and hot press methods. The FML systems were coded as UGFRP, UGFML 1/2-2, UGFML 2/3-1, UGFML 4/5-0.5, WGFRP, WGFML 1/2-2, WGFML 2/3-1, WGFML 4/5-0.5 according to their types of glass fibers, thickness of GI and stacking sequence. Quasi-static indentation (QSI) tests were performed according to ASTM D6264 using hemispherical crosshead at 5 mm/min speed rate. It was found that both unidirectional and woven systems of FML 1/2-2 exhibited the highest energy absorption capacity, with enhancement of 28 times and 11 times more than UGFRP and WGFRP composite, respectively. At maximum compression, FML 2/3-1 displayed the highest ultimate load, while FML 1/2-2 displayed the highest displacement for both fiber systems. Damage area inspection revealed severe matrix crack, fiber fracture and delamination upon penetration and perforation.

On the interfacial adhesion of fiber metal laminates using surface modified aluminum 7475 alloy for aviation industries – a study

Aluminum-based hybrid laminates are used extensively during the fabrication process of structural components in aviation industries due to its light weight and mechanical properties. A majority of airframe components are usually fitted with adhesion joints and, hence, surface adhesion has a great deal with surface and subsurface properties. To promote adhesion between substrates, various surface activating techniques could be followed. The main objective of this work is to enhance the interfacial adhesion strength between the thin aluminum alloy (AA 7475) and glass fiber. Experimentation was carried out to monitor the increase in the interfacial adhesion, by investigating the change in surface free energy which is influenced by the effect of surface etching. Aluminum sheets were treated using alkali (NaOH), iron (III) sulfate (Fe2(SO4)3) and potassium dichromate (K2Cr2O7). Etching effects were analyzed using water contact angle (WCA), profilometry, scanning electron microscope (SEM images), X-ray diffractometer (XRD) and Fourier transformed infrared spectroscopy (FTIR-ATR). Tensile strength testing was done to evaluate the interfacial adhesion strength. The outcome of experimentation proves that, iron (III) sulfate treated condition laminates have higher tensile strength and it has also increased the interfacial adhesion.

Retrofitting RC infills by a glass fiber mesh reinforced overlay and steel dowels: experimental and numerical study

Many existing Reinforced Concrete (RC) buildings infilled with masonry panels are vulnerable to seismic actions due to lack of proper seismic detailing. For buildings located in low-moderate seismicity regions, a possible retrofitting option could be a reinforced mortar coating applied on the building facades in order to significantly increase its seismic resistance. The present paper studies thin glass fiber mesh reinforced mortar overlays for strengthening RC weak frames infilled with hollow brick masonry. Attention is devoted to the steel dowel connection between the masonry panel and the RC frame to reduce shear sliding. An experimental evaluation of the effectiveness of this enhanced technique is presented and compared against previous results in which shear sliding significantly limited the structural response. In addition, a finite element model has been developed and calibrated to properly simulate the response of the test specimens.

Compression after Impact Behaviour and Failure Analysis of Nanosilica-Toughened Thin Epoxy/GFRP Composite Laminates.

Nanosilica particles were utilized as secondary reinforcement to enhance the strength of the epoxy resin matrix. Thin glass fibre reinforced polymer (GFRP) composite laminates of 3 ± 0.25 mm were developed with E-Glass mats of 610 GSM and LY556 epoxy resin. Nanosilica fillers were mixed with epoxy resin in the order of 0.25, 0.5, 0.75 and 1 wt% through mechanical stirring followed by an ultrasonication method. Thereafter, the damage was induced on toughened laminates through low-velocity drop weight impact tests and the induced damage was assessed through an image analysis tool. The residual compression strength of the impacted laminates was assessed through compression after impact (CAI) experiments. Laminates with nanosilica as secondary reinforcement exhibited enhanced compression strength, stiffness, and damage suppression. Results of Fourier-transform infrared spectroscopy revealed that physical toughening mechanisms enhanced the strength of the nanoparticle-reinforced composite. Failure analysis of the damaged area through scanning electron microscopy (SEM) evidenced the presence of key toughening mechanisms like damage containment through micro-cracks, enhanced fiber-matrix bonding, and load transfer.

Localized failure analysis of internally pressurized laminated ellipsoidal woven GFRP composite domes: Analytical, numerical, and experimental studies

This paper presented a systematic approach toward localized failure inspection of internally pressurized laminated ellipsoidal woven composite domes. The domes were made of thin glass fiber reinforced polymer (GFRP) woven composite layups [0,0,0], [0,30,0], [0,45,0], and [0,75,0]. The analytical results demonstrated that the circumferential regions near meridian φ=45° in prolate ellipsoidal domes and near meridian φ=90° in oblate ellipsoidal domes sustain the highest deformation under internal pressure. This observation was then confirmed by the numerical and experimental results. In addition, the numerical and experimental results showed localized rather than uniform failure in those regions, irrespective of changes in laminate stacking sequence. It was observed that localized failure occurs since the woven fibers configuration in some areas of woven remains in initial geometry (square shape), while the rests are deformed into the rhombic shape. In other words, by moving along the circumferential direction from the area close to θ=0° to θ=45° and θ=45° to θ=90°, the shape of woven fibers gradually changes from square (strong area) to rhombic (weak area), and rhombic to square, respectively. Thus, to minimize failure pressure, the meridian region vulnerable to failure must initially be identified. Afterwards, the rhombic regions in the circumference corresponding to that meridian must be strengthened.

Large Area Graphene Deposition on Hydrophobic Surfaces, Flexible Textiles, Glass Fibers and 3D Structures

Graphene and its derivatives have many superior electrical, thermal, mechanical, chemical, and structural properties, and promise for many applications. One of the issues for scalable applications is the lack of a simple, reliable method that allows the deposit of a well-ordered monolayer using low-cost graphene flakes onto target substrates with different surface properties. Another issue is the adhesion of the deposited graphene thin film, which has not been well investigated yet. Following our former finding of a double self-assembly (DSA) process for efficient deposition of a monolayer of graphene flakes (MGFs), in this work we demonstrate that the DSA process can be applied even on very challenging samples including highly hydrophobic polytetrafluoroethylene (PTFE), flexible textiles, complex 3D objects, and thin glass fibers. Additionally, we tested adhesion of the graphene flakes on the flat glass substrate by scotch tape peel test of the MGFs. The results show that the graphene flakes adhere quite well on the flat glass substrate and most of the graphene flakes stay on the glass. These findings may trigger many large-scale applications of low-cost graphene feedstocks and other 2D materials.

Automated Production of Large Fibre Metal Laminate Aircraft Structure Parts

Fibre metal laminate (FML, GLARE©) materials, consisting of alternating layers of thin aluminium sheets and glass fibre prepregs, can be used for aircraft structure parts. For optimal structural properties and weight, large aluminium sheet sizes are desirable, making manual handling of the parts difficult. This paper introduces a software toolchain for the automated production of an aircraft body part using cooperating industrial robots. Multiple robots are required due to aluminium sheet of lengths up to 5800 mm and widths up to 1000 mm. No manual robot programming is required; all robot control programs are automatically created from CAD files and can be previewed in a 3D simulation environment. A full-scale demonstrator has been built using this toolchain.