Epoxy Plate Research Articles

Influence of tool parameters on ultrasonic assisted drilling of GFRP composites

Glass fiber reinforced polymer (GFRP) composites are widely used in aviation, aerospace, sports and special vehicles because of their light weight, high wear resistance, good fatigue resistance and low thermal expansion coefficient. However, the anisotropy and low interlaminar strength easily lead to defects such as wire drawing, delamination and tearing during drilling process, which seriously restricts the development of GFRP composites. In this study, the effects of drilling tool material and geometrical parameters on the machining quality of GFRP composites in ultrasonic-assisted drilling are revealed through single-factor experiment. Unidirectional laminated GFRP epoxy plates of 80 × 50 × 5 mm are used in the experiment, and the thrust in the machining process is collected by a dynamometer. An industrial camera is used to record the exit morphology of the hole, and then MATLAB is used for image processing to convert it into a greyscale map. Finally, the size of the delamination factor Fd is obtained according to the equation. The experiment results indicate that using the carbide drilling bit with a diameter of 4 mm and a point angle of 120° is beneficial to reduce the thrust and suppress the machining defects.

Ar/HMDS Plasma Jet as a Tool for Superhydrophobic Coatings on Epoxy Resin

During actual operation, the superhydrophobic surface provides excellent resistance to condensation and icing due to its low wettability. This study used an Ar/HMDS mixture as the working gas and a low-temperature plasma jet induced in an atmospheric pressure environment to create a superhydrophobic coating with a water contact angle of up to 172.6°, utilized a typical epoxy resin plate as the substrate. XPS analysis indicated the presence of a significant number of low surface energy functional groups containing Si and O on the epoxy resin surface. Scanning electron microscope (SEM) revealed the presence of dense microstructure and nanostructure on the surface. The process of plasma jet water-repellent modification of epoxy resin surface was further analyzed from two perspectives: particle collision in the electric field, molecular bond breaking and reorganization reaction of monomer, and grafting reaction of free radicals formed on the surface of epoxy resin by high-energy jet bombardment, combined with XPS test of high-purity discharge products in the jet tube. The results indicate that the epoxy resin surface modified by plasma jets achieves superhydrophobicity. The modification time is extended to 180 s, and the static water contact angle is increased from 72.4° to 172.6°. Dense microparticle and nanoparticle are formed on the surface. For the secondary binary composite rough structure, the percentage of Si and O elements increased to 41.3% and 27.8%, respectively. The Si(CH₃)O_3/2 system contributed the most, accounting for 40.5%.

Anti-interfering method for environmental foreign bodies for the microstrip antenna sensor

As a result of the rapid development of intelligent equipment, the importance of intelligent sensing technology for use in structural health monitoring applications is increasing. Among the emerging intelligent structure monitoring methods, microstrip antenna sensing technology is attracting considerable attention. The working environments for mechanical equipment are often harsh and highly differentiated. Multiple environmental jamming factors, including water, dust, ice, and other foreign bodies, will reduce the parameter monitoring reliability of microstrip antenna sensors. In this paper, an anti-interfering method for these environmental foreign bodies based on antenna cladding technology is presented. First, a multi-physical numerical model is established to study the mechanism by which the environmental foreign bodies affect the resonant frequency of the antenna sensor. The effects of the foreign bodies on the sensor’s resonant frequency are analyzed via simulations. The anti-interfering cladding design method for environmental bodies is then studied. The structure,a shape, and size of the environmental anti-interfering cladding are designed using an FR4 epoxy plate with good heat and moisture resistance, largely causing the fluctuation level of the sensor’s resonant frequency with changes in the environment to be reduced by more than 95%. The simulation and experimental results show that the proposed anti-interfering method for environmental foreign bodies using antenna cladding technology greatly improves the reliability of the microstrip antenna sensor and has considerable engineering application value.

Effect of friction on a crashworthiness test of flat composite plates

The diffusion of fiber reinforced plastics in crashworthiness applications is continuously growing thanks to the excellent balance between high mechanical performances and low weight, resulting in most cases in a Specific Energy Absorption (SEA) of composite structures higher than that of the corresponding metallic structures. In this paper, a new fixture to test composite plates applying an in-plane load has been used to investigate the effect of the impact velocity and of the friction caused by the fixture on the SEA of carbon fiber reinforced epoxy plates. The tests have been carried out using a drop tower testing machine and the effect of the friction has been studied varying the clamping force given by the fixture. Splaying is the main failure mechanism found in the specimens during the tests; SEA values (43.6 kJ/kg in average) increase with the clamping force due to the higher friction level induced by higher clamping force; impact velocity does not significantly influence the results. To avoid an overestimation of the SEA due to the excessive friction force (+5.6% when the clamping force increases from 0.8 kN to 8 kN), a Polytetrafluoroethylene (PTFE) coating has been applied to the anti-buckling supports to reduce the friction. The effect of this modification has been studied by carrying out a new test in which the specimen slides between the anti-buckling supports with a given clamping force. A significant reduction (-48% with same clamping force) of the friction force is obtained when the lubricant is applied.

A three-dimensional (3D) printing approach to fabricate an isolation chip for high throughput in situ cultivation of environmental microbes.

The full plethora of environmental bacteria is often poorly represented in vitro as the majority remain difficult, if not impossible, to culture under standard laboratory settings. These bacteria often require native conditions for the formation of cell masses that collectively have higher chances of survival. With that, a 3D-printed version of the isolation chip (iChip) was used to cultivate bacteria from a tropical peat swamp in situ prior to growth and maintenance in vitro. Briefly, plates made from either acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), or epoxy resin were tested in terms of their usability and durability under acidic conditions similar to those of peat matter. The epoxy resin plates were then found to be most optimal for the sampling conditions. Peat soil samples were collected from the base of a Koompassia malaccensis tree and reconstituted in molten 10% (wt/vol) tryptone soy agar (TSA) prior to inoculation. The iChips were subsequently assembled and buried in the site of origin. As a comparison, bacteria from the same soil sample were cultivated directly on TSA and incubated at 28 °C for two weeks. Thereafter, agar plugs from the iChip were transferred to TSA plates to allow microcolonies within each plug to grow. Each pure isolate from both cultivation approaches that grew was then pooled and extracted for total DNA prior to 16S rRNA gene amplification and sequencing via Illumina MiSeq. Taxonomic abundance comparison revealed that the bacterial taxa at the level of order were significantly different between the two approaches, particularly in the orders, Burkholderiales, Xanthomonodales, Enterobacteriales, and Actinomycetales (differences of 12.0, 7.1, 8.0, and 4.2%, respectively). This indicated that the 3D-printed iChips present a possible low-cost tool for the isolation of bacterial genera that may not be able to grow on media directly in vitro.

Development of a New Temporary Attachment Technique for Detecting Debonding of a Composite Structure Using Impedance Based Non-Destructive Testing Method

To date, the application of composite materials has been used throughout the globe due to its advantages, such as corrosion resistance, high strength, design flexibility, and light weight. However, the joining of composite materials is usually achieved with adhesives, where debonding of parts can cause unexpected failure. Thus, detecting and locating defects due to impact or fatigue stresses at an early stage is crucial to ensure safety. Various non-destructive testing (NDT) techniques have been used to detect defects in composite structures, where this study proposes an improved approach of using one of the NDT techniques to detect and locate debonding of glass fiber epoxy plates. Here, the electromechanical impedance (EMI) technique is used with a new way of detecting defects using a movable device. This idea could reduce the overall cost of the monitoring system as the conventional EMI technique requires one to permanently attach a large number of piezoelectric transducers when monitoring large structures. The performance of the proposed idea is tested against another temporary attachment method to investigate the possibility of using the new idea for monitoring debonding in composite structures.

A graded negative refraction-index phononic crystals plate lens for focusing A0 mode Lamb wave and energy harvesting

In this paper, a method of rotating scatterers was used to design a graded negative refraction index phononic crystal (GNRI PC) plate lens. The present plate lens contains the periodic perforated three-fan holes as the scatterers in the epoxy plate matrix. For a given rotation angle of the scatterer, the rotation would result in a variation of the second A0 band dispersion curve, which is related to a specific negative refraction index. Based on the Snell’s law, the negative refraction index was calculated by utilizing the equifrequency contour and wave vector space for the different rotation angle. Then, the graded negative refraction index plate lens was designed by the specific distribution of the rotation angle of the scatterer. The results show that the plate lens exhibits an obvious focus efficiency in the work frequency range from 16 kHz to 19 kHz. The influence of the work frequency and the dimension of the lens on the focal length was also discussed. Combining with the present plate lens, the energy harvesting analysis was performed numerically, and the energy harvesting efficiency with the plate lens is about 10.5 times larger than that without a lens. This work provides a new way to fabricate GNRI PC plate lens and energy harvesting devices.

Carbon fiber reinforced poly(ether ether ketone) rivets for fastening composite structures

Although composite materials are now commonly present in numerous aerospace applications, metallic bolt-type fasteners are still currently used despite their several drawbacks regarding weight, corrosion, and lightning strike hazards. This study explores an alternative fastening solution with the use of an innovative carbon fiber reinforced poly(ether ether ketone) (CF/PEEK) rivet. To produce such rivets, an automated riveting machine was developed. CF/PEEK blanks were cut from pultruded continuous fiber rods. The blanks were then heated beyond the matrix's melting temperature, by Joule effect. They were then molded directly into carbon fiber reinforced epoxy plates. The duration of the riveting process was 35 s from the beginning of the heating until the opening of the riveting robot to recover the joint. CF/PEEK rivets submitted to shear held up to 8.7 kN/g, while titanium fasteners held up to 4.7 kN/g. In tension, CF/PEEK rivets held up to 5.7 kN/g, while titanium fasteners held up to 3.0 kN/g. While the titanium fasteners showed a different mechanical behavior based on the hole-to-shank gap, the CF/PEEK rivets adapted to the different hole dimensions and no differentiated mechanical behavior was observed for the hole diameter investigated.

A generalized 2D Bézier-based solution for stress analysis of notched epoxy resin plates reinforced with graphene nanoplatelets

In this study, a robust Bezier-based multi-step method is extended to accurately solve the governing fourth-order complex partial differential equation (PDE) in linear elastic fracture mechanics (LEFM) problems. The Bezier technique was first introduced by the authors to solve initial value problems in one dimension. Now, the method is further extended to simultaneously solve Boundary Value Problems (BVPs) in orthogonal directions. To examine the accuracy and performance of the present method, the first-mode normalized stress intensity factor (SIF) of a 2D epoxy resin plate having an initial edge crack and reinforced with randomly oriented graphene nanoplatelets (GnP) is determined and compared with the associated exact analytical solution using the Bayesian statistical analysis. Besides, the impact of GnP aspect ratio on the normalized crack opening displacement (COD) of the reinforced matrix is elaborated for the first time in the literature. Results of the present study suggest that GnPs with maximum aspect ratio are most effective to enhance elastic properties of the plate and potentially limit the edge crack propagation. Specifically, inclusion of 0.5 and 1.0% of needle-shaped GnPs in a notched epoxy resin plate decrease the maximum normalized COD by 33 and 50%, respectively, while for square-shaped GnPs, these reductions are limited to 20 and 37%, respectively.

Reconfigurable waveguides defined by selective fluid filling in two-dimensional phononic metaplates

We investigate two-dimensional phononic metaplates consisting of a periodic array of cups on a thin epoxy plate that is perforated with periodic cross holes. The cups are individually filled with water or remain empty, in view of creating reconfigurable phononic waveguides. Phononic band gaps exist for empty or filled epoxy cups, leading to waveguides defined with either positive or negative contrast. Straight and 90° bent waveguides are considered experimentally. Lamb waves are excited by a piezoelectric patch glued onto the metaplate and are imaged using a scanning laser vibrometer. Experimental results are compared to a three-dimensional finite element model of fluid–structure interaction. Passing and forbidden frequency ranges are identified for positive and negative contrast, and confined propagation is observed along the waveguides. Significantly, the propagation of acoustoelastic waves in the 90° bent waveguides is observed experimentally. Reconfigurability and reusability are thus realized based on the coupling of elastic waves in the solid and acoustic waves in the fluid. The results show plenty of potentiality for the practical design of multiplexed and programmable acoustic devices implemented with reconfigurable waveguides printed on demand in a phononic metaplate.

Experimental study on the interaction between oblique incident blast stress wave and static crack by dynamic photoelasticity

In this paper, the interaction between the oblique incident blast stress wave and the prefabricated crack is studied using the dynamic photoelastic method and numerical simulation method. First, blast loading dynamic photoelastic experiment system is established. Second, blast stress wave and crack interaction experiments are carried out. Epoxy resin plate is used as specimen material, while lead azide explosive is used to apply blasting load. In the experiment, the evolution of stress field at crack wall and crack tip are observed by a high-speed camera. The experimental results show that incident angle of blast stress wave has a great influence on the way the stress wave interacts with the crack and the field at the crack tip. Finally, based on the experimental results, two numerical models are conducted using FEM software. The numerical results of stress field are in good agreement with photoelastic experiment, which verifies the experimental analysis.

Investigation of vibro-acoustic characteristics of FRP plates with porous foam core

Both theoretical and experimental investigations are performed on vibro-acoustic characteristics of composite plate comprising fiber-reinforced polymer (FRP) laminates with a porous foam core (PFC) subjected to planar acoustic wave (PAW) excitation in present work. Firstly, a theoretical model of the PFC-FRP plates is established through a combination of the advantages of analytical and finite element methods. The equivalent Young's and shear moduli and density of porous foam core with different porosity distributions is considered. The free and forced vibration equations subjected to PAW load are derived to solve natural frequencies, modal shapes and vibration responses of the PFC-FRP plates on the basis of the first-order shear deformation theory and the four-node quadrilateral isoperimetric finite element method. To solve the acoustic radiation powers (ARP), the Rayleigh integral approach is used to determine the quantitative relationships between the vibration velocity responses and acoustic radiation pressures. The sound transmission loss is further determined with the pre-defined proportional expression involving the ARP and the incident acoustic power (IRP). After the theoretical model is validated coarsely based on the separated literature results, a TC300 carbon/ GEL2 epoxy resin plate specimen is fabricated and an integrated vibro-acoustic experiment system is set up to give further validation of the proposed model, of which vibration and acoustic results are measured simultaneously without changing boundary conditions of the specimen. Finally, a detailed parametric study is conducted to obtain the optimum suppression performance of vibration and noise of this kind of composite plate.

Effect of adding carbon nanotubes into the matrix material on the buckling behavior of glass/epoxy composite plates: An experimental study

In this research, buckling of polymer matrix composite plates containing unidirectional glass fibers under in-plane pressure load is investigated. Moreover, the effect of adding carbon nanotubes as reinforcement into the matrix material on the critical buckling load of composite plates is studied. Using hand lay-up method, rectangular glass/epoxy composite plates with and without carbon nanotubes were fabricated. 0.25, 0.5 and 1.0 weight percent of carbon nanotubes were added to the epoxy resin and composite plates were subjected to the longitudinal in-plane pressure load. The plates were tested under fix ended boundary conditions utilizing Instron hydraulic universal testing machine. Based on the results, adding 0.5 weight percent of carbon nanotubes has the most influence on the critical buckling load of the plates. Results show that adding 0.5 weight percent of carbon nanotubes into the matrix material increases the critical buckling load of the carbon nanotubes /glass/epoxy plate more than two times with respect to that of glass/epoxy composite plate. Furthermore, when the carbon nanotubes weight percent reaches 1 %, because of carbon nanotubes agglomeration, carbon nanotubes are not dispersed well into the epoxy resin and the critical buckling load of the composite plate decreases. To validate the results, buckling analysis of glass/epoxy composite plate was done in Abaqus finite element software. Finite element models confirm the experimental results obtained.

An experimental investigation on low-velocity impact response and compression after impact of a stochastic, discontinuous prepreg tape composite

The present paper investigated the impact and compression after impact behavior of thin carbon fiber epoxy plates manufactured from prepreg platelet molding compound (PPMC) with two different discontinuous fiber length, 25.5 mm and 12.7 mm, and compared it with the behavior of continuous fiber quasi-isotropic composite laminate with a similar plate thickness. The results of dynamic testing showed that PPMC/12.7 mm exhibited larger amount of absorbed energy, which correlated with larger damage area measured by ultrasonic inspection. Micro-CT analysis showed that a discontinuous fiber composite developed significant amount of through-thickness damage. C-scan measured damage area correlated well with the compression after impact testing results, which indicated that longer fibers provide for better damage tolerance.

Synchronization Patterns of Two Coupled Oscillators in a Closed Electrochemical Bipolar Cell

We investigate the dynamical behavior of the oscillatory electrodissolution of two nickel and hydrogen reduction reaction in a closed electrochemical bipolar cell. In the bipolar setup, two half U cells are separated by an epoxy plate with two embedded nickel wires; the oxidation and reduction reactions take place at the two ends of the same wire. By tuning the concentration of electrolyte in the anode and cathode compartments, the current level and the dynamics of the oscillatory range can be varied without any external resistance. Phase analysis of the chronopotentiometric measurements showed that the potential oscillations of the two nickel anodes are completely in-phase synchronized, and thus strongly coupled, when 1.00 mm diameter electrodes were employed. The complete in-phase synchronization and strong coupling effect was lost as the electrode diameter was decreased from 1.00 mm to 0.25 mm. The synchronization effects were interpreted by the charge transfer resistance of the hydrogen reduction reaction as the main coupling element in the cell. The experiments demonstrate the use of bipolar electrochemical cells for the investigation of coupling and synchronization in chemical oscillatory processes.

Evaluating the influence of radiative heat flux on convective heat transfer from a vertical plate in air using an improved heating plate

This article examines the influence of radiative heat flux on the accuracy of the results of free convective heat transfer in air. In order to carry out these tests, based on the experience gained during the operation of a plate heated on one side, compensated by a reverse heat loss flux counter-heater, a unique double-sided heating sandwich plate was designed and built, consisting of three thin epoxy resin plates reinforced with glass fibre. The paths of surface resistance thermometers were etched using photolithography on the two outer plates laminated on one side with copper. The traces of two resistance heaters were etched on both sides of the third, bilaterally laminated middle plate.This paper provides a detailed technical description of the new type of plate, the method of its implementation and determination of its operational range, calibration procedures (separately for integrated thermometers and heaters). Also described are the methods for conducting experimental tests in the vertical using the balance method in air and in water, and the gradient method using a thermal imaging camera and a detection mesh in order to validate the results obtained.

The effect of nano- and micron-scale filler modified epoxy matrix on glass-fiber reinforced polymer insulator component behavior

Glass-fiber reinforced polymer (GFRP) composite rods with epoxy matrix filled with electrically nonconducting particles find widespread use in high-voltage electrical insulator applications. The service loads require a range of different, minimum material property values, e.g. toughness, tensile, or compressive strength, but also component-specific performance, e.g. pull-out friction of surface crimped metal fittings or electric breakdown strength. The contribution discusses selected examples of the effects of different particle filler types on the properties of filled epoxy resin as well as on the behavior of GFRP rods with such a matrix. In all investigated systems CaCO3 was used as micron-sized filler, complemented by different amounts of either nanosilica or core-shell rubber (binary filler), or by both, nanosilica and core-shell rubber (ternary filler). With ternary filler combinations at a content of 36 wt%, fracture toughness GIC was improved in nanocomposite epoxy plates and in GFRP rods by 60% and 100%, respectively compared to a matrix with 20 wt% CaCO3 (used as reference system). The glass transition temperature Tg for some ternary systems dropped from 160 °C (for neat epoxy), to approximately 140 °C, the maximum allowed drop in Tg in view of requirements from further processing steps of the electrically insulating components. The ternary fillers yield transfer of the improvements of fracture properties from epoxy nanocomposite plates into the GFRP rods beyond that of the system with CaCO3 filler only. Compressive strength of the GFRP rods was improved by about 20% only for the binary nanosilica and CaCO3 filler, and was not significantly enhanced with the ternary systems. That combination, however, did not yield improvements in toughness beyond the CaCO3-filled nanocomposite plates and rods. With the range of filler types and contents investigated here, it was hence not possible to simultaneously optimize both, fracture toughness and compressive strength of the GFRP insulator rods.

Ductile failure analysis of epoxy resin plates containing multiple circular arc cracks by means of the equivalent material concept

Ductile failure of polymeric samples weakened by circular arc cracks is studied theoretically and experimentally in this research. Various arrangements of cracks with different arc angles are considered in the specimens such that crack tips experienced the mixed mode I/II loading conditions. Fracture tests are conducted on the multi-cracked specimens and their fracture loads are achieved. To provide the results, the equivalent material concept (EMC) is used in conjunction of dislocation method and a brittle fracture criterion such that there is no necessity for performing complex and time-consuming elastic-plastic damage analyses. Theoretical and experimental stress intensity factors are computed and compared with each other by employing the fracture curves which demonstrate the appropriate efficiency of proposed method to predict the tests results.

Nondestructive characterization of mechanical properties on metallic and polymer plates using hybrid laser-air coupled ultrasonic techniques

Ultrasonic non-destructive techniques have been extensively used in various applications such as material characterization to extract important properties of materials. This work presents a non-contact hybrid system which integrates laser ultrasound and air-coupled transducer for generation and detection of guided waves. Furthermore, by adjusting the air-coupled transducer for an estimated angle, A0 S0 Lamb modes and longitudinal waves was detected in aluminum, stainless steel, and epoxy resin plates. Subsequently, the experimental measurements of dispersion curves are computed and Young’s modulus, thickness were calculated using inversion technique. Results show that the error percentage of Young’s modulus and thickness was about 7.60% and 9.26% for aluminum plate while the steel plate showed with 3.98% and 3.58%. Besides, the error percentage of Young’s modulus and thickness was about 4.05% and 5.88% for epoxy resin plate. The obtained experimental measurements were in good agreement with inversed material properties, which verified that the hybrid laser-air coupled ultrasonic technique can prove that the system is feasible, and the accuracy can be improved in the future to measure the material properties and geometrical character of metallic and polymer plates.

An Improved Method for Dynamic Behaviour Prediction of Carbon Fibre Reinforced Epoxy (CFRE) using Finite Element Model Updating

The dynamic behaviour prediction scheme of carbon fibre composite structures are extremely challenging to be performed due to the geometrical ply-by-ply properties and the ply orientation issues. In this paper, a laminated carbon fibre reinforced epoxy plate with elastic and linear layers was used with aim to investigate the dynamic behaviour of the carbon fibre reinforced epoxy using practical modelling scheme via finite element modelling and updating method. A simplified FE model of the CFRE plate was developed using shell element properties known as PSHELL to represent geometrical laminated properties. Subsequently, the dynamic behaviour of the FE model was calculated using Nastran SOL103. Potential updating parameters of the FE model was analysed and identified using the sensitivity analysis. The model updating method was then used to update the initial FE model of the CFRE plate based on the experimental modal analysis (EMA) result. The comparison of the results were used in verifying the accuracy of the updated FE model of the CFRE plate. The result suggested that the PSHELL properties can be used efficiently to represent the geometrical laminated properties of the CFRE plate without considering the geometrical effect of ply-by-ply properties.