Plastic Laminates Research Articles

Comparison of different surface modifications on mechanical properties of HNTs incorporated CFRP for fine particle accumulation

This paper presents an investigation into the effect of particle accumulation on an amorphous halloysite nanotube (A-HNT)/Carbon fiber reinforced plastic (CFRP) laminate, fabricated through Vacuum-assisted Resin Transfer Molding (VaRTM). Resin blending and Electrophoretic deposition (EPD) methods were impeded to incorporate the A-HNTs. Bending, short beam shear (SBS), and end-notched flexure (ENF) tests were individually conducted on three sections, which were divided from an integral CFRP laminate. The anchoring effect of the carbon fibers and the scouring effect of the resin flow together lead to the different A-HNT accumulation patterns in both incorporation methods, and thus caused the observed distinctions in the properties of each separated section. Extensively incorporated A-HNTs showed a tendency to aggregate, resulting in the degradation of the material’s properties.

Performance of D-Limonene/Ethanol in the Selective Recovery of PE from LDPE/VMPET/PET Laminates

The prevalent sachet economy in the Philippines has led to the country becoming the third largest polluter of oceans in the world. The sachets used for packaging are made of plastic laminates which typically consist of varying polymeric layers combined with other modifiers to improve barrier properties. In this study, applicability of D-limonene and ethanol as solvent/non-solvent pair for the separation of polyethylene (PE) from vacuum-metallized polyethylene terephthalate (VMPET) and polyethylene terephthalate (PET) was established. PE recovery from LDPE/VMPET/PET laminates were calculated to be 50.79% w/w.

Whole‐field strain analysis and strength prediction of fiber laser machined CFRP laminate at elevated temperature

AbstractHigh power fiber laser was proved to be feasible to cut carbon fiber reinforced plastic (CFRP) laminate with high efficiency, while the machined quality on mechanical performance was not fully understood. This paper studied the effect of high temperature up to 220°C on tensile strength degradation and strain distribution of unidirectional CFRP laminate with open hole machined with fiber laser. Differential scanning calorimetry (DSC) was firstly employed to determine the glass transition temperature (Tg) of polymer‐matrix composite. Digital image correlation technique was applied to evaluate whole‐field strain distribution and crack propagation/evolution of CFRP laminate featured with open hole under tensile loading. Results showed that the tensile strength of laser machined CFRP laminate degraded significantly during working in high temperature above 100°C. The value of strains distributed around center hole was highly related to the elevated temperature and applied load levels. Splitting was the prevalent failure mode of CFRP laminate under elevated temperature up to 180°C. Finally, semi‐empirical model was developed for evaluating tensile performance of laser machined CFRP laminate at elevated temperature based on regression analysis.

Effectiveness of Shear and Flexural Repair and Strengthening of Box section Steel Beams using CFRP Laminates

Steel structures are generally subjected to damages and defects due to different causes such as corrosion, fracture cracking, fire, buckling…etc. Damaged or defected parts may include girders, columns, welds, splices, base plates…etc. There is a wide range of techniques used for repair and strengthening starting with using protective coatings and ending up with full replacement of the damaged parts. Fiber Reinforced Plastic (FRP) laminates are widely used now in the field of repair and strengthening of different types of structures (reinforced concrete structures, steel structures, masonry structures, timber structures….etc.). The main goal of this research is to investigate the effectiveness of using Carbon Fiber Reinforced Plastic (CFRP) laminates in repair and strengthening of steel beams (in both flexural and shear). A total of five box-section steel beams were tested in three point load flexure test to determine the stiffness and ultimate load carrying capacity of the strengthened and repaired beams using CFRP laminates and compare the obtained results for these beams with those of the fifth beam which used as a control beam (without CFRP laminates). Test results showed that the effectiveness of using CFRP laminates for repair and strengthening of steel beams depends mainly on the obtained modes of failure. Highest effectiveness was obtained in tension failure modes while almost no effectiveness obtained in compression failure modes.

Monitoring of hole surface integrity in drilling of bi-directional woven carbon fiber reinforced plastic composites

Fiber-reinforced plastic is one of the top priorities lightweight materials with excellent mechanical properties for the aerospace industries in recent years. However, it is difficult to machine despite having unique properties due to its non-homogeneous and abrasive nature in alternate fiber and matrix layers. Thus, it is found to be a challenging task to drill hole on such hard-to-machine materials, which is highly essential for the development of most of the engineering structural components. The present work addresses various drilling-induced defects such as delamination, circularity error, and roughness variations in the hole surface during drilling of quasi-isotropic cross-fiber oriented bi-directional woven-type carbon fiber reinforced plastic laminate using a full factorial design of experiments for different drill geometry. The response surface methodology was considered for the regression model development, which was found to be highly significant. The machining forces with associated torque have also been acquired during drilling, which was divided and further analyzed in time domain to correlate with drilling flaws. The drilling-induced delamination was found to be higher at a high feed rate using a higher drill point angle due to substantial thrust force generation at the initial stages in the drilling cycle. However, the internal surface finish with associated circularity error was reduced for higher spindle speed with less feed rate using a low drill point angle because of low torque fluctuation at the final drilling phases. The axial thrust force was found to be a prime indicator of drilled hole surface delamination, whereas drilling torque precisely indicated internal surface roughness as well as circularity error. The global root mean square, along with a local peak of thrust and torque, both were highly essential to completely characterize the drilled hole quality.

The effect of fiber orientation on tool wear in edge-trimming of carbon fiber reinforced plastics (CFRP) laminates

This paper investigates the impact of fiber orientation on tool wear when edge-trimming carbon fiber reinforced plastics (CFRP) with particular ply angles of 0°, 45°, 90°, and 135° with 6.35 mm diameter tungsten carbide end-mills at a constant feed of 0.3 m/min under two spindle speeds. The tool wear progress was examined qualitatively and quantitatively using the scanning electron microscopy and digital light microscopy at eight cutting distances between 0.25 and 8 m. The 45° plies resulted in extensive flank wear while the 90° plies yielded the worst edge radius rounding and worn area regardless of the rotational speed. Edge rounding is related to aggressive 2-body abrasion by the broken carbon fibers interacting with the cutting edge. The 0° ply angle has the least amount of tool wear due to the minimal interactions between the carbon fibers and cutting edge with the delamination in the chip formation.

Three-point bending analysis with cohesive surface interaction for improved delamination prediction and application of carbon fibre reinforced plastics composites

Carbon fibre reinforced plastics laminates were loaded through to fracture in a three-point bending configuration, to gain understanding of the cohesive interaction between plies and validate mechanical properties and predictive capability of the FE model. The effect of mesh refinement, scaling techniques, failure models and cohesive surfaces were investigated. Fibre orientations investigated were parallel, 45° and perpendicular to the loading. Experimental results showed a larger radius punch promoted failure on the intended bottom side, tensile stresses region, allowing for the Aramis strain camera to record the failure. When the fibre orientation was perpendicular to the punch load, all failure models show similar rate of force increment with respect to displacement. No difference in failure prediction is observed for the different 0° models, except for a 4.18% under prediction by LaRC02 compared to the experiment. With fibre orientations at 45° and 90°, the Maximum Strain and LaRCO2 failure models were more suitable in terms of accuracy and convergence. Incorporating cohesive surfaces between instances improve nonlinearity prediction of 45° and 90° layups. Small span-to-thickness ratio analysis predicts interlaminar shear failure, delamination, versus large span-to-thickness ratio determine normal stresses to dominate failure in laminate. The model was setup in multi-fibre orientation and cross-ply layups for extended application and was shown to successfully predict material response described in literature.

Talbot-Lau interferometry-based x-ray imaging system with retractable and rotatable gratings for nondestructive testing.

We develop an x-ray imaging system based on Talbot-Lau interferometry equipped with a mechanical structure for retracting and rotating gratings from the optical axis, which enables not only x-ray phase contrast imaging but also conventional x-ray imaging with high-magnification such as microcomputed tomography (μCT). We investigate the characterization of carbon fiber reinforced plastic (CFRP) laminates using this apparatus. Microcracks and fiber orientations are visualized in the dark-field images. Compared with the obtained μCT images, the relationship between the CFRP microstructures and the contrasts in the dark-field images are recognizable.

Linear damage localization in CFRP laminates using one single fiber-optic Bragg grating acoustic emission sensor

Highly sensitive ultrasonic fiber-optic Bragg gratings (FBGs) have been used as acoustic emission (AE) sensors in the non-destructive inspection (NDI) for analyzing damage progression during the material tests of carbon fiber reinforced plastic (CFRP) laminates. Localization of the damage-induced AE source is one of the desirable functions for enhancing the efficiency of the AE-based NDI method. Hence, we attempted to establish a linear source localization method in a coupon-shaped CFRP test specimen with a highly sensitive FBG sensor. In particular, to protect the FBG-AE detection from influence caused by the static strain in a test specimen, the FBG sensor was installed by a remote adhesive configuration, i.e., one point of optical fiber was glued on the specimen, and the FBG sensor in the optical fiber was located away from the adhesive point. In the particular bonding way, the FBG sensor detected AE wave through an optical-fiber-based ultrasonic waveguide. In the first half of the paper, an ultrasonic experiment was conducted to show this installation technique can stably and accurately detect the behavior of Lamb wave modes in AE signals. With the help of the sensing characteristics, we clarified that a time difference between the arrival of S0 and A0 modes in a one AE signal had a linear relation to the distance between the AE source and the adhesion point when the length of optical fiber-based waveguide was fixed. Based on the examination, the linear AE source localization method was established using only one single FBG sensor. After confirming the ability of the proposed approach through a simulated AE experiment in a cross-ply CFRP laminate, we used the strategy to localize the actual damage-induced AE sources during a three-point bending test of the laminate.

Study on the fractal dimension and evolution of matrix crack in cross-ply GFRP laminates

Damage evolution and failure criterion are the focus of structural strength research in fiber reinforced plastic (FRP) composites. In this paper, quasi-static tests and fatigue tests at different stress levels of cross-ply glass fiber reinforced plastic (GFRP) laminates were carried out to obtain the stiffness degradation curves and matrix damage images. Based on the discovery that the matrix damage morphology has statistical self-similarity, the evolution of the matrix damage and its fractal dimension were studied. It is found that the evolution of matrix damage’s fractal dimension can be divided into three stages, and the fractal dimension of matrix damage corresponding to the characteristic damage state is independent of load type and stack sequence. When transverse crack initiation, transverse crack saturation and laminate failure occur, the fractal dimensions are Dbi = 1.39, Dbs = 1.81, Dbf = 1.90 respectively. Due to these advantages, the fractal dimension of matrix crack could be an appropriate damage state parameter.

Effect of Carbon Fiber Type on Splitting Growth Behavior in Unidirectional Carbon Fiber Reinforced Plastic Laminates

Effect of Carbon Fiber Type on Splitting Growth Behavior in Unidirectional Carbon Fiber Reinforced Plastic Laminates

Characterization of Fatigue Damage Behavior in Unidirectional Carbon Fiber Reinforced Plastic Laminates

Characterization of Fatigue Damage Behavior in Unidirectional Carbon Fiber Reinforced Plastic Laminates

Validation of tensile strength of notched hybrid polymer composite using Whitney-Nusimer point stress model

In recent years, a few research attempts were made on the feasibility of hybridization using selected natural and synthetic fibers which provide good structural properties. Most of the structural assembling operations, the fiber reinforced plastic laminates were used which involve several riveted joints. This requires the presence of various sizes of hole and eventually a zone of stress concentration. This leads to a tensile strength analysis study by the effect of various sizes of open-hole made on the laminate composites. This is a crucial step in defining their suitability in applications. In the present work, investigation on mechanical properties of a hybrid combination of natural fibers human hair-coconut coir and synthetic glass fiber-laminate has been carried out. Eight sets of tensile and impact specimens were prepared with centrally drilled various sizes of hole and experimentally tensile and impact strength were recorded. Additionally, Whitney Nusimer point stress model was used to validate the experimental values. The stress distribution around the centre hole was studied by the Finite Element Method (FEM). An increase in hole diameter found to increases hole sensitivity. The finite element analysis indicated a much higher stress concentration region along the tensile loading direction.

Calibration of the material parameters of a CFRP laminate for numerical simulations

The aim of present paper is to show a procedure to calibrate mechanical properties to be used in a finite element model for a carbon fibre-reinforced plastic laminate that use solid elements. A reduced experimental programme including tensile test, tensile test on specimen with a central hole, three-point bending test and three-point bending test on short beam test were carried out. Every test was numerically reproduced by means of an explicit solver. Properties are determined from the tensile test and unmodified for the other load scenarios which are used as validation benchmarks. Finally, it is demonstrated that the properties determined with the simple tensile tests can guarantee accurate results when adopted to simulate much more complicated stress patterns.

Boron nitride inclusions within adhesive joints: Optimization of mechanical strength and bonded defects detection

Non Destructive Testing (NDT) by active InfraRed Thermography (IRT) of bonded Carbon Fibers Reinforced Plastic (CFRP) laminates is a very challenging issue. Adding Boron Nitride (BN) particles within the joint material provides an interesting solution to better capture bonding defects. Though increasing additives leads to the improvement of NDT, the validation of this solution requires the mechanical characterization of the new joint material. In this way, the influence of particles on the mechanical properties of the adhesive joint is first investigated via double strap lap shear tests for different BN volume fraction. At the same time, controlled size void inclusions are generated within composite assemblies in order to evaluate the IRT ability to detect bonded defects inside BN-based adhesives. It is demonstrated that thermal data post-processing methods such as Singular Values Decomposition (SVD) and Principal Component Thermography (PCT) help to get the best trade-off between mechanical performance and defect detection.

Increased breaking strain of carbon fiber-reinforced plastic and steel hybrid laminate composites

Synergistic effects of carbon fiber-reinforced plastic (CFRP) and steel hybrid laminate composites were investigated systematically by static and dynamic tensile testing. Various hybrid laminate composites were prepared by varying the adhesion between the CFRP and steel, the layup sequence, and the volume fraction of the CRFP. The fracture strain of the CFRP within the hybrid laminate composites increased, e.g., from 1.94% for pure CFRPs to 2.21% for the steel/CFRP/steel case. Finite element analysis and fractography established that transverse compressive stress was the main source of the improvement. Different Poisson’s ratios led to transverse compressive stress on the CFRP layer after yielding of the steel during the tensile test. This stress delayed the fiber-splitting behavior of the CFRP, leading to further deformation and thus increasing the breaking strain and tensile strength of the CFRP within the hybrid laminate composites. Our results provide insight into the design of ductile composites using CFRP and steel through optimization of the laminate structure.

Relationship Between Matrix Cracking and Delamination in CFRP Cross-Ply Laminates Subjected to Low Velocity Impact.

The effect of matrix cracking on the delamination morphology inside carbon fiber reinforced plastics (CFRP) laminates during low-velocity impact (LVI) is an open question. In this paper, the relationship between matrix cracking and delamination is studied by using cross-ply laminates. Several methods, including micrograph, C-scan, and visual inspection, were adopted to characterize the damage after LVI experiments. Based on the experimental results, finite element (FE) models were established to analyze the damage mechanisms. The matrix cracking was predicted by the extended finite element method (XFEM) and the Puck criteria, while the delamination was modeled by cohesive elements. It was revealed that the matrix crack in the bottom ply not only promoted the outward propagation of delamination but also contributed to the narrow delamination beneath the impact location. Multiple matrix cracks occurred in the middle ply. The ones close to the plate center initiated the delamination and prevented large-scale delamination beneath the impact location. For the cracks that were far away, no significant effect on delamination was found. In conclusion, the stress redistribution caused by the crack opening determines the delamination.

Failure behavior of notched CFRP laminates subjected to tensile load

An experimental study was conducted to determine the tensile failure mechanism of notched quasi-isotropic carbon-fiber-reinforced plastic (CFRP) laminates. Three sets of specimens were prepared to study the effects of specimen dimensions and stress concentration factor on damage initiation, accumulation and final failure. The damage accumulation processes of the specimens were observed with an X-ray CT system, by suspending the tension test several times and carefully resetting the specimen in the test apparatus each time until final failure. Micrographs of polished section of damaged specimens revealed the damage states. The damage initiation and accumulation process strongly depended on specimen size as well as notch size. Interesting coupling behavior of defects involving, for example, matrix cracks, delamination, and fiber breakages were observed. Kinking failure in 90° layers was found along ±45° inclined matrix cracks tangent to the notch end in neighboring ±45° layers.

Evaluation of mechanical behaviour of carbon fiber reinforced nanoclay filled IPN matrix composite

A standard ratio of vinyl ester (VER) and polyurethane (PU) were chosen as the blend (matrix) in order to obtain the complete Interpenetrating Polymer Networks (IPN) matrix. In this present study, the mechanical property of the Carbon reinforced IPN (blend) matrix with incorporation of nanoclay (particulate) were studied to find out the mechanical strength of the Carbon Fiber Reinforced Plastic laminate (CFRP) by altering the nanoclay percentage level of 0%, 1%, 3%, 5%, 7%, and 9%. In addition to that, to assess the mechanical strength of the laminate tests like tensile, flexural and impact were conducted. The test results reveal that, the incorporation of the nanoclay increases the strength of the laminate to many folds; surprisingly the gain of the strength was limited up to the level of 5% nanoclay incorporation. Whereas the deteriorating level of trend were observed for remaining set of nanoclay (7% and 9%) addition. Additionally the fracture specimens were further analysed with help of the Scanning Electron Microscope (SEM) to understand the complete morphology of the rise and fall trend in strength aspect. As well, to validate the experimental results obtained from the mechanical study, were further analysed with help of the analytical software ANSYS. It was found that both the experimental and analytical results were shown the similar trend of the (good agreement) data’s with minimum error.

Temperature dependence of statistical fatigue strengths for unidirectional carbon fiber reinforced plastics under tension loading

The formulation for time- and temperature-dependent statistical static and fatigue strengths for carbon fiber reinforced plastics laminates is newly proposed based on the physically serious role of resin viscoelasticity as the matrix of carbon fiber reinforced plastics. In this study, this formulation is applied to the tensile strength along the longitudinal direction of unidirectional carbon fiber reinforced plastics constituting the most important data for the reliable design of carbon fiber reinforced plastics structures which are exposed to elevated temperatures for a significant period of their operative life. The statistical distribution of the static and fatigue strengths under tension loading along the longitudinal direction of unidirectional carbon fiber reinforced plastics were measured at various temperatures by using resin-impregnated carbon fiber reinforced plastics strands as specimens. The master curves for the fatigue strength as well as the static strength of carbon fiber reinforced plastics strand were constructed based on the time–temperature superposition principle for the matrix resin viscoelasticity. The long-term fatigue strength of carbon fiber reinforced plastics strand can be predicted by using the master curve of fatigue strength.