Fiber Reinforced Polymer Composite Laminates Research Articles

Experimental investigation on mechanical properties of Basalt/Jute/SiC reinforced hybrid polymer composites

Recent years, researchers focuses on hybridization of composite with natural fiber reinforcement and adding fillers for improving thermal and mechanical thermal behaviour of composites. These natural fiber reinforced bio polymers acts as partial eco-friendly materials. It makes the need for creating design database for hybrid composite materials.. In the present work, hybrid composite laminates were fabricated with Basalt and Jute fiber reinforcements using the hand layup technique with 5% and 10% Silicon carbide and also absence of it. There are six hybrid composite laminates were fabricated along with five stacks alternative fiber layers and Five stacks of basalt and jute fiber reinforced polymer composite laminate with 5% and 10% SiC filler. All such composite laminates are compared with five stacks of five layered composite laminates made of individual Basalt and Jute fiber to analyse mechanical behaviours like tensile, flexural and wear properties using ASTM standards. Results were analysed and fractured surfaces were examined using scanning electron microscope.

The isothermal curing kinetics of a new carbon fiber/epoxy resin and the physical properties of its autoclaved composite laminates

This study investigated the effects of different isotherm temperatures on the thermal behavior and physical properties (i.e., degree of cure, density, fiber volume fraction, and void content) of quasi-isotropic carbon fiber reinforced polymer composite laminates. First, the curing kinetics of a new commercial prepreg, Hexply®8552S, was investigated by isothermal differential scanning calorimetry (DSC). The nth-order, autocatalytic, and Kamal & Sourour models were used to determine curing kinetic parameters that fit the experimental data. The results showed that the phenomenological model of Kamal & Sourour was the most appropriate, as indicated by the relatively high values of the adjusted R square. Based on the kinetics results, autoclave processing was used to produce laminated composites. The isothermal curing temperatures were 160, 180, 190, and 205 °C, respectively. The results showed that the isotherm temperature significantly influenced the final degree of cure, density, and void content. At 180 °C, the highest values of degree of cure and density were obtained, while the lowest values of void content were remarqued.

Effects of the Electrophoretic Deposition of CNTs on the Mechanical Properties of Ti/CFRP Composite Laminates.

The interfacial performance between metals and resins significantly affects the mechanical properties of fiber–metal laminates. In this study, CNTs were deposited on a titanium surface via electrophoretic deposition (EPD) to improve the interfacial performance of Ti/carbon fiber-reinforced polymer composite laminates. Before EPD, the titanium plates were treated by either sandblasting, anodizing, or sandblasting/anodizing. A macroscopically rough surface and an oxide layer were formed by sandblasting and anodizing, then CNTs were deposited, and a porous layer was obtained, which improved the wettability and bonding strength. Finally, the static mechanical properties (single-lap properties, bending properties, and interlaminar shear properties) and dynamic mechanical properties (impact resistance) of the laminates were systematically explored. The introduction of CNTs played an important role in dispersing and carrying loads and providing a strong crack propagation resistance, which improved the laminates’ static mechanical properties and reduced the delamination damage under dynamic impact. Compared with the original composite laminates, the bond strength, bending strength, and interlaminar shear strength of the laminates deposited with CNTs after sandblasting were increased by 117.94, 46.85, and 145.61%, respectively. When the impact energy was 35 J, the damage area of the composite laminate deposited with CNTs was decreased by 27.75%.

Recent Developments and Challenges on Machining of Carbon Fiber Reinforced Polymer Composite Laminates

Recent Developments and Challenges on Machining of Carbon Fiber Reinforced Polymer Composite Laminates

On the importance of finite element mesh alignment along the fibre direction for modelling damage in fibre-reinforced polymer composite laminates

A finite element mesh, aligned along the fibre direction, has often been purported to yield more accurate results in the modelling of damage in composite structures constructed from unidirectional fibre reinforced polymer laminates. However, there has been a lack of a systematic assessment of this approach. This issue is addressed through modelling a selection of test cases; (i) end notched tension (ENT) coupons, (ii) simple tensile/compressive specimens, (iii) open-hole tension (OHT), (iv) low velocity impact (LVI) and (v) compression-after-impact (CAI) of laminated plates. In each case, two models were constructed, one using a uniform mesh, aligned with the global coordinate system, and independent of the fibre direction, and the other where each ply mesh was aligned along the fibre direction. In both cases the local material axes in each ply were correctly represented. Results show that a finite element mesh aligned along the fibre direction plays an important role in the prediction of damage, particularly in the presence of a crack. However, when matrix crack paths are not established a priori, or may not be the dominant damage mode, fibre mesh alignment is unnecessary. Rather, long-established approaches of refined meshes, robust damage models and well-defined material data and boundary conditions, are shown to be sufficient requirements.

Effect of stacking sequence on the performance of hybrid natural/synthetic fiber reinforced polymer composite laminates

Here, the effect of stacking sequence on the mechanical and thermomechanical properties of composites using natural fiber (jute), synthetic fiber (glass) and unsaturated polyester resin, is presented. The fabricated composite laminates were neat jute/polyester, neat glass/polyester, and hybrid jute/glass/polyester. It was revealed that neat glass/polyester laminate showed better mechanical performance than the other laminates, and glass fiber hybridization significantly affects the properties of the hybrid laminates. Furthermore, three selected composites were studied using Dynamic Mechanical Analysis (DMA) and Scanning Electron Microscopy (SEM) imaging. Lastly, to improve the mechanical properties of the developed composites, 1 kGy dose of γ-irradiation was applied. As a result, the tensile strength, bending strength, tensile modulus, and bending modulus was increased 10.7, 26.7, 21.5, 36.5% for neat jute/polyester composites; 6.2, 10.9, 50.3, 18.0% for neat glass/polyester composites; and 8.9, 11.9, 21.7, 19.9% for hybrid composites, respectively.

Mechanical properties of hybrid fibre reinforced polymer-timber veneer laminates

Hybrid fibre reinforced polymer (FRP)-timber (HFT) thin-walled structural members made out of thin-timber veneer and fibre reinforced polymer composite laminates are a sustainable alternative to light-weight steel and aluminium thin-walled structural members. Preliminary studies on HFT structures have demonstrated the potential of HFT thin-walled structures to be used as high performing structural members. This study is aimed at investigating the effect of manufacturing pressure and the fibre type on the mechanical properties of the HFT laminates. Two different manufacturing pressures and three types of FRPs were used in the investigation. Series of experiments were carried out to determine the tensile, compressive, shear, and flexural properties of the laminates. Best manufacturing pressure as well as the fibre type to use were found to be dependent on the type of loads (membrane and/or flexural) applied on the HFT laminate. Classical laminate theory was found to be accurate in calculating membrane properties of the HFT laminate, but was found to result in significant inaccuracies when calculating the flexural properties.

An engineer's guide to eXplainable Artificial Intelligence and Interpretable Machine Learning: Navigating causality, forced goodness, and the false perception of inference

While artificial intelligence (AI), and by extension machine learning (ML), continues to be adopted in parallel engineering disciplines, the integration of AI/ML into the structural engineering domain remains minutus. This resistance towards AI and ML primarily stems from two folds: 1) the fact that coding/programming is not a frequent element in structural engineering curricula, and 2) these methods are displayed as blackboxes; the opposite of that often favored by structural engineering education and industry (i.e., testing, empirical analysis, numerical simulation, etc.). Naturally, structural engineers are reluctant to leverage AI/ML during their tenure as such technology is viewed as opaque. In the rare instances of engineers adopting AI/ML, a clear emphasis is displayed towards chasing goodness metrics to imply “viable” inference. However, and just like the notion of correlation does not infer causation, forced goodness is prone to indicate a false sense of inference. To overcome this challenge, this paper advocates for a modern form of AI, one that is humanly explainable; thereby eXplainable Artificial Intelligence (XAI) and interpretable machine learning (IML). Thus, this work dives into the inner workings of a typical analysis to demystify how AI/ML model predictions can be evaluated and interpreted through a collection of agnostic methods (e.g., feature importance, partial dependence plots, feature interactions, SHAP (SHapley Additive exPlanations), and surrogates) via a thorough examination of a case study carried out on a comprehensive database compiled on reinforced concrete (RC) beams strengthened with fiber-reinforced polymer (FRP) composite laminates. In this case study, three algorithms, namely: Extreme Gradient Boosted Trees (ExGBT), Light gradient boosted trees (LGBT), and Keras Deep Neural Networks (KDNN), are applied to predict the maximum moment capacity of FRP-strengthened beams and the propensity of the FRP system to fail under various mechanisms. Finally, a philosophical engineering perspective into future research directions pertaining to this domain is presented and articulated.

Advanced Glass Fiber Polymer Composite Laminate Operating as a Thermoelectric Generator: A Structural Device for Micropower Generation and Potential Large-Scale Thermal Energy Harvesting.

This study demonstrates for the first time a structural glass fiber-reinforced polymer (GFRP) composite laminate with efficient thermal energy harvesting properties as a thermoelectric generator (TEG). This TEG laminate was fabricated by stacking unidirectional glass fiber (GF) laminae coated with p- and n-type single-wall carbon nanotube (SWCNT) inks via a blade coating technique. According to their thermoelectric (TE) response, the p- and n-type GF-SWCNT fabrics exhibited Seebeck coefficients of +23 and -29 μV/K with 60 and 118 μW/m·K2 power factor values, respectively. The in-series p-n interconnection of the TE-enabled GF-SWCNT fabrics and their subsequent impregnation with epoxy resin effectively generated an electrical power output of 2.2 μW directly from a 16-ply GFRP TEG laminate exposed to a temperature difference (ΔT) of 100 K. Both experimental and modeling work validated the TE performance. The structural integrity of the multifunctional GFRP was tested by three-point bending coupled with online monitoring of the steady-state TE current (Isc) at a ΔΤ of 80 K. Isc was found to closely follow all transitions and discontinuities related to structural damage in the stress/strain curve, thus showing its potential to serve the functions of power generation and damage monitoring.

An Approach toward the Realization of a Through-Thickness Glass Fiber/Epoxy Thermoelectric Generator.

The present study demonstrates, for the first time, the ability of a 10-ply glass fiber-reinforced polymer composite laminate to operate as a structural through-thickness thermoelectric generator. For this purpose, inorganic tellurium nanowires were mixed with single-wall carbon nanotubes in a wet chemical approach, capable of resulting in a flexible p-type thermoelectric material with a power factor value of 58.88 μW/m·K2. This material was used to prepare an aqueous thermoelectric ink, which was then deposited onto a glass fiber substrate via a simple dip-coating process. The coated glass fiber ply was laminated as top lamina with uncoated glass fiber plies underneath to manufacture a thermoelectric composite capable of generating 54.22 nW power output at a through-thickness temperature difference οf 100 K. The mechanical properties of the proposed through-thickness thermoelectric laminate were tested and compared with those of the plain laminates. A minor reduction of approximately 11.5% was displayed in both the flexural modulus and strength after the integration of the thermoelectric ply. Spectroscopic and morphological analyses were also employed to characterize the obtained thermoelectric nanomaterials and the respective coated glass fiber ply.

Instability-driven shape forming of fiber reinforced polymer frames

Thin fiber reinforced polymer (FRP) composites are widely implemented in adaptive and morphing structures. However, realization of the necessary complex 3-dimensional FRP structures requires the use of expensive molds thereby limiting the design space and flexibility. Using the elastic strain energy of pre-stretched membranes holds potential for addressing this challenge. In this work, a novel manufacturing technique for fabricating 3-dimensional FRP structures moldlessly is presented where pre-stretched membranes are used to drive out-of-plane buckling instabilities of FRP composite shells. To explore the potential of this approach, a simple square frame design is investigated. An analytical model based on high deformation beam buckling theory is developed for understanding the parameters driving the out-of-plane behavior of these structures. Experimental and finite element results are used for model validation and reveal excellent agreement, with errors less than 10% over a large portion of the design space. Analytical and finite element models demonstrate that the out-of-plane deformation can be tailored by varying the structure’s geometric and material parameters. A new design space for FRP composite laminates is characterized, enabling highly flexible design. The manufacturing and modeling techniques can be extended to other geometries for the realization and analysis of arbitrarily complex surfaces.

The Effect of High Glass Fiber Content and Reinforcement Combination on Pulse-Echo Ultrasonic Measurement of Composite Ship Structures

Ship structures made of glass fiber-reinforced polymer (GFRP) composite laminates are considerably thicker than aircraft and automobile structures and more likely to contain voids. The production characteristics of such composite laminates were investigated in this study by ultrasonic nondestructive evaluation (NDE). The laminate samples were produced from E-glass chopped strand mat (CSM) and woven roving (WR) fabrics with different glass fiber contents of 30–70%. Approximately 300 pulse-echo ultrasonic A-scans were performed on each sample. The laminate samples produced from only CSM tended to contain more voids compared with those produced from a combination of CSM and WR, resulting in the relative density of the former being lower than the design value, particularly for high glass fiber contents of ≥50%. The velocity of the ultrasonic waves through the CSM-only laminates was also lower for higher glass fiber contents, whereas it steadily increased for combined CSM–WR laminates. Burn-off tests of the laminates further revealed that the fabric configuration of the combined CSM–WR laminates was of higher quality, prevented the formation of voids, and improved inter-layer bonding. These findings indicate that combined CSM–WR laminates should be used to achieve more accurate ultrasonic NDE of GFRP composite structures.

Bio-inspired composite laminate design with improved out-of-plane strength and ductility

Low failure strain and catastrophic failure are the most critical challenges of carbon fiber reinforced polymer composite laminates. To tackle these challenges, inspired by core shells, we created discontinuities in the laminate microstructure to activate extra energy dissipation mechanisms that improves flexural response. In bio-inspired laminates, embedded defects and delaminations are imposed at different thickness positions of the laminate during lamination process. The flexural properties of the proposed bio-inspired laminates were characterized using three-point bending test. Different damage modes and their sequences in conventional and bio-inspired laminates were identified using microcomputed tomography. Experimental results showed that, the flexural properties of bio-inspired composites can be tailored by changing the through-the-thickness delamination position and size. It was demonstrated that, the strength, failure strain and energy absorption ability of the optimized bio-inspired laminates, with 10 mm delamination diameter at the nearest interface to the indenter, were improved by 11.9%, 208% and 288.1% compared to conventional laminate. Moreover, these bio-inspired composites showed a progressive damage mode with pseudo-ductility response, where a slight degradation of the strength occurred followed by increased strain and sustaining the same strength up to failure strain two times larger than the initiation strain. Therefore, the proposed bio-inspired laminates showed a metal-like failure that provides warning alert to the final failure, which makes them applicable in many industrial applications.

Modelling the interfacial damage of carbon fiber reinforced polymer composite laminate under the low-velocity impact loading

This paper presents the performance of three-dimensional Puck failure criteria emphasising on the gradual degradation law to predict the structural responses, as well as the onset and propagation of failure due to different interface modelling technique. The proposed damage model is performed using Abaqus explicit analysis. Four different cohesive models are analysed using three-dimensional finite element model based on low-velocity impact loading. The structural responses are compared with experimental data taken from literature to measure the performance of such damage model. It is found out that the model adopted here responses well with test curves and demonstrates the high capability of predicting the damage in the direction of in-plane as well as out-of-plane in a composite laminate. The simplified model using combination of tie-cohesive layer technique demonstrated the balance performance between the quality of the result as well as calculation time.

Effect of interfacial fibre orientation and PPS veil density on delamination resistance of 5HS woven CFRP laminates under mode II loading

This paper presents an experimental study on the effect of interfacial fibre orientation and interleaved thermoplastic veil on Mode II interlaminar fracture toughness of 5-harness satin woven carbon fibre reinforced polymer composite laminates. Three-point End-Notched Flexure tests were carried out to determine delamination resistance, GIIC, of specimens with five fibre orientation biases and two veil densities at the midplane. Results show that delamination resistance of 5-harness satin woven laminates depends on the layup configurations at the midplane with 90/45 fibre orientation bias exhibiting the greatest resistance. The delamination resistance enhancement from polyphenylene sulfide (PPS) veil interleaves is also fibre orientation dependent but a further increase of the veil density from 10 gm−2 to 20 gm−2 offers little extra benefit. Fracture surface morphologies were examined under SEM to understand the failure mechanism and fracture process of the woven laminate under the combined effects of the interfacial fibre orientation and the veil density. Fibre orientation relative to the delamination path, surface texture misfit, and veil density are the three main contributors identified for the variation of delamination resistance of 5HS woven laminates.

On the Temperature Dependent Mechanical Response of Dynamically-loaded Shear-dominated Adhesive Structures

A mode II mechanical characterisation of the adhesive joints is performed testing shear lap joint specimens in a Split Hopkinson Tensile Bar (SHTB), equipped with a temperature chamber. The experimentallyobtained traction-separation curves were used to develop a Cohesive Zone Model (CZM) capable of representing the strain-rate and temperaturedependent mechanical response of the adhesive joints. To validate the model, End Notch Flexure (ENF) multi-material specimens made from titanium and carbon fibre reinforced polymer composite laminates were tested at different temperatures using a Split Hopkinson Pressure Bar setup with an in-house made temperature chamber. The finite element (FE) simulations of such tests employing the developed CZM showed the model’s ability to accurately predict the adhesive joints’ failure as well as to understand the failure sequence of multi-material adhesive joint combinations.

On the use of acoustic emission to identify the dominant stress/strain component in carbon/epoxy composite materials

Acoustic Emission (AE) is casually employed for monitoring the mechanical behaviour of composite media as the amount of damage and the different fracture modes can be well characterised through the evolution of the AE characteristics. However, the sensitivity of the technique allows for more than just classification of the existing damage modes in composite materials. In the present paper, the limits of AE are further pushed as it is used to characterise the stress/strain field developing in composite laminates even before damage mechanisms become evident. In addition, the change of the strain field due to damage evolution during quasi-static and fatigue experiments, as monitored by real-time Digital Image Correlation (DIC), is depicted on the shift of the AE parameters. This is of great importance in cases that detrimental shear stresses are generated in the material, leading to important interlaminar delaminations and mechanical deterioration. AE can be used in this direction to predict the upcoming damage modes and to take the necessary measures to avoid final catastrophic failure by applying intermediate repair approaches. The examined material in this study is angle-ply Carbon Fibre Reinforced Polymer (CFRP) composite laminates consisting of different off-axis plies, in which different multiaxial conditions are generated due to the inherent anisotropy of composite materials. It is demonstrated that AE can identify the dominant stress/strain component rather than just the occurring damage mode even at early loading stages, before severe fracture influences the mechanical capacity of the material.v© 2020 The Authors. Published by Elsevier Ltd.

Enhanced Infrared Sparse Pattern Extraction and Usage for Impact Evaluation of Basalt-Carbon Hybrid Composites by Pulsed Thermography.

Nowadays, infrared thermography, as a widely used non-destructive testing method, is increasingly studied for impact evaluation of composite structures. Sparse pattern extraction is attracting increasing attention as an advanced post-processing method. In this paper, an enhanced sparse pattern extraction framework is presented for thermographic sequence processing and defect detection. This framework adapts cropping operator and typical component extraction as a preprocessing step to reduce the dimensions of raw data and applies sparse pattern extraction algorithms to enhance the contrast on the defect area. Different cases are studied involving several defects in four basalt-carbon hybrid fiber-reinforced polymer composite laminates. Finally, comparative analysis with intensity distribution is carried out to verify the effectiveness of contrast enhancement using this framework.

Investigating the roles of fiber, resin, and stacking sequence on the low-velocity impact response of novel hybrid thermoplastic composites

This study investigates the effects of fiber type, resin type, and stacking sequence on the dynamic response of fiber-reinforced polymer composite (FRPC) laminates under low-velocity impact (LVI) tests. Novel thermoplastic (TP) laminates are fabricated with a newly developed liquid methyl methacrylate thermoplastic resin, Elium® 188, at room temperature. FRPCs comprising woven ultra-high molecular weight polyethylene (UHMWPE) fabrics, woven carbon fabrics, and two different hybrid systems with alternative stacking sequences of those fibers are fabricated by the vacuum-assisted resin infusion (VARI) method. Besides, equivalent thermosetting-based (TS) composites with two epoxy systems are fabricated to compare the role of matrix type. Impact tests at different energy levels are performed on the TP and TS laminates to investigate the impact characteristics, namely contact force, deflection, energy attributes, structural integrity, and failure/damage modes. Besides, the mechanics of structure genome (MSG) and the commercial finite element code ABAQUS are used to verify the experimental results for one of the developed laminates. The results demonstrate that the hybrid system with UHMWPE fibers on the sides exhibits lower structural loss up to 47% and lower absorbed energy by 18% compared to those presented by the other type of hybrid system comprising carbon fabrics on the sides. Besides, it is found that the newly developed TP laminate underwent extended plasticity and presented a ductile behavior. The newly developed TP laminate demonstrated lower structural loss up to 200%, lower contact force by 14%, and lower absorbed energy by 48% compared to those of TS counterparts.

Strength degradation and fractographic analysis of carbon fiber reinforced polymer composite laminates with square / circular hole using scanning electron microscope micrographs

AbstractIn this article, experimental study has been carried out to obtain comparative information intended for designing and assembly of structural components made of carbon fiber reinforced polymer (CFRP) composite. Investigation on tensile strength has been done on unidirectional CFRP composite laminates with hole. Effect of stacking sequence, hole size, and hole shape on tensile strength has been examined independently by open hole tensile (OHT) test. Reduction in OHT strength is observed when stacking sequence is changed from [0]8 to [0/90]2s and when the hole size is increased. However, OHT strength is noticed to get increased when hole shape is changed from circular to square. Laminates containing square shaped hole demonstrate less sensitiveness towards tensile strength and show negligible effect of stacking sequences on the normalized strength than the circular hole. Fractographic analysis figures out the failure mechanism of tested specimens by correlating their mechanical properties. SEM micrographs and data analysis reveal that axial splits and local delamination effectively blunt the stress concentration around the hole resulting in higher OHT strength and less notch sensitiveness towards tensile strength.