Polymer Composite Laminates Research Articles

Tailoring of tensile and dynamic thermomechanical properties of interleaved chemical-treated fine almond shell particulate flax fiber stacked vinyl ester polymeric composites

Natural fiber and particulates are being exploited to attain eco-friendly products for construction and automotive sectors. These sectors are moving towards the use of high damping characteristic natural biofibers and particulate-reinforced polymer composite as part of the structural components. In this work, woven flax fiber (0° and 90°) and almond shell particulates were used. They were subsequently treated with alkaline and acetylene chemical solution separately. Polymer composite laminates were prepared using a vinyl ester resin as matrix and by stacking flax fibers and almond particulates interleaved in an alternative sequence using the hand layup technique. This was followed by hydraulic pressing. Composite laminates were fabricated by varying the almond shell particulate weight fraction of 0%, 5%, 10%, and 15%. Mechanical properties such as tensile and flexural strength were experimentally measured. Dynamic thermomechanical analysis was conducted on the alkaline-treated and untreated composites with different frequencies for the assessment of the damping characteristics. The alkaline-treated interleaved almond shell and flax fiber composite showed considerably higher damping characteristics. This could be due to the improved adhesion between the matrix and reinforcements. An addition of almond shell particulate positively increased the strength and stiffness of composites.

Temperature effects on joint strength and failure modes of hybrid aluminum–composite countersunk bolted joints

This paper presents the effects of temperature on the damage initiation and growth in the carbon fiber-reinforced polymer composite laminate of a hybrid aluminum–composite countersunk bolted joints designed for the bearing failure mode. Strain gage measurements conducted using an Instron testing machine coupled to a temperature-controlled chamber together with a detailed three-dimensional finite element model incorporating geometric, material and friction-based full contact nonlinearities are used to investigate the temperature effects on the progressive damage analysis of the orthotropic material model. The progressive damage analysis material model integrates the lamina nonlinear shear deformation, Hashin-type failure criteria and strain-based continuum degradation rules, being developed using the UMAT user subroutine in the MSC Patran-Nastran (MSC Software Corporation) commercial software. The results showed that the temperature effects on damage initiation and failure modes are quite accurately predicted by the progressive damage analysis material model, which proved to be computationally efficient and therefore can predict failure propagation and damage mechanisms. A low temperature increases the limit and ultimate forces and produces net-section failure, while a high temperature favors a bearing failure and even shear-out of the composite adherend of the hybrid aluminum–composite countersunk bolted joint.

Experimental investigation on novel drilling strategy of CFRP laminates using variable feed rate

This study focused on the influences of drilling parameters on hole quality and thrust force in drilling of carbon fiber-reinforced polymer (CFRP) composite laminates via variable feed rate. Drilling experiments were carried out by using three different cutting speeds, feed rates and the qualities of tungsten carbide drill. Scanning electron microscopy and coordinate measurement machine were used for hole surface damage and diameter analyses, and also a portable instrument and 3D optical profilometer were utilized for surface roughness measurement. It was identified that thrust force (Fz), delamination factor (Fd) and average surface roughness (Ra) values attained in drilling processes by variable feed rate are lower than those of constant feed rate with average of 14%, 3% and 18%, respectively. Besides, the hole diameter (D) values obtained with variable feed rate in hole exit were higher than those of constant feed rate. Moreover, the higher Fz values were obtained with diamond-coated and TiAlN-coated drills than those of uncoated drill with 55% and 77%, respectively. The interactive influences of drilling parameters on machinability factors were evaluated via analysis of variance, and then, the most significant parameter was specified as the feed rate for Fd, just as the drill quality for Fz, Ra and D. According to the experimental and statistical results, we suggested that the novel drilling strategy is a significant alternative for the step hole and conventional drilling of CFRP laminates.

Low-velocity impact damage research on CFRPs with Kevlar-fiber toughening

This paper provides a comprehensive understanding of the influence mechanism of short fiber toughening on low-velocity impact resistance of carbon fiber reinforced polymer composite laminates (CFRPs). Three kinds of layup laminates with and without short Kevlar-fiber toughening were designed and experimental tests were conducted using a drop-weight impact machine. After the low-velocity impact test, ultrasonic C-scan and industrial computed tomography (ICT) were utilized to comprehensively reveal the internal damage, including damage area and damage distribution. Based on the energy absorption and the impact dynamic responses, mechanical behaviors of CFRPs were analyzed in detail. Furthermore, the residual compression strength and failure strain of CFRPs with and without short Kevlar-fiber toughening were tested. It was observed that damage resistance of toughened laminates at lower impact energy did not show obvious advantages, but the compression-after-impact (CAI) strengths and the failure strain values improved under all energy levels with short Kevlar-fiber toughening. Three-dimensional distribution of internal damage and electron microscope analysis, together with fracture toughness analysis, were employed to explain the experimental findings and relevant mechanisms.

Tensile and flexural damage response of symmetric angle‐ply carbon fiber‐reinforced epoxy laminates: Non‐linear response and effects of thickness and ply‐stacking sequence

Advanced fiber reinforced composites have excellent specific strength and stiffness properties, but tend to be limited by linear elastic response and sudden, brittle failure. This lack of ductility greatly limits the structural efficiency of reinforced composite designs. Hence, achieving some non‐linear behavior is desirable and it can help composite structures to maintain functionality even when they are overloaded to improve safety and reduce the applied safety factors. The aim of this study is to characterize and assess the effect of laminate thickness and the type of scaling technique on the damage response of symmetric angle‐ply carbon fiber‐reinforced polymer (CFRP) composite laminates subjected to tensile and flexural loading. This study considers the different behavior of the composite material under tension and compression in order to evaluate their influence on the failure modes. Tensile and three‐point bending tests were carried out to determine the mechanical response in terms of strength and stiffness of the different CFRP laminates. Optical micrographs of failed samples were used to assess damage mechanisms of the different configurations. It was observed that non‐linear behavior and high strains to failure could be achieved with angle‐ply laminates. Furthermore, the maximum flexural strength increased and maximum flexural strain decreased as laminate thickness increased. Finally, the results obtained demonstrate that introducing ply clustering had a negative effect on the mechanical performance and pseudo‐ductility exhibited by angle‐ply laminates. POLYM. COMPOS., 40:3678–3690, 2019. © 2019 Society of Plastics Engineers

A Fatigue Damage Model for FRP Composite Laminate Systems Based on Stiffness Reduction

This paper introduces a stiffness reduction based model developed by the authors to characterize accumulative fatigue damage in unidirectional plies and (0/θ/0) composite laminates in fiber reinforced polymer (FRP) composite laminates. The proposed damage detection model is developed based on a damage evolution mechanism, including crack initiation and crack damage progress in matrix, matrix-fiber interface and fibers. Research result demonstrates that the corresponding stiffness of unidirectional composite laminates is reduced as the number of loading cycles progresses. First, three common models in literatures are presented and compared. Tensile viscosity, Young’s modulus and ultimate tensile stress of composites are incorporated as key factors in this model and are modified in accordance with temperature. Four types of FRP composite property parameters, including Carbon Fiber Reinforced Polymer (CFRP), Aramid Fiber Reinforced Polymer (AFRP), Glass Fiber Reinforced Polymer (GFRP), and Basalt Fiber Reinforced Polymer (BFRP), are considered in this research, and a comparative parameter study of FRP unidirectional composite laminates with different off-angle plies using control variate method are discussed. It is concluded that the relationship between the drop in stiffness and the number of cycles also shows three different regions, following the mechanism of damage of FRP composites and the matrix is the dominant factor determined by temperature, while fiber strength is the dominant factor that determine the reliability of composite.

Matrix cracking in polymer matrix composites under bi-axial loading

A model to predict the matrix crack evolution in a continuous fiber polymer composite laminate under in-plane bi-axial static loading has been presented in the current work. Oblique co-ordinate based shear lag analysis was used to estimate the stress distribution inside the cracked [0/90] s cross-ply T300/934 carbon fiber reinforced plastic (CFRP) laminate. Weibull probability distribution has been used to account for the variation in ply transverse strength. Size-dependent strength due to variation in ply thickness has been accounted for by appropriate volume scaling based Weibull scale factor. The Weibull parameters have been estimated using a ‘master laminate’ crack evolution data. By applying incremental stress to the laminate, using the probabilistic variation of transverse strength and the stress at a material point, the new crack location has been identified using the Hashin matrix cracking criterion. The reciprocal of the normal distance between two cracks has been termed as crack density. The crack density evolution for cross-ply laminates with an increase in applied loading has been estimated for various bi-axial ratios and compared with the data available from the literature. A good correlation is found to exist between the literature evolution data and current simulation predictions.

Cost-effective and efficient resin-injection device for repairing damaged composites

Traditionally, the main structural components of land transport vehicles, e.g. passenger vehicles and trucks, have been made of metals such as steel and aluminium. As the number of vehicles increases on the road, global effort to reduce pollutant emission has put pressure on the vehicle manufacturers to design and manufacture fuel-efficient vehicles using strong and light-weight structures made of materials such as fibre-reinforced polymer composite (FRP) laminates [1] . For instance, with regard to the new Volvo performance car, Polestar 1, a majority of the parts in the upper body, including doors, bonnet and boot lid, are made of carbon FRP (CFRP) laminates [2] . Interestingly, this design not only provides for maximum stiffness and lightness, but reduces the weight of the upper body, lowers the vehicle’s centre of gravity that results in enhanced handling, performance and drivability [2] .

Effect of nanofiller on fibre laser drilling quality of carbon fibre reinforced polymer composite laminates

Laser machining of carbon fibre reinforced polymer composites is a challenging task due to a significant difference between physical and thermal properties of the constituent materials, i.e. polymer matrix and carbon fibres. This results in extended heat-affected zone (HAZ), taper kerf and poor surface finishing. This paper focuses on an investigation, attempting to minimise the divergence in the decomposition temperature of carbon fibres and epoxy resin by adding multi-walled carbon nanotubes in polymer matrix as a secondary reinforcement. High thermal conductivity of multi-walled carbon nanotubes increases the thermal diffusivity of polymer matrix, which in turn reduces the matrix recession. In addition, laser power and scan speed was also considered as an input parameter and their influence on output responses such as HAZ, taper angle and surface roughness has been studied. To analyse the effect of multi-walled carbon nanotubes on the resultant thermal damage, an innovative technique, i.e. scanning acoustic microscopy was used. This technique provides a ply-by-ply damage analysis. C-scans of the top and bottom surface of the machined holes in the composite were also carried out. Further, micrographs of the holes were taken to analyse the quality of the holes using field-emission scanning electron microscope. The obtained results indicated that HAZ, taper angle and surface roughness of holes decreased by ∼30%, ∼47% and ∼43%, respectively, with 1.5 wt% multi-walled carbon nanotubes doped carbon fibre reinforced polymer laminates, when compared with the results obtained from experiments with neat carbon fibre reinforced polymer composite laminates.

Direct monitoring of hole damage in carbon fibre-reinforced polymer (CFRP) composites

Carbon fibre-reinforced polymer (CFRP) composite laminates have good specific material properties, these composites are therefore widely used by the high tech industries. Machining operations are often necessary in order to achieve dimensional requirements. However, CFRP is a difficult-to-cut material due to its non-homogenous and anisotropic features and the strong wear-effect of carbon fibres on the cutting tool. Increasing hole numbers causes the increase of cutting edge radius of the cutting tool, therefore hole damages (uncut fibres, delamination etc.) occur more often. The main objective of the present paper is to minimize uncut fibres in CFRP using direct monitoring of hole damage. Firstly, numerous orbital drilling experiments were conducted and the characteristics of uncut fibres were analysed. Secondly, the orbital drilling experiments were repeated with direct monitoring of uncut fibres and process control was applied in order to decrease the size of the burr area. Results show that hole damage decreased with the application of the used process control.

Fabrication and impact output voltage characteristics of carbon fiber reinforced polymer composites with lead-free piezoelectric nano-particles

Wearable Internet of Things (IoT) devices for sports require an innovative design of a self-powered technology that is able to wirelessly transmit and receive the signal (force, ambient condition) forms a body wearing item, relying upon the vibration/impact energy harvesting materials that possess lightweight but excellent resistance to intense exercise. In this study, piezoelectric hybrid carbon fiber reinforced polymer (CFRP) composite laminates are developed by embedding potassium sodium niobate (KNN) nano-particle filled epoxy interlayer, and the composite samples are successfully polarized. The output voltage of the samples due to impact load is then measured. The results show that a voltage higher than 50 mV is generated. Our work represents an important step forward in the development of piezoelectric CFRP composite materials for energy harvesting applications and opens the door for further development of lightweight, robust and efficient energy harvesting sport equipment.

Comparative Structural and Mechanical Studies on Polyamide 6 Knitted‐Reinforced Single Polymer Composites Prepared by Different Reactive Processing Techniques

Single polymer laminate composites based on anionic polyamide 6 (PA6) matrix‐reinforced by PA6 knitted textile structures (KSPC) were produced by nylon reactive injection molding and powder coating/compression molding (PCCM) processing techniques. The effect of the reinforcement's structure and the fiber volume fraction on the mechanical properties of the knitted‐reinforced PA6 composites resulting from the two methods were investigated and compared. The morphology and the crystalline structure of KSPC materials were studied to identify the main factors determining the tensile properties. The results showed that the PCCM method produced laminate composites with higher Young's modulus and mechanical strength in tension. Microscopy, differential scanning calorimetry and X‐ray diffraction experiments were carried out to correlate the morphology and crystalline structure of the composites and their precursors with the different tensile behavior of KSPC prepared using the two techniques. The microscopy and X‐ray scattering studies suggested the formation of a transcrystalline layer at the matrix/reinforcement interface. POLYM. COMPOS., 40:E886–E897, 2019. © 2018 Society of Plastics Engineers

A micromechanical model for the analysis of multidirectional fiber reinforced polymer laminates

A new three-dimensional (3D) micromechanical model is proposed to simulate the arbitrary multidirectional carbon fiber reinforced polymer (CFRP) composite laminates. Carbon fiber is assumed as transversely isotropic and linear elastic, matrix is assumed as isotropic and elastic–plastic. Maximum strain criterion is used to describe the failure of fiber and matrix. The stresses, strains and damage are described in the fiber and matrix levels, but the debonding between the fiber and matrix and the delamination between two plies are not modeled in the present analysis. Numerical analyses of nonlinear mechanical behavior of angle-ply [±θ]2s under tension are conducted to verify the validity of the present micromechanical model. Numerical results of nonlinear mechanical behavior, negative Poisson’s ratio through the thickness direction, and stress distribution on the free edge show good agreement with previous experimental and analytical results.

Microstructural-mechanical properties relationship in single polymer laminate composites based on polyamide 6

This paper studies the flexural and the impact properties of polyamide 6-based knitted reinforced single polymer composites (KSPCs) prepared by compression molding of powder-coated textile structures. To prepare matrix component, polyamide 6 microparticles (MPs) were synthesized by activated anionic ring-opening polymerization of ε-caprolactam in solution and then used for powder-coating of the knitted structures. The influence of the reinforcements' architecture, plies orientation, stacking order and fiber content on the final mechanical properties of KSPCs were investigated. Rib1 × 1 and Jersey knitted structures were selected as reinforcements and treated by a stretching-annealing procedure to modify their mechanical properties. The anisotropic tensile and compression properties imparted by the knitted structures were found to be the major factors determining the impact and flexural behavior of KSPCs. Moreover, reinforcement's crossover points, the plies orientation and the presence of a transcrystalline layer at the matrix-reinforcement interface were identified as relevant parameters. The fracture mechanism of KSPCs was linked to the morphology and crystalline structure of the resulting composites and investigated by simulation and finite element analysis of knitted reinforcements.

In-situ structural health monitoring of glass fiber reinforced composites by tufted reinforcement

Through-the-thickness reinforcement (TTR) techniques have been increasingly applied to fiber-reinforced polymer composite laminates to reduce the issues caused by the weak out-of-plane properties which can reduce significantly their load-bearing capacity. The present work investigates the electrical response of carbon tuft threads as reinforcements of GFRP omega stiffened panel. Besides the mechanical contribution of the tuft reinforcements to the composites structures, this study focuses on the evaluation of the electrical response on the tufted yarns as a means of monitor the structural health. The first studies consisted of evaluating GFRP composite laminate plates reinforced with carbon tufts by means of the electrical response through tufts to damage generated by multiple low-velocity impacts. Once the tufts exhibited their ability to respond continuously while increasing damage, pull-off mechanical tests were performed in the omega stiffeners assisted by electrical resistance measurements as well as acoustic emission (AE) and Digital Image Correlation (DIC). The results showed that the measures of electric resistance on the yarns are capable to distinguish important events during the mechanical tests, as the delamination and tuft failure. Furthermore, they are in common agreement with the cumulative energy on AE and strain field response on DIC.

Evaluation of Bonding Quality in the Carbon Fiber--Reinforced Polymer (CFRP) Composite Laminates by Measurements of Local Vibration Nonlinearity

ABSTRACTA new approach to monitoring the quality of adhesive bonding in the carbon fiber--reinforced polymer (CFRP) is developed by using a local nonlinear response of the laminate. It is shown that a degraded (contaminated) boundary layer of the adhesive contributes to an overall nonlinear response of the laminate that enables to evaluate and quantify bonding quality caused by various types and levels of single contaminations. In the context of aviation applications, two typical stages during the life of a structural part for which the adhesive properties of a bonding joint could be degraded were considered: the production process and the maintenance/repair scenario. All kinds of single contaminations studied result in enhancement of the nonlinear response of the CFRP laminate, which is an indication of deterioration of the bonding quality. The effect of multiple contaminations confirms a cumulative decline of adhesion caused by increase of the contents of single contamination components.

Damage Progression in Thick Curved Composite Laminates under Static and Fatigue Loading

In this study, damage behavior of curved carbon fiber reinforced polymer (CFRP) composite laminates that are important sub-structures (ribs, shear webs and spar flanges etc.) for wind turbine blades are investigated under static and fatigue loading conditions. Cross-ply curved specimen consisting of groups of three 0° and 90° layers is used for clear observation of the matrix cracking in thicker plies. Damage mechanisms and locations under static and fatigue loadings are examined. In the experiments, failure is found to initiate in the first group of 90° layers under static loading while it is found to occur in the second group of 90° layers under fatigue loading. The overall goal of the project is to contribute to development of design techniques or local reinforcement methods to increase fatigue life and durability of these curved sub-structures used in wind turbine blades.

3D particle models for composite laminates with anisotropic elasticity

Abstract This paper presents an assessment of three different particle based approaches for 3D modelling of fibre reinforced polymer (FRP) composite laminates with anisotropic elasticity, namely 3D Discrete Lattice model, 3D Hexagonal Close Packing model and Extended 2D Hexagonal and Square Packing model. These approaches are compared and evaluated against experimental results using a 0 ∘ ply lamina case. It has been confirmed that the Extended 2D Hexagonal and Square modelling approach in Discrete Element Method (DEM) is capable of modelling 3D composite laminates with better efficiency. Angle-ply lamina and two different laminates are modelled with the chosen particle approach. Good agreements between DEM, Finite Element and theoretical results prove the capability of this developed DEM approach for modelling the elastic behaviour of general FRP composite lamina and laminates.

3D finite element analysis of slot milling of unidirectional glass fiber reinforced polymer composites

The applications of glass fiber reinforced polymer composite materials are increasing in many industries, such as automobile, aerospace, construction, marine, and defense. The slot milling is an important machining operation to reduce the excess material and to bring the component to the required final shape and size. However, machining the glass fiber reinforced polymer composite laminate is still challenging due to its non-homogeneity and anisotropic properties. In this research, 3D finite element model is developed using ABAQUS/explicit to investigate the cutting forces, chip formation process, and the laminate failure modes. The material model is created using Autodesk HELIUS PFA and the 3D Hashin’s criteria are incorporated to characterize the failure modes. The finite element model effectively analyzes the interaction between tool and laminate, to evaluate the possible failure modes of the GFRP laminate, effects of cutting forces for different cutting speeds, and feed rates during the slot milling process. Moreover, the finite element simulation results are validated by comparing with the experimental results and the literature. From the investigation, it is found that the effect of cutting speed and feed rate involves more in the chip characteristics, which is confirmed with the scanning electron microscope images of the milled chips. The chips obtained are mostly discontinuous fractured chips in powder form with fiber pullout and delaminated fibers.

Eddy current pulsed thermography for ballistic impact evaluation in basalt-carbon hybrid composite panels.

In this paper, eddy current pulsed thermography was used to evaluate ballistic impact damages in basalt-carbon hybrid fiber-reinforced polymer composite laminates for the first time, to our knowledge. In particular, different hybrid structures including intercalated stacking and sandwich-like sequences were used. Pulsed phase thermography, wavelet transform, principle component thermography, and partial least-squares thermography were used to process the thermographic data. Ultrasound C-scan testing and X-ray computed tomography were also performed for comparative purposes. Finite element analysis was used for validation. Finally, an analytical and comparative study was conducted based on signal-to-noise ratio analysis.