Thermoplastic Matrix Composites Research Articles

Automated manufacturing of composites

Long fibre reinforced polymer composite materials have found many applications in many industries, such as aerospace, automotive, marine, wind turbine, and sports. Techniques for the manufacturing of structures used in these industries have been mainly Hand Lay Up (HLU), and Liquid Composite Moulding. While there are a few automated methods of manufacturing, such as Filament Winding and Pultrusion, these techniques are restricted to make structures that consist of surfaces of revolution, or fibres that are aligned only along one direction. The conventional methods of manufacturing of composites are therefore very restricted, either in slow rate of production, or in the shapes of structures that can be made. The advent of Automated fibre Placement (AFP) machines and automated tape lay up machines have brought forward new capabilities where structures of different shapes may be manufactured at relatively higher speeds. This paper presents an overview of the applications of AFP for the processing of structures made from thermoset matrix and thermoplastic matrix composites. Advantages and disadvantages, along with issues associated with the use of this new technique in the processing of each type of material will be discussed.

Effects of Styrene-Acrylic Sizing on the Mechanical Properties of Carbon Fiber Thermoplastic Towpregs and Their Composites.

Thermoplastic towpregs are convenient and scalable raw materials for the fabrication of continuous fiber-reinforced thermoplastic matrix composites. In this paper, the potential to employ epoxy and styrene-acrylic sizing agents was evaluated for the making of carbon fiber thermoplastic towpregs via a powder-coating method. The protective effects and thermal stability of these sizing agents were investigated by single fiber tensile test and differential scanning calorimetry (DSC) measurement. The results indicate that the epoxy sizing agent provides better protection to carbon fibers, but it cannot be used for thermoplastic towpreg processing due to its poor chemical stability at high temperature. The bending rigidity of the tows and towpregs with two styrene-acrylic sizing agents was measured by cantilever and Kawabata methods. The styrene-acrylic sized towpregs show low torque values, and are suitable for further processing, such as weaving, preforming, and winding. Finally, composite panels were fabricated directly from the towpregs by hot compression molding. Both of the composite panels show superior flexural strength (>400 MPa), flexural modulus (>63 GPa), and interlaminar shear strength (>27 MPa), indicating the applicability of these two styrene-acrylic sizing agents for carbon fiber thermoplastic towpregs.

Sensitivity thermal analysis in the laser-assisted tape placement process

Nowadays, the production of large pieces made of thermoplastic composites is an industrial challenging issue as there are yet several difficulties associated to their processing. The laser-assisted tape placement (LATP) process is an automated manufacturing technique to produce long-fiber reinforced thermoplastic matrix composites. In this process, a tape is placed and progressively welded on the substrate. The main aim of the present work is to solve an almost state of the art thermal model by using an efficient numerical technique, the so-called Proper Generalized Decomposition (PGD) that considers parameters (geometrical and material) as model extra-coordinates. Within the PGD rationale the parametric temperature field is expressed in a separated form, as a finite sum of functional products, where each term depends on a single coordinate (space, time or each one of the parameters considered as extra-coordinates). Such a separated representation allows the explicit expression of the sensitivity fields, from the temperature derivative with respect to each parameter. These sensitivity fields represent a very valuable methodology to analyze and establish the influence of the critical input parameters on the thermal response, and therefore, for performing process optimization and control, as well as for evaluating the effect of parameters variability on the thermal response.

Processing of thermoplastic matrix composites through automated fiber placement and tape laying methods

Fiber-reinforced composite materials are replacing metallic components due to their higher specific strength and stiffness. Automation and thermoplastics emerged to overcome the time and labor intensive manual techniques and the long curing cycles associated with processing thermoset-based composites. Thermoplastics are processed through fusion bonding which involves applying heat and pressure at the interface. Together with automated techniques (such as automated fiber placement, and automated tape laying), a fast, clean, out-of-autoclave, and automated process can be obtained. A detailed review of thermoplastic composites processing through automated methods is presented. It sheds the light on the materials used and the different heat sources incorporated with the pros and cons of each, with concentration mainly on hot gas torch, laser, and ultrasonic heating. A thorough illustration of the several mechanisms involved in a tow/tape placement process is tackled such as heat transfer, intimate contact development, molecular interdiffusion, void consolidation and growth, thermal degradation, crystallization, and so on. Few gaps and recommendations are included related to materials, laser heat source, heat transfer model, and the use of silicone rubber rollers. A review of optimization studies for tape placement processes is summarized including the main controllable variables and product quality parameters (or responses), with some of the major findings for laser and hot gas torch systems being presented. Both mechanical and physical characterizations are also reviewed including several testing techniques such as short beam shear, double cantilever beam, lap shear, wedge peel, differential scanning calorimetry, and so on. Challenges, however, still exist, such as achieving the autoclave-level mechanical properties and complying with the porosity levels required by the aerospace industry. More work is still necessary to overcome these challenges as well as increase the throughput of the process before it can be totally commercialized.

Aplicaciones de caucho reciclado: Una revisión de la literatura

La generación de residuos de caucho se ha convertido en una preocupación global por su impacto negativo en el medio ambiente y en la salud humana. La legislación ambiental sobre la disposición de este tipo de residuos ha venido aumentando las exigencias a los fabricantes, comercializadores y usuarios, con lo cual se ha acelerado la búsqueda de alternativas para el reaprovechamiento de los residuos de caucho. Este artículo presenta una revisión bibliográfica acerca de las principales tendencias en la utilización del caucho reciclado, incluyendo aplicaciones actualmente comercializadas y otras derivadas, tanto de estudios terminados, como de líneas de investigación en desarrollo. Las aplicaciones con mayor potencial de volumen consumido son del sector infraestructura y construcciones civiles, especialmente asfaltos, concretos y materiales aislantes para construcción liviana. Algunas aplicaciones con potencial en el futuro cercano son los filtros para la limpieza de aguas contaminadas y como componente en materiales compuestos con matriz termoplástica o en poliuretano. Por último, se evidencia la pertinencia de continuar investigando sobre esta temática que posee unos retos científicos de alta relevancia, los cuales ameritan la mayor atención por el problema ambiental significativo asociado al manejo de los residuos de caucho.

An Overview of Impregnation Methods for Carbon Fibre Reinforced Thermoplastics

Carbon fibre reinforced plastics (CFRPs) can be classified according to whether the matrix is a thermoset or a thermoplastic. Thermoset-matrix composites are by tradition far more common, but thermoplastic-matrix composites are gaining in importance. There are several techniques for combining carbon fibres with a thermoplastic-matrix system. The composite’s characteristics as well as its manufacturing costs are dependent on the impregnation technique of the carbon fibre and the textile structure respectively. Carbon fibre reinforced thermoplastics (CFRTPs) are suitable for fast and economic production of high-performance components. Despite the higher material costs thermoplastic-matrix systems show cost benefits in comparison to thermoset-matrix due to substantial time savings in the production process. Moreover CFRTPs can be manufactured in large production runs. The commingling of reinforcement fibres with matrix fibres is a well-established process. Another approach is the coating of the carbon fibre with a thermoplastic subsequent to the carbon fibre production (carbonization, activation and deposition of sizing). The latter point is currently subject of research and is a promising method for further increasing the production speed. This paper presents the different possibilities of impregnating carbon fibres with a thermoplastic matrix. Diverse technologies along the process chain of the CFRTP production will be discussed.

Ultrasonic Fatigue of CFRP - Experimental Principle, Damage Analysis and Very High Cycle Fatigue Properties

Structural aircraft components are often subjected to more than 108 loading cycles during their service life. Therefore the increasing use of carbon fiber reinforced polymers (CFRP) as primary lightweight structural materials leads to the demand of a precise knowledge of the fatigue behavior and the corresponding failure mechanisms in the very high cycle fatigue (VHCF) range. To realise fatigue investigations for more than 108 loading cycles in an economic reasonable time a novel ultrasonic fatigue testing facility (UTF) for cyclic three-point bending was developed and patented. To avoid critical internal heating due to viscoelastic damping and internal friction, the fatigue testing at 20 kHz is performed in resonance as well as in pulse-pause control resulting in an effective testing frequency of ~1 kHz and the capability of performing 109 loading cycles in less than twelve days. The fatigue behavior of carbon fiber twill 2/2 fabric reinforced polyphenylene sulfide (CF-PPS) and carbon fiber 4-H satin fabric reinforced epoxy resin (CF-EP) was investigated. To study the induced fatigue damage of CF-PPS and CF-EP in the VHCF regime in detail, the fatigue mechanisms and damage development were characterized by light optical and SEM investigations during interruptions of constant amplitude tests (CAT). Lifetime-oriented investigations showed a significant decrease of the bearable stress amplitudes of CF-PPS and CFEP in the range between 106 to 109 loading cycles. The ultrasonically fatigued thermoset matrix composite showed a significantly different VHCF behavior in comparison to the investigated thermoplastic matrix composite: No fiber-matrix debonding or transversal cracks were present on the specimen edges, but a sudden specimen failure along with carbon fiber breakage have been observed. The fatigue shear strength at 109 cycles for CF-PPS could be determined to τa, 13 = 4.2 MPa and to τa, 13 = 15.8 MPa for the thermoset material CF-EP.

The influence of fiber arrangement on the mechanical properties of short fiber reinforced thermoplastic matrix composite

The influence of fiber arrangement on the mechanical properties of short fiber reinforced thermoplastic matrix composite

Forming of Thermoplastic Matrix Composites with Gas Pressure – the Influence of Blank Holder and Sheet Temperature on the Forming Pressure and Drawing Ratio

Abstract New processes for continuous fiber-reinforced thermoplastics (“organo-sheets”) offer new possibilities e. g. for the production of closed hollow bodies. In the Twin-O-Sheet Process the forming is done via gas pressure without separate diaphragms. This brings new demands on the organo-sheets with respect to gas density. In this article the influence of the forming parameters blank holder temperature and sheet temperature on the achievable gas pressure and drawing ratios with twill-weave PA6/GF organo-sheets are investigated. The results show that higher blank holder temperatures lead to higher drawing ratios despite of lower pressures. Compared to the blank holder temperature the influence of the sheet temperature on the drawing ratio is minor.

The mechanism of rate-dependent off-axis compression of a low fibre volume fraction thermoplastic matrix composite

This paper reports on the mechanism of rate-dependent off-axis compression of a unique unidirectional composite with unusually high matrix volume fraction of 65%. The test material is an E-glass fibre reinforced polypropylene composite and was subjected to quasi-static, medium and high strain rates (with strain rates from 10-3s−1 to 103s−1). This paper has shown experimental evidence of significant rate-dependence of yielding, strain softening and fracture strain of the test composite. Also, the study reports on the effect of strain rates on evolution of different failure modes of the composite. The observed rate-dependence was shown to result from the influence of the pure matrix on the constitutive behaviour of the composite. The work has used a two-process Ree-Eyring yield model of the matrix to demonstrate the origin of the observed rate-dependent yielding of the composite. The data derived in this study will be significant for further micro-mechanical modelling of finite deforming composites used in especially damage tolerant applications. Composite design engineers and stress analysis experts should benefit also from the findings in this work.

Design and manufacturing of long fiber thermoplastic composite helmet insert

Long fiber thermoplastic composite (LFT) is one type of thermoplastic polymer matrix composites reinforced with discontinuous fibers above critical fiber length. It has been increasingly used in various applications due to its excellent specific strength and specific modulus in addition to its infinite shelf life, intrinsic recyclability, and high-volume processability even for complex geometries. In this work, long carbon fiber reinforced polyphenylene sulphide (LFT C/PPS) is used to prototype a helmet insert with high rigidity for stiffening a relatively soft ballistic shell. The helmet insert is designed to have a rim along its periphery in order to offer extra rigidity and facilitate a readily clip-on with the ballistic shell. Static structural analysis is carried out for evaluating the performance of the insert. Comparison was made among different patterns of the helmet insert in their rigidity. A compression molding tool is designed and machined and the helmet insert is prototyped using LFT C/PPS. A compression test is conducted for the ballistic shell integrated with the helmet insert to validate the stiffening capability of the LFT C/PPS helmet insert.

Finite element modeling of continuous induction welding of thermoplastic matrix composites

Continuous induction welding for thermoplastic matrix composites requires an accurate modeling of the temperature distribution in the laminates, depending on the electromagnetic field. In this work, a transient three-dimensional finite element (FE) model was developed in order to study the heat transfer phenomena, and melting and crystallization in the welding area during the continuous induction welding of carbon fiber reinforced Poly(ether ether ketone) (CF/PEEK) laminates. The multiphysics problem was solved by coupling electromagnetic and heat transfer equations considering matrix melting and crystallization behavior. The model was able to simulate the continuous process along a linear path at a constant speed. The computed temperatures were in good agreement with experimental measurements. Several numerical simulation were used for selecting a processing window as a function of coil speed and current, for the welding of CF/PEEK joints. The results of welding experiments were evaluated by single lap shear tests and morphology characterization of the welded interfaces and fracture surfaces.

Effect of Natural Fibers Surface Treatment and their Reinforcement in Thermo- Plastic Polymer Composites: A Review

In previous years natural fibers are frequently used to reinforce materials. The biodegradability is the main advantage of natural fibers. The disadvantage of using natural fibers in polymer composite material is their poor adhesion ability with a polymeric matrix which affects the various physical and mechanical properties of the composite material. To overcome this disadvantage, the surface of the natural fibers needs to be modified so that a good fiber-matrix adhesion can be established. The various treatment methods such as physical treatment and chemical treatment methods for the improvement of fiber-matrix adhesion have been discussed in this paper. So the overall objective of this review paper is to highlight the previous and recent studies related to the surface treatment of natural fibers and their reinforcement in thermoplastic polymer matrix composites. The improvement in various properties specifically mechanical properties by reinforcing these fibers into thermoplastic polymer matrix composites has also been reported in this paper. Keywords: Fibers, surface modification, composites, polyethylene, polypropylene & PVC.

Hemp fiber reinforced polypropylene composites: The effects of material treatments

Abstract Natural fiber reinforced thermoplastic matrix composites have been increasingly used in semi-structural applications in automotive applications because of their good specific strength and modulus, low carbon footprint and recyclability. This research work studies the effects of material treatment(s) on the mechanical behaviors of hemp fiber reinforced polypropylene (PP) composites. The material treatment(s) are realized by chemically treating the hemp fiber with different concentration NaOH and/or adding maleic anhydride grafted polypropylene (MAPP) to the PP matrix. The purpose of the material treatment(s) is to enhance the bonding between the hemp fibers and the polypropylene matrix which otherwise has low surface energy and limited bonding. The mechanical behaviors are investigated with different combinations of material treatment(s) such as 5 wt% MAPP, 5% NaOH treated hemp fiber, 10% NaOH treated hemp fiber, and 5% NaOH + 5 wt% MAPP. 15 wt% and 30 wt% hemp fiber loadings are used in the composites with these material treatments. It is found that the material treatment(s) result(s) in composites with better mechanical properties compared to the composites without any treatment(s). The composites with 5 wt% MAPP addition show the best mechanical properties.

Additive manufacturing of thermoplastic matrix composites using fused deposition modeling: A comparison of two reinforcements

Fused deposition modeling is a fast growing additive manufacturing technology with advantages of low cost, low operation temperature, consistent prototype accuracy, and flexible material change. Fiber-reinforced plastic composite parts have been developed by the fused deposition modeling process to improve the mechanical properties of fused deposition modeling-fabricated pure thermoplastic parts which cannot be used as load-bearing parts in the actual applications. However, porosity found at the fracture interfaces of fused deposition modeling-fabricated fiber-reinforced plastic composite parts may limit their potential for direct replacement in the functional applications. The problem may result from the larger length–diameter ratio of the chopped thin fibers used in fiber-reinforced plastic composite parts fabricating. One of the possible methods to reduce the porosity is employing small length–diameter ratio particles/flakes (such as graphite) instead of chopped thin fibers as reinforcements. However, mechanical performances of the graphite-reinforced thermoplastic composites are still unknown. In this article, comparisons on porosity and tensile properties between the specimens of carbon fiber-reinforced thermoplastic and graphite-reinforced thermoplastic fabricated by fused deposition modeling process were conducted in order to test the effects of reinforcements. Fracture interfaces of the specimens after tensile testing were observed.

耐熱性熱可塑樹脂複合材料の炭素繊維再利用を主眼としたリサイクル方法

耐熱性熱可塑樹脂複合材料の炭素繊維再利用を主眼としたリサイクル方法

On the Alternate Direction Implicit (ADI) Method for Solving Heat Transfer in Composite Stamping

Thermostamping of thermoplastic matrix composites is a process where a preheated blank is rapidly shaped in a cold matching mould. Predictive modelling of the main physical phenomena occurring in this process requires an accurate prediction of the temperature field. In this paper, a numerical method is proposed to simulate this heat transfer. The initial three-dimensional heat equation is handled using an additive decomposition, a thin shell assumption, and an operator splitting strategy. An adapted resolution algorithm is then presented. It results in an alternate direction implicit decomposition: the problem is solved successively as a 2D surface problem and several one-dimensional through thickness problems. The strategy was fully validated versus a 3D calculation on a simple test case and the proposed strategy is shown to enable a tremendous calculation speed up. The limits of applicability of this method are investigated with two parametric studies, one on the thickness to width ratio and the other one on the effect of curvature. These conditions are usually fulfilled in industrial cases. Finally, even though the method was developed under linear assumption (constant material properties), the strategy validity is extended to multiply, temperature dependant (nonlinear) case using an industrial test case. Because of the standard methods involved, the proposed ADI method can readily be implemented in existing software.

Integrated Defect Classification in Manufacturing of Carbon Fibre Reinforced Thermoplastic Polymer Matrix Composites

Thermoplastic polymer matrix composites with continuous carbon fibre reinforcements are of crucial relevance in automotive industry. The mix of high performance and cost effective manufacturing makes them attractive for high volume production. However, it could be shown that production integrated end of line quality control is of strong importance to ensure continuous and traceable part quality. Besides, typical non destructive testing method specifications, higher production volumes additionally require short testing times. Herein, the application of active thermography as end of line quality control in composite production is evaluated and compared with results obtained by X-ray radiometry. It could be revealed that transient pulse phase thermography is a powerful tool to analyse part quality of continuous thermoplastic polymer matrix composites in short testing times.

About the origins of residual stresses in in situ consolidated thermoplastic composite rings

In a context of cost reduction, in situ filament winding of thermoplastic matrix composites becomes an appealing process. As residual stresses could considerably affect the produced part, models were proposed to predict process-induced residual stresses. After developing a validated thermal model of the process, mainly three different aspects are here addressed: the continuous bonding occurring during the process, the effect of the processed layer on the structure, and the effect of the curvature of the mandrel. While stresses coming from the continuous bonding appeared to be negligible, consequent levels of stresses can be achieved due to an iterative compression of the structure by the tow (supposed to be under tension). The mandrel properties and the tow tension profile followed during winding are essential parameters that might induce several different stress states. A comparison between measured and computed end-to-end openings of split rings illustrates the accuracy of the proposed models.

Composite Cylinders for Deep Sea Applications: An Overview

In order to develop the knowledge base necessary to design deep sea pressure vessels, it is essential to understand the full chain from design and manufacturing through nondestructive testing (NDT) and characterization to long-term behavior under hydrostatic pressure. This paper describes results from European and national research programs focusing on the use of composites for underwater applications over the last 20 years. Initial tests on small glass/epoxy cylinders were followed by large demonstration projects on carbon/epoxy cylinders with implosion pressures of up to 600 bar, corresponding to 6000 m depth. Numerical modeling has enabled end closures design to be optimized for test performance. Thin and thick wall cylinders have been tested under quasi-static, and long-term loading. Both thermosetting and thermoplastic matrix composites have been tested to failure, and the influence of defects and impact damage on implosion pressure has been studied. These deep sea exploitation and exploration studies were performed for oceanographic, military, and offshore applications, and extensive data are available. The aim of this paper is to indicate existing results, particularly from European projects, in order to avoid costly repetition.