The influence of moisture content on the heat affected zone and the resulting in-plane shear strength of laser cut thermoplastic CFRP

Abstract

In this paper investigations on the effect of the moisture content of thermoplastic CFRP on the laser induced heat affected zone (HAZ) and the resulting in-plane shear properties are presented. For this purpose carbon fibre reinforced polyetherimide (PEI) and polyphenylene sulphide (PPS) sheets were conditioned to different moisture contents and were then used for laser machining test specimens with contour and multipass cutting strategies. The extents of the HAZ were measured and in-plane shear tests were performed, revealing that the shear properties decrease when cutting material with high moisture content. This behaviour can be correlated with the type of HAZ which contains porosity caused by the vapourisation of water.     

Effect of electron-beam radiation on thermoplastic composites

Abstract

The effect of electron beam (EB) radiation on carbon fibre reinforced (CF) thermoplastic (PBT, PPS, PA) composites was investigated. To clarify whether crosslinking could take place without or only with the presence of a crosslinking agent, special attention was paid to the incorporation of this agent into polymer sheets with a carbon fibre content of 50% by volume. The thermal and mechanical properties of the materials before and after exposure under different irradiation doses were evaluated. For materials based on PBT, PPS and PA46, no significant changes in properties after irradiation could be observed. However, CF/PA66 exhibited some changes in the presence of a crosslinking agent after irradiation, which could be related to an irradiation-induced crosslinking reaction. The effect of irradiation on the flexural properties was insignificant but an improvement in the creep behaviour was observed. Non-reinforced PA66 plates were also manufactured and a gel content measurement indicated that crosslinking was successfully induced. Additional studies allowed the changes in the polymer due to this crosslink to be quantified.     

Effect of nitric acid surface treatment on tensile and tribological properties of thermoplastic polyimide composite filled with carbon fibre

Abstract

Polyacrylonitrile based carbon fibres were submitted to nitric acid oxidation treatments to improve the interfacial adhesion of the carbon fibre reinforced polyimide (CF/PI) composite. The carbon fibre surfaces were characterised by X-ray photoelectron spectroscopy. Nitric acid oxidation not only affects the oxygen concentration, but also produces an appreciable change in the nature of the chemical functions, namely the conversion of hydroxy type oxygen into carboxyl functions. Nitrogen concentration of nitric acid oxidation treated carbon fibre is ～1·2 times higher compared with untreated one. The mechanical and tribological properties of the CF/PI composites treated with nitric acid oxidation were investigated. Results showed that the tensile strength of the CF/PI composites improved remarkably due to nitric acid treatment along with enhancement in friction and wear performance.     

Variable frequency microwave processing of thermoplastic composites

Abstract

The range of applications for variable frequency microwave (VFM) facilities (2–18 GHz) has been extended to thermoplastic composites. Five thermoplastic polymer matrix composites are processed and discussed, including 33 wt-% random carbon fibre reinforced polystyrene [PS–CF (33%)], and low density polyethylene [LDPE–CF (33%)]; 33 wt-% random glass fibre reinforced polystyrene [PS–GF (33%)], low density polyethylene [LDPE–GF (33%)]and Nylon 66 [Nylon 66–GF (33%)]. Bond strengths of lap joints were tested in shear and results were compared with those obtained using fixed frequency (2·45 GHz) microwave processing. The primer or coupling agent used was a 5 min, two part adhesive containing 100%liquid epoxy and 8% amine, which was more readily microwave reactive than the composites themselves. The VFM was operated under software control, which provided automatic data logging facilities. Results indicate that VFM can produce strong bonds for PS and LDPE.     

先进热塑性树脂预浸料用原材料

研究分析表明,现有碳纤维与热塑性树脂的相容性差,且其使用的环氧上浆剂不能承受250℃以上工艺温度,不宜用于热塑性树脂预浸料的制备;此外,目前热塑性树脂预浸料制备方法多种多样,不同的工艺方法要求热塑性树脂的形态也不尽相同。指出必须尽快开发出适合热塑性树脂预浸料的碳纤维,满足不同预浸工艺要求和形态各异的热塑性树脂基体。     

Glass fibre orientation within injection moulded automotive pedal: Simulation and experimental studies

Abstract

Modelling and measurement of the fibre orientation distribution within a reinforced thermoplastic automotive clutch pedal are presented. Products have been manufactured on an injection moulding machine equipped with accurate process monitoring. The fibre orientation distributions at selected points within the pedal were measured using a fully automated, polished section/reflection microscopy image analysis system. Simulation was undertaken using commercial software with a fibre orientation prediction algorithm. The predicted fibre orientation distributions are compared with experimental results in order to assess the accuracy of the software in both thin and thick (～5 mm) sections of the pedal.     

New GMT material suitable for various polymers and high glass fibre content

Abstract

As a kind of long fibre reinforced thermoplastic, a new glass mat thermoplastic (GMT)-like material is introduced. It is designed to be suitable for various polymers and high glass fibre (GF) content, which might be a promising attempt to overcome the limit of conventional GMT material (PP matrix and maximum 40 wt-% GF). The concept is based on a multi-layered hybrid structure consisting of several thin GF sub-layers and polymer films having an inherently high viscosity. They are then needle-matted all together. The capability of higher GF content was derived from the porosity changes under pressure and the cross-sectional view after impregnation. It was finally confirmed by measurement of flexural properties up to 70 wt-% of GF content in PP grade. Moreover, PA6 grade was investigated to show the other capability of multi-layered hybrid mat for various polymers.     

Mechanical and viscoelastic properties of butadiene–styrene thermoplastic and oxidized carbon fibre composites

The mechanical and dynamic properties of oxidized carbon fibre and butadiene–styrene thermoplastic elastomer (SBS) composites were studied as a function of the level of fibre oxidation and in comparison with the properties of composites reinforced with untreated commercial carbon fibre. As a general rule, fibre oxidation gives rise to materials with improved mechanical properties—greater tensile and tear strengths. The improvements accomplished depend on the degree of fibre oxidation. The effects of long exposure times to oxidizing agents were tested on the experimental samples, i.e. increase in the number of functional surface groups and loss in mechanical strength due to a decrease in the L/d ratio, properties which act in opposite directions in the composite. Storage modulus retention with increasing strain amplitude is directly proportional to the number of functional groups incorporated into the fibre surface, whereas at low strain amplitude it is proportional to fibre strength, measured in terms of the L/d ratio after processing. It is suggested that improved adhesion at the matrix–fibre interface is obtained through the functional groups of the oxidized fibre. As a consequence of fibre–matrix interface and at any frequency, the damping peak temperature is shifted towards higher ranges and at the same time the apparent activation energy of the relaxation process is observed to increase.     

Fire reactions of ceramic and polymer moulding composites

Abstract

Abstract

Low cost ceramic dough moulding compounds/composites (CDMC) are composed of inorganic metal silicates and chopped fibre reinforcements. This paper investigates the fire reactions of these materials under severe thermal and heat conditions. This research is targeted to potential applications in the replacement of glass fibre reinforced polymeric insulation materials such as phenolic composites as engine heat shields which experience high temperature and heat transmission. The materials developed can provide good properties, including heat insulation with high thermal stability for engine drafts, where traditional glass/phenolic composites were used and gave a very short life cycle. This work compares the thermal properties of the glass fibre reinforced phenolic composites and metal silicate composites produced under the same processing conditions. The results show that CDMC possesses significantly better thermal stability and heat resistance in comparison with phenolic moulding composite (phenolic dough moulding composites). The indication was that under the testing condition of heat flux of 75?kW?m^?2 intended for materials used for applications in marine, transport and possibly nuclear waste immobilisation, the integration of the CDMC was kept intact and survived as a high temperature insulation material.     

剑麻预处理对热塑性淀粉复合材料力学性能及降解性能的影响

采用碱、蒸汽爆破等对剑麻纤维进行预处理,考察了不同预处理方法对剑麻纤维增强热塑性淀粉力学性能及降解性能的影响。结果表明:碱处理能够提高复合材料的力学性能,延长材料降解周期,是制备剑麻纤维增强热塑性淀粉复合材料有效的预处理方法;剑麻纤维增强热塑性淀粉的机理是甘油在淀粉及剑麻纤维之间起到桥梁作用,提高了热塑性淀粉与剑麻纤维的界面结合力,从而提高了复合材料的力学性能。     

The effect of traditional flame retardants,nanoclays and carbon nanotubes in the fire performance of epoxy resin composites

The effectiveness of distinct fillers, from micro to nano‐size scaled, on the fire behaviour of an epoxy resin and its carbon fibre reinforced composites was assessed by cone calorimetry. The performance was compared not only regarding the reaction to fire performance, but also in terms of thermal stability, glass transition temperature and microstructure. Regarding the fire reaction behaviour of nanofilled epoxy resin, anionic nanoclays and thermally oxidized carbon nanotubes showed the best results, in agreement with more compact chars formed on the surface of the burning polymer. For carbon fibre reinforced composite plates, the cone calorimeter results of modified resin samples did not show significant improvements on the heat release rate curves. Poorly dispersed fillers in the resin additionally caused reductions on the glass transition temperature of the composite materials. Copyright © 2016 John Wiley & Sons, Ltd.     

Investigation on flame retardancy and rheological and thermomechanical characterisation of multiwall carbon nanotube reinforced nanocomposites

Abstract

In the present work, the influence of multiwalled carbon nanotubes (MWCNTs) on the flame retardancy and rheological, thermal and mechanical properties of polybutilen terephthalate (PBT) and polypropylene (PP) matrixes has been investigated. The carbon nanotube content in the thermoplastic materials was 2 and 5?wt‐%. The nanocomposites were obtained by diluting a masterbatch containing 20?wt‐% nanotubes using a twin‐screw extruder and the thermal properties were analysed by differential scanning calorimetry and thermogravimetric analysis; thermomechanical properties were determined by dynamic mechanical thermal analysis and the rheological behaviour was studied by a Thermo Haake Microcompounder. The results concerning the flame retardancy show that the MWCNTs are not equally effective as flame retardants in PP and PBT. The ignition time is increased only for PBT whereas the extinguishing time is decreased for PP and PBT. The reinforcement of the thermoplastics with multiwall carbon nanotubes is improved regarding the mechanical and thermal properties of the nanocomposites compared to pristine materials and the behaviour of thermoplastic nanocomposites regarding fire retardancy depends on the nature of the polymeric matrix.     

The effect of titanium surface treatment on the interfacial strength of titanium – Thermoplastic composite joints

Co-consolidated titanium – carbon fibre reinforced thermoplastic composite hybrid joints show potential for application in aerospace structures. The strength of the interface between the titanium and the thermoplastic composite is crucial for the strength of the entire hybrid joint. Application of a surface treatment on the titanium is an effective way to improve this interfacial strength. This paper evaluates the effect of several titanium surface treatments on the interfacial strength between titanium and carbon fibre reinforced polyetheretherketone (PEEK) or polyetherketoneketone (PEKK). Furthermore, the underlying bonding mechanisms, activated by these surface treatments, are studied. The research result shows that the grit blasted titanium – carbon fibre reinforced PEKK interface outperforms the other interfaces.     

Effect of low UD carbon fibre content on mechanical properties of in situ polymerised cyclic butylene terephtalate

Abstract

Carbon fibre reinforced cyclic butylene terephtalate were produced by a low pressure method, the impregnating temperature and the cooling speed were investigated using plate–plate rheometry and differential scanning calorimetry. The effects of low fibre volume fraction of carbon fibre reinforcement (～20?vol.‐%) on the mechanical properties were examined by tensile and flexural tests and Charpy dynamic impact test. The results showed a significant increase in Young’s modulus and ultimate strength and were supported by scanning electron microscopy pictures of the broken surfaces to study fibre wet‐out.     

Comparison of water permeation behaviour in poly(dimethylsiloxane), poly(ether ether ketone), and glass fibre reinforced composites using dielectric spectroscopy

Abstract

This paper describes the use of dielectric spectroscopy to characterise the absorption of water by three different classes of polymeric materials: an elastomer, poly(dimethylsiloxane); a thermoplastic, poly(ether ether ketone); and two composites, polyester and vinyl ester glass fibre reinforced laminates (GRP). Novel approaches have been used to assess water absorption by the elastomer and the GRP and the results are critically assessed. The data for all the materials are discussed in the context of their molecular structures. The applicability and limitations of these dielectric methods for the assessment of water absorption in polymeric materials that have considerably different physical properties is demonstrated.     

Predicting mechanical properties of multiscale composites

Abstract

The effect of carbon nanotube (CNT) integration in polymer matrixes (two-phase) and fibre reinforced composites (three-phase) was studied. Simulations for CNT/polymer composites (nanocomposites) and CNT/fibre/polymer composites (multiscale) were carried out by combining micromechanical theories applied to nanoscale and woven fibre micromechanic theories. The mechanical properties (Young’s modulus, Poisson’s ratio and shear modulus) of a multiscale composite were predicted. The relationships between the mechanical properties of nano- and multiscale composite systems for various CNT aspect ratios were studied. A comparison was made between a multiscale system with CNTs infused throughout and one with nanotubes excluded from the fabric tows. The mechanical properties of the composites improved with increased CNT loading. The influence of CNT aspect ratio on the mechanical properties was more pronounced in the nanocomposites than in the multiscale composites. Composites with CNTs in the fibre strands generated more desirable mechanical properties than those with no CNTs in the fibre strands.     

Effect of short fibers on residual permeability and mechanical properties of hybrid fibre reinforced high strength concrete after heat exposition

Mechanical and permeability performance of fibre reinforced high strength concrete after heat exposition were evaluated in the experimental study. Cylindrical concrete specimens were exposed to heat with the rate of 10 °C/min of up to 400 °C. In order to study the effect of short fibres on residual performance of heated high strength concrete, polypropylene and steel fibres had been added into the concrete mix. The melting and vaporization of its fibre constituents were found to be responsible for the significant reduction in residual properties of polypropylene fibre reinforced high strength concrete. In terms of non-destructive measurement, UPV test was proposed as a promising initial inspection method for fire damaged concrete structure. Furthermore, the effect of hybrid fibre on the residual properties of heated fibre reinforced high strength concrete was also presented.     

Energy based method for numerical fatigue analysis of multidirectional carbon fibre reinforced plastics

Abstract

This paper describes experiments on multiaxial fibre reinforced plastic laminates, which were performed to obtain calibration data for numerical fatigue analyses. For this purpose, fatigue tests of laminates with multidirectional layers subjected to constant amplitude and block loading (0?≤?R?<?1 or R>1) were analysed. The presented simulation results display the fatigue behaviour of carbon fibre reinforced plastics for unidirectional loading conditions and a selected laminate.     

Hemp fibre as alternative to glass fibre in sheet moulding compound Part 1 – influence of fibre content and surface treatment on mechanical properties

Abstract

Hemp fibre mat reinforced unsaturated polyester composites were fabricated using a conventional sheet moulding compound process. The influence of fibre and CaCO₃ filler content on strength and stiffness of these hemp fibre reinforced sheet moulding compounds is reported and compared with data for chopped glass fibre reinforced sheet moulding compounds. In addition the influence of alkaline and silane treatments of the hemp fibres is evaluated. The experimental data are compared to modified versions of the Cox–Krenchel and Kelly–Tyson models, supplemented with parameters of composite porosity to improve the prediction of composite tensile properties. A good agreement was found between the modified models and experimental data for strength and stiffness. The results indicate that hemp fibre reinforced sheet moulding compounds are of interest for low cost engineering applications that require high stiffness to weight ratios.     

Interlaminar toughness characterisation of 3D woven carbon fibre composites

Abstract

The addition of reinforcement in the through thickness direction using three-dimensional (3D) weaving techniques has been shown to improve the delamination toughness of composite materials, mitigating the reduced out of plane performance of traditional composite materials. At present, the optimum architecture for improving delamination resistance is uncertain. To address this, three geometries of 3D woven carbon fibre reinforced epoxy composites were evaluated in mode I using the double cantilever beam test method. Mode II testing was also carried out using the end loaded split and four-point end notch flexure test methods. For large delaminations (i.e. when the R curve reaches its plateau value), an orthogonal weave is found to be most effective in resisting delamination propagation in mode I and is comparable to the layer to layer architecture in mode II. In all cases, an angle interlock weave appears to be less effective than either the orthogonal or layer to layer weaves.