Evaluation of the interfacial properties of polypropylene composite laminates,reinforced with paper sheets

Laminates, composed of different papers and polypropylene (PP), were fabricated by a manual stacking and hot pressing. The laminates were characterized by mechanical testing and the results were compared to glass fiber reinforced PP. Furthermore, a detailed evaluation of the interfacial properties and the paper structures was carried out by means of data modeling via rule of mixtures (ROM), as well as electron microscope (SEM) analysis. For investigating the influence of the laminate’s composition on the water adsorption behavior, water diffusion coefficients were determined. As a result, laminates with a tensile modulus up to 6 GPa and a tensile strength of 80 MPa were obtained. The property changes of the papers upon processing were successfully modeled, revealing a significant increase of the paper’s mechanical properties after fiber embedding. In general, the obtained results indicate a high potential of paper as a suitable reinforcement material for low to middle strained applications.     

The effects of Clay on fire performance and thermal mechanical properties of woven glass fibre reinforced polyamide 6 nanocomposites

The effects of small amount of organically modified Clay (Clay) in polyamide 6 (PA6) on fire performance and thermal mechanical properties of Clay/PA6/woven glass fibres (GF) laminates are investigated by cone calorimeter test, dynamic mechanical thermal analysis (DMTA), and heat distort temperature (HDT) measurement. The mechanical properties, such as tensile and flexural properties of Clay/PA6 composites and Clay/PA6/GF laminates were also measured. Up to 3 wt.% Clay in a Clay/PA6/GF laminate with fibre volume fraction of 30 vol.% delayed the ignition time and peak heat release rate (PHRR) time by 55% and 118%, respectively, even though the value of the PHRR or the HDT was not significantly affected. 2 wt.% Clay increased flexural modulus and strength of the Clay/PA6/GF laminate by 10% and 16%, respectively, but more Clay did not increase the mechanical properties accordingly. Small amount of Clay does not affect glass fibre dominated properties, such as HDT, but do affect matrix dominated properties, and significantly affect the fire performance in terms of delaying ignition time and PHRR time. Optimization of laminate making process could benefit from additions of more Clay, therefore further improve fire performance and enhance mechanical properties.     

Positive size and scale effects of all-cellulose composite laminates

Negative size effects are commonly reported for advanced composite materials where the strength of the material decreases with increasing volume of the test specimen. In this work, the effect of increasing specimen volume on the mechanical properties of all-cellulose composites is examined by varying the laminate thickness. A positive size effect is observed in all-cellulose composite laminates as demonstrated by a 32.8% increase in tensile strength as the laminate thickness is increased by 7 times. The damage evolution in all-cellulose composite laminates was examined as a function of the tensile strain. Enhanced damage tolerance concomitant with increasing specimen volume is associated with damage accumulation due to transverse cracking and strain delocalisation. A transition from low-strain failure to tough and high-strain failure is observed as the laminate thickness is increased. Simultaneously, scale effects lead to an increase in the void content and cellulose crystallinity at the core, with increasing laminate thickness.     

Design and manufacture of all-PP sandwich panels based on co-extruded polypropylene tapes

This paper describes the creation of polypropylene sandwich panels, based on all-polypropylene (all-PP) composite laminates combined with a polypropylene based honeycomb or foam core. These all-PP composite laminates are based on high modulus polypropylene tape reinforcing a polypropylene matrix. Sandwich panels containing these all-PP composite laminate faces are compared with sandwich panels containing conventional glass fibre reinforced polypropylene laminate faces, and the mechanical properties, failure modes, and design requirements of these different materials are discussed.     

Hybridisation effect on diffusion kinetic and tensile mechanical behaviour of epoxy based flax–glass composites

This paper aims at investigating the hybridisation effect on the diffusion kinetic and the tensile mechanical behaviour of flax–glass fibres reinforced epoxy composites. For this purpose, hybrid composites composed of flax and glass fibre laminates with different stacking sequences were consolidated by compression moulding and subjected to environment ageing. The obtained results show that the water uptake and the diffusion coefficient are clearly reduced by the addition of glass fibre layers in flax laminate. The ageing conditions performed show that the flax–glass hybridisation presents a positive effect in a wet environment at low temperatures (∼20 °C) in the Young’s modulus and the tensile strength. For example, the Young’s modulus fell by 50% and 41% for hybrid laminates with 6% and 11% of glass fibres, and by 67% for the Flax laminate. However, the flax–glass hybridisation was not necessarily a relevant choice when the hybrid laminates were exposed in a wet environment at high temperatures. Indeed, at 55 °C, this hybridisation had a negative effect on the tensile strength and on the specific tensile strength.     

Effects of nano-sized and micro-sized carbon fibers on the interlaminar shear strength and tribological properties of high strength glass fabric/phenolic laminate in water environment

In order to clarify the effects of carbon fiber size on the properties of carbon fiber/high strength glass fabric (HSGF)/phenolic laminate, two kinds of laminates modified by nano-sized carbon fibers (CNFs) and micro-sized carbon fibers (CMFs), were respectively fabricated. The interlaminar shear strength (ILSS) and tribological properties of HSGF/phenolic laminates modified by CNFs and CMFs in water environment were comparatively investigated. Results showed that CNFs at proper contents ranging from 1.0% to 3.0% can enhance ILSS of HSGF/phenolic laminate, while CMFs deteriorated the ILSS. After water immersion, ILSS of the laminates modified by CNFs at 1.0–3.0% were just slightly decreased; however, those of the laminates modified by CMFs suffered larger drop. On the other hand, however, CMFs were more effective than CNFs in improving the wear resistance of HSGF/phenolic laminate in water.     

Influence of prepreg conditions on the void occurrence and tensile properties of woven glass fiber-reinforced polyimide composites

The influence of prepreg solvent content on void occurrence in woven glass fiber-reinforced polyimide composites and their tensile properties was studied. A precursor solution of SKYBOND 703 was diluted in an additional solvent (n-methyl pyrrolidone) and the glass woven fabric was immersed in about 40 wt.% polyamic acid, in solvent. Prepregs were dried at 373 K for different time intervals, ranging from 2 to 24 h. Prepregs with varying residual solvent content under each condition were laid up, and their [(0/90)]₄ composite laminates were formed by autoclaving at a hydrostatic pressure of 0.7 MPa. The relationship of drying time with the amount of residual prepreg solvent, as well as with the volume fractions of fiber and voids was investigated. The void geography and content for each composite laminate, and the tensile strength and modulus at room temperature were also evaluated. The results clearly indicated that, depending on the altering residual solvent content in the prepreg, the void geometry and location influenced reduction of the tensile properties of woven fabric composite laminate. An appropriate prepreg resin viscosity during curing, which avoids reduction of the tensile properties, was revealed.     

Flexural and impact response of woven glass fiber fabric/polypropylene composites

Impact tests with a falling dart and flexural measurements were carried out on polypropylene based laminates reinforced with glass fibers fabrics. Research has shown that the strong fiber/matrix interface obtained through the use of a compatibilizer increased the mechanical performance of such composite systems. The improved adhesion between fibers and matrix weakly affects the flexural modulus but strongly influences the ultimate properties of the investigated woven fabric composites. In fact, bending tests have shown a clear improvement in the flexural strength for the compatibilized systems, in particular when a high viscosity/high crystallinity polypropylene was used. On the contrary, the low velocity impact tests indicated an opposite dependence on the interface strength, and higher energy absorption in not compatibilized composites was detected. This result has been explained in terms of failure mechanisms at the fiber/matrix interface, which are able to dissipate large amounts of energy through friction phenomena. Pull-out of fibers from the polypropylene matrices have been evidenced by the morphological analysis of fracture surfaces after failure and takes place before the fibers breakage, as confirmed by the evaluation of the ductility index.     

Mechanical and thermal behavior of non-crimp glass fiber reinforced layered clay/epoxy nanocomposites

Mechanical and thermal properties of non-crimp glass fiber reinforced clay/epoxy nanocomposites were investigated. Clay/epoxy nanocomposite systems were prepared to use as the matrix material for composite laminates. X-ray diffraction results obtained from natural and modified clays indicated that intergallery spacing of the layered clay increases with surface treatment. Tensile tests indicated that clay loading has minor effect on the tensile properties. Flexural properties of laminates were improved by clay addition due to the improved interface between glass fibers and epoxy. Differential scanning calorimetry (DSC) results showed that the modified clay particles affected the glass transition temperatures (T_g) of the nanocomposites. Incorporation of surface treated clay particles increased the dynamic mechanical properties of nanocomposite laminates. It was found that the flame resistance of composites was improved significantly by clay addition into the epoxy matrix.     

Rheological characterisation of discrete long glass fibre (LGF) reinforced thermoplastics

Three experimental techniques have been employed to assess the rheological behaviour of discrete long glass fibre reinforced polypropylene and propylene/ethylene copolymers. A Carri Med cone and plate rheogoniometer has been used to determine shear viscosity as a function of strain rate and time at temperatures relevant to the extrusion and injection moulding processes. A bubble inflation test (BIT) has been designed and used to characterise the behaviour of these composites under the extensional flow fields typical of blow moulding and thermoforming. Finally a squeeze load test (SLT), similar to those developed for sheet moulding compounds (SMC) and glass mat thermoplastics (GMT), has been used to explore the rheological behaviour of the long glass fibre (LGF) materials under compression moulding conditions, in particular to assess the relative importance of shear and extensional flow.     

Fatigue behaviour of glass fibre reinforced epoxy composites enhanced with nanoparticles

Nanoparticle reinforcement of the matrix in laminates has been recently explored to improve mechanical properties, particularly the interlaminar strength. This study analyses the fatigue behaviour of nanoclay and multiwalled carbon nanotubes enhanced glass/epoxy laminates. The matrix used was the epoxy resin Biresin® CR120, combined with the hardener CH120-3. Multiwalled carbon nanotubes (MWCNTs) 98% and organo-montmorillonite Nanomer I30 E nanoclay were used. Composites plates were manufactured by moulding in vacuum. Fatigue tests were performed under constant amplitude, both under tension–tension and three points bending loadings. The fatigue results show that composites with small amounts of nanoparticles addition into the matrix have bending fatigue strength similar to the obtained for the neat glass fibre reinforced epoxy matrix composite. On the contrary, for higher percentages of nanoclays or carbon nanotubes addition the fatigue strength tend to decrease caused by poor nanoparticles dispersion and formation of agglomerates. Tensile fatigue strength is only marginally affected by the addition of small amount of particles. The fatigue ratio in tension–tension loading increases with the addition of nanoclays and multi-walled carbon nanotubes, suggesting that both nanoparticles can act as barriers to fatigue crack propagation.     

Effect of resin system on the mechanical properties and water absorption of kenaf fibre reinforced laminates

The objective of this study is to compare the mechanical and water absorption properties of kenaf (Hibiscus cannabinus L.) fibre reinforced laminates made of three different resin systems. The use of different resin systems is considered so that potentially complex and expensive fibre treatments are avoided. The resin systems used include a polyester, a vinyl ester and an epoxy. Laminates of 15%, 22.5% and 30% fibre volume fraction were manufactured by resin transfer moulding. The laminates were tested for strength and modulus under tensile and flexural loading. Additionally, tests were carried out on laminates to determine the impact energy, impact strength and water absorption. The results revealed that properties were affected in markedly different ways by the resin system and the fibre volume fraction. Polyester laminates showed good modulus and impact properties, epoxy laminates displayed good strength values and vinyl ester laminates exhibited good water absorption characteristics. Scanning electron microscope studies show that epoxy laminates fail by fibre fracture, polyester laminates by fibre pull-out and vinyl ester laminates by a combination of the two. A comparison between kenaf and glass laminates revealed that the specific tensile and flexural moduli of both laminates are comparable at the volume fraction of 15%. However, glass laminates have much better specific properties than the kenaf laminates at high fibre volume fractions for all three resins used.     

A multi-objective optimization approach for design of blast-resistant composite laminates using carbon nanotubes

A reliable process for the design of blast-resistance composite laminates is needed. We consider here the use of carbon nanotubes (CNTs) to enhance the mechanical properties of composite interface layers. The use of CNTs not only enhances the strength of the interface but also significantly alters stress propagation in composite laminates. A simplified wave propagation simulation is developed and the optimal CNT content in the interface layer is determined using multi-objective optimization paradigms. The optimization process targets minimizing the ratio of the stress developed in the layers to the strength of that layer for all the composite laminate layers. Two optimization methods are employed to identify the optimal CNT content. A case study demonstrating the design of five-layer composite laminate subjected to a blast event is used to demonstrate the concept. It is shown that the addition of 2% and 4% CNTs by weight to the epoxy interfaces results in significant enhancement of the composite ability to resist blast.     

NaBF4 as a hygrothermal durability enhancer for glass fibre reinforced polypropylene composites

The long term performance of composite materials is highly desired for their expanding application range. Tuning the interphase properties has been proven to be a practical way to enhance the performance of composites. In this study, short glass fibre (GF) reinforced polypropylenes (PPs) with improved hygrothermal durability were obtained by incorporating NaBF₄ into the sizing and thus the interphases of GF/PP composites. Detailed investigations were performed on the surface properties of sized GFs and the mechanical properties of virgin and aged composites. It was found that the retention in both ultimate tensile strength and Charpy impact toughness of aged composites monotonically increased with increasing NaBF₄ content. The improvement in hygrothermal durability was related to the enhanced fibre/matrix adhesion strength induced by the presence of NaBF₄ as indentified by fracture surface analysis using field-emission scanning electron microscopy and single fibre pull-out test.     

Jute and glass fibre hybrid laminates

Hybrid laminates have been fabricated from randomly oriented jute fibre mats and woven glass fabrics with a common polyster resin matrix. Hand lay up techniques were used to simulate practical production methods in the field. A variety of laminate constructions were mechanically tested and some laminates were in addition assessed for environmental stability. Modified rule of mixtures expressions successfully predicted the tensile properties of the laminates and the jute plies were seen to control the failure of hybrid laminates at about 0.8% strain. Fracture toughness measurements of G_IC andK _IC indicate that hybrid laminates have maximum toughness (G _IC 12 kJ m^–2 when jute plies are sandwiched between glass fabric facings. All the hybrid laminates were found to be tough in impact, although here fabric plies used as the laminate core maximize the work of fracture at a value of approximately 45 kJ m^–2. Hybrid laminates with jute facings are, as expected, least able to withstand hot moist environments. However, significant moisture uptake by the polyester resin matrix was measured for all laminates. Optical and scanning electron microscopy have been used to explain the mechanical performance and environmental resistance of the hybrid laminates.     

Fatigue crack growth in thin notched woven glass composites under tensile loading. Part I: Experimental

Helicopter blades are made of composite materials mainly loaded in fatigue and have normally relatively thin skins. A through-the-thickness crack could appear in these skins. The aim of this study is to characterize the through-the-thickness crack propagation due to fatigue in thin woven glass fabric laminates. A technological test specimen is developed to get closer to the real loading conditions acting on these structures. An experimental campaign is undertaken which allows evaluating crack growth rates in several laminates. The crack path is linked through microscopic investigations to specify damage in woven plies. Crack initiation duration influence on experimental results is also underlined.     

模压工艺对玻璃纤维增强聚丙烯复合材料层合板力学性能的影响

利用热模压工艺制备玻璃纤维增强聚丙烯（GF/PP）复合材料层合板,通过差示扫描量热（DSC）法试验分析,确定相变参数,运用ANSYS有限元分析,将复合材料热力学参数与温度的非线性关系定义到材料特性中,研究模压成型过程中温度场变化情况,为模压成型工艺制度的确立提供理论指导和依据。以压缩强度、层间剪切强度和冲击韧性作为力学性能评价指标,采用响应曲面法探讨和分析制备工艺对GF/PP复合材料层合板力学性能的影响,得到最优模压工艺制备参数,获得最高复合材料层合板力学性能,为GF/PP复合材料自动铺放奠定铺放工艺基础。试验结果表明:模压加热工艺参数对复合材料层合板力学性能的影响度（从大到小）依次为:热压温度、热压时间、热压压力。较优的模压加热工艺参数为:热压温度228℃、热压时间6 min、热压压力1.1 MPa,在此工艺条件下制备的GF/PP复合材料层合板,层间剪切强度为31.12 MPa,压缩强度为100.96 MPa,冲击韧性为2.27 kJ/cm2。      

Influence of fibre length and concentration on the properties of glass fibre-reinforced polypropylene: Part 3. Strength and strain at failure

In this report we present the results from the third part of a study on the influence of fibre length (0.1–50 mm) and concentration (3–60% w/w) on the properties of glass fibre-reinforced polypropylene laminates. These laminates were prepared in the laboratory using a wet deposition method and compared with samples prepared on a commercial melt impregnation GMT line. We found that laminate tensile strength increased linearly with fibre concentration up to 60% w/w. Laminate strength was also found to increase with increasing fibre length. At high values of fibre length (> 3–6 mm) the strength reached a plateau level which was directly dependent on fibre content. The matrix molecular weight appeared to have little direct influence on the level of laminate strength. However, the glass fibre sizing compatibility was found to have a strong effect on the tensile strength of both laboratory made wet deposited laminates and commercially prepared GMTs. The tensile strength of the GMT samples also showed a clear correlation with the measured fibre strength. A modified version of the Kelly-Tyson model gave calculated values of laminate strength which correlated well with the experimental data. We propose that the tensile strength of these laminates is governed by the properties of the fibres which have an orientation close to parallel with the loading direction.     

New development of self-damping MWCNT composites

Epoxy resin modified with nanofillers cannot be used alone for high performance structural applications due to their low-mechanical properties. Therefore, the objective of this work is to hybridize unidirectional and quasi-isotropic glass fiber composite laminates with 1.0 wt% multi-walled carbon nanotubes (MWCNTs). Results from flexural and damping characterizations showed that the flexural strength and modulus, storage modulus, and damping ratio of MWCNT/E nanocomposite are improved by about 7% ± 1.5% compared to neat epoxy. The enhancement in the flexural strength of quasi-isotropic laminate (20.7%) is about ten times higher than that for unidirectional laminate (2.1%). The flexural moduli of the nano-hybridized laminates are reduced by about 7.5–10.8%. Accordingly, the ultimate failure strain and damping properties are evidently improved. The improvement in damping ratio in some cases is about 100%. The high correlation coefficient (0.9995) between flexural and storage moduli suggests using the dynamic nondestructive tests for evaluation the elastic properties of composites.     

Compression properties of z-pinned composite laminates

The effect of z-pinning on the in-plane compression properties and failure mechanisms of polymer laminates is experimentally studied in this paper. The reduction to the compression modulus, strength and fatigue performance of carbon/epoxy laminates with increasing volume content and diameter of pins is determined. The elastic modulus decreases at a quasi-linear rate with increasing pin content and pin diameter. Softening is caused by fiber waviness around the pins and reduced fiber volume content due to volumetric swelling of the laminate from the pins. A simple model is presented for calculating the compression modulus of pinned laminates that considers the softening effects of fiber waviness and fiber dilution. The compression strength and fatigue life also decrease with increasing volume content and diameter of the pins. The strength and fatigue properties are reduced by fiber kinking caused by fiber waviness around the pins and the reduced fiber content caused by swelling. The deterioration to the compression properties is also dependent on the fiber lay-up pattern of the laminate, with the magnitude of the loss in properties increasing with the percentage of 0° (load bearing) fibers in the laminate. The paper gives suggestions for minimizing the loss to the compression properties to laminates due to pinning.