聚芳醚酮树脂非等温结晶动力学及其复合材料湿热老化性能EI北大核心CSCD

聚芳醚酮(poly(aryl ether ketone),PAEK)热塑性复合材料因其突出的韧性、耐老化性能、耐疲劳性能,以及成型加工低成本、高效率、可回收等一系列优势,得以替代部分传统热固性复合材料,并已在国外航空等高端工业领域取得成功应用。PAEK是一种半结晶高聚物,复合材料不同的成型工艺条件导致树脂基体聚集态结构的差异,对其力学性能、耐老化性能等均存在显著的影响。对国产PAEK树脂的结晶动力学进行了研究,通过控制成型降温条件,采用模压工艺制备了树脂结晶度不同的连续碳纤维增强复合材料,并对其进行了湿热老化处理,评价了老化处理前后复合材料的弯曲性能。结果表明:采用较大的降温速率能够提高树脂的结晶速率,但会降低树脂的结晶度。在随炉冷却、空气冷却和水冷却三种不同的降温条件下,制备的复合材料结晶度分别约为36.3%,29.7%,26.5%,结晶度的显著差别导致复合材料的弯曲强度随结晶度的降低而减小。经湿热老化处理240 h后的弯曲强度保留率分别为88.8%,86.7%,86.6%,较高的结晶度能够较好地抵抗水对复合材料界面的破坏,提升复合材料的耐湿热老化性能。     

Impact fatigue behaviour of vinylester resin matrix composites reinforced with alkali treated jute fibres

An impact fatigue study has been made for the first time on 35% jute/vinylester composites containing both untreated and alkali treated fibres. Longer alkali treatment removed the hemicellulose and improved the crystallinity and gave better fibre dispersion. The flexural strength properties of the composites made from treated fibre were superior. 4 h alkali treated jute fibres gave the optimum combination of improved interfacial bonding and fibre strength properties. However this was not reflected in their impact fatigue behaviour. On the contrary, the composites reinforced with 8 h alkali treated fibres displayed superior impact fatigue properties. Here, the fibres suffered catastrophic fracture with microfibrillar pull-out at some places and improved the fatigue resistance property of the composites as evident from SEM micrographs.     

The environmental fatigue behaviour of carbon fibre reinforced polyether ether ketone

The fatigue behaviour of carbon fibre/PEEK composite is compared with that of carbon/ epoxy material of similar construction, particularly in respect of the effect of hygrothermal conditioning treatments. Laminates of both materials were of 0/90 lay-up, and they were tested in repeated tension at 0° and at 45° to the major fibre axis. The superior toughness of the polyether ether ketone and its better adhesion to the carbon fibres results in composites of substantially greater toughness than that of the carbon/epoxy material, and this is reflected in the fatigue behaviour of the carbon fibre/PEEK. The tougher PEEK matrix inhibits the development of local fibre damage and fatigue crack growth, permitting a 0/90 composite with compliant XAS fibres to perform as well in fatigue as an epoxy laminate with stiffer HTS fibres. Hygrothermal treatments have no effect on the fatigue response of either material in the 0/90 orientation. The fatigue response of a cross-plied carbon/PEEK laminate in the ±45° orientation is much better than that of equivalent carbon/epoxy composites, again because the superior properties of the thermoplastic matrix.     

Interlaminar shear fatigue of pultruded graphite fibre-polyester composites

The effect of cyclic loading on the interlaminar shear strength of pultruded graphite fibre-polyester was determined. Two fibre volume fractions, 0.5 and 0.33, were studied. The results indicate that the deterioration in the interlaminar shear strength with cycling is significantly greater than in flexural fatigue. The higher volume fraction material showed a greater drop in the interlaminar shear strength than the lower volume fraction material. Unlike the monotonic strengths, the effect of the fibre volume fraction on interlaminar shear fatigue strength at high cycles is small, indicating that there is little advantage in increasing the fibre volume fraction to improve the interlaminar shear strength in high cycle fatigue environments. A critical stress was determined above which interlaminar shear fatigue failure did not occur within 10⁷ cycles for the materials tested.     

Quantification of flexural fatigue life and 3D damage in carbon fibre reinforced polymer laminates

Carbon fibre reinforced polymer (CFRP) laminated composites have become attractive in the application of wind turbine blade structures. The cyclic load in the blades necessitates the investigation on the flexural fatigue behaviour of CFRP laminates. In this study, the flexural fatigue life of the [+45/−45/0]_2s CFRP laminates was determined and then analysed statistically. X-ray microtomography was conducted to quantitatively characterise the 3D fatigue damage. It was found that the fatigue life data can be well represented by the two-parameter Weibull distribution; the life can be reliably predicted as a function of applied deflections by the combined Weibull and Sigmodal models. The delamination at the interfaces in the 1st ply group is the major failure mode for the flexural fatigue damage in the CFRP laminate. The calculated delamination area is larger at the interfaces adjacent to the 0 ply. The delamination propagation mechanism is primarily matrix/fibre debonding and secondarily matrix cracking.     

The influence of the stitching pattern on the internal geometry,quasi-static and fatigue mechanical properties of glass fibre non-crimp fabric composites

This paper discusses the experimental results of a study comparing several aspects of the mechanical behaviour of two quasi-unidirectional non-crimp fabric composites based on non-crimp fabrics that differ only in stitching pattern. A NEW stitching pattern was compared to an industry common type (ICT). The properties studied include fabric and laminate thickness, fibre volume fraction, static tensile modulus and strength in longitudinal and transverse direction, high-speed tensile strength and tension–tension fatigue life. Statistically significant differences were observed for fabric and composite thickness, which was found to be higher for the ICT type composite. A higher fibre volume fraction was observed for the NEW stitching pattern material, as well as a higher longitudinal tensile strength at high and low speeds and a slightly higher fatigue life.     

Some aspects of the fatigue behaviour of fibre reinforced thermosetting resins

This paper reports the continuing work to establish the fatigue response of commercial fibre reinforced plastics now being specified by designers, particularly those materials using thermosetting resins as the matrix.

Results are reported of the flexural fatigue of balanced needled fabrics and of the tensile fatigue of filament wound E-glass and R-glass rings. Only a small dependence on the ratio of the minimum to the maximum stress (R-ratio) has been observed for flexural fatigue between R = 0·05 and R = 0·6.

It is shown that the fatigue behaviour of a wide variety of glass fibre reinforced composites (unidirectional/bidirectional, long and short fibres, epoxy and polyester resins), subject to either tensile or flexural loading, can be rationalised, like others have done, by normalising the maximum fatigue stress with respect to the corresponding ultimate tensile or flexural strength, obtained at an equivalent strain rate.     

Mechanical properties of randomly oriented short Sansevieria cylindrica fibre/polyester composites

The tensile, flexural and impact properties of randomly oriented short Sansevieria cylindrica fibre/polyester (SCFP) composites are described for the first time in this work. Composites were fabricated using raw S. cylindrica fibres (SCFs) with varying fibre lengths and weight percents of fibre. When the length of the SCFs was increased, the tensile, flexural and impact properties of the composite were increased up to a 30-mm fibre length, and then a curtailment in properties occurred for higher fibre length composites. SCFP composites showed a regular trend of an increase in properties with fibre weight percent until 40% and afterwards a decrease in properties for composites with greater fibre weight percent. Tensile tests revealed that the tensile strength was about 76 MPa, the Young’s modulus was 1.1 GPa and the elongation at break was between 7% and 8.3%. The flexural strength and modulus were estimated to be around 84 MPa and 3 GPa, respectively. Impact tests exhibited a strength of approximately 9.5 J/cm². The analysis of the tensile, flexural and impact properties of short SCFP composites displayed a critical fibre length and optimum fibre weight percent of 30 mm and 40%, respectively. Scanning electron microscope (SEM) studies were carried out to evaluate the fibre/matrix interactions. The experimental tensile strengths were compared with the theoretical predictions and found to be in good agreement with Hirsch’s model. An X-ray diffraction (XRD) analysis of the composites exposed the presence of cellulose IV with a crystallinity index of 60% and crystallite size of 68 nm.     

碳纤维-AlN/聚醚醚酮复合材料的制备与性能

以聚醚醚酮(PEEK)为基体树脂、碳纤维(CF)和氮化铝(AlN)为填料,通过模压成型的方法制备了抗静电耐热型CF-AlN/PEEK复合材料。采用高阻计、导热系数测定仪、热失重、差示扫描量热仪和SEM研究了CF-AlN/PEEK复合材料的抗静电性能、热性能、力学性能以及降温速率对复合材料性能的影响,并探讨了后期热处理对力学性能的影响。结果表明:当CF和AlN的质量分数均为10%时,CF-AlN/PEEK复合材料的性能较优,其表面电阻率达到108 Ω,比PEEK的表面电阻率提高了6个数量级;导热系数为0.418 W·(m·K)-1,初始分解温度高达573℃;拉伸强度提高了40.4%;降温速率越低,复合材料的熔点越高;后期热处理会影响CF-AlN/PEEK复合材料的力学性能,在270℃下热处理2 h,其拉伸强度可达146 MPa,表明在生产过程中,加工温度是影响复合材料性能的因素之一。      

聚醚醚酮和烯丙基化合物改性双马来酰亚胺复合材料微观结构及力学性能

采用浓H₂SO₄氧化聚醚醚酮（PEEK）得到磺化聚醚醚酮（SPEEK）,以3,3'-二烯丙基双酚A （BBA）、双酚A双烯丙基醚（BBE）为活性稀释剂、SPEEK为改性剂、双马来酰亚胺（BMI）树脂为基体,浇注成型制备SPEEK/BBA-BBE-BMI复合材料,同时研究了SPEEK的改性效果及复合材料微观形貌与力学性能。结果表明：SPEEK改性效果较好,在FTIR中存在明显的磺酸基团特征峰,SEM和能谱分析表明,SPEEK微观形貌变化明显,硫元素含量较高;SPEEK/BBA-BBE-BMI复合材料的微观形貌显示,SPEEK在基体中呈现直径为2 μm左右的多孔状两相结构,且分散均匀,此多孔结构改善了复合材料的断裂形貌,由脆性断裂转变为韧性断裂,当断裂纹遇到SPEEK组分时受阻而出现不规则发散,此变化会赋予复合材料更加优异的性能。力学性能测试结果显示,当SPEEK含量为5wt%时,SPEEK/BBA-BBE-BMI复合材料的弯曲强度和冲击强度达到最佳,分别为147.93 MPa和15.74 kJ/mm²,分别比基体提高了49.47%和66.21%。     

Experimental and theoretical studies on the properties of injection moulded glass fibre reinforced mixed plastics composites

Recycled mixed post-consumer and post-industrial plastic wastes consisting of HDPE, LDPE and PP were injection moulded with short glass fibre (10–30% by weight) to produce a new generation composite materials. Intensive experimental studies were then performed to characterise the tensile, compression and flexural properties of glass fibre reinforced mixed plastics composites. With the addition of 30 wt.% of glass fibre, the strength properties and elastic modulus increased by as much as 141% and 357%, respectively. The best improvement is seen in the flexural properties due to the better orientation of the glass fibres in the longitudinal direction at the outer layers. The randomness and length of the glass fibre were accounted to modify the existing rule of mixture and fibre model analysis to reliably predict the elastic and strength properties of glass fibre reinforced mixed plastics composites.     

Mechanical properties of glass-fibre mat/PMMA functionally gradient composite

Glass-fibre mat (GFM) reinforced poly(methyl methacrylate)(PMMA) composites with different fibre content and four kinds of functionally gradient material (FGM) composites were fabricated. To investigate the effects of glass-fibre content and spatial gradient, flexural test and instrumented impact test were conducted. Flexural modulus increased with the increment of fibre content. However, the flexural strength and the impact absorption energy of the composite exhibited maximum values at 30 vol.%. FGM composite with GF-rich side at both outer layers showed the highest flexural strength. Compared with isotropic composite, higher flexural modulus were obtained from the FGM composites. Impact absorption energies of four FGM composites were similar but their ductility indices (DI) were quite different. FGM composites with proper spatial gradient could have improved mechanical properties compared with conventional isotropic composites.     

Mechanical and microstructural properties of Nylon-12/carbon black composites: Selective laser sintering versus melt compounding and injection molding

Composites of Nylon-12 reinforced with 4 wt.% carbon black (CB) manufactured by selective laser sintering (SLS) are compared in terms of flexural strength and flexural modulus, tensile strength and tensile modulus, and impact strength to composites made by extrusion and injection molding (Ex-IM). The Nylon-12 system made by SLS had 25% and 35% higher flexural and tensile modulus, respectively, compared to the Nylon-12 system made by Ex-IM and ∼10% higher strength. However, upon addition of CB both the modulus and the strength of the composites made by SLS were significantly lower compared to composites made by Ex-IM. This is due to the poor dispersion of nanoscale CB and due to the higher porosity of the composites made by SLS, which also explains the relatively low impact strength observed. Based on XRD and DSC studies, it is concluded that the composites made by the two processing methods did not differ significantly in their crystallization characteristics such as the degree of crystallinity, crystal type, and lamellar thickness. However, it was found that CB acted as a nucleating agent for Nylon-12 when Ex-IM was used, leading thus to smaller but more numerous polymer crystals.     

Mechanical properties of natural fibre reinforced polyester composites: Jowar,sisal and bamboo

In this paper, the experiments of tensile and flexural tests were carried out on composites made by reinforcing jowar as a new natural fibre into polyester resin matrix. The samples were prepared up to a maximum volume fraction of approximately 0.40 from the fibres extracted by retting and manual process, and compared with established composites like sisal and bamboo developed under similar laboratory conditions. Jowar fibre has a tensile strength of 302 MPa, modulus of 6.99 GPa and an effective density of 922 kg/m³. It was observed that the tensile strength of jowar fibre composite is almost equal to that of bamboo composite, 1.89 times to that of sisal composite and the tensile modulus is 11% and 45% greater than those of bamboo and sisal composites, respectively at 0.40 volume fraction of fibre. The flexural strength of jowar composite is 4%, 35% and the flexural modulus is 1.12 times, 2.16 times greater than those of bamboo and sisal composites, respectively. The results of this study indicate that using jowar fibres as reinforcement in polyester matrix could successfully develop a composite material in terms of high strength and rigidity for light weight applications compared to conventional sisal and bamboo composites.     

Polypropylene composites with enzyme modified abaca fibre

Abaca fibre reinforced PP composites were prepared using a high speed mixer followed by injection moulding with 30 wt.% of fibre load. Prior to composite production, the fibres were modified by fungamix and natural enzyme. The effects of modification of the fibre were assessed on the basis of morphology and thermal resistance and as well as on mechanical, thermal and environmental stress corrosion resistance properties of the resulting composites. Coupling agent (MA-PP) was also used with unmodified abaca fibre to observe the coupling agent effect on resulting composites properties. The moisture absorption of the composites was found to be reduced 20–45% due to modification. Tensile strength found to be 5–45% and flexural strengths found to be 10–35% increased due to modification. Modified fibre composites found to better resistance in acid and base medium.     

The durability of controlled matrix shrinkage composites

During fatigue of aligned fibre pultrusions, the flexural modulus decreases continuously when the applied stresses are tensile and directed along the fibres (R=0.1). In addition, the Poisson's ratio increases continuously, and so does the energy absorbed during the fatigue cycle. Holes in the specimens continuously increase in size in a direction at right angles to the applied stress, but change little in the stressing direction. These effects are enhanced by including compressive stresses in the cycle (R=–0.3) and are reduced by reducing the polymer cure shrinkage pressure. There are notable similarities between fatigue failure and compressive failure in aligned fibre composites, and evidence that matrix stresses are produced at right angles to the fibres, which are probably large enough to cause matrix fatigue failure. These observations lead to the conclusion that the fatigue failure may well originate from misaligned fibres, which generate off-axis stresses. These cause interface failure and polymer fragmentation, which can then lead to fibre failure (and thus composite failure) even when the applied stresses are always tensile.     

Wood Fibre Reinforced Polypropylene Composites: Effect of Fibre Geometry and Coupling Agent on Physico-Mechanical Properties

Wood fibre reinforced polypropylene composites at fibre content 50% by weight have been prepared and different types of wood fibres (hard wood fibre, soft wood fibre, long wood fibre and wood chips) were treated with coupling agent (MAH-PP) to increase the interfacial adhesion with the matrix to improve the dispersion of the particles and to decrease the water sorption properties of the final composite.The present study investigated the tensile, flexural, charpy impact and impact properties of wood fibre reinforced polypropylene composites as a function of coupling agent and fibre length and structure.From the results it is observed that wood chips-PP composites showed better tensile and flexural properties comparative with the other wood fibre-PP composites with the addition of 5%MAH-PP, which is around 65% and 50% for tensile strength and flexural strength respectively. Hard wood fibre-PP composites showed better impact characteristic values comparative to other wood fibre-PP composites with the addition of 5%MAH-PP and damping index decreased about to 60%. Charpy impact strength also increased up to 60% with the addition of 5%MAH-PP for long wood fibre-PP composites. Water absorption and scanning electron microscopy of the composites are also investigated.     

A comparative study of the fatigue and post-fatigue behavior of carbon–glass/epoxy hybrid RTM and hand lay-up composites

The paper presents a study of the fatigue and post-fatigue behavior of a hybrid carbon–glass biaxial fabric reinforced epoxy composite manufactured by the resin transfer molding (RTM) and the hand lay-up (HL) processes, with the main objective of assessing whether a material characterization run at the prototype level of a handicraft technology could be significant for a mass production technology and whether a comparison on static properties (a viable task at an industrial level) could ensure the same level of agreement for the fatigue life and residual properties. Tensile and flexural static tests as well as displacement-controlled bending fatigue tests (R ratio of 0.10) were conducted on two sets of standard specimens, having fiber orientation parallel to the loading direction (on-axis specimens) and at 45° to the loading direction (off-axis specimens). Specimens were subjected to different fatigue loading, with the maximum load level up to 60% of the average ultimate flexural strength, and damage in the laminate was continuously monitored through the loss of bending moment during cycling. After 10⁶ cycles, the fatigue test was stopped and residual properties were measured. Micrographs of sample sections revealed some voidage for HL specimens while resin rich areas were observed for RTM specimens. Results of the static tensile and flexural tests pointed out lower mechanical properties for the RTM specimens when tested on-axis and slightly higher properties when tested off-axis. Regardless of specimen fiber orientation, the fatigue and post-fatigue performance of RTM samples was inferior to that of HL specimens with the gap increasing for increasing fatigue load levels. The result was ascribed to the presence in RTM samples of resin-rich areas, which are reported to have limited influence on the laminate static properties but which may act as initiation sites for fatigue cracks.     

On the notch sensitivity of flax fibre metal laminates under static and fatigue loading

Damage progression and failure characteristics of open‐hole flax fibre aluminium laminate (flax‐FML) specimens subjected to quasi‐static tensile or tension‐tension fatigue loading were experimentally investigated. Notched and unnotched flax‐FML composites exhibited brittle fracture with little or no fibre pull‐out and minimal delamination at the aluminium/adhesive interface. The flax‐FMLs were tested to failure under tension‐tension fatigue loading conditions (R ratio of 0.1; frequency of 10 Hz; applied fatigue stresses ranging between 30% and 80% of the respective ultimate tensile strength values). The fatigue cycles to failure decreased with the increase in the applied fatigue stress and hole diameter. A phenomenological modelling technique was developed to evaluate the fatigue life of an open‐hole flax‐FML composite. Fatigue tests on specimens subjected to a maximum load equivalent to 35% of the respective tensile failure strength were interrupted at around 85% of the corresponding fatigue life. The accumulated fatigue damage in these specimens was characterised using X‐ray computed tomography. For benchmarking purposes, the fatigue performance and related damage progression in the flax‐FML composite were compared with those of the glass‐FMLs.     

The effect of fibre content on the mechanical properties of glass fibre mat/polypropylene composites

Glass fibre mat was prepared by the fibre mat-manufacturing machine developed in our laboratory. Glass fibre mat reinforced polypropylene (PP) composites were fabricated with the variation of glass fibre content. Tensile, flexural and high rate impact test was conducted to investigate the effect of glass fibre content on the mechanical properties of the glass fibre mat/PP composite. Deformation and fracture behaviour of the glass fibre mat/PP composites was investigated to study the relationship with the mechanical property data. The tensile and flexural modulus increased with the increment of glass fibre content. However, the tensile and flexural strengths exhibited maximum values and showed a decrease at the higher glass fibre content than this point. The impact absorption energy also exhibited a similar result with the tensile and flexural property data.