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.     

Hot water resistance of glass‐fiber and glass‐bead reinforced thermoplastics

The hot water resistance of three kinds of short glass fiber or glass bead‐reinforced plastics [polyphenyleneether (PPE), polyphenylenesulfide (PPS), and polyoxymethylene (POM)] was studied by hot water immersion testing, tensile testing and water‐hammer fatigue testing. It was found that the degradation of the strength was observed only for the reinforced plastics under hot water immersion and that the change of the tensile strength was most drastic in glass fiber‐reinforced PPS (GFPPS). Scanning electron microscope (SEM) observations of the tensile fracture surface revealed that the change in tensile strength was attributable to the deterioration of the interface between the glass fiber and the matrix resin. The results of acoustic emission analysis also supported the conclusion that the change in strength was due to the deterioration of the interface. Although the change in the tensile strength of glass fiber‐reinforced PPE (GFPPE) was small compared with that of GFPPS, debonding between the glass fiber and the matrix resin and surface cracks was observed on the surface of the GFPPE specimens.     

两种玻璃纤维增强复合材料体系的湿热老化研究

玻璃纤维增强复合材料在湿热环境下性能的退化是工程研究中待解决的问题,而实验室人工加速老化则是较好地研究该问题的常用方法。通过人工加速老化方法,结合露天储水环境,研究两种玻璃纤维增强复合材料在35℃水浸泡、65℃水浸泡及盐雾三种环境下的吸水率、巴氏硬度和弯曲强度的变化,并运用两种模型预测材料的使用寿命。研究表明:不同湿热环境下,材料的巴氏硬度前期变化明显,后期趋向稳定;吸水率基本符合Fick定律;温度对弯曲强度保留率影响显著,盐雾影响次之;中值老化公式比经验公式拟合度高7.6%。     

用于煤矿井下充填的玻璃纤维增强聚氯乙烯热塑性复合管材的设计与制造

针对煤矿膏体输送所用的无缝钢管耐磨性差、更换困难等问题,制备了玻璃纤维增强聚氯乙烯热塑性复合管(PVC?RTP)用于煤矿井下充填,对管材的组成、连接方式、工艺流程和工艺参数进行了全面介绍,并检测了公称压力为9.5 MPa的管材的性能.结果表明,管材爆破压力为38.95 MPa,大于4倍公称压力;当试验压力为14.25 ...     

Glass optical fibre sensors for detection of through thickness moisture diffusion in glass reinforced composites under hostile environments

A combination of evanescent wave optical sensors (EWOSs) and fibre Bragg gratings (FBGs) were embedded in an epoxy vinyl ester and an epoxy vinyl ester based glass reinforced polymer (GRP) composite to measure fluid ingress that would result in degradation under hostile conditions. Samples were subjected to accelerated aging in the form of single sided exposure to simulated sea water at 120°C in a pressurised stainless steel vessel. Low cost EWOSs were prepared from a standard multimode glass optical fibre and compared to commercially available FBGs. Both sensors were able to detect the early stage of moisture diffusion into the GRP matrix. The evanescent sensors showed a reduction in the transmitted signal intensity between 1500 and 1650?nm with an increasing exposure time due to a change in the optical properties of the polymer, whereas a peak shift was observed for the FBGs due to the swelling of the resin with the absorption of water. Additionally, the glass optical fibre sensors were embedded in a configuration that allowed the extent of diffusion through the thickness of the GRPs to be monitored, with the fibres in the closest position to the exposure face showing a greater signal change than those positioned further away.     

High temperature failure envelopes for thermosetting composite pipes in water

Abstract

This paper presents the results of an investigation of the biaxial stress–strain behaviour of filament wound glass fibre reinforced composite pipes exposed to high temperature water. Two matrix systems were investigated: cycloaliphatic amine cured epoxy resin; and siloxane modified phenolic alloy. Water absorption tests on pipe using the two systems at 95°C showed equilibrium moisture contents of 0.5 and 4.5%, respectively, saturation being achieved within seven days at this temperature in both cases. The axial moduli of the pipes were determined at temperatures up to 160°C, using a bending test. Reductions were observed in the T _g of both systems in the water saturated condition. Biaxial loading tests were carried out on the two pipe systems at temperatures from 20 to 160°. The results are presented in the form of failure envelopes and stress–strain relationships under load. At the highest temperatures (above its T _g ), significant weakening of the epoxy system was observed, especially in matrix dominated loading conditions. In contrast, the failure envelopes for the phenolic system showed remarkably little temperature influence.     

Smart composite materials for self-sensing and self-healing

Abstract

The various methods of self-sensing and self-healing developed within the Composite Systems Innovation Centre, University of Sheffield, are reviewed. Damage sensing using electrical resistance in carbon fibre reinforced composite or using the fibres as optical sensing elements in glass fibre reinforced composite is demonstrated. Amelioration of low level damage is demonstrated in both monolithic composite materials and sandwich structures using direct chemical reactions within the matrix without the use of encapsulants. These reactions can be activated by resistive heating of the material itself. The use of a combination of these techniques could create a truly smart structure able to both sense and repair damage and degradation.     

Development of glass fibre reinforced polyethylene pipes for pressure applications

Abstract

Thermoplastic filament winding with in line melt impregnation has been investigated for the manufacture of continuous glass fibre reinforced thermoplastic pipes. With polyethylene matrixes it was found that the high melt viscosity hindered full melt impregnation and resulted in high pull forces in the case of pipe grade polyethylene. Using a lower viscosity polyethylene it was possible to operate the melt impregnation process, but the product obtained exhibited a high void content. Surprisingly, it was found that filament winding resulted in a considerable decrease in void content, to an acceptable level. It was found possible to wind good quality pipes and achieve high failure pressures that fully reflected the strength of the reinforcement.

The non-linear strain response of glass–polyethylene pipes can be modelled using laminate theory modified to take account of the non-linearity of the matrix and the change in fibre angle that occurs as the pipe deforms.     

Strain response and damage modelling of glass/epoxy pipes under various stress ratios

Abstract

This paper presents the stress–strain response and general lifetime damage modelling of glass fibre reinforced epoxy (GRE) composite pipes subjected to multi-ratios stress loadings at room temperature (RT). This particular modelling work was developed to predict the non-linear stress–strain response caused by the fatigue static and cyclic loading in the multiaxial ultimate elastic wall stress (UEWS) tests by considering the effects of matrix cracking within the laminates. Although the UEWS procedure is not a standard protocol used for qualification of GRE pipes, it appears to offer an option to existing procedures delineated in ASTM D2992. The ply properties initially expressed as a function of crack density was computed as a function of increasing stress and strain using shear lag approximation. In general lifetime damage model, the effects of stress developed in each ply from ultimate elastic wall stress (UEWS) test were expressed in a single quadratic term of axial and hoop stress. The term then solved to produce limits with respect to axial and hoop stress, which represented in a graphical form of failure envelope. The predictions from both models are found to be in good agreement with the data from the multiaxial UEWS tests of ±55° filament wound GRE pipes. These models thus enable for the long term performance prediction of the pipes under combined loadings.     

高屏蔽耐温酚醛环氧重防腐涂料的制备及性能研究

针对大型海水淡化关键设备制造成本高、防腐期效短等问题,基于金属表面屏蔽阻隔原理,采用酚醛改性环氧树脂和改性聚酰胺为基料,以氧化铁红、硫酸钡、片状填料等为防腐填料,获得应用于新型低合金耐蚀钢或碳钢基材表面的高屏蔽耐温酚醛环氧重防腐涂料。实验结果表明：该涂料吸水率 1. 2%,抗氯离子渗透性 0. 9×10^-3 mg/cm²·d,柔韧性 1 mm,耐冲击性 50 cm,耐 88 ℃海水浸泡 6 000 h,耐盐雾 10 000 h,涂层耐阴极剥离性能测试被剥离涂层距人造漏涂孔外缘平均距离为 4. 5 mm,经 33 d 88 ℃海水浸泡 0. 01 Hz低频阻抗（ |Z|_{0. 01 Hz}）条件下该涂层电化学交流阻抗值由 8. 28×10¹⁰ Ω·cm²降为 1. 18×10⁸ Ω·cm²,且曲线平滑,说明该涂层具备优异的防腐性能。     

石墨烯改性涂层防护性能研究

为减少团聚,提高石墨烯在涂层中的分散性,研究采用纳米分散技术预先制备了石墨烯分散液,再将其分散至环氧树脂中获得石墨烯改性复合涂层。通过对石墨烯含量为 0、0.3%、0.6%的复合涂层进行盐水浸泡、盐雾、阴极剥离实验及电化学性能测试,证明石墨烯的加入显著增强了涂层的防护性能。石墨烯复合涂层在 3.5%盐水中浸泡 1 008 h后,涂层低频阻抗仍大于 106 Ω·cm²比未添加石墨烯的涂层提高了 3个数量级,且盐雾实验 6 000 h后涂层表面仍保持完好;含 0.6%石墨烯,的涂层耐蚀行为劣于石墨烯含量为 0.3%的涂层。     

Effect of saline degradation on the mechanical properties of vinyl ester matrix composites reinforced with glass and natural fibers

One important application of polymeric composites reinforced with natural fibers is in the area of naval engineering design. The objective of this work was to study the influence of saline degradation on the mechanical properties of vinyl ester matrix composites reinforced with glass, sisal, and coconut fibers and natural fibers modified with bitumen. All samples presented mass loss after exposure in a salt spray chamber. All materials, except the composite reinforced with coconut–bitumen, showed a decrease in toughness after a salt spray test. The fracture of the vinyl ester resin with sisal and sisal–bitumen fibers showed a fiber bridging mechanism. These materials showed the highest value of toughness among the materials studied. The presence of fiber pullout was observed in the samples of vinyl ester resin reinforced with glass, coconut, and coconut fibers covered with bitumen. In these samples, poor adhesion between the fiber and matrix was observed. The treatment of fibers with bitumen increased the mass loss and decreased the stability of samples in a saline atmosphere. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Preliminary investigations of the dimensional stability of super-critically carbonated glass fibre reinforced cement

The dimensional changes occurring during the super-critical carbonation of glass fibre reinforced cement (GRC) and its subsequent environmental exposure have been investigated. Sheet samples, with embedded stainless steel pins 200 mm apart, were fabricated and then subjected to super-critical carbonation. Test coupons were subsequently exposed to a range of environments including continuous immersion in water, cyclic wetting/drying and outdoor exposure. The super-critical carbonation process resulted in a slight expansion of GRC. This is contrary to the behaviour observed during natural carbonation where irreversible shrinkage normally occurs. Exposure to the various environments mentioned above showed that super-critically carbonated samples had much greater resistance to swelling and shrinkage than uncarbonated specimens. These observations are particularly significant in relation to the practical application of GRC in environments of fluctuating moisture content.     

Effect of hygrothermal ageing on the monotonic and cyclic loading of glass fiber reinforced polyamide

The properties of short glass fiber reinforced thermoplastic based on polyamide 6 in humid environment are studied. Conditioning was conducted at 90°C. The combined action of water and heat (90°C) affects progressively the mechanical properties. When the injection molded samples were subjected to moisture, decrease in tensile strength and elastic modulus was observed whatever in distilled water or in salt solution. However, there is an enhancement of elongation at break with increasing exposure to humidity. After immersion in water, the fatigue life time is drastically reduced. Scanning electron microscope (SEM) was used in order to examine the fractured samples feature. Results show that water diffuses into the polymer leading to a reduction of the interfacial stress transmissibility. The major contributor of the stiffness loss is the adhesion loss between the fibers and the polymer. POLYM. COMPOS., 35:501–508, 2014. © 2013 Society of Plastics Engineers     

不同腐蚀试验的电化学阻抗谱评价

采用电化学阻抗谱分析了环氧涂层的介质浸泡、ASTM-B117盐雾试验、PROHESION循环试验的性能变化。实验结果表明:介质浸泡更侧重考察涂层的屏蔽作用,对环氧-聚酰胺体系酸性电解质更容易导致涂层失效;而盐雾试验更容易导致涂层吸收水分,干湿交替增加了有机涂层吸水能力;划痕试验表明样板在ASTM-B117和PRO-HESION遵循不同的腐蚀机理。     

Fatigue fracture of fully saturated bonded joints

The objective of this study was to compare the fatigue crack growth characteristics of adhesively bonded joints at several temperatures in air and salt water. Motivated by current trends in automotive structures, the specimens consisted of urethane adhesive bonding composite adherends with swirled glass fibers in an isocyanurate matrix. A modified cracked lap shear configuration under four-point bending was used to load the specimens, which were reinforced in order to ensure that cracking at or near the interface could be examined under all conditions. Potentially ambiguous diffusion transients were removed by fully saturating the specimens that were to be tested in salt water. Paris Law parameters and threshold values of energy release rate were extracted for each environmental condition that was studied. In air, both high and low temperatures increased crack growth rates and reduced threshold values relative to room temperature. Increasing temperature from 10°C consistently lowered the bond durability in salt water. The effects of load level, temperature, and environment on the fracture parameters were related to fracture mechanisms via recorded side views and fractographic evidence.     

高耐性水性环氧富锌底漆的制备与研究

为了制备高耐性的水性环氧富锌底漆,本文研究了环氧乳液粒径及其分布,活泼氢和环氧基的物质的量比对水性环氧富锌底漆的耐性尤其是耐盐雾、初期耐水性和耐闪锈性能的影响。实验结果表明,当环氧乳液粒径 ≤500 nm,且粒径分布均一,同时活泼氢和环氧基的物质的量比在 0. 8左右时,所得水性环氧富锌底漆的耐盐雾、初期耐水和耐闪锈性能达到最佳,其中耐中性盐雾可达 3 000 h,初期耐水性大于 480 h。此外,本文还研究了分散体系和防闪锈剂对耐盐雾、耐水和耐闪锈性能的影响,结果表明,选择高分子分散剂和与体系相容性好的防闪锈剂时,上述性能达到最佳。     

Short glass fibre reinforcedpoly(butylene terephthalate) Part 2 –Effect of hygrothermal aging onmechanical properties

Abstract

The mechanical properties of injection moulded poly(butylene terephthalate) (PBT) containing various loadings of short glass fibres (SGF) have been investigated. Properties studied include tensile, flexural, and impact. Effect of hygrothermal aging on the mechanical properties was investigated by immersing the respective specimens in distilled water at 30, 60, and 90°C. All the materials tested showed poor retention in mechanical properties upon exposure to hygrothermal aging. The effect became particularly pronounced at an immersion temperature of 90°C. Fractographic inspection of the fracture surfaces revealed that both PBT and SGF–PBT composites embrittled owing to a hydrolitic degradation process. Hydrolysis not only suppressed the matrix ductility but also reduced the bonding quality between PBT and SGF. Poor interfacial bonding was indicated by the absence of polymer matrix adhering to the fibre surfaces. The decrease in the impact strength of hygrothermally aged SGF–PBT composites provided further evidence that hygrothermal aging at high temperature reduces the contribution of fibre related toughening mechanisms. The residual mechanical properties of both PBT and its composites were not fully recovered after redrying. The permanent damage to these materials was attributed to severe hydrolytic degradation of PBT.     

Consequence of Intermittent Exposure to Moisture and Salt Fog on the High-Temperature Fatigue Durability of Several Ceramic-Matrix Composites

Fatigue behavior of four ceramic-matrix composites (CMCs) was documented at 1000°C, and a fifth composite was documented at 1200°C. Additional fatigue specimens were cycled for set blocks of cycles, removed from the fatigue machine, and exposed in a cyclic corrosion tester for 24 h with a fog of deionized water and a fog of deionized water containing 0.05 wt% NaCl. BN-fiber-coated Nicalon™/SiNC and Nicalon/Al₂O₃ experienced a pronounced decrease in fatigue life (∼86%) with salt fog exposure. Nicalon/C experienced rapid loss of the SiC exterior seal coat and a 30% decrease in life with salt fog exposure. Nextel610/AS and Nextel720/Al₂O₃ demonstrated no loss in fatigue performance or retained strength with water or salt fog exposure. Changes to the constituents of Nicalon/SiNC were evaluated to determine if they influenced moisture sensitivity. BN fiber coatings, BN or BN/SiC, alternate matrix prepreg, and matrix filler type had no influence on improving moisture resistance. Direct exposure to moisture fog produced accelerated rates of degradation in the BN fiber coating and greatly decreased fatigue durability.     

Durability of non-crimp fabric composites in aqueous environments

Abstract

Glass fibre composites subjected to hot water exhibit a reduction in stiffness and strength owing to a combination of matrix plasticisation and fibre/matrix interfacial degradation. If the composite system is subjected to some form of mechanical damage such as cracking from an external impact, the net consequence of water exposure is more difficult to predict.

This paper reports on the effects of water exposure at two temperatures (65 and 93°C) on non-crimp, quadriaxial, glass fabric systems with a polyester matrix. The residual properties are measured using the compression after impact test. It is shown that the residual properties of laminates tend to reach a minimum plateau after extended exposure to water, the value of which is dependent on the temperature of the water. It is also seen that the effects of impact damage vary depending on whether or not the impact is experienced before or after the water exposure. Impacting after conditioning produces a greater density of through thickness damage, which results in a lower compression after impact strength than impacting before conditioning.