Compression properties of fire-damaged polymer sandwich composites

The effect of fire-induced damage on the edgewise compression properties of polymer sandwich composites is investigated. Fire tests were performed using a cone calorimeter on sandwich composites with high or low flammability. The highly flammable composite had a poly(vinyl chloride) foam core, while the flame resistant composite had a phenolic foam core. The residual edgewise compression properties of the burnt composites were determined after fire testing at room temperature. The compression stiffness and strength of the two sandwich composites decreased rapidly with increasing heat flux and heating time of the fire due to thermal decomposition of the face skin and foam core. A large reduction to the edgewise compression properties of the phenolic-based sandwich composite occurred despite having good flame resistance, and the reasons for this are described. Preliminary analytical models are presented for estimating the edgewise compression failure load of fire-damaged sandwich composites that fail by core shear or buckling.     

Post-fire flexural properties of fibre-reinforced polyester, epoxy and phenolic composites

The effect of fire damage on the flexural properties of fibre-reinforced polymer (FRP) composites is investigated. The FRP composites studied contained glass, carbon or Kevlar fibres with a polyester, epoxy or phenolic resin matrix. Artificial fire tests were performed on the composites using a cone calorimeter. The residual flexural modulus and strength of the burnt composites were determined at room temperature after the fire tests. The post-fire flexural properties of all the composites decreased rapidly with increasing heating time. Even the properties of the fibre-reinforced phenolic materials were severely degraded despite their low flammability and excellent fire resistance. The flexural properties of the phenolic-based composites were reduced due to thermal degradation and cracking of the resin matrix. In comparison, the properties of the polyester- and epoxy-based composites were reduced by combustion of the resin and formation of delamination cracks. A model is presented for determining the post-fire flexural properties of FRP composites with good accuracy.     

Post-fire mechanical properties of marine polymer composites

Changes to the tensile and flexure properties of marine-grade glass-reinforced polyester, vinyl ester and resole phenolic composites after exposure to radiant heat are investigated. The properties were determined at room temperature after the composites had been exposed to heat fluxes of 25–100 kW/m² for 325 s or to a heat flux of 50 kW/m² for increasing times up to 1800 s. The stiffness and failure load of all three composites decreased rapidly with increasing heat flux or time due mainly to the thermal degradation of the resin matrix. The post-fire tension and flexure properties of the resole phenolic composite were similar to the properties of the other composites, despite its superior fire resistance. Models are presented for determining the post-fire mechanical properties of fire-damaged composites, and are used to estimate the reductions in failure load of composite ship materials caused by fire.     

Review of fire structural modelling of polymer composites

This paper presents a critical review of research progress in modelling the structural response of polymer matrix composites exposed to fire. Models for analysing the thermal, chemical, physical, and failure processes that control the structural responses of laminates and sandwich composite materials in fire are reviewed. Models for calculating the residual structural properties of composites following fire are also described. Progress towards validation of the models by experimental characterisation of the structural properties of composites during and following fire is assessed. Deficiencies in the fire structural models are identified in the paper, which provide the focus for future research in the field.     

Modeling of post-fire stiffness of E-glass fiber-reinforced polyester composites

A new model is proposed to estimate the post-fire stiffness of FRP composites after different fire-exposure times. The model considers the E-modulus recovery of the material if cooled down from temperatures between glass transition and decomposition during the fire. Furthermore, based on this model, the through-thickness temperature gradients and remaining resin contents (RRC) can be calculated. Post-fire stiffness estimated by the new model and refined two- and three-layer post-fire models based on temperature or RRC criteria was compared with experimental results. A good agreement of calculated and measured post-fire stiffness of two full-scale cellular GFRP panels subjected to mechanical and thermal loading was found for fire-exposure times up to 2 h.     

Post fire behavior of carbon fibers Polyphenylene Sulfide- and epoxy-based laminates for aeronautical applications: A comparative study

Through the comparison of two carbon fiber-reinforced polymers (Epoxy and Polyphenylene Sulfide – PPS), this work was aimed at investigating the influence of different fire conditions on the high temperature tensile mechanical behavior. In order to better understand the influence of matrix nature on post-fire properties, the fiber – or matrix-dominated mechanical responses of laminates have been investigated by means of quasi-isotropic or angle-ply stacking sequences. Compared to carbon/PPS laminates, the mechanical properties of carbon/Epoxy laminates are higher in the virgin state (no prior fire exposure). The analysis of the post fire tensile properties shows that prior severe fire exposures are more detrimental to carbon/Epoxy than to carbon/PPS laminates. Although the PPS matrix behavior is highly ductile at a test temperature higher than glass transition temperature, it clearly appears that the decrease in the tensile properties laminates of PPS-based composites is much slower than the one observed in carbon/Epoxy laminates subjected to severe prior fire conditions. Provided the heat flux is high enough to lead to the outset of pyrolysis, PPS-based composites yield higher amounts of char, whose formation retains the structural integrity of fire-damaged composites.     

Tensile and Compressive Properties of FRP Composites with Localised Fire Damage

The effect of localised fire damage on the tensile and compressive properties of fibre-reinforced polymer (FRP) composites is investigated. A simple model based on rule-of-mixtures is presented for determining reductions to the tensile stiffness, tensile strength, compressive stiffness and compressive strength of composite panels with localised fire damage of any shape and size. The validity of the model is rigorously tested against experimental tension and compression property data for a glass/polyester composite with localised fire damage in the shape of a circle, oval, square, diamond or in a irregular shape. The model is found to accurately predict the tension and compression properties of composites with localised fire damage of any shape, and is expected to be a useful model for estimating the residual structural integrity of fire-damaged composite panels.     

Finite difference analysis of thermal response and post-fire flexural degradation of glass fiber reinforced composites coated with carbon nanofiber based nanopapers

In this study, a 1D transient finite difference model was developed to predict the thermal response and post-fire flexural modulus degradation of glass fiber reinforced polyester composites subjected to various levels of heat flux. A carbon nanofiber (CNF) based hybrid nanopaper was coated onto the surface of the composites. The protective nanopaper coating was treated as to impose a temperature boundary condition in the model. A temperature dependent post-fire mechanical property model proposed in an earlier study was implemented with the thermal model in which the porosity and permeability of the material were taken into account. By comparing the post-fire residual flexural moduli, the model prediction showed reasonable agreement with the experimental data and expected physical behaviors. The model numerically demonstrates how the coating of nanopaper helps retain the structural integrity of the composite material, namely, the nanopaper coating leads to a reduction in mass loss, reduced cold side temperature, and eventually improved mechanical property. Furthermore, the parametric study of the model suggested that the porosity of the material has profound influence on the residual moduli of the composites.     

Self-reinforced poly(ethylene terephthalate) composites by hot consolidation of Bi-component PET yarns

Self-reinforced polymer composites or all-polymer composites have been developed to replace traditional glass-fibre-reinforced plastics (GFRP) with good lightweight, mechanical and interfacial properties and enhanced recyclability. Poly(ethylene terephthalate) (PET) is one of the most attractive polymers to be used in these fully recyclable all-polymer composites, in terms of cost and properties. In this work, unidirectional all-PET composites were prepared from skin–core structured bi-component PET multifilament yarns by a combined process of filament winding and hot-pressing. During hot-pressing, the thermoplastic copolyester skin or sheath layers were selectively melted to weld high-strength polyester cores together creating an all-PET composite. Physical properties of the resulting composites including thickness, density and void content were reported. The effect of processing parameters, i.e. consolidation temperature and pressure on mechanical properties and morphology was investigated in order to balance good interfacial adhesion with residual tensile properties of the composite.     

The effective properties and local aggregation effect of CNT/SMP composites

A micromechanics model of the thermomechanical constitutive behavior and micro-structural inhomogeneity of carbon nanotubes (CNTs)/shape memory polymer (SMP) composites is presented. It is assumed that the CNTs are elastic and the SMP obeys a thermomechanical constitutive law. The effective properties of CNT/SMP composites are examined using a micro-mechanics method. The effect of CNT aggregation in the composite, frequently encountered in real engineering situations, is studied. The degree of aggregation is described by an aggregation coefficient, and the effective properties of SMP composites with aggregated CNTs are calculated using a stepping scheme. It is shown that the degree of CNT aggregation dramatically influences the effective properties of the CNT/SMP composites. A homogeneous microstructure leads to maximum levels of effective composite properties.     

Overall behavior and microstructural deformation of R-CNT/polymer composites

Carbon nanotubes (CNTs) are an excellent candidate for the reinforcement of composite materials owing to their distinctive mechanical and electrical properties. Reticulate carbon nanotubes (R-CNTs) with a 2D or 3D configuration have been manufactured in which nonwoven connected CNTs are homogeneously distributed and connected with each other. A composite reinforced by R-CNTs can be fabricated by infiltrating a polymer into the R-CNT structure, which overcomes the inherent disadvantages of the lack of weaving of the CNTs and the low strength of the interface between CNTs and the polymer. In this paper, a 2D plane strain model of a R-CNT composite is presented to investigate its micro-deformation and effective stiffness. Using the two-scale expansion method, the effective stiffness coefficients and Young’s modulus are determined. The influences of microstructural parameters on the micro-deformation and effective stiffness of the R-CNT composite are studied to aid the design of new composites with optimal properties. It is shown that R-CNT composites have a strong microstructure-dependence and better effective mechanical properties than other CNT composites.     

Review of the mechanical properties of carbon nanofiber/polymer composites

In this paper, the mechanical properties of vapor grown carbon nanofiber (VGCNF)/polymer composites are reviewed. The paper starts with the structural and intrinsic mechanical properties of VGCNFs. Then the major factors (filler dispersion and distribution, filler aspect ratio, adhesion and interface between filler and polymer matrix) affecting the mechanical properties of VGCNF/polymer composites are presented. After that, VGCNF/polymer composite mechanical properties are discussed in terms of nanofibers dispersion and alignment, adhesion between the nanofiber and polymer matrix, and other factors. The influence of processing methods and processing conditions on the properties of VGCNF/polymer composite is also considered. At the end, the possible future challenges for VGCNF and VGCNF/polymer composites are highlighted.     

纳米碳形貌对纳米碳/聚乙烯导电复合材料性能的影响

分别以纺锤形碳酸钙表面改性的二维片状石墨烯微片（CGM）和多壁碳纳米管（MWCNTs）作为导电剂填充改性聚乙烯（PE）制备导电复合材料。重点研究了二维或一维纳米碳/PE复合材料形成导电网络时力学与电学性能。CGM/PE或MWCNTs/PE复合材料达到抗静电要求时CGM的质量分数为8wt%,而MWCNTs的质量分数为1wt%。填充8wt% CGM的复合材料表现出优异的综合性能,而填充0.5wt% MWCNTs的复合材料综合力学性能达到最大值还未能达到抗静电要求,达到抗静电要求时MWCNTs/PE复合材料的综合力学性能出现下降趋势。通过形貌及流变学分析了复合材料不同的力学与电学性能的微观作用因素。CGM/PE复合材料流变渗流阈值与导电渗流阈值存在比较好的相关性,MWCNTs/PE复合材料达到流变渗流阈值还不能形成导电网络。结果表明,与二维CGM相比,一维MWCNTs不易均匀分散于聚合物基体中,并降低MWCNTs/PE复合材料的力学性能。     

In vitro release kinetics and physical, chemical and mechanical characterization of a POVIAC ? /CaCO 3 /HAP-200 composite

Coralline calcium-hydroxyapatite and calcium carbonate from Porites Porites coral were added to a polymeric matrix based on polyvinyl acetate (POVIAC^?), to obtain a novel bone substitute composite as well as a system for the controlled drug (cephalexin) release. Composite samples with different compositions were characterized by physical–chemical and mechanical methods. Furthermore, the in vitro release profile of cephalexin and the kinetic behavior of its release from these composites were analyzed by appropriate mathematical models. It was shown that there is no chemical interaction between the inorganic filler and the polymer matrix, each conserving the original properties of the raw materials. The compressive mechanical strength and Young modulus of the composite with 17.5% of POVIAC^?, has better mechanical properties than those of cancellous bone. The variation of POVIAC^? content can affect the cephalexin release kinetic in the composite. The cephalexin release mechanism from the composites can be considered as the result of the joint contribution of a prevailing Fickian diffusion and of polymer chain relaxation. It was also demonstrated that cephalexin is occluded inside the composites and not on their surface.     

Influence of mineral on the load deformation behavior of polymer in hydroxyapatite-polyacrylic acid nanocomposite biomaterials: a steered molecular dynamics study

Composites of hydroxyapatite and polymers are widely studied for bone replacement. To perform satisfactorily in the human body, these composites need to be biocompatible and exhibit optimum mechanical properties. The load-deformation behavior of composites is often investigated using experimental techniques. However, the molecular mechanisms of load deformation behavior are not clearly understood. We have used Steered Molecular Dynamics to evaluate the load-deformation behavior at interfaces in polyacrylic acid-hydroxyapatite (HAP) composite models. The polymer is pulled at constant velocity in close proximity of HAP. On comparing the results obtained for deformation behavior of polymer in vicinity of mineral and in the absence of mineral, it was found that energy required to pull the polymer in close proximity of HAP is significantly higher. Also, structural details of the load transfer mechanisms in composite were investigated under both conditions. Our simulations indicate that there is a significant role of mineral-polymer interactions on the mechanical response of polymer.     

Effective reinforcement in carbon nanotube-polymer composites

Carbon nanotubes have mechanical properties that are far in excess of conventional fibrous materials used in engineering polymer composites. Effective reinforcement of polymers using carbon nanotubes is difficult due to poor dispersion and alignment of the nanotubes along the same axis as the applied force during composite loading. This paper reviews the mechanical properties of carbon nanotubes and their polymer composites to highlight how many previously prepared composites do not effectively use the excellent mechanical behaviour of the reinforcement. Nanomechanical tests using atomic force microscopy are carried out on simple uniaxially aligned carbon nanotube-reinforced polyvinyl alcohol (PVA) fibres prepared using electrospinning processes. Dispersion of the carbon nanotubes within the polymer is achieved using a surfactant. Young's modulus of these simple composites is shown to approach theoretically predicted values, indicating that the carbon nanotubes are effective reinforcements. However, the use of dispersant is also shown to lower Young's modulus of the electrospun PVA fibres.     

Modeling the tensile stress–strain response of carbon nanotube/polypropylene nanocomposites using nonlinear representative volume element

This paper presents a finite element model for predicting the mechanical behavior of polypropylene (PP) composites reinforced with carbon nanotubes (CNTs) at large deformation scale. Existing numerical models cannot predict composite behavior at large strains due to using simplified material properties and inefficient interfaces between CNT and polymer. In this work, nonlinear representative volume elements (RVE) of composite are prepared. These RVEs consist of CNT, PP matrix and non-bonded interface. The nonlinear material properties for CNT and polymer are adopted to solid elements. For the first time, the interface between CNT and matrix is simulated using contact elements. This interfacial model is capable enough to simulate wide range of interactions between CNT and polymer in large strains. The influence of adding CNT with different aspect ratio into PP is studied. The mechanical behavior of composites with different interfacial shear strength (ISS) is discussed. The success of this new model was verified by comparing the simulation results for RVEs with conducted experimental results. The results shows that the length of CNT and ISS values significantly affect the reinforcement phenomenon.     

Compression creep rupture behavior of a glass/vinyl ester composite laminate subject to fire loading conditions

The growing use of polymer matrix composites in civil infrastructure, marine and military applications provides the impetus for developing mechanical models to describe their response under combined mechanical and fire loading. A viscoelastic stress analysis using classical lamination theory is conducted on an E-glass/vinyl ester composite. The model includes a characterization of the non-linear thermo-viscoelasticity and its inclusion into a compression strength failure criterion for the prediction of laminate failure under combined compressive load and temperature profile simulating fire exposure. By accounting for the viscoelastic non-linearity at T_g, the proposed model yields good predictions for lifetimes of the studied composite ([0/+45/90/−45/0]_S).     

生物质纤维填充聚合物复合材料的界面行为

将木粉和聚合物加入HAAKE流变仪中熔融共混制备了木粉/聚合物复合材料,对比不同木粉预处理方式(碱处理、酸处理)及相容剂改善木粉与聚合物界面相容性的效果。红外光谱(FT-IR)结果表明,碱处理木粉去除了木粉中的小分子物质,酸处理木粉使木粉表面被酯化。木粉碱处理提高了木粉/聚合物复合材料的力学性能,扫描电镜(SEM)照片表明预处理后木粉与聚合物间的相容性得到了改善。使用合适的相容剂也可以改善木粉与聚合物的相容性,提高复合材料的力学性能。同时相容剂和碱处理木粉及酸处理木粉存在协同效应。     

Properties of lime composites containing a new type of pozzolana for the improvement of strength and durability

The basic material characteristics, mechanical and fracture-mechanical properties, durability characteristics, hydric parameters, and thermal properties of several lime–pozzolana composites with different dosage of the burnt Czech clay shale are investigated. Within the studied range of the pozzolana:lime (P:L) ratio of 0.2:2.3–1.7:0.8, the mix with P:L = 0.9:1.6 is found to be the most effective solution. Its compressive strength, bending strength, effective fracture toughness, fracture toughness, and fracture energy are up to ten times higher, as compared with the reference lime composite without pozzolana addition, the water transport parameters are several times lower, the water vapor transport parameters are only about two times higher, the freeze/thaw resistance is significantly better, and the thermal properties are comparable. In a comparison with the reference lime–metakaolin composite, the corresponding material with burnt Czech clay shale is found to achieve similar mechanical and fracture-mechanical properties, its freeze/thaw resistance is somewhat worse, the water absorption coefficient is slightly lower, the water vapor diffusion coefficient is slightly higher, and the thermal properties are comparable. Therefore, the new lime–pozzolana composites have a good potential to be used as surface layers of building structures instead of lime composites without any addition, as an alternative solution to lime–metakaolin composites.