尼龙无纺布增韧RTM复合材料的湿热老化性能

采用尼龙无纺布(PNF)作为结构化增韧层,利用树脂传递模塑(RTM)工艺制备了PNF层间增韧改性的碳纤维增强环氧树脂基复合材料(U3160-PNF/3266),研究了U3160-PNF/3266复合材料的吸湿特性及湿热老化对其耐热性能的影响。结果表明:增韧前后复合材料具有相似的吸湿动力学特性,但在吸湿初期,U3160-PNF/3266复合材料具有更大的吸湿速率,达到饱和吸湿后,U3160-PNF/3266复合材料的饱和吸湿率约为0.96%,略大于非增韧复合材料U3160/3266的0.87%。随着湿热老化时间的增加,两种复合材料的玻璃化转变温度均逐渐降低,并随着吸湿率的饱和而趋于平稳,达到饱和吸湿后,U3160-PNF/3266和U3160/3266复合材料的玻璃化转变温度分别下降了约15%和14%。     

Fracture behavior of stitched warp-knit fabric composites

Pilot studies are conducted to characterize the macroscopic fracture resistance behavior using linear elastic fracture mechanics and attempt to quantify the fracture parameters in which may govern the fracture and failure patterns of stitched warp-knit fabric composites. Methods based on the J-integral method and Betti's reciprocal theorem in extracting the fracture parameters, critical stress intensity factors, T-stress, and the second term of _y(r,0) near the crack tip prior to fracture initiation are formulated. Two fracture criteria, [_c,r _c] and [_c,r _c] are attempted to characterize the failure initiation for the fiber-dominated failure mode and self-similar crack extension in a given thickness of the laminate. Based on linear elastic fracture mechanics principle, these criteria are transformed into crack-driving forces [K _Q,T] and [K _Q,g ₃₂]. The two-parameter fracture criteria, [K _Q,T] and [K _Q,g ₃₂] provide a good correlation for the CCT and SENT specimens, but not for the high constraint CT specimens. With the limited experimental data, the results tend to show that the large tensile T-stress and large magnitude of negative g ₃₂ may inhibit the crack extension in the same crack plane and promote crack kinking.     

Initial fracture behavior of satin woven fabric composites

Final fractures of composites is considered to be caused by cumulation of the microfractures, so that, the initiation of microfracture, namely, initial fracture is important factor to know the mechanical properties. Microfracture behaviors in textile composites were regarded to be decided by the geometry of textile fabric quantitatively. In this study, initial fracture in plain and satin woven fabric composites was investigated and the effect of weaving structure on initial fracture behavior was clarified. First, in order to investigate the geometry of textile fabric, crimp ratio and aspect ratio were measured. Tensile testing was performed and knee point on the stress–strain curve was identified. Fracture process of composites was observed by replica method. Initial fracture in plain woven fabric composite was confirmed as transverse crack in weft fiber bundle, on the other hand, in satin woven fabric composites both transverse crack and filament fracture at the same time was observed. The effects of changes in crimp ratio and aspect ratio on the initial fracture of woven fabric composites were discussed.     

Effect of fabric types on the impact behavior of cement based composites in flexure

Two different fabric types were used to investigate the effect of the fabric types on the static and impact behavior of fabric reinforced cement based composites by using three point bending tests for various drop heights of hammer and position of the specimens on the supports. For each fabric type, 18 specimens with dimensions of 50 mm × 150 mm × 12 mm were produced with the pultrusion process. The vertical specimens have more stiffness, less ultimate deflection and higher load carrying capacity than the horizontal specimens for same drop heights. However, the horizontal specimens subjected to impact loads have higher stresses than the vertical specimens due to the section properties. The tests showed that polyvinyl alcohol (PVA) fabric reinforced cement based composites carried higher impact loads, were stiffer and had less deflection than other composites. At the drop heights over 100 mm, the impact strength of the horizontal specimens sharply decreased, while that of the vertical specimens was remained same.     

Impact and post impact behavior of layer fabric composites

In this study, the effect of impact and post impact behavior of E-glass/epoxy composite plates having different layer fabrics were investigated by considering energy profile diagram and the related load–deflection curves. Different impact energies (5 J–60 J)were subjected to the plates consisting of eight layers of plain weave (1D), double (2D) and triple (3D) layer fabrics. The impact tests were continued until complete perforation of layer fabrics. The damage modes and damage processes of layer fabrics under varied impact energies were also discussed. At the end of the impact tests, the damaged samples were mounted into a compression apparatus to determine the Compression After Impact (CAI) strength of layer fabric samples. The results of these impact and post impact tests showed that contact force occurring between the impactor and the composite specimen increased and the CAI strength reduced by increasing the impact energy. The objective of this study was to determine the perforation threshold of E-glass/epoxy composite plates having different layer fabrics as plain weave (1D), double (2D), and triple (3D) layer fabrics.     

Scalable fabrication of novel SiC nanowire nonwoven fabric

Flexible papers constructed by one-dimensional nanowires have attracted much attention due to their various applications. Herein, a novel nonwoven fabric with paper-like qualities composed of zinc blende SiC (β-SiC) nanowires was fabricated by a scalable rolling process. The SiC nanowires were synthesized by the carbothermal reduction reaction of the carbon fiber and carbonaceous silica xerogel. The crystal phase, morphology and microscopic structure of the as-prepared SiC nanowires were characterized by field emission scanning electron microscope, X-ray diffraction and high-resolution transmission electron microscopy. The nanowire vapor–solid growth mechanism and preparation process for SiC nanowire nonwoven fabric were also discussed. The freestanding SiC nanowire nonwoven fabric exhibited high flexibility, high mechanical strength, excellent refractory performance and thermal stability. With high flexibility, high mechanical strength, superior nonflammability and thermal stability, the flexible paper-like 3C-SiC nanowire nonwoven fabric materials would be expected to have some potential applications, such as ceramic matrix composites, metal matrix composites, energy storage, catalyst supports, radiation-proof fabric, filtration and separation.     

Tensile strength,peel load,and static puncture resistance of laminated composites reinforced with nonwoven fabric

Nonwoven fabrics were used as reinforcement to laminated composites to improve the mechanical properties and damage behaviors. The needle-punched Kevlar/LMPET nonwoven interlayer and two TPU covers were combined via thermal bonding to form the laminated composites. Tensile strength, peel load, and static puncture resistance of the laminated composites were evaluated in terms of needle punching rate and depth of the nonwoven interlayer. Results showed that tensile strength and static puncture resistance depended on the needle punching depth, primarily on the tangled fiber points. The peel load was dependent on the needle punching rate, especially on the resulting melted LMPET fibers. The laminated composites exhibited desirable tensile properties, peel load, and static puncture resistance.     

Design of artificial lotus leaves using nonwoven fabric

The apparent contact angles of a droplet deposited on the surfaces of thermal-bonded nonwoven fabrics were presented, and the characteristics required for a superhydrophobic surface were described. For a nonwoven superhydrophobic surface, the Cassie–Baxter model describes the wetting of rough surfaces. Using topological and chemical surface modifications of nylon 6,6 nonwoven fabric, artificial Lotus leaves having water contact angles >150° were prepared. Good agreement between the predictions based on the original Cassie–Baxter model and experiments was obtained. The angle at which a water droplet rolls off the surface has also been used to define a superhydrophobic surface. Superhydrophobic surfaces were prepared by two criteria: a low-surface energy and a properly designed surface roughness.     

The properties of polyurethane hybrid materials based on castor oil

The goal of this work was to investigate the properties of environmentally friendly, castor oil based polyurethane hybrid materials with titanium(IV) oxide nanoparticles, as a filler, and different types of diisocyanate (toluene diisocyanate and isophorone diisocyanate). In the sample synthesis, different ratios of the reactive groups (NCO/OH), r, were used (1, 1.15 and 0.92). In the composite preparation, only toluene diisocyanate was used, and the filler particles were premixed in a glass vessel with the castor oil polyol before the reaction with diisocyanate. For all the composite samples, the r value was 1. Polyurethane formation was confirmed by ATR-FT-IR by detecting the urethane band at 1515 cm⁻¹. It was determined that the hydroxyl groups had reacted because the broad band corresponding to the OH groups (3400 cm⁻¹) was not detected or detected at a reduced intensity depending on the r value. As was expected, the presence of the unreacted NCO groups was detected only for samples with r > 1 (band at 2300 cm⁻¹, which corresponds to the existence of these groups). The dynamic mechanical measurements were performed at a temperature range from −50 °C to 100 °C at different frequencies. For investigation of reinforcement effect of filler on polymer matrix, tensile testing was applied. The glass transition temperature, T_g, was determined by DSC measurement. It was estimated that the T_g of the samples decreased as the nanofiller content increased due to the changes in the segmental mobility influenced by the interaction between the nanoparticles and polymer chains.     

Synthesis and characterization of castor oil based polyurethane-polyacrylonitrile interpenetrating polymer networks

A series of interpenetrating polymer networks (IPNs) of castor oil based polyurethane/polyacrylonitrile (PU/PAN: 80/20, 60/40, 50/50, 40/60 and 20/80) were synthesized by condensation reaction of castor oil with methylene diisocyanate and acrylonitrile, employing benzoyl peroxide (BPO) and ethylene glycol dimethylacrylate (EGDM) as initiator and crosslinkers respectively. The physical, chemical, optical and some of the mechanical properties of PU/PAN were studied. Phase stabilization in IPNs was investigated by wide angle X-ray (WAXS) profile analysis. Variation of crystal size distribution was studied in these polymer networks. Paper presented at the 5th IUMRS ICA98, October 1998, Bangalore     

纳米SiO2/蓖麻油封端聚氨酯/环氧树脂复合体系的合成及表征

采用活性稀释剂的环氧基团与纳米SiO2反应这种新型的改性方法,达到对纳米SiO2的表面改性、防止团聚等目的;以环氧树脂(E44)和缩水甘油(glycidyl)同时对蓖麻油聚氨酯预聚体进行封端,与TDE-85环氧树脂共混,组成纳米SiO2/蓖麻油聚氨酯/环氧树脂的复合体系。采用FT-IR、TGA、SEM和万能试验机对体系的相关性能进行表征并采用DMA对体系的阻尼性能进行了测试,结果表明,与传统的蓖麻油聚氨酯/环氧树脂体系相比,这种新型的纳米SiO2/蓖麻油聚氨酯/TDE-85的复合体系具有更加优异的热性能和力学性能,断面形貌显示体系相容性好且纳米SiO2没有发生团聚;加入改性后的纳米SiO2后,提高了复合体系的阻尼性能,随着改性后纳米SiO2的量不断增加,体系的阻尼性能也不断增强。     

Low velocity flexural impact behavior of AR glass fabric reinforced cement composites

Fabric–cement composites developed using the pultrusion production process have demonstrated impressive tensile and flexural properties. For instance fabric reinforced composites with bonded Alkali Resistant (AR) glass fabrics exhibit strain-hardening behavior, tensile strength in the range of 20–25 MPa, and strain capacity of the order of 2–5% under static conditions. Properties of these composite systems were investigated under three point bending conditions using an instrumented drop weight impact system. Samples were studied from the viewpoint of the variations of impact load, deflection response, acceleration and absorbed energy. Development of the testing system in terms of components and acceleration response are discussed in detail. Methods of the impact load measurement using three different ways of acceleration response, piezoelectric load washer and conventional strain gage based load cell are discussed. Cement composites with two different fabric contents and four different drop heights of hammer (dropping mass) were tested. Experimental results indicate that for the same drop height, the stiffer beam type specimens have a lower ultimate deflection but a higher load carrying capacity than the plate type specimens. The maximum flexural stress and absorbed energy of composites increase with drop height. In beam specimens, complete fracture does not take place as cracks form and close due to rebound and significant microcracking in the form of radial fan cracking is observed, whereas interlaminar shear is the dominant failure mode in the plate specimens.     

Mechanical behavior of cellulignin based composites

A powder derivative of acid pre-hydrolysis processing of cellulosic wastes, known as cellulignin, was used as filler in resin matrix composites. The flexural mechanical properties of cellulignin-polyester, epoxy or urea-formaldehyde matrix composites was evaluated. The results obtained show that the urea-formaldehyde and epoxy based composites can be used as alternative materials for low cost and low strength applications. Their advantages over the common wooden agglomerates or composites are presented and are based on the fact that cellulignin can be obtained virtually from any cellulosic waste.     

Analytical simulation of tensile response of fabric reinforced cement based composites

A model simulating the tensile behavior of fabric–cement composites is presented to relate the properties of the matrix, fabric, interface and the damage parameters to the overall mechanical response of the composites. Crack spacing parameters measured during tensile tests are used to define the damage parameters, and related to the stiffness degradation as a function of the applied strain. This procedure is integrated in composite laminate theory using an incremental approach to model the uniaxial tensile response. Two approaches of linear and nonlinear fabric bridging models are used. The model is capable of using interface parameters for different fabrics, matrix properties, and processing parameters. Simulation results are studied by means of parametric simulation and a validation of a variety of experimental observations which vary the matrix formulation with flyash, changes in pressure after casting, and fabric type.     

Tough blends of polylactide and castor oil

Poly(l-lactide) (PLLA) is a renewable resource polymer derived from plant sugars with several commercial applications. Broader implementation of the material is limited due to its inherent brittleness. We show that the addition of 5 wt % castor oil to PLLA significantly enhances the overall tensile toughness with minimal reductions in the modulus and no plasticization of the PLLA matrix. In addition, we used poly(ricinoleic acid)-PLLA diblock copolymers, synthesized entirely from renewable resources, as compatibilizers for the PLLA/castor oil blends. Ricinoleic acid, the majority fatty acid comprising castor oil, was polymerized through a lipase-catalyzed condensation reaction. The resulting polymers contained a hydroxyl end-group that was subsequently used to initiate the ring-opening polymerization of l-lactide. The binary PLLA/castor oil blend exhibited a tensile toughness seven times greater than neat PLLA. The addition of block copolymer allowed for control over the morphology of the blends, and even further improvement in the tensile toughness was realized-an order of magnitude larger than that of neat PLLA.     

Effects of through-the-thickness stitches on the elastic behavior of multi-axial warp knit fabric composites

In order to improve the resistance to delamination and some in-plane and out-of-plane properties of composite materials for structural integrity, through-the-thickness reinforcement must be provided. The reinforcement is achieved by using the stitched multi-axial warp knit (MWK) fabrics as preforms for the fabrication of composite structures. In this study, the influence of stitches on the elastic behavior of MWK fabric composites under tensile and shear loadings was investigated by utilizing a unified micromechanical model. In the analysis, the in situ constituent properties and fiber volume ratios of insertion and stitching fibers determined from the geometric parameters set by the representative volume were used. The crucial step in the analysis was to correlate the averaged stress states in the constituents by adopting the bridging matrix. The experimental results were compared with the predicted results. It was found that the predicted results are in reasonably good agreement with the experimental results.     

Structure-property relationship of castor oil based diol chain extended polyurethanes (PUs)

A series of 1,4-butane diol and 1,6-hexane diol based chain extended polyurethanes (PUs) have been prepared using castor oil with different diisocyanates such as methylene bis (phenyl isocyanate) (MDI), toluene-2,4-diisocyanate (TDI) and hexa methylene diisocyanate (HMDI) as crosslinkers. The prepared aliphatic diol based chain extended PU's have been characterised for physico-mechanical properties such as density, tensile strength, percentage elongation at break, tensile modulus and surface hardness; and optical properties like total transmittance and haze. The properties imparted by the chain extenders and diisocyanates on PUs have been explained on the basis of chemical structure. Effect of heat aging on mechanical properties of PUs have also studied. These changes have been interpreted quantitatively in terms of microcrystalline parameters computed using wide-angle X-ray scattering (WAXS) data.     

Fracture toughness of weft-knitted fabric composites

The mode I inter-laminar fracture toughness of advanced knitted textile composites was investigated. Two complex weft-knitted glass fabrics were selected for the study: a triple rib knit and a Milano knit were impregnated with a tough epoxy resin and tested using a double cantilever beam geometry. For both knitted composites, the influence of the growth direction was studied by investigating crack propagation in both the wale and course directions. The fracture toughness was quantified by determining the critical strain energy release rate (G_IC) using the modified beam theory. The specimens had to be stiffened with layers of glass woven composites added on top and bottom of the beams. This was necessary in order to avoid plastic deformation of the beams and crack deviation out of the inter-laminar plane. The results clearly showed that knitted fabric composites have exceptional inter-laminar fracture toughness properties, namely, more than 7000 J/m². The origin of the high G_IC values, which are superior to woven or UD laminates, lies in the very complex fabric architecture. The three-dimensional loop structure induces various energy consuming mechanisms, which do not occur in other composites. Toughening mechanisms such as crack branching, friction, yarn bridging and breakage were identified using scanning electron microscopy.     

A stiffness volume averaging based approach to model non-crimp fabric reinforced composites

A representative volume element (RVE) based model to evaluate the mechanical performance of non-crimp fabric (NCF) composites has been developed and presented hereafter. By means of the stiffness averaging method, the modelling procedure is able to simulate the NCF’s elastic properties taking into account the effects of process-induced defects and final geometrical configuration. Microscopy analysis has been used to quantitatively evaluate the effects of tow waviness, stitching geometrical parameters and matrix porosity; these features have been included as sub-models into the final model. Numerical predictions have been compared to the results of tensile tests performed on composite coupons. A geometrical parameter characterising the undulation of the tows has been introduced and a sensitivity analysis has been performed on the model with different undulations.