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21.
《Composite Interfaces》2013,20(1):17-39
The singular behaviour at the free edges of the fibre-matrix interface is analysed for the fibre push-out test geometry based on the boundary element method. The fibre push-out test has been extensively used to measure the fibre-matrix interfacial properties in polymer, ceramic and metal matrix composites. There are two free edges in the fibre push-out specimen: one is at the loaded fibre end and the other at the supported fibre end. The singular stresses can be expressed as a function of singular exponent and singular stress intensity. It is shown that the singular exponents obtained at both fibre ends are characteristic of composite constituent properties, such as Young's moduli of fibre and matrix, and does not vary with specimen dimensions. The singular exponents are real and identical for the shear and radial stress components at fibre ends where the wedge angles are the same. The singular stress intensities are also implicit in material properties, and vary with specimen dimensions, such as fibre to matrix radius ratio, fibre aspect ratio and support hole size. An interfacial failure criterion is proposed here based on the average stress concept to determine the critical singular stress intensities in mode I and mode II loads. 相似文献
22.
《Composite Interfaces》2013,20(5-6):361-391
We propose a new model for characterization of strength properties of fiber-polymer interfaces by means of a single fiber pull-out test. Our model is based on shear-lag analysis using a bilinear bond law (stress–slip relationship) which, in turn, is a simplified representation of the true stress behavior as a function of strain for cold-drawing polymers. According to this law, the fiber-polymer interface is subjected to the following successive processes: (1) linear loading within the elastic region; (2) yielding and subsequent bond strengthening with increasing strain; (3) local debonding and interfacial crack propagation along the interface; (4) post-debonding friction. Both crack propagation and extension of the yielded zone can be stable and unstable, depending on the values of interfacial parameters and the load applied to the free fiber end. The procedure of construction of theoretical force–displacement curves for a pull-out test is described in detail. Theoretical curves exhibit such features as multiple kinks and non-linear regions, whose positions and shape are related to interfacial parameters. By fitting experimental curves with theoretical ones, these parameters can be determined for each separate pull-out specimen. Practical examples are provided for basalt fiber–polypropylene and glass fiber–polypropylene specimens. 相似文献
23.
《Composite Interfaces》2013,20(2-3):311-319
The transverse tensile properties of phenolic composites reinforced with spun-type carbon fabrics (spun C/P composites) have been investigated in order to evaluate the adherent failure behavior of composites in the transverse (90°) direction due to tension. The transverse tensile strength of the spun C/P composite is about 3.4 times higher than that of the conventional composite reinforced with filament type carbon fabrics (filament C/P composites). It is found from stress–strain curve of composites that it exhibits above 4 times higher failure strain than the filament C/P composite. However, the transverse tensile modulus of the spun C/P composite is similar to that of the filament C/P composite. The results indicate that the protruded fibers of spun yarns between the interlaminar layers in the spun C/P composite play an important role in improving the transverse tensile properties by the effects of fiber bridging. Consequently, this result suggests that use of spun yarn type carbon fabrics as reinforcement in a phenolic composite may significantly contribute to improving the interfacial properties of carbon/phenolic composites. 相似文献
24.
《Composite Interfaces》2013,20(8-9):659-684
Talc, calcium carbonate (CaCO3), and kaolin hold considerable promise in the development of polymer composites for good mechanical properties and stability. Comparative studies on the usage of these minerals as single fillers in polypropylene (PP) have shown varying degrees of reinforcement due to their differences in terms of particle geometry, surface energy and affinity towards the matrix polymer. In this study, comparisons were made in terms of mechanical, thermal and weatherability properties between hybrid-filler PP composites (i.e. PP filled with either talc–CaCO3 or talc–kaolin hybrid filler combinations), with particular attention directed towards the effect of surface modification of the fillers. The talc/CaCO3 hybrid composites have shown exceptional performance in terms of flexural and impact properties. The contribution of talc in the talc–kaolin hybrid composite system has been significant in terms of enhancing the overall tensile and flexural properties. The ability of silane and titanate coupling agents in boosting the resistance of the composites to severe damage and degradation due to natural weathering has been shown. 相似文献
25.
Silvestre Ragusa 《General Relativity and Gravitation》1999,31(3):275-286
The field equations of a proposed nonsymmetrictheory of gravitation are solved exactly for the case ofa static and spherically symmetric point singularity.The physical consequences of the solution are analyzed for the precession of perihelia,deflection of light, red-shift and radar-echodelay. 相似文献
26.
Bing Na Qin Zhang Hong Yang Qiang Fu Yong-feng Men 《高分子科学》2007,(3):285-290
<正>In this communication, by means of stress relaxation experiments, the viscous stress at various strains during tensile deformation of oriented polyolefin samples including high density polyethylene (HDPE), linear low density polyethylene (LLDPE) and isotactic polypropylene (iPP), has been determined. The viscous stress in the oriented samples takes up to 50%-70% of the total stress, which is unusually high compared with their isotropic counterparts. The unusual high viscous stress was discussed based on mainly the existence of shish structure in oriented polyolefins, which could enhance the inter-lamella coupling significantly. 相似文献
27.
Qin-jian Yin Xue Yun Zhao-jun Chen Wen Cao Qin Zhang Qiang Fu 《高分子科学》2007,(3):319-324
<正>In order to improve the tensile properties of poly(ethylene terephthalate)(PET), we used the direct esterification method to synthesize PET in a home-made facility, and a certain amount of ethylene glycol (EG), one of the two starting monomers, was substituted by glycerin (GE). Four PETs with different GE contents were prepared to investigate the effect of GE on the crystallization and tensile properties of the prepared copolyester. The results showed largely improved tensile properties and increased crystallization temperature due to the possible erosslinking structure in PET by using a small amount of GE. 相似文献
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《Composite Interfaces》2013,20(4):371-381
The effects of electron radiation on natural fibre reinforced polypropylene have been analyzed with the single fibre fragmentation test. Specimens of single hemp, flax, ramie and cotton fibres/fibre bundles embedded in a polypropylene sheet were irradiated with electron radiation of 10 MeV with intensities of 5, 15 and 33 kGy. The radiation led to a strain reduction of the polypropylene but did also improve the adhesion between polymer and flax, hemp and cotton fibres/fibre bundles. The critical fragmentation length and the interfacial shear strength (IFSS) of the composite specimens have been determined showing a clear increase of the IFSS of up to 50% compared to specimens with applied coupling agents. Due to the high strain reduction of the PP at intensities of 15 and 33 kGy the different fibres could only be compared at 5 kGy. The ramie fibre specimens could be analyzed at 5 and 15 kGy intensity showing higher IFSS values at the higher intensity. A possible explanation for the improvement is the forming of radicals with the cellulose chains of the natural fibres and the polypropylene molecules leading to crosslinking and, therefore, better adhesion between the different components. 相似文献