摘要:

Dielectric studies have been carried out on semi-crystalline poly(ether-ether-ketone) at temperatures from 100 to 300°C and at frequencies between 20 Hz and 10 kHz. A relaxation is seen in the isochronal curves and in the Cole-Cole plots, which is attributed to a Maxwell-Wagner-Sillars polarization taking place at the interface between the crystalline inclusions and the amorphous matrix. The intensity of this relaxation is presented in relation to the morphology of the crystalline part which is known to depend on annealing conditions.

DOI:10.1163/156855496X00191

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The features of infrared spectra of woodflour obtained by transmission and diffuse reflectance (DRIFT) are discussed. Intrinsic differences between the two techniques, as well as differences in sample preparation for transmission (pressed pellet) or DRIFT (simple mixing with powered KBr), affect the appearance of the spectra recorded. Other important differences arise from the water content in the sample, as well as in the KBr powder utilized as reference and dilution. Some of these differences are discussed since they occur in regions usually utilized to check modifications in the wood. The effect of sample concentration is investigated for both techniques. In transmission, the opacity of the pellet limits the sample concentration to about 2 wt% in KBr in order to obtain useful spectra. While no concentration limitations are present for DRIFT, distortion of the intensities of bands occur, mainly at low wavelengths. Finally, the use of DRIFT subtraction to detect small surface variations in the woodflour (chemical and physical adsorption of a modifier) is illustrated.

DOI:10.1163/156855496X00209

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The processing of polymer matrix composites requires the formation of an autohesive bond between the surfaces of adjacent polymer entities as well as with the fiber surface. This autohesive bond strength development in amorphous polymers has been extensively studied and modeled. This paper describes a study undertaken to describe the development of the autohesive bond between polymer surfaces in semi-crystalline matrix composites. The results show that the development of the autohesive bond competes with the formation of crystals and actually results in the decrease of fracture strength at long processing times.

DOI:10.1163/156855496X00218

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

In this paper, interphase properties of carbon fibre/epoxy resin single-fibre model and unidirectional (UD) composites are reported. To study the contribution of the carbon fibre surface chemistry and morphology and of the resin itself to the overall properties of the composites, untreated, oxidized and sized fibres are used with bi- and tetrafunctional, diglycidylether of Bisphenol A, DGEBA and tetraglycidyl 4,4'-diaminodiphenylmethane, TGDDM-based resins, cured with amine and anhydride hardeners. Adsorption measurements and single fibre contact angle experiments, as well as the pull-out test were applied to characterize the surface of carbon fibre and the interfacial shear strength with different matrices. It was shown that the presence of the size on the surface can drastically affect the wettability as well as the starting rate of the cure reaction of epoxide in the vicinity of the fibre surface, as revealed by FTIR microscopy. Different elastic-plastic behavior of model composites before debonding is found for untreated, oxidized and sized fibres, due to the various interphase structures formed. Both micro-and macromechanical properties of the composites are found to be significantly affected by the matrix properties. The role of the surface treatment of fibers becomes especially important in high performance resin systems.

DOI:10.1163/156855496X00227

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The tensile strength of monofilamentary weakly bonded SiC fiber/γ-TiAl intermetallic compound matrix composite, prepared by the sputtering method, was measured and analysed using a fracture mechanical technique. The main results are summarized as follows: (1) The fracture of TiAl occurred prior to that of fiber, resulting in formation of circumferential cracks on the fiber. Interfacial debonding occurred during tensile test, resulting in long pull-out of the fiber. (2) The strength of the fiber in the TiAl matrix was nearly the same as that of the bare fiber. (3) The fracture mechanical analysis showed that (i) the interfacial debonding grows unstably upon initiation and (ii) the stress distribution in the fiber in the cross-section, where the matrix is fractured, approaches to that of bare fiber with increasing debonded length. The reason why the fiber strength was maintained in spite of the formation of cracks on the fiber surface due to the premature fracture of the matrix was accounted for by the fully blunted crack-tip from the above calculation result.

DOI:10.1163/156855496X00236

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor