Strength of armos fibres in axial compression

Abstract

Highly oriented aramid fibres and the construction materials made from them have high tensile mechanical indexes but their properties are much worse in axial compression. There are no sufficiently simple and objective methods for assessing the strength of individual fibres, and the information required for determining the causes of compressive failure in complexly stressed states in construction materials is thus lacking.In previous studies [1, 2], we reviewed the existing methods and gave a brief theoretical examination of the kink bands. We will only add here that the theoretical substantiation of the recoil method in [3], which is considered one of the simplest and most frequently used methods [4][5][6], contains a maj or error and the results of this method are a function of the basic distance used to a significant degree.The microcompression method [7][8][9][10][11], where almost pure longitudinal compressive stresses are created in microsamples, has been increasingly frequently used recently for studying longitudinal compression of fibres. We used an improved microsetup ( Fig. l) which allows creating pure axial compressive stresses in the individual fibre to obtain a clearer picture of axial compression of high-modulus fibres and determine the mechanical characteristics [7,8], In contrast to similar instruments [9][10][11], in our setup one end of the fibre sample 10-16 btm in diameter is held with special holder 1, in which it can be attached with an adhesive or moved freely, and on the other end by holder 4, in which it moves relatively freely without loss of stability in compression or is also attached with an adhesive. The basic difference between holders is 2.5 sample diameters. A dynamometer is mounted in holder 4. The signals from the dynamometer and motion sensor are fed to the inlet of an ADC board; a piezoelectric crystal which assigns movement is controlled from the DAC channel.The compression curves of Armos monofibres --initial and heat-treated --up to fracture were obtained with this microsetup and the kinetics of fomlation of kink bands on the real time scale was established (Fig. 2). One kink band is initially formed due to the creation of pure axial loads in the fibres, confirmed by the load--deformation curves. Figure 2 shows that the formation of a kink band in the heat-treated fibre is more pronounced than in the initial fibre. As our studies showed, this is due to the onset of loss of stability of the initial fibre, which leads to its bending and the appearance of a complex stressed state.In addition, a series of features characteristic of heat-treated fibres was also revealed [7,8]. The measurements on individual fibres from complex yam showed that the width of the slip line and the average angle between the axis ofmicrofibrils (macromolecules) in this line and the axis of the fibre for the same shear stress are constant within the limits of the error of the measurements. Although the thickness of the band varies within wide limits for fibres of the same kind, it is constant for fibre...

Study on continuous heat treatment of Aramid III

“…There are two kinds of para-aramid products, the para-aramid homopolymer fiber represented by Kevlar 1,2 and the para-heterocyclic aramid copolymer fiber represented by Russia Armos 3,4 and Chinese Aramid III. 5 Kevlar is a kind of binary polymer that is polymerized by monomer p-phenylenediamine(PPDA) and terephthaloyl chloride(TPC).…”