Experiments on single layer textile composites

Abstract

A mechanical characterization activity on composite fabrics is documented in this paper. In the framework of this characterization, a study and thorough test procedure stage were required because of the high scattering of results, and also because tests were frequently nullified due to failure near the tabs of test specimens. In this context, the cause of problems was searched in the material, which may be affected by damage during manufacturing – the extension of damage is related to fiber features and to the kind of process, and in the test procedures which, although standardized, should be considered in relation to the special features of the material referred to herein. In the first work stage, investigations were carried out on the presence of a certain degree of material damage in supply conditions. Although its technological causes have not been identified, the incidence of the damage, for the lot of material considered, was established in terms of the reduction of resisting sections. However, it may not immediately be established that this damage affects material's stiffness features. The second stage of the analysis was focused on geometrical characteristics and the preparation of test specimens, in order to check stress decay processes and reduce scattering of results. In spite of the important improvements obtained in terms of accuracy of the material mechanical characterization, it is still not clear whether the standard tests were adequate, for they were based on a hypothesis of a uniaxial stress state for a kind of material the performance of which, if used in single layer, strongly depends on the stress acting on the off-axis fibers. The study was carried out in cooperation with Alenia Aerospazio, a leader in the Italian aerospace industry, for the project of a new generation of satellite antennas. It can be assumed that in the application of textiles, the experimental procedure is of capital importance because users normally proceed only with experimental evaluation of mechanical properties. Moreover, the development of a reliable experimental procedure is essential for the validation of analytical and numerical models for design and research activities.