Non-Linear Characterisation of Kevlar and Silicon Carbide Fibres for Structural Health Monitoring Applications

Uncertainties about the long term bearing capacity of aramid fibres have made designers reluctant to utilize them for external pre-stressing for cable-stayed bridges. Recent research carried out on cable-stayed bridges has found that the steel cables, although well protected from the external environment, are subject to corrosion, resulting in a risk of structural defects and malfunctions. The question that prompted this study is whether simple and non-destructive non-linearity tests can be used for assessing structural damage in aramid fibres or elements. The concept is to detect weak non-linearities in the dynamic response measured on fibres and ropes and to use the level of non-linearity as an indicator for evaluating the residual life span of aramid elements, cables and ropes. In perspective, a non-linearity test may be easily integrated in structural health monitoring protocols to be employed on aramid cables and elements to collect timely notifications about possible anomalies in the structural behaviour. In order to investigate the sensitivity of such an approach to structural health monitoring, non-linearity characterisation tests were conducted on aramid fibres by applying controlled sweep-sine excitations at different loading levels. In order to have a comparative term and to test the setup machine, a similar characterisation procedure was also applied to a novel material, the silicon carbide, which is known to exhibit a purely brittle behaviour, with no appreciable plastic deformation.