We are pleased to announce that Dr Sébastien Joannès, from Mines-ParisTech, PSL Research University, France, will present a keynote lecture at the forthcoming 9th International Conference on Applied Hair Science, titled ‘The fascinating world of technical fibres: Thermomechanical characterisation at the single fibre scale and statistical assessments of their properties’. To book your ticket go to www.triprinceton.org
Fibres, whether natural, man-made by regenerating cellulose, or purely synthetic are remarkable forms of matter, some of which possess properties near the limits of what physics allows. Technical fibres, particularly polymeric ones, are able to withstand impressive loads while having diameters 8 to 10 times smaller than a hair fibre. For example, a single aromatic polyamide fibre with a diameter of 12 microns can withstand a load of almost 40 g. A rope, a few millimetres in diameter, manufactured with the same fibres is capable of bearing a load equivalent to the weight of a car! Such high-performance fibres can advantageously replace metals used as reinforcements, ropes or cables in a multitude of applications that require weight savings.
In use, these fibres have to cope with very high loads in a complex thermo-mechanical environment. A tyre reinforcement is a prime example: fibres are twisted in the assembly process to form a rope, and undergo multi-axial loads as well as cyclic fatigue, encountered during the lifetime of a tyre. Fibre mechanical properties are linked to their highly oriented structure leading to a pronounced anisotropic behaviour. To optimise composite structures such as tyres, thermo-mechanical measurements are required at the fibre level in various configurations and loadings. This presentation will address questions related to the thermo-mechanical characterisation of single technical fibres with a particular focus on strength assessment and cyclic/fatigue loadings. Beside longitudinal tensile tests (SFT), Single Fibre Compression Tests (SFCT) will be presented as a way to evaluate the anisotropic nature of polymeric fibre mechanical properties.
At such small scales, one must particularly pay attention to the analysis of the measurement data and to the evaluation of uncertainties which are too rarely quantified. Reliability-based designs and lifetime assessments require accurate data to feed into micro-mechanical models and advanced statistical descriptions of fibre properties. Relevant predictions cannot be solely based on measured average values and standard deviations. Fibre property distributions should be inferred as reliably as possible, meaning it is essential to estimate measurement uncertainties. In other words, answering the following questions is key to obtain data sets that would describe fibre populations: how accurate is the measurement? How representative is the sample? How many fibres should be tested to reach a certain level of confidence? The most challenging part of this process is the acquisition of reliable data. Furthermore, data quality is a feature quite complex to determine. Those points will be illustrated with concrete examples drawn from forty-year experience at the Mines-ParisTech fibre laboratory. Emphasis will be placed on tools, methods and pitfalls to avoid, providing a better understanding of the fascinating world of fibres.
For more information about the conference contact us at www.triprinceton.org