This research project aimed to develop diagnostic options for in situ use within future materials ageing experiments in complex engineering environments. The techniques developed were required to be suitable for multi-decade deployment and have minimal impact upon the experimental chemical ageing evolution. Optical fibre based diagnostic options for measuring temperature, barometric pressure, and gaseous concentrations were reviewed. The long-term suitability of fibre Bragg grating (FBG) temperature sensors, fibre Fabry-Pérot (FFP) pressure sensors, O2sensing fluorescence probes, and optical fibre switches were assessed experimentally in experiments that lasted up to 1 year. A bespoke fibre-coupled multi-pass spectroscopic gas cell was developed for the detection of H2O with a path-length of (6.47±0.05)m, along with novel techniques to package FBG and FFP sensors, hermetically pass optical fibres into the experimental volume, and route optical fibres. Custom optical fibre connectors for use both inside and outside the experiment were designed and evaluated. To support the diagnostics investigated, a bespoke interrogation system was created, with a design focus on modularity, redundancy, and long-term support. The research was evaluated against the project requirements, and together formed a potential concept for future materials ageing experiments requiring comprehensive and enhanced embedded diagnostic capabilities. The developed technologies were assessed as ranging in technology readiness level (TRL) from 2 to 6. For use in an experiment, further work would be required to mature the techniques up to TRL 9, and potential maturation routes are presented.Engineering and Physical Sciences Research Council (EPSRC) Grant number EP/L01596X/1
