The dimensional stability of a CFRP structure probed with sub-micrometer accuracy in varying external condition

The paper presents the thermal deformations of a CFRP High Dimensional Stability Structure. With an experimental facility designed and tested to undergo negligible deformations, ten points of the UV-spectrometer' support (Test Article, TA) have been monitored with triaxial capacitive transducers, both in vacuum and in dry nitrogen atmosphere, with temperature variations in the range 253÷333K. The measured deformations differ from point to point: +4.05±0.01μm/K has been the largest dimensional variation measured in one point of TA and in one direction, whereas -0.05±0.02μm/K has been the smallest one, in another point and in a different direction. All the obtained results agree within ±2μm/K with the computer simulated tests accomplished in the design of TA. A complete analysis of the sources of uncertainty assures the displacement' measurements' accuracy has been ≤0.1μm, whatever the experimental conditions. The dimensional stability of the TA has been verified finally with a series of hygro-thermal cycles The results show that permanent deformations not larger than ±2μm occurred in a limited number of points.