2216 epoxy bonds for TMT: performance, and precautions

Glen Cole; Benjamin B. Gallagher; Eric Hansen

doi:10.1117/12.2559896

13 December 2020 2216 epoxy bonds for TMT: performance, and precautions

Glen Cole, Benjamin B. Gallagher, Eric Hansen

Proceedings Volume 11445, Ground-based and Airborne Telescopes VIII; 114451P (2020) https://doi.org/10.1117/12.2559896
Event: SPIE Astronomical Telescopes + Instrumentation, 2020, Online Only

Abstract

ScotchWeld 2216 is the selected epoxy for the Thirty Meter Telescope primary. The Invar interface components are adhered to the Clearceram segments with this epoxy. The work presented quantifies the bond strength sensitivities for TMT and validates the design. Coupons were subjected to numerous tensile and shear destructive tests. The bond preparation parameters were perturbed, and the sensitivities were evaluated. An attempt at artificial aging of the epoxy bonds was made using cyclical loads and environments. Non-destructive creep testing was evaluated interferometrically with 200mm test articles. Strength was enhanced (33%) by “conditioning” or an elevated cure (100C for 1 hour). The epoxy is strengthened (54%) at the site temperature of 2C. We measured reduced cohesive strengths for thick primer (36% weaker) and for Invar oxide (70% weaker), among other process-related degradations. For artificial aging, cyclical stresses had a minimal impact on strength, but cyclical temperature-humidity tests did significantly reduce strengths (36% weaker). 2216 epoxy exhibits visco-elastic creep in shear. For structural applications, this is unimportant, but for the TMT original design, it resulted in a surface figure degradation (2 nm P-V) over a 9-hour observation window. With alternate epoxies, with much higher Tg’s glass transition temperatures, we saw similar creep responses. 2216 epoxy provides for good strength margins for the TMT design as long as attention to the preparation details is strictly adhered to, and its properties are understood in the context of the overall design performance.

Conference Presentation

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Glen Cole, Benjamin B. Gallagher, and Eric Hansen "2216 epoxy bonds for TMT: performance, and precautions", Proc. SPIE 11445, Ground-based and Airborne Telescopes VIII, 114451P (13 December 2020); https://doi.org/10.1117/12.2559896

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