The influence of ionizing radiation on the mechanical properties of structural adhesive joints in space

• Der Einfluss von ionisierender Strahlung auf die mechanischen Eigenschaften von strukturellen Klebungen im Weltraum

Zimmermann, Jannik; Schröder, Kai-Uwe (Thesis advisor); Reisgen, Uwe (Thesis advisor)

Aachen : Shaker Verlag (2022)
Book, Dissertation / PhD Thesis

In: Aachener Berichte aus dem Leichtbau 2022/02
Page(s)/Article-Nr.: xiv, 163 Seiten : Illustrationen

Dissertation, RWTH Aachen University, 2022

Abstract

The utilization of structural adhesives in the space sector has expanded significantly in recent years. Adhesively bonded joints offer many advantages compared to traditional joining techniques like welding, screws, bolts and rivets. Nevertheless, the space environment imposes a major challenge in terms of durability on structural adhesives. Existing handbooks and guidelines lack information regarding the effect of ionizing radiation on the mechanical properties of structural adhesive joints. In fact, there are contradicting statements, whether the effect of ionizing radiation should be considered in an early design phase or not. Therefore, in this thesis, a design framework is developed which enables the consideration of radiation induced degradation of structural epoxy adhesives for space applications. For this purpose, radiation simulations are conducted for a variety of target orbits to obtain the total ionizing dose that the adhesive joint is exposed to. Using radiation interaction simulation, the absorbed dose is determined for each position within the adhesive layer. Irradiation experiments of bulk adhesive specimens are conducted for a 20 year low earth orbit mission. For higher dose levels that represent 20 year geostationary missions, radiation damage test data from literature is considered. A novel analytical calculation scheme for determining the stiffness of single-lap joints is developed. This approach takes the out of plane deformation of the adherends into account and enables parametric investigations of radiation-induced stiffness degradation of single-lap joints. The method is validated with experimental tests and FE calculations. With the proposed model a significant improvement of the accuracy is achieved when compared to existing analytical approaches. Using the cohesive zone model, the effect of ionizing radiation on the strength of single-lap joints is evaluated. Here, the cohesive zone parameters are degraded depending on the previously determined dose-depth curve. With this approach, for the first time, a single-lap joint is virtually exposed to an actual radiation spectra that corresponds to a certain orbit. The analysis shows that for overlap lengths below 10 mm the ionizing radiation has an effect on the single-lap joint strength which could be compensated by increasing the overlap length or the joint width in the design process. For overlap lengths above 10 mm the effect of ionizing radiation can be neglected.

Institutions

• Chair and Institute of Structural Mechanics and Lightweight Design [415610]