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Digital archive of theses discussed at the University of Pisa


Thesis etd-12022022-153125

Thesis type
Tesi di dottorato di ricerca
Thesis title
The effect of γ-radiation on epoxy structural adhesives: a commercial case preliminary study
Academic discipline
Course of study
tutor Prof. Monelli, Bernardo Disma
supervisore Prof. Beghini, Marco
supervisore Ing. Raffaelli, Fabrizio
  • adhesives
  • aging
  • cohesion
  • cohesive properties
  • epoxides
  • finite element stress analysis
  • gamma radiation effects
  • mechanical properties of adhesives
Graduation session start date
This Thesis describes the Ph. D. work of the author, which regards the investigation of the effect of γ-radiation on the mechanical behavior of a commercial epoxy adhesive named 3MTM Scotch-WeldTM 2216 B/A Gray. Besides the comprehension of the adhesive behavior itself, this preliminary study aims to define a pathway to characterize the bulk characteristics of this glue starting from a standard-based approach and to use those data in the design of joints.
In Chapter 1 a brief introduction to the adhesive world has been given, composed of fundamental definitions, a description of the adhesion phenomena, the pros and cons of this kind of junction, and a general classification of polymeric structural adhesives. Then, a description of the interaction between adhesives and the environmental conditions present in nuclear, high energy physics, and aerospace fields has been given, in particular for what concerns ionizing radiations. The results of a detailed literature review have been summarized, highlighting the necessity to concentrate the studies on one adhesive since no general trends are recognizable.
In Chapter 2 are described the materials and methods used for the experimental campaigns. After a description of the chosen adhesive, an excursus on bulk and in situ specimens is proposed, which outcome is that a complete experimental campaign should involve both types of specimens. The produced specimens are then described, together with their production procedure, which is based on literature and standards and adapted to the specific case. In the second part of the Chapter, the equipment to perform the different tests (tensile test, shear test, 60Co γ-rays irradiation, ATR-FTIR, ESR spectroscopy, and colorimetric analysis) is briefly described.
Chapter 3 contains the results of the performed tests together with a critical discussion. First, an unattended post-cure effect has been detected in bulk specimens, also in absence of γ irradiation. A complete characterization of the phenomena has been conducted, and a description of the non-irradiated specimens elastoplastic behavior has been given. The variation of the behavior at different values of absorbed dose (up to 500kGy) has been described and related to the outcomes of the spectroscopic analyses. In the last part of the Chapter, results for in situ specimens are exposed. Developed ad hoc FEM models and analytical solutions based on bulk mechanical characteristics are in good agreement with the experiments for what concerns the overall stiffness of the joints but underestimate their strength because of the relevant quantity of defects encountered in bulk specimens despite the taken precautions.
The last Chapter reports a summary of the whole Thesis, extrapolating the conclusions of the work. Some potential further developments of the work are proposed, based on the obtained results and the criticalities encountered during the experimental campaigns.