An experimental/analytical comparison of strains in encapsulated assemblies

• Main Authors: Guess, T.R., Burchett, S.N.
• Language: unknown
• Published: 2008
• Subjects: 36 MATERIALS SCIENCE; 45 MILITARY TECHNOLOGY; WEAPONRY; AND NATIONAL DEFENSE; 42 ENGINEERING; EPOXIDES; ENCAPSULATION; STRAINS; URETHANE; CASTING; CURING; FINITE ELEMENT METHOD; KOVAR; MATERIALS TESTING; TEMPERATURE DEPENDENCE; TUBES; ALLOYS; CARBAMATES; CARBONIC ACID DERIVATIVES; CARBOXYLIC ACID SALTS; COBALT ALLOYS; FABRICATION; IRON ALLOYS; IRON BASE ALLOYS; MANGANESE ADDITIONS; MANGANESE ALLOYS; NICKEL ALLOYS; NUMERICAL SOLUTION; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; ORGANIC OXYGEN COMPOUNDS; TESTING; Carbonic acid
• Online Access: http://www.osti.gov/servlets/purl/6187028; https://www.osti.gov/biblio/6187028; https://doi.org/10.2172/6187028

A combined experimental and analytical study of strains developed in encapsulated assemblies during casting, curing and thermal excursions is described. The experimental setup, designed to measure in situ strains, consisted of thin, closed-end, Kovar tubes that were instrumented with strain gages and thermocouples before being over-cast with a polymeric encapsulant. Four bisphenol A (three diethanolamine cured and one anhydride cured) epoxy-based materials and one urethane elastomeric material were studied. After cure of the encapsulant, tube strains were measured over the temperature range of {minus}55{degrees}C to 90{degrees}C. The thermal excursion experiments were then numerically modeled using finite element analyses and the computed strains were compared to the experimental strains. The predicted strains were over estimated (conservative) when a linear, elastic, temperature-dependent material model was assumed for the encapsulant and the stress free temperature T{sub i} was assumed to correspond to the cure temperature {Tc} of the encapsulant. Very good agreement was obtained with linear elastic calculations provided that the stress free temperature corresponded to the onset of the glassy-to-rubbery transition range of the encapsulant. Finally, excellent agreement was obtained in one of the materials (828/DEA) when a viscoelastic material model was utilized and a stress free temperature corresponding to the cure temperature was assumed. 13 refs., 20 figs., 3 tabs.