Publications

Glass-to-metal (GTM) seal development using finite element analysis: Assessment of material models and design changes

Tandon, Rajan; Neilsen, Michael K.; Jones, Timothy C.; Mahoney, James F.

Glass-to-metal (GTM) seals maintain hermeticity while allowing the passage of electrical signals. Typically, these seals are comprised of one or more metal pins encapsulated in a glass which is contained in a metal shell. In compression seals, the coefficient of thermal expansion of the metal shell is greater than the glass, and the glass is expected to be in compression. Recent development builds of a multi-pin GTM seal revealed severe cracking of the glass, with cracks originating at or near the pin-glass interface, and propagating circumferentially. A series of finite element analyses (FEA) was performed for this seal with the material set: 304 stainless steel (SS304) shell, Schott S-8061 (or equivalent) glass, and Alloy 52 pins. Stress-strain data for both metals was fit by linear-hardening and power-law hardening plasticity models. The glass layer thickness and its location with respect to geometrical features in the shell were varied. Several additional design changes in the shell were explored. Results reveal that: (1) plastic deformation in the small-strain regime in the metals lead to radial tensile stresses in glass, (2) small changes in the mechanical behavior of the metals dramatically change the calculated stresses in the glass, and (3) seemingly minor design changes in the shell geometry influence the stresses in the glass significantly. Based on these results, guidelines for materials selection and design of seals are provided.