I am trying to model the stresses induced by thermal contraction of a conformal coating (epoxies, urathanes) on the glass envelope of a fragile bodied component. The glass is bonded to a metal post and the coating is then applied to the part. The glass is fracturing when the system is cooled. The fractures always start at the glass to metal seal at one end and propagate outwards through the glass envelope into the coating. I modeled this like an ice cream sandwich and have calulated the tensile stress (perpendicular to the longitudinal axis of the part) and the shear stress (length contraction of the epoxy bond at the bond-to-glass interface). To combine the two stresses I was converting the shear to a torque (pivoting around the center of the glass)and then equating Fshear x d1 = Fend x d2 to get a force acting in the radial direction at the end of the glass(where it is fracturing). I am assuming an area equal to the fracture origin when converting the stresses to a force. Once I have the Fend then I can combine the forces. I am posting this to simply get a sanity check. Thanks for any response.
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