Predicting the Initiation of Thermoset De-Bonding

Abstract

Napkin ring adhesion tests over a broad range of experimental conditions suggested a de-bonding mechanism for glassy thermosets associated with ''runaway'' nonlinear viscoelasticity. Finite element analyses of these tests using a high fidelity, nonlinear constitutive equation were used to identify a single, scalar metric that consistently predicted the initiation of de-bonding, a critical value of the maximum principal strain in the ''interphase'' zone. In principle, such a de-bonding metric enables evaluation of design margins in practical components.

Cure mechanisms of diglycidyl ether of bisphenol A (DGEBA) epoxy with diethanolamine

“…Additional studies of DGEBA/DEA have been published sporadically. These include investigations of the gelation process [22][23][24][25], of the coefficient of thermal expansion [13], of mechanical properties [26][27][28][29][30][31][32][33][34][35][36], and of copolymers based on the DGEBA/DEA system [37].…”

Mechanisms of degradation in adhesive joint strength: Glassy polymer thermoset bond in a humid environment

“…The temperature dependence of the experimental shear stress at failure for the napkin-ring joint coincides with the temperature dependence of the predicted shear "yield" stress of the adhesive, 6 where polymer adhesive viscoelastic relaxation rates increase to the point that stress decays faster than incremented by the loading ramp in what has been termed "run-away" nonlinear viscoelasticity. 2 Figure 4 further illustrates the correlation, with multiple adhesives and multiple methods of predicting shear yield. Specifically, predictions in Figure 4 are associated with (1) the adhesive shear yield stress evaluated under a simple shear loading in a single element analysis and (2) the maximum stress sustained in a napkin-ring joint under a torsional load.…”