Links between surface morphology changes and damage in a toughened epoxy adhesive. Issue 9 (4th July 2022)

• Record Type: Journal Article
• Authors: Trimiño, Luis; Cronin, Duane
• Is Part Of: Journal of adhesion. Volume 98:Issue 9(2022)
• Page Start: 1218
• Page End: 1259
• Publication Date: 2022-07-04
• Subjects: Structural epoxy adhesives -- cavitation -- crack opening -- craze-like -- strain whitening -- shear banding -- damage measurements; Adhesion -- Periodicals; 541.33
• DOI: 10.1080/00218464.2021.1887737
• Languages: English
• ISSNs: 0021-8464

Abstract

ABSTRACT: With the increased use of toughened epoxy adhesives in current transportation lightweighting efforts, it is critical that damage mechanisms, such as strain whitening, are understood and quantified. Damage quantification is needed for the constitutive models used in structural design; however, thin bond lines in adhesive joints limit direct observation. In this study, microscope observations of bulk toughened epoxy adhesive specimens subjected to tensile loading were linked to damage. Cracks on the surface opened during loading, leading to strain whitening at the crack tips and the initiation and propagation of shear bands. The stresses approximated at the crack tips suggested that particle cavitation could be occurring in these regions. Changes in specimen stiffness were linked to crack growth and the formation of shear bands. Material damage calculated using traditional load-unload stiffness (D ~ 35%) was higher than other methods such as change in material strength (D ~ 18%) and damage from changes in stiffness during load-reload (D ~ 19%). The differences were attributed to short-term viscoelastic effects. A new approach calculated damage from the strain whitening on the free surface (D ~ 21%). Values were in agreement with damage figures from other methods. The technique can quantify damage over the loading history and identify areas of damage localization.