Links between Surface Changes with Strain whitening, Shear Banding and Damage in a Toughened Epoxy Adhesive
Abstract
Owing to the increased use of toughened epoxy adhesives in current transportation light
weighting efforts, it is critical that the damage mechanisms observable as strain whitening
in these materials are understood and quantified. Quantification of damage is needed for
finite element constitutive models used in structural design; however, thin bond lines in
adhesive joints limit direct observation of the adhesive. In this study, microscope
observations of bulk material specimens subjected to tensile loading were linked to strain
whitening and damage in a toughened epoxy adhesive. Cracks on the surface were
observed to open during loading, with strain whitening at the crack tips and with the
initiation and propagation of shear bands. The stresses approximated at the crack tips
suggested that particle cavitation could be occurring in these regions. Image analysis
showed that strain whitening was present at crack tips and that these areas served to initiate
the shear-bands.
Changes in tensile specimen stiffness and strength were evaluated during load-unload and
reload testing, and were linked to the presence of crack growth, as well as the formation
of shear bands. Considering changes in strength, the predicted damage level before failure
(D~18%) was lower than that predicted using traditional load-unload stiffness (D~35%),
attributed to short-term viscoelastic effects; however, damage calculated from load-reload
material stiffness (D~19%) was in good agreement with the damage estimated from
changes in strength. A new approach, calculating damage from direct image analysis of
strain whitening on the free surface (D~21%) was in good agreement with damage
quantified by changes in strength and stiffness, with the benefit of quantifying damage
over the loading history of the test sample and identifying areas of damage localization.
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Cite this version of the work
Luis Trimiño, Duane Cronin
(2021).
Links between Surface Changes with Strain whitening, Shear Banding and Damage in a Toughened Epoxy Adhesive. UWSpace.
http://hdl.handle.net/10012/19191
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