Maximum prime vertical strain criterion to predict rupture of core-shell microspheres

Abstract

Characterization of the rupture behavior is of great significance to evaluate the service life for microcapsules. Due to the small dimension, complex core-shell structure and curved surface of microcapsules, it is challenging to quantitatively determine the rupture position and rupture strength. In the present work, a microsphere-compression model for characterizing the rupture behavior of microcapsules was established. Through the quantitative investigation of the compression rupture behaviors of microcapsules from the extended finite element models, the cracks were found to initiate at the same parallel circle (latitude) of microcapsule where the curvature change of the deformed shell (i.e., prime vertical strain) is the largest. With the increase of compression displacement, microcapsules show three crack propagation modes. Based on such findings, a maximum prime vertical strain criterion, i.e., cracks initiate when the maximum prime vertical strain exceeds a critical value, for estimating the rupture initiation of microcapsules under compression was proposed. The proposed criterion was validated by both numerical simulations and experiments. It demonstrates that the critical prime vertical strain of rupture is independent of the microcapsule dimensions and is an intrinsic parameter to judge the rupture of microcapsules. The critical prime vertical strain of rupture for n-hexadecane@PMMA microcapsules is 0.023±0.003. The proposed model avoids complicated stress analysis and provides an intrinsic criterion.