Journal
POLYMER
Volume 221, Issue -, Pages -Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.polymer.2021.123560
Keywords
Epoxies; Fracture toughness; Network topology
Categories
Funding
- U.S. Department of Commerce, National Institute of Standards and Technology as part of the Center for Hierarchical Materials Design (CHiMaD) [70NANB19H005]
- MRSEC Program of the Materials Research Center at Northwestern University [NSF DMR-1720139]
- Department of Defense (DoD) through the National Defense Science and Engineering Graduate (NDSEG) program
- Richter Trust Funds
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The study investigated the effect of nanoscale heterogeneity on the mode I fracture toughness of model epoxy networks, with results showing that high toughness is achieved in heterogeneous networks.
The role of nanoscale heterogeneity on the mode I fracture toughness, KIc, of model epoxy networks has been investigated. Model systems utilized consist of diglycidyl ether of bisphenol A (DGEBA) as the epoxide with a stoichiometric amine mixture of a rigid cycloaliphatic diamine (PACM) and a more flexible, polypropylene glycol based diamine (Jeffamine) at different molar ratios. The molecular weight of the Jeffamine was adjusted to further tailor the epoxy properties. Fracture toughness was measured using single edge notched bend samples and hardness was measured by Vickers indentation. Both measurements were performed at temperatures as low as - 100 ?C to above ambient temperatures. Results are interpreted in the context of the Dugdale model of material toughness where the fracture toughness is expressed in terms of a cohesive zone stress (related to the hardness), the elastic modulus (measured directly) and the crack tip opening displacement (obtained from images of the fracture surfaces). High toughness is obtained in heterogeneous networks where a decrease in the cohesive zone stress is offset by sufficiently large increases in the crack tip opening displacement.
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