Abstract
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.
Original language | English (US) |
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Article number | 123560 |
Journal | Polymer |
Volume | 221 |
DOIs | |
State | Published - Apr 14 2021 |
Funding
This work was performed under the following financial assistance award 70NANB19H005 from U.S. Department of Commerce, National Institute of Standards and Technology as part of the Center for Hierarchical Materials Design (CHiMaD). This work made use of the MatCI Facility which receives support from the MRSEC Program ( NSF DMR-1720139 ) of the Materials Research Center at Northwestern University. We also acknowledge helpful discussion with J. Lenhart at the Army Research Laboratory. M.D. Eaton acknowledges the support of the Department of Defense (DoD) through the National Defense Science and Engineering Graduate (NDSEG) program as well as through the Richter Trust Funds.
Keywords
- Epoxies
- Fracture toughness
- Network topology
ASJC Scopus subject areas
- Organic Chemistry
- Polymers and Plastics
- Materials Chemistry