Tuesday  |  Milwaukee  |  09:20 AM–09:40 AM

#19421, Characterization of Interfacial Adhesion in Frontally Cured Composites

Frontal curing is a rapid energy-efficient alternative to autoclave/oven curing for manufacturing high-performance fiber-reinforced polymer composites (FRPCs). Frontal curing leverages the exothermic heat of polymerization to propagate a self-sustaining reaction wave through the matrix after initiation with a small triggering stimulus (e.g. heat). Frontally cured carbon-fiber/poly(dicyclopentadiene) (CF/pDCPD) woven composites have been fabricated with fiber volume fractions (Vf > 60 %,) glass transition temperatures, (Tg ~ 170 °C), and mechanical properties (E ~ 55 GPa, Ftu ~ 600 MPa) similar to traditional carbon-fiber/BPA-epoxy composites. However, the non-polar nature of pDCPD contributes to a comparatively weak fiber-matrix interface in CF/pDCPD composites compared to a strong CF/epoxy interface, compromising in-plane shear and compression performance. Additionally, the rapid propagation of a large thermal gradient in frontal curing imparts a residual stress state different from traditional bulk curing. To capture the impact of front propagation, we investigate interfacial adhesion in CF/pDCPD using single fiber fragmentation (SFF) testing.
Composite systems with strong interfacial shear strength (IFSS), such as CF/epoxy, exhibit symmetric birefringence patterns surrounding fiber fractures during SFF testing under cross-polarized optical microscopy. Conversely, weak interfaces, such as the CF/pDCPD interface, fail by interfacial debonding, which manifests as an asymmetric birefringence pattern in SFF testing. In this work, we quantify the weak IFSS observed in frontally cured AS4C/pDCPD single fiber composites using shear lag theory. Additionally, we leverage SFF experimentation and numerical models to evaluate several strategies to improve interfacial bonding of the CF/DCPD interface including the effect of residual stress and fiber surface treatments.

Tyler Price   University of Illinois Urbana-Champaign
Warren Wellington   University of Illinois Urbana-Champaign
Nancy Sottos   University of Illinois Urbana-Champaign