Self-Healing for Improved Fatigue Life

摘要

A novel approach is explored for improving the fatigue life of thermosetting polymers through thernaddition of self-healing functionality. Thermosetting polymers are used in a wide variety ofrnapplications ranging from composite structures to adhesive joints to microelectronic packaging. Duernto their low strain-to-failure these polymers are highly susceptible to damage in the form of cracks.rnFatigue loading is particularly problematic, giving rise to the initiation and propagation of smallrncracks deep within the structure where detection is difficult and repair is virtually impossible. Theserncracks often lead to catastrophic failure of the material. We utilize a strategy based on recentrndevelopments in self-healing technology to autonomically repair fatigue cracks and extend thernservice-life of many polymeric components. The material under investigation is an epoxy matrixrncomposite, which utilizes embedded microcapsules to store a healing agent and an embeddedrncatalyst. A propagating crack exposes particles of catalyst and ruptures the microcapsules, whichrnrelease healing agent into the crack plane. Polymerization of the healing agent is triggered byrncontact with the catalyst, which bonds the crack faces closed.rnA comprehensive experimental program is carried-out to assess the fatigue behavior of arnself-healing polymer. The testing program has two primary thrusts. The first is to obtain the inherentrnfatigue characteristics of the matrix material. In this case the ability to self-heal and the self-healingrneffects on the fatigue behavior are precluded. Here we embed unfilled microcapsules (no healingrnagent) along with the catalyst in the epoxy matrix. The second testing thrust is to characterize thernfatigue characteristics of the self-healing materials system. Fatigue crack propagation in neat epoxyrnand epoxy with embedded microcapsules is accurately captured by the Paris power-law. The slope nrnof the power-law regime is strongly dependent on the content of microcapsules, varying from n = 10rnfor neat epoxy to n = 4 for 10 wt% microcapsules. The inherent fatigue characteristics of the selfhealingrnmaterial and its ability to extend component life are currently being investigated.