Life extension of self-healing polymers with rapidly growing fatigue cracks

Abstract

Self-healing polymers, based on microencapsulated dicyclopentadiene and Grubbs' catalyst embedded in the polymer matrix, are capable of responding to propagating fatigue cracks by autonomic processes that lead to higher endurance limits and life extension, or even the complete arrest of the crack growth. The amount of fatigue-life extension depends on the relative magnitude of the mechanical kinetics of crack propagation and the chemical kinetics of healing. As the healing kinetics are accelerated, greater fatigue life extension is achieved. The use of wax-protected, recrystallized Grubbs' catalyst leads to a fourfold increase in the rate of polymerization of bulk dicyclopentadiene and extends the fatigue life of a polymer specimen over 30 times longer than a comparable non-healing specimen. The fatigue life of polymers under extremely fast fatigue crack growth can be extended through the incorporation of periodic rest periods, effectively training the self-healing polymeric material to achieve higher endurance limits.

Self-healing of fatigue crack in epoxy materials with epoxy/mercaptan system

“…Most polymeric materials suffer from poor fatigue resistance and would fail at stress levels much lower than the critical stress intensity, K IC . Therefore, imparting self-healing capability to polymers and polymer composites [1][2][3][4][5][6][7][8][9] should be an effective way to solve the problem. It is hoped that the fatigue cracks can be autonomously eliminated soon after their emergence.…”

“…The results might serve as a reference for further improving the performance of the healant system under fatigue circumstances. Vol.5, No.1 (2011) 47-59 Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2011.6 * Corresponding author, e-mail: ceszmq@mail.sysu.edu.cn © BME-PT responding to propagating fatigue cracks by autonomic processes that led to higher endurance limit and life extension, or even complete arrest of cracking [5][6][7][8], in addition to the ability to repair the cracks generated by monotonic fracture [9]. The degree of fatigue life extension was found to be dependent on the relative magnitude of mechanical kinetics of crack propagation and chemical kinetics of healing.…”

Self-healing polymers and composites

“…[30][31][32] The second approach, developed by Lewis and co-workers 33,34 and shown in equation (7), is similar to the first, but instead utilises the mean fatigue crack propagation rate (FCPR) 49,162,163 The efficiencies of many self-healing systems that show promise for coating applications have been measured by depositing the polymer as a film over a metal electrode and measuring the current that can flow through healed polymers. [53][54][55][56] Wilson and co-workers developed an approach to calculate the average retention of healing capabilities r avg of polymers and composites that were initially fabricated at different temperatures.…”

“…29 In addition to healing large cracks, fatigue lifetime of these systems could be improved to over 30 times longer than that of a polymer without a self-healing functionality, and under certain conditions (low applied stress and short rest periods), fatigue crack growth was indefinitely retarded. [30][31][32] Most utilisations of the DCPD/Grubbs' catalyst based healing agent system have been used to heal structurally dissimilar polymer matrices [predominately epoxies, but other polymers have also been healed, such as PMMA bone cement, 33,34 epoxy vinyl esters 35 and poly(styreneb-butadiene-b-styrene) 36 ]. Given that most living organisms ultimately repair their damaged cell tissue with structurally similar (often identical) tissue material, these ROMP based healing systems are not entirely biomimetic.…”

Fatigue of self-healing hierarchical soft nanomaterials: The case study of the tendon in sportsmen

“…Drawing inspiration from these natural systems, self-healing artificial materials have also been designed and produced, using diverse approaches and various constituents, from systems based on "microcapsules" containing a healing agent 4,5 , to "vascular-based" systems 6,7 , to "molecular-based" systems 8,9 . In particular, self-healing was found to be particularly effective in increasing fatigue life of composites 10,11 and polymers 12 ,…”