Why is mechanical fatigue different from toughness in elastomers? The role of damage by polymer chain scission

Abstract

Although elastomers often experience 10 to 100 million cycles before failure, there is now a limited understanding of their resistance to fatigue crack propagation. We tagged soft and tough double-network elastomers with mechanofluorescent probes and quantified damage by sacrificial bond scission after crack propagation under cyclic and monotonic loading. Damage along fracture surfaces and its spatial localization depend on the elastomer design, as well as on the applied load (i.e., cyclic or monotonic). The key result is that reversible elasticity and strain hardening at low and intermediate strains dictates fatigue resistance, whereas energy dissipation at high strains controls toughness. This information serves to engineer fatigue-resistant elastomers, understand fracture mechanisms, and reduce the environmental footprint of the polymer industry.

Highly Durable and Tough Liquid Crystal Elastomers

“…At 0.5 s –1 , the fatigue threshold of DNLCEs was measured to be 131.22 Jm –2 , while the threshold for SNLCEs was 36.25 Jm –2 . In a recent work on double network elastomers with covalent bonds, strain hardening using a stiff first network and the resulting stabilization of the damage zone has been shown to considerably improve the fatigue threshold . This shows that judicious fine tuning of the mechanical properties of the networks allows substantial improvement of the fatigue and fracture properties.…”

Hierarchically Structured Deformation‐Sensing Mechanochromic Pigments

“…Different strategies have been developed to render polymer materials mechanochromic, [6,10,14,19] including the release of (latent) dyes from rupturing capsules, [20] rearrangements of plasmonic materials, [21] the separation of optically active moieties that engage in inter- [22,23] or intramolecular interactions, [24][25][26] conformational changes of conjugated polymers [27] and small conjugated groups in polymers, [28] unit cell changes of photonic nanostructures, [12,[29][30][31][32][33][34][35][36][37][38] as well as the covalent incorporation of mechanically labile molecular moieties referred to as "mechanophores". [6,10,39] The origin of the color change, the stress and strain ranges in which the optical response occurs, the spatial and strain resolution, the possibility to provide quantitative information about the deformation, and the ease of implementation vary greatly between the different approaches. [6,26,34] Indeed, many of these platforms have only been tested in tailor-made materials.…”

Regiochemical effects for the mechanochemical activation of 9‐π‐extended anthracene‐maleimide Diels–Alder adducts

“…Here, we investigate the regiochemical effects in the mechanochemical retro DA reaction of 9‐π‐extended A‐M DA adducts where the substituent location is varied at the π‐extended phenyl moiety from o ‐ over m ‐ to p ‐substitution (Scheme 1). This popular fluorogenic mechanophore class is being used for the visualization of force‐induced bond scission events in polymer materials due to its excellent photophysical properties 29–35 . While we have implemented structural modifications of the aryl units in 9‐position of the anthracene before, 36–38 the effects of pulling point locations have not yet been investigated.…”

“…This popular fluorogenic mechanophore class is being used for the visualization of force-induced bond scission events in polymer materials due to its excellent photophysical properties. [29][30][31][32][33][34][35] While we have implemented structural modifications of the aryl units in 9-position of the anthracene before, [36][37][38] the effects of pulling point locations have not yet been investigated. We here combine three methods to understand the influence of the pulling point location on the mechanochemical reactivity of the mechanophore.…”