Self-Organization at the Crack Tip of Fatigue-Resistant Thermoplastic Polyurethane Elastomers

Abstract

Despite their technological relevance, the resistance of soft thermoplastic polyurethanes (TPU) to crack propagation in cyclic fatigue has never been investigated in detail. In particular a clear shortcoming in the literature for this class of materials is the lack of connection between the cyclic 2 fatigue resistance and the large strain behavior that has a fundamental role in defining the material's resistance to crack propagation. We demonstrate here for the first time that when the strain-induced stiffening mechanism of TPU (already observed for large deformation) is combined with the presence of the not-homogeneous strain, as in case of cyclic fatigue, it produces a selective reinforcement in the crack tip area which is the key to explain the remarkable cyclic fatigue resistance of TPU. Using commercial TPU with similar modulus (~8 MPa) but different large strain behavior we show that the described mechanism is intrinsically linked to the multi-phase nature of TPU and is not necessarily linked to a specific large strain property as the case of TPU which undergo strain-induced crystallization.

Mechanistic Understanding of Sticker Aggregation in Supramolecular Polymers: Quantitative Insights from the Plateau Modulus of Triblock Copolymers

“…An important perspective of these simulations regards the rationalization of the mechanical behavior of crystallizable triblock (and possibly multiblock) copolymers under intermediate and large deformations. The first challenge resides in following the decrease in N ce upon uniaxial stretching slightly above the linear regime to connect the number of HS-pull out events to the loss of modulus observed at the MBC yield point. − More ambitiously, it would also be of great interest to monitor both the fraction and the dynamical behavior of each type of SS beads for several discrete values of large strain after having reached the equilibrium. This information would notably help to clarify the origin of the strain hardening beyond static chain stretching considerations.…”

Enhance Fracture Toughness and Fatigue Resistance of Hydrogels by Reversible Alignment of Nanofibers

“…At the crack tip, L = 58 nm at λ = 1.5 and L = 46 nm at λ = 3. The reduction of the long period from λ = 1.5 to λ = 3 demonstrates the further alignment of CNCs along the stretching direction. , The long period L of the bulk area and the crack tip are basically the same under the same stretch, further indicating that the stress concentration is alleviated by CNC alignment.…”

Fast Evaluation and Comparison of the Energy Performances of Elastomers from Relative Energy Stored Identification under Mechanical Loadings

“…The energy involved in the hysteresis loop is therefore almost not converted into heat and the higher the stretch level the higher the relative energy stored in the material. This strong similitude with the unfilled natural rubber is explained by the fact that the TPU considered here crystallizes under tension, but also by the fact that the multi-phase nature of TPU induces strong self-organization as suggested in [27] and regardless of whether it crystallizes or not as shown in [61]. It should be noted that for a strain rate of four times lower, the ratio is close to 1 whatever the stretch applied.…”