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Fatigue cracking of thermoplastic elastomers

Abstract : Soft thermoplastic polyurethane elastomers (TPU) are a class of block copolymers characterised by a low linear modulus (<10MPa), reversible elasticity and excellent abrasion resistance already used in several rubber‐like applications such as soles, wheels, flexible cables, etc. Yet, their fatigue behaviour under cyclic loading has not been fully investigated so far, leaving several open questions about how predicting long‐term durability of TPUs for a safe design. In this work we proposed a reproducible experimental protocol to assess and compare the resistance to crack propagation in cyclic conditions of TPU, with that of classical filled rubbers by using a fracture mechanics approach. Furthermore, we characterized the mechanical response under cyclic loading at large and small strain of three commercial TPUs with similar linear moduli and rheology but different large strain behaviours: extended softening, strain hardening and strain hardening enhanced by SIC. Irrespectively of their composition, all TPUs presented an unconventional strain induced stiffening in step‐cyclic experiment. Using DIC and X‐Ray in situ experiments we showed that, the strain gradient at the crack tip generates a spatial re‐organization of the TPU microstructure consistent with a volume locally stiffer than the bulk. This heterogeneity in the deformability reduces the strain intensification at the crack tip explaining the high fatigue resistance in TPU. The local stiffening was ultimately associated to the fragmentation of original hard domains in smaller but more numerous units increasing the degree of physical crosslinking.
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Submitted on : Monday, February 22, 2021 - 5:37:39 PM
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  • HAL Id : tel-03149063, version 1

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Giorgia Scetta. Fatigue cracking of thermoplastic elastomers. Polymers. Université Paris sciences et lettres, 2020. English. ⟨NNT : 2020UPSLS022⟩. ⟨tel-03149063⟩

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