Stretchable materials of high toughness and low hysteresis

In materials of all types, hysteresis and toughness are usually correlated. For example, a highly stretchable elastomer or hydrogel of a single polymer network has low hysteresis and low toughness. The single network is commonly toughened by introducing sacrificial bonds, but breaking and possibly r...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2019-03, Vol.116 (13), p.5967-5972
Main Authors: (王正锦), Zhengjin Wang, Xiang, Chunping, Yao, Xi, Le Floch, Paul, Mendez, Julien, Suo, Zhigang
Format: Article
Language:English
Subjects:
Adhesion
Adhesive strength
Bonding
Chemical bonds
Composite materials
Constituents
Crack propagation
Elastomers
Engineering Sciences
Fatigue
Fatigue failure
Fibers
Fracture toughness
Hydrogels
Hysteresis
Interfaces
Mechanical properties
Modulus of elasticity
Physical Sciences
Reforming
Stress concentration
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Summary:In materials of all types, hysteresis and toughness are usually correlated. For example, a highly stretchable elastomer or hydrogel of a single polymer network has low hysteresis and low toughness. The single network is commonly toughened by introducing sacrificial bonds, but breaking and possibly reforming the sacrificial bonds causes pronounced hysteresis. In this paper, we describe a principle of stretchable materials that disrupt the toughness–hysteresis correlation, achieving both high toughness and low hysteresis. We demonstrate the principle by fabricating a composite of two constituents: a matrix of low elastic modulus, and fibers of high elastic modulus, with strong adhesion between the matrix and the fibers, but with no sacrificial bonds. Both constituents have low hysteresis (5%) and low toughness (300 J/m²), whereas the composite retains the low hysteresis but achieves high toughness (10,000 J/m²). Both constituents are prone to fatigue fracture, whereas the composite is highly fatigue resistant. We conduct experiment and computation to ascertain that the large modulus contrast alleviates stress concentration at the crack front, and that strong adhesion binds the fibers and the matrix and suppresses sliding between them. Stretchable materials of high toughness and low hysteresis provide opportunities to the creation of high-cycle and low-dissipation soft robots and soft human–machine interfaces.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1821420116