Polyurethane (PU) elastomers are among the most used rubberlike materials due to their combined
merits, including high abrasion resistance, excellent mechanical properties, biocompatibility, and good
processing performance. A PU elastomer exhibits pronounced hysteresis, leading to a high toughness on
the order of 104 J/m2. However, toughness gained from hysteresis is ineffective to resist crack growth
under cyclic load, causing a fatigue threshold below 100 J/m2. Here we report a fatigue-resistant PU
fiber–matrix composite, using commercially available Spandex as the fibers and PU elastomer as the
matrix. The Spandex fibers are stiff, strong, and stretchable. The matrix is soft, tough, and stretchable.
We describe a pullout test to measure the adhesion toughness between the fiber and matrix. The test
is highly reproducible, showing an adhesion toughness of 3170 J/m2. The composite shows a maximum
stretchability of 6.0, a toughness of 16.7 kJ/m2, and a fatigue threshold of 3900 J/m2. When a composite
with a precut crack is stretched, the soft matrix causes the crack tip to blunt greatly, which distributes
high stress over a long segment of the Spandex fiber ahead the crack tip. This deconcentration of stress
makes the composite resist the growth of cracks under monotonic and cyclic loads. The PU elastomer
composites open doors for realistic applications of fatigue-resistant elastomers
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Composites retard hydrolytic crack growth
Degradable polymers are under intense development for sustainability and healthcare. Evidence has accumulated that the chemical reaction that decomposes a polymer an also grow a crack. Even under a small load, the crack speed can be orders of magnitude higher than the overall rate of degradation, leading to premature failure. Here, we demonstrate that a crack slows down markedly in a composite of two degradable materials. In a homogeneous degradable material, the stress concentrates at the crack tip, so that a relatively small applied stretch induces a high stress and a high rate of reaction. The fracture behavior of a composite that consists of two degradable materials, a stiff material for the fibers and a compliant material for the matrix, with strong adhesion between both, is different: The soft matrix blunts the crack and distributes the stresses at the crack tip over a long length of the fibers. The same rate of reaction requires a larger applied stretch. This stress de-concentration retards crack growth in the composite. We demonstrate this concept using a composite made of stiff polydimethylsiloxane (PDMS) fibers in a soft PDMS matrix. In the presence of water molecules in the environment, siloxane bonds in the PDMS hydrolyze, causing hydrolytic crack growth. We show that a hydrolytic crack grows much more slowly in a PDMS composite than in homogeneous PDMS, and may even arrest in the composite. It is hoped that this concept will contribute to the development of degradable materials that resist premature failure.
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- Award ID(s):
- 2011754
- NSF-PAR ID:
- 10501579
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Extreme Mechanics Letters
- Volume:
- 48
- Issue:
- C
- ISSN:
- 2352-4316
- Page Range / eLocation ID:
- 101433
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.eml.2021.101433
