Fatigue-resistant polyurethane elastomer composites

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.