Why is it easier to cut than to tear elastomers?

Cutting soft yet tough materials like rubber, leather, or even meat is significantly easier with a sharp blade than by tearing— even when the tear is initiated by a notch. Researchers from the SIMM laboratory [1] at ESPCI Paris – PSL have uncovered the mechanism behind this phenomenon: cutting significantly reduces deformation and molecular damage within soft materials. Their findings were recently published in Nature Communications [2].

When a soft material is subjected to force, it undergoes substantial deformation near the crack tip—a phenomenon known as blunting. This deformation leads to the rupture of numerous molecular bonds, requiring a large amount of energy to propagate a tear. In contrast, using a blade significantly reduces blunting by concentrating the deformation in a localized area, thereby limiting damage to the molecular network.





To explore this effect, the scientists used polydimethylsiloxane (PDMS), an elastomer embedded with fluorescent molecules that respond to mechanical force (mechanophores). When a chemical bond breaks, these fluorescent markers are activated, allowing precise quantification of molecular damage caused by cutting or tearing.

The results reveal that when PDMS is cut with a blade under moderate pre-stretching, the energy required to propagate the crack is significantly lower than in the case of pure tearing. Specifically, using a blade reduces by half the average number of molecular layers that break, thus lowering the total energy needed.

These findings open up practical avenues for designing materials that respond differently to cutting and tearing, tailored to the specific demands of industrial applications. Potential fields of use include medical devices, sports equipment, personal protective gear, and even the food industry—where precise cutting with minimal internal damage is crucial to maintaining product integrity.


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Contact
Scientific communication of ESPCI Paris – PSL : Paul Turpault,

Reference
Zhao, D., Cartier, A., Narita, T. et al. Why cutting is easier than tearing elastomers. Nat Commun 16, 3203 (2025). https://doi.org/10.1038/s41467-025-58483-1

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