An extreme toughening mechanism for soft materials

Area of Science:

• Materials Science
• Polymer Science
• Mechanics of Materials

Background:

• Soft yet tough materials are essential in nature and daily life.
• Toughness enhancement in soft materials is traditionally attributed to bulk dissipation mechanisms like Mullins effect and viscoelasticity.
• Existing models often underestimate the actual toughness enhancement observed in these materials.

Purpose of the Study:

• To investigate and identify the primary mechanisms responsible for the extreme toughness enhancement in soft materials.
• To propose a new theoretical framework and scaling law that accurately predicts toughness enhancement.
• To demonstrate the universal applicability of the proposed mechanism across various soft material types.

Main Methods:

• Combined experimental investigations with theoretical modeling.
• Analyzed energy dissipation mechanisms at both bulk and near-crack levels.
• Developed a new scaling law based on proposed toughening mechanisms.

Main Results:

• Bulk dissipation mechanisms alone significantly underestimate the toughness enhancement of soft tough materials.
• A novel mechanism involving near-crack dissipation, including polymer-chain entanglement, is identified as crucial for extreme toughening.
• The proposed mechanism and scaling law accurately account for the toughness enhancement in diverse soft materials, including various hydrogels and rubbers.

Conclusions:

• Soft material toughness enhancement is governed by both bulk hysteretic dissipation and near-crack dissipation.
• Near-crack dissipation, unlike bulk dissipation, does not always induce significant bulk stress-stretch hysteresis.
• The newly proposed mechanism offers a universal explanation for extreme toughening in a wide range of soft materials.