Granular crystals as strong and fully dense architectured materials.

Area of Science:

• Materials Science
• Mechanical Engineering
• Solid Mechanics

Background:

• Dense topologically interlocked panels utilize stiff building blocks with frictional contact for enhanced mechanical properties.
• Existing strategies focus on panels, limiting applications for bulk materials.

Purpose of the Study:

• To extend the concept of topologically interlocked structures to fully dense, 3D architectured materials using space-filling grains.
• To investigate the mechanical behavior and deformation mechanisms of these novel granular crystals.

Main Methods:

• 3D printing of rhombic dodecahedral and truncated octahedral grains.
• Assembly of grains into face-centered cubic and body-centered cubic granular crystals using mechanical vibrations.
• Triaxial compression testing to evaluate mechanical performance and deformation mechanisms.
• Development of a three-length scale theoretical model to capture observed phenomena.

Main Results:

• Granular crystals demonstrated up to 25 times greater strength than randomly packed spheres.
• Materials exhibited nonlinear deformations, crystal plasticity, geometrical hardening, shear-induced dilatancy, and microbuckling.
• A novel pressure-dependent granular crystal plasticity with interlocked slip planes was observed, forbidding slip in certain directions.
• Recycling of tested grains showed no loss of material strength.

Conclusions:

• The study successfully created robust 3D architectured materials with exceptional strength and damage tolerance through controlled grain assembly.
• Observed unique deformation mechanisms, including granular crystal plasticity, offer new avenues for material design.
• These materials show potential for advanced applications requiring high performance, repairability, and recyclability.