Microstructure and mechanical properties of hard Acrocomia mexicana fruit shell

Area of Science:

• Materials Science
• Biomaterials Engineering
• Mechanics of Materials

Background:

• Fruit and nut shells are known for their hardness and toughness.
• The Cocoyol palm fruit (Acrocomia mexicana) from Yucatan, Mexico, is anecdotally known for its extreme difficulty to break, referenced in historical accounts and local legends.
• Previous scientific literature lacked quantitative data on the mechanical performance of the Cocoyol endocarp.

Purpose of the Study:

• To scientifically quantify the mechanical properties (compressive strength, microhardness) of the Cocoyol palm fruit shell.
• To investigate the microstructure of the Cocoyol endocarp.
• To establish structure-property relationships that explain the material's hardness and toughness.

Main Methods:

• Mechanical testing was performed to determine compressive strength under quasi-static and high strain rate loading conditions.
• Microhardness measurements were conducted.
• Microstructural analysis was used to examine the shell's hierarchical structure.

Main Results:

• Compressive strength reached up to approximately 150 MPa (quasi-static) and 250 MPa (high strain rate).
• Microhardness values were measured up to approximately 0.36 GPa.
• The Cocoyol shell exhibits a complex, hierarchical, and functionally graded structure with distinct radial layers.

Conclusions:

• The Cocoyol shell possesses significant hardness and toughness, validated by quantitative mechanical data.
• Its unique layered, functionally graded microstructure is key to its superior mechanical performance.
• These findings provide a basis for developing novel bioinspired synthetic materials with enhanced properties.