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New mechanism for strengthening materials


Dr. Kasra Momeni, assistant professor of mechanical engineering and director of the Advanced Hierarchical Materials by Design Lab at Louisiana Tech University, has discovered a new mechanism for strengthening nanomaterials and tailoring their properties to build superior structures.

This additional dimension added to the material design opens new doors to build superior materials by engineering their atomic structure. The proposed approach can also be used to adjust the chemistry of the material, which is of importance for designing new catalytic materials enhancing the chemical processes.

“Stacking faults in nanomaterials drastically changes the stress distribution, as the long-range stress fields interact with the boundaries in these materials,” said Momeni.

“The complex nature of the stresses formed in nanowires, as a result of superposition of the stress fields from surface relaxation and reconstruction as well as the stacking fault stress fields, changes the failure mechanism of the nanowires.”

Atomistic simulations indicate that the presence of stacking faults results in an inhomogeneous stress distribution within the nanowires, due to the change in the sign of stress fields on the two sides of stacking faults (i.e. compressive stress on one side and tensile stress on the other side). This inhomogeneous stress field results in a non-symmetrical mechanical response of the nanowires under tensile and compressive loadings. The defected nanowires with diameters smaller than 1.8nm and a single stacking fault, surprisingly, have a higher yield stress compared to their counterparts with perfect structures.

“This surprising behavior is due to the interaction between the stress fields of stacking faults with the stress field of relaxed and reconstructed surfaces in thin nanowires,” said Momeni.

“We expect similar results in other 1D nanomaterials with stacking faults, where inhomogeneous stresses form. The developed atomistic model paves the way to study the effect of different stacking fault distributions and engineering defects to tailor material properties.”

“[Momeni’s] discovery of a method to strengthen materials through the interaction of atomic-level material features is a significant and fundamental contribution in computational mechanics,” said Dr. David Hall, director of civil engineering, construction engineering technology and mechanical engineering at Louisiana Tech.

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