Local relative density modulates failure and strength in vertically aligned carbon nanotubes.

Area of Science:

• Materials Science
• Mechanical Engineering
• Nanotechnology

Background:

• Vertically aligned carbon nanotubes (VACNTs) possess unique mechanical properties.
• Controlling and understanding the microstructural variations within VACNTs is crucial for their application.
• Density gradients can significantly influence material behavior under stress.

Purpose of the Study:

• To investigate the relationship between relative density gradients and the mechanical response of VACNTs.
• To identify a microstructural figure-of-merit for predicting VACNT mechanical behavior.
• To validate experimental findings with theoretical modeling.

Main Methods:

• Micromechanical experiments were conducted to assess mechanical properties.
• Scanning electron microscopy and edge detection analysis quantified local density.
• Theoretical modeling using a 2D viscoplastic solid model predicted material response.

Main Results:

• Local failure events and compressive stresses in VACNTs are directly linked to relative density gradients.
• Samples with lower bottom density exhibited sequential bottom-to-top buckling and hardening.
• A reversed or insubstantial density gradient resulted in delayed bottom buckling and a flat stress plateau.
• Model predictions aligned with experimental observations, relating hardening slope to stiffness and density gradients.

Conclusions:

• The effective relative density serves as a quantifiable microstructural figure-of-merit for VACNTs.
• This figure-of-merit can accurately predict the mechanical response of VACNTs.
• Understanding density gradients is essential for tailoring VACNT mechanical performance.