Session: 03-06-01: Damage, Fatigue, and Fracture

Paper Number: 151704

151704 - Fracture Toughness of Carbon Nanofiber-Reinforced Stacked Bilayer Graphene: A Mixed-Dimensional Approach With Real-Time Crack Analysis 

Graphene, praised for its exceptional intrinsic mechanical strength of ~130 GPa and Young’s modulus of ~1 TPa, offers great potential for high load bearing applications. However, its brittle nature results in low fracture toughness, particularly under complex loading conditions, a combination of shear and tensile stresses, limiting its effectiveness as a reinforcement material. To address this, we propose enhancing the extrinsic fracture toughness of pristine graphene by incorporating one-dimensional (1D) carbon nanofibers (CNFs). These CNFs retard crack propagation, thereby increasing the load-bearing capacity of graphene.

In addition to the mechanical reinforcement provided by CNFs, the conformity of graphene around these nanofibers is crucial for optimizing stress transfer and load distribution. Effective graphene conformity ensures minimal surface energy and reduces internal strain energies around the 1D reinforcements, improving mechanical properties. In contrast, non-conformal configurations may act as stress concentrators, creating weak points that compromise the structural integrity of the composite and could lead to premature failure.

This study introduces a novel technique to synthesize mixed-dimensional carbon nanomaterials by depositing CNFs on graphene and sandwiching this composite with another layer of graphene to obtain carbon nanofiber/stacked bilayer graphene (CNF/SBLG). This freestanding composite is transferred onto transmission electron microscopy (TEM) grids for mechanical testing. We perform high-throughput, real-time observations of crack propagation in CNF/SBLG composite using a scanning electron microscope (SEM), under displacement-controlled loading. This enables the measurement of the mode-I stress intensity factor as a function of crack length. Finite element analysis (FEA) further complements the experimental data by modeling the stress intensity factors for mode-I crack propagation and assessing the fracture toughness of the mixed-dimensional graphene system. Additionally, molecular dynamics (MD) simulations are conducted to quantify the effects of graphene conformity around CNFs on the tension within the graphene layers, offering further insights into the mechanical performance of this composite material.

Presenting Author: Muhammad Usama Arshad Texas A&M University

Presenting Author Biography: Usama is a Ph.D. student at Texas A&M University. He is working on the fracture mechanics of graphene with and without the reinforcement of carbon nanofibers under scanning electron microscope for real time analysis of crack propagation. Before joining Texas A&M University, he completed his master's degree from National Central University, Taiwan major in Energy Engineering. In his master's, he worked on functionalized graphene polymeric composite for severe corrosion protection.