2021 Theses Doctoral

Enhanced Strength and Frictional Properties of Copper-Graphene-Copper Nanolaminates

Rastogi, Shruti

Understanding the deformation mechanism in nanocomposites is critical to realizing a host of next-generation technologies like stretchable electronics, three-dimensional multifunctional surfaces, and nanoscale machines. Graphene’s unparalleled mechanical strength and stability – owing to its two-dimensional geometry, high intrinsic strength, and Young’s modulus – have opened up new opportunities to engineer composites of higher strength-to-weight ratios for various practical applications. The ability of graphene (Gr) to act as a strength enhancer depends on the interface interactions and the composite’s microstructure. Here we demonstrate a microstructure design of Cu-Gr-Cu nanolaminate that enhances the composite’s load-bearing capacity, improves the composite’s strength, and reduces its coefficient of friction.

The mechanical and frictional properties of Cu-Gr-Cu nanolaminate were probed using the nanoindenter. A series of nanoindentations performed on Cu-Gr-Cu nanolaminate exhibit an effective yield strength of 320 MPa and effective flow strength of 0.5 GPa. Scratch tests performed on the free surface of the Cu-Gr-Cu nanolaminate show a considerable decrease in the coefficient of friction from 0.3 to 0.2. The cantilever bending test performed on Cu-Gr-Cu nanolaminate showed an increase in flow strength and strain hardening compared to Cu-Cu. The enhancement in the mechanical and friction properties of Cu-Gr-Cu nanolaminate suggests a build-up of dislocations at the Cu-Graphene interface. FEA simulations of the nanoindentation on Cu-Gr-Cu nanolaminate confirm the effectiveness of graphene as a barrier to plastic deformation. The pile-up of dislocations at the Cu-Graphene interface implies large plastic strain gradients near the interface. We developed a strain gradient plasticity computational model of the beam bending experimental system based upon Gudmundson’s higher-order theory and implemented it as a user element in ABAQUS. A set of material parameters is identified that reproduce the experimental for