Interface failure modes explain non-monotonic size-dependent mechanical properties in bioinspired nanolaminates

Indentation-induced plastic behaviour of nanotwinned Cu/high entropy alloy FeCoCrNi nanolaminate: an atomic simulation

Using large-scale molecular dynamics (MD) simulations, the effects of interface and layer number in the nanoindentation response of experimentally observed nanotwinned Cu/high entropy alloy (HEA) FeCoCrNi nanolaminate are studied. The dislocations are nucleated and emitted, which are more limited to the first twinning layer > second twinning layer > HEA layer. The stacking fault strengthening is pronounced due to the obvious difference of stacking fault energy between Cu and HEA, which can be rarely observed from the previous work in traditional alloys and metals. After the indentation induced deformation, the nanotwinned Cu/HEA FeCoCrNi nanolaminates for different layer numbers generate a mass of Shockley partial dislocations to cause the good plasticity, attributed to the strong strain gradient effect. The strong layer number and interface structure effects found here can provide insight for the design of advanced nanolaminate with high strength and good plasticity.

Analysis of optimal crosslink density and platelet size insensitivity in graphene-based artificial nacres

Exploration of graphene-based artificial nacres with excellent mechanical properties demonstrates the potential to surpass natural nacre. Recent experimental studies report that optimal crosslink density defined as concentration of the surface functional groups is usually observed in these artificial nacres towards superb mechanical performance. A hybrid model integrating a nonlinear shear-lag model and atomistic simulations reveals the emergence of an optimal crosslink density at which the maximum strength and toughness are achieved. The origin is due to the balance among the reduction of in-plane tensile properties of the graphene sheets, the enhancement of the shear strength of the interlayer and the reduction of interface plasticity. In addition, our results also reveal that the size insensitivity of the graphene sheet appears when the shear stress of the interlayer is highly localized, the increase of the crosslink density intensifies the nonuniformity of the shear stress and the optimal mechanical properties of the artificial nacre cannot be further enhanced by tuning the size of the graphene sheets. Three kinds of interface molecular interactions with their optimal crosslink densities are also proposed to simultaneously maximize the strength and toughness of graphene-based artificial nacres.