While initial interest in nanocomposites was to explore size effects in mechanical behavior, current research is focused around the new paradigm of interface-dominated/enabled mechanical behavior. The use of advanced computational tools to accelerate the discovery, design, and fundamental understanding of behavior is highlighted along with novel synthesis and in situ nanomechanical characterization tools. Designed interfaces can be used as building blocks to create new forms of hierarchical composites with unprecedented mechanical and physical behavior. New frontiers in the field of mechanical behavior of nanocomposites involving metallic, nanocarbon, bioinspired, and biomaterials are reviewed.

The mechanical deformation behavior of nanocomposite metals depends on the dimensions of their constituents, due to the interactions of dislocations with grain and phase boundaries. It is now becoming apparent that the mechanical behavior of these materials also depends on the constituent shapes. This article summarizes experimental and modeling investigations on two types of metal nanocomposites composed of intricately interpenetrating phases—those formed by phase separation in physical vapor codeposited alloys and those synthesized by liquid-metal dealloying. The opportunities and challenges these materials present for investigating complex microstructural morphologies and their effects on mechanical behavior are discussed.

Superior structural properties of materials are generally desired in harsh environments, such as elevated temperatures, high rates of impact, and radiation. Composite nanolaminates, built with alternating stacks of crystalline layers, each with nanoscale individual thickness, are proving to exhibit many of these target properties. In principle, the nanolaminate concept can be applied to any two-phase, bimetallic system; however, for a number of reasons, they have been limited to combinations of metals with a cubic crystal structure. There is growing demand to increase the number of advanced materials systems containing noncubic metals, since these metals bear several desirable intrinsic properties. In this article, we cover recent modeling and experimental efforts to understand the complexity in structure, mechanisms, and behavior of noncubic/cubic nanolaminates. We hope this article will facilitate and encourage future studies in this promising area.

Nanocarbon materials, such as carbon nanotubes, graphene, and their derivatives, are regarded as promising reinforcing agents in metal matrix composites (MMCs) because of their excellent intrinsic mechanical properties. Considering the various types of nanocarbons with different defect states and intrinsic properties, there is a potential for tailoring the mechanical behavior of nanocarbon-reinforced MMCs. This article reviews recent developments in both the processing and the structure–property correlations of these composites. Particular emphasis is given to the structure and properties of the nanocarbon–metal interfaces, as the external mechanical load is transferred between the nanocarbon and the metal matrix across their interfaces. Moreover, in addition to the intuitive load-bearing effect of the nanocarbon reinforcements, a copious interplay between nanocarbons and dislocations in the metal matrix has been found, which alters the deformation behavior that leads to additional strengthening. For structural applications, scalable fabrication routes for the nanocarbon-metal composites need to be developed, and studies on the mechanical behavior under real service conditions are needed.

Biological materials such as bone, teeth, and nacre boast remarkable structures and toughening mechanisms, many of them unmatched by engineering materials. In these materials, fracture toughness is key to fulfill critical structural functions and achieve high strength, reliability, robustness, damage tolerance, and notch performance. In this article, we review and discuss some of the main toughening strategies found in hard biological materials. In particular, we underline a “universal” strategy where well-defined microarchitectures, stiff building blocks, and weak interfaces operate in synergy to resist crack propagation. These natural materials have been inspiring the development of a myriad of synthetic materials that duplicate some of these features at the nanoscale and at larger scales. While recent materials show impressive properties, duplication of the architectures and mechanisms seen in natural materials still presents formidable challenges.

Silk and carbon nanomaterials, such as graphene oxide, graphene, and carbon nanotubes, have complementary mechanical properties that feature superior toughness and strength, respectively. Different strategies have been devoted to developing silk/carbon nanocomposites, but challenges remain to fully integrate the mechanical advantages of these two components into one synergistic material system. In this article, we provide a critical summary of structure–mechanics relationships in silk/carbon nanocomposites and highlight the impact of the interaction between silk and carbon nanomaterials on mechanical properties of the hybrid materials. We describe the challenges involved and directions for future designs of silk/carbon nanocomposites.

The water and energy sectors of an economy are inextricably linked. Energy is required in water production, distribution, and recycling, while water is often used for energy generation. In many geographical locations, the energy-water nexus is exacerbated by the shortage of both fresh water resources and energy generation infrastructure. New materials, including metamaterials, are now emerging to address the challenges of providing renewable energy and fresh water, especially to off-the-grid communities struggling with water shortages. Novel nanomaterials have fueled recent technology breakthroughs in solar water desalination, fog and dew collection, and cloud seeding. Materials for passive thermal management of buildings and individuals offer promising strategies to reduce the use of energy and water for heating and cooling. While many challenges remain, emerging materials and technologies improve sustainable management of water and energy resources.