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The superior intrinsic mechanical properties of graphene have been widely studied and utilized to enhance the mechanical properties of various composite materials. However, it is still unclear how heterostructures incorporating graphene behave, and to what extent graphene influences their mechanical response. In this work, a series of graphene/Al2O3 composite films were fabricated via atomic layer deposition of Al2O3 on graphene, and their mechanical behavior was studied using an experimental-computational approach. The inclusion of monolayer chemical vapor deposited graphene between ultrathin Al2O3 films (1.5–4.5 nm thickness) was found to enhance the overall stiffness by as much as 70% compared to a pure Al2O3 film of similar thickness (∼150 GPa to ∼250 GPa). Here, for the first time, the combination of graphene and Al2O3 in vertically-stacked heterostructures results in advanced hybrid films of unprecedented mechanical stiffness that also possess qualities desirable for graphene-based transistors and flexible electronics.

With the advent of additive manufacturing, fabrication of complex structures with high efficiency for energy absorption and blast and impact mitigation has entered a new era. In this research the role of the architecture and material properties on the static and dynamic energy absorption properties of additively-manufactured complex cellular structures out of two different materials were studied under puncture and crush tests. A finite element simulation of the unit cell was also conducted to study the effect of loading rate on the final response of the material where the results showed good agreement with the experimental observations. It is shown that the studied additively manufactured structures were able to recover their shape significantly after a major deformation due to the impact. These results show the potential of additive manufacturing as a versatile tool for creating structures with complex geometries for energy absorption.

This review paper discusses the recent progress in laser shock peening (LSP) of additively manufactured (AM) parts. LSP is an advanced post-processing technique that optimizes the service lives of critical components for various applications by inducing severe plastic deformation accompanied by the enhancement of surface properties in treated materials. Material improvement is enabled through the generation of high-density dislocations, grain refinement, and beneficial phase transformations. These mechanisms produce high magnitude compressive residual stresses which harden treated regions to depths exceeding 1 mm. However, a major roadblock for AM parts stems from the various fabrication processes themselves where detrimental tensile residual stresses are introduced during part manufacturing, along with near-surface voids and cracks, all of which severely limit their applications. In addition to post-fabrication heat treatment that is typically required to homogenize the microstructure and relieve the residual stresses of AM parts, post-processing surface treatments have also been developed to manipulate the residual stresses of AM materials. Tensile residual stresses generated during manufacturing affect the fatigue life of AM material negatively and could potentially surpass the material’s yield strength, resulting in acute geometric distortion. Recent studies have shown the potential of LSP to mitigate these stresses, modify the mechanical properties of the AM parts, and to close near-surface voids and cracks. Furthermore, the thermal stability of favorable microstructural modifications in laser peened AM parts, which allows for its use in high temperature environments, is not well understood and is currently limiting its effective utilization in these scenarios. The main goal of this review is to provide the detailed insight needed for widespread acceptance of this technique as a post-processing method for AM materials.

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