The influence of pore size on the indentation behavior of metallic nanoporous materials : a molecular dynamics study

In general, the influence of pore size is not considered when determining the Young's modulus of nanoporous materials. Here, we demonstrate that the pore size needs to be taken into account to properly assess the mechanical properties of these materials. Molecular Dynamics simulations of spherical indentation experiments on single crystalline nanoporous Cu have been undertaken in systems with: (i) a constant degree of porosity and variable pore diameter; and (ii) a constant pore diameter and variable porosity degree. The classical Gibson and Ashby expression relating Young's modulus with the relative density of the nanoporous metal is modified to include the influence of the pore size. The simulations reveal that, for a fixed porosity degree, the mechanical behavior of materials with smaller pores differs more significantly from the behavior of the bulk, fully dense counterpart. This effect is ascribed to the increase of the overall surface area as the pore size is reduced, together with the reduced coordination number of the atoms located at the pores edges

Nanomechanical behavior of 3D porous metal–ceramic nanocomposite Bi/Bi2O3 films

The nanomechanical properties of three-dimensional (3D) porous metal/metal oxide composite (Bi/Bi2O3) films grown by direct current electrodeposition have been studied by nanoindentation at two different loading rates. The synthesized films exhibit a mixture of crystallographic phases of metallic Bi and α-Bi2O3, as evidenced by X-ray diffraction. An in-situ compaction of the sample during the nanoindentation assays has been observed. This in-situ compaction has an influence over both the hardness and elastic modulus of the material, being more important on the latter and, therefore, on the determination of the degree of porosity of the composite film. The influence of the loading rate on the mechanical properties has been investigated. In addition, time-dependent deformation processes (creep tests) have been also performed, revealing an anelastic behavior irrespective of the loading rate. From these creep tests, a viscoelastic non-Newtonian behavior of the sample is evidenced, which is well-described by a three-element Voigt model

Mechanical behavior of Cu/TiN multilayers at ambient and elevated temperatures: Stress-assisted diffusion of Cu

The deformation and failure mechanism of a multilayered thin film consisting of alternating soft Cu and hard TiN interlayers has been studied by in situ SEM compression of micro-pillars and finite element simulations. While the yielding of the multilayer is governed by the 'size-dependent' strength of Cu, the failure was found to occur by shearing of the columnar grains of TiN. At elevated temperatures of 200 and 400. °C, the yielding of the multilayers is governed by the stress-assisted diffusion of the Cu interlayers, which coalesce into microcrystals and grow into larger faceted crystals

Back-stresses and geometrical hardening as competing mechanisms enhancing ductility in HCP metals

Inside the folder "Textures" researchers can find the sets of orientations obtained through EBSD for the three HCP materials studied in the publication "Back-stresses and geometrical hardening as competing mechanisms enhancing ductility in HCP metals" The Origin file data_for_curves.opj contains the data coming from VPSC and CPFEM simulations of uniaxial tensile tests on the aforementioned HCP metals

Understanding the mechanical behaviour of fiber/matrix interfaces during push-in tests by means of finite element simulations and a cohesive zone model

The present work represents a progress towards the understanding of the mechanical behavior of the fiber/matrix interface during push-in tests of fiber-reinforced polymer-matrix composites. Finite element simulations incorporating a cohesive zone model are used for this purpose. Different values of interface strength, interface fracture toughness, fiber diameter and friction coefficient are considered to study how they affect the load-displacement curves. A critical value of the displacement exists, being independent of the fiber diameter for given values of interface strength and fracture toughness, marking the separation between two regimes: (i) a cohesive-dominated zone interaction and (ii) a frictional contact between debonded fiber and matrix. Maps showing the different regimes are constructed, proving their helpfulness to tune the mechanical properties of the interface in order to favor a certain mechanical response. Finally, we study the debonding velocity and how this is affected by the mechanical properties of the interface providing an empirical relation

Reusable and long-lasting active micro-cleaners for heterogeneous water remediation

Self-powered micro-machines are promising tools for the future environmental remediation technology. Waste water treatment and water reuse is an essential part of environmental sustainability. Herein, we present reusable Fe/Pt multi-functional active micro-cleaners that are capable of degrading organic pollutants by generated hydroxyl radicals via Fenton-like reaction. Various different properties of micro-cleaners such as the effect of their size, short-term storage, long-term storage, reusability, continuous swimming capability, surface composition and mechanical properties are studied. We find that micro-cleaners can continuously swim for more than 24 hours and can be stored more than 5 weeks during multiple cleaning cycles. Micro-cleaners can also be reused, which reduces the cost of the process. Over the reuse cycles, the outer iron surface of the Fe/Pt micro-cleaners generates in-situ heterogeneous Fenton catalyst and releases a low concentration of iron into the treated water while the mechanical properties also appear to be improved due to both surface composition and structural changes. Results have been characterized by SEM, XPS, Nanoindentation and Finite Element Modeling (FEM)

Nanomechanical behavior of 3D porous metal-ceramic nanocomposite Bi/Bi2 O3 films

The nanomechanical properties of three-dimensional (3D) porous metal/metal oxide composite (Bi/Bi2O3) films grown by direct current electrodeposition have been studied by nanoindentation at two different loading rates. The synthesized films exhibit a mixture of crystallographic phases of metallic Bi and α-Bi2O3, as evidenced by X-ray diffraction. An in-situ compaction of the sample during the nanoindentation assays has been observed. This in-situ compaction has an influence over both the hardness and elastic modulus of the material, being more important on the latter and, therefore, on the determination of the degree of porosity of the composite film. The influence of the loading rate on the mechanical properties has been investigated. In addition, time-dependent deformation processes (creep tests) have been also performed, revealing an anelastic behavior irrespective of the loading rate. From these creep tests, a viscoelastic non-Newtonian behavior of the sample is evidenced, which is well-described by a three-element Voigt model