Using the dynamic mechanical analysis (DMA) method with the application of a harmonic oscillating load, the elastic modulus E' , loss modulus E ", and loss tangent tgδ in the microstructure of beech wood ( Fagus orientalis ) were determined. It was found that in the range of 0.01-66.66 Hz, no frequency dependence of all three studied characteristics was observed within the accuracy of the experiment. At the same time, the dependence of the elastic modulus E' on the static stress was established.

Using a small oscillating load (continuous stiffness measurement, CSM), in addition to the main quasi-static load, we determine the hardness, Young’s modulus, storage and loss moduli, mechanical loss coefficient ( tanδ ), and the plasticity characteristics in various components of the nanostructure and microstructure of pine (Pinus sylvestris) and spruce (Picea abies) wood. The contribution of structures of different scales to the ratio of the viscoelastic properties of early and late wood in the composition of one annual ring is determined. The plasticity characteristic δА is determined, and the influence of an additional oscillating load on the dynamic parameters of wood is assessed.

Wood as a material is a natural composite with a complex hierarchically arranged structure. All scale levels of wood structure contribute to its macroscopic mechanical properties. The nature of such characteristics and deformation modes differs radically at different scale levels. Wood macroscopic properties are well studied, and the relevant information can be easily found in the literature. However, the knowledge of the deformation mechanisms at the mesoscopic level corresponding to the cellular structure of early and late wood layers of annual growth rings is insufficient. It hinders building the comprehensive multiscale model of how wood mechanical properties are formed. This paper described the results of scanning of mechanical properties of softwood and hardwood samples, such as common pine, small-leaf lime, and pedunculate oak, by means of nanoindentation (NI). The NI technique allows varying the size of deformed region within a wide range by altering maximal load (Pmax) applied to the indenter so that one can repeatedly and non-destructively test wood structural components at different scale levels on the same sample without changing the technique or equipment. It was discovered that the effective microhardness (Heff) and Young's modulus (Eeff) decreased manifold with Pmax growing from 0.2 to 2 000 mN. This drop in Heff was observed when the locally deformed region grew, and resulting from Pmax increase generally follows the rule similar to the Hall-Petch relation for yield stress, strength, and hardness initially established for metals and alloys, though obviously in those cases the underlying internal mechanisms are quite different. The nature and micromechanisms of such size effect (SE) in wood revealed using NI were discussed in this study. At Pmax < 0.2 mN, the deformed area under the pyramidal Berckovich indenter was much smaller than the cell wall width. Hence, in this case, NI measured the internal mechanical properties of the cell wall material as long as free boundaries impact could be neglected. At Pmax > 200 mN, the indentation encompassed several cells. The measured mechanical properties were significantly affected by bending deformation and buckling collapse of cell walls, reducing Heff and Eeff substantially. At Pmax ≈ 1–100 mN, an indenter interacted with different elements of the cell structure and capillary network, resulting in intermediate values of Heff and Eeff. Abrupt changes in Heff and Eeff at annual growth ring boundaries allow accurate measuring of rings width, while smoother and less pronounced changes within the rings allow identification of earlywood and latewood layers as well as any finer changes during vegetation season. The values of ring width measured using NI and standard optical method coincide with 2%−3% accuracy. The approaches and results presented in this study could improve the understanding of nature and mechanisms lying behind the micromechanical properties of wood, help to optimize the technologies of wood farming, subsequent reinforcement, and utilization, as well as to develop new highly informative techniques in dendrochronology and dendroclimatology.

Zirconia nanofiber mats containing filaments with the average diameter of less than 100 nm were fabricated. It is found that the hardness and Young’s modulus of the mats are sensitive to the microstructure, phase composition and average diameter of the zirconia nanofibers. The hardness and Young’s modulus of the prepared zirconia nanofiber mats vary from 0.86 to 1.67 MPa and from 133 to 362 MPa, respectively, wherein an increase in hardness is accompanied by the rise in Young’s modulus.

Wet high-energy milling and uniaxial pressing are used to fabricate CaO-stabilized tetragonal zirconia polycrystalline ceramic (Ca-TZP) with decent mechanical characteristics, i.e., a hardness of 11.5 GPa, Young’s modulus of 230 GPa, and fracture toughness of 13 MPa·m0.5. The effect of CaO concentration and the sintering temperature on phase composition and mechanical characteristics of CaO-stabilized zirconia ceramic made of baddeleyite is investigated.

The mats of yttria-stabilized tetragonal zirconia nanofibers were prepared using electrospinning. The effect of calcination temperature in the range of 600–1200 °C on their microstructure, phase composition and mechanical properties was investigated. Phase composition of the nanofibers did not change in all ranges of the calcination temperatures, while the average grain size increased from 8 to 39 nm. Nanoindentation testing of the mats showed a decrease in the hysteresis loop energy in samples with higher calcination temperature. Hardness and the elastic modulus measured with the indentation technique were the highest for the mats calcined at 900 °C.

Изучено влияние водяных паров на структурную устойчивость и механические свойства керамик на основе бадделеита (природного минерала диоксида циркония) и химически осажденного ZrO2, армированных углеродными нанотрубками. Показано, что эти композиты обладают высокими физико-механическими свойствами и повышенной устойчивостью к старению в гидротермальных условиях. Полученные в работе композиты на основе бадделеита и стабилизированные СаО характеризуются скоростью старения более чем на порядок меньшей, чем в случае коммерческих керамик, стабилизированных Y2 О3. Введение углеродных нанотрубок в состав композитов и использование метода искрового плазменного спекания способствуют ингибированию роста размеров зерна, уменьшению масштабного эффекта в твердости, при этом трещиностойкость KC в гидротермальных условиях уменьшается слабее, чем в композитах, не содержащих нанотрубок.

The influence of water vapor on structural stability and mechanical properties of ceramics based on baddeleite (natural zirconia mineral) and chemically deposited ZrO2 reinforced with carbon nanotubes is studied in this work. These composites are shown to possess high physical and mechanical properties and elevated hydrothermal aging resistance. Composites based on baddeleite and stabilized СаО are characterized via ageing rate of an order of magnitude lower than in the case of commercial ceramics stabilized with Y2О3. The embedding of carbon nanotubes in the composites and the use of spark plasma sintering inhibits the grain growth and amplifies the scale effect in hardness. With that, crack resistance KC under hydrothermal conditions decreases to a lesser extent than in nanotube-free composites.

Abstract The paper describes the technology for producing silver electrochemical coatings containing multi-walled carbon nanotubes (MWCNTs). The MWCNT effect on the roughness, structure and tribological properties of silver coatings obtained with the addition of the nanotubes to an electrolyte in the low concentration range (0 to 80 mg/L). An increase in the microhardness and a decrease in the coefficient of friction were found for the modified coatings at the MWCNTs concentrations in the electrolyte of 40 and 60 mg/L, respectively.

The spherification method was adapted to macroporous tetragonal polycrystalline zirconia ceramic fabrication from baddeleyite. Dependences of the material microstructure, its porosity, phase composition and mechanical properties on the sintering temperature were investigated. The opportunity for controlling the porosity and mechanical properties of produced spherical macroporous zirconia ceramic via the sintering temperature variation was revealed. Beads sintered at 1100 °С are characterized by the optimal combination of porosity, hardness, Young’s modulus and breaking force.

The spherification method was adapted to baddeleyite-based ceramics fabrication. Novel calcia stabilized tetragonal zirconia (Ca-TZP) ceramics with sufficiently high values of hardness (11.73 +/- 0.12 GPa), fracture toughness (9.15 +/- 0.24 MPa m(0.5)) and Young's modulus (217 +/- 14 GPa) was produced. Dependences of the material microstructure, its phase composition and mechanical properties on sintering temperature and the doping agent concentration were investigated. Fabricated spherical Ca-TZP ceramics made from baddeleyite may be considered as perspective engineering ceramics, for example, for milling processes as an alternative to grinding media made of chemically precipitated zirconia.

The influence of porosity on the mechanical properties of zirconia ceramics in dynamic nanocontact is studied by the Oliver–Pharr method and continuous stiffness measurement. Oscillations with an amplitude up to 8 nm are found not to affect the harmonic stiffness of poreless ceramic. However, the presence of pores causes a dependence of the Oliver–Pharr hardness, elastic modulus, harmonic stiffness, and strength on the porosity and the indentation depth. Oscillations with an amplitude of 2 nm or larger lead to the softening of porous ceramic. In contrast to dense and low-porosity ceramics, the stiffness and the hardness of ceramic with 38% porosity increase during the penetration of an indenter rather than decreasing.

The relationship between synthesis conditions, structure, and properties of the baddeleyite-based engineering nanostructured composite zirconia ceramic (natural zirconia mineral) with modifying alloying elements is studied. The elaborated composites possess high physical and mechanical properties at a level that is not only not inferior, but even superior to those of analogous ceramics prepared from precipitated zirconia (e.g., density is 0.95 of the theoretical value, the hardness reaches 12 GPa, the Young modulus is 220 ± 15 GPa, and the fracture toughness reaches 9 MPa m 0.5 ). The embedding of carbon nanotubes (CNTs) is shown to alter the physical and mechanical properties of ceramics: the hardness is somewhat reduced, but fracture toughness K C gains more than 10%.

The effect low-amplitude oscillations have on the mechanical properties of Al and W in nanocontacts is studied by means of continuous stiffness measurements (CSM). It is established that the additional superpositioning of oscillations until a critical amplitude is reached has no effect on the mechanisms, kinetics, or plastic deformation of a material. The threshold amplitudes and frequencies of such oscillations are determined for Al (2.5 nm) and W (3.5 nm).

A continuous stiffness measurement method allowing one to obtain physical-mechamical characteristics of materials in the process of indentation during gradually increasing loading has been scrutinized. The limits of applicability of this approach depend on the testing conditions at which the additional smallamplitude oscillations exert no influence on the mechanics, kinetics, and plastic strain of material being in contact with the indenter. As is shown by taking as examples specimens with amorphous structure, and fcc and bcc lattices, various techniques for determining the nanocontact characteristics of materials are different by their sensitivity to small-amplitude load oscillations. The oscillation amplitudes and the indentation depth ranges where one can neglect the oscillation effects have been evaluated. The impacts of the oscillations on the behavior of the contact (local) characteristics of the studied materials in supercritical modes have been established.