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Relations between Structure, Micro- and Nanomechanical Properties of Materials

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Mechanics of Materials".

Deadline for manuscript submissions: closed (20 December 2022) | Viewed by 8575

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Prof. Dr. Miroslav Slouf

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Institute of Macromolecular Chemistry, Czech Academy of Sciences, Heyrovskeho nam. 2, CZ-162 06 Praha, Czech Republic
Interests: polymer morphology; electron microscopy; micromechanical properties; UHMWPE for total joint replacements; biocompatible and/or biodegradable polymers

Prof. Dr. František Lofaj

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Institute of Materials Research Slovak Academy of Sciences, Kosice, Slovakia
Interests: PVD deposition technologies for hard coatings; nanoindentation and tribology of PVD coatings; relationship microstructure- mechanical properties of bulk ceramic materials and coatings; fractography of brittle materials high temperature mechanical properties of bulk ceramics; creep of silicon nitride and other structural ceramics properties and structure of the oxynitride glasses; corrosion of glasses for the devitrification of nuclear waste electron microscopy of ceramic materials; atomic force microscopy; development of the methods for testing mechanical properties of brittle materials

Special Issue Information

Dear Colleagues,

The Special Issue on “Relations between structure, micro- and nanomechanical properties of materials” should bring together scientists working at universities, research institutes, and industry to summarize, describe and discuss state-of-the-art research in the field of micro- and nanomechanical characterization of materials.

In the current research, all types of materials starting from metals and alloys, through ceramics and rocks, to polymers and soft materials are characterized in multiple length scales. Nevertheless, the correlations among structure, macroscopic mechanical properties, and local mechanical properties measured in micro- or nanoscale are still not fully elucidated. The dominating methods for characterization of local mechanical properties are microindentation and nanoindentation, but other methods such as scanning probe microscopy or micro-tensile testing are employed as well. Recent development in the field enabled to characterize very soft materials (such as polymers or hydrogels) or perform fast and precise local properties mapping with micrometer resolution.

This Special Issue accepts both research articles and reviews discussing all aspects of relations between structure and mechanical properties of materials that are measured in micro- or nanoscale. Contributions discussing relations between macroscale properties and local properties are welcome as well.

Prof. Dr. Miroslav Slouf
Prof. Dr. František Lofaj
Guest Editors

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Keywords

micromechanical properties
nanomechanical properties
microindentation
nanoindentation
local mechanical properties
structure-properties relations

Published Papers (5 papers)

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Research

26 pages, 10944 KiB

Open AccessArticle

Morphology, Micromechanical, and Macromechanical Properties of Novel Waterborne Poly(urethane-urea)/Silica Nanocomposites

by Veronika Gajdošová, Milena Špírková, Yareni Aguilar Costumbre, Sabina Krejčíková, Beata Strachota, Miroslav Šlouf and Adam Strachota

Materials 2023, 16(5), 1767; https://doi.org/10.3390/ma16051767 - 21 Feb 2023

Cited by 1 | Viewed by 1471

Abstract

Morphology, macro-, and micromechanical properties of novel poly(urethane-urea)/silica nanocomposites were analyzed by electron microscopy, dynamic mechanical thermal analysis, and microindentation. The studied nanocomposites were based on a poly(urethane-urea) (PUU) matrix filled by nanosilica, and were prepared from waterborne dispersions of PUU (latex) and SiO₂. The loading of nano-SiO₂ was varied between 0 (neat matrix) and 40 wt% in the dry nanocomposite. The prepared materials were all formally in the rubbery state at room temperature, but they displayed complex elastoviscoplastic behavior, spanning from stiffer elastomeric type to semi-glassy. Because of the employed rigid and highly uniform spherical nanofiller, the materials are of great interest for model microindentation studies. Additionally, because of the polycarbonate-type elastic chains of the PUU matrix, hydrogen bonding in the studied nanocomposites was expected to be rich and diverse, ranging from very strong to weak. In micro- and macromechanical tests, all the elasticity-related properties correlated very strongly. The relations among the properties that related to energy dissipation were complex, and were highly affected by the existence of hydrogen bonding of broadly varied strength, by the distribution patterns of the fine nanofiller, as well as by the eventual locally endured larger deformations during the tests, and the tendency of the materials to cold flow. Full article

(This article belongs to the Special Issue Relations between Structure, Micro- and Nanomechanical Properties of Materials)

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26 pages, 4853 KiB

Open AccessFeature PaperArticle

Correlations between Microscale Indentation Creep and Macroscale Tensile Creep of Polymers

by Miroslav Slouf, Milos Steinhart, Pavel Nemecek, Veronika Gajdosova and Jiri Hodan

Materials 2023, 16(2), 834; https://doi.org/10.3390/ma16020834 - 15 Jan 2023

Cited by 3 | Viewed by 1195

Abstract

We compared the results of various microscale indentation creep (microcreep) measurements with macroscale tensile creep (macrocreep) measurements of three common polymers: high-density polyethylene (PE), polypropylene (PP), and polystyrene (PS). The main objective was to verify if the short-term microcreep experiments could predict long-term macrocreep behavior of the selected polymers, whose properties ranged from very soft and ductile (PE) to very hard and brittle (PS). The second objective was to compare several creep predictive schemes: the empirical power law model (PL) and several types of phenomenological elasto-visco-plastic models (EVP). In order to facilitate this task, we developed a universal program package named MCREEP, which fits PL and EVP models to both tensile and indentation creep data. All experimental results and theoretical predictions documented that: (i) regardless of the creep experiment type, both micro- and macrocreep resistance increased in the following order: PE < PP < PS, (ii) the short-term microcreep experiments could be used to predict qualitatively the long-term macrocreep behavior, and (iii) the simple empirical power law model yielded better predictions of long-term creep behavior than the more sophisticated elasto-visco-plastic models. Full article

(This article belongs to the Special Issue Relations between Structure, Micro- and Nanomechanical Properties of Materials)

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27 pages, 7660 KiB

Open AccessArticle

Reactive HiTUS TiNbVTaZrHf-N_x Coatings: Structure, Composition and Mechanical Properties

by František Lofaj, Lenka Kvetková, Tomáš Roch, Jozef Dobrovodský, Vladimír Girman, Margita Kabátová and Matúš Beňo

Materials 2023, 16(2), 563; https://doi.org/10.3390/ma16020563 - 6 Jan 2023

Cited by 5 | Viewed by 1424

Abstract

High entropy metal sub-lattice stabilized nitride coatings based on multicomponent refractory transition metals (TM = Ti, Nb, V, Ta, Zr, Hf) are promising candidates for extreme conditions due to their high thermal, mechanical, and corrosion properties. The aims of the current work included the investigations of the possibilities of the novel High Target Utilization Sputtering (HiTUS) technique applied to reactive sputtering of TiNbVTaZrHf–xN coatings from the viewpoints of hysteresis behavior during reactive sputtering as well as the structure, composition, stoichiometry, and mechanical properties of the resulting coatings. With increasing nitrogen content, coating structures varied from amorphous in metallic alloy coatings to textured nano-columnar fcc structures. Despite certain deviations of TM from equiatomic concentrations, homogeneous solid solutions corresponding to single-phase multicomponent nitride analogous to high entropy stabilized compounds were obtained. Mechanical properties were found to be proportional to nitrogen content. The highest hardness H_IT ~ 33 GPa and indentation modulus E_IT ~ 400 GPa were found in a slightly sub-stoichiometric (~42 at% nitrogen) composition. H_IT/E_IT and limited pillar split measurements suggested that these coatings exhibit low fracture toughness (around 1 MPa.m^1/2). The work confirmed that reactive HiTUS is suitable for the preparation of multicomponent nitrides with the control of their stoichiometry and mechanical properties only via nitrogen additions. Full article

(This article belongs to the Special Issue Relations between Structure, Micro- and Nanomechanical Properties of Materials)

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17 pages, 7457 KiB

Open AccessArticle

Numerical Simulation of Failure Behavior of Brittle Heterogeneous Rock under Uniaxial Compression Test

by Jia Liu, Fengshan Ma, Jie Guo, Tongtong Zhou, Yewei Song and Fangrui Li

Materials 2022, 15(19), 7035; https://doi.org/10.3390/ma15197035 - 10 Oct 2022

Cited by 5 | Viewed by 1465

Abstract

Rocks have formed heterogeneous characteristics after experiencing complex natural geological processes. Studying the heterogeneity of rocks is significant for rock mechanics. In this study, a linear parallel bond model with Weibull distribution in two-dimensional particle flow code (PFC2D) is adopted to study the mechanical characteristics and brittle failure mode of granite rock specimens with different heterogeneity. Firstly, we selected several combinations of key micro-parameters of the parallel bond model. Then, we subjected them to a Weibull distribution to satisfy heterogeneity, respectively. Finally, we chose one optimal combination plan after comparing the stress–strain curves of heterogeneous rock specimens. We analyzed the simulated results of heterogeneous rock specimens. The crack distribution of rock specimens under peak stress shows different characteristics: a diagonal shape in rock specimens with low heterogeneity indexes, or a rotated “y” shape in rock specimens with high heterogeneity indexes. As for failure mode, the numerical simulation results show high consistency with the laboratory experiment results. The rock specimen breaks down almost diagonally, and the whole specimen tends to form an x-shaped conjugate shear failure or the well-known “hour-glass” failure mode. With the increase of the homogeneity index of the rock specimen, the shear rupture angle becomes larger and larger. Generally, the crack number increases with time, and when the rock specimen reaches the peak failure point, the number of cracks increases sharply. The development of cracks in numerical rock specimens under compression test is a result of the coalescence of many microscopic cracks. Furthermore, tensile cracks formed initially, followed by shear behavior along the macroscopic crack plane. We also preliminarily study the mechanical characteristics of heterogeneous rock specimens with discontinuous structural planes. The discontinuous structural planes are simulated by the smooth-joint model. We can conclude that the discontinuous structural planes and the microscopic structural planes which contribute to the heterogeneity have a mutual influence on each other. Full article

(This article belongs to the Special Issue Relations between Structure, Micro- and Nanomechanical Properties of Materials)

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22 pages, 9161 KiB

Open AccessEditor’s ChoiceArticle

Biodegradable Thermoplastic Starch/Polycaprolactone Blends with Co-Continuous Morphology Suitable for Local Release of Antibiotics

by Veronika Gajdosova, Beata Strachota, Adam Strachota, Danuse Michalkova, Sabina Krejcikova, Petr Fulin, Otakar Nyc, Adam Brinek, Marek Zemek and Miroslav Slouf

Materials 2022, 15(3), 1101; https://doi.org/10.3390/ma15031101 - 30 Jan 2022

Cited by 8 | Viewed by 2450

Abstract

We report a reproducible preparation and characterization of highly homogeneous thermoplastic starch/pol(ε-caprolactone) blends (TPS/PCL) with a minimal thermomechanical degradation and co-continuous morphology. These materials would be suitable for biomedical applications, specifically for the local release of antibiotics (ATB) from the TPS phase. The TPS/PCL blends were prepared in the whole concentration range. In agreement with theoretical predictions based on component viscosities, the co-continuous morphology was found for TPS/PCL blends with a composition of 70/30 wt.%. The minimal thermomechanical degradation of the blends was achieved by an optimization of the processing conditions and by keeping processing temperatures as low as possible, because higher temperatures might damage ATB in the final application. The blends’ homogeneity was verified by scanning electron microscopy. The co-continuous morphology was confirmed by submicron-computed tomography. The mechanical performance of the blends was characterized in both microscale (by an instrumented microindentation hardness testing; MHI) and macroscale (by dynamic thermomechanical analysis; DMTA). The elastic moduli of TPS increased ca four times in the TPS/PCL (70/30) blend. The correlations between elastic moduli measured by MHI and DMTA were very strong, which implied that, in the future studies, it would be possible to use just micromechanical testing that does not require large specimens. Full article

(This article belongs to the Special Issue Relations between Structure, Micro- and Nanomechanical Properties of Materials)

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