Vlastimil Králík

Mechanical Properties of Single and Double-Layered PVA Nanofibers

Multi-layered nanofiber textiles can be utilized in many applications. In such case the individual layers are laid in more stages and the question arises whether the connection is perfect. Two kinds of samples of PVA nanotextiles having the weight of 1.3 g/m2 (single-layered, AI) and 2.8 g/m2 (double-layered, AII), respectively. It was shown that mechanical properties, in particular the average tensile strength (24 N/mm for AI and 51 N/mm for AII) and stiffness (950 N/mm for AI and 1600 N/mm for AII), are independent of the number of layers, only their weight per unit area matters. This indicates that the bond between the individual layers is perfect.

Local Mechanical Characterization of Metal Foams by Nanoindentation

This paper deals with microstructure and micromechanical properties of two commercially available aluminium foams (Alporas and Aluhab). Since none of the materials is available in a bulk and standard mechanical testing at macro-scale is not possible the materials need to be tested at micro-scale. To obtain both elastic and plastic properties quasi-static indentation was performed with two different indenter geometries (Berkovich and spherical tips). The material phase properties were analyzed with statistical grid indentation method and micromechanical homogenization was applied to obtain effective elastic wall properties. In addition, effective inelastic properties of cell walls were identified with spherical indentation. Constitutive parameters related to elasto-plastic material with linear isotropic hardening (the yield point and tangent modulus) were directly deduced from the load–depth curves of spherical indentation tests using formulations of the representative strain and stress introduced by Tabor.

MICROSTRUCTURE DESCRIPTION AND MICROMECHANICAL PROPERTIES OF SPRUCE WOOD

The knowledge about the microstructure and morphology of individual phases also allows an artificial modification of the material, or its processing, to produce engineered products with required properties. The purpose of our work was to investigate the distribution of elastic stiffness within the tissues of individual cells using the finest equipment and to observe the morphology of individual phases. A quasi-static nanoindentation was carried out on the cell walls of earlywood and latewood tracheids of spruce wood. The dynamic modulus mapping, also known as nanoDMA, was utilized to obtain the map of elastic moduli over the entire tracheid cross-section. In particular, it was found that the stiffness cells walls is approximately 10.5 GPa and 12.5 GPa in the case of earlywood and latewood tracheids, respectively. The difference between earlywood and latewood elastic stiffness is attributed to a different chemical composition and orientation of fibrils. The acquired data are indispensible for micromechanical modeling and design of engineered products with superior mechanical properties.

Identification of Stress-Strain Relation of Aluminium Foam Cell Wall by Spherical Nanoindentation

The aim of this paper is to identify, in addition to elastic properties, inelastic properties of tiny aluminium foam cell walls that can be directly deduced from the loaddepth curves of spherical indentation tests using formulations of the representative strain and stress. Constitutive parameters related to plastic material with linear isotropic hardening, the yield point (122 ± 17 MPa) and tangent modulus (950 ± 377 MPa), were obtained in this work. Spherical indentation and uniaxial tension experiments have also been performed on a standard aluminium alloy EN AW 6060 to explore the accuracy of the analytical models used to predict the uniaxial stressstrain in wide strain ranges. Some deviations received from different tests arose and, therefore, their effect on the evaluation of inelastic properties was discussed.

Comparison of Modulus of Elasticity of Glued Laminated Timber

This article focuses on testing of glued laminated timber beams and researching their properties. The article mainly focuses on comparison of measured modulus of elasticity obtained by two different methods. First method used was method of spike which has non-destructive character. This method was used to measure properties of glued laminated timber (GLT) on macro mechanical level in form of modulus of elasticity. Second method was used to determine micromechanical properties of material and is called nanoindentation. Tested material will be also described the article along with principle of testing and presenting results. Those results of individual measurements will be compared with respect to percentage representation of individual phases on micromechanical levels to measurement on macromechanical level.

Composite Middle Lamella Hardness and Young’s Modulus of Artificial Dried Spruce Wood by Nanoindentation

The presented article deals with the influence of the drying process on the micro-mechanical properties of the composite middle lamella. The purpose of the composite middle lamella is to connecti individual cells. Micromechanical properties were obtained using nanoindentation and directly continuous stiffness measurement technique. Indentation modulus of tested samples was 11.45 GPa for natural dried wood and 12.51 GPa for artificial dried wood.

Definition of Effective Material Properties of Recycled Plastic: Image Analysis and Homogenization

The influence of foaming agent on the properties of steel-reinforced beams made of recycled plastic material is studied in the paper. The foaming agent creates a porous core in the recycled plastic elements. This core must be reflected when deriving the beam effective properties to be used in macroscopic simulations. To that end, standard image analysis combined with nanoindentation and the Mori-Tanaka micromechanical model is adopted to identify elastic material properties of the plastic material both inside and outside of the core. These are expected to enter an independent macroscopic analysis of the steel-reinforced beams.

Testing of Energy Absorption Capability of Sandwich Structures Based on Metal Foams for Design of Protective Helmets

Purpose of this study is investigation of energy absorption capability of the sandwich structures composed of combination of polystyrene and metal foam element and their suitability as new structure for design of protective helmets. Two types of the metal foams were experimentally tested and evaluated: Alporas (Shinko Wire Ltd., Japan) and Aluhab (Aluinvent Plc., Hungary). Samples of the sandwich structure are composed of two layers: bottom expanded polystyrene (EPS 200S) layer and upper metal foam layer which are glued together. Prepared samples are tested using a drop tower experiment to measure sample response (acceleration, reaction force) at different strain rates and energies. From acceleration/time history the Head Injury Criterion (HIC) is calculated as significant parameters in terms of protective helmets. Moreover, measured and derived characteristics are compared with pure EPS samples to obtain comparison of deformation behaviour between conventional structure for protective helmets and designed sandwich structures.

Comparison of Micromechanical Parameters of Different Dental Implants Using Nanoindentation

The aim of this work is the description of microstructure and comparison of micromechanical properties of cylindrical shaped intraosseous parts of dental implants with plasma modified surface and with threaded modification. Differences in elastic parameters (such as reduced modulus (Er) and hardness (H)) of investigated implants within the supporting part of the shaft and surface layer in two different directions (proximal and lateral) are compared using experimental method of nanoindentation. Machined implants of titanium alloys Ti6Al4V with plasma modified surface of sprayed titanium with hydroxyapatit (HA) Ca10(PO4)6(OH)2 from different batches of product were available for measurements. SEM element analysis revealed a heterogeneous structure and various concentrations of the essential chemical elements (C, O, P, Ca) on the surface of implants. Results of elastic moduli and hardness was monitored in different locations. On a large statistical set of measurements was indicated that average reduced modulus of implant shafts of titanium alloy is approximately 126 GPa. Differences of Er in case of peripheral hydroxyapatite layer are in range of ~145 GPa – ~163 GPa according to the exact composition of surface modification in the individual batches of the product. The difference of measured values on individual samples in a proximal/lateral direction is approximately 10%.

Micromechanical Properties of Spruce Tissues Using Static Nanoindentation and Modulus Mapping

This paper discusses characterization of physical and mechanical properties of tissues of Norway spruce. Cell wall is composed of several layers, which is, due to their small size, difficult to characterize. For this reason, the work uses a combination of methods, atomic force microscopy (AFM) and nanoindentation. AFM is used to determine the topography of samples and nanoindentation to determine micromechanical properties of wood tissues. Prepared samples of glue laminated timber were tested by quasi-static and dynamic nanoindentation (modulus mapping technique) method.