Key Engineering Materials Vol. 662

Abstract: Bonding has experienced an enormous expansion in the various applications during the last few years in the field of material joining, due to which it is classified as a new joining technology, although it is, in fact, very old. Compared with the conventional joining methods (riveting, screwing and welding), bonding provides a new material combination possibilities and it allows us to obtain special shapes and properties, which can not be formed by conventional methods. To create a high-quality bonded joint, it is important to wet the bonded surface very well wetted by a wetting liquid. The wettability of the material is characterized by a contact angle of wetting, by which the surface energy is subsequently determined. For a high quality of the joint, the bonded material must have higher surface energy than the witting liquid (adhesive) [1-3]. This paper describes the effect of plasma surface treatment on the surface properties (surface energy, microhardness) of low-density polyethylene (LDPE) and high-density polyethylene (HDPE), and also on the final strength of bonded joints. The measured results indicate, that plasma surface treatment is very effective tool for improvement of surface properties and strength of bonded joints of HDPE and LDPE. The strength of bonded joints after plasma surface treatment was increased up to 350 % compared to untreated material. A similar trend was observed even for surface energy and microhardness of materials.

Abstract: Mechanical properties of two stainless steels (AISI 316L and AISI 410) processed by spark plasma sintering (SPS) were evaluated by four different types of indentation-based tests: hardness mapping, evaluation of indentation stress-strain curves, instrumented indentation and bonded-interface technique. Obtained results showed that the used combination of relatively simple experiments may provide a deeper understanding of mechanical behavior of materials prepared by SPS.

Abstract: The contribution is devoted to investigation of the fracture process zone (FPZ) in a fine-grained cement-based composite made from hydrated Portland cement. Particularly, experimental investigations and description of the stable crack propagation using fracture mechanics model are conducted. Three-point bending tests on small composite beams with a central edge notch were performed. The damage due to fracture was monitored by means of nanoindentation performed around the macroscopically observable crack. Acoustic emission events were recorded during the three-point bending test and correlated with load–displacement data. The beneficial effect on the fracture resistance of fine-grained mortar specimens compared to plain cement pastes was quantified.

Abstract: The state-of-the-art nano-diffraction technique available at the P06 beamline of the synchrotron radiation source PETRA III was used to observe the strain distribution induced within bulk metallic glass by nano-indentation. Bulk metallic glass (BMG) with nominal composition Zr_52.5Ti₅Cu_17.9Ni_14.6Al₁₀ at.% was prepared by conventional copper mold injection casting. Using the Berkovich indenter a series of indents forming a line was introduced on to the polished surface of the BMG sample. It has been shown that spatially resolved matrix scans with a nanometer sized beam (600 × 600 nm²) can identify positions of the indents and quantitatively describe the strain state after nano-indentation.

Abstract: The influence of microstructural variations on the tribological properties and nanohardness of liquid phase sintered silicon carbide (LPS SiC) has been observed. In order to modify the microstructures samples were further heat treated at 1650°C and 1850°C for 5 hours to promote grain growth. The depth-sensing indentation tests of SiC materials were performed at several peak loads in the range 10-400 mN. The pin-on-flat dry sliding friction and wear experiments have been made on SiC ceramics in contact with Al₂O₃ ceramic ball at 10-50 N loads in an ambient environment. The nanohardness of samples with plate-like microstructure was about 34 GPa i.e. 3 GPa higher than nanohardness of SiC with fine globular microstructure. The SiC materials with coarser plate-like microstructure had similar COF (0.4-0.55) and better wear resistance (one order of magnitude at normal forces 10-20N) than SiC materials with fine globular microstructure.

Abstract: 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.

Abstract: The Paper Shows Results of the Finite Element Modelling of Contact of a Rigid Spherical Body (indenter) with a Body from Elastic-Plastic Material. both the Proces of Loading and Unloading are Modelled. in Addition to Stresses, Also Energies are Investigated, Including their Distribution in the Plastically Deformed Core and the Elastically Deformed Outer Region. Attention is Devoted to Residual Stresses and Energies as well. Influence of Various Factors is Investigated, such as Various Values of Strain-Hardening Parameters (e.g. in Johnson-Cook Model), Relative Depth of Penetration (h/R), Coefficient of Friction.

Abstract: Plastic zone around a fatigue crack in AISI 304 stainless steel was studied experimentally using nanoindentation and numerically by the finite element analysis. Results obtained from one experimental observation of crack propagating under constant amplitude loading showed that nanohardness can be correlated to strain hardening caused by the cyclic deformation in the vicinity of the crack. However, for the material chosen for this study, exact plastic zone shape is hard to evaluate due to the scattering of experimental results.

Abstract: The aim of the paper is to present developed methodology for evaluation of mechanical properties using nondestructive (NDT) methods. The final methodology will focus on evaluating the mechanical properties of the heterogeneous weld structure. The mechanical properties are determined by conducting NDT instrumented Vickers hardness test. The developed methodology for the basic mechanical properties determining is based on the inverse FEM modeling of instrumented hardness test and the indentation curve and the measured surface imprint are the output of indentation. The outputs from the experimental hardness test (the corresponding values from indentation curve and measured surface) are not always corresponding. These differences affect the accuracy of the developed methodology, because it is achieved of the basic material mechanical properties by comparing the outputs of the experimental instrumented hardness test and modeled hardness test using FEM.

Abstract: Using stiff particles mixed into polymer matrix may significantly improve global mechanical response of the composite. Unfortunately, this process leads to other side effects, for example, presence of stress concentration at the particle-matrix interface or negative influence on the fracture toughness. The paper presents an approach to estimate the influence of particles on the micro-crack propagation. Material properties of matrix and particles were estimated experimentally. A two-dimensional computational model was proposed and all calculations were done in software ANSYS. On the base of linear elastic fracture mechanics, the influence of the particle shape on the micro-crack propagation paths was analyzed via numerical studies. The results of numerical simulations show that the shape of the particles can significantly influence the micro-crack path as well as the stress intensity factor on the crack tip, which corresponds to fracture toughness of polymer composite filled with rigid particles. The conclusions of this paper could contribute to better understanding of the behavior of the polymer composites.