Vladimír Šleger

Green methanol, ethanol, and diesel-based hydrotreated vegetable oils are some of the renewable liquid fuels that show satisfactory performance in diesel engines. A notable advantage of these fuels is that they are renewable and do not require significant modifications in the existing engines for successful operation. Suitable fuel systems, especially their material compatibility, remain unresolved, and therefore, it is a weak link in their large-scale adaptation. Elastomer-based sealing O-rings lose their mechanical properties after a short exposure time to these fuels, adversely impacting their functionality. This research study evaluated the long-term material compatibility of different elastomer-based sealing materials by immersing the O-rings in these test fuels (hydrotreated vegetable oil, methanol, ethanol, and diesel) for different time intervals (i.e., up to 15 months). The material compatibility was assessed mainly by investigating these changes in various mechanical properties of these O-rings, namely tensile strength (ΔT_s), elongation at break (ΔE_b), Shore A hardness (ΔH), and mass (ΔM). The degradation of mechanical properties was studied and analyzed during the immersion interval from 0.9 to 15.2 months and compared with O-rings kept in a normal atmosphere. It was noted that individual fuels affect various mechanical properties significantly. In a short interval of 0.9 months (28 days), significant changes in the mechanical properties of the sealing O-rings were observed.

In this paper, the fatigue behavior of polylactic acid (PLA) material with bamboo filler printed by 3D additive printing using fused deposition modelling (FDM) technology at different infill densities and print nozzle diameters is investigated. The mechanical test results are supported by the findings from SEM image analysis. The fatigue behavior was tested at four consecutive 250 cycles at loads ranging from 5 to 20, 30, 40, and 50% based on the limits found in the static tensile test. The results of the static tensile and low-cycle fatigue tests confirmed significant effects of infill density of 60%, 80%, and 100% on the tensile strength of the tested specimens. In particular, the research results show a significant effect of infill density on the fatigue properties of the tested materials. The influence of cyclic tests resulted in the strengthening of the tested material, and at the same time, its viscoelastic behavior was manifested. SEM analysis of the fracture surface confirmed a good interaction between the PLA matrix and the bamboo-based filler using nozzle diameters of 0.4 and 0.6 mm and infill densities of 60%, 80%, and 100%. Low-cycle testing showed no reductions in the mechanical properties and fatigue lives of the 3D printed samples.

Significant attention has been paid to combustion engines for the utilization of new liquid fuels and their testing at the present. Research activities in ensuring the optimum function of the engine by watching sealing and distribution rubber elements, which are part of fuel systems, should be an integral part of fuels research. When evaluating fuels utilization in combustion engines, the issue has to be judged in a complex. However, when using biofuels in combustion engines, it is not always simple owing to the different degradation properties of these products. Elastomer material is not entirely resistant to various types of fuels. More or less, it is possible to expect changes in its mechanical properties. For the evaluation of the functionality of elastomer sealing elements based on ACM, HNBR and FVMQ type O-rings with pure and blended fuels, the evaluation of changes in mass, hardness Shore A, permanent deformation CS, tensile strength TS and deformation Eb after immersion with the tested fuel is mainly used. Permanent changes were found by the tests. The degradation of elastomer O-rings was more pronounced for the tested fuels containing ethanol, iso-butanol, n-butanol, methanol and dodecanol. HVO 100 fuel containing hydrotreated vegetable oil did not show significant degradation of elastomer O-ring seals. Of the O-rings tested, the FVMQ type O-rings showed the best performance in terms of material compatibility for all fuels tested.

Additive production is currently perceived as an advanced technology, where intensive research is carried out in two basic directions—modifications of existing printing materials and the evaluation of mechanical properties depending on individual production parameters and the technology used. The current research is focused on the evaluation of the fatigue behavior of 3D-printed test specimens made of pure PLA and PLA reinforced with filler based on pinewood, bamboo, and cork using FDM (fused deposition modeling) technology. This research was carried out in response to the growing demand for filaments from biodegradable materials. This article describes the results of tensile fatigue tests and image analysis of the fracture surface determined by the SEM method. Biodegradable PLA-based materials have their limitations that influence their applicability in practice. One of these limitations is fatigue life, which is the cyclic load interval exceeding 50% of the tensile strength determined in a static test. Comparison of the cyclic fatigue test results for pure PLA and PLA reinforced with natural reinforcement, e.g., pinewood, bamboo, and cork, showed that, under the same loading conditions, the fatigue life of the 3D-printed specimens was similar, i.e., the filler did not reduce the material’s ability to respond to low-cycle fatigue. Cyclic testing did not have a significant effect on the change in tensile strength and associated durability during this loading interval for PLA-based materials reinforced with biological filler. Under cyclic loading, the visco-elastic behavior of the tested materials was found to increase with increasing values of cyclic loading of 30%, 50% and 70%, and the permanent deformation of the tested materials, i.e., viscoelastic behavior (creep), also increased. SEM analysis showed the presence of porosity, interlayer disturbances, and at the same time good interfacial compatibility of PLA with the biological filler.

Composite materials with natural fillers have been increasingly used as an alternative to synthetically produced materials. This trend is visible from a representation of polymeric composites with natural cellulose fibers in the automotive industry of the European Union. This trend is entirely logical, owing to a preference for renewable resources. The experimental program itself follows pronounced hypotheses and focuses on a description of the mechanical properties of untreated and alkali-treated natural vegetable fibers, coconut and abaca fibers. These fibers have great potential for use in composite materials. The results and discussion sections contribute to an introduction of an individual methodology for mechanical property assessment of cellulose fibers, and allows for a clear definition of an optimal process of alkalization dependent on the content of hemicellulose and lignin in vegetable fibers. The aim of this research was to investigate the influence of alkali treatment on the surface microstructure and tensile properties of coir and abaca fibers. These fibers were immersed into a 5% solution of NaOH at laboratory temperature for a time interval of 30 min, 1 h, 2 h, 3 h, 6 h, 12 h, 24 h, and 48 h, rinsed and dried. The fiber surface microstructures before and after the alkali treatment were evaluated by SEM (scanning electron microscopy). SEM analysis showed that the alkali treatment in the NaOH solution led to a gradual connective material removal from the fiber surface. The effect of the alkali is evident from the visible changes on the surface of the fibers.

Analysis of the physical-mechanical properties of a pelleted chicken litter organic fertiliser | Anna Brunerová, Miroslav Müller, Gürkan Alp Kağan Gürdil, Vladimír Šleger, Milan Brožek | Agricultural Journals

This research evaluates the mechanical properties of hybrid adhesive bonds with various 100% cotton fabrics in static and quasi-static conditions and the influence of alkali surface treatment (NaOH) of the cotton fabrics on the mechanical properties. Biological fibers in polymers are characterized by low wettability with the matrix, which decreases mechanical properties. Adhesive bonds usually operate in cyclic stress, which causes irreversible failure before maximal strength. In this paper, a quasi-static test was used to load the adhesive bonds in 5–50% (192–1951 N) and 5–70% (192–2732 N) intervals with 1000 cycles. The results of SEM analysis showed good wettability of alkali treated cotton fabric with NaOH solution in hybrid adhesive bonds. The static test proved the influence of reinforcing cotton fabrics on shear tensile strength against pure resin, i.e., sample Erik up to 19% on 14.90 ± 1.15 MPa and sample Tera up to 21% on 15.28 ± 1.05 MPa. The adhesive bonds with pure resin did not resist either quasi-static tests. Reinforcing cotton fabrics resisted both quasi-static tests, even shear tensile strength increases up to 10% on 16.34 ± 1.24 MPa for the fabric Erik. The results of strain difference of adhesive bonds with Tera and Erik confirmed that a lower value of the difference during cyclic loading positively influenced the ultimate shear tensile strength.

Technology of adhesive bonding belongs to prospective bonding methods. The limit of adhesive bonds is cyclic loading which usually significantly decreases the service life of adhesive bonds and causes deformation of adhesive and cohesive bonds inside of adhesives. The article deals with the research of adhesive bonds exposed to cyclic loading. The aim of research was establishing an influence of the filler based on meshed coffee beans waste added into two-component epoxy matrix for bonding. The differences of mechanical properties of adhesive bonds with filler based on meshed coffee beans waste were evaluated at static and cyclic loading with 1000 cycles at first interval loading between 5 to 30% and second interval 5% to 70% of the static shear tensile strength.

The paper is focused on the research of the cyclic loading of hybrid adhesive bonds based on eggshell microparticles in polymer composite. The aim of the research was to characterize the behavior of hybrid adhesive bonds with composite adhesive layer in quasi-static tests. An epoxy resin was used as the matrix and microparticles of eggshells were used as the filler. The adhesive bonds were exposed to cyclic loading and their service life and mechanical properties were evaluated. Testing was performed by 1000 cycles at 5–30% (165–989 N) and 5–70% (165–2307 N) of the maximum load of the filler-free bond in the static test. The results of the research show the importance of cyclic loading on the service life and mechanical properties of adhesive bonds. Quasi-static tests demonstrated significant differences between measured intervals of cyclic loading. All adhesive bonds resisted 1000 cycles of the quasi-static test with an interval loading 5–30%. The number of completed quasi-static tests with the interval loading 5–70% was significantly lower. The filler positively influenced the service life of adhesive bonds at a higher amount of quasi-static tests, i.e., the safety of adhesive bonds increased. The filler had a positive effect on adhesive bonds ABF2, where the strength significantly increased up to 20.26% at the loading of 5–30% against adhesive bonds ABF0. A viscoelasticity characteristic (creep) of the adhesive layer occurred at higher values of loading, i.e., between loading 5–70%. The viscoelasticity behavior did not occur at lower values of loading, i.e., between loading 5–30%.