The paper presents the effect of sandblasting on surface properties of steel for adhesion. The investigated parameters included pressure (1, 2 and 4 bars) and four types of abrasive material, each ...material type being of different granulation. In the experiments the effect of the above variables on the surface roughness, contact angle Θ, work of adhesion Wa and surface free energy γ was investigated. It has been shown in this research that surface properties are more affected by abrasive material type applied rather than by the sandblasting process parameters.
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.
The objective of the study is to investigate the erosion effects of periodic water clusters interacting with flat AISI 304 surface to evaluate erosion regimes, surface morphology and variation in the ...subsurface microhardness below the disintegrated grooves. Stairs trajectory within the standoff distance 5–101 mm with step height 2 mm and length 20 mm was used. The pulsating water jet was changed by varying the supply pressure of the liquid from 40 MPa–100 MPa, at a traverse speed of 5 mm/s which is equivalent to constant impingement distribution of 4000 impingements per mm. Morphology of the PWJ defines different erosion regimes based on specific value of supply pressure and standoff distance. Increasing of supply pressure shifts prevalence of both impact pressure and stagnation pressure at higher standoff distances leading to the delay in formation of incubation, acceleration, culmination, depletion, and termination regime. Impinged surface features such as micro-pits, craters, upheaved surface and isolated voids near the periphery of the trace were observed along with PWJ footprint. The values of the micro-hardness showed strengthening of material subsurface at selected standoff distances. At certain standoff distance effect of supply pressure is inverse to micro-hardness values. Determination of studied technological parameters can be used for effective surface peening operation at v > 5 mm and surface activation of the metals. Results opens a new avenue for determination of erosion resistance of material.
•Erosion effects of pulsating water jet as function of standoff distance and flow rate was investigated.•Linear offset of erosion stages and erosion intervals due to interaction of water flow rate and standoff distance was found.•Different erosion stages were observed due to non-uniform plastic deformation with the variation of standoff distance.
The plant Ensete ventricosum is used in agriculture in Africa. It is a source of fibres, which can be used in the interaction with polymers. This study deals with a material utilization of these ...fibres with a length of 1 to 2 mm, 2 to 3 mm, and 3 to 5 mm, together with reactoplastics resin ChS Epoxy 1200/324, following requirements of developing countries. Some areas of the African continent suffer from a lack of wood, and material based on epoxy and fibres can substitute for many wood products. The aim of this experiment was to describe basic mechanical properties (tensile strength σm, strain at the break εb, modulus of the elasticity Et, and impact strength an) of the composite material reinforced with fibres of the false banana plant, Ensete ventricosum. The plant, which originated in Ethiopia, is exploitable in developing countries. Geometrical aspects and morphology of the used fibres was characterized by scanning electron microscopy (SEM). The addition of fibres increased the modulus of elasticity and the impact strength, whereas the tensile strength and the strain at break were decreased.
This article deals with the analysis of the subsurface deformation effects of materials due to the periodic action of liquid droplets, each with a constant volume of approximately 36 mm3 distributed ...with a spatial frequency of 20,000 i/mm. Sample grooves were analyzed within standoff distances where the prevailing mechanism is acceleration culmination depletion using the stair trajectory to avoid a possible Doppler effect. Using X-ray μ-CT, a network of cavities corresponding to a fractal shape was identified below the surface. It is apparent that the ability to erode does not end with the formation of a groove but continues into the core of the material in the form of microjetting, tunneling, or piercing. From that perspective, two types of these cavities have been identified, blind and transient, with diameters of a few micrometers. The topological changes in the subsurface region of the sample were analyzed using X-ray μ-CT progressive sectioning. The anticipated subsurface deformation was further explored and analyzed using SEM analysis. The integrity of the material around the cavities was assessed according to microhardness to explain the microjetting, tunneling, and piercing propagation. The results suggest that the effect of the lateral jetting after droplet collapsing causes extensive hydrodynamic tunneling in the material that is much higher during the intense periodic action of water droplets, even at subsonic speeds.
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•The origin of subsurface voids is clarified.•Subsurface network microcavities are identified.•Blind and transient subsurface cavities are observed.•Relative and real erosion depths are identified.•Residual water microjetting is observed to be multidirectional.
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.
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 (Δ
), elongation at break (Δ
), Shore A hardness (Δ
), and mass (Δ
). 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.
This study addresses the erosion transition of an aluminium surface arising from the periodic impact of a tangentially acting pulsating water jet (PWJ) with a spatial frequency of f = 20 kHz. The ...erosion effect was observed as a function of the standoff distance z (mm) along an incline (from 5 mm to 90 mm) and constant trajectory (at standoff distances of z = 25 mm, 75 mm and 125 mm) at a jet pressure of 100 MPa and traverse speed v = 10 mm/s. The aim of this study is to assess the manner in which the erosion along the PWJ pathway changes the measured dynamic signal (by means of acoustic emission measurements). The effects of hydrodynamic erosion, such as elastic and plastic deformation, were observed with the aid of a scanning electron microscope and compared with time records in terms of acoustic emission (AE) recorded during impact. Moving the PWJ head and gradually changing the standoff distance along the inclined trajectory resulted in different erosion regimes. With a gradual increase in the standoff distance (from 5 mm–90 mm), the observed erosion regimes were observed in terms of micro-pitting action, crack and crater formation and material folding/upheaving. The erosion effects of a PWJ compared with those of a continuous water jet were investigated at constant standoff distances of z = 25 mm, z = 75 mm and z = 125 mm. The differences in the erosion phenomenon under different conditions were observed in terms of the material damage, crater dimensions and surface and sub-surface features. The AE recorded during the impact of the PWJ demonstrates a correlation between the ongoing erosion phenomenon and the AE signals. This relation for the encoded complex waveform (PWJ) confirms the significant information about the ongoing process in terms of material deformation and dislocation movement.
•Standoff distance affects generating different erosion regions.•A clear presence of isolated sub-surface voids were observed.•The time records exhibit increase amplitudes when erosion occurs.•The depth values correlate with dynamic signal.
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.
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