No abstract

This study assessed the impact of alkali treatment of hemp and flax fibers on mechanical properties (determined by means of the uniaxial tensile test, impact tensile strength test and hardness test), processing properties (the course of the extrusion and injection process) and usable properties (shrinkage of molded pieces, degree of water absorption) of biocomposites on the base of poly (3-hydroxybutyric-co-3-hydroxyvaleric acid) (PHBV) biopolymer. For this purpose, 1 mm of length flax and hemp fibers was surface-modified by means of aqueous solution of NaOH (sodium hydroxide) with concentrations of 2%, 5% and 10%. The composites were made using the extrusion technology. The test specimens were produced by injection molding technology. In total, eight types of biocomposites with modified and non-modified fibers were produced, and each biocomposite contained the same filler content (15 wt.%). Their properties were compared in some cases with pure PHBV polymer. In the case of biocomposites filled with hemp fibers, it was noted that an increase of the alkalizing solution concentration improved most of the tested properties of the obtained biocomposites. On the other hand, in the case of flax fibers, there was a significant decrease in most of the mechanical properties tested for the composite containing fibers etched by 10% NaOH solution. The obtained results were verified by examining fibers and the destroyed specimens with a scanning electron microscope (SEM) and an optical microscope, which confirmed, especially, the significant geometry changes of the flax fibers etched by 10% NaOH solution. This procedure also resulted in a significant change of processing properties—a composite of this fiber type required about 20 °C lower temperature during the extrusion and injection molding process in order to obtain the right product. These results lead to the important conclusion that for each filler of the plant-origin and polymer matrix, the fiber alkalization method should be selected individually in order to improve the specific properties of biocomposites.

In this paper the experimental studies of the screen working in the parametric resonance condition are discussed. The investigations are conducted for laboratory parametric resonance screen. The measuring test is performed for four cases of tension force values. The full sheet metal instead of the sieve is used. For each considered case the natural frequency of the plate and the parameter modulation frequency are determined. The achieved results are presented and discussed. It is shown that the highest sieve plate amplitude is obtained when the parameter modulation frequency is two times larger than natural frequency of the sieve plate. This parametric resonance vibration was observed only for tension force equal to 4000 N because of the rotational speed limits of electrical vibratos.

No abstract

<p>In the paper the strain hardening effect on the contact of a rigid ball and elastic-plastic flat is considered using experiments and finite element method. The experiments were carried out for DC04 steel sheet metal. The flat samples of 20 mm width and 200 mm length were straightened using uniaxial tensile test to receive different strain values: 5, 10, 15, 20, 25 and 30%. The indentation tests were performed using a modified Zwick Roell Z030 operated in the compression mode. The diameter of bearing steel indenter was 6 mm. It was found that the strain hardening phenomenon and anisotropy of material have a great influence on the ball indentation value and the maximal indentation force. The linear dependence between the normal load and penetration depth is observed. Furthermore, it was found that the value of penetration depth for specific force value decreases non-linearly with the increase of sample strain. Pre-strained samples cut transverse to the rolling direction exhibit higher deformation resistance than samples cut along the rolling direction. The springback analysis in ABAQUS is executed for studying the actual indentation depth after the indenter is unloaded.</p>

The problem with obtaining high efficiency screening process in the coal, metal mining, building and other industries lead to invent new constructions of the screeners. The rapid progress of screening techniques and screen design was observed in the past and nowadays the development of screen is stabilized and most of equipment produced by various machines companies is very similar. In spite of this, there is always a need to improve the performance of screens. Increase capacity and efficiency of screening process on the one hand, and decrease its ecological footprint are the main goals of development of a new screening equipment. The screening machines inventive method is parametric resonance excitation of the screen sieve mesh. The model of laboratory screener based on parametric resonance for fine granular materials is presented in this paper. The working principle of the screener is included showing, that the parametric resonance screener could obtain a complex motion of the sieve, which is desirable with processing naturally wet fine granular materials.

The goal of the work reported was to determine the influence of selected shot peening parameters on the deflection of the Almen strip and the load capacity of single-lap adhesive joints made of 2-mm-thick aluminium alloy EN AW-2024-T3. Moreover, the research was aimed at checking the possibility of using the Almen strip deflection indicator to predict the load capacity of adhesive joints after shot peening. The analysis was carried out according to Hartley’s PS/DS-P:Ha3 plan. The input factors were the shot peening parameters: treatment time t (60–180 s), ball diameter dk (0.5–1.5 mm) and compressed air pressure p (0.3–0.5 MPa). It has been proved in this work that shot peening treatment of the outer surface of single-lap adhesive joints can be used to strengthen the joint. The maximum increase in the load capacity of the shot peened joints was 33.4%. It was observed that the load capacity of the joints decreases with an increase in the deflection of the Almen strip (in the assumed area of variability of technological parameters). Moreover, the results obtained indicate that the adoption of too intensive treatment, manifested in high values of deflection of the Almen strip, may weaken single-lap adhesive joints.

In recent years, there has been an increasing interest in the composite materials reinforced with natural fibers. Due to the easy and cheap methods of obtaining raw materials, the possibility of recycling, biodegradability, production and processing safe for health, such materials can be a good alternative to the composite materials reinforced with glass or carbon fibers. However, due to the lower mechanical properties of natural composites, their use as construction materials is still limited. Nevertheless, natural fiber composites have the characteristics that can be used in structural applications as long as the mechanical behavior is well understood, reliable and predictable. The paper presents the results of numerical calculations of the compression process of a composite reinforced with a fabric made of flax and jute fibers (trade names: Biotex Flax 400g/cm 2 and Biotex Jute 400 g/cm 2 ) on a basis of Kinetix R240 epoxy resin. The data necessary for the numerical analysis were calculated in the Digimat software using the Double Inclusion micromechanical model, while the simulations of compression of the details were carried out in the Ansys software. Sections with different number of layers were tested. The results were compared with the experiment. The buckling forces obtained in the numerical analysis are comparable to the experimental results. Two types of C -section buckling modes were obtained and they consisted of two or three half-waves of buckling.