Influence of Bifilm Defects Generated during Mould Filling on the Tensile Properties of Al–Si–Mg Cast Alloys

Entrapped double oxide film defects are known to be the most detrimental defects during the casting of aluminium alloys. In addition, hydrogen dissolved in the aluminium melt was suggested to pass into the defects to expand them and cause hydrogen porosity. In this work, the effect of two important casting parameters (the filtration and hydrogen content) on the properties of Al–7 Si–0.3 Mg alloy castings was studied using a full factorial design of experiments approach. Casting properties such as the Weibull modulus and position parameter of the elongation and the tensile strength were considered as response parameters. The results suggested that adopting 10 PPI filters in the gating system resulted in a considerable boost of the Weibull moduli of the tensile strength and elongation due to the enhanced mould filling conditions that minimised the possibility of oxide film entrainment. In addition, the results showed that reducing the hydrogen content in the castings samples from 0.257 to 0.132 cm3/100 g Al was associated with a noticeable decrease in the size of bifilm defects with a corresponding improvement in the mechanical properties. Such significant effect of the process parameters studied on the casting properties suggests that the more careful and quiescent mould filling practice and the lower the hydrogen level of the casting, the higher the quality and reliability of the castings produced.

Effect of Mix Proportions on Fresh and Rheological Properties of Cementitious Mixture Containing Natural Fibre: Modelling Using Factorial Design

This paper aims to discuss the influence of mix composition of cement mortar on fresh and rheological properties of cement mortar. Two different natural fibres, basalt (BA) and sisal (SL) are selected based on fresh and rheological behaviour for its usability in a cementitious mixture. The workability and rheological behaviour are evaluated by flow table test, cone penetrometer and slump test of the mixture. A full factorial design method was used to investigate the effects of four mix components: dosage of cement content (B), percentage of fly-ash (FA) by mass of cement, dosage of basalt fibre (BA) and dosage of superplasticizer (SP) along with a water/binder ratio of 0.41. A mathematical model which predicts the main effect and interactions of these components for each of the measured properties are derived using the factorial design. The proposed mixtures consist of two levels of binder content as 550 kg/m3 and 650 kg/m3, FA as 5% and 20% by mass of cement, BA as 1 kg/m3 to 3 kg/m3 and SP as 2 kg/m3 to 4 kg/m3. By reducing the number of test batches needed, the mathematical models produced with this method can expedite optimizing the mixture proportions of cement mortar to achieve desired fresh and rheological properties.

Influence of Bile Acids in Hydrogel Pharmaceutical Formulations on Dissolution Rate and Permeation of Clindamycin Hydrochloride

Clindamycin hydrochloride is a widely used antibiotic for topical use, but its main disadvantage is poor skin penetration. Therefore, new approaches in the development of clindamycin topical formulations are of great importance. We aimed to investigate the effects of the type of gelling agent (carbomer and sodium carmellose), and the type and concentration of bile acids as penetration enhancers (0.1% and 0.5% of cholic and deoxycholic acid), on clindamycin release rate and permeation in a cellulose membrane in vitro model. Eight clindamycin hydrogel formulations were prepared using a 23 full factorial design, and they were evaluated for physical appearance, pH, drug content, drug release, and permeability parameters. Although formulations with carbomer as the gelling agent exerted optimal sensory properties, carmellose sodium hydrogels had significantly higher release rates and permeation of clindamycin hydrochloride. The bile acid enhancement factors were higher in carbomer gels, and cholic acid exerted more pronounced permeation-enhancing effects. Since the differences in the permeation parameters of hydrogels containing cholic acid in different concentrations were insignificant, its addition in a lower concentration is more favorable. The hydrogel containing carmellose sodium as a gelling agent and 0.1% cholic acid as a penetration enhancer can be considered as the formulation of choice.

Experimental Investigations into Assessment of Thrust Force and Temperature in Bone Drilling

Drilling of bone is a challenging task for surgeons due to its effect on bone tissues. During drilling, it is noted that the temperature of bone increases. This increase in temperature if above 47°C causes thermal necrosis. Experiments were conducted to study the effect of input drilling parameters and drill bit parameters on bone health. To plan experiments a full factorial design method was used. An analysis is done on the effect of input parameters on thrust force and temperature of bone. The analysis of results shows an increase in thrust force and temperature when the feed rate increases and the spindle speed decreases. Further, the analysis of results shows an increase in thrust force and temperature when point angle increases and helix angle decreases. The increase in thrust force results in temperature rise. Scanning electron microscopy is done to analyze the surface topography of drilled hole. SEM image analysis shows an increase micro-crack in the drilled area when the thrust force and temperature increases.

Novel Four-Cell Lenticular Honeycomb Deployable Boom with Enhanced Stiffness

Composite thin-walled booms can easily be folded and self-deployed by releasing stored strain energy. Thus, such booms can be used to deploy antennas, solar sails, and optical telescopes. In the present work, a new four-cell lenticular honeycomb deployable (FLHD) boom is proposed, and the relevant parameters are optimized. Coiling dynamics analysis of the FLHD boom under a pure bending load is performed using nonlinear explicit dynamics analysis, and the coiling simulation is divided into three consecutive steps, namely, the flattening step, the holding step, and the hub coiling step. An optimal design method for the coiling of the FLHD boom is developed based on a back propagation neural network (BPNN). A full factorial design of the experimental method is applied to create 36 sample points, and surrogate models of the coiling peak moment (Mpeak) and maximum principal stress (Smax) are established using the BPNN. Fatigue cracks caused by stress concentration are avoided by setting Smax to a specific constraint and the wrapping Mpeak and mass of the FLHD boom as objectives. Non-dominated sorting genetic algorithm-II is used for optimization via ISIGHT software.

Competitive Biosynthesis of Bacterial Alginate Using Azotobacter vinelandii 12 for Tissue Engineering Applications

This study investigated the effect of various cultivation conditions (sucrose/phosphate concentrations, aeration level) on alginate biosynthesis using the bacterial producing strain Azotobacter vinelandii 12 by the full factorial design (FFD) method and physicochemical properties (e.g., rheological properties) of the produced bacterial alginate. We demonstrated experimentally the applicability of bacterial alginate for tissue engineering (the cytotoxicity testing using mesenchymal stem cells (MSCs)). The isolated synthesis of high molecular weight (Mw) capsular alginate with a high level of acetylation (25%) was achieved by FFD method under a low sucrose concentration, an increased phosphate concentration, and a high aeration level. Testing the viscoelastic properties and cytotoxicity showed that bacterial alginate with a maximal Mw (574 kDa) formed the densest hydrogels (which demonstrated relatively low cytotoxicity for MSCs in contrast to bacterial alginate with low Mw). The obtained data have shown promising prospects in controlled biosynthesis of bacterial alginate with different physicochemical characteristics for various biomedical applications including tissue engineering.

Studying joint influence of a number of factors on borehole cleaning

Studying the behavior of cuttings transport under various conditions using experimental observations and computational fluid dynamics is the main method for analyzing the influence of cuttings, fluid and operating parameters on well cleaning. Despite the existing abundant models and recommendations of researchers, still there are problems with the accuracy of determining the cuttings layer height, critical velocity and other key parameters, which complicates the task of effective solution of the problem of borehole cleaning. The purpose of the study is to analyze the models obtained via the organization of a full factorial experiment and variance analysis to identify the influence of such factors as viscosity and flow rate of the drilling fluid in the annular space and the inclination angle of the well on the degree of cuttings transport. The studies of the kind are carried out using special devices called flow loops. Experimental data were taken from literature sources. To organize a full factorial experiment, the data of the dependent variable were combined into a combinational square, which simplified the coding of factor values. After setting the full factorial experiment, the models were obtained that made it possible to assess the contribution of the studied factors to the process of destruction product removal within the intervals determined while setting the research tasks. The obtained models allowed to determine the influence degree of each of the factors on the process under investigation. The results of the succeeding analysis of variance confirmed the indicated degree of influence and determined the rank of each of the factors in percentage.

Estimation of ergonomic indicators of special purpose clothing for patients with thermal injuries

This article discusses the determination of the optimal design allowances for a full factorial experiment in the development of special-purpose clothing for patients with thermal injuries in a hospital. To assess the ergonomic performance of special-purpose clothing, was used of pressure exerted by clothing on the human body. Based on the results of the study, a mathematical model was developed based on a full factorial experiment. In accordance with the presented mathematical models, the minimum values of contact pressures are obtained for the following values of construction parameters: for a cut with a sewn-in sleeve Warmhole = 15 cm, Ifa = 5,0 cm, Ic = 9 cm, Hse = 10 cm; for a cut with a raglan sleeve Warmhole = 15 cm, Ifa = 6 cm, Ic = 10 cm; for a cut with a one-piece sleeve Warmhole = 16 cm, Ifa = 6 cm, Ic = 11 cm.