Melese Shiferaw Kebede

A poly(bromocresol green)-modified screen-printed carbon electrode (PBCG/SPCE) was fabricated through electropolymerization for the electrochemical determination of uric acid (UA).

Active Suspension system of vehicles plays a crucial role in ensuring the ride comfort and stability of vehicles, particularly for cargo vehicles converted into passenger buses, where variation in payload and center of gravity height significantly affect dynamic performance. This study proposes a robust H∞ controller for a seven degree of freedom (7 DOF) full vehicle active suspension system to simultaneously improve the ride comfort, road holding and rollover stability under parameter uncertainties. The controller is developed using an augmented generalized plant with appropriately designed frequency dependent weighting functions. The vehicle model considers four independent road disturbance inputs and lateral acceleration during cornering. The proposed controller is evaluated under single bump, triple bump and ISO 8608 class D random road excitations and is compared with passive suspension and linear quadratic regulator (LQR) control strategies. Under single bump excitation, the proposed controller reduces the weighted RMS heave acceleration, roll acceleration, suspension deflection and tire deflection by 77.1%, 40.2%, 94.6% and 89.4% respectively, compared with the passive suspension system. Similar improvements are achieved under triple and random road conditions. Robustness analysis under 30% variations in sprung mass and center of gravity height demonstrate that the proposed controller maintains superior performance with significantly smaller performance degradation than both passive and LQR controlled suspension systems. Frequency domain analyses, including power spectral density and singular value analyses, further confirm that the proposed H∞ controller excellent disturbance rejection capability and robust performance. These results demonstrate that the proposed robust H∞ controller effectively balances the conflicting requirement of ride comfort, suspension travel, road holding and rollover stability, making it a best solution for cargo to passenger vehicle conversions operating under varying operating conditions.

This study applies an integrated Taguchi-Gray Relational Analysis (GRA) method to optimize CNC end milling parameters for AISI 4130 low-alloy steel, aiming to simultaneously maximize Material Removal Rate (MRR) and minimize surface roughness (Ra). Experiments were designed using an L9 orthogonal array, varying spindle speed (1200, 1400, 1600 rpm), feed rate (0.009, 0.014, 0.019 mm/tooth), and depth of cut (0.1, 0.15, 0.2 mm) under dry conditions with a high-speed steel end mill. The multi-response data were converted into a single Gray Relational Grade (GRG) for optimization. Analysis identified the optimal parameter set as 1600 rpm spindle speed, 0.019 mm/tooth feed rate, and 0.2 mm depth of cut. Analysis of Variance (ANOVA) on the GRG indicated spindle speed as the most statistically significant factor, accounting for 83.73% of the performance variation, followed by feed rate (10.11%) and depth of cut (2.25%). Confirmation experiments at the optimal settings validated the results, achieving a GRG improvement of 10.7% over the initial best run, with MRR of 31.65 cm ³ /min and Ra of 0.37 µm. The findings provide a practical framework for enhancing productivity and surface finish in the machining of AISI 4130 steel components.

Sansevieria forskaoliana and echinatus fibers are abundant natural resources native to the central and western regions of Gondar, Ethiopia, and offer significant potential as sustainable reinforcement materials in polymer composites. This study investigates the mechanical and microstructural properties of hybrid Sansevieria/echinatus fiber‐reinforced polyester composites. The natural fibers were chemically treated with 5% and 10% sodium hydroxide (NaOH) solutions to remove surface impurities, reduce lignin content, and enhance interfacial bonding with the polyester matrix. Composite laminates were fabricated using the hand lay‐up technique followed by compression molding, with fiber weight fractions of 25, 30, 35, and 40 wt.% and different lamina stacking sequences (90/0/45, 0/45/90, and 45/90/0). The experimental design was developed based on the Taguchi method to evaluate the influence of processing parameters. Mechanical characterization, including tensile, flexural, and impact testing, revealed that the composite containing 35 wt.% hybrid fibers with a 90/0/45 lamina orientation exhibited the highest tensile strength (95.55 MPa) and impact strength (201.03 kJ/m ² ). Microstructural analysis confirmed improved fiber–matrix adhesion and reduced fiber pull‐out at this optimal configuration. Overall, the hybrid composites demonstrated superior mechanical performance compared to single‐fiber composites and laminates with non‐optimal orientations. The results indicate that Sansevieria/echinatus hybrid fiber‐reinforced polyester composites possess enhanced strength and interfacial bonding characteristics, making them promising candidates for lightweight structural and load‐bearing applications.

Natural fiber-reinforced polymer composites are gaining attention in engineering industries due to their high strength-to-weight ratio and the wide availability of fibers. In this study, sisal fiber was selected for reinforcement in a polyester resin matrix. Fiber incorporation enhances mechanical properties, particularly tensile strength, but polymers exhibit viscoelastic behavior that can lead to failure under compression. Therefore, evaluating compressive strength is essential before practical application. The composite was fabricated using the hand lay-up method, with sisal fibers treated in sodium hydroxide to remove non-cellulosic materials. This treatment improved fiber–matrix adhesion and interfacial shear strength. Specimens were prepared and tested for compressive strength according to ASTM standards to assess their suitability for engineering use. To evaluate the compressive strength, three approaches were employed: analytical evaluation using classical lamination theory, simulation analysis using ANSYS software, and experimental testing. The fiber orientation was varied during testing to examine its effect on compressive behavior. The maximum ultimate compressive strength, breaking force, failure strain, and deflection were found to be 60.5 MPa, 20.17 kN, 7.2%, and 3.25%, respectively, for fiber orientations of (0°, 45°, 45°) ₃ and (45°, 90°, 90°) ₃ .

Fabric scrap waste in the textile and garment industry consists of leftover or unused fabric pieces from the cutting and sewing processes. Managing fabric waste is essential for environmental sustainability and cost-effectiveness in the textile sector. Common types of fabric scrap include trim waste, cutting room scrap, and defective or off-cut pieces. Efficient scrap management reduces environmental impact, lowers costs, and enhances operational efficiency. As sustainability demands grow, industries are adopting innovative strategies to minimize waste and optimize production. This study investigates the mechanical (tensile, flexural, and impact) and thermal properties of fabric scrap-reinforced composite materials. Thermogravimetric analysis was performed to assess their thermal stability. Experimental results revealed that chopped fabric scrap composites outperformed sandwich and laminated forms in mechanical performance. The optimal composition was identified as a 40% reinforcement and 60% matrix weight ratio. According to the test results, the maximum tensile and flexural strength were obtained at chopped orientation, with values of 110 and 112 MPa, respectively. Regarding the hardness test, almost all three orientations showed similar results at the described ratio. The findings suggest that fabric scrap-reinforced polyester composites have significant potential for automotive applications, particularly in vehicle hoods, bumpers, and roofing. Moreover, this study emphasizes the role of recycled textile composites in promoting a circular economy, bridging the automotive and textile industries. By integrating waste materials into high-performance composites, this approach supports sustainability efforts through waste reduction and resource optimization, making it a viable solution for eco-friendly manufacturing.