Journal of The Brazilian Society of Mechanical Sciences and Engineering最新文献

In order to enhance productivity and automate the rough milling process of pockets, it is crucial to select the optimal set of tools that offer reduced cutting time. In this article, a new method for the automatic selection of a toolset has been developed to effectively remove material during the roughing stage of a pocket with any contour, whether formed by line–line or line–arc, convex or concave. The proposed software selects a maximum of three tools based on the pocket's boundary. These algorithms test available tool combinations on the machine tool and provide the suitable toolset that minimizes cutting time further. This is done through a visual test, and if the residue in the corners takes the form of a polygon, an algorithm adds a third tool. In this case, the software will choose the best combination, either two or three tools, that minimizes machining time even more. The good news is that the machining simulation and the result file are obtained in a reduced time. It also provides the toolpath coordinates that can be transferred directly to the machine. To demonstrate the effectiveness of our approach, we also conducted a detailed comparison with conventional methods found in the literature. The results obtained show that our new approach minimizes both toolpath length and cutting time with the optimal toolset compared to other methods.

Graphical Abstract

This study aimed to fabricate hybrid metal matrix composites of AZ91D magnesium reinforced with varying various weight percentages of SiC and constant weight percentages of BN particles through the stir-squeeze casting method. The influence of the particle ratio on the microstructure and wear behaviour of the composites was studied. The dispersion patterns of particles within the matrix and the interactions between the alloy and the particles were thoroughly investigated using a variety of techniques, including optical microscopy, SEM, EPMA, and EDS.XRD analysis of the AZ91D/SiC/BN hybrid composite revealed a significant volume proportion of the strong Mg17Al12 phase. The synthesized magnesium hybrid composites (AZ91D/9%SiC/3%BN) experienced a volume loss reduction of up to 36.16% under a maximum load of 30 N and a maximum speed of 1 m/s when compared with the monolithic material AZ91D. The results of these analyses demonstrated that the resulting composites exhibited an even dispersion of particles, superior grain structure, and strong interfacial bonding between the AZ91 alloy and the reinforcing particles. The newly developed magnesium hybrid composites have better wear performance than monolithic AZ91D alloys. These findings highlight the enhanced wear resistance of the fabricated composites for antiwear applications.

In this study, glass/epoxy (GFRP), carbon/epoxy (CFRP) and glass-carbon/epoxy hybrid (GCFRP) composites were aged in seawater, engine oil and diesel fuel degradation environments for 30, 60 and 90 days. The effect of aging environment and time on the structural strength of the composite was examined by applying tensile, three-point bending and low-velocity impact tests to aged composites. Scanning electron microscopy analyses were compared to detect fracture damage occurring in the internal structure of the composites. It was concluded that the degradation environment that most affects the mechanical strength of composites is seawater. Degradation resistance is improved due to the glass/carbon hybridization effect. It has been determined that the glass-carbon hybridization effect in GCFRP composites significantly changes their mechanical strength compared to GFRP and CFRP composites stacked alone. By comparing the glass-carbon hybridization effect in CFRP composites with GFRP and CFRP composites stacked alone, their advantages under different tests are clearly emphasized.

Elevator is an important part of modern life. A reasonable health evaluation plays an important role in avoiding elevator failures and ensuring the safety and normal operation of elevators. This paper establishes an index system for comprehensively evaluating the performance of elevators by analyzing the structure of elevators. The index system includes 11 detection indicators (including continuous and discrete indicators) that can fully evaluate the health status of elevators. By monitoring the running signals of elevators through professional elevator testing equipment and extracting multiple time-domain and frequency-domain features, different methods are used to evaluate discrete and continuous variables based on the different characteristics of different types of indicators: continuous variables are evaluated based on statistical quality control ideas, and discrete variables are evaluated based on standards and historical data, and the evaluation scores of each indicator are obtained. Finally, Decision-Making Trial and Evaluation Laboratory and Analytical Network Process (called D-ANP) is used to clarify the relationship between each indicator, calculate the weight of each indicator in the system and obtain the comprehensive evaluation score of elevator health. And this evaluation model is applied to actual experimental applications, evaluating and assessing experimental elevators with different health levels, verifying the effectiveness of this model. The results show that the proposed method has good applicability and is expected to be applied to daily elevator maintenance and inspection, playing a promoting role in the field of elevator health evaluation and maintenance.

The development of variations of the GMAW process, where metal transfer is assisted by the electromechanical movement of the wire (Dynamic Feed—DF), has contributed to the increasing interest in wire and arc additive manufacturing (WAAM) technology. This technology holds the potential to change traditional manufacturing processes. Studies on GMAW variants suitable for WAAM are essential, as it provides opportunities to enhance control over welding outcomes and broaden the application range for different materials. This paper presents an analysis of how current waveform parameters in the GMAW-DF process influence metal transfer and the overall process. The study, conducted with proprietary equipment developed by the Welding and Mechatronics Institute (LABSOLDA) for researching and developing new processes aimed at root pass applications, coating, and parts recovery through additive manufacturing (AM), varied the time and amplitude of the current pulse during the short-circuit phase. The objective was to analyze its effect on the process and the weld bead. The findings indicate that the pulse helps constrict the metal bridge and reduces arc height at the moment of metal bridge rupture, allowing for a reduction in motor movement amplitude and increasing detachment frequency. The methodology also identified errors caused by extrapolating pulse parameters, which are considered crucial for process mapping.

The demand for underwater robots is on the rise, driven by increasing needs in oceanographic engineering and the urgent exploration of underwater resources. Traditional underwater robots face practical limitations due to their large size, high operational costs, and substantial energy requirements. However, smart material-based underwater robots offer a promising solution, thanks to their unique attributes such as low power consumption, robustness, versatility, and superior efficacy compared to conventional counterparts. This article investigates the utilization of ionic polymer metal composite (IPMC) as a propeller for underwater biomimetic propulsors, leveraging its exceptional electromechanical property of converting electrical signals into mechanical deformation and vice versa. The study focuses on modeling an underwater biomimetic propulsor utilizing IPMC as a propeller tail, mimicking body caudal fin motion (BCF) for swimming. However, the motion of IPMC in an open-loop configuration presents challenges such as irregular deformation, extended settling time, water back diffusion, and hysteresis. To address these issues, the study implements three different controller design approaches—PID, Fuzzy Logic control, and H∞ control—to effectively regulate the positioning of IPMC. The primary objective is to control the tip displacement at the tail end of the biomimetic IPMC propulsor model. A key novelty of this research lies in conducting a comprehensive comparison of the controller's performance with experimental results, assessing the accuracy and swiftness with which each controller achieves the desired output motion while mitigating the effects of noise. The study also evaluates the controller's performance across two different input signals to validate its accuracy and precision.

This research investigates the impact of cutting conditions and tool geometry on flank wear during turning. A thermomechanical model was developed while considering abrasion as the mechanism of wear. The proposed model validation was performed using experiments from the literature with an uncoated carbide tool while turning an AISI 1045 workpiece. Furthermore, a parametric study is conducted to investigate the impact of tool geometry parameters and cutting conditions on flank wear growth. Therefore, a robust regression model with an R² of 97.6% for tool life as a function of the most influential parameters is established. Results collected from analytical and regression models reveal a significant correlation between flank wear and cutting speed, feed rate, rake angle, and nose radius. It was found that cutting tool life enhancement requires a cutting tool with a higher nose radius and a positive rake angle, besides machining with controlled cutting speed and feed rate. Furthermore, it was shown that decreasing the edge direction angle reduces flank wear and extends the tool’s life. These findings underscore the need to consider tool geometry to optimize cutting performance and reduce wear-related issues. The study’s outcomes have practical implications for turning operations, enabling the selection and design of cutting tools. This approach might be used to extend tool life and reduce tooling costs, leading to more effective machining operations and enhanced productivity.

The motion accuracy and service life of robot precision reducers are directly affected by the assembly accuracy and stability, and the correct establishment of the assembly dimension chain is a crucial factor in ensuring the precise assembly of reducers. Therefore, a mathematical model of the multi-dimensional chain (MDC) is proposed based on distance over balls and pre-loading, which can effectively enhance the assembly accuracy of the reducers and ensure the consistency of product quality. The MDC model is built by applying a series of methods. The first-dimensional chain is established based on the distance over balls of the cycloidal gear and the pin housing, which ensures the lost motion and transmission error of the reducers. The second-dimensional chain is established according to the structure of the crank bearing. The influence of shape and position errors on operating torque fluctuation is compensated by controlling the clearance of the crank bearing. The third-dimensional and fourth-dimensional chains are established, respectively, through the axial pre-loading of the main bearing and tapered bearing, so the appropriate operating torque fluctuation of the reducers is guaranteed. Meanwhile, the relationship of the dimension chain and backlash is described through analyzing the error accumulation of the MDC. Finally, the comparative experiments are conducted, respectively, based on the MDC and manual random assembly methods. The results show that the assembly accuracy and efficiency of reducers can be improved effectively by applying the MDC, which can ensure the consistency of the accuracy and provide the theoretical guidance and technical support for the effective control of the motion accuracy of the reducers.

This paper investigates the combustion performance of a scramjet engine in which hydrogen fuel is injected into the flow field through transverse injectors. An unsteady numerical method is developed based on the Reynolds-averaged Navier–Stokes equations. Under a Mach number of 2.5, total temperature of 1350 K, and total pressure of 1.75 MPa condition, the flow characteristics are compared with those obtained through experiments. By analyzing the non-reacting and combustion chemical reacting flows, an evolution law of the wave system is derived, and the thermodynamic parameters of the flow field are studied for hydrogen equivalence ratios of 0.1–0.5. The results show that the non-reacting flow field exhibits periodic oscillation due to the flow structures and the low-speed separation zones, where the oscillation period is 6.9 ms. In a certain degree, the transverse injection scheme reduces the propagation of shock systems in the flow channel. When the critical value is exceeded, the shock train in the isolator is very sensitive to the back pressure from the combustion release. The local low-speed regions in the flow field will lead to the aggravation of thermal diffusion, the complication of flow structures, and the reduction in the thrust performance.

In order to improve the machining efficiency of Zirconia (ZrO₂) ceramics, the material is removed by brittle fracturing during turning ceramics, creating a discontinuous cutting process. Impact loading occurs when the rake face of the tool makes contact with the workpiece, and excessive impact loading force affects machined surface quality and tool wear. However, considering the continuous cutting process, it might not be appropriate enough to reflect the realistic situation. Considering the effect of impact loading phenomenon (ILP) on the removal and cutting force of ZrO₂ ceramics, the impact loading stage and static cutting stage have been proposed by brittle solid fracture mechanics and crack propagation for the first time in this paper to solve the problem. The rake face static resultant force of the tool has been theoretical modeled in the static cutting stage by using the theory of maximum tensile stress of mixed crack fracture with the consideration of crack path, cutting parameters and tool geometry angle. The dynamic coefficient was calculated by energy transfer theory in the impact loading stage, and the rake face impact loading resultant force of the tool was modeled by considering dynamic coefficient. Finally, the theoretical model of total cutting force was modeled based on the influence of elastic recovery of workpiece’s machined surface on the flank face of the tool. The experimental validation results indicate that the maximum relative error for the total tangential force is 12.76%, and the maximum relative error for the total radial force is 12.83%. When the cutting speed exceeds 48.36 m/s, the impact phenomenon becomes significant. The comparison between the analytical predictions and the experimental results presents a good agreement. This study has also proved that, as expected, the initial crack is formed during the impact loading stage. Once the initial crack propagation stabilizes, the static cutting stage deflects the initial crack. Moreover, the variations in the direction of initial crack propagation during the impact loading stage under different cutting parameters are also discussed. The proposed relationship between ZrO₂ ceramics material removal and cutting force, considering the ILP, suggests that by reducing the cutting speed and appropriately increasing the cutting depth and feed rate, the influence of impact loading can be mitigated and the initial crack path altered. This approach not only improves the machining efficiency but also enhances the surface quality of ZrO₂ ceramic workpieces and reduces tool wear. This work provokes more in-depth thoughts about ILP in the cutting ceramics process and provides the guiding significance for industrial ZrO₂ ceramics machining.