Journal of the Brazilian Society of Mechanical Sciences and Engineering

Literature survey related to the nanoparticles reveals that nanofluids are getting popularity in hematological treatment. Development in this direction motivated us to write a theoretical study on unsteady blood motion in stenosed vessel with nanoparticles. Geometry of a stenosed arterial section is being written mathematically by an appropriate geometric expression. The constitutive equation of Carreau fluid model is used to characterize the dynamical behavior of the blood. The rheology of the blood is formulated mathematically by coupled partial differential equations. Similarly, the effects of nanoparticles are incorporated mathematically into governing equations by using Buonjiornio’s formulation. Mild stenotic condition is employed to reduce the two-dimensional differential equations to simple form. Numerical technique is being used to obtain the numerical solution to the existing problem. The obtained simulation reveals that the magnitude of velocity shows an accelerating behavior for Brownian motion parameter and shows deceleration trend on increasing the thermophoresis parameter. Similarly, the instantaneous behavior of blood flow pattern is shown through streamlines.

Geometrical variation is present in any production process and needs to be controlled, to ensure compliance with design requirements and minimize costs. Tolerancing of injected plastic parts (IPPs) is mostly performed in practice without using consistent criteria, many times resulting in tolerances which are unnecessarily narrow and incompatible with the respective manufacturing process capabilities. In this paper, a new method is proposed to support IPPs dimensional production tolerancing in early design phases, based on historical measurement data reuse and similarity analysis. Rule-based reasoning has been employed together with a scoring system to identify reliable and similar cases stored in a database, involving attributes of both the parts and the dimensional characteristics. Two different approaches for data recovery were considered, providing the ability to choose between a simplified and a more accurate analysis. The method feasibility is demonstrated by a case study involving 20 different IPPs and 24 dimensional characteristics from three suppliers. The proposed method outperformed the use of standard DIN 16742 to estimate production tolerances. Comparisons between the estimated production tolerances and the respective process capabilities resulted in maximum mean absolute deviation of 10% and Pearson’s r of about 0.6.

Present investigation is focused to study the impact of different lubricating environments using pure canola oil and graphene mixed in canola oil, on the performance of uncoated carbide textured tools in minimum quantity lubrication (MQL) turning of AISI 4340 hardened steel. The influence of using twin jet and single jet was also studied under MQL. The turning performance was evaluated in terms of flank wear (VBmax), cutting forces, cutting temperature, and chip morphology. The results showed that MQL mist supplied simultaneously on rake and flank face of the textured tool by twin-jet nozzle performed better than MQL mist supplied on the rake face of textured tool by the single-jet nozzle. Out of all the tested lubricating environments, best tool life was achieved with nanoparticle minimum quantity lubrication (NMQL) using the twin jet followed by only oil using twin jet as compared to all other conditions tested in this study. The outcome of the study illustrates that MQL mist of graphene which is mixed in canola oil on a textured tool with the twin-jet nozzle can be successfully applied for finish turning of hardened steel.

This paper focuses on the path planning improvement for mobile robots in cluttered environments. Due to the uncertainty of searching direction in traditional path planning algorithms, each node often searches for its following path node in irrelevant directions, which increases the time cost and the number of invalid nodes. In this study, an artificial potential field guided jump point search algorithm is proposed to solve this low-efficiency problem. This method builds an APF and a direction map, which represent resultant force distribution and node directionality to the target node, respectively. Then, with consideration of APF influence and direction map guidance, an expansion direction priority for path planning is calculated, which guides and improves the search for subsequent jump points. To evaluate its performance and efficiency, the APF-JPS algorithm is compared with the conventional JPS, RRT, APF and 8-domains A* algorithms in simulation and mobile robot experiments. The experimental results indicate that the APF-JPS algorithm not only plans the shortest available path with the least time cost, but also reaches the highest node utilization rate. Comparing with the conventional JPS algorithm, which ranks second in overall performance, both the number of key nodes and the path planning time decrease by 45.0% and 53.8%, respectively, while the node utilization rate increases by 23.4%. Therefore, the APF-JPS algorithm shows its advantages in path planning, mainly by reducing the system computational load, improving the real-time performance, and increasing the mobile robot endurance time.

Experimental results show that when the loading sequence of fatigue loads changes, the fatigue cumulative damage prediction based on Miner's rule will have a large error, even as high as 252.83%. In an effort to improve the fatigue life predictions, based on the residual strength degradation rule, a power exponential fatigue equivalent damage model is presented in this paper, which contains two material parameters. Experimental data were cited to verify the residual strength model, and the statistical results showed that this model is capable of describing the residual strength degradation of materials. Furthermore, a fatigue cumulative damage model based on residual strength is established to predict the fatigue life. The Miner's rule and other models were compared to validate the model by referring to the test data of different materials under different loading stress levels. And the accuracy of the fatigue life predicted by this model is twice as good as that predicted by others models.

Variations in in-plane mixed-mode fracture toughness versus changes in thickness of shear CT (CTS) specimens and loading direction and effects of yield strength of different aluminum alloys have been investigated by experimental testing and numerical analysis. Several samples were made by Al2024-O, Al6061-T6 and Al7075-T6 alloys. Based on the results, increasing the thickness reduces the mixed-mode fracture toughness and near to the critical thickness, this reduction is lesser. Increase in mixed-mode loading angle for brittle materials has not significant effects on the toughness while in softer materials by changing the angle from 15° to 60°, the amount is halved. Near the mode I fracture conditions, there is no meaningful relationship between the yield strength and fracture toughness but with an increase in the second mode effects, these parameters will be proportional. The mixed-mode toughness of the alloys with different thicknesses can be calculated numerically with a precise accuracy by applying failure load in the analysis.

Trong bài báo này, một mô hình toàn diện của vòng bi bi lăn với sự xem xét đến biến dạng và sự sai lệch góc của vòng bi được đề xuất để nghiên cứu các thuộc tính động học của vòng bi. Các tương tác hình học giữa trạng thái lắp ráp và biến dạng của vòng bi được suy diễn dựa trên các điều kiện phối hợp biến dạng. Sau đó, quá trình áp dụng tải trước cho vòng bi được phân tích để làm rõ các nguyên tắc cho hai loại cơ chế tải trước. Một phương pháp tính toán hiệu quả dựa trên phương pháp sai phân hữu hạn được áp dụng để phân tích độ cứng của vòng bi, và độ chính xác cũng như tính khả thi của các kết quả tính toán được xác minh bằng cách so sánh với dữ liệu thực nghiệm. Cuối cùng, ảnh hưởng của giá trị can thiệp ban đầu, tốc độ quay trục, và sự sai lệch góc của vòng bi được thảo luận. Kết quả cho thấy rằng các biến dạng của vòng bi và sự sai lệch góc của vòng bi thay đổi đáng kể các thuộc tính động học của vòng bi. Mặc dù tải trước cố định cải thiện hiệu suất làm việc của vòng bi, nhưng tuổi thọ mỏi giảm. Sự sai lệch góc của vòng bi làm thay đổi phân phối tải, và giảm hoặc tăng độ cứng của vòng bi theo hướng cụ thể.

This paper presents the evaluation of the vibration control on the performance of magneto-rheological fluid damper (MR damper in short) for gun recoil system. In this study, a magneto-rheological (MR) damper type RD-8040 manufactured by Lord Corporation is used. Then, characterization of MR damper is carried out by varying recoil energy and input currents to obtain its behavior. The MR damper is then modeled using adaptive neuro-fuzzy inference system (ANFIS) technique. The mathematical model of the gun recoil system (plant in control structure) is formulated, and a control strategy known as a hybrid skyhook active force control (H-SAFC) is proposed. Then, a current generator is designed using inverse ANFIS method to supply accurate amount of input currents to the MR damper coils. The simulation analysis of control strategy is conducted by varying the recoil energy and its performance compared with passive damper system. In order to improve the H-SAFC performance, an adaptive mechanism is developed for the adapting with various recoil energies. The performance of adaptive H-SAFC is evaluated by the simulation and experiment, and the performance criteria such as jerk, accelerations and forces of the gun recoil system are analyzed in the time domain.

Undershot waterwheels (USWW) are recommended as a power plant for remote or rural areas because of their construction simplicity. The USWW is considered old technology; while the characteristics of its technology are not yet comprehensive, the effect of the number of blades on its performance is debatable. This study investigated the effect of the blade number on pico scale USWW performance and the hydraulic behaviors due to rotational speed of wheel by computational and validated with experimental data. The four blade numbers investigated were 8, 12, 16, and 20 blades. The relation of blade number to USWW performance is parabolic and can express using empirical laws. The empirical laws can predict performance change by blade’s number and identify the optimum blade's number at 16 blades.