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

Sandwich structures and auxetic materials have had a significant impact on various applications as energy absorbers. The purpose of this study is to manipulate the deformation mechanism of sandwich beams by using a combination of rigid and flexible material components in the core structure, thus improving their absorption capacity and flexural behavior. The effects of flexible and rigid material layer arrangements and the percentage of flexible/rigid material in the core structures were investigated by using experimental and numerical methods. Three-point bending tests of fourteen different multi-material auxetic cores and two different single material core structures were carried out using flexible TPU and rigid PLA 3D printed layers. Then, the FE analysis was performed parametrically to reveal the effects of t/l ratios of the unit cell on the flexural behavior and energy absorption performance of the sandwich beams. Experimental studies shows that the TPPP, PTPT, and TTPT hybrid core arrangements exhibit greater energy absorption capacities (9.07 J, 9.61, and 9.60 J, respectively). The deformation mechanism of the flexible and rigid materials and inclined struts of the core structures play a key role in the flexural strength and energy absorption capacities. For example, the plastic deformation mechanism could be spread over a wider area to delay the localized fractures by reinforcing the rigid auxetic core with flexible material. Also, the strength and energy absorption could be increased when the bottom layer is made of rigid material. It is recommended to avoid using adjacent layers of the flexible material because they have lower flexural strength. The parametric analysis show that the energy absorption performance could be increased within the range of ~ 5 to ~ 20% when the t/l ratio decreases.

This paper proposes a bridge moving load identification method based on the fractional conjugate gradient (FCG) method to address the low identification accuracy of traditional conjugate gradient methods. Firstly, the mathematical framework for detecting the moving load in the vehicle-bridge system is established by utilizing both the time-domain deconvolution technique and modal superposition approach. Secondly, the derivation of the discrete moving load identification system matrix equation enables its formulation as an unconstrained optimization problem. Finally, the load information is obtained iteratively by the FCG method. Experimental results demonstrate that, compared with the Hestenes–Stiefel conjugate gradient (HSCG) method, the Flether–Reeves conjugate gradient (FRCG) method, and the Polak–Ribire–Polyak conjugate gradient (PRPCG) method, the FCG method has faster identification speed, smaller identification error, and higher identification accuracy and noise resistance in identifying bridge moving loads at different noise levels.

An experimental investigation was undertaken to study the shock structure and wall pressure distribution in a laboratory model of a scramjet combustor with a wall-mounted un-swept compression ramp. The ramp surface was provided with a V-groove and the semi-groove angle (SGA) was varied from 87.5° to 70° in the experiments. Some numerical simulations were also performed to study the possible enhancement of vorticity behind the ramp aft surface (RAS) as a result of the presence of V-groove on the ramp surface. A combustor inlet total pressure of 1000 kPa was maintained with air as medium for all the cold flow experiments in the present investigation. The laboratory model had a 50-mm long constant area section followed by a 150-mm long diverging section. A constant inclination of 2° to the bottom wall was made by the combustor top wall in the diverging section. A constant width of 25 mm throughout the length of the rectangular cross-sectional combustor was maintained. The entry Mach number to the combustor inlet (M_e) was 2.55. Schlieren images of shock structure in the internal flow and wall pressure (p_w) distributions were obtained from the experiments. A significant enhancement in vorticity in the symmetry plane immediately downstream of the un-swept ramp with surface V-groove (semi-groove angles between 70° and 80°) over the plain un-swept and swept ramp configurations (without groove) was observed from the numerical computations.

The detection beam is the carrier of the track irregularity detection system. The high-precision estimation of the detection beam’s roll angle is the key technology to improve the detection accuracy of the cross-level irregularity and other items. Nevertheless, the traditional complementary filtering method has the drawbacks of low model approximation and an ambiguous cut-off frequency. To solve the above problems, a measuring system is designed on the inclinometer and the gyroscope to realize the high-precision tracking estimation of the detection beam’s roll angle. The sensor error model and the angular motion model of the detection beam are combined to establish a large system model. Then a novel strong maneuvering nonlinear tracking algorithm (SMNT) for the detection beam’s roll angle is proposed. A multi-body dynamic model is created in Simpack to replicate the angular motion of the detection beam. The simulation data are superimposed on the sensor noise to the SMNT algorithm. The simulation results show that the SMNT algorithm is the best among the four algorithms by considering convergence speed, estimation error, and robustness. The SMNT algorithm converges after 25 m, the maximum root mean square error is 0.0029° and the maximum cross-level irregularity error is 0.1028 mm. This SMNT algorithm can provide support for improving the detection accuracy of track irregularity parameters.

Deterministic lateral displacement (DLD) is a microfluidic passive method for bioparticle separation and isolation, based on particle size and shape with high sample volume and low latency. Despite widespread application and research, experts report various fundamental, practical, and commercial challenges faced in the field of DLD represented in the literature. One of the fundamental challenges is the fluid’s flow behaviour and the fluid–structure interaction inside the DLD array. To address this problem, this paper investigates the modelling of a three-dimensional DLD array constructed by considering lateral displacements and wall boundaries. Nine different geometric shapes of the symmetrical pillars are reported in the literature opted for the study which are examined with different velocities to analyse how pillar shape impacts the flow patterns inside the DLD array. Also, an investigation of the two-way interaction between the fluid and the pillar structure is carried out. The response of the fluid due to the interaction with the pillar and the pillar response due to the interaction with the fluids is reported. Additionally, the realistic influence of the fluid flow and the surrounding pillars on the middle pillar in the array are examined in 3D simulations. The simulation was carried out using the finite element software COMSOL Multiphysics.

Graphical Abstract

Acoustoelasticity has been widely studied for stress measurements in metallic materials, such as steel and aluminum, mainly for structural health evaluation and monitoring. Applying it requires careful consideration of the influence factors on wave propagation, particularly temperature, texture and non-uniformities. However, for fiber composite materials, it is crucial to consider additional factors such as delamination and waviness of the fiber. Due to the thickness of structural composites parts, longitudinal critically refracted (L_CR) waves are one of the most suitable NDE methods to be used to measure stresses, especially because of the high sensitivity of its speed to strain. This paper focuses on evaluating the effects of the main influence factors, aiming to verify if it is possible to use L_CR wave to measure stresses in carbon-epoxy composites even in the presence of them. The factors are temperature, non-uniformities, delamination and waviness. Because these waves travel a fixed distance, the effects are measured on the wave time-of-flight. The results show that the magnitude of the influence is similar to manufacturing non-uniformities, as well as delamination and waviness. A standard deviation of 15 MPa (< 1% S_ut) is found for samples with and without defects when the stress-free reference time is taken in the same sample where the measurement is performed and about 62 MPa (< 4% S_ut) using a global reference time for this composite material.

The objective of this paper is to investigate the cavitation performance of the annular-slit rotational hydrodynamic cavitation reactor (ASRHCR) with emphasis on degradation characteristics of methylene blue (MB) by the ASRHCR. The transparent ASRHCR is utilized to carry out the experiments, the internal cavitating flow and pressure fluctuation of the ASRHCR are synchronously available using high-speed camera and pressure fluctuation testing technique. The independent effect of rotational speed, flow rate, inlet pressure and initial concentration of solution on the degradation of MB is evaluated in sequence. The experimental results indicate that the ASRHCR has sufficient head for transporting fluid medium. Three cavitation patterns are induced by the ASRHCR: separation cavitation, vortex cavitation and shear cavitation, where the shear cavitation is the main cavitation pattern and shows obviously quasi-periodic growth, shedding and collapse, which dominates the cavitation intensity and degradation of MB. The rotational speed, flow rate and inlet pressure significantly affect the cavitation patterns, resulting in different degradation characteristics of MB, the degradation rate of MB increases when the shedding frequency of shear cavitation is intensified. Furthermore, there is an optimal initial concentration of MB solution that helps achieve the best degradation performance of the ASRHCR. These findings provide valuable insight into the design of rotational hydrodynamic cavitation reactor.

This study explores the intricate dynamics of droplet impact on adjacent cylindrical surfaces. Utilizing the multiphase lattice Boltzmann method and the Allen-Cahn equation, the research delves into how various factors such as droplet size, velocity, surface wettability, and cylinder proximity influence the impact dynamics. It is found that increasing the distance between the cylinders enhances the penetration of the liquid phase and the maximum extent of the liquid ligament. As the distance between the cylinders increases from six to 20 lattice points, the length of the liquid ligament increases from one time the droplet radius to four times the droplet radius. The study also examines the impact of Reynolds and Weber numbers on droplet dynamics. A reduction in the Reynolds number diminishes the impact inertia, leading to a decrease in the initial length of the liquid ligament and the wetted surface area. Over time, however, the final length of the liquid between the cylinders and the wetted surface is higher for lower Reynolds number impacts due to less liquid separation from the cylinder surfaces. An increase in the Weber number, conversely, reduces surface tension effects relative to inertial force, causing more extensive spreading of the droplet on the cylinder surfaces and altering the movement of separated droplets postimpact. Furthermore, the study highlights the influence of surface wettability. As the contact angle increases, hydrophobic effects repel the liquid phase, resulting in more elongated droplets postimpact. The length of the liquid ligament has increased from 2.5 times the droplet radius at a 30°contact angle to four times the droplet radius at a 150°contact angle. At lower contact angles, the predominance of surface adhesion facilitates quicker equilibrium attainment, while higher contact angles lead to prolonged equilibrium due to oscillatory droplet behavior. These findings offer novel insights into the interactions between droplets and adjacent curved surfaces, with significant implications for optimizing industrial processes and developing new technologies in fields such as inkjet printing and spray coating.

Effective trajectory tracking control is a crucial assurance for the optimal vibration suppression results of trajectory optimization. Based on the dynamic model of the Delta robot, the trajectory tracking strategy of the Delta high-speed parallel robot was investigated to cater to the rapid response requirements during high-speed operations. In this study, a predefined-time non-singular terminal sliding mode controller is proposed, wherein the improved non-singular terminal sliding surface ensures that tracking errors converge to zero within a predefined timeframe. The Simulink model of the Delta high-speed parallel robot control system was constructed, and the tracking effect of the proposed predefined-time non-singular sliding mode controller is simulated and analyzed. The simulation results indicate that, compared to the fixed-time terminal sliding mode controller, the designed controller achieved tracking within a predefined time of 0.002 s, substantially enhancing tracking precision.

The ASTM A297/A297M-19 HP steel is a commonly used material in high-temperature structural components. In this study, researchers examined the effects of niobium modification on the mechanical properties of HP steel. The tests included hardness, tensile, creep, fatigue, and metallographic analysis. The heat treatment of aging at 927 ºC for 1000 h resulted in the precipitation of secondary carbides and G-phase presence. The aging caused intense precipitation in the interdendritic space, where the chromium carbides coalesced and became coarser. The aged specimens showed an increase in hardness by approximately 17%. The tensile tests showed an increase in mechanical resistance parameters and a decrease in total elongation. The Charpy impact tests presented lower values at 927 ºC. In the creep tests, the stress exponent showed a sharp decrease at the highest temperature of 1093 ºC. The fatigue crack propagation rate was higher at 927 ºC than at 25 ºC due to the material’s better ductility at high temperatures. In creep crack growth tests, a decrease in the crack growth rate was observed in the second stage. These experimental results are important for understanding the ability of the modified HP steel to withstand fatigue and creep mechanisms at elevated temperatures from a time-dependent fracture mechanics perspective.