Search Results (26)

Shear slip along structural planes in jointed rock masses is the primary trigger for rock slope instability, threatening geotechnical engineering safety. Direct shear tests were conducted on prefabricated granite specimens with regular sawtooth structural planes (undulation angles: 15°, 30°, 45°; tooth spacing: 10 mm) under 2, 4 and 6 MPa normal stresses, with synchronous acquisition of acoustic emission (AE) and infrasonic signals to explore shear failure characteristics, acoustic spectral features and instability precursors. Results show (1) peak shear stress and stiffness rise significantly with increasing undulation angle and normal stress, and failure modes evolve from sliding friction-dominated to asperity shearing-dominated, finally to composite asperity shearing and compressive crushing. (2) The spectral characteristics of both acoustic emission (AE) and infrasonic signals are closely related to the shear fracture mechanism. (3) Approaching peak shear stress, dominant frequency ratio correlation dimension drops to a minimum and the ib-value rises to a pre-sudden-drop critical point; higher undulation angles align these values with stress closer to the peak, valid as instability precursors. (4) A two-level early warning model (early to imminent warning) is proposed via cross-frequency band AE-infrasonic monitoring, providing a fundamental basis for rock slope stability monitoring using these signals. Full article

In response to the practical demands of high rate, long distance, low cost and miniaturized equipment for underwater wireless communication, an underwater wireless optical communication experimental system with Fresnel lenses as optical receiving antennas has been established. Using 488 nm and 520 nm lasers as the test light sources, the relationship curves between the focusing performance of several Fresnel lenses with different light transmission aperisions and focal lengths after passing through the underwater channel and the lens surface, laser wavelength, and incident angle were obtained. The influence of the laser incident angle on the focusing spots of 488 nm and 520 nm lasers was measured. The experimental results indicate that the Fresnel lens exhibits excellent light concentration performance, with the overall system concentration efficiency being higher than that of conventional lenses, significantly enhancing the received optical power in underwater wireless optical communication systems. Additionally, configuring the sawtooth surface as the incident surface of the Fresnel lens can improve the concentration efficiency by approximately 1% to 5% compared to using a smooth incident surface. Full article

Burrs generated during the drilling of carbon fiber-reinforced plastics (CFRPs) would seriously reduce the service life of the components, potentially leading to assembly errors and part rejection. To solve this issue, this paper proposed a finite element (FE) model with multiscale modeling to investigate the formation and distribution of burrs at various processing conditions. The FE model comprised the microscopic fiber and resin phases to predict the formation process of burrs, while part of the CFRP layers was defined to be macroscopic equivalent homogeneous material (EHM) to improve the computational efficiency. A progressive damage constitutive model was proposed to simulate the different failure modes and damage propagation of fibers. The impact of strain rate on the mechanical properties of the resin and CFRP layers was considered during the formulation of their constitutive models. With this numerical model, the formation process of the burrs and the drilling thrust force were accurately predicted compared to the experimental measurements. Then, the burr distributions were analyzed, and the influences of the drill bit structures and drilling parameters on burrs were assessed. It was concluded that the burrs were easily generated in the zones with 0° to 90° fiber cutting angles at the drilling exit. The sawtooth structure could exert an upward cutting effect on burrs during the downward feed of the tool; thus, it is helpful for the inhibition of burrs. More burrs were produced with higher feed rates and reduced spindle speeds. Full article

After rolling, TP2 copper tubes exhibit defects such as sawtooth marks, cracks, and uneven wall thickness after joint drawing, which severely affects the quality of the finished copper tubes. To study the effect of drawing process parameters on wall thickness uniformity, an ultrasonic detection platform for measuring the wall thickness of rolled copper tubes was constructed to verify the accuracy of the experimental equipment. Using the detected data, a finite element model of drawn copper tubes was established, and numerical simulation studies were conducted to analyze the influence of parameters such as outer die taper angle, drawing speed, and friction coefficient on drawing force, maximum temperature, average wall thickness, and wall thickness uniformity. To address the problem of the large number of finite element model meshes and low solution efficiency, the wall thickness uniformity was predicted using a radial basis function (RBF) neural network, and parameter optimization was performed using the particle swarm optimization (PSO) algorithm. The research results show that the RBF neural network can accurately predict wall thickness uniformity, and using the PSO optimization algorithm, the best parameter combination can reduce the wall thickness uniformity after drawing in finite element simulation. Full article

Blazed gratings are periodic surface structures of great interest for applications such as friction control, light trapping, and spectrometry. While different laser processing methods have been explored to produce these elements, they have not yet surpassed conventional surface manufacturing techniques, often based on lithography processes or mechanical ruling. This work introduces a new approach based on the combination of ultrashort pulses and triangular beam shaping, which enables the generation of asymmetrical grooves in a single step. The main advantage of this strategy is that by simply changing the laser processing direction we can induce a significant modification in the ratio of asymmetry between the sidewall angles of the machined channels. The paper includes a comprehensive study, which has been supported by statistical tools, of the effect of this and other experimental parameters on the morphology of grooves machined on stainless steel. As a result, we achieved a wide range of geometries, with asymmetry ratios spanning from 1 to 5 and channel depths between 3 and 15 µm. Furthermore, we demonstrate the validity of the approach through the successful manufacture of blazed gratings of various slopes. The results reflect the versatility and cost-efficiency of the proposed fabrication strategy, and thus its potential to streamline the production of sawtooth gratings and other devices that are based on asymmetrical features. Full article

A “random-type” sand–concrete interface shear test was developed based on the sand cone method, with a focus on the most commonly encountered triangular contact surface morphology. A “regular-type” triangular interface, matched in roughness to the “random-type”, was meticulously designed. This “regular-type” interface features five distinct triangular groove inclinations: 18°, 33°, 50°, 70°, and 90°. A series of sand–concrete interface direct shear tests were conducted under consistent compaction conditions to investigate the impact of varying compaction densities and triangular groove inclinations on the shear strength at the interface. Particle flow simulations were utilized to examine the morphology of the shear band and the characteristics of particle migration influenced by the triangular contact surface. This analysis is aimed at elucidating the influence of the inclination of the triangular groove on the shear failure mechanism at the sand–concrete interface. The findings indicate that: (1) The morphology of the interface significantly impacts the shear strength of the sand–concrete interface, while the shape of the stress-displacement curve experiences minimal alteration. (2) At smaller inclination angles, particle contact forces are arranged in a wave-like configuration around the sawtooth tip, resulting in a non-uniform stress distribution along the sawtooth slope. However, as the inclination angle grows, the stress concentration at the sawtooth tip diminishes, and the stress distribution across the sawtooth slope becomes more consistent. (3) Particle migration is significantly influenced by the sawtooth’s inclination angle. At lower angles, particles climb the structure’s tip through sliding and rolling. As the angle increases, particle motion shifts to shear, accompanied by a transition in friction from surface friction to internal shear friction. This leads to the formation of a wider shear band and an increase in shear strength. Full article

A microwave photonic Doppler frequency shift (DFS) and angle of arrival (AOA) measurement method based on a dual-parallel dual-drive Mach–Zehnder modulator (DP-DDMZM) is proposed and demonstrated. A sawtooth wave signal is used to drive the DC port of the modulator to realize the optical frequency shift, and thus the direction discrimination of DFS is realized. Due to single-sideband modulation, the proposed system can avoid periodic power fading and the separation of the remote antenna unit (RAU) and central office (CO) can be achieved. In the experiment, the microwave DFS is estimated with a clear direction and a maximum measurement error of 0.25 Hz over an ultrawide operation frequency from 6 to 36 GHz. The experiment also proves that the phase error of AOA measurement is less than 1.5 degrees. Compared with the traditional electronic microwave measurement scheme, the proposed scheme has great competitive advantages in future broadband electronic applications due to the features of multifunction, large bandwidth and anti-interference. Full article

In a reservoir area, landslides can generate waves that pose a significant threat to bridge piers, endangering both property and human safety. This study utilized three-dimensional water tank experiments to simulate the generation of landslide-induced waves and their impact on bridge piers located on both riverbanks. The analysis focused on the types and distribution patterns of wave pressures on bridge piers. The results reveal the following key findings: (1) The results show that the wave pressures on the piers can be classified into two types: Pulsating pressure ($P_{pu}$) and Resonance pressure ($P_{re}$). $P_{pu}$ represents the pressure generated during the wave action process. $P_{pu}$ closely corresponds to the wave height-time process, with frequencies ranging from 0.2 to 0.5 Hz. $P_{re}$ occurs prior to $P_{pu}$. $P_{re}$ represents high-frequency vibrational waves generated when bridge piers resonate during wave action. $P_{re}$ is observed primarily in deep water conditions and on the opposite riverbank, with frequencies ranging from 300 to 900 Hz. (2) On the bridge piers of the opposite riverbank, $P_{pu}$ exhibits a nearly vertical distribution along the water depth, while on the same side, $P_{pu}$ exhibits a sawtooth-like decrease along the water depth. $P_{pu}$ increases with greater landslide volume and steeper landslide angles, and the maximum wave pressure distribution occurs near the water surface. (3) The distribution of $P_{re}/P_{pu}$ along the water depth exhibits three forms: multiple-peak, single-peak, and no-peak, with the maximum positions for all conditions of $P_{re}/P_{pu}$ occurring at approximately one-third of the water depth from the surface ($Y/h=0.3$). Finally, predictive formulas for the maximum wave pressures are provided. Full article

Accurate oscillating saw tool calibration is an important task for mandibular osteotomy robots to perform precise cutting operations. However, in contrast to traditional tool calibration which just calibrates the tool center position (TCP) or the tool feed axis, both the position and the plane orientation of the saw should be carefully calibrated. Therefore, aiming at this problem, in this paper, we propose a method to carry out oscillating saw calibration by employing an optical stereo vision tracking system. At first, hand–eye calibration is conducted to ascertain the spatial pose of the vision frame within the manipulator’s base frame. Subsequently, employing a probe, the positions of the sawtooth points on the oscillating saw plane are captured within the vision frame. These positions are then translated to the manipulator’s end-effector frame using the positional elimination algorithm proposed in this paper. Finally, the pose of the oscillating saw plane within the manipulator’s end-effector frame is extrapolated from the positions of the three sawtooth points. The result shows that the position errors of the points on the oscillating saw plane are within 0.25 mm and the variance of the plane normal direction is $1.{93}^{\circ }$ in the five experiments. This approach enables accurate calibration of the oscillating saw plane’s position and orientation within the manipulator’s end-effector frame. Furthermore, it mitigates the necessity of continual adjustments to the joint angles of the manipulator as required by the “six-point method”. However, this approach is hinged upon the availability of precision-oriented 3D positioning equipment. Full article

This study focuses on the crucial role of the shear characteristics of the mortar–rock interface (MRI) in geotechnical engineering. These properties largely determine the effectiveness of engineering reinforcement measures such as anchoring and grouting. The mechanical and deformation properties of the MRI with different roughness characteristics will be investigated. To achieve this, an indoor direct shear test was conducted on the mortar–rock binary medium (MRBM). The interface was numerically modeled from the test data using finite difference fractional value software. Direct shear simulation of the MRI by changing the normal stress (σ_n) and the sawtooth angle (α) was carried out. The results showed that as the normal stress and sawtooth angle increased, the shear stiffness of the MRI also increased. The shear stiffness was found to have a linear relationship with both the normal stress and the sawtooth angle. The peak shear displacement was identified as an indirect indicator of the shear failure mode of the binary medium interface (BMI). Quantitative relationships between the shear strength (τ), cohesion (c), angle of internal friction (ϕ), residual shear strength (τ_r), residual angle of internal friction (ϕ_r ), and degradation rate of the shear strength of the BMI were established based on the two influencing factors. Additionally, the study investigates how the sawtooth angle and the normal stress affect the variation in the normal displacement during direct shear testing of the MRBM. The findings revealed a correlation between the peak dilation angle of the BMI and the normal stress and sawtooth angle. Full article

An optimized scheme can improve the navigation accuracy of RINS without changing the inertial devices. In the multi-position stop scheme, the IMU remains stationary for most of the time, which makes motor control easier. However, the installation errors and the scale factor errors of FOG can cause platform misalignment after a certain angle of rotation around the horizontal axis, resulting in a velocity error. Continuous rotation can suppress time-varying errors better, which is of particular importance for FOG, but it can also increase the sawtooth error of the navigation output, and the error in the direction of rotation cannot be offset. To integrate the advantages of both rotation schemes, we propose an improved rotational modulation scheme for tri-axis RINS. In this scheme, the inner gimbal rotates in a two-position and four-order manner, while the middle and outer gimbals rotate continuously in the order of forward-reverse-reverse-forward. Simulation and navigation test results demonstrate that this improved rotational modulation scheme can effectively improve navigation accuracy by 50% and 25% compared with continuous rotation around the azimuth axis and a 16-position scheme with the same inertial devices, which is of great importance for RINS with FOG. Full article

In this study, novel recommendations are presented and substantiated for selecting the number of modes and optical thicknesses of flat lattice slabs that make up microreliefs, which minimize the computational complexity of the rigorous coupled-wave analysis calculation of the diffraction efficiency (DE) of a sawtooth two-layer two-relief microstructure, while maintaining the specified reliability of the calculation results. The computational complexity can be controlled by allowing one or another level of oscillation of the DE curves, depending on the angle of incidence of the radiation incident on the microstructure. In particular, the complexity of the thousands of DE calculations in the optimization process can be reduced by using the proposed methodology as well as increased computational complexity to verify the accuracy of the solution obtained as a result of the implemented optimization. Full article

The influence of the improvement of the finned tube radiator unit structure on the fluid flow and heat transfer effect of the locomotive was studied. A saw-toothed fin structure with aluminum instead of copper was proposed to keep the position and size of the flat copper hot water pipe unchanged. CFD simulation analysis was carried out by ICEPAK17.0, under the conditions of an ambient temperature of 24.6 °C, atmospheric pressure of 85,040 Pa and air density ρ = 0.94 kg/m³, to compare the changes of velocity field, temperature field, turbulence field and field synergy angle. The sawtooth structure of the new heat sink increases the turbulence effect of the fluid, reduces the thickness of the outer boundary layer of the water pipe, and strengthens the heat transfer effect of the radiator. Finally, the baffle height, wing window width and sawtooth angle of the sawtooth structure were selected, and the heat transfer coefficient and pressure under three conditions of low, medium and high were used as indexes to analyze the influence of each parameter on the performance of the radiator. The results show that the heat dissipation effect of the serrated aluminum sheet is higher than that of the copper sheet, the heat transfer coefficient is increased by about 1.3%, the average pressure is reduced, the turbulence performance is improved, the synergy angle is reduced by about 2.3°, and the new radiator has better performance. The fin factor has the greatest influence on the heat transfer coefficient and the least influence on the pressure. When the baffle is about 0.15 mm high, the heat transfer coefficient is the largest, and the height change has the highest effect on the pressure. The included Angle factor has the least influence on the heat transfer effect, and the influence on the pressure is higher. By changing the fin window structure, the thermal performance of the finned tube radiator can be improved. Full article

To analyze the shear characteristics and mesoscopic failure mechanism of irregular serrated rock discontinuities, a great deal of interview samples of irregular serrated structures were made by 3D printing technology, and laboratory shear tests were carried out on them under different normal stresses. At the same time, PFC numerical simulation software is used to establish relevant models to study the evolution of microcracks and the distribution characteristics of the force chain on the rock discontinuity during the shear process. The results show that the shear mechanical properties of irregular serrated rock discontinuities are affected by normal stress, undulating angle, and undulating height. The shear strength increases with the increase of normal stress and undulating height, and decreases with the increase of undulating angle. The numerical simulation results show that the irregular structural surface cracks under different undulation angles, which first start at the near force end serration root on both sides and further evolve to the adjacent serrations, while the irregular structural surface cracks under different undulation heights, which first start at the serration root with the lowest height and expand to the adjacent serrations. At the same time, the number of cracks increases with the increase of normal stress and the force chain is mainly distributed near the sawtooth surface. The force chain is more concentrated near the near force end sawtooth and at the tip and root of the rest of the sawtooth. At the same time, the direction of the force chain is approximately perpendicular to the force surface of the sawtooth. The research results are helpful in further understanding the shear mechanical properties and differences of irregular serrated rock discontinuities. Full article

The implementation of magnesium alloys in a multitude of industries has been proven to be a mere effect of their attractive light weight, corrosion resistant, and biodegradable properties. These traits allow these materials to portray an excellent sustainable machinability. However, with increasing demand, it is essential to explore sustainable means of increasing production while mitigating reductions in sustainability. The current work aims to assess and optimize the high-speed machinability of AZ91 with the use of a vegetable oil-based minimum quantity lubrication (MQL) system using the grey relational analysis (GRA) on the basis of chip morphology and tool wear. The investigation entailed a full factorial design with MQL flow rate, cutting speed, and feed rate as the control parameters and flank wear, land width, chip contact length, saw-tooth pitch, chip segmentation ratio, chip compression ratio, and shear angle as the output responses. The optimal control parameters predicted and experimentally confirmed were an MQL flow rate of 40 mL/h, cutting speed of 300 m/min, and feed rate of 0.3 mm/rev. The usage of said optimal parameters results in a grey relational grade improvement of 0.2675 in comparison to the referenced first experimental run. Moreover, the MQL flow rate was regarded as the critical variable with a contribution percentage of 20% for the grey relational grade. Full article