Search Results (6)

This work investigates the impact of load-dump stress on p-GaN HEMTs under floating gate condition. The experiments show that preconditioning the device with a small load-dump stress (150 V, @t_d = 100 ms and t_r = 8 ms) enhances its robustness against a larger stress (190 V, @t_d = 100 ms and t_r = 8 ms). If a large load-dump stress (≥160 V, @t_d = 100 ms and t_r = 8 ms) is applied directly to the device’s drain, the device will burn out. This occurs because the rapidly changing drain voltage during a load-dump event can generate a capacitive coupling current, leading to transient positive charge accumulation in the gate region. Consequently, the channel under the gate is turned on, allowing a large current to flow through it. The coexistence of high current and high voltage leads to substantial Joule heating within the device, resulting in eventual burnout. When a small load-dump stress is initially applied, the resulting charging of electron traps in the gate region increases the threshold voltage. As a result, the device can withstand a larger load-dump stress before the channel turns on, which explains the device’s enhanced robustness. This work clarifies the failure threshold of p-GaN HEMTs under the load-dump stress, providing key support for improving the devices’ reliability in the practical applications. It can provide a basis for adding necessary protective measures in device circuit design, and clarify the triggering voltage threshold of protective measures to ensure that they can effectively avoid device damage due to the load-dump stress. Full article

The agricultural front-end loader is an implement attached to the front of tractors to transport various agricultural materials, including soil. Since they are subjected to various loads due to the working environment, their safety analysis in consideration of actual working conditions is required. However, there are no official standardized test codes to consider various actual working environments currently. In this study, the structural safety of a front-end loader for static and fatigue failures was evaluated using new test code reflecting actual working environments. Thirty-four measurement locations were determined as the stress concentration spots of each component of the front-end loader derived through multibody dynamic simulation. The total testing time was set to 1 h, and the test time for each task was determined considering the duty percentage of the actual loader work. The measurement results showed that the maximum stress that exceeds the material’s yield strength occurred at two locations of the mount, which is the connection to the tractor body, resulting in static yielding. For tasks, the pulling and dumping exhibited the highest stress. The task that had the largest impact on fatigue damage was the dumping. The static safety factor was found to be over 1.93 and the fatigue life met the required lifespan at all measurement locations except for those exhibiting static yielding. Therefore, the most vulnerable part of the front-end loader is the mount, and it is necessary to secure the overall structural integrity by robust design for the mount. Full article

The foundation of a large river crossing bridge is often located on high and steep slopes in mountainous area, and the stability of the slope has a significant impact on the safety of the bridge. Not only the bridge load, but also the hydro-dynamical action in the reservoir area has a significant impact on the stability of the bank slope where the bridge foundation is located, especially for the toppling bank slope. This paper takes the stability of the toppling bank slope where the one major bridge foundation is located at on the Lancang River in China as an example. Through on-site exploration, drilling data and core conditions, and television images of the borehole, the geological structure of the on-site bank slope were conducted. Based on the development of the dumping body obtained from on-site exploration, corresponding indicators have been proposed from the perspectives of rock inclination, deformation, and rock quality to clarify the degree of dumping along the depth of the bank slope. The failure mechanism of the overturned bank slope under the action of a bridge was analyzed from a mechanical perspective. Numerical simulations were conducted using GeoStudio 2018:SEEP/W and FLAC3D 6.0 software to analyze the failure modes of bridge loads and hydrodynamic forces under different water levels and rainfall conditions. The seepage field characteristics, failure modes, and stability characteristics were analyzed from a two-dimensional perspective, while the displacement characteristics, plastic zone, and stress–strain characteristics were explored from a three-dimensional perspective, which revealed the evolution mode of overturned deformation under the action of bridge foundation loads. Finally, the stability of the wide slope was numerically calculated using the strength reduction method, and the stability calculation data was combined with the numerical simulation results to determine the optimal location of the bridge foundation. Full article

This research deals with determination of the loading of an open container during operating modes. The special feature of this container is its convex walls. This engineering solution increases the useful capacity of a container by 8% in comparison to that of the prototype. The elastic elements in the bearing structure of a container were introduced to decrease the dynamic loads. The dynamic loads in the vertical plane were dumped by means of the dry friction forces between the components of the cross bearers of the container’s base. The dynamic loads in the longitudinal plane were dumped by means of the dry friction forces between the horizontal parts of fittings and fixed lashing components. This study presents the modelling of the dynamic loading of a container in a vertical plane. The dynamic loads of a container in the longitudinal plane were determined with a mathematical model. The authors determined the basic strength characteristics of the bearing structure of a container; and found that the maximum stresses to a container were about 200 MPa, concentrated near the front fittings. The maximum displacements were recorded in the cross bearers of the base and amounted to about 4 mm. Full article

In the Pacific Northwest, forest roads have the potential to cause significant environmental degradation, especially to water resources due to increased sediment production. The goal of this research is to improve the understanding of road degradation during hauling by improving our understanding of the aggregate degradation process. We correlate the wear rates to standard material property tests that may allow for improved prediction of the impacts from forest roads based on the selection of aggregate surfacing. Finally, we determine the changes in stress distribution between the subgrade and aggregate interface. High-, medium-, and low-quality aggregates were used from three quarries in western Oregon for this project. These aggregates are indicative of the range of materials used on forest roads in the region. Two material property tests, namely the Los Angeles (LA) abrasion and micro-Deval tests, were used to determine their ability to predict aggregate performance during hauling by relating values for aggregate wear to these aggregate properties. Eighteen nonwoven geotextile bags were created, measuring 60 cm (two-feet long) and 20 cm (eight inches) in diameter, with a pore size equivalent to a 0.149 mm (# 100) sieve. They were filled with a known quantity and particle size distribution of aggregate and embedded into a newly constructed forest road. Stress gages were installed in the road surface between the aggregate and subgrade levels to record the changes in stress at the subgrade level. Samples were subjected to three levels of traffic (500, 950, and 1500 passes) using a loaded dump-truck that had a steering axle and one tandem drive axle, weighing 25,038 kg or 55,200 lb. The results showed that less breakage occurred with the medium- and high-quality aggregates than the low-quality aggregate. There was a correlation between the material property test (either the micro-Deval or the LA abrasion test) and the fine index, indicating the predictability of these tests in terms of aggregate performance. Finally, the higher quality aggregate was able to better distribute the stresses from the wheel better than the lower quality aggregate and was able to reduce the stress reaching the subgrade. Although the results are limited to the three types of rock used in this study, they indicate the ability of the high-quality aggregate to lessen the environmental impacts from forest roads. Full article

With respect to heavy carrying tasks and uneven road surface in open pit mine, the mechanical performances of electric wheel dump truck frame regarded as the main bearing component are extremely important for its safe operation. For the problem of insufficient strength and stiffness, an interval multi-objectives optimization design method based on blind number theory is presented in this paper, taking into account uncertain factors caused by manufacturing process. The allowable interval strength of welding material and permissible interval bending and torsional stiffness are obtained by means of experiments and simulations, using the blind number theory. Based on Latin hypercube sampling technique, the strength and stiffness of frame under different conditions is estimated. It shows that in the case of braking interference between interval strength and interval dynamic stress appears. Strength and stiffness are considered as optimization objectives, while the thicknesses of top longitudinal beam, stiffener, lateral longitudinal beam and hanging ear in the frame are deeded as design variables, and Young’s modulus and Poisson’s ratio are taken as uncertain variables. The optimized results show that the stress and deformation of the frame due to dynamic loading decreased. This result enables to formulate the following sentence: the mechanical performance of frame is improved. Full article