Development and validation of vehicle wheel load scaling method for formation of durability testing loading cycle

For a vehicle durability study, performed with simulation or laboratory testing, impact on the object should be described as set of time-domain load signals, which reflects accelerated service modes of a vehicle operation. For a newly developed vehicle these load signals can be based on previously prepared loading cycle of a similar vehicle with use of the load scaling theory. Importance and certainty of the load scaling theory is approved by active use among foreign car makers and engineering centers. However, mathematical description of the theory and scaling procedure are strictly classified, despite of being based on fundamentals of vehicle dynamics. In this paper the method of scaling of time-domain wheel and driveline loads is suggested; the method is based on proportions of size and mass properties of the original and the new vehicles. Assumed that previously recorded loading cycle corresponds to the service life of a vehicle. It is worth noting that level of loading and damage accumulation, shown with scaled loading cycle and after first prototypes testing on a proving ground, will be different because of impact of chassis stiffness and damping properties. Suggested scaling theory is being studied in FSUE “NAMI” and is on the validation and verification stage. First completed experiments showed that a multiaxial test rig could perform the vehicle suspension loading cycle, obtained with the theory, with a satisfactory accuracy. This makes utilization of the theory limited to early stages of vehicle development.

Continuous Control of an Underground Loader Using Deep Reinforcement Learning

The reinforcement learning control of an underground loader was investigated in a simulated environment by using a multi-agent deep neural network approach. At the start of each loading cycle, one agent selects the dig position from a depth camera image of a pile of fragmented rock. A second agent is responsible for continuous control of the vehicle, with the goal of filling the bucket at the selected loading point while avoiding collisions, getting stuck, or losing ground traction. This relies on motion and force sensors, as well as on a camera and lidar. Using a soft actor–critic algorithm, the agents learn policies for efficient bucket filling over many subsequent loading cycles, with a clear ability to adapt to the changing environment. The best results—on average, 75% of the max capacity—were obtained when including a penalty for energy usage in the reward.

Measurement of moment coupling in fretting fatigue experiments

Moment coupling in fretting fatigue experiments refers to the generation of moments when a shear force is applied, caused by the difficulty in designing fretting fatigue experiments where the shear is reacted out on the same plane as the contact. Digital Image Correlation is used to measure the effect of moment coupling, and a model is created to calculate the effect of the applied moment at any point during a loading cycle on near-edge contact properties. The effects of the changing contact pressure on the slip zone sizes are considered. Finally, the model derived is used to find a load cycle including the effect of normal contact force that creates a truly constant near-edge contact pressure distribution at one edge of the flat and rounded pad. Although the calibrations found in this paper are valid only for the specific rig and specimen geometry used in this paper, the method could be readily applied to other experiments.

Performance analysis of hydrodynamic mechanical power-split transmissions

The objective of this study was to evaluate the performance of 24 basic hydrodynamic mechanical power-split (HMPS) transmission designs effectively based on their torque multiplication capacities (TMCs) and efficiencies. Firstly, four schemes were preliminarily selected. Secondly, the matching between the four schemes and a reference wheel loader was considered, and an expression for the TMC was developed based on the traditional transmission and a second reference transmission. Thirdly, two performance metrics in terms of the TMC and efficiency – the average torque multiplication capacity (ATMC) and average efficiency – were defined to eliminate the couplings of four transmission parameters with the vehicle speed and speed ratio. Finally, the performances of the two best schemes and traditional hydrodynamic mechanical (HM) transmission were carefully compared. The results show that a transmission with power recirculation cannot present energy savings potential regardless of the ATMC, whereas a transmission with a power split can achieve an ATMC of 0.255, an average efficiency increment of 0.0143 in the short loading cycle, and a miniscule efficiency increment in the long loading cycle compared with the HM transmission.

Fatigue Performance of Rubber Concrete in Hygrothermal Environment

It is widely accepted that the rubber concrete (RC) originating from waste is a promising material that can contribute to the conservation and rational use of natural resources and the protection of the environment. However, the fatigue performance in a hygrothermal environment is a major concern because little pertinent information is available in the relevant literature. In this study, a cyclic loading test was carried out on RC subjected to different wet-dry cycles at different temperatures. The loading strain, plastic strain, and elastic strain of the concrete were compared and analyzed. The results revealed that the loading strain and plastic strain of the RC were obvious after the 1st loading cycle. As the number of loading cycles increased, the stress-strain curve became denser and the RC exhibited good elasticity. As the wet-dry cycles increased, the average plastic strain in the 10th–60th loading cycle increased while the elastic strain decreased. After 28 wet-dry cycles, the average plastic strain at 60°C increased by 42.31% compared with 20°C. In fact, as the temperature became higher, the plastic damage incurred by the RC became more severe. Finally, the damage variable was defined based on the elastic modulus and plastic strain to evaluate the fatigue performance of the RC in a hygrothermal environment. The findings of this study can provide a useful reference for RC applications.

The impact of transverse components on resistance and ultimate strength of 6-strand tendon repairs

We assessed the effects of tendon core sutures' transverse components on the tensile resistance of two commonly used 6-strand tendon repairs. Tang and Yoshizu #1 repairs (6-strand) were tested and compared with 4-strand rectangular and double Kessler sutures (4-strand). A total of 40 pig flexor tendons were tested under cyclic loading. We recorded the number of tendons that formed a 2-mm gap between two tendon ends during 20 cycles of cyclic loading test, stiffness at the 1st and 20th loading cycle, and gap distance at the repair site and the ultimate repair strength at the 20th cycles. We found that the Yoshizu #1 repairs were more prone to form gaps and their ultimate strength was significantly lower than that of the Tang repair. The transverse components in a 6-strand repair affect gap formation and failure strength.

Investigation of Low-Cycle Fatigue on Structural Carbon Steel

It is possible to explain the phenomenon of fatigue destruction and the patterns that are observed only in the deep study of the processes taking place in the material under conditions of repeated-variable loading, i.e. in the development of the physical theory of metal fatigue. Despite the large number of work on this issue, there is currently no single interpretation of the process of fatigue destruction of metals, which is primarily due to the exceptional complexity of the problem. The purpose of the study is to study low-cycle corrosion fatigue of steel using the example of A 414 Grade A steel. The work solved problems, such as research of kinetics of crack development in conditions of low-cycle loading of metal structure made of carbon structural steel A 414 Grade A. Regression analysis has also been applied to predict a change in the thermodynamic stability of the metal during cyclic loading. Analysis of fatigue crack development at alternating loading cycle was carried out. The results of calculations based on the proposed model of elastoplastic deformation near the top of the crack at the sign-alternating loading cycle can be described by non-linear dependence. The regression analysis revealed that the correlation coefficient of the selected model is-0.93, which indicates a relatively strong relationship between the variables. In experimental way it has been proved that reduction of thermodynamic stability of metal in corrosive medium is connected with increase of number of loading cycles, which leads to accumulation of fatigue damages.