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ABSTRACT This study aims to investigate the influence of moisture contents and grouser heights on traction force exerted on different surfaces in the track-soil interaction system. A sandy loam was employed for acquiring the soil parameters, such as kc, kφ, n, C, Ca, δ, φ, and γ. These parameters were obtained through the mean of the bevameter technique. Moisture contents of the sandy loam were changed from low to high levels, which could be listed as 1.4%, 8.0%, 14.7%, and 22.2% at last. The direct shear and penetration tests were performed for each soil condition of the moisture content, respectively. The model of the single-grouser-shoe (track model) had a length of 9 cm, a width of 15 cm, and varied grouser heights from 0 to 15 cm with a 0.5 cm interval. Based on the calculation result, in general, the shearing force produced by the bottom surface always performs better than either the shear force on the grouser-tip surface or two lateral surfaces. Simultaneously, prediction results also show that the shearing forces were significantly influenced by the level of moisture content in the soil.

The wind turbine blade is the core component of the wind turbine. However, wind turbine blades will suffer fatigue and internal crack defects, which seriously affect the safety service performance in harsh environments. The current detection mode is mainly traditional manual detection and shutdown maintenance, with high risk and low efficiency. Therefore, this research proposed a method to conduct a non-stop online inspection of the wind turbine blade’s internal defects using ultrasonic inspection mounted unmanned aerial vehicle. As the vital component of this inspection system, the optimized design of the negative pressure adsorption car was carried out. The structural characteristics of the negative pressure adsorption car were determined experimentally, followed by multivariate analysis and an integrated development and performance test study of the test system. Based on the test results, the detection rate of this test system for internal wind power blade faults is 100%. This research offers novel concepts of and theoretical insights into the intelligent and security identification of internal flaws in wind turbine blades.

ABSTRACT Aiming at the low mechanization of paddy field weeding and lack of dedicated agricultural machinery for paddy field weeding in China, a self-propelled system of paddy field weeding machine was designed. The overall structure and working principle of self-propelled system were illustrated and analyzed. The interaction mechanism of wheel-soil during weeding was analyzed. The wheel-soil interaction model was established, then, wheel traction and surface flatness were selected as the evaluation indexes for discrete element simulation experiment. The steering performance, stability, and over ridge ability of self-propelled system were analyzed, and field experiment was carried out. The simulation experiment results show that the wheel traction is approximately 600 N and the surface flatness is less than 30 mm. The field experiment results show that the minimum turning radius of the prototype is 2,050 mm in paddy, overturning limit angle of the prototype is 36°, and maximum height over the ridge is 400 mm. The speed range of the weeding machine on the road and weeding operation was 0~16.20 km/h and the 0~5.40 km/h respectively. The weeder can meet the speed demands of weeding operation. The study results can provide reference for research and development of paddy field operation machinery.

Bone fracture is an extremely dangerous health risk to human. Actually, cortical bone is often subjected to the complicated loading patterns. The mechanical properties and deformation mechanism under the complicated loading pattern could provide a more precise understanding for the bone fracture. For this purpose, the mechanical response and multi-scale deformation mechanism of cortical bone material were investigated by in-situ experimental research using the compression-torsion coupling loads as an example. It was found that the torsion strength and shear modulus all decreased under the compression-torsion coupling loads than single torsion load. This indicated bone would suffer greater risk of fracture under the compression-torsion coupling loads. Based on in-situ observation, it was found that the rapid reduction of the anisotropy of bone material under the compression load was the potential influencing factor. Because of the redistribution of the principal strain and the variations of cracks propagation, the comprehensive fracture pattern containing both transverse and longitudinal fracture was shown under the coupling loads, and finally resulted in the reduction of the torsion properties. This research could provide new references for researches on mechanical properties of cortical bone material under complicated loading patterns.

The design and performance of tillage components such as subsoiler are generally characterized by the fracture features of soil mass in agricultural engineering, thus making the improvements of those tillage tools challenging due to the fact that the soil fracture mechanisms cannot be accurately explored and implemented. To alleviate this issue, in this paper, a physical three-point bending (TPB) test is conducted for investigating the fractural and fragmental characteristics of the compacted clay beams (CCB) with offset notches under the framework of mixed-mode I + II fracture, and the crack initiation as well as its propagation of the CCB is observed and fractural mechanisms of the CCB are discussed. Meanwhile, numerical simulation is also conducted utilizing two finite element methods, i.e., the extended finite element method (XFEM) and the combined finite-discrete element method (FDEM), for the CCB under three typical scenarios with notch offset ratios C = 0, C = 0.375, and C = 0.625, respectively. The authenticity and availability of both experimental test and numerical simulation are validated correspondingly. Results indicate the following: (1) The average peak load, the distance between the terminal crack point and the center line of the CCB, and the average displacement will be increased with increases of the offset ratio, while initial crack angle will be decreased with increases of the offset ratio. (2) The initial crack will be extended from the bottom center of the CCB rather than the offset notch when the offset ratio is higher than 0.717. (3) The crack propagation and its mechanical properties (e.g., load-displacement curves) predicted by numerical simulation match well with those obtained from the physical test.

Sandy clay loam has the characteristics of both sand and clay. Because of these characteristics, both frictional resistance and adhesive resistance occur between the soil and tillage tool. The combined effect of the two frictional forces increases the external friction angle between the soil and tillage tool, thus increasing the working resistance. To address this issue, this study investigated the coupling effect of high pressure and hot air on the external friction angle by using a self-developed device to measure the external friction angle. Test results showed that high-pressure air between the soil and tillage tool formed a high-pressure air curtain layer which acted as a lubricant, thereby reducing the external friction angle. The external friction angle decreased as the airflow pressure increased. The reduction in the moisture content of the subsoil to less than 30% by the high-pressure hot air reduced the resistance between the soil and tillage tool. The approach with the high-pressure hot air curtain was verified in tests on a subsoiling shovel; the working resistance of the shovel under high-pressure hot air was reduced by 14.8%, demonstrating that this approach was effective in reducing the working resistance of the shovel.

Objective service load is the load pattern of cortical bone in practical conditions. The objective service load conditions of cortical bone are complicated, usually including two or more load patterns. The mechanical behavior and deformation mechanism of cortical bone material under coupling load pattern and single load pattern are diametrically different. However, nowadays, researches on the mechanical response of cortical bone have been heavily focused on the single load pattern, which couldn’t reveal the potential deformation mechanism accurately. For the purpose of obtaining the objective mechanical properties under complicated loading patterns, the mechanical response and deformation mechanism of bone material under compression-bending coupling load were investigated by in-situ test. The research shows that bending strength increased under the compression-bending coupling load than the single bending load. By in-situ observation, the variations of surface strain distribution and cracks directions were the potential reasons for the increase of the bending strength. It was found that the cracks changed from transverse fracture to integrated patterns with transverse fracture and longitudinal fracture. Larger fracture range and tortuous crack propagation increased the fracture energy dissipation, which led to an enlarged bending strength under the compression-bending coupling load. Through theoretical analysis and numerical calculation, the impeded effect to the increasing of bending deflection was dominant before the final fracture with the adding of the compression load. The numerical calculation result was consistent with the result of the experiment. This present work would provide new references to further studies on the mechanical behavior of cortical bone under complicated loading patterns.

The objective of this study is to clarify the differences of tractive performances generated by the sandy loam-grouser system and the clay soil-grouser system. The tractive performances of the grouser/track shoes are widely researched by previous researchers. However, it is essential to illustrate the influences of the soil properties on the tractive performances of the grouser shoe. Sandy loam and clay soil were used as the test soils for investigating soil parameters in this study. Moisture contents of soil were from 7.5% to 27%, dry basis. Parameters of sandy loam were obtained through direct shear tests, penetration tests, bulk density, and moisture content measurements in laboratory. The grouser shoe was made of steel. Based on the prediction result of tractive performances, the clay soil will always be performed better than the sandy loam no matter which dimension was chosen for single grouser shoe. Based on the experimental results, the grouser height of the track should be 5 cm in order to provide enough traction force, if a tracked vehicle is operated on the environment of either clay soil or sandy loam.

The development of high-speed camera systems and image processing techniques has promoted the use of vision-based methods as a practical alternative for the analysis of non-contact structural dynamic responses. In this study, a deviation extraction method is introduced to obtain deviation signals from structural idealized edge profiles. Given that the deviation temporal variations can reflect the structural vibration characteristics, a method based on singular-value decomposition (SVD) is proposed to extract valuable vibration signals from the matrix composed of deviations from all video frames. However, this method exhibits limitations when handling low-level motions that reflect high-frequency vibration components. Hence, a video acceleration magnification algorithm is employed to enhance low-level deviation variations before the extraction. The enhancement of low-level deviation variations is validated by a light-weight cantilever beam experiment and a noise barrier field test. From the extracted waveforms and their spectrums from the original and magnified videos, subtle deviations of the selected straight-line edge profiles are magnified in the reconstructed videos, and low-level high-frequency vibration signals are successfully enhanced in the final extraction results. Vibration characteristics of the test beam and the noise barrier are then analyzed using signals obtained by the proposed method.

In order to investigate the soil reactions influenced by the single plate with the inclination angles from 0° to 75°, an in-house code of 2D DEM has been developed in this study. An iron flat plate penetrated soil by a constant velocity of 1 mm/s in the study. In the penetration test, the maximum vertical force was 753.8 N which was generated by the 0° plate. In addition, it was found that the less the inclination angle, the greater the vertical force. Furthermore, a greater force in the horizontal direction has been generated at 45° of the inclination angle. This research can provide a theoretical reference for optimizing tools that contact soil, for example, patterns/lugs on wheels, earthmoving blades (such as rotary cultivators, bulldozers, weeding machines etc.) and grouser of tracks. [ABSTRACT FROM AUTHOR]

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Aiming to solve problems in organic rice weeding a type of post-seat weeding machine was designed for rice paddies. The differences in the strengths and lengths of the root systems between the rice seedlings and the weeds were studied, and the motion track of the weeding wheel was analyzed to obtain the structural parameters of the weeding wheel. Then, the structural model of the weeding wheel was designed. The interaction process between the weeding wheel and soil in the paddy fields was simulated and analyzed based on the discrete element method, so as to investigate the working resistance change tendency of the weeding wheel and the orderliness of the soil disturbances. An orthogonal test was designed in this study, with three factors: the hoeing depth, the rotation rate of the weeding wheel, and the forward speed of the device. The influences of different operation parameters of the weeding machine on the weeding torque and soil disturbance speed were obtained based on a variance analysis of the test results. A multi-index comprehensive weighted scoring method was used to evaluate the simulation results. A soil bin test was conducted to verify the simulation results. Field experiments were carried out to test the working performance of the weeding machine. The comprehensive scoring results indicated that a better working performance of the weeding operation could be obtained when the hoeing depth was 50 mm, the rotation rate of the weeding wheel was 240 r/min, and the forward speed was 0.6 m/s. The results of the soil bin test were consistent with the simulation results. The results of the field experiment revealed that the weeding machine met the requirements for organic rice weeding. These results can provide a reference for the design of weeding machines for paddy fields. [ABSTRACT FROM AUTHOR]