The Contact Mechanics for Indentation of Single Asperity and Rough Surfaces

A Finite Element Analysis of a rigid sphere contact with a deformable elastic-plastic plat called indentation model is studied. The numerical results are applied on the rough surfaces contact of the GW model. A series of the relationships of the rough surfaces contact parameters are obtained. The contact parameters of the indentation model and the flattening model are compared in detail and the reasons for their differences are analyzed. In the case of single asperity contact, for ω/ωc > 1, the Indentation model reaches the initial plastic yield while the flattening model is ω/ωc = 1. In ω/ωc = 10, the plastic yield reaches the contact surface for the first time, and the corresponding point of ψ = 0.5 the flattening model is relatively earlier in . The contact parameters of rough surface in different plasticity indexes are compared again. On the point of ω/ωc = 6, the contact parameters of the flattening model and the indentation model coincide perfectly. For 0.5 < ψ < 4, the difference between the parameters curves become larger and larger. To the point of ψ = 4, when the distance difference reaches the maximum, it begins to decrease until the two curves are close to coincide again. The dimensionless elastic-plastic contact hardness is introduced. The relation between real contact area and the contact pressure of the indentation model can be acquired quickly. The results show that the geometric shape of deformable contact parts has an important effect on the contact parameters, especially for the extension of plastic deformation region within a specific range of plasticity index.

Experimental and Numerical Investigation of Contact Parameters in a Dovetail Type of Blade Root Joints

this paper focuses on the contact characteristics of the blade root joints subjected to the dry friction damping under periodic excitation. The numerical method and experimental procedure are combined to trace the contact behavior in the nonlinear vibration conditions. In experimental procedure, a novel excitation method alongside the accurate measurements is used to determine the frequencies of the blade under different axial loads. In numerical simulations, local behavior of contact areas is investigated using the reduction method as a reliable and fast solver. Subsequently, by using both experimental measurements and numerical outcomes in a developed code, the global stiffness matrix is calculated. This leads to find the normal and tangential stiffness in the contact areas of a dovetail blade root joints. The results indicate that the proposed method can provide an accurate quantitative assessment for investigation the dynamic response of the joints with focusing the contact areas.

Calibration and Verification Test of Lily Bulb Simulation Parameters Based on Discrete Element Method

In the simulation analysis of the lily harvesting process, the intrinsic parameters of the lily bulb and the contact parameters between the lily bulb and the lily mechanized harvesting equipment (Q235 steel) are deficient. Thus, the three-axis size, density, moisture content, Poisson’s ratio, elastic modulus, and other parameters of lily bulbs are measured in this paper with lily bulbs as the research object. Moreover, the discrete element model of the lily bulb was established using 3D scanning technology. The contact parameters between the lily bulb and Q235 steel were calibrated through bench test and simulation parameter test. The relative error between the measured value of the lily bulb accumulation angle and the simulated value is taken as response value to calibrate three parameters (collision recovery coefficient, static friction coefficient, and dynamic friction coefficient between lily bulbs). A regression model of the relative error of the stacking angle and three parameters is established, and the response surface is optimized. The results demonstrate that collision recovery coefficient, static friction coefficient, and dynamic friction coefficient between lily bulb and Q235 steel are 0.301, 0.423, and 0.063, respectively; these coefficients between lily bulbs are 0.455, 0.425, and 0.158, respectively. Additionally, a better combination of parameters is adopted to perform the simulation stacking test. The measured stacking angle is 32.31°, which is 0.34% in error with the stacking angle obtained by the physical stacking test. The test results suggest that the discrete element model and contact parameters of the lily bulb can be used in the discrete element simulation test. Furthermore, these research results could provide references for simulation tests, such as mechanized harvesting and post-harvest processing, of lily.

Analysis of Inter-particle Contact Parameters of Garlic Cloves Using Discrete Element Method

Purpose The discrete element method (DEM) can be used in agricultural fields such as crop sowing, harvesting, and crop transportation. Nevertheless, modeling complex crops as appropriately shaped particles remains challenging. The modeling of particles and the calibration of input parameters are important for simulating the realistic behaviors of particles using the DEM. Methods In this study, particle models representing the morphological characteristics and size deviations of garlic cloves were proposed. Additionally, the coefficients of friction were analyzed as the contact parameters of the particles based on the heap formation experiments and simultations of the swing-arm method using 150 garlic cloves. Results The simulation results were analyzed that the residual number of particles, a bulk property that can be measured simply in the experiment, is related to the coefficients of friction. In the heap formation experiments with low particle counts, the bulk properties were more clearly differentiated by the residual number of particles than the angle of repose. Moreover, the bulk properties similar to the actual garlic could not be expressed as a spherical particle model. Thus, an equation for predicting the residual number of particles was derived for the non-spherical garlic clove particle model. Five sets of coefficients of friction were presented using the prediction equation, and all the simulation results were close to the actual residual number of particles and angle of repose of the garlic. Conclusions Although the sizes of garlic cloves have a wide distribution, appropriate inter-particle contact parameters could be predicted. Therefore, the calibration process of the DEM can be shortened using the proposed prediction equation for the residual number of particles with non-spherical particles.

CONSTRUCTION OF A DISCRETE ELEMENT MODEL OF BUCKWHEAT SEEDS AND CALIBRATION OF PARAMETERS

In view of the lack of seeds contact parameters that can be used as a reference for the design of key mechanical components such as buckwheat planting, harvesting, and processing, this study combines simulation optimization design experiments and physical experiments to calibrate the parameters of simulated discrete element of buckwheat seeds. The non-spherical particle model of buckwheat seeds was established using the automatic filling method, and the simulation accumulating test and physical accumulating test were carried out using the bottomless conical cylinder lifting method; the repose angle of buckwheat seeds was taken as the response value, and the initial parameters were screened for significance based on the Plackett-Burman test; and a second-order regression model of the error value for the repose angle and the significance parameter was established based on the steepest climb test and Box-Behnken test. On this basis, the minimum error value of the repose angle was used as the goal to optimize the significance parameter, the optimal combination of contact parameters was obtained, and parameter validation tests were carried out. The significance screening test showed that the buckwheat-buckwheat static friction coefficient, the buckwheat-stainless steel rolling friction coefficient, and the buckwheat-stainless steel restitution coefficient had significant effects on the repose angle of buckwheat (P<0.05). The optimization test showed that the buckwheat-buckwheat static friction coefficient was 0.510, the buckwheat-stainless steel rolling friction coefficient was 0.053, and the buckwheat-stainless steel restitution coefficient was 0.492. The validation test showed that the repose angle of buckwheat seeds under such parameter was 25.39°, and the error with the repose angle of the physical test was 0.55%, which indicated that the optimal parameter combination was reliable. This study could provide a seed model and simulation contact parameters for the research and development of buckwheat sowing, threshing and hulling machinery.

Development of experimental vibro-acoustic transfer function for a system with combined rolling-sliding motion

Combined rolling-sliding contact is present in popular non-linear systems such as cam-follower, gears, clutches, and brakes. These systems produce significant noise due to complex contact between the components during operation. The noise generated is a strong function of the contact parameters and excitation to the system. The objective of this study is to develop a transfer function to quantify the vibro-acoustic noise for various contact conditions. Acceleration, reaction forces, and acoustic pressure measurements are made on a cam-follower setup with combined rolling-sliding contact. Experiments are performed under different conditions of friction, lubrication, load, and speed. Contact forces are back-calculated using the kinematics. The transfer function relating the acoustic pressure to different forces is estimated. It is observed that the contact parameters govern the transfer function and hence the vibro-acoustic systems. The developed transfer function is useful in designing better sub-systems with combined rolling-sliding contact to reduce noise exposure, as a direct technique to relate the contact parameters to the noise does not exist. This study can be extended to other complex systems such as gears and clutches.