Contact Parameters Research Articles

Modal characteristics of blade-disk including rough interfaces and geometric deviations

The inaccurate prediction of vibrations in blade-disk structures leads to frequent occurrences of failures in rotating machinery, such as air-engines. Existing methods often empirically treat the contact parameters of interfaces as globally constant and rarely consider manufacturing and assembly deviations, resulting in a deviation of prediction models from reality. This work presents a model for complex assembly structures that includes non-uniform distributions of normal contact stiffness and tangential friction coefficients at rough interfaces, while also introducing experimentally measured geometric deviations to enhance alignment with real-world conditions. Taking fir-tree blade-disk structure as an example, the accuracy of the proposed method is comprehensively verified by four measurement experiments and one modal experiment. Subsequently, the combined influence of rough interfaces and three experimentally measured geometric deviations on the overall modal characteristics of blade-disk structure are investigated, and their influencing mechanisms are revealed. The results indicate that ignoring the interface roughness and geometric deviations may significantly affect the prediction accuracy of the modal characteristics. The proposed method has great potential in the field of predicting the modal characteristics for complex assembly structures and optimizing the design of their machining and assembly processes.

Nonlinear vibration characteristics of an aeroengine cantilever flexible rotor considering interference fit and unbalance

Aeroengine power turbine rotor is a typical nonlinear rotor system, in which the interference connection between long shaft and short shaft has a prominent influence on the coupling vibration of the system, especially at high speed, the nonlinear stiffness change of interference contact is more obvious. Therefore, the paper considers the change of the contact characteristics of the long shaft and the short shaft of the turbine rotor, and the nonlinear restoring force of the bearing to analyze the dynamic characteristics of the rotor. Firstly, according to the theory of elasticity, the contact parameters under different speed states are calculated, the contact stiffness model under interference fit is established, and the relationship between contact stiffness and speed is analyzed. Secondly, according to the Hertz contact theory, a bearing nonlinear restoring force model considering time-varying characteristics is established. Finally, the dynamic model of the bearing-flexible rotor coupling considering interference contact is established. The influence of contact parameters and unbalance parameters on the nonlinear vibration characteristics of the rotor is analyzed by amplitude-frequency curve, bifurcation diagram, time-domain waveform, spectrum diagram, trajectory diagram and Poincaré diagram. In addition, the simulation results are compared with the experiment results of the rotor test rig to verify the accuracy of the established dynamic model. By analyzing the influence of different parameters such as interference magnitude, unbalance position, unbalance magnitude and unbalance couple on the nonlinear vibration of the rotor, the basis for the design and vibration control of the cantilever turbine rotor is provided.

花生籽粒物理参数测定与离散元参数标定

This study measured the intrinsic and contact parameters through physical experiments to improve the accuracy of discrete element simulation analysis of peanut seeds. Discrete element models for five different peanut seed filling ball numbers were established. The simulation parameters were calibrated through a combination of physical and simulation experiments. Firstly, the Plackett-Burman test was used to screen the significance of simulation parameters. Then, the steepest climbing test was conducted to determine the optimal range of significance parameters using the relative error be-tween the simulated and the physical experimental as the evaluation index. Finally, a response surface experiment with three factors and three levels was conducted using the repose angle as the response value. The static and rolling friction coefficients among peanut seeds were set as 0.43 and 0.50 separately, and the rolling coefficient between peanut seeds and steel plate was set as 0.12. During verification experiments, the simulated repose angle was 25.18°, with a relative error of 2.42% compared to the physical repose angle, further verifying the reliability of the simulation model. The re-search group used different numbers of filling balls with optimal parameters in the repose angle experiment. Then they evaluate the simulation time and the error value of repose angle between the simulated and physical experiment. The optimal number of filled balls is the Sphere 1178. The research results indicate that discrete element model of peanut seeds and calibration parameters are reliable. Based on the results of this research, an intelligent peanut precision sowing machine can be developed.

小区小麦联合收获机割台清理离散元仿真参数标定

The analysis of the clearing process of the cutting deck of a small plot wheat combine harvester requires the use of discrete element simulation methods. However, the current simulation test lacks the contact parameters such as wheat stalk and stalk-seed. In this paper, the wheat stalks and seeds at harvest time were taken as the research objects, and the calibration study of the discrete element simulation model parameters of stalks and stalk-seeds was carried out by means of mechanical test determination and EDEM software simulation. The stiffness coefficients of wheat stalks were determined by mechanical tests; the average values of wheat stalk stacking angle of 39.22° and wheat stalk-seed stacking angle of 44.41° were obtained by stacking angle tests. By the steepest climb test and binary regression test, the stalk normal stiffness coefficient was determined to be 5e+08N/m2 and tangential stiffness was determined to be 6.35e+08N/m2; the stalk-stalk collision recovery coefficient was obtained to be 0.551, static friction coefficient was obtained to be 0.797, and rolling friction coefficient was obtained to be 0.079 by the two-level analytical factorization test, the steepest climb test, and the three-factor response surface test. Based on this, the average value of wheat stalk-seed stacking angle was obtained to be 39.22° and the average value of wheat stalk-seed stacking angle was obtained to be 44.41° by the stacking angle test. On this basis, the coefficient of recovery of stalk-stalk collision was 0.434, the coefficient of static friction was 0.884, and the coefficient of rolling friction was 0.339 obtained by the three-factor response surface test. Three validation experiments were carried out by substituting the obtained parameters into the simulation test, and the error values were close to the error value %0.255 in the model, which proved that the experimental data were reliable.

Анализ контакта конических зубьев шестерен на основе машинного обучения

In this paper, we study the analysis of the contact of bevel gear teeth based on machine learning methods. Bevel gear teeth are widely used in various industrial and mechanical systems to transmit rotational motion with high precision and reliability. Traditional methods of gear contact analysis are based on mathematical models and empirical formulas, which may be limited in accuracy and applicability. In recent years, machine learning has become a powerful tool in the field of engineering and mechanics to more accurately model and predict the contact behavior of bevel gear teeth. The paper proposes the use of machine learning methods, such as neural networks or deep learning algorithms, to train models capable of analyzing the contact of bevel gear teeth. Wear, load, and gear geometry data can be used to train models, which can then predict contact parameters and evaluate contact performance.

Parametric study for model calibration of a friction-damped turbine blade with multiple test data

Model updating using multiple test data is usually a challenging task for frictional structures. The difficulty arises from the limitations of nonlinear models which often overlook the uncertainties inherent in contact interfaces and in actual test conditions. In this paper, we present a parametric study for the model calibration process of a friction-damped turbine blade, addressing the experimentally measured response variability in computational simulations. On the experimental side, a recently developed test setup imitating a turbomachinery application with mid-span dampers is used. This setup allows measuring multiple responses and contact forces under nominally identical macroscale conditions. On the computational side, the same system is modeled in a commercial finite element software, and nonlinear vibration analyses are performed with a specifically developed in-house code. In numerical simulations, the multivalued nature of Coulomb’s law, which stems from the inherent variability range of static friction forces in permanently sticking contacts, is considered to be the main uncertainty. As the system undergoes vibration, this uncertainty propagates into the dynamic behavior, particularly under conditions of partial slip in contacts, thus resulting in response variability. A deterministic approach based on an optimization algorithm is pursued to predict the limits of the variability range. The model is iteratively calibrated to investigate the sensitivity of response limits to contact parameters and assembly misalignment. Through several iterations, we demonstrate how uncertain initial contact conditions can be numerically incorporated into dynamic analyses of friction-damped turbine blades. The results show a satisfactory level of accuracy between experiments and computational simulations. This work offers valuable insights for understanding what influences test rig response and provides practical solutions for numerical simulations to improve agreement with experimental results.

Experimental and numerical analyses of crushing resistance of unbound road materials

ABSTRACT Aggregate breakage in unbound pavement layers can lead to pavement distresses that affect their functionality and service life. Thus understanding the mechanics and clarifying the factors affecting materials breakage resistance are important for ensuring adequate performance of these layers. In this study, aggregate breakage in unbound granular materials (UGM) is investigated experimentally and numerically. Experimentally, aggregate breakage under uniaxial compression is examined for two UGMs prepared with the same aggregate type but different gradations. To capture the experimentally observed influence of gradation and load magnitude on aggregate breakage, a Discrete Element Method (DEM) model was developed, based on granular mechanics particle contact and failure laws. A simple procedure to identify the contact and failure law parameters from experiments is proposed. With those parameters, the model’s capability of capturing the effect of gradation and loading on the aggregate breakage in UGM is evaluated. Based on comparison with experimental findings, it is shown that the model can capture macro-scale properties of UGM, such as its deformation response under uniaxial compression, as well as the amount of aggregate breakage in the material.

Coupled DEM-FDM numerical model for EPB shield tunnelling simulation with foam conditioning

It is widely recognized that an appropriate application of soil conditioning significantly improves the tunnelling performance of earth pressure balance (EPB) shield tunnel boring machines (TBMs). This study presents a numerical approach that simulates an EPB shield tunnelling, considering the injection of foam into the soil. To enhance computational efficiency and reduce the number of particles simulated in the ground formation, the numerical study coupled the discrete element method (DEM) and the finite difference method (FDM). The properties of in-situ soil and foam-conditioned soil were incorporated into the DEM domain by determining the contact parameters of particles using two calibration models: the triaxial compression test and the pressurized vane shear test models. With the established model, tunnelling analyses were conducted under specific TBM operation conditions, such as the penetration rate, and rotational speed of the cutter head and the screw conveyor. The effect of foam injection on EPB shield TBM operation was evaluated by adjusting the contact parameters of DEM elements. The numerical simulations revealed that foam conditioning reduced the torque, thrust force, and forces on cutting tools. These simulations provided valuable insights into the applicability of the numerical approach in assessing foam conditioning for EPB shield TBMs.

Effect of interference magnitude on fretting wear and fatigue strength of scaled press-fitted railway axles

Railway axles represent a typical example of interference fit structures that are vulnerable to fretting fatigue induced by rotational bending loads. This study investigated the influence of interference magnitude on the fretting wear and fatigue of scaled press-fitted railway axles. In this study, the fretting fatigue strength was tested at three interference magnitudes within the standard range, and the fretting wear and fretting cracks were analyzed. The results indicate a trend where the fretting fatigue strength initially rises and then declines with increasing interference magnitude. 3D finite element models, with and without considering the fretting wear, were developed to investigate the variation in contact parameters in the press-fitted region, and the Smith-Watson-Topper multiaxial fatigue model was employed to evaluate the fretting fatigue behavior. The results demonstrate that the competition between contact pressure and axial slip produces relatively slight fretting wear when the interference magnitude takes the middle value, thereby causing a minor stress concentration and ultimately leading to higher fretting fatigue strength.

Numerical investigation on the densification of granulated porous indium tin oxide powders before compaction

Dense and uniform initial packing structures of powders are of key significance in powder metallurgy process, which can provide the precondition for the fabrication of high-performance components with low cost and high efficiency. In this paper, the packing densification of indium tin oxide (ITO) granulated micro powders with continuous size distributions and internal porosity under three-dimensional vibrations was numerically investigated by discrete element method (DEM). Firstly, the DEM model was validated by physical experiments, and the contact parameters between particles and the porosity therein were determined. Then the effects of operating parameters on the macro/micro properties (e.g., packing density, coordination number (CN), pores, and forces) of the packing structures were analyzed. Results show that the mean CN cannot intuitively reflect the packing structure due to the complex and varied inter-particle contacts caused by the inhomogeneity of the particle size in a multi-sized granular system. Additionally, the excellent packing structure of porous ITO particles is always obtained from low amplitude when the vibration intensity is the same. Corresponding mechanism analyses reveal that higher amplitude normally causes strong convective diffusion, leading to more pores in the packing. This increases the probability of wedging effect occurring during settling, thereby reducing the packing density. However, optimal packing quality with low amplitude can only be achieved when coupled with high frequency. Therefore, applying vibration is an effective way to achieve dense packing of porous spherical particles, especially at low amplitude and high-frequency operating conditions.

Analytical determination of the dynamic response of layered saturated frozen foundation to moving loads under plane strain conditions

Based on the theory of solid porous media with pores, a calculation model of two-dimensional layered saturated frozen soil foundation is established. The study focuses on the dynamic response of layered saturated frozen soil medium placed on an impermeable rigid bedrock when subjected to a uniform surface moving strip load in motion. Firstly, the governing equation of saturated frozen soil is established. Then, the Helmholtz vector decomposition theorem, coordinate transformation, and Fourier integral transformation are used to decouple the governing equation of saturated frozen soil, and the general solution of the potential function is obtained, and the general solution of the stress and displacement of each layer of saturated frozen soil is derived. Using the transfer and reflection matrix (TRM) method, the semi-analytical solution of layered saturated frozen soil medium in the frequency domain is derived. Finally, the dynamic response of each phase of the saturated frozen soil in the time domain is obtained by the fast Fourier transform. After verifying the accuracy of the solution by comparing the model degradation with the existing literature, the effects of soil shear modulus, load moving speed, temperature, porosity, contact parameter, and frequency on the dynamic response of homogeneous foundation, soft interlayer foundation, and hard interlayer foundation are analyzed in detail. The results show that the stratification of the foundation is of great significance for accurately evaluating the dynamic response of saturated frozen soil.

Application of Poisson’s ratio structures and decoupling algorithm for 3D force sensing

Flexible tactile electronic devices are extensively used in the fields of robotics, medical detection, and human-computer interaction. Monitoring contact parameters, including force magnitude, direction, and contact location, is particularly vital for skin-like tactile sensing devices. Herein, a 3D force sensor is designed based on porous structure with deliberately designed Poisson’s ratios. A genetic algorithm (GA) optimized back propagation neuronal network (BPNN) model is proposed to support the 3D force decoupling, which can greatly improve the decoupling accuracy. The introduction of the GA-BPNN significantly enhances decoupling accuracy compared to the initial neural network. Micro-porous structures with varied Poisson’s ratios are embedded into the sensing unit to achieve better sensibility. Significantly, this study underscores that the decoupling accuracy of the force components along the Z-axis can be further improved by substituting the solid unit with a designed porous structure unit featuring a specific Poisson’s ratio in an arrayed 3D force sensor.

Estimation of vehicle tire effective rolling radius and vertical wheel/road contact force

In a vehicle, knowledge of physical wheel/road contact parameters is valuable for the design of dynamic control and active safety systems. In this paper, a new method is designed to estimate the effective rolling radius and the vertical wheel/road contact force using an extended Kalman filter and the Pacejka magic formula. Moreover, it allows the estimation of the longitudinal force, the rolling resistance force, and the longitudinal slip. The method is designed in four blocks. First, a comparison with other research is carried out to validate both the controller and quarter-vehicle model blocks. Then, the blocks of the extended Kalman filter and the Pacejka magic formula are applied to estimate all parameters. The relative mean estimation errors are calculated, and the results show that the developed method is capable of estimating all parameters simultaneously and in real-time with satisfactory accuracy.

Finite Element Analysis of Solid and Hollow Roller Bearings to Predict the Influence of Contact Factors on Cage Slip

This study examines the influence of contact factors such as bearing deformation, contact width and contact pressure on cage slide in cylindrical roller bearings. A cylindrical shaped roller bearing test setup is designed in order to determine the operating speed of bearing components under varying working circumstances. Solid and hollow roller bearings are analyzed using finite element technique, and the contact parameters are obtained. The cage slip obtained by experimental work is correlated with the contact parameters of hollow and solid shaped roller bearings. The specific load acting on solid rollers at various angular positions and the corresponding bearing deflection are obtained by FEA and the bearing run out is estimated. A new methodology is developed for deriving the contact mechanics of hollow roller to predict contact pressure and contact width from the roller deflection. The effect of hollowness on these parameters is derived and the corresponding cage slip is correlated. The effect of hollowness on bending and resultant stresses is obtained by numerical and analytical methods to correlate the stability of hollow roller bearing with the percentage of hollowness.

The Effects of Surface Oxidation and H-Termination Processes Applied to Si Using Electrolytic Hydrogen Peroxide Solution to The Produced Cu/p-Si Schottky Contact Parameters

By using electrolytic hydrogen peroxide (H2O2) solution, oxidation and H-termination processes were applied to the p-Si crystal surface, which will be used for Cu/p-Si Schottky contact production, in a selective and controlled manner. Before the oxidation and H-termination processes, the p-Si(100) wafer used in this study was subjected to conventional chemical cleaning, and ohmic contact was made using pure aluminum (99.99%) metal on its back surface. The p-Si/Al with ohmic back contact was divided into three parts. A rectifying contact was immediately made to the front surface of one of them by using pure copper (99.98%) metal and called the REF (Reference) sample. The front surface of one of the remaining two p-Si/Al parts was oxidized, and the front surface of the other was H-Terminated. Rectifier contacts were made for both using pure copper (99.98%) metal and were named MIS (metal-insulator-semiconductor) and SP (surface passivated), respectively. Current-voltage (I-V) measurements of Schottky diodes of REF, MIS, and SP samples were performed at room temperature and in the dark. From the obtained data, the ideality factor (n), barrier height (Fbo), and series resistance (Rs) values of the samples were determined. As a result of the investigations, it was observed that the surface oxidation and H-Termination processes caused a decrease in the rectification factor and Fbo values of MIS and SP samples. These interesting situations were interpreted by the double-layer theory, which Bardeen predicted could exist on the surface of a semiconductor crystal and contribute to its work function.

Роботизация в авиастроении

Some cses of robotized systems and complexes (RS and RC) in the aircraft industry are considered. A robotic cell for resistance spot welding is viewed, the main components of which are an industrial robot (IR), welding guns, a linear displacement module of IR, an inverting unit. Here the IR performs welding, it is equipped with welding guns as a hand. An inverting unit equipped with a stepper motor rotates the panel around the axis and sets the part to be welded within the whole welding process. The movement of the IR is also carried out due to the linear displacement module. The robotization of harnesses production is viewed, using automatic lofts and collaborative robots, which, moving along specialized lofts, with the help of a linear displacement module, install holders on the loft and ties wires into harnesses. After the operation is completed, made-up harness is put into a storage hopper. A robotized complex (RC) for manufacturing parts of the «rib» type is studied. It includes a machine equipped with a vacuum gripper, technological equipment, consisting of a cutting machine and a bending press. The technological process has two stages: cutting and bending. The cut blanks are blown out of the press onto the receiving tray. The IR performs feeding of blanks into the working area of the technological equipment and laying in the appropriate storage unit. 3D models of robotized sites are presented, their components are listed. In conclusion, the importance of analyzing the process operation is proved, when the feasibility of robotization is evident. An algorithm for analyzing the process operation is presented. It has been understood that the introduction of robotics in certain technological processes reduces the impact of hazardous production factors.

Nonlinear model updating of the rotor-bearing system by multi-harmonic balance method and analytical sensitivity derivation

Responses of the bearing system are usually predicted or tested, to analyze its nonlinear dynamic characteristics. However, responses predicted from the bearing model constructed by Hertz contact theory usually show differences with their tested counterparts, denoting the improper setting of the nonlinear contact parameters. It is compulsory to reduce such differences and obtain a precise bearing model using nonlinear model updating techniques. In this paper, a novel nonlinear model updating framework is proposed following the Multi-Harmonic Balance Method (MHBM) and the analytical sensitivity analysis, for updating of the rotor-bearing system using the nonlinear responses in the frequency domain. With the derivation of bearing response sensitivities to the nonlinear contact parameters, increments of the nonlinear parameters can be ascertained by the sensitivity inverse and updating of the nonlinear bearing model can be implemented in an iterative way, until a precise bearing model with the response differences reduced to minima is obtained. Firstly, a novel MHBM model is derived for the bearing system, which is fully described by matrix operations and used to further deduce the analytical sensitivity formulations of the bearing responses to the design parameters. Afterwards, the bearing responses and sensitivities in the frequency domain are predicted by the continuation strategy. Finally, model updating is conducted for the bearing system using the traditional inverse-sensitivity framework. Two cases are used to demonstrate the feasibility of the method. The first case is to update bearing parameters of contact stiffness, clearance and eccentricity of a 2-DOF bearing system in order to match the predicted bearing responses with the measured ones in strong nonlinearity with the multivalued phenomenon. The next is to update the Hertz contact parameters of the left and right bearings, together with the disc eccentricity, of a Finite Element (FE) rotor-bearing system. These results show the validity and superiority of the proposed method.

Discrete Element Method–Multibody Dynamics Coupling Simulation and Experiment of Rotary Tillage and Ridging Process for Chili Pepper Cultivation

Rotary tillage, ridging, and mulching are commonly used cultivation methods for crops such as chili peppers, tomatoes, and strawberries in the arid regions of Northwest China. An integrated machine for rotary tillage, ridging, and mulching was designed by considering the growth characteristics of pepper root systems and the agronomic requirements of ridge beds. The structural parameters and their value ranges for key components such as the rotary tillage device and the ridging device were determined. By introducing the Bonding contact parameter, the soil cohesion between soil particles during the process of rotary tillage and ridging can be simulated. A coupled simulation model using the Discrete Element Method (DEM) and Multibody Dynamics (MBD) is established. The experimental factors selected were rotary tillage depth, ridging roller speed, and machine forward speed. The evaluation indexes were the traction resistance of the stemming roller and the soil compactness of the ridges. A response surface Box–Behnken Design test was carried out to obtain the best working parameters of the rotary tillage and ridging process for chili pepper cultivation as follows: the rotary tillage depth was 176 mm, the ridging roller speed was 283.71 r/min, and the machine forward speed was 0.55 m/s. Field experiments with optimal parameters showed that the ridge top width was 549.2 mm, the ridge bottom width was 750.5 mm, the ridge height was 222.9 mm, the ridge spacing was 1173.1 mm, the surface smoothness of the ridge was 12.3 mm, the width of soil covering the film edge was 76.3 mm, the stability coefficients of the ridge size parameters were all above 91.73%, and the soil compactness after operation was 60.82 KPa. All indicators meet the requirements for the rotary tillage and ridging cultivation of chili peppers in arid regions, providing reference for the design of rotary tillage and ridging mulching implements and the development of sustainable agriculture.

Energy-minimizing configurations for an elastic rod with self-contact energy close to the inextensible–unshearable and hard-contact limits

We study self-contact configurations of elastic rods by adding a repulsive energy to the bend, twist, shear, and stretch energies of a classical elastic rod. We use a discretized approach, with the parameters of the discrete rod calibrated to approach the continuous case as the number N of rod segments goes to infinity, and use a quasi-Newton approach to minimize the discretized energy. We explore convergence of the results as N→∞, and also as we vary shear, stretch, and contact parameters to approach the inextensible–unshearable and hard-contact limits. For a straight and isotropic rod, we present results for three sets of boundary conditions – loop, buckled strut, and hairpin, in each case as an imposed twist angle is increased – and compare energies and configurations for the non-contact and contact problems. Finally, we show how our results change when isotropy is broken in two ways: by the rod being bent in its undeformed state, or by the rod having unequal bending stiffnesses.

Measurement and calibration of gluten pellets discrete element parameters at varied moisture content.

To quickly calibrate the discrete element parameters (DEP) of pellets with different moisture content (MC), the angle of repose (AoR) was taken as the target value to conduct experimental and simulation research on gluten pellets. The experimental method obtained the intrinsic parameters, contact parameters, and AoR of pellets with different moisture content. The parameters differed significantly under different moisture content (p<0.05). The AoR-MC model (R2 =0.987) was established. The Plackett-Burman test, steepest ascent test, and center compound test were carried out to establish the AoR-DEP model (R2 =0.969) with a relative error less than or equal to 2.07%. The MC-DEP model was derived, and verified by the side plate lifting method with a relative error less than or equal to 2.58%. This paper provides a new method for calibrating DEP under different moisture content.