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The accurate estimation of road friction coeffi- cient in the active safety control system has become increasingly prominent. Most previous studies on road friction estimation have only used vehicle longitudinal or lateral dynamics and often ignored the load transfer, which tends to cause inaccurate of the actual road friction coef- ficient. A novel method considering load transfer of front and rear axles is proposed to estimate road friction coef- ficient based on braking dynamic model of two-wheeled vehicle. Sliding mode control technique is used to build the ideal braking torque controller, which control target is to control the actual wheel slip ratio of front and rear wheels tracking the ideal wheel slip ratio. In order to eliminate the chattering problem of the sliding mode controller, integral switching surface is used to design the sliding mode sur- face. A second order linear extended state observer is designed to observe road friction coefficient based on wheel speed and braking torque of front and rear wheels. The proposed road friction coefficient estimation schemes are evaluated by simulation in ADAMS/Car. The results show that the estimated values can well agree with the actual values in different road conditions. The observer can estimate road friction coefficient exactly in real-time andresist external disturbance. The proposed research provides a novel method to estimate road friction coefficient with strong robustness and more accurate.

In this paper, simulations of deep drawing tests at elevated temperatures were carried out with experimental validation. The aim of this work was to study the effect of process parameters on formability and mechanical properties of aluminum alloy 7075 in hot stamping process.Process parameters, including blank temperature, stamping speed, blank holder force and friction coefficient, were studied. Stamping tests were conducted at temperatures between 350 and 500 ℃, blank holder force between 0 and 10 kN, stamping speed between 50 and 150 mm·s^-1, and friction coefficient between 0.1 and 0.3. Based on the analysis, it is shown that thickness homogeneity could be improved when the blank is formed at lower temperature,lower blank holder force and lower friction coefficient.Formability could be improved when the blank was well lubricated at about 400 ℃. Formability at stamping speed 50 mm·s^-1 is far better than those at other speeds. The mechanical property analysis shows that the hot stamping process could make the formed part to obtain high quality.

A mathematical model of friction coefficient was proposed for the roll force calculation of hot-rolled strips. The online numerical solving method of the roll force calculation formula based on the proposed friction model was developed and illustrated by the practical calculation case. Then, the friction coefficient during hot strip rolling was estimated from the measured roll force by force model inversion. And then, the expression of friction model was proposed by analyzing the calculation process of stress state coefficient, and the model parameters were determined by the shared parameter multi-model nonlinear optimization method. Finally, the industrial experiments demonstrated the feasibility and effectiveness of the related models. The accuracy of the new roll force model based on the built friction model was much higher than that of the traditional Sims model, and it could be applied in the online hot rolling process control.

Hard coatings are used to improve the wear resistance of metals which largely depends on adhesion between substrate and coating. The wear and friction behavior of uncoated and TiCN-coated D2, M2 and M4 steels were evaluated by a pin-on-disk test under lubricated conditions. In order to evaluate the influence of lubricant on wear performance, dry friction tests were also performed. The results showed that friction coefficients were very similar for both uncoated and TiCN-coated steels. Under lubricated conditions, the uncoated D2 tool steel exhibited the lowest friction coefficient, but the TiCN-coated D2 steel presented the smallest wear rate. Abrasion was the main wear mechanism in all the tribocouples. Additionally, microhardness measurements were carried out, finding an influence of the steel substrate on the hardness of the coatings. Besides, adhesion test was conducted, suggesting a good adhesion of class 1 between substrates and TiCN coatings.

A finite element model is constructed for a sliding friction bearing in a seismically isolated bridge under vertical excitation with contact/friction elements. The effects of vertical excitation on the seismic performance of a seismically isolated bridge with sliding friction bearings and different bearing friction coefficients and different stiffness levels （pier diameter） are discussed using example calculations, and the effects of excitation direction for vertical excitation on the analysis results are explored. The analysis results shows that vertical excitation has a relatively large impact on seismic performance for a seismically isolated bridge with sliding friction bearings, which should be considered when designing a seismically isolated bridge with sliding friction bearings where vertical excitation dominates.

Wear properties of two different crushers used for grinding raw materials of cement industry are compared using pin-on-disk wear test.The wear test was carried out with different loads on a pin.Abrasive wear behavior of two alloys was evaluated by comparing mass loss,wear resistance,microhardness and friction coefficient.The microstructure of the specimens was detected using optical microscope.The results showed that abrasive wear of high chromium cast iron is lower than that of Hadfield steel.Due to the presence of M7C3 carbides on the high chromium cast iron matrix,impact crushers exhibited higher friction coefficient

Vehicle state and tire-road adhesion are of great use and importance to vehicle active safety control systems. However, it is always not easy to obtain the information with high accuracy and low expense. Recently, many estimation methods have been put forward to solve such problems, in which Kalman filter becomes one of the most popular techniques. Nevertheless, the use of complicated model always leads to poor real-time estimation while the role of road friction coefficient is often ignored. For the purpose of enhancing the real time performance of the algorithm and pursuing precise estimation of vehicle states, a model-based estimator is proposed to conduct combined estimation of vehicle states and road friction coefficients. The estimator is designed based on a three-DOF vehicle model coupled with the Highway Safety Research Institute（HSRI） tire model; the dual extended Kalman filter （DEKF） technique is employed, which can be regarded as two extended Kalman filters operating and communicating simultaneously. Effectiveness of the estimation is firstly examined by comparing the outputs of the estimator with the responses of the vehicle model in CarSim under three typical road adhesion conditions（high-friction, low-friction, and joint-friction）. On this basis, driving simulator experiments are carried out to further investigate the practical application of the estimator. Numerical results from CarSim and driving simulator both demonstrate that the estimator designed is capable of estimating the vehicle states and road friction coefficient with reasonable accuracy. The DEKF-based estimator proposed provides the essential information for the vehicle active control system with low expense and decent precision, and offers the possibility of real car application in future.

The AISI316L stainless steel composites reinforced with 2, 4, 6, and 8 vol% titanium diboride （TiB2） particles were sintered by the high pressure-high temperature method. Ball-on-disk method was carried out to study wear behavior of the composites. Tests were carried out at room temperature. The TiB2 particles improved the hardness and tribological properties of the composites. The friction coefficient of the composites decreased with the increasing content of TiB2. The reduction of the wear rate with the increasing of the content of TiB2 particles in the steel matrix was also observed. It is demonstrated that the friction coefficient of composites with the same content of TiB2 particles depend on the sintering conditions.

The identification of maximum road friction coefficient and optimal slip ratio is crucial to vehicle dynamics and control.However,it is always not easy to identify the maximum road friction coefficient with high robustness and good adaptability to various vehicle operating conditions.The existing investigations on robust identification of maximum road friction coefficient are unsatisfactory.In this paper,an identification approach based on road type recognition is proposed for the robust identification of maximum road friction coefficient and optimal slip ratio.The instantaneous road friction coefficient is estimated through the recursive least square with a forgetting factor method based on the single wheel model,and the estimated road friction coefficient and slip ratio are grouped in a set of samples in a small time interval before the current time,which are updated with time progressing.The current road type is recognized by comparing the samples of the estimated road friction coefficient with the standard road friction coefficient of each typical road,and the minimum statistical error is used as the recognition principle to improve identification robustness.Once the road type is recognized,the maximum road friction coefficient and optimal slip ratio are determined.The numerical simulation tests are conducted on two typical road friction conditions（single-friction and joint-friction）by using CarSim software.The test results show that there is little identification error between the identified maximum road friction coefficient and the pre-set value in CarSim.The proposed identification method has good robustness performance to external disturbances and good adaptability to various vehicle operating conditions and road variations,and the identification results can be used for the adjustment of vehicle active safety control strategies.

The compressive behaviors of medium carbon steel specimens were investigated over a wide range of temperatures and strain rates using a Gleeble-3500 thermo-simulation machine. The results show that the flow stress increased with strain at first, and then gradually decreased after reaching a peak value. The flow stress softening rate at a high strain rate was larger than that at a low strain rate. The effects of deformation heating and friction on flow stress were analyzed. A new friction correction method, wherein the effect of strain on frictional coefficient was considered, was established here. The stresses revised by the new method deviated from the measured stresses with increasing strain. Meanwhile, the apparent frictional coefficient variation law with strain was obtained. The frictional coefficient increased as the strain increased and then slightly decreased after maintaining a constant value. The stress was corrected by considering deformation heating. The accuracy of the temperature correction method was verified using a special experiment. The results of the verification experiment show that the temperature correction method exhibited a good accuracy in calculating the variation of stress caused by deformation heating. A constitutive model considering strain was proposed here to describe the deformation behaviors. Compared with experimental data, the modified constitutive model exhibited a good accuracy as to constitutive correlation.