The Thermo-mechanical-indirect Coupling Analysis For Large Mine Car Brake Friction

With the large mine car as the main force in the mining transport, its brake is a reliable guarantee for the safe operation of the car. But today, against the development of the mine cars with large size, intelligence and security, braking failure has caused huge losses annually, thereby drawing people’s attention to the study of brake. Continuous and rapid accumulation of heat and thermal stress produced in brake friction can easily induce hot crack, thermal decay and warp age of brake friction pair, further leading to braking failure. That is why many domestic and foreign researchers are gradually exploring the study of large car disc brake.This study is based on disc brake working principles and numerical simulation methods, adopting the general CAE software ANSYS with the actual size of a large car brake for reference, so as to establish a corresponding three-dimensional transient finite element model. Under different operating conditions, it uses the thermodynamic theory to simulate and analyze the temperature field and stress field of the disc brake systemically and elaborately.The main work of the research is as follows:Firstly, it introduces the main performance parameters and working modes of the large mine car and disc brake, summarizing the research status and deficiencies of thermal force coupling in the disc brake and explains the fundamental theories about it, including a series of basic principles of friction contact, friction heat, heat transfer and thermal mechanical coupling methods.Secondly, combined with the parameters like actual material properties for large car brake discs and the friction pieces, this research establishes the network model, and analyzes initial and boundary conditions as well as material thermal physics of factors with the cyclic displacement applied heat flux method, distinguishing the temperature simulations unfolding in the multi-working conditions. The results show that the distribution of the temperature field has the characteristics of regional, periodic and non axial symmetry. The temperature gradient is the largest on the surface of the brake disc, and the nodes in the inner layer are slow and the temperature hysteresis is obvious. In the different working conditions, the braking time is changeable and the time when the temperature peak will emerge differently. The longer time braking requires, the later the peak appears. But the highest point of the total time occurs at the point of about 3/5 in braking. It is indicated that the thermal expansion and deformation of the material are more likely to be caused in the mid-late period of braking, and the surface of the brake disc is more prone to produce cracks.Thirdly, with the comparative analysis of the temperature of brake disc junctions in different conditions and with the independent analysis of the relationship between the total duration of the braking and the disc surface temperature values, it discovers the initial velocity is proportional to the brake disc surface temperature, while the total length of braking is inversely proportional to the maximum temperature of the disk surface. Under emergency conditions, the rate of temperature rise is higher than that in the normal operating conditions, and the highest temperature is about160℃. Its overall temperature is often higher and more prone to suffer from heat damage. The highest temperature of the brake disc is concentrated on the disc and the friction contact area. The temperature of the area is shocking periodically in the process of braking, which can easily lead to thermal recession and thermal fatigue that will cause braking failure.Finally, under emergency conditions, with the analysis of mechanical stress on the friction pair in the brake finite element model, it is found that the stress on both sides of the brake disc and on the friction plate is of basically symmetrical distribution and the stress in taper region is larger and more concentrated, which shows that the peripheral friction is relatively serious and also explains why it is necessary to do chamfering or arc processing on the rim of the friction plate. Mechanical stress force peaks on the edge of the inner hole at the value of 67.8MPa, which is much lower than 45Mn yield limit. The indirect coupling method can make the temperature field as body load and the cyclic loading temperature field method serves to the antipyretic stress field. Stress nephogram presents annular distribution, but the distribution to the edge is asymmetric. With the continuation of braking, stress will tend to the disc and the non-friction area. The earliest range of the stress appears not only in the area of friction, but also in the inner diameter of the hole. The minimum stress value occurs in a circular band near the friction area. It is found that the stress gradient in the minimum friction radius of the brake disc is relatively large, which is easy to cause the stress and deformation of the material. The equivalent stresses of Von Mises in the condition of coupling and the single field stress exist in the area of the brake friction, but the maximum of the former is more than that of the latter one. So, it can be seen that the research on the stress of the brake disc should focus on the analysis of the thermal stress.Wholly speaking, the paper analyzes the actual parameter of the friction pair in the disc brake and explores its working conditions. It projects theoretical basis for its operation and failure. Furthermore, it provides some valuable references to optimize the safety structure of the disc brake in the large mine cars.