Contact Area Coefficient Research Articles

Influence of contact area coefficient on the results of u-p formation dynamic equations of fluid-saturated porous media

The principle of effective stress is the keystone of modern physics, which becomes the basic difference between soil mechanics and general solid mechanics. Terzaghi’s effective stress principle has been controversial since it was put forward, especially for the calculation of effective stress, many scholars have revised it from different aspects. The pore pressure is reduced in all different modified formulas, that is, the pore pressure need to be multiplied by a pore pressure factor. However, the variation of pore pressure factor has always been ignored because the reduction of pore pressure is very small. In this paper, the effective stress expression considering the contact area coefficient is modified to the u-p formation dynamic equation, and the influence of the change of contact area coefficient on the dynamic characteristics of soil is studied.

Influence of the initial hydrostatic pressure on contact area coefficient under drainage condition

The expression of effective stress proposed by Terzaghi has always been questioned. Many correction formulas are modification of pore pressure term. The pore pressure factor is related to porosity, contact area and other factors. When the particles are in point contact, the expression of the effective stress is that proposed by Terzaghi, while for the surface contact particles, the actual effective stress increases the stress produced by pore pressure passing through the contact surface based on the Terzaghi effective stress. There are many factors that affect the development of contact area and pore pressure, therefore, a series of the drained triaxial tests were carried out on four groups of sand samples with different initial hydrostatic pressures to study the influence of different initial hydrostatic pressures on the effective stress due to the term of contact area (σα). The test results show that the shear strength is increases with the initial hydrostatic pressure under the same effective confining pressure, which indirectly indicates that the initial hydrostatic pressure increases the contact area stress.

Theoretical calculation and experiment of the surface residual stress in the plane ultrasonic rolling

The service life of the workpiece is largely determined by residual stress on the workpiece surface, which is the most important parameter of anti-fatigue. In order to study the characteristics of residual stress on workpiece surface, the theoretical model of residual stress on the surface of the single impact workpiece is established based on the elastoplastic theory. Subsequently, the relationship between the rolling depth and the rolling force in the plane ultrasonic rolling is established based on the Hertz contact theory, and the contact area coefficient is established to correct the theoretical model. Then, the plane ultrasonic rolling experiments are carried out to validate the model. The results exhibit that the rolling force linearly increases with the increase of rolling depth. The effect of step has a highest relationship with the contact area coefficient, moderate with the feed rate, and minor with the static force. With the increase in static force, the residual compressive stress increased as a whole. The residual compressive stress decrease with the increase in step and the feed rate has little influence on the residual stress. The results reveal that the modified theoretical model can improve the prediction accuracy of residual stress.

Effects of particle contact characteristics on heat transfer performance of calcined petroleum coke heat exchanger

The present paper investigated the effect of particle contact characteristics (contact area coefficient) on heat transfer performance of heat exchanger. An unsteady heat transfer model of single-layer calcined petroleum coke was established. The average temperature, heat storage, heat transfer contribution rate and wall heat transfer coefficient were studied with different times. The research shows that with increase of contact area coefficient, the heat conduction capacity is enhanced and the average temperature of particles layer reduction rate and the heat storage reduction rate are obviously accelerated. The average contribution rate of solid phase heat transfer, wall comprehensive heat transfer coefficient and heat release rate increase, and the effective heat transfer time decreases. When the contact area coefficient increased from 0.03 to 0.07, the average contribution rate of solid phase heat transfer increased from 83.4% to 90.5%. The wall heat transfer coefficient increased from 12.7 W/(m2·K) to 27.1 W/(m2·K), the heat release rate increased from 83.79% to 98.2%, and the effective heat transfer time decreased from 8.02 h to 5.07 h.

Finite element modeling of consolidation process of SiC fiber-reinforced titanium matrix composites via matrix-coated fiber method

The consolidation process of SiCf/Ti-6Al-4 V composites by matrix-coated fiber (MCF) method via hot pressing was investigated using finite element modeling (FEM). By analyzing the elastic–plastic contact deformation of the representative aligned coated fibers, the consolidation maps delineating the time–temperature–pressure relationship for full densification were constructed. Both the flow coefficient and the contact area coefficient used to describe the contact deformation were calculated according to the model. In addition, the effect of fiber content on matrix stress distribution was analyzed. The results show that fiber content is a significant factor that influences the densification process. Higher fiber content will lower the consolidation rate.

Tread wear and footprint geometrical characters of truck bus radial tires

Wear and mileage performance are the foremost performances for truck bus radial (TBR) tires. There are a lot of researches about the tire wear performance as well as the contact patch phenomenon by using finite element analysis (FEA) method or testing. But there is little published data on the correlations between the footprint geometry and the tread wear performance of tires. In this paper, an experiment on tire-ground performance of TBR tires is carried out by using Tekscan. The real-time changes of contact-area pressure distribution that occurred during the process of continuous load and unload are recorded. Three types of tires that act differently in behavior under normal usage are analyzed. A new method of researching in tire tread wear, which focuses on the geometrical characters of the footprint, is put forward. The experimental results of the three tires are described by using footprint geometrical characters. On the basis of studying the changing laws of footprint geometrical characters during the loading process and considering consumer survey and factory feedback information, the correlations between the geometrical character of footprints and tread destruction form are built. The analyzed results show that a greater contact area coefficient and a steady coefficient of contact result in a better wear performance for TBR tires. The footprint-shape coefficient changing laws in the process of loading are found to have a very good coincidence with the tread wear of the three types of tires. Tires with a smaller footprint-shape coefficient are likely to have an average tread wear while avoiding the shoulder wear first. The proposed research provides a new solution to predict tire-ground performance at the point of footprint and several useful references for improving tire design.

The effect of moisture content on the compression and bond-formation properties of amorphous lactose particles

A lactose solution was spray-dried and the particles obtained were stored at relative humidities of 0, 11, 22 and 33%. The moisture content (gravimetric analysis), crystallinity (microcalorimetry), particle density (air pycnometry) and glass transition temperature (differential scanning calorimetry) of the particles were determined and compacts were prepared (50–200 MPa). From porosity-applied pressure profiles, the yield pressure for the materials was calculated and the tensile strength and porosity of the compacts were determined. Compacts were also examined in an electron microscope. The moisture content of the amorphous material varied between 0 and 6.2 wt% and an increased moisture content related rectilinearly to a reduced particle density, a reduced glass transition temperature and a reduced yield pressure. An increased moisture content gave an increased tablet tensile strength and a reduced tablet porosity. Different relationships between tablet strength and porosity were obtained dependent on the moisture content of the particles, while a single relationship seemed to exist between tablet strength and a contact area coefficient. To conclude, amorphous lactose powders reduced in volume due to particle deformation, and powder compression was facilitated by an increased moisture content due to an increased deformability of the particles in their glassy state. The particle deformability controlled the area of contact formed between the particles during compression, which controlled the tablet tensile strength. Particles seemed to bind by adsorption bonding and, at high compaction pressures, by solid bridges.