Contact Friction Behavior Research Articles

Mesoscale numerical investigation on the size effect of concrete uniaxial compressive strength under different contact friction

• The concrete mesoscale concretization model is established to consider the heterogeneity of meso-components. • The effect of contact friction on the compressive failure behavior of concrete is studied. • Increasing the friction coefficient makes the size effect more pronounced. • A modified size effect law DHF-SEL is established. The purpose of this work is to examine the quantitative influence of contact friction on the compressive strength of concrete and the corresponding size effect under uniaxial compression. The concrete mesoscale concretization model (CMCM) is established to consider the heterogeneity of meso-components based on the statistical distribution and local spatial correlation theory. The interaction between concrete and steel loading platens is evaluated by defining the contact friction behavior. The uniaxial compression behavior of concrete with different cross-section diameters, height-diameter ratios, and friction coefficients is simulated to analyze the quantitative effect of contact friction. The numerical results show that the hoop effect caused by contact friction constrains the lateral deformation and damage initiation at the loading boundaries of concrete, thus increasing the compressive strength; when the friction coefficient μ = 0 , the slight size effect is mainly caused by the wall effect, while when the friction coefficient μ > 0 , the severe size effect is primarily driven by the contact friction constraint; increasing the friction coefficient improves the sensitivity of compressive strength to sample size, making the size effect more pronounced. The Size Effect Law considering the diameter, height-diameter ratio and friction coefficient (DHF-SEL) is proposed based on the classical Bažant size effect law and CMCM, and then verified with the numerical results and experimental data.

Compaction characteristics assessment of Hot-Mix asphalt mixture using Superpave gyratory compaction and Stribeck curve method

A compaction model of asphalt mixture combined with Stribeck curve theory was established to evaluate the contact friction behavior of compaction characteristics. The results show that the viscosity of asphalt has a linear relationship with temperature in the double logarithmic coordinate, whereas the viscosity of asphalt mastic has a good linear relationship with the temperature in the semi-logarithmic coordinate. The proposed designed compaction stage energy index DCEI can well characterize the compaction characteristics of asphalt mixture. When the asphalt viscosity is in the range of 200–400 mPa·s or the mastic viscosity is in the range of 1–3 Pa·s, the DCEI value shows a low peak value, which is consistent with the Stribeck curve theory. The compactability of asphalt mixture during compaction decreases firstly and then increases with viscosity of the mastic. The DCEI value also decreases firstly and then increases with the average mastic film thickness. The relationship between the viscosity/thickness of the mastic and the DCEI conforms to the trend of the Gaussian formula. When the Stribeck curve theory is applied to the compaction process of asphalt mixture, the compaction process is divided into three states: boundary lubrication, mixed lubrication and hydrodynamic lubrication. The research results help to reveal the compaction mechanism and provide a simple mixture design method to compact easily during construction.

Numerical and experimental study on the joint forming mechanism in the pneumatic splicing process

This study presents an investigation on the joint forming mechanism of pneumatic splicing by numerical and experimental methods. A one-way coupling numerical model concerning interaction between fluid and filaments was established to simulate the complex motion of a flexible body in a spiral flow field. The airflow field in the splicing chamber, which contributes to longitudinal and normal aerodynamic force along a filament regarded as a digital chain composed of a series of interconnected rods, was obtained by a two-equation turbulent computational fluid dynamics model. Contact-friction behavior within filaments was also taken into consideration. An iterative algorithm was adopted to update the displacement of filaments and the corresponding aerodynamic force. A high-speed visualization test bench was built to record the sequence motion of filaments in the splicing process. The splicing mechanism within flexible filaments was identified by comparison between the experimental data and numerical results. The filament portion located in the homolateral rotating channel with respect to orifice is blown to bent by the jet airflow. It contributes to a frontal area in the axial airflow direction, causing the filament to be retracted toward its fixed end. Meanwhile, the portion in the contralateral rotating channel tries to wrap around the opposite filaments due to the spiral airflow. The interaction between filaments generates the contact force and related friction force, which commonly resists the retracting force exerted on the homolateral filament portion. The competition between the two forces determines whether the joint can be formed. Furthermore, the influence of the overlapping length on splicing behavior was discussed.

An experimental method for characterizing friction properties of sheet metal under high contact pressure

Contact friction is present on interacting surfaces of steel thin-walled structural members under axial folding during vehicle crash, and often occurs under relatively high contact pressure (∼100MPa) and sliding velocity (∼6m/s). The contact friction could affect structural deformation mode and kinetic energy absorption capacity, and yet has not received sufficient attention in the area of automotive crashworthiness. The lack of knowledge on contact friction behavior and friction data of sheet metal has long affected the reliability and predictability of vehicle crash simulations. The objective of this study is to develop an appropriate experimental method for friction measurement on self-paired sheet metal under high contact pressure conditions. A fixture is designed for applying clamping pressure of 1–100MPa on contact interfaces, under which sliding friction is generated by additional loading devices. Using a standard material test machine and a drop tower, two experimental configurations are set up for measuring the friction properties of steel sheet couples under the pressures of 1–100MPa and the sliding velocities of 0–6m/s. The test method is proved to be valid and viable in friction tests on a typical high-strength steel sheet. The results show distinct friction behaviors of the high steel under different loading conditions, which has also been discussed.

Contact friction simulation in powder compaction process based on the penalty approach

In this paper, the influence of powder–tool friction on the mechanical properties of the final product is investigated in pressing metal powders. A computational algorithm is presented for simulation of frictional contact in the compaction process of powder. The large deformation finite element (FE) formulation is characterized by the use of penalty approach in which a plasticity theory of friction is incorporated to simulate sliding resistance at the powder–tool interface. The constitutive relations for friction are derived from a Coulomb friction law. A double-surface cap plasticity model is employed together with the nonlinear contact friction behavior in numerical simulation of powder material. The contact friction algorithm together with the cap plasticity model is incorporated within the framework of large FE deformation in order to predict the non-uniform relative density distribution during large deformation of powder die pressing. Finally, the numerical schemes are examined for efficiency in modeling of a set of powder components.

Modeling of large deformation frictional contact in powder compaction processes

In this paper, the computational aspects of large deformation frictional contact are presented in powder forming processes. The influence of powder–tool friction on the mechanical properties of the final product is investigated in pressing metal powders. A general formulation of continuum model is developed for frictional contact and the computational algorithm is presented for analyzing the phenomena. It is particularly concerned with the numerical modeling of frictional contact between a rigid tool and a deformable material. The finite element approach adopted is characterized by the use of penalty approach in which a plasticity theory of friction is incorporated to simulate sliding resistance at the powder–tool interface. The constitutive relations for friction are derived from a Coulomb friction law. The frictional contact formulation is performed within the framework of large FE deformation in order to predict the non-uniform relative density distribution during large deformation of powder die pressing. A double-surface cap plasticity model is employed together with the nonlinear contact friction behavior in numerical simulation of powder material. Finally, the numerical schemes are examined for efficiency and accuracy in modeling of several powder compaction processes.