Study On Lubrication Behavior Of Non-Newtonian Fluid Food Under Soft Contact

With the improvement of the quality of life,people’s daily diet are not only to fill themselves,but also to put forward higher requirements for food palatability.Good eating experience can enhance consumers’feelings and pleasures.Studying the friction characteristics of food between the tongue and palate is important for understanding the true oral processing rules and improving the taste of food.In this thesis,the oral lubrication behavior of non-Newtonian fluid foods under soft contact were explored.It provides a reference for restoring authentic oral processing,food perception,and food development.Firstly,lubrication experiments of the non-Newtonian fluid foods in the simulated soft oral environment were conducted.Silicone rubber discs were used as soft tongue substitutes.Silicone rubber balls and nitrile butadiene rubber balls were applied as soft palate substitutes to simulate the mechanical responses of biological tissues within the oral cavity.In addition,304 steel balls were adopted as traditional substitutes for the upper jaw to compare the effects of itself and the above soft friction pair configurations on fluid food lubrication.Two non-Newtonian fluid foods（milk,yogurt）and pure water were tested for oral lubrication in vitro.It was found that different maxillary substitutes changed the frictional behavior of the experimental samples in the contact area.For fluids with low viscosity and low storage/loss modulus,soft friction pairs have more significant viscoelastic responses and larger friction coefficients.For fluids with high viscosity and high storage/loss modulus,the interaction between interfaces are small,and the contribution of the viscoelastic responses of the contact bodies to the friction coefficients are reduced.Increasing wettability and particle size of fluid components can improve lubrication properties.Due to the increase in fluid entrainment area and the reduction in roughness,the rising load will cause the friction curves to move downward and left.Therefore,when conducting in vitro food oral lubrication experiments,maxillary substitutes have an apparent impact on lubrication behavior.Compared to rigid maxillary substitutes,the viscoelasticities of rubbers are more compatible with the mechanical responses of biological tissues.Then,soft contact configurations of silicone rubber balls and silicone rubber discs were used to simulate the oral processing environment.And lubrication experiments of honey-water solutions with different mass fractions honey were carried out.A complete Stribeck curve of non-Newtonian fluid honey-water solution was successfully constructed.The results showed that with the increase of honey mass fraction,the boundary lubrication regimes of the fluid friction curves decreased and the lubrication state transition occurred at lower speeds.Higher viscosity and wettability enhance the film forming and entrainment capabilities of the fluid,and reduce the friction coefficients in the boundary and mixed regimes.However,changes in wettability have little impact on the elastohydrodynamic lubrication regime.The honey-water solution has the best lubricity when the V（Speed×Viscosity）value is around 9.7×10^-4.Finally,a tongue-upper jaw lubrication model was established by the finite element method to investigate the effects of velocities,fluid viscosity and viscoelastic parameters of the friction pairs on fluid lubrication.It was found that variations in sliding velocities,fluid viscosity and solid viscoelasticity could change the distribution of fluid pressure field and film thickness.The film thickness exhibited a horseshoe shape,and the second pressure peak existed near the exit region.The empirical formula was modified based on the contribution of deformation loss of soft solids to friction.The lubrication curves of honey-water solution in the elastohydrodynamic lubrication regime was successfully fitted.It provides a reference for the study of tongue-upper jaw lubrication.