Investigation Of Viscoplastic Deformation Of Cotton Fabric Reinforced Polypropylene Composite

In order to explore a new way of using waste cotton fabrics,cotton fabric reinforced PP composites are prepared by hot pressing.The mechanical test results show that the tensile strength and impact toughness of the composites are quite remarkable,and they are complementary to the performance of wood plastic composites.The cotton fabric reinforced PP composites are expected to be used in the field of ecological buildings and green decorative.In order to systematically study the viscoplasticity of cotton fabric reinforced PP composite,new cotton fabric is used to prepare cotton fabric reinforced PP composites to avoid large fluctuations in experimental data due to heterogeneous of waste cotton fabrics.The viscoplastic deformation behavior of the composites during the tensile process is analyzed by using of models fitting,and the influence of viscoplastic deformation on the properties of the materials is revealed.Based on the constitutive relationship of the nonlinear differential model and the kinetic model,the time-varying mechanical properties of cotton fabric reinforced PP composites are deduced.Typical waste cotton fabrics and waste cotton-polyester blended fabrics are used to prepare waste cotton fabric reinforced PP composites.On the basis of characterizing its major physical and mechanical properties,the model research conclusions are verified.The main contents and results are summarized as follows:(1)The cotton fabric reinforced PP composite is an anisotropic,the distribution of tensile strength,flexural strength,tensile modulus and flexural modulus of the composite is related to the orientation of cotton fiber,the smaller the angle between the test direction and the warp direction of the fabric,the larger the above parameters.In the cotton fabric reinforced composites,the impact strength,tensile yield elongation are related to the number of cotton yarns in the cross section,that is,the more cotton yarns passing through the test cross section,the greater the value of the two parameters.According to the maximum strength theory in mechanics of materials,the distribution of tensile strength of cotton fabric reinforced PP composite is fitted.According to the maximum energy absorption theory,the impact strength distribution of cotton fabric reinforced PP composites is fitted.(2)The results of static tensile test and Ramberg-Osgood model fitting analysis show that the plastic deformation of cotton fabric reinforced composites is significantly increased with the increase of tensile strength and modulus.The plastic strain of the composites during tensile testing is quantitatively analyzed by the Ramberg-Osgood model.The results show that the plastic deformation of both new and used cotton fabric reinforced composites are higher than that of pure PP except for the orientation 0o of composite.Static tensile tests at different rates show that viscous deformation significantly reduce the tensile strength of cotton fabric reinforced PP composites.The same conclusion is obtained by cyclic tensile test.During the cyclic tensile process,as viscous deformation increased,the strain response to stress increased.Finally,the composites are fractured quickly under cyclic tensile stress which is far lower than the tensile strength.(3)In order to describe the viscoplastic deformation with time,several models are used to fit the tensile processes of cotton fabric reinforced PP composites.The nonlinear differential constitutive model can accurately describe the static and cyclic tension process of cotton fabric reinforced composites,which proved that the stress-strain relationship of cotton fabric reinforced polypropylene composite is nonlinear in the tensile process.By fitting the migration process of molecular segments in cotton fabric reinforced PP Composites under stress,a kinetic model is obtained to describe viscoplastic deformation behavior under constant and cyclic stresses.Both the kinetic model and the nonlinear differential constitutive model prove that the inelastic deformation in the tensile process of cotton fabric reinforced PP composites can be decomposed into independent viscous deformation and plastic deformation.(4)The work hardening process and degradation of mechanical property of cotton fabric reinforced PP composites are explained from the perspective of the trend of viscous deformation rate and plastic deformation rate.The nonlinear differential constitutive model and kinetic model are used to fit the tensile process of cotton fabric reinforced PP composites,and the same conclusion is obtained.At the initial stage of cyclic tensile test,the plastic strain and viscous strain rate of composites are higher,while with the process of the experiment,the plastic strain rate and viscous strain rate decreased.There is an intersection point between the viscous deformation rate curve and the plastic deformation rate curve of the cotton fabric reinforced polypropylene composite,that is the equivalent point.The experimental and theoretical analysis of different models shows that the response of strain corresponding to stress changes at both ends of the equivalent point.Before the equivalent point,the plastic deformation of cotton fabric composites in a single test cycle is greater than the viscous deformation,while the strain response to stress decreases,and the material shows the hardening behavior.After the equilibrium point,the plastic deformation of cotton fabric composites in a single test cycle is lower than viscous deformation,the strain response to stress is enhanced,the properties of the composites decrease gradually.Therefore,the competition of viscoplastic deformation rate is the reason for the time-varying mechanical properties of cotton fabric reinforced PP composites.(5)Four typical waste cotton fabrics and two typical waste cotton-polyester blended fabrics are used to prepare waste cotton fabric reinforced PP composites,and their density,water absorption,swelling in water,static and dynamic mechanical properties,and viscoplastic deformation are carried out.The comprehensive analysis and model fitting results show that the PP-based composites prepared from waste cotton fabrics are generally similar to which made from new cotton fabrics,and the waste cotton fabrics can be used to strengthen the PP composites.In summary,cotton fabric can greatly improve the properties of polypropylene composite,and increase the energy absorption at fracture of the composites,while increase the viscoplasticity to a certain extent.Different models are used to analyze and fit the stress-strain behavior of cotton fabric reinforced composite in different forms of tensile process.This study not only comprehensively analyses the stress-strain behavior of cotton fabric reinforced composite in the tensile process,but also provides a reference method for the study of nonlinear viscoplasticity tensile behavior of fiber-reinforced composite.