Study On Thermal Viscoelastic-plastic Forming Mechanism Of Polymeric Micro-hot Embossing

Aiming at the key scientific problems that it is difficult to accurately predict the essential characteristics of yield,softening and hardening of thermo-viscoelastic plastic deformation in polymer micro-hot embossing process,a new thermal viscoelasticviscoplastic stress-strain constitutive model which can scientifically describe the intrinsic characteristics of yield,softening and hardening of thermo-viscoelastic deformation in polymer micro-hot embossing process was established.Based on above constitutive model,the Thermo-viscoelastic-plastic micro-hot embossing mechanism model and its corresponding numerical simulation method were constructed.The simulation of micro-hot embossing process of bionic self-cleaning functional surface structure of polymer microstructures arrays with the bionic superhydrophobic characteristic of rice leaves was systematically carried out.The co-relation theory of processing parameters-polymer performance parameters-micro-hot embossing characteristics was studied and constructed,and the mechanism of micro-hot embossing was revealed.which lays a scientific theoretical foundation for enriching and developing the rheological theory of polymer micro-hot embossing.The main achievements are as follows:A new thermal viscoelastic-viscoplastic stress-strain constitutive model which can scientifically describe the intrinsic characteristics of yield,softening and hardening of thermo-viscoelastic deformation in polymer micro-hot embossing process was established.Based on above constitutive model,a numerical simulation method for thermo-viscoelastic-plastic micro-hot embossing process was constructed,in which the technical bottleneck of thermal viscoelastic-plastic finite element simulation of polymer solid phase with strain softening characteristics has been effectively solved.It provides technical support for high precision simulation of polymer micro-hot embossing process with microstructural characteristics.The relationship between hot embossing temperature,filling height,substrate deformation stress and hot embossing force was studied and constructed by means of the simulation of micro-hot embossing process of polymer bionic self-cleaning functional surface of microstructures arrays with the bionic superhydrophobic characteristic of rice leaves.Research shown that under the condition of the same filling height,the equivalent stress of polymer substrates is negatively correlated with the hotpressing temperature,and,when the hot-pressing temperature is constant,the equivalent stress on the substrate is approximately linearly and positively correlated with the filling height,under the condition of the same filling height,the embossing force is negatively correlated with the hot-pressing temperature,and under the condition of same hot-pressing temperature,the embossing force is positively correlated with the filling height.It is found that the equivalent stress of the polymer substrate increases gradually from the bottom surface of the substrate to the top surface of the hot pressing,then suddenly drops,and finally restores the evolutionary law of the gradual increase in the thermal viscoelastic-plastic solid state.It shows that a local low stress ring region with sudden drop of equivalent stress appears near the upper surface of hot pressing,and the strain softening characteristic is embodied.Increasing the temperature of micro-hot embossing can make the polymer substrate evolve from elastic-plastic solid state to thermo-viscoelastic high elastic state,and make polymer substrate enter semi-solid state.Which the stress required for filling deformation can be drastically reduced.This is the technical precondition for low pressure micro-hot embossing of bionic Super-sparse characteristics and self-cleaning functional surfaces with microstructures arrays.