Solid-like Polymer Stress-strain Laws In The Process Of Micro Hot Embossing

In modern society, the level of manufacturing industry is a direct manifestation of the strength of a country. Especially with the advancement and development of nanotechnology, micro machining technology based on molecular and even atomic level occupies an increasingly important position in the field of traditional equipment manufacturing industry. In our life, the material with micro or nano structures is closely related to our basic necessities. And in many areas of our daily life, especially in many areas where precision structures are necessary, the microstructures have a pivotal position. These microstructures with micrometer or nano scale dimensions are often referred to as "micro structure". Also, the processing and manufacturing processes of micro structures are important parts of the transition from theory to application. Micro hot embossing technology is a kind of micro structure machining method which has the advantages of low-cost, high precision, large scale and high efficiency. Based on the advantages of micro hot embossing methods, solid-like isothermal micro hot embossing process is a significant shortening of the micro hot embossing technology processing cycle. At the same time, this new technique could reduce the cost of production and improve the replication rate of the micro structures.With the development of new technology of polymer solid-like isothermal hot embossing, it is so significant to study the variation law of polymer viscoelastic properties and the forming mechanism of micro structures in the process of production. In order to promote the large scale industrial production of polymer products with micro or nano structures,we are supposed to make the most accurate optimization and improvement of the machining process. Of course, all of these could be achieved when the stress and strain behavior of the polymer material in the process of micro hot embossing has been fully understood.This thesis is based on the above content, to meet the experimental requirements, adding a temperature control module and a data acquisition module to the tensile compressive creep relaxometer device in the laboratory. In order to obtain the related properties of the polymer material near its glass transition temperature, the polymethyl methacrylate (PMMA)is selected as the experimental material. And the stress relaxation experiments are carried out under its glass transition temperature. At the same time, the experimental results are summarized and analyzed based on the Arrhenius equation from the energy point of view. When the ambient temperature (T) is lower than the glass transition temperature (Tg) of the polymer, the relationship between the relaxation time constant ? and the outside temperature T of the PMMA is found. Also, the experimental results provides theoretical support for the determination of the moving factor aT of the polymer below its glass transition temperature.The speed of the polymer stress relaxation process is described by defining the physical quantity of the relaxation rate. Based on the glass transition temperature of PMMA, the temperature range of 30 ? to 130 ?is divided into two parts. The stress relaxation experiments of PMMA specimen are carried out under several different temperature conditions,and the relaxation rates of the polymer material under different temperatures are calculated and analyzed. According to the relaxation rate of PMMA specimen under different temperature conditions, the relaxation rate - temperature (p - T) curve is drawn. Also, based on the exponential model and the experimental data, the relaxation rate - temperature (p - T)exponential model for PMMA is established. The relaxation rate and relaxation time constant of PMMA under different temperature conditions can be calculated and analyzed by using this model.In order to obtain polymer products with high reproducibility in the solid-like micro hot embossing process, considering the different effects of the cooling rate on the relaxation process of the polymer micro or nano structures, a series of experiments on the relaxation process of the polymer material under different cooling rates are also carried out from this thesis.Besides, the calculation method and quantitative analysis of the experimental data and the experimental results are carried out. The stress relaxation variation model of the polymer material is established by calculating the appropriate parameters. This model has certain reference value and guidance significance for the selection of the holding time and the control of the cooling rate in the solid-like micro hot embossing process.The method of molecular dynamics simulation is used to simulate and analyze the process of solid-like micro hot embossing. It is an effective method to study the viscoelasticity of the polymer material and the stress-strain law during the process of micro hot embossing. Based on the Materials Studio software, the molecular model for the simulation of solid?like micro hot embossing system is constructed. And the microstructural filling stage and the packing relaxation stage are simulated and analyzed.The viscoelastic properties of the polymer material and the correlation between stress and strain in the solid-like micro hot embossing process are summarized and analyzed from the aspects of energy, molecular density,molecular size change, velocity distribution and velocity correlation function.