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

Nowdays,functional devices such as micro-nano optics,fluidic devices,micro-reactors,and tiny-heat sinks,as well as functional materials such as super-hydrophobic materials,light-reflective materials,and conductive/thermally conductive composite materials,are used in biomedicine,automobile manufacturing,and information communication,etc,and there are more and more applications in these fields.The micro-hot embossing method,as one of the typical polymer micro-nano fabrication technologies,has continuously become the source and driving force for promoting the "China Made 2025" innovation and development and continuous progress.Under the background of the rapid development of polymer micro-nano fabrication and the research foundation of the hot embossing method in solid-like state greatly shorting the embossing cycles.Aiming at a series of fundamental scientific issues such as complex constitutive relations that exist in the process of micro-hot embossing in solid-like state,this paper selected the combination of experiments,simulation,and theoretical analysis as research method,and used nanoindentation experiments,creep experiments,stress relaxation experiments,microstructure hot embossing experiments,establishment of constitutive model,relaxation model,and finite element simulation(DEFORM,ABAQUS)as research technique to integrate the stress-strain,creep,and stress relaxation characteristics of polymethyl methacrylate(PMMA)materials at different stages,included mold filling,holiding,and demoulding,and explored the influence law on micro-structured products in the process of micro-hot embossing.Through the results of nano indentation experiments in the PMMA solid-state hot-embossing temperature zone,a first-order single-index constitutive model was established to characterize the stress-strain relationship.Also,it was used to determine the material properties of DEFORM simulation software,and numerical simulation of solid-state micro-hot embossing mold filling was performed,and then the embossing process parameters were optimized.PMMA creep experiments was performed by using a self-built tensile compression creep relaxation tester in solid-state temperature zones,and a three-element correction model with a high degree of non-linear fit was selected from the generalized Kelvin model,standard linear body model,and three-element correction model to establish creep compliance expression.In addition,creep experiments at room temperature for V-shaped groove structure products and micro-lens structure products showed that creep at room temperature is very slow,and there is no significant influence on the geometric characteristics and optical properties of the embossed microstructures in a sufficiently long time.According to the stress relaxation test and the creep law,a stress relaxation theory model was established to achieve the transformation between creep compliance and relaxation modulus.Through the micro-structure solid-state micro-hot embossing experiments of V-groove and hemisphere array under different temperatures and holding times,the applicability and guiding significance of the three-element modified model of stress relaxation for the selection of polymer micro-hot embossing and holding time were verified.Based on the relevant data of the stress relaxation experiment,a Prony viscoelastic constitutive model was constructed,and ABAQUS nanoindentation simulations were performed,and intrinsic link between stress relaxation and nanoindentation was established,and we analyzed its reference value for micro-nano hot embossing.