Online Measurement Of Stress-induced Birefringence In Polymer Materials

The properties of raw materials obtained through rheological research play an important guiding role in daily manufacturing.The study of rheological properties of materials is a bridge between process design and product performance prediction,so the measurement of rheological properties is very important.Optical measurement has been widely used in rheology.In the 21 st century,many optical test methods have been applied to solve rheological problems（for example,polarization state measurement,scattering,diffraction,laser Kepler velocity measure ment）,most of the applications are based on polarization measurement or analysis of the interaction between laser polarization and samples.When the polymer material is deformed,the refractive index and stress become anisotropic.The relationship between refractive index and stress is always an important subject in rheological optics.Therefore,this paper meets the requirements of real-time testing of tensile stress of samples,and can study the variation of tensile degree and orientation of polymer chain in more detail through online measurement of tensile stress.Therefore,in this paper,the refractive index tensor is tested by designing optical structure and arranging optical elements to extract sufficient information of light polarization state,so as to uniquely determine the anisotropy of refractive index tensor.First of all,a preliminary design to light source,polarizer,sample table,polarizer,detector composed of the test light path.The birefringence and orientation information of polymer material during tensile orientation were obtained by selecting the appropriate arrangement of optical elements of polarizer and polarizer.In the construction process of test optical path,the change of polarization state of polarized light after passing through linear optical element is analyzed by Jones matrix,the refractive index of material is analyzed by Muller matrix,and the information of the final light is expressed by Stokes vector.After constructing the optical path of stretching birefringence of polymer materials,the program written by Lab VIEW FPGA is used to collect optical signals and analyze data.A quarter wave plate is used to test the constructed birefringence measurement optical path to obtain the results of birefringence.By comparing the obtained experimental data,the accuracy of the designed polymer material birefringence measurement optical path is verified.Linkam tensile heat table is assembled on the sample table of the testing optical path and connected with the testing optical path to monitor the relationship between the stress and the change of birefringence during the processing of polymer materials in real time,so as to better improve the processing process.The change of birefringence was obtained by tensile test of industrial polystyrene spline,and the change of stress was obtained by stress optical rule.At the same time,the dynamics of three-dimensional spherical polymer can be studied by rheological optics testing platform.