The Research Of Measuring Method Of Polymer Sheet Surface Internal Stress Based On Ultrasonic Technology

The Surface internal stress of polymer sheet is the key to affecting using performance, the precision of geometric size and quality, which is the most easily neglected factors. In polymer sheet products precision injection molding process, how to effectively control the size of the surface stress can improve the surface quality of the plastic sheet products, and prolong its service performance. However, how to accurate measure the size of the surface stress is the premise of effective controlling surface stresses in the s polymer sheet products. Because internal stress in the products is a very complex stress state, this article come up with Rayleigh wave method of measuring surface stresses based on acoustic elasticity theory through the research of internal surface stress model, the characteristics of Rayleigh wave propagation in the products surface and polymer sheet products structure characteristics. The change of Rayleigh wave velocity is dependence of surface internal stress of polymer sheet products, which realize the surface characterization and measurement of internal stress of polycarbonate sheet products. Main content is as follows:1.Through consulting the relevant literature about measuring internal stress by ultrasonic, and the analysis of ultrasonic stress birefringence effect and polymer products structure characteristics under the effect of internal stress structure proves the feasibility of which ultrasonic measures internal stress.2.Through the transmission characteristics of Rayleigh wave and the analysis of the characteristics of the polymer sheet products structure, this article proposes that Rayleigh wave measures surface stresses of polymer sheet products, and set up the model of surface stress. Rayleigh surface wave acoustic elasticity formula is deduced through acoustic elasticity theory and transmission characteristics of Rayleigh wave. In order to further simplify the measuring process, this article puts forward the characterization methods, which realize fast and qualitative characterization of surface internal stress of polymer sheet products.3.This article, we set up different experimental apparatus, including one-way dynamic stress experiment device and testing experiment device of surface stresses of flat and curved sheet products based on Rayleigh wave theory of measuring surface stresses of polymer sheet products and the shape of polycarbonate sheet specimen samples.4.The accuracy of the measured surface stresses of polymer sheet products is further validated through the experiment, and the measured results has good consistency with the method of photo elastic measurement. The experimental results show that Rayleigh wave velocity has different trends with the different stress of the polymer products. Tensile stress reduces Rayleigh wave velocity, while compressive stress increase the Rayleigh wave velocity. The Rayleigh wave velocity is different at different positions of polymer products, which show that the internal stress is different at different positions.