Research On Three-wavelength Digital Photoelasticity Stress Measurement Technology

In many fields such as aerospace,transportation,shipbuilding,and so on,internal stress distribution is an important factor causing aging and damage of components,and it is objectively required to measure the internal stress distribution.However,the internal stress distribution of components is very complex.To meet the application in different fields,many stress measurement methods have been developed,such as resistance sheet strain method,fiber grating method,holographic interferometry,moire interferometry,speckle interferometry,digital photoelasticity method,and so on.Among them,the digital photoelastic method has a wide range of applications and high accuracy and has prominent advantages in determining the internal stress distribution,stress concentration coefficient,and full field principal stress direction of components.The basic principle is to make an optically sensitive material into a model similar to the physical shape and place it in a polarized light field.The refractive index of the optical material will change with the magnitude and direction of the stress in the model.By measuring the interference fringes formed by the transmitted light,and after computer analysis and processing,the magnitude and distribution of the stress in the model can be obtained.The traditional digital photoelasticity method adjusts the polarization state of the illumination light through the mechanical rotation of the polarization device,so the measurement device is very complex and the measurement speed is slow.The main work of this article is as follows:1.This paper proposes a dual-wavelength photoelastic stress measurement technique.By using two light sources with similar wavelengths to irradiate the model in turn and record the photoelastic stripes,the proposed dual-wavelength algorithm is used to analyze and process the photoelastic stripe patterns,and the internal stress distribution of the model can be obtained.In this paper,the theoretical analysis,simulation,experimental verification,and error analysis of dual-wavelength technology under two different conditions,namely,circular polarized light field and linear polarized light field,are presented.A comparative analysis of the measurement results of dual-wavelength method and traditional six-step phase shift method is also presented.Due to avoiding the rotation of the polarizer required by traditional photoelastic techniques,the data collection of this method is very rapid,and it is possible to use very simple and compact optical devices to achieve dynamic sample measurement.2.In order to improve the accuracy of the dual-wavelength technique,this paper further optimizes the algorithm and proposes a three-wavelength photoelastic stress measurement technique.By introducing a third light source with a similar wavelength and using the proposed three-wavelength algorithm to remove errors,the measurement accuracy is improved,and the maximum range?_max expands to 15394 nm,which is about 24 levels of photoelastic fringes.In addition to theoretical analysis,the simulation and experimental verification of the three-wavelength method are also presented,as well as a comparative analysis of the measurement results with the six-step phase shift method.The simulation results show that the error of the six-step phase shift method is about 0.61‰,the error of the three-wavelength method in the circularly polarized light field is about 0.34‰,and the error of the linear polarized light field is about 0.41‰.The experimental results show that compared to the measurement results using the six-step phase shift method,the maximum absolute error of the measurement results using the three wavelength method in the circularly polarized light field is about 15 nm,and the average error is about 3.0 nm;The maximum absolute error of the measurement results under linearly polarized light field is about 13 nm,and the average error is about 2.4 nm.This indicates that the measurement accuracy of the three-wavelength method proposed in this paper has reached or even exceeded the measurement accuracy of the traditional six-step phase shift method.The three-wavelength photoelastic stress measurement technology proposed in this paper can achieve rapid measurement of stress in a model with high accuracy,providing a new idea for the measurement of dynamic samples,and providing a scientific basis for the further development of digital photoelastic methods,which has certain reference value and help in solving practical engineering problems.