Study Of Thermal Stress Measurement Based On DSSPI

Thermal stress measurement has been an important subject in the field of modern measurement technology for a long time,and there are a great number of important application scenarios in many fields,such as in the fields of novel materials,aerospace,microelectronic chips,and railway transportation industries.The traditional thermal stress measurement method has various shortcomings that the measurement accuracy is not high,they are a kind of contact measurement,or the structure is complex and poor in reliability.Most of them are hard to meet the needs of thermal stress measurement perfectly.Aiming at solving the problems in traditional measurement methods,this dissertation proposes a novel thermal stress measurement system based on digital shearing speckle pattern interferometry.Compared with the existing technology,it can realize the real-time and simultaneous measurement of multi-component thermal stress,and also has the advantages of non-contact and full-field measurement,strong resistance to noise,high accuracy,and flexible adaptive ability.The main innovativeness of this dissertation are summarized as follows:(1)Aiming at solving the problem that the existing thermal stress measurement methods cannot realize the real-time,full-field,multi-component and non-contact measurement,this dissertation puts forward a novel thermal stress measurement method based on digital shearing speckle pattern interferometry.This method is of high accuracy and good real-time performance.It can realize real-time full-field thermal stress measurement without contacting the object under test,and it can measure multiple components in the strain matrix at the same time and then obtain the corresponding components of the stress matrix of the object.(2)To solve the problem that in the traditional shearography it is required to lighting and acquisition twice with the symmetrical angles to obtain the in-plane components,this dissertation improves the optical path in the measurement system for in-plane components and presents a novel computing method to obtain the in-plane components.The result of the experiment proves that the novel method can ensure the accuracy and realize the real-time measurement of in-plane components,in which the in-plane and the out-of-plane components are obtained at the same time rather than gradually and both the optical path and the process of measurement are optimized.(3)Aiming at solving the background noise problem of the traditional Wollaston prism under high power illumination light,this dissertation optimized the shearography optical path based on the above multi-component thermal stress measurement system,and a novel shearing device based on the Rochon prism is proposed.The experimental results show that the maximum relative measurement error in the out-of-plane component measurement system using the Rochon prism is 4 %,while the maximum relative measurement error of the out-of-plane component measurement system using the traditional Wollaston prism as the shearing device is 6 %.It is proved that the novel shearing device with Rochon prism can reduce the noise caused by the shearing path,improve the stability of the shearing device under high power illumination,and improve the measurement accuracy of the multi-component measurement system.(4)Based on the above multi-component thermal stress measurement system,this dissertation presents a heterodyne modulation device,which is suitable for the multicomponent shearography system to solve the problem that optical system is susceptible to environmental infection.The heterodyne device is based on lithium niobate crystal and realize the synchronous modulation to two polarization directions orthogonal to each other by the way of electro-optical effect,which is suitable for the multi-component shearography system.The result of the experiment shows that the maximum relative error of out-of-plane component measurement under vibration is reduced from 140% to less than 6% after modulation,which proves the effectiveness of the modulation device in improving the resistance to noise.