Prediction Of Full-field Strain Using Vibration Displacement Of Limited Points

In the health monitoring of structures,the dynamic stress and strain test is the main method to determine its overall fatigue,and excessive stress will seriously affect the strength of the structure,resulting in deformation or even fracture of the structure,thereby affecting the reliability of the experiment and the service life of the workpiece.Therefore,it is of great significance to test the dynamic stress and strain of the structure.At present,the commonly used methods of stress and strain measurement include strain electric measurement,acoustic measurement or optical measurement,etc.Although these methods have achieved certain applications in the measurement of stress and strain,they are difficult for lightweight or rotating structures,and these methods measure the strain data at finite points.The defects or failures at the unmeasured points may not be found,and it is not realistic to arrange sensors in all positions on the structure.These methods cannot obtain full-field strain data,so they cannot be monitored in all aspects.Therefore,it is of great significance to develop a non-contact full-field dynamic strain method.In this paper,a full field dynamic strain measurement method based on finite point dynamic displacement information is proposed.The concrete realization step is to obtain the vibration displacement data of finite measured points on the structure by binocular stereo vision technology,and to extend the displacement of finite measured points to full field displacement information by means of modal expansion theory combined with its modal mode shape.According to the relationship between displacement and strain in mechanics of materials,the full-field strain of the structure is obtained.In order to verify the validity and applicability of this method,the paper carries out numerical simulations of simply supported beams under sinusoidal loads and random loads,experiments on three different excitations of a cantilever beam,and experiments of sinusoidal and random loads on the cantilever plate.The results were compared with the strain gauge measurement data.All the numerical simulation and experimental results show that this method is feasible in predicting the full field dynamic strain,and the accuracy of the predicted strain is higher.