Research On Measurement Of Blade’s Deformation And Section Stiffness Based On DIC

The blade is an important component of the helicopter.In the working state of the helicopter,the paddle is under a complex load.The deformation of the blade and torsional rigidity of the blade section,the vibration stiffness and the wielding stiffness have great influence on the mechanical properties of the helicopter rotor system.At present,the method of measuring the stiffness of blade section mainly includes laser triangulation method,resistance strain gauge method and so on,these methods have low measurement accuracy and reliability.This paper presents a measurement method based on computer vision and digital image correlation.The three-dimensional surface of the blade before and after loading is reconstructed using digital image correlation to obtain the blade deformation before and after loading,and then the torsional rigidity,the vibration stiffness and the wielding stiffness of the blade section are calculated and analyzed.In this paper,the key technologies of the static deformation and stiffness measurement of the blade based on digital image correlation are studied.The main research contents and innovations are as follows:First,study the theory of the digital image correlation deeply.The methods of displacement model,correlation,optimization algorithm,subpixel interpolation and growth matching in digital image correlation are studied in detail.And the classical DIC is programmed.Aiming at the shortcoming of the classical DIC method,the DIC method combined with the inverse compositional matching strategy and the Gauss-Newton optimization algorithm is used to improve the matching speed of the DIC method.Secondly,the strain measurement method based on 3D DIC is studied,and the surface strain algorithm based on grid technology is proposed.In this paper,3D DIC method based on binocular stereoscopic vision is used to reconstruct the dense 3D surface before and after the deformation of the material,which is similar to the orthogonality grid fabricated on the sheet metal surface.Based on this,a strain calculation method based on non-orthogonal grids is proposed.Thirdly,the torsional deformation,wiggle deformation and waving deformation of helicopter blades are deeply analyzed.Torsion model and bending model are established,and the formula of torsional rigidity,pendulum stiffness and wielding stiffness are deduced according to the model.Last,do experiments to verify the algorithm,count the repeat error and analyze the source of error.The experimental results show that the proposed strain measurement method based on DIC and non-orthogonal grid technique is feasible.In this paper,the method of measuring the torsional stiffness,waving stiffness and vibration stiffness of the profile has high repeatability,and can be used as a supplement or an alternative method of laser triangulation and strain gauge method.