Identification Methods Of Mechanical Properties Based On Full-field Measurements And Its Applications

Faced with the extreme measurement environment,such as high-temperature thermo-mechanical coupling and the limited measurement space etc.,it is very difficult to measure multi-parameter for the traditional identification method based on single point deformation measurement.Recently,the mechanical parameter inversion method based on full-field deformation measurement has been developed rapidly.The tested parameters could be measured by analyzing the full-field deformation of tested specimen with the help of deformation field post-processing technique based on the constitutive relation of materials.Due to the various and sufficient mechanical response provided by the full-field deformation data,a variety of thermo-mechanical parameters could be obtained simultaneously through one experiment.In this paper,the integrated digital image correlation(I-DIC)method was improved.The decoupling of the thermo-mechanical coupling deformation and simultaneous identification of thermo-mechanical multi-parameter were realized.To solve the problem caused by blind area during the characterization of mechanical parameters based on indentation deformation measured by optical method,the diffraction-assisted image correlation(DAIC)technology for 3D morphology and deformation measurement were improved in this paper.Then,the 3D no-blind full-field indentation deformation of the tested specimen was retrieved using the improved DAIC method,an indenter-fixed in-situ loading and a no-blind area imaging device designed and developed here.In this paper,during the study of I-DIC method,the analytical solution of the full-field displacement of three-point bending test was deduced based on linear elasticity theory.The shape function of thermo-mechanical coupling deformation was constructed,which includes the rigid-body translation,rigid-body rotation and thermal expansion.According to Lucas-kanade nonlinear optimization principle,the objective function and iterative increment of the I-DIC method developed in this paper were constructed,the iterative optimization algorithm was realized by programming.With the help of high temperature speckle fabrication technology(Invention Patent,China,ZL201210146916),high temperature filter imaging system and the I-DIC method developed in this paper,the decoupling of the thermo-mechanical coupling deformation and simultaneous identification of thermo-mechanical multi-parameter of Ni-base alloy were accomplished,the reliability of the I-DIC method was proved by error analysis.In the mechanical inversion based on 3D indentation deformation measurement,parameter calibration method of the diffraction-assisted image correlation(DAIC)system was improved,and the completely image-based parameter calibration method was achieved.By using a more accurate optical imaging model,the precision of this method for 3D deformation measurement was improved.The accuracy of improved parameter calibration method and 3D deformation measurement equation were testified through 3D topography and displacement measurement experiments.By using the indenter-fixed in-situ loading,the no-blind area imaging device and the improved DAIC method,the 3D full-field deformation of silica gel surface was achieved,the feasibility of mechanical parameters measurement for isotropic material based on the measured deformation were discussed.