Reliable fracture simulations are expected to contribute to the longer life cycle of structures. The phase-field fracture (PFF) model is anticipated to be a robust approach to reproducing crack propagation and branching. Measurement techniques for detecting cracks and fractures have also advanced and are widely used for health monitoring. In the field of structural analysis, a data assimilation method using the full-field measurement data obtained by digital image correlation has been proposed. The data assimilation method is attracting attention as a method of improving the simulation accuracy by utilizing the time-series measurement data obtained from such measurement techniques. In this study, we apply for the first time the nonsequential data assimilation method minimizing the cost function using treestructured Parasen estimator (DMC-TPE method) to assimilate full-field strain measurement data into PFF simulations. In this paper we validate the proposed data assimilation method through numerical experiments, where data assimilation is performed using the pseudo-measurement data obtained from PFF simulations conducted with parameters assumed as true values. The results demonstrate that the proposed method enables the simultaneous inverse estimation of multiple parameters included in the PFF model. The validation results revealed that, although the DMC-TPE depends on the initially estimated values, the parameters that significantly impact the simulation results were accurately estimated.

To improve the accuracy of sheet forming analysis, it is necessary to model an anisotropic yield surface on the basis of the measurement of biaxial stress status. To measure the plastic anisotropy, uniaxial tensile tests with an angle inclined to the rolling direction are carried out. Biaxial tensile tests with cruciform specimens are also preferred to be carried out with an angle between the axes of principal stress and the anisotropy. However, the accuracy of measured stress and the direction of plastic strain increment in the inclined biaxial tensile tests has not been verified. In this study, cruciform biaxial tensile tests with an inclined angle were analyzed using the finite element method. Using the finite element analysis as a virtual experiment, the stress points on equal plastic work contours and the directions of plastic strain increment were obtained from the tensile load and local strain. The results of virtual experiments were compared with the yield surface and normal direction derived from the yield function used in the finite element analysis. It was verified that the yield surface can be measured properly in biaxial tensile tests using cruciform specimens with an inclined angle.