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In full-field 3D displacement measurement, stereo digital image correlation (Stereo-DIC) has strong capabilities. However, as a result of difficulties with stereo camera calibration and surface merging, 360-deg panoramic displacement measurements remain a challenge. This paper proposes a panoramic displacement field measurement method in order to accurately measure the shape and panoramic displacement field of complex shaped objects with natural textures. The proposed method is based on the robust subset-based DIC algorithm and the well-known Zhang's calibration method to reconstruct the 3D shape and estimate the full-field displacements of a complex surface from multi-view stereo camera pairs. The method is used in the determination of the scale factor of the 3D reconstructed surface and the stitching of multiple 3D reconstructed surfaces with the aid of the laser point cloud data of the object under test. Based on a discussion of the challenges faced by panoramic DIC, this paper details the proposed solution and describes the specific algorithms implemented. The paper tests the performance of the proposed method using an experimental system with a 360-deg six camera setup. The system was evaluated by measuring the rigid body motion of a cylindrical log sample with known 3D point cloud data. The results confirm that the proposed method is able to accurately measure the panoramic shape and full-field displacement of objects with complex morphologies. [ABSTRACT FROM AUTHOR]

Stereo digital image correlation (stereo-DIC) technique has received special attention in detection and monitoring for quantifying and monitoring the displacement alterations on the surfaces of historical buildings. However, in the field of structural health monitoring of cultural relic, the method of prefabricating speckle patterns on the monitored object is inappropriate. And the method proposed in several literature sacrifices the scale information or the calibration board is used multiple times. This paper provides a practical and effective deformation monitoring system based on stereo DIC for 3D deformation evaluation of the stern of archaeological wooden shipwreck. To calibrate the stereo camera for archaeological wooden object measurement, a self-calibration is proposed to calibrate extrinsic parameters of fixed cameras using the objects surface shape and texture without using a calibration board and sacrificing scale information. In particular, the deformation monitoring data can be used to compensate for the differences in material properties between mo and archaeological wood. The experiment demonstrated that the proposed deformation monitoring system and self-calibration methods are feasible and accurate. Based on this, the measures displacement fields of the archaeological wooden shipwreck stern are presented, and the material properties of the finite element analysis of the shipwreck during the design of the supporting structure were corrected by the deformation monitoring data. The results show that the proposed method has the advantages of good flexibility, strong applicability, and high precision on 3D structural deformation monitoring and structural design of archaeological wooden relics. [ABSTRACT FROM AUTHOR]

Heterogeneous materials are widely applied in many fields. Owing to the spatial variation of its constitutive parameters, the mechanical characterization of heterogeneous materials is very important. The virtual fields method has been used to identify the constitutive parameters of materials. However, there is a limitation: constitutive parameters of one material have to be a priori; then, constitutive parameters of the other one can be identified. Aiming at this limitation, this article presents a method to identify the constitutive parameters of heterogeneous orthotropic bimaterials under the condition that constitutive parameters of both materials are all unknown from a single test. A constitutive parameter identification method of orthotropic bimaterials based on optimized virtual field and digital image correlation is proposed. The feasibility of this method is verified by simulating the deformation fields of a two-layer material under three-point bending load. The results of numerical experiments with FEM simulations show that the weighted relative error of the constitutive parameter is less than 1%. The results suggest that the variation coefficient-to-noise ratio can perform a priori evaluation of a confidence interval on the identified stiffness components. The results of numerical experiments with DIC simulations show that the weighted relative error is 1.44%, which is due to the noise in the strain data calculated by DIC method. [ABSTRACT FROM AUTHOR]

• An IRT indicator that can provide precursor information on wood instability and failure is proposed. • A precursor point to distinguish the elastic and plastic stages of wood is proposed. • Verified that the IRT distribution on the wood surface conforms to the Gaussian distribution. Anomalies in infrared radiation temperature (IRT) are usually accompanied via the sprouting and expansion of cracks. Precursor information of crack sprouting and extension is essential for predicting the condition as a material of structural fields. In order to investigate the precursor information of instability and failure of wood, the infrared radiation characteristics of wood during failure were analyzed by a three-point bending test. Based on the IRT probability distribution conforming to the Gaussian distribution, an indicator is defined in this paper: the peak probability density (PPD) of IRT. The changes in PPD were combined with the four stages of typical damage to determine the precursor information, and identified a precursor point on the PPD-time curve. The relations between IRT indicators and wood fracturing were also investigated to explain the anomalies in IRT indicators, the precursor point characterize the transition zone from the elastic to the plastic phase of deformation when the wood is under pressure. Besides, the samples before and after the precursor point were also compared by macroscopic (digital image correlation, DIC) and microscopic (scanning electron microscope, SEM), the results proved the validity of the precursor information. Comparison with other IRT indicators, the IRT indicator proposed in this paper has a higher sensitivity to IRT abnormalities in the failure process of wood structures. [ABSTRACT FROM AUTHOR]

The correlation-based image subset matching methods such as digital image correlation (DIC) are widely used for measuring the deformation fields. The specimen surface must be covered with speckle patterns, or more exactly, random intensity distributions with sufficient contrast, which act as a carrier of deformation information, to acquire reliable and accurate matching in the correlation calculation. The requirement of the artificial speckles on the specimen surface inevitably contaminates the specimen. To maintain the cleanliness of the specimen surface, an in situ deformation estimation method without speckle fabrication is developed and its result is demonstrated. Topological similarity measurement (TSM) is a feature vector-based displacement estimating algorithm for full-field deformations that uses feature vectors that encode the relative positions of neighboring mark spots. Compared with the DIC method, this approach makes up for its deficiency in displacement estimation of speckle-free flat surface by incorporating a topological arrangement-based feature vector, subpixel center location method, and biharmonic spline interpolation method. Experimental results indicate that the proposed TSM method is feasible to become the preferred displacement estimation method for uniform deformation. As a complement to the DIC method, the TSM method is more suitable for uniform deformation distribution, which requires high measurement accuracy but cannot use DIC. [ABSTRACT FROM AUTHOR]