Abstract The ring‐core method is a mechanical technique used to determine the residual stresses on the surface of materials by milling a narrow circular groove around the point of interest and monitoring the strain variation.Original stress can be evaluated by using the relaxed strain through the linear elasticity theory. In case of a highly stressed field, the yielding of the material around the groove and its bottom causes an error related to the hypothesis of the basic theory of the method.In this paper, the plasticity effect of calculated residual stresses was considered. For this purpose, the ring‐core development and stress relaxation in a generally stressed body were simulated using a 3D parametric finite element model and the stress calculation errors were obtained by comparing calculation stress with the actual one. According to the results, the error value was affected by some parameters such as ring depth, stress magnitude and state, and material behaviour. In general, for residual stresses above 65% of the local yield strength, the plasticity‐induced errors were significant, as an error close to 35% was found.Based on the result, a correction procedure was proposed for the evaluation of the high level residual stresses in steel materials by the ring‐core method. By the method, true stresses can be obtained with considering the calculated stresses state, material properties, ring geometry, and estimated plasticity‐induced errors.

Abstract Mechanical properties of the skin, the external organ of the human body, are important for many applications such as surgery or cosmetics. Due to the highly hierarchical structure of the tissue, it is interesting to develop microstructural models that have better predictability and should reduce the consequences of sample variability. However, these models generally include a quite large number of mechanical parameters. Therefore, complex assays are required to achieve a proper identification of the microstructural models. We investigated here the best experimental protocol to identify a nonlinear, anisotropic, model of skin behaviour, namely, the Holzapfel law, using displacement field and force measurements. This was done through a sensitivity analysis of the different parameters. We determined first the optimal assay, which appears to be a biaxial test with an alternated loading: first a stretch in one direction, then in the perpendicular one, and so on. To further improve the quality of the assay, we also determined the optimal geometry. Interestingly, slightly asymmetric geometries are more adequate than symmetric ones, while being easier to realise.

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Abstract A multi‐modal experimental approach for analysing the embedment behaviour of timber connections with steel dowels is proposed in this study. In this approach, a standard mechanical embedment test on single‐dowel connections is combined with an optical measurement of surface deformations of the connection based on digital image correlation principle and an X‐ray micro‐computed tomography examination of the deformations in the dowel‐wood interface. The latter is conducted on cylindrical cores including the dowel hole, physically extracted from the loaded specimen at three characteristic points of the load‐deformation curves. The major challenge of this procedure is disrupted load transfer between the cylindrical core specimens and the external material they were plugged in for further analysis. Despite its challenges and limitations, the method revealed a potential for an unprecedented insight into the micromechanics of dowel connections and for effective correlation of the micro‐level observations with the external macroscopic load‐deformation characteristics.

Abstract A novel adaptive isogeometric digital height correlation (DHC) technique has been developed in which the set of shape functions, needed for discretization of the ill‐posed DHC problem, is autonomously optimized for each specific set of profilometric height images, without a priori knowledge of the kinematics of the experiment. To this end, an adaptive refinement scheme is implemented, which refines the shape functions in a hierarchical manner. This technique ensures local refinement, only in the areas where needed, which is beneficial for the noise robustness of the DHC problem. The main advantage of the method is that it can be applied in experiments where the deformation mechanisms are unknown in advance, thereby complicating the choice of suitable shape functions. The method is applied to a virtual experiment in order to provide a proof of concept. A second virtual experiment is executed with stretchable electronics interconnects, which entail localized buckles upon deformation with complex kinematics. In both cases, accurate results were obtained, demonstrating the beneficial aspects of the proposed method. Moreover, the technique performance on profilometric images of a real experiment with stretchable interconnects was demonstrated.

Abstract Fibre Bragg grating (FBG) sensors have been increasingly adopted to detect the dynamic strain of structures. When the sensor is attached on the surface, adhesive material is employed to assist the installation, which leads to indirect contact of sensing fibre and the monitored structure. To correct the strain transfer error induced by the shear lag effect and improve the measurement accuracy of FBG sensors under dynamic response, strain transfer mechanism of a three‐layered testing model constituted of sensing fibre, adhesive layer and host material has been studied in this paper. Laboratory test on steel beam attached with FBG sensor under fatigue load has been projected to investigate the feasibility of the derived strain transfer formula, and numerical simulation by MATLAB has been used as a supporting tool to offer the reference dynamic strain. Based on the analysis, sensitive parameters that affect the strain transfer coefficient have been discussed to instruct the application design of FBG sensors. Results indicate that strain transfer coefficient under dynamic response is much lower than that in static state, and error modification is particularly significant; in the dynamic testing model, bonded length, shear modulus and thickness of adhesive layer are more sensitive, which should be precisely selected in practical engineering to guarantee the effective strain measurement.