Numerical and digital image correlation analysis of tensile behavior of thin-ply hybrid laminates with discontinuous carbon sandwiched by continuous glass and carbon

Thin-ply hybrid laminates of glass and carbon fibers have been widely adopted in engineering pseudo-ductility. In this study, a Finite Element model is proposed using Abaqus to predict pseudo-ductility in thin-ply laminates consisting of three materials. These materials comprise continuous carbon (CC) and continuous glass sandwiching partial discontinuous carbon (DC). The model adopts the Hashin criterion for damage initiation in the fibers and the mixed-mode Benzeggagh-Kenane criterion on cohesive surfaces for delamination initiation and propagation. Numerically predicted stress–strain results are verified with experimental results under tensile loading. Results show pseudo-ductility increases with the increase in DC layers, and pseudo-yield strength and strain increase with the increase in CC layers. 3D-Digital Image Correlation results indicate delamination growth on pseudo-ductile laminates, and the calculated Poisson’s ratios show pseudo-ductility occurs below 0.27. Moreover, Poisson’s ratio decreases with an increase in pseudo-ductility.

Joint stiffness identification of industrial serial robots using 3D digital image correlation techniques

Industrial robots have been widely used in manufacturing for advantages of flexibility and high efficiency, while there exists a critical problem of low stiffness. Measuring the stiffnesses of joints accurately have a positive effect on optimizing the stiffness through compensation or posture adjustment. This study proposed a new method for stiffness identification of serial industrial robots using 3D digital image correlation (3D-DIC) techniques, which exhibits high accuracies. External forces are applied to the robot end and its 6-dimensional displacements are recorded with a 3D-DIC system. The values of joint stiffness are evaluated from the data of robot configurations, displacements and forces. The proposed method is implemented on the KUKA KR600-2830 robot experimentally and the average absolute value of relative error is 5.8%, which demonstrates that the proposed method provides much improved accuracy compared to the traditional method.

A Complex Review of the Possibilities of Residual Stress Analysis Using Moving 2D and 3D Digital Image Correlation System

Understanding the levels of residual stresses in the material is very important in predicting the service life of structural elements. One of the most widely used techniques to quantify them is the drilling method, where a small hole is milled in the structure. If the residual stresses are present, stress redistribution will occur, resulting in deformation of the hole surroundings. Nowadays, there is an effort to replace the conventionally used strain gauges, i.e. special strain gauge rosettes, with full-field optical experimental techniques. This paper deals with analysing the possibilities of measuring the relieved strains/stresses with a unique drilling/measuring device, which, unlike other non-commercial measuring systems, uses the moving digital image correlation (DIC) system. Since correlation systems do not tend to move during operation, an analysis was performed describing the effect of changing the position of the single and stereo camera correlation systems on the quality of the results of the strain/stress analysis performed in the vicinity of the milled hole. The conclusion from the analyses performed is that there is no significant accumulation of correlation errors during measurement. Therefore, the information on the magnitudes of the strains/stresses relieved obtained by the moving DIC system can be used to quantify the residual stresses with an expected error corresponding to the sensitivity of this full-field optical experimental technique.