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Ramberg-Osgood (R-O) type stress-strain models are commonly employed during elasto-plastic analysis of metals. Recently, 2-stage and 3-stage R-O variant models have been proposed to replicate stress-strain behavior under large plastic deformation. The complexity of these models increases with the addition of each stage. Moreover, these models have considered deformation till necking only. In this paper, a simplistic multi-stage constitutive model is proposed to capture the strain-hardening non-linearity shown by metals including its post necking behavior. The constitutive parameters of the proposed stress-strain model can be determined using only elastic modulus and yield strength. 3-D digital image correlation was used as an experimental tool for measuring full-field strains on the specimens, which were subsequently utilized to obtain the material parameters. Our constitutive model is demonstrated with an aerospace-grade stainless steel AISI 321 wherein deformation response averaged over the gauge length (GL) and at a local necking zone are compared. The resulting averaged and local material parameters obtained from the proposed model provide interesting insights into the pre and post necking deformation behavior. Our constitutive model would be useful for characterizing highly ductile metals which may or may not depict non-linear strain hardening behavior including their post necking deformations.

This paper demonstrates a unique application of DIC wherein the structural performance and structural integrity have been evaluated together almost in real-time. The results obtained from the ground level tests, simulating the bonding between the TPS to the base structure of a space crew module, are reported to find the adequacy of two different adhesives prior to actual bonding. The test objective was to characterize the adhesives based on the structural performance (deflection and strain behavior) of the TPS and conduct health monitoring in real-time (i.e. abort the test whenever the TPS fails). The dual objective could be met using DIC in a full-field and non-contact manner, which was essential due to the limitations of the contacting type measurements.

Digital fringe multiplication is a useful technique for obtaining fractional fringe orders in photoelasticity at regions with very feeble retardations. In this paper, the effectiveness of the existing fringe multiplication techniques is investigated theoretically and experimentally. A new approach for fringe multiplication, using background nullified fringes, is developed to overcome the prevailing issues. Three options for obtaining background nullified fringe patterns are explained. Further, quadrature transformation of these fringe patterns is carried out to fetch uniform modulation. Moreover, a simplified fringe multiplication method is worked out to obtain fractional fringes from the uniformly modulated fringe patterns. The proposed procedures have been demonstrated through simulated as well as experimental images. A parametric study is carried out to understand the influence of pixel resolution and bit depth of the images on fringe multiplication. A criterion is established for finding out the maximum possible fringe multiplication for a given initial pixel/fringe resolution. It is observed that, for higher levels of fringe multiplication, larger bit depth of the image in conjunction with sufficient fringe resolution would be essential. The same also holds for fringe multiplication at areas with stress concentrations.

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