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Speckle Methods in Experimental Mechanics
Published in Rajpal S. Sirohi, Speckle Metrology, 2020
Photoelasticity and the method of caustics have been frequently used in fracture mechanics. Photoelasticity requires a biréfringent specimen. However, an optically smooth surface is needed to apply the method of caustics. Laser speckle photography has no such restrictions; it can be applied to all materials with no surface preparation. The measurement of displacements around crack tips in sheets of Araldite CT200 has been carried out by Luxmoore [39] using speckle photography at unit magnification.
Introduction to Experimental Stress Analysis
Published in Keith L. Richards, Design Engineer's Sourcebook, 2017
Two types of fringe patterns can be observed in photoelasticity: isoclinic and isochromatic fringes are viewed when the source light is monochromatic. These fringes appear as light and dark fringes, whereas with white light illumination, colored fringes are observed. The difference in principal stresses is related to the birefringence, and hence the fringe color through the stress optic law.
Photoelasticity
Published in Rajpal S. Sirohi, Mahendra P. Kothiyal, Optical Components, Systems, and Measurement Techniques, 2017
Rajpal S. Sirohi, Mahendra P. Kothiyal
Photoelasticity is an experimental technique for obtaining stress distribution on a body subjected to an external load. The technique is carried out on scaled down models. It is based on the fact that certain materials when subjected to stress become birefringent; the refractive index of the material becomes direction dependent. The state of polarization of the wave propagating through a birefringent medium changes. The transmitted wave is analyzed for its state of polarization, and the stress distribution is then computed. The birefringence of the material is related to the stress through the stress—optic law, which forms the basis of photoelasticity.
Numerical investigation of bimaterial interfacial crack with interaction of voids and inclusions using XFEM
Published in Mechanics Based Design of Structures and Machines, 2023
Chow, Beom, and Atluri (1995) developed the hybrid finite element to obtained the stresses, displacements, and SIFs near an interfacial crack tip for the dissimilar anisotropic media. Deng (1995) presented the asymptotic studies of debonding and delamination in composite. Lee, Hawong, and Choi (1996) presented the SIFs in orthotropic material under dynamic mode. Belytschko and Black (1999) presented the minimal remeshing in FEM to evaluate the crack growth with curved crack problem. Bjerkén and Persson (2001) numerically evaluated the various interfacial crack bi-material cases to investigate the SIFs. Shukla et al. (2003) investigated the static and dynamic fracture analysis for an isotropic and orthotropic material interface through the photoelasticity. Sukumar et al. (2004) developed the discontinuity enrichment function of the bimaterial interface crack cases to evaluate the mixed-mode SIFs.
Theoretical solution for thermo-mechanical crack-tip stress field for transversely graded materials
Published in Journal of Thermal Stresses, 2022
Soumyadeep Mondal, Servesh Kumar Agnihotri, Anshul Faye
Noda and Jin [12] and Jin and Noda [13] analyzed crack-tip fields in a nonhomogeneous material subjected to thermo-mechanical loading. They concluded that the classical inverse square root crack-tip singularity observed in the homogeneous material is not affected by heat flux or temperature. Jain et al. [14] developed an asymptotic expansion of crack-tip fields for a stationary crack in a functionally graded material subjected to thermo-mechanical loading. Later Kidane et al. [15] extended the asymptotic analysis for a mixed-mode dynamic crack in graded materials subjected to thermo-mechanical loading and studied the effect of non-homogeneity and temperature fields over the crack-growth direction and speed. All studies discussed above are limited to plane analysis. Wadgaonkar and Parameswaran [16] first addressed a problem of graded material where the mechanical property gradation was along the crack front. This type of gradation makes the problem three-dimensional in nature. They derived near crack-tip fields for transversally graded materials and studied the effect of three-dimensionality on the crack-tip stress fields. Complexities associated with three-dimensional fracture problems are discussed by Sih [17] in detail. Finite element analysis can avoid difficulties associated with analytical solutions. Recently, Hein and Kuna [6] developed a J-integral formulation for three-dimensional cracks in functionally graded thermoelastic materials. However, the expansion of near-tip stress and displacement fields can be advantageous in obtaining the stress intensity factor using experimental techniques such as coherent gradient sensing, digital image correlation, or photoelasticity.
Brittle fracture development through sets of preexisting small-scale cracks under quasi-static and dynamic impact loading
Published in Mechanics of Advanced Materials and Structures, 2023
The mechanical characteristics of a solid containing a single crack, or a source of further fractures under various loading and environmental conditions, have been comprehensively investigated and concisely summarized in textbooks such as the one by Anderson [3]. In fact, however, quite a few cracks may concurrently exist, expand and interact with each other in quasi-static and/or dynamic ways. Periodic crack systems under some specific loading conditions can be mathematically analyzed, see e.g. [4], but the collective or global characteristics of a number of cracks, as well as their connection with each individual or local crack behavior, have not been thoroughly clarified yet. Here, therefore, by utilizing the experimental technique of dynamic photoelasticity in conjunction with high-speed cameras, fracture development is observed in initially linear elastic rectangular brittle specimens where sets of preexisting small-scale parallel cracks are placed in some areas by a digitally controlled laser cutter. First, using a tensile testing machine, external uniaxial tensile load with a prescribed quasi-static constant strain rate is applied to a transparent birefringent polycarbonate specimen that represents a typical brittle material and is suitable for photoelastic observations [5]. Then, in addition to the external load below the static limit, dynamic impact is given to the bottom surface of a specimen by a projectile that is launched with an airsoft gun. In both quasi-static and dynamic loading cases, local fractures evolving around pre-cracked areas or “damage zones” are recorded and compared with the global behavior and wave motion in the polycarbonate specimen with the mass density 1,200 kg/m3, shear modulus 820 MPa and Poisson’s ratio 0.37.