Some applications of combined thermoelastic-photoelastic stress analysis

Abstract

Combined thermoelasticity-photoelasticity integrates the use of reflection photoelasticity to determine the difference in the principal stresses with thermoelastic stress analysis to evaluate the sum of the principal stresses, the advantage gained from this combination being the independent separation of the principal stresses at all points in the field of view. The principle has been established in prior research and suitable instrumentation designed and employed on classical test specimens. This work is extended here with the analysis of two more complex components, namely a composite panel subject to a biaxial strain field and a compressor blade excited at approximately 250 Hz. The methodology for applying combined thermoelasticity-photoelasticity under these conditions is described and the difficulties encountered highlighted and discussed. The results demonstrate that the technique and instrumentation are relatively robust and can be successfully used in these demanding applications.

Phase Shifting Full-Field Interferometric Methods for Determination of In-Plane Tensorial Stress

“…Among the single experimental and theoretical/numerical hybrid methods are photoelasticity and a shear difference method, which calculates stress components on a raster scan from initial values of stress determined by photoelastic parameters at the boundary points [5,6], a hybrid photoelasticity and finite element method technique [7], and a hybrid technique combining thermoelasticity, which relates to the change in the sum of principal stresses with surface temperature, and both theoretical and numerical methods [8,9]. A double experimental hybrid technique utilizes reflection photoelasticity as a strain witness and thermoelasticity [10,11]; the opaque nature of photoelastic coatings in the infrared spectrum allows these techniques to be investigate the same surface of the specimen [6,12]. Interferometric photoelasticity gives both the isochromatic phase, related to the difference of principal stresses, and the isopachic phase, related to the sum of principal stresses; these two fields may be separated using a Mach-Zehnder interferometer combined with a circular polariscope [13].…”

“…This paper concentrates on the hybrid technique in transmission; further analysis would be required to determine if this method could be used in reflection, where the separation of the principal strains are considered. The use of this method in reflection would be similar to the combined reflection photoelasticity/ thermoelasticity [6,12], but in this case, a photoelastic coating would affect the displacement derivative measurement on the same surface using reflection-CGS.…”

Investigation of nonstationary thermo-photo-elastic effect using the polarization modulation of radiation

“…The results demonstrate that the technique and instrumentation are relatively robust and can be successfully used in demanding applications [10]. …”

“…It is important to make a point that polarization modulation method is the best approach in this case, it is approved by high detectivity to the relative change in refractive index ( 10 …”

The use of digital image correlation in a parametric study on the effect of edge distance and thickness on residual strains after hole cold expansion

“…One of the benefits of using a full-field optical technique like image correlation is the ease of strain separation, something that in other techniques such as thermoelasticity or photoelasticity can be quite difficult [15][16][17]. Analysing the plots of first and second principal strains of the various coupons, several overall observations were made.…”