An Integrated Approach to the Separation of Principal Surface Stresses Using Combined Thermo-Photo-Elasticity

Abstract

A new instrument capable of the full-field separation of principal stresses on the surface of a component is presented. The instrument combines the techniques of thermoelastic stress analysis and reflection photoelasticity in a single optical head, permitting the simultaneous capture of both data from the same point of view. A single strain witness coating is employed for the acquisition of both the thermoelastic and photoelastic data, which is both birefringent under applied stress conditions and opaque at the infrared wavelengths to which the thermoelastic analysis system is sensitive. This enables the combined technique to be performed continuously from the same surface during loading. The performance of the new instrument is validated in the analysis of a classical laboratory specimen of known geometry. Separated stress data from the experiment is compared to simulated data, demonstrating that the accuracy of the stress separation technique is comparable to that of the individual thermoelastic and photoelastic techniques, and it is concluded that combined thermo-photo-elasticity is a powerful tool for the experimental separation of principal surface stresses.

Determining individual stresses thermoelastically

“…Such approaches enjoy the advantages of not necessarily being associated with a traction-free edge, and the feasibility of recording both PSA and TSA data from a common birefringent coating since the latter are opaque in the infrared spectrum [38]. Reference [36] describes an instrument that allows the simultaneous collection of the PSA and TSA data from a common optical path using a beam splitter to divide the visible and infrared light, and reference [39] applied this approach to industrial components Fig. 9 Normalized stresses along a vertical line in a horizontal aluminium beam subjected to threepoint bending [29] with some success.…”

Numerical-experimental hybrid method for stress separation in digital gradient sensing method

“…Photoelasticity measures principal stress difference and the principal direction, and thus the stress components themselves cannot be obtained directly. Several methods have been proposed for stress separation in photoelasticity such as the shear difference method [14,15]; numerical analysis of the compatibility equation; oblique incidence and hybrid methods of photoelasticity and another experimental method [16][17][18][19]. However all the above methods for stress separation in photoelasticity are not suitable for that in the DGS method.…”

Separating Stresses Thermoelastically in a Central Circularly Perforated Plate Using an Airy Stress Function

“…Representative thermoelastic stress analyses, some of which supplemented TSA information with other measured data, are described [2–22]. Several of these approaches used complex variables in their stress functions and mapping techniques, but the current Airy stress function technique offers the convenience of real variables.…”