Analysis of thermal strains and stresses in heated fibre metal laminates

Abstract

Current trends in aircraft design are to increase the economic efficiency by integrating different features in multifunctional materials. One strategy is to embed resistance heater elements between glass‐fibre epoxy layers in (heated) fibre metal laminates and to use them as anti or de‐icing devices in leading edges of wings. Heated glass fibre reinforced aluminium (GLARE) is an example of such a multifunctional material where heating functionality was added to the (certified) structural feature of GLARE. As heated fibre metal laminates are an innovative and rather new material, the possible (local) effects of embedded heating on the stress–strain state have not yet been investigated. This research couples experimental characterisation of heated GLARE surface behaviour and numerical modelling analysis to investigate the surface and the through‐the‐thickness strain‐stress state and temperature distributions due to the embedded heating. For the experimental part, the surface strains and the temperatures of a developed specimen were measured in a slow heating regime (temperature increase from 22.7 to 39.4 °C within 120 s) using, respectively, a developed shearography instrument and thermocouples with an infrared camera. Then a numerical model of heated GLARE was developed and verified with experimental results. Further, the numerical model was used to predict strains, stresses, and temperatures during a temperature increase similar to that used for de‐icing in a real operation (temperature increase from −25 to 86.7 °C within 4.8 s).

Application of shearography with thermal loading for the structural inspection of Rembrandt’s Night Watch

“…The final inspection results include the in-and out-of-plane phase maps with the shear in the x-(horizontal) and y-(vertical) directions corresponding to the surface relaxation during cooling. These phase maps were calculated using the calibration information about the instrument geometry and 3D shearography processing methods 13,14 .…”

“…To minimize the exposure of the paint layers to the light and heat from the shearography heating source, these two areas were inspected from the reverse of the painting. For the in-situ inspection of The Night Watch, the previously reported 3D shape shearography instrument 13,14 was adapted and fixed on a motorized rigid platform (Figure 2) to enable controlled scanning of the painting and further image stitching. A fourth shearing camera was added to the instrument close to parallel to the laser beam to provide pure out-of-plane surface strain measurement.…”

Application of shearography and the percussion method for the structural inspection of wall paintings: a case study of St. Christopher in Maria Church, Nisse

“…Shearography theory and the principle of its operation are well described in literature [14][15][16][17] . For this inspection, one channel of the previously developed and reported 3D shape shearography instrument 18,19 was used (Figure 3) together with thermal loading (heating) of the painting. The choice of one shearing camera oriented perpendicular to the painting with the main sensitivity to the out-of-plane surface displacement gradient was made based on a preliminary inspection of a representative reconstruction with intended internal delamination.…”

3D shape shearography technique for surface strain measurement of free-form objects

“…For the experimental evaluation of the proposed approach for the surface strain measuring of curved surfaces, a 3D shape shearography system prototype was developed (Fig. 5) [47,48]. Three spatially distributed shearing cameras, a laser with beam expansion optics, and the projector were placed in a "T" configuration using an Alufix modular fixture system.…”