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Composite sandwich constructions are very widely employed in the modern aircraft industry, honeycomb panels among them. The principal defects of honeycomb sandwiches are cover detachment because of cell collapse or poor adhesive, which can lead to water penetration in cells. Recently, the thermal method of non-destructive testing (infrared thermography) has begun to be applied to the diagnostics of honeycomb constructions, and has some advantages over traditional methods. However, thermal processes are transient, and this complicates the selection of optimal parameters for monitoring. The purpose of this work is to investigate the possibilities of the thermal method for honeycomb panel inspection using computer simulation. The COMSOL Multiphysics package was used for the simulations. A 3D model of the honeycomb panel was proposed, and two possible defects considered: the detachment of the panel cover from the filler and the presence of water in the defective cell. The implementation of the proposed 3D model made it possible to investigate the effect of a defect on the thermal field of the panel surface. The simulation results showed that optimal testing time is significantly different for various types of panels. The correct selection of testing parameters increases the accuracy of the testing procedure. The results of experimental investigation confirmed the adequacy of the proposed model for thermal testing.

Composite sandwich constructions are very widely employed in the modern aircraft industry, honeycomb panels among them. The principal defects of honeycomb sandwiches are cover detachment because of cell collapse or poor adhesive, which can lead to water penetration in cells. Recently, the thermal method of non-destructive testing (infrared thermography) has begun to be applied to the diagnostics of honeycomb constructions, and has some advantages over traditional methods. However, thermal processes are transient, and this complicates the selection of optimal parameters for monitoring. The purpose of this work is to investigate the possibilities of the thermal method for honeycomb panel inspection using computer simulation. The COMSOL Multiphysics package was used for the simulations. A 3D model of the honeycomb panel was proposed, and two possible defects considered: the detachment of the panel cover from the filler and the presence of water in the defective cell. The implementation of the proposed 3D model made it possible to investigate the effect of a defect on the thermal field of the panel surface. The simulation results showed that optimal testing time is significantly different for various types of panels. The correct selection of testing parameters increases the accuracy of the testing procedure. The results of experimental investigation confirmed the adequacy of the proposed model for thermal testing. [ABSTRACT FROM AUTHOR]

An infrared thermographic experimental set-up has been proposed and evaluated towards the capability to measure thermoelastic-effect-induced temperature changes. A standard infrared thermocamera with a nominal noise-equivalent temperature difference (NETD) resolution of 0.12 K has been employed to measure the temperature from unidirectional glass-reinforced plastic tensile coupons under cyclic sinusoidal loads. The raster scanning mode of the camera single detector produces a time delay in acquiring the signal from two succeeding pixels on the same row, and from consecutive scanned rows. By exploiting the acquired dwell times, it was possible to produce a periodic pattern on the thermal maps, caused by and correlated with the thermoelastic-effect-induced temperature changes. The acquired raw data have then been post-processed with a lock-in algorithm implemented in MATLAB® and based on a two-dimensional fast Fourier transform analysis. The filtered thermoelastic component from the lock-in analysis showed good linearity with the load applied, up to values of the temperature change one order of magnitude lower than the NETD resolution limits of the thermocamera. In the light of this the present experimental set-up and processing methodology can be proposed as a potential low-cost tool for thermoelastic stress analysis investigations. [ABSTRACT FROM AUTHOR]

In this study, a thermal elastic-plastic stress analysis is carried out on symmetric cross-ply (0°/90°)2 and angle-ply (30°/-30°)2, (45°/-45°)2, (60°/-60°)2 aluminum metal-matrix composite laminated plates. Temperature changes parabolically from T0 up to -T0 along the thickness. It is zero on the middle axis. The composite material is assumed to be linear strain hardening. The Tsai-Hill Theory is used as a yield criterion. The elastic-plastic solution is carried out for small plastic deformations. The distributions residual stress components of σx and σy are illustrated along the thickness of the laminated plates. All the residual stress moments are in static balance with respect to middle plane of the laminates since they are symmetric in opposite signs. [ABSTRACT FROM AUTHOR]