Characterization of local effects at core junctions in sandwich structures using thermoelastic stress anaylsis

Abstract

Local effects at core junctions in sandwich structures are studied using thermoelastic stress analysis (TSA). At the core junctions, large stress gradients occur owing to local bending of the face sheets and tension and compression of the adjacent cores. In the neighbourhood of large stress gradients it is known that non-adiabatic behaviour occurs which causes significant departures from the isentropic assumption that underpins TSA. Analytical estimates of the boundaries of adiabatic behaviour are made which show that TSA cannot capture the local effects using practical loading frequencies with thin aluminium face sheets, and this is confirmed experimentally. An experimental model of the sandwich beam is designed that shows that the local effects can be captured using TSA. It is also demonstrated that TSA can be used to assess local effects in sandwich constructions with glass-fibre-reinforced plastic face sheets. Reference data obtained from independently validated finite element analyses were used for comparison with the TSA results. A discussion on the effect of surface pattern and the introduction of noise due to motion is included in the paper. The data are presented in terms of stress and calibration tests on the constituent materials are carried out and reported in the paper.

Numerical analyses of stress and deformation in sandwich-structured composites

“…The governing equation, that is, equation (3) is discretized using the central difference formula for ∂ 4 f/∂x 4 , ∂ 4 f/∂x 2 ∂y 2 , and ∂ 4 f/∂y 4 , which is given by equation (9):…”

“…The face sheets in a sandwich structure are loaded in a membrane-stress state where the core carries the normal and shear stresses. 2 The applications of such composites are vastly found in aviation, satellite, marine, and automotive industries where low weight, high structural stability, and resistance to deformation are required. Therefore, investigating the performance of the sandwich-structures under the action of different mechanical loadings is important while designing such composite structures.…”

Enhanced thermographic inspection of woven fabric composites by k-space filtering

“…Examples of such structured thermal background are displayed in Figure 1 for various defected woven fabric composites. These background disturbances have been frequently observed in literature [9,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. In [9,[19][20][21]34], woven composites are inspected using flash thermography, and the various weave patterns are clearly observable in the (post-processed) thermal images and limit the detection and evaluation of small and/or deep defect features.…”

“…In [9,[19][20][21]34], woven composites are inspected using flash thermography, and the various weave patterns are clearly observable in the (post-processed) thermal images and limit the detection and evaluation of small and/or deep defect features. In [20,[22][23][24][25][26][27][28]33], the surface temperature of woven composites during mechanical testing (static/fatigue loading) is inspected with infrared thermography, either by analyzing the raw thermal images or through thermoelastic stress analysis. Also here, the thermal background related to the weave pattern is found to be disturbing and deteriorates the evaluation of the thermal images.…”