Aircrafts damages caused by lightning strikes have been known since the early days of aviation. However, the physical effects on the aircraft structure are still being investigated. This work seeks to evaluate the lightning strike effects in the aluminum alloy 7075-T6. Samples were submitted to lightning strike simulation in laboratory and the damages evaluated through characterization techniques. Ultrasound and profilometry tests have shown material loss to 0.272 mm depth in the damaged region. In addition, it was detected the material accumulation occurrence in the damage vicinity of the region. Below the damage, it was found a region where metallurgical changes were identified. The tensile and microhardness tests results have shown reduction in the percentage elongation and hardness increasing in the material affected by lightning. These results are corroborated by the X-Ray Diffraction (XRD) and Rietveld Method (red line) that indicated an increasing in dislocation density and micro-deformation in the material matrix. Optical microscopy results have shown the presence of microcracks on the normal and cross-section surface of the samples damaged. The Energy Dispersive X-Ray Spectroscopy (EDXS) and Electron Backscattered Diffraction Test (EBSD) found coarse intermetallic phases and precipitates compounds with dimensions greater than 1 μm in length. They were responsible for nucleation of the microcracks that propagate along the material grain boundaries. 相似文献
Delamination represents one of the most severe failure modes in composite laminates, especially when they are subjected to uniaxial compression loads. The evaluation of the delamination damage has always been an essential issue of composite laminates for durability and damage tolerance in engineering practice. Focusing on the most typical and representative elliptical delamination issue, an analytical model simultaneously considering the conservative buckling process and non-conservative delamination propagation process is implemented. Various computational cases considering different delamination depths, directions, aspect ratios, and areas are established, and the predicted results based on the analytical model are carefully compared. Effects of these geometrical delamination parameters on the buckling, delamination propagation, and failure behaviors of composite laminates are thoroughly analyzed, and innovative evaluation principles of the delamination damage have been concluded. It is found that the delamination area is the key factor that truly affecting the failure behaviors of delaminated composites, and the local / global buckling and failure loads show clear linearity with the delamination area, whilst the delamination depth and direction only have slight effects. 相似文献