复合材料内多处横向冲击损伤的光纤图像检测

MULTI POSITION TRANSVERSE IMPACT DAMAGE DETERMINATION WITHIN COMPOSITE LAMINATES BY FIBRE OPTIC IMAGE RECONSTRUCTIONS 1)

基于埋设在复合材料层板中的多方位多模光纤网络的特点，提出了检测层板内部发生多处横向冲击损伤的重构算法．根据光纤损伤图像检测系统获得的图像信号，可实时、定量、直观重构并显示出层板内部各处损伤的位置和各处的损伤程度．在复合材料多点冲击损伤检测试验中，屏幕显示的损伤图示与对半透明试件同时做反向照明检测的结果相一致。

By now the multi model fibre optic network embedded in composite laminates for damage detection in which fibre optic bundles are arranged in quadrature or in one direction can only qualitatively show the approximate range of damage. In order to display structural damages accurately and quantitatively, we draw into the concept of reconstruction, as well as the fibre optic damage image processing method, to form a new algorithm for the multi places damage determination within composite laminates. The fibre optic damage image processing method is the combination of image processing technique and the fibre optic incorporation. All the fibre optic bundles embedded in composite structure are connected to a target surface by image transmission cables at the output interface. In the image of the target surface, the intensities of the lights transmitted through the optical fibres are showed as light spots which have different grey scale values and occupy different areas. In the damage detecting process, the grey scale value declines of each light spots show the damage levels of corresponding fibre optic bundles, which are used for the damage region reconstruction in composite structure. For the reconstruction of the damage levels, the detecting region is devided into elements. we raise an algorithm using `four directions fibre optic network' to perform the reconstruction, which has two major steps. (A) The analysis of the damage levels of the elements for each structural damage is carried out by three steps. First, determine the position of the damage central element and its damage level. Second, determine the damage rates of the elements at the tangent points of the damage region by other fibre optic bundles. Third, determine the damage levels of other elements by linear interpolation. (B) If the structure is damaged at different positions, the influences of these damages can be superimposed. That is, any fibre optic bundle can still be used to detect later damages in structure if it is not 100% damaged, and any element can be further damaged if it is not 100% damaged. In the experiment of multi positions transverse impacts damage determination within composite laminates, the graphic presentations for the multi positions damage ranges and their extents are quickly, quantitatively and visually displayed, which coincide well with the backlighting outcomes through the translucent composites, thus proved the correctness of the reconstructions.