Full-field Optical Measurement For Composite Laminates Panel Under Buckling Process

Carbon fiber reinforced composite is very suitable for the structure design of aeronautics and astronautics because of its high specific strength and stiffness. The most structures of composite are thin-walled, it's easy to buckling, but the structures'buckling mode are totally obtained by finite element analysis results in general, and rarely could be recorded in the experiments. This paper uses digital projection fringe technique recording the morphology of stiffened composite plates during the compression process in real time, it's the first time using it as a effective measurement method applied to aeronautics and astronautics field.Taking the advantages of real-time, non-contact measurement and simple testing system structure,we can use the digital projection fringe morphology measurement method measuring the morphology of object,and the evolution process of the surface morphology.In the optical measurement system of this paper, combining the modern high-speed development of computer technology,creating the virtual sine grating fringe which has high brightness and high black-white contrast,we can choose the grating period and contrast quite convenient combined the size of specimen,and use the projector to project, can automatically control.realize phase shifting simply. Which makes the system can adapt different geometry size, and the overall operation become very convenient, so as to increase the precision of the obtical measurement system.and expand its application field.This paper describes the basic principles of the digital fringe projection measurement method which used in three-dimensional morphology. According to the problem of the traditional calibration method of the system, we improve the calibration methods by using least square method and the system measuring precision. In the experiment, four fringe image of sinusoidal phase-shift is projected onto the surface of the reinforced composite laminated plate, detecting the morphology' change of the stiffened composite laminated plate by using phase-shifting method under the compression process in real-time. After analysis the deflection of the key positions, we know the local buckling deflection in the grid is increased when the load increased based on the bending of the specimen. Measurement results show that the local buckling wave packets appear in the grid, near the end is performance as wave peak, and wave trough in the middle.With the evolution of the stiffened plate buckling mode shape by time, through the analysis of the stability and strength of the structure stiffened plate, the local buckling is occurred between the bar on the laminated plate, but the strength does not destruct, the result shows that the data is useful for discussing the destruction mechanism and the failure mode mode of the stiffened composite laminated plate.