OPTICAL NONDESTRUCTIVE EXAMINATION OF GLASS-FIBER-REINFORCED PLASTIC HONEYCOMB STRUCTURES

In a study,( )a HNDT experimental unit comprising a special heat-loadi ng device was designed and made. This paper shows the experimental set -up and typical double-exposure holographic fringe patterns of GFRP ho neycomb structures with various kinds of defects. In this paper the fe asibility of using holographic detective methods to check the bonding quality of a GFRP honeycomb structure is studied. The skin of the stru cture is 1.2 mm thick and the honeycomb core is 8 mm high. Discussion is made on the holographic interference patterns for defects located a t different depths, and defects of different equivalent areas and type s. The colour of the surface layer of the honeycomb structure is also explored and discussed. Factors affecting the quality of the hologram are explored, such as selection of beam path, the angle between the re ference and object beams, the ratio of the object beam intensity to th e reference beam intensity, and especially selection of the type of he at-loading source and its technique parameters, etc. The optimum techn ical parameter is obtained. Measurement of the mechanical properties o f both the detective and nondefective specimens shows that single defe cts of equivalent area less than 4cm(2) do not affect the mechanical s trength of the GFRP honeycomb structures at room temperature. This inf ormation is useful in the selection of an acceptance criterion for GFR P honeycomb structures. With the integrated analysis method, and accor ding to the form of the interference fringe, the size and property of defects can be defined. The depth of the defects can also be estimated , by experience.