THE DETECTION OF DEFECTS IN GRP LATTICE STRUCTURES BY VIBRATION MEASUREMENTS

For certain types of glass-reinforced plastic (GRP) structure, methods of nondestructive testing (NDT) based on the detection of altered or unusual modal properties can be cost-effective alternatives to conventional techniques. Changes in natural frequencies and the occurrence of anomalous mode shapes determined from quick and simple measurements were used as indicators of structural damage in a series of tests on GRP space-frame lattice structures for which other forms of NDT were not appropriate. The modal analysis techniques used to identify a set of modal characteristics to be used as indicators of damage, and the methods of identifying significant changes in these characteristics, are described. The methods were able to detect various forms of damage such as severed members, delamination and crushing. It is concluded that a combination of visual and modal checks would form an effective means of detecting flawed structures,