Abstract
Due to their superior weight to strength ratio of composites to common metallic structures, composite technology is widely used in aerospace industry. Assessment of damage in composites has gained interest after a large number of accidents caused by unanticipated damages in the composite structures. Many different structural health monitoring applications were developed over the years due to the fact that composite materials may inherit damage from within, not always visible from surface. The most common types of errors encountered in the industry are due to misaligned fibers, a mix-up in ply order, and delaminations: all presenting changes in the vibro-acoustical performance of the composite structure. This paper discusses the change in the dynamic properties of a composite structure contains a manufacturing error such as a ply lay-up error, and a ply angle error. Both plate and cylindrical structure types were considered for the stated error types. Effect of symmetric errors, unsymmetrical and unbalanced errors, and mid-plane errors were considered in the case of ply orientations, and dynamic stiffness matrix was used to identify the error. Identification of the structure’s layup properties and manufacturing error identification is employed. From the measured modal properties of the structure, a back-tracking strategy was used to generate the ply lay-up of the composite structure. Prepreg plates of a single carbon fiber system and filament wound hybrid cylinders consisting of glass and carbon fibers were manufactured for testing. Modal tests on plates and cylindrical composite structures were performed and compared with the analysis. A good match between the finite element model and experiment was shown in natural frequencies and mode shapes.
