Damage detection using LDV

Composite structures are prone to unpredicted failures due to greater complexity of design, high operational loads and longer service life. Fiber-reinforced composites mainly exhibit four types of damages namely- fiber breakage, matrix cracking, delamination and debonding. Generally, failure occurs due to combination of two or more of these damage types. In this chapter, detection of delamination in composite plates using dynamic analysis is studied. Delamination is a debonding or separation between individual plies in composite laminates. High strength of fibrous composites in the direction of reinforcement is accompanied by a low resistance against interlaminar shear and transverse tension. This may cause delamination leading to initiation and propagation of cracks. Delamination may arise at the fabrication stage itself ( e.g., incomplete wetting, air entrapment), during transportation (mishandling, low intensity impacts) and/or during its use (e.g., low velocity impact, bird strikes on aircraft panels). Delaminations present nearer to the surface are greatly affected by local buckling. When situated deep inside the bulk of the material, they act similar to a crack in the medium. The presence of delamination significantly reduces the stiffness and strength of the structure and affects critical design parameters. If modified dynamic response of the structure due to damages is closer to the operating frequency range during the use, it may cause serious damage to the structure due to uncontrolled vibration response.