A Study of a Normalized Natural Frequency Strategy for Localization and Quantification of Defects and Material Degradation in Fixed–Fixed Metal Beam Structures

Structural Health Monitoring (SHM) plays an important role in ensuring the safety and reliability of engineering structures such as bridges, aircraft components, and mechanical systems. Among the available techniques, vibration-based methods have gained significant attention because structural defects lead to measurable changes in dynamic properties, particularly natural frequencies. Detecting and quantifying such changes can provide valuable information for early defect identification and maintenance planning. This work presents a vibration method using normalization of natural frequencies to identify defects in a beam structure. This method is followed by performing the normalization ratio of natural frequencies from defected to intact finite element (FE) models of fixed–fixed beam structures. These normalized ratios are used to locate and estimate the extent of defects. Different defects cases are investigated using the normalized ratio of natural frequencies. Several numerical steps are performed to evaluate the applicability of the proposed method. The defect can be localized by considering normalized frequencies with the different divided defect zones in the beam. In addition, the defect magnitude can be estimated by calculating the normalized natural frequencies values to variations of defect magnitudes. The numerical study demonstrates that the proposed normalized frequency approach can effectively localize defects and estimate their severity, highlighting its potential for practical SHM applications in beam-type structures.