Detection of barely visible multi-impact damage on carbon/epoxy composite plates using frequency response function correlation analysis

Composite structures are susceptible to impacts capable of producing Barely Visible Impact Damage (BVID). The existence and extent of the damage cannot be clearly determined without further inspection but could lead to an important weakening of the structure. This work investigates the usefulness of Frequency Response Function (FRF) Correlation analysis (based on the analysis of differences between FRFs corresponding to intact and damage states) for BVID detection in carbon/epoxy plates due to multi-impact events. Several indexes are proposed to detect internal damage, all of them proved as useful to detect delamination areas lower than 8% of the composite plate surface, and some of them even lower than 4%. In addition, the influence of the number of measurements was studied through quick tests (reducing the test effort) proving its feasibility. The conclusion is that the proposed method can be applied to efficient structural health monitoring systems for composite structures.