Damage Modeling in Honeycomb Panels for Tap Testing

Effect of damage on Composite Honeycomb panel due to low speed impact is of significance. The result of such impact is damage such as crushing or buckling of the core, core to face de-bonding and local de-lamination of the plies. The damage, however, may be invisible to human eye but can result in significant degradation of stiffness and strength of Honeycomb structure. Of all the NDE techniques available, Tap Test seems to be the cheapest and most suited for the detection of damage in face-sheets, the face-sheet to core de bonding, and core damage. Instrumented Tap Testing with scanning capability makes it a very attractive NDE tool. This work is concerned with modeling the Tap Test on composite honeycomb panels by Finite Elements in both static and dynamic modes. Interactive Finite Element model has been developed having option of creating multiple defects of varying size at desired location within the core material. Model is generated using Graphite/Epoxy quasi-isotropic laminate as face sheet material with Nomex paper core, simulating condition of crushed core. The model was analyzed by applying point load (equivalent force of the impacting projectile) at the node of concern. The defect is modeled as a gap in the core. Samples were made having defects at different core height and were analyzed using Finite Element Methods (ANSYS) and by Tap Testing under same boundary conditions and loading. The sensitivity of FE model and Tap Test to damage location and size has been studied and the results are presented.