Post-Impact Fatigue Durability Assessment of Composite Laminates for Enhanced Aircraft Sustainment

A means by which the strength of composite aircraft structures can degrade significantly in-service is via low-velocity impact induced while in maintenance (e.g., tool drop). Discrete damage modeling (DDM) has been used successfully for post-impact compressive strength. The current study considered the post-impact fatigue durability via DDM for matrix failure and continuum damage mechanics (CDM) for progressive fiber failure, and validated using advanced experimental techniques. Specifically, 1) new methods for mapping the damage from nondestructive inspection, 2) new techniques for tracking the development of damage experimentally, and 3) new methods for predicting remaining life of the damaged composite under compression-compression loading are proposed. The new models proposed predicted the development of subcritical damage and damage development relatively accurately once the inclusion of progressive fiber failure was introduced. The study presents new experimental data in sufficient detail to verify new methodologies proposed using DDM in combination with CDM for predicting the remaining fatigue life following a low-velocity impact.