An Approach for Experimental Characterization of Damage Processes in Thick Rotorcraft Composite Components

Experimental characterization of rotorcraft structures is a key step in their certification, specification of service requirements (e.g., inspection, life, repair), and improvement and validation of predictive modeling capabilities. With respect to characterization of composite components, the focus is on mitigation of three major challenges. The first is a gap between overall sizes of typical rotorcraft structures and relatively small local domains of internal damages controlling the entire structural performance. The second issue is complexity of micro-structure of thick composite components requiring capabilities to capture details of local damage network. Finally, in the case of impact characterization, implementation of dynamic test conditions is much more expensive and time-consuming than corresponding static or quasi-static statements (the third challenge). Thus, the objective of this work is to a) develop a general experimental approach to analyze progressive failure process in thick rotorcraft composite structures under static and impact load; and b) demonstrate the efficiency on an example of a representative main rotor blade (MRB) composite spar. To overcome the challenges, multi-scale analysis is applied. In addition, different test scenarios are applied with increased complexity at every follow-up step. This gives an important opportunity to significantly optimize the test matrix by maximizing parametric testing at lower, relatively inexpensive steps and minimizing much more costly full-scale testing at higher steps. Details of experimental implementations are systematically discussed along with lessons learned and recommendations for future efforts. In summary, it is shown that combination of multi-scale and multi-step testing statements can significantly improve cost and range of generated results in experimental characterization of rotorcraft composite components.