Targeting our overall SBIR objectives of (a) developing concepts for airframe full-scale fatigue testing utilizing the latest advancements in test hardware and sensor technology to correctly impart low and high frequency loads and capture data with high fidelity, and (b) demonstrating such a concept by building and testing reduced model substructure of airframe, we build upon Phase I effort on an initial 3-DOF test system set up and preliminary tests. Continuing our initial Phase I effort testing using 3-DOF test set up on an idealized structure, we propose to achieve in Phase II (a) completion of tests of the idealized structure using 3-DOF system and (b) conduct tests on a non-idealized structure, either by reconfiguring the 3-DOF test rig or by designing and building a completely a new 6-DOF test system. These efforts will provide a solid platform to develop a complete test of rotorcraft major airframe substructure.
Benefit: The main product of this research and development will be a hybrid fatigue testing system with the capability of more accurately loading the full-scale aircraft test article for both HCF and LCF, which is necessary to accurately assess fatigue and durability of aircraft structures. This mixed mode testing methodology, with many advanced technologies incorporated, are verified by the idealized test frame and the reduced scale subcomponent test frame, built and tested in Phase I and Phase II, respectively. The hybrid fatigue testing methodology developed will enable new platform developers to accurately substantiate fatigue lives and durability of newer platforms such as the current Joint Military Rotorcraft (JMR) program. For existing aircraft already in service, the hybrid fatigue testing methodology with advanced technologies and software packages implemented will provide OEMs and aircraft operators unique opportunities for substantiating fatigue lives and durability of many airframe components currently in service. Our research has confirmed that many of the previous airframe tests did not include the HCF loading conditions. Hence, it is expected that many of the existing aircraft in service may have numerous fatigue cracking issues due to the unaccounted mixed mode loadings conditions during the substantiation of their airframe fatigue lives. Therefore, all rotorcraft platforms will benefit by the use of the developed technology. In addition, use and application of the hybrid fatigue testing system is not only limited to aircraft industry. This technology will be useful to other industry sectors such as engine manufacturers, automotive, ship, wind turbines, and heavy machinery to assess the performance and remaining useful life of their critical components. Two platform development programs, the CH-53K and JMR, will be the first two candidates TDA will pursue to propose to use the developed hybrid testing methodology for their FSFT. Other helicopter platforms flown by, the Army and Navy, and their OEMs will also be approached by TDA to introduce the developed methodology to re-substantiate fatigue lives of airframe components for their major fleets (i.e., MH-60s and AH-1Z/UH-1Y) to improve the safety of aircraft and reduce the overall fleet maintenance cost.
Keywords: Load Actuators, idealized and non-idealized structure testing, 3-DOF test system, Rotorcraft Airframe Fatigue Testing, digital strain imaging, Hybrid Fatigue Testing System, Mixed Mode Fatigue Testing of Scaled Airframe Components, 6-DOF test system