Methodology for Predicting and Testing the Onset of Matrix Damage in Fiber Reinforced Composites under High Cycle Fatigue Loading - P4888

The Department of the Navy (DON) has issued a broad agency announcement as part of the Small Business Innovative Research (SBIR) program soliciting methods for better understanding high cycle fatigue in composites. Typically, fatigue design allowables rely on testing either a single component to multiple design lives or testing a large number of smaller coupons and sub elements to a single design life. Both these solutions take a significant amount of time to complete and for designs with long design life (greater than 109 cycles), these solutions can take decades to complete. In order to fully utilize the benefits of composites, quicker methods for understanding their high-cycle fatigue response must be developed. MSC has previously developed and validated computational tools to evaluate damage in composites under repetitive loading events. However, validation has not been completed for fatigue at cycles on very high orders of magnitude (109 cycles). During this effort, MSC will develop and demonstrate methods to complete fatigue tests up to 109 cycles while maximizing the load rate and thus minimizing the total test time. For example, the R.R. Moore Rotating Beam Test has been the standard solution for high cycle fatigue in metals. By completing one cycle of loading with one rotation of the beam, cycling can be driven with a motor at speeds upwards of 10,000 RPM, resulting in 600,000 cycles per hour. MSC will leverage the pedigree of the R.R. Moore Rotating Beam Test to devise similar approaches for high-cycle fatigue evaluation of composite materials. During these high-speed loadings, MSC will also determine methods to observe changes in stiffness of the specimen, which are a result of internal matrix damage within the composite. One method is the use of embedded fiber optic strain sensors. These sensors can be embedded into a laminate and are able to monitor stiffness changes in real time during testing. During this effort, MSC will demonstrate fiber optic stain sensors for low cycle and high load fatigue testing and determine the initiation of damage within the specimen. This data will be used to validate and verify the computational tool set, and this approach will then be repeated for longer high-cycle fatigue testing.