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CROR Blade-Out Impact Simulations and Sample Manufacturing

Periodic Reporting for period 3 - BLADEOUT (CROR Blade-Out Impact Simulations and Sample Manufacturing)

Reporting period: 2018-07-01 to 2018-12-31

The main goal of the proposed research was to develop a robust, computationally efficient, multi-scale numerical simulation model, based on ABAQUS EXPLICIT FE solver, for the virtual-testing of partial (sectioned blades) and scaled CROR blade impacts. The envisioned modelling tool addressed issues rising during the design and simulation of CROR blade impact and the airframe shielding. Following common practice, a building block test and simulation approach was employed to validate its predictive capabilities with respect to impact behaviour for both the blade and the shielding structure. Thus, the objectives are:

Obj. 1: Design of Representative Blade Specimens. Partial composite blade sections were designed as were full CROR composite blades. The selection of composite materials was also performed for optimal conformation to project requirements and certification procedures.

Obj. 2: Development of Multi-Scale explicit impact Finite Element Models. Based on previous experience of Consortium and findings for current designs, computationally efficient explicit FEA models were developed for the simulation of CROR composite blade impacts.

Obj. 3: Manufacturing of Representative Specimens. The preparation of RTM mold and system for composite plates fabrication (specimens for characterization and low level impact testing) was completed. A series of representative specimens were manufactured using RTM process based on a building-block approach; i.e. ranging from simple characterization specimens to representative impact components were utilized to validate the simulation models.
The project completed the following major tasks. The Blade concept was designed as a full and scaled model. The scaled model design was simulated and shown to cause the same damage as the full model on the fuselage and as seen by the damage mechanisms in the blade and the rate of energy absorption. Material coupons and impact plates were modeled, manufactured/fabricated, and tested which led the way for calibration of the composite multi scale progressive failure models to be developed. Low level plate impact testing was performed which determined the ballistic limit for this specific composite. Impact simulations validated the testing results and showed failure mechanisms inside the composite. Blade sections were then designed for specific mass and stiffness requirements with three choices for layups determined. One was down selected. The simulations began on the full and scaled blade models which had the blade impacting the fuselage at two different angles. It was shown that the fuselage could survive the blade impact and that the scaled model with a tuned layup different from the full blade can be utilized in test to save cost of manufacturing and test plan.

The project began with an initial blade designs from analytical and FE models meeting Airbus requirements of mass and stiffness distribution along the length of the blade.
For the Initial Blade Design, three admissible material and lamination scenarios were determined, in compliance with requirements set by Airbus. These scenarios include the following conceptual cases: (1) single material & uniform section layup, (2) multiple materials & uniform section layup, and (3) multiple materials & stiffened sections. The third scenario with both fabric (0/90) and (+-45) for skin and unidirectional materials for girders was chosen as the best candidate. The blade design was enhanced with additional reinforcement layers on the FE model and Rohacell HT71 foam inside the blade and was shown to meet all stiffness requirements for flapping, lead-lag, tension, and torsion.

The material class was chosen and finalized as IM7-RTM-6. Manufacturing of coupons and low level plate impact specimens began. The following coupons were tested for unidirectional coupons: in plane tension, compression, and shear tests. For the weave tension, compression, three point bending, DCB fracture, and ENF fracture. Multi scale multi physics composite durability and damage tolerant models were built using unidirectional tests as calibration and weave tests as validations. This completely formed the progressive failure damage mechanics models for impact predictions.

Detailed plate impact testing was performed on 300x300x5mm3 Woven-Carbon/RTM6 Epoxy plates with a 30mm spherical steel impactor. Various velocities were to be considered in order to experimentally determine the ballistic limit. Three different energy levels were decided, namely under/at/over the ballistic limit of the material. The velocities corresponding to these cases were 56, 80 and 96m/s. Each case was repeated twice to ensure repeatability of testing with high speed cameras showing impact event and NDE C-Scans revealing damage area around footprint. Simulations were performed with success with correlation between test and simulations. Ballistic limits were simulated, along with other velocities under the limit, showing fiber, matrix, and delamination damage similar in size and shape to C scans.

Blade impact models on curved fuselage structures with both full and scaled models were performed. Using an innovative damage equivalency technique that designed scaled models, impact simulations of the full and scaled FE models showed similar damage patterns on the fuselage and energy absorption rate. The scaled blades, 70% of full model, could be manufactured to save manufacturing cost and produce same test results as the full blade. The impact simulations showed the fuselage to survive Airbus impact requirements. The models showed the amount of plastic deformation was small and no penetration happened.
With all the building block simulations, manufacturing, and test verifications performed this was a successful project.

The only item left uncompleted for unfortunate reasons was to manufacture scaled blades and ten (10) partial blade components sections from root, mid, and tip.
The potential impact of the activities performed are:
• CROR blades with their fuel cost savings can hopefully be more common through safety assessment programs like these, which, we can hope will have savings trickle down to consumers of air travel and other indirect economic factors.
• The methodology of impact investigations of CROR blade fragments has been made more economic (reduced testing, reduced manufacturing cost) which will further assist towards the development of lighter airworthy blade/airframe shielding systems.
• The approach was based on numerical simulations instead of a massive experimental campaign, which enables an economical and efficient CROR blade design process, potentially leading to lower product development turn-around-time, and better products in terms of performance over weight ratios due to in-depth knowledge of the energy absorption and damage/fracture mechanisms.
• The use of validated RTM manufacturing methodologies ensures low manufacturing costs, high-production rates and repeatable net-finish quality.
• An innovative set of impact scaling laws and methods were developed that helped predict full scale model impact behavior (impact damage and damage mechanisms) when only a scaled model can be tested. Scaled bladed can be designed and tested which can save time and money when certifying blade for impact requirements.
• All methods followed a building block verification strategy which adheres to FAA and other aircraft and Clean Sky guidelines.