FA8650-19-S-5001-Atch5.pdf

FA8650-19-S-5001

Statement of Objectives Attachment 5

Progressive Damage Model Benchmarking for Ceramic Matrix Composite Components in

Turbine Engine Applications

Background and Scope

The Air Force Research Laboratory seeks to develop and transition technology for the certification of life critical turbine engine components utilizing advanced high temperature ceramic matrix composite (CMC) materials. Traditionally, life critical engine components are certified and sustained through a damage tolerance assessment approach where part inspection enables safe operation when accurate means are available to predict rate of damage growth. While progressive damage models are well developed and certified for damage tolerance based design and sustainment of metal based components, they are not for CMCs. To this end, the Air Force Research Laboratory is seeking to benchmark current capability of progressive damage models for damage tolerance assessment of CMC turbine engine components.

Recently, the 2700F SiC/SiC Development Program funded at the Air Force Research Laboratory has invested in the development of preliminary tools for damage assessment of CMCs in turbine engine applications. This program funded several contracts to develop tools capable of predicting damage evolution due to the influence of environment coupled with structural loading in turbine engine application environments. Several promising approaches were demonstrated in these programs that were able to predict residual strength after exposure of tested CMC coupons and/or sub-elements.

The Air Force Research Laboratory believes that recent technical developments for progressive damage modeling of CMC structure demonstrated in the 2700F SiC/SiC Development Program along with current capability for the non-destructive evaluation of CMC components will enable damage tolerant design concepts for life critical CMC components. Prior to potentially undertaking a major research effort to address many issues related to this transition, AFRL proposes to undertake an initial effort focused on assessing and quantifying the benefits of using a progressive damage modeling based damage tolerant design approach for certain types of damage that has been observed in CMC based turbine engine components.

Statement of Objectives

The overarching objective of this proposed research effort is to determine the technical feasibility of implementing a damage tolerant design approach for CMC based life critical gas turbine engine components, and to quantify, at an initial level, the benefits, costs, and problems using the existing technical capability to predict and model progressive damage in CMC structures. Additionally, this effort may enable further development of currently available analysis methods adding capability to account for damage modes that have not been previously considered. This exercise and experiment will be conducted at a relatively fundamental level using simple specimens and sub-element configurations.

The contractor shall identify promising analysis methods to predict progressive damage in CMC based components, select the most promising methods and use them to predict the behavior of sub-components tested in the program. The contractor shall also be responsible for procuring materials and generating all required test data. Individual modeling teams will be assembled to calibrate and exercise each method that will be isolated from the team overseeing the coupon and sub-component testing. The methods are to be calibrated based on standard coupon data provided to the modeling teams from the experimental team. The methods will then be exercised to make blind predictions of several sub-component tests where the geometry, loads and boundary conditions are known, but the result of the tests are not known to the modeling teams until the predictions are completed. The methods should be evaluated for currently expected static (e.g., tension, compression, shear) and time dependent (e.g., creep, fatigue, dwell fatigue, oxidation) damage modes for CMCs in gas turbine engine applications.

Progressive damage should be characterized at both room temperature and at the service temperatures expected in the hot section of gas turbine engines.

The material systems considered in this program, should be current state-of-the-art silicon carbide reinforced silicon carbide matrix (SiC/SiC) CMCs having a history of reproducibility and demonstrated relevance to current or planned components for gas turbine engine components.

To demonstrate versatility of the progressive damage modeling approaches for varying fiber architectures, two CMC systems should be included in the program: one with a unidirectional ply based balanced layup and one with a woven ply based balanced layup.

Task 1 The contractor shall identify state-of-the-art and promising emerging analysis methods capable of predicting the initiation and propagation of damage in CMC components.

Consideration of each method should be based on ability to predict damage type, location, extent, and residual strength as a function of both static stress level and cyclic loading behavior at room and at intended service temperatures. The contractor is encouraged to identify and propose promising methods of predicting such damage.

Task 2

• The contractor will provide basic material properties for two state-of-the-art CMC systems including one with a unidirectional ply based balanced layup and one with a woven ply based balance layup to assembled modeling teams for model calibration.

• The contractor will predict static behavior (e.g., tension, compression, shear) including damage progression, stiffness, and strength for a sub-element test where the geometry, loads and boundary conditions are known, but the result of the tests are not known to the modeling teams until the predictions are completed.

• The contractor will recalibrate their model to match static results.

Task 3

• Using the same models calibrated previously in Task 2, the contractor will predict time dependent behavior (e.g., creep, fatigue, dwell fatigue) including damage progression, stiffness degradation, residual strength, and remaining useful life for a sub-element test where the geometry, loads and boundary conditions are known, but the result of the tests are not known to the modeling teams until the predictions are completed.

• The contractor will recalibrate their model to match time dependent results.

Details:

The contractor shall evaluate a limited number of methods as identified in Task 1 and as approved by the Air Force program manager. This evaluation shall be performed by using the selected methods to predict damage type (e.g. matrix cracking, delamination, oxidation), damage location, and damage for static (Task 2) and time dependent (Task 3) behavior at room and at elevated temperature. The selected methods shall also be employed to predict residual strength for run out specimens in time dependent testing for all run out specimens from Task 3.

Shortcomings of existing analysis methods should be documented for consideration for further development.

It is expected that the program will have to develop or provide through cost share the following data for calibration of the models considered.

Calibration Properties

• Values for constituent properties (fiber strength/stiffness/Poisson’s ratio, matrix strength/stiffness/Poisson’s ratio)

• Basic monotonic properties (E1, E2, XT, YT, Xc, Yc, Poisson’s ratio, transverse flexural strength)

• Fiber volume fraction

• Basic time dependent properties (e.g., creep, fatigue, dwell fatigue)

• Double cantilever beam (GI)

• End notch flexure (GII)

• 3 point bend

Program Management: The contractor shall perform program management of all technical tasks necessary to ensure performance to the contract. This should include coordinating meetings, travel and integration of the work performed by the various contractors as necessary.

The contractor shall plan for a kick-off meeting and final reviews with the Government team.

The contractor shall hold the kick-off meeting within 30 days after contract award at Wright- Patterson AFB. The contractor shall hold the final reviews at the conclusions of the study also at Wright-Patterson AFB. Interim reviews can be proposed and be held via video or teleconference as necessary.

Documentation and Deliverables: The contractor shall document the results of the study in a final report.

Operations Security: The contractor shall train personnel in, and follow appropriate Operations Security (OPSEC) measures during the performance of this contract.

Period of Performance: The period of performance shall be 24 months technical effort plus 3 months for a Final Report.

Operations Security (OPSEC) Requirements:

All contractors shall follow appropriate OPSEC measures required for this particular contract.

This is required in an effort to reduce program vulnerability from successful adversary collection of possible sensitive unclassified and/or proprietary information, and violations of export control requirements. The prime contractor will ensure that all subcontractors, if applicable, conform to these requirements as required by the prime contractor. Guidance can be provided by AFRL/RX Security as needed.

Program Protection Plan (PPP) - Any potential critical program information (CPI) generated as part of this effort will be reviewed to determine the need for a PPP.