N141-082 TITLE: Non-Linear Behavior Models for Design of Carbon-Carbon Composite Components

TECHNOLOGY AREAS: Materials/Processes

ACQUISITION PROGRAM: Strategic Weapons Systems: Trident II D5 (ACAT I)

RESTRICTION ON PERFORMANCE BY FOREIGN CITIZENS (i.e., those holding non-U.S. Passports): This topic is "ITAR Restricted". The information and materials provided pursuant to or resulting from this topic are restricted under the International Traffic in Arms Regulations (ITAR), 22 CFR Parts 120 - 130, which control the export of defense-related material and services, including the export of sensitive technical data. Foreign Citizens may perform work under an award resulting from this topic only if they hold the "Permanent Resident Card", or are designated as "Protected Individuals" as defined by 8 U.S.C. 1324b(a)(3). If a proposal for this topic contains participation by a foreign citizen who is not in one of the above two categories, the proposal will be rejected.

OBJECTIVE: To develop improved non-linear materials behavior models for the design of Carbon/Carbon thermal protection components.

DESCRIPTION: Thermal protection systems (TPS) for current and future Navy hypersonic reentry bodies include flight critical components fabricated from 2D and 3D woven carbon-carbon (C/C) composite materials. TPS component designs are validated by Finite Element Analysis (FEA) during pre-flight Preliminary and Critical Design Reviews (PDR & CDR). These C/C materials are orthotropic in nature and exhibit extreme non-linear behavior across a very wide temperature range of 70-5000F, and above. Use of linear elastic behavior models results in over prediction of material stress state, and possibly over conservative designs. Efficient design with these materials requires that onset and development of material non-linearity be accounted for. For 3D C/C, this has historically been accomplished by use of a material behavior model (UMAT) that enables the FEA code to calculate the material stress/strain at all points within the component at discrete points during reentry. While the UMAT model is relevant to 3D C/C composites in general, the utilization in a reentry environment requires applicability to problems with distributed external pressure loads, and severe transient thermal loads. Damage and non-linearity are primarily driven by these transient thermal loads.

The UMAT material model contains coefficients derived from characterization tests. Historically, this was not a concern as the C/C material was derived from constituent materials with a stable manufacturing base; the composite material was well characterized and much data was available by which these coefficients were obtained. However, this is no longer the case; fibers and matrix materials become obsolete almost as soon as they are selected, and pre-flight PDR/CDR design validation for current generation TPS materials is often required before full characterization data and material model coefficients become available. Furthermore, output of the material model is limited to stress/strain state and gives no indication as to the onset or extent of non-linearity (damage) within the material or critical failure mode within the cell structure of the material.

This topic seeks to take advantage of recent improvements in computational power/resources in developing new/improved methods for thermo-mechanical design validation of new/emerging 2D and 3D C/C TPS components.

PHASE I: Conceptualize approach for improved design methodology for non-linear FEA of 2D and 3D C/C. Evaluate methods which take into account onset and development of material non-linearity under transient and multi-directional thermo-mechanical stress state developed during reentry. Evaluate methods at to provision of insight into onset and evolution of damage, and dominant failure mode. Evaluate methods which can automate or ease the development of material coefficients from limited new data sets from candidate replacement materials. Methods which integrate with the commercial ABAQUS finite element method are preferred. Evaluate preliminary approach and perform partial functionality using current materials/test data. Define criteria for Phase II success.

PHASE II: Continue to develop and refine methodology for C/C component design taking into account onset and development of material non-linearity under thermo-mechanically induced tension, compression or shear loads. Demonstrate extraction of material coefficients using reduced material data sets from replacement materials. Evaluate fidelity of response against test data from complex thermo-mechanical load conditions. Evaluate the concept for applicability in a Nosetip reentry environment. Deliver code/models to Navy for evaluation.

PHASE III: Transition non-linear material design methodology for potential use in a multitude of military and commercial applications. If successful, this methodology would transition into a future Navy Program of Record. Package and market methodology for commercial applications.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: 3D reinforced composite materials have many potential uses in space, air transport, and automotive applications. Improved methods for design validation of these materials would be very attractive. Examples include: Missile NoseTips, Missile Launch Abort Systems, Throttling Divert and Attitude Control Systems (T-DACS), and Thermal Protection Systems for hypersonic vehicles.

REFERENCES:
1. Rosen, B.W., Chatterjee, S.N. and Kibler, J.J. (1977) "An Analysis Model for Spatially Oriented Fiber Composites," Composite Materials: Testing and Design, ASTM STP 617: 243-254.

2. Hashin, Z. (1996). Finite Thermoelastic Fracture Criterion with Application to Laminate Cracking Analysis, J. Mech. Phys. Solids., 44(7): 1129�1145.

3. Puck, A. and Schurmann, H. (1998). Failure Analysis of FRP Laminates by Means of Physically Based Phenomenological Models, Composites Science and Technology, 58: 1045�1067.

4. ABAQUS 6.13 User�s Manual (2012). Dassault Systemes, Pawtucket, RI, USA.

KEYWORDS: Composite materials; 2D Carbon/Carbon; 3D carbon/carbon; reentry; design; finite element methods; material behavior models.

** TOPIC AUTHOR (TPOC) **

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