OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Materials The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws. OBJECTIVE: Develop a system for the detection, identification, and quantification of volatile gasses evolved during the manufacturing of high-temperature polyimide composites cured in autoclave equipment. DESCRIPTION: Polyimide-based polymer matrix composites (PI-PMC) are used in extreme environment aerospace applications, such as turbine engines and exhaust-washed structures, as a lightweight alternative to traditional metals. However, PI-PMCs have not been fully integrated into these applications because of the frequent need for part-specific cure processes that typically result in low yield rates during Engineering and Manufacturing Development (EMD) and Low Rate Initial Production (LRIP) phases. Challenging vacuum bag materials are susceptible to leaks and tears, while exceedingly high cure temperature and consolidation pressure combined with volatile management issues result in increased time to develop cure processes, complications with scale-up, and high scrape rates for parts. What is desired is a gas detection system that can be placed in-line with the autoclave vacuum pump in order to provide quality control feedback for the vacuum bag assembly (leak check), and to detect, identify, and quantify volatile compounds generated during the first and second phase of the cure process described below. The system must be capable of withstanding effluent gas temperatures up to 700 degrees Fahrenheit with a pressure up to 200 Pounds per Square Inch (PSI), and differentiate between volatile compounds generated as a result of cure mechanisms and those produced from off-gassing of vacuum bag consumables. The cure process for PI-PMCs is composed of three phases that occur with significant overlap: (1) solvent extraction, (2) oligomerization/volatile by-product management, and (3) consolidation and crosslink formation. During the first phase, excess solvent is removed from the composite assembly using elevated temperature isothermal soaks and vacuum. This process may occur up to 350 degrees Fahrenheit and is typically managed using extended room temperature debulk followed by slow heating rates (less than 1 degree Fahrenheit per minute) and/or long isothermal dwells at intermediate temperatures. Excess solvent consists of methanol and/or ethanol added for increased prepreg tack. During the second phase, imide monomers react (condensation reaction) and produce volatile by-products (water, methanol and/or ethanol). This phase can continue up to approximately 600 degrees Fahrenheit. The third phase occurs at temperatures up to 700 F and utilizes consolidation pressure (~200 PSI) to suppress void formation. The assignment of criteria for the application of pressure is complicated due to the overlapping temperature regime of the second and third phases. Examples of process-related issues include fiber distortion, porosity, and variation in volume fraction ratios. Incomplete solvent extraction typically results in excessive loss of resin, caused by resin thinning and the subsequent wetting of vacuum bag breather materials, and fiber distortion caused from a rapid generation of volatiles within the Polymer Matrix Composite. Likewise, premature application of pressure before completion of the second phase results in excessive porosity. Solvent removal can be managed through the use of long debulk times, slow heating rates, and/or multi-step processing, however identification of proper and optimized processes parameters is typically accomplished using tribal knowledge and may not yield consistent results. Consequently, the parameters are not easily adapted for part scale-up or new/different part configurations/designs and lead to unnecessary variability in part quality. Incomplete oligomerization is a more difficult issue to manage. Variations in the heat transfer coefficient within the autoclave coupled with tool geometry and thermal mass, and part complexity (e.g. thickness changes in pad-up regions) can lead to significant temperature variation within a specific part. Temperature variations, especially those occurring in the thick regions of the PMC, may not be detected and result in incomplete oligomerization and part porosity. It is desired that the envisioned gas detection system provide necessary feedback that can be used for cure process development as well as real-time identification of cure process deficiencies. PHASE I: As this is a Direct-to-Phase-II (D2P2) topic, no Phase I awards will be made as a result of this topic. To qualify for this D2P2 topic, the Air Force expects the applicant(s) to demonstrate feasibility by means of a prior Phase I-type effort that does not constitute work undertaken as part of a prior or ongoing SBIR/STTR funding agreement. The feasibility study shall prove through prior research and development that the offeror has demonstrated a gas detection system with the following capabilities: (1) detect, identify and quantify volatile products evolved either during the cure of a resin system or during debulk processes, (2) manage temperature variability for incoming gases and (3) detect vacuum bag leaks. This can be demonstrated separately or combined within a system. Proof can be provided by direct demonstrations of any or all of the aforementioned capabilities, or through a combination of direct demonstrations and proposed modifications to an existing system to achieve the project goals. In the latter case, the offeror shall provide in-depth details on modifications necessary to achieve the desired capability. Modifications should utilize commercially available technologies. PHASE II: Under the Phase II effort, the awardee(s) shall sufficiently develop the technology in order to conduct a small number of relevant demonstrations. The final prototype system shall be capable of (1) detecting, identifying and quantifying volatile by-products evolved during cure of resin systems, (2) managing high temperature variability for incoming gases while ensuring volatile compounds of interest are not inadvertently removed prior to their identification, (3) detecting vacuum bag leaks and (4) monitoring the evolution of volatile by-products during the autoclave cure of a 700 degree Fahrenheit-curing polyimide composite. Additionally, the prototype system must be developed with a graphical user interface (GUI) to provide manufacturing engineers with real-time analysis of the effluent gases. The system must be able to differentiate between acceptable and deficient cure processes. The final configuration must be capable of integrating with industry standard autoclave systems, such as ASC. The offeror must identify technology hurdles they are expected to encounter during the development program, as well as potential solutions to mitigate risk to the program. PHASE III DUAL USE APPLICATIONS: The awardee(s) can expect to pursue commercialization of the various technologies developed in Phase II for transitioning the technology to various composite manufacturers. Identification of other transition opportunities outside of the program's intended focus area of high-temperature polyimides is preferred because of the limited market share of these composite systems. Additionally, the offeror should identify commercial partners for autoclave control systems to ensure the gas detection system can easily be integrated with industry-standard autoclave systems and their control software; streamlined integration will reduce the burden placed on manufacturing facilities to learn and adopt the new technology. Direct access with end users and government customers will be provided with opportunities to receive Phase III awards for providing the government additional research & development, or direct procurement of products and services developed in coordination with the program. REFERENCES: 1. Mary Ann B. Meador and J.C. Johnston, Elucidation of the Cross-Link Structure of Nadic-End-Capped Polyimides Using NMR of 13C-Labeled Polymers, Macromolecules 1997, 30, 515-519. 2. Yuntao Li, Roger J. Morgan, Thermal Cure of Phenylethynyl-Terminated AFR-PEPA-4 Imide Oligomer and a Model Compound, J. Appl. Polym. Sci., 101: 4446-4453. Doi:10.1002/app.24047. KEYWORDS: volatile gas detection; identification and quantification of volatile gasses; autoclave cure processes; real time in-situ monitoring of autoclave cure processes; polyimide composite cure processes; autoclave air pressure leak detection
