Priority Technical Areas
The committee identified two interrelated technical categories that merit more attention by the SBIR program. These areas can be classified broadly as corrosion (other than general corrosion, but including galvanic corrosion and corrosion fatigue) and nondestructive evaluation and investigation (NDE/NDI). Specific topics are described below.
Corrosion modeling. Corrosion modeling, especially for hidden forms of corrosion (galvanic corrosion, crevice corrosion, pitting, intergranular corrosion, stress corrosion cracking, and corrosion fatigue) is a priority R&D area. In general, corrosion is currently detected from empirical data, and the onset of corrosion or the propagation of corrosion in the presence of stress or fatigue cannot be predicted. Predicting the onset of corrosion for a particular component or a particular aircraft, with or without other damage mechanisms, is very difficult. However, susceptible structures could be identified and corrosion rates predicted.
Models of the effect of multiple coating layers on corrosion behavior would be useful for predicting the remaining life of systems. Such models could be developed through the SBIR program to provide concepts, a general framework, and assumptions for different materials. Models would be key elements in determining structural life (see Figure 2-4). If significant innovations are achieved in modeling corrosion growth rates, strong commitments for Phase III funding will be necessary. Because the modeling of corrosion phenomena is of considerable interest to many agencies, leveraging of funds is a good possibility.
Nondestructive evaluation and investigation. NDE/NDI modeling to detect subsurface cracks and hidden corrosion in fastener holes and beneath coatings is one of the most significant areas for R&D. The development of several NDI systems is being done by small businesses; the Air Force will need new techniques or hybrid techniques to improve both the identification and quantification of the defect. Quantified values, which could then be fed back into models developed to predict remaining life, would play a vital role in determining maintenance or inspection intervals, both of which affect operation and support
costs. Small business programs are ideally suited for the development of these NDE/NDI methods, which address specific, focused areas that could result in Phase III successes.
Senior technologies. Significant developments in sensor technologies are being made rapidly. Sensors and sensor analysis—including embedded and external sensors for measuring pressure, temperature, humidity, gases, color, corrosion, cracking, thickness, local strain, and chemical composition—are important for the future of aging aircraft. Sensors come in many forms, shapes, sizes, and qualities, and each type can provide useful information for modeling. Sensors can also serve as early warning systems of impending failures or the need for accelerated maintenance. Sensors that can measure thickness at regular intervals could become an integral part of future aircraft systems. Many advances are being made in optical, ultrasonic, and chemical sensors, as well as MEMS, miniature systems, wireless technologies, and diagnostic and prognostic analysis tools.
Coatings. Coatings are used on aircraft for many reasons, ranging from camouflaging to corrosion protection. Coatings protect surfaces from the environment and contribute synergistically to overall service life, but they may weather with time and use. The removal of coatings without leaving traces of ingredients that may adversely affect the surface or the environment is an important area that merits attention by the SBIR program. Health issues associated with the removal of coatings also merit attention.
The AFRL medium-term coatings development program has been very successful. Attention has now shifted to the difficult issues of long-term coatings development. The SBIR community could make contributions in this area as significant as those it made for earlier coatings. Materials development for the long-term program includes new polymer technology, chromate-free corrosion inhibitors as the core of the permanent primer, and innovative tailoring of the total coating system for durability and cost-effectiveness.
Surface treatments. Surface treatments (mechanical and thermal) to relieve stresses or to create residual stresses would increase fatigue life. Issues related to the role of these stresses and their interactions with the environment can influence the safety factors incorporated in designs for aircraft structures. Prolonging service life through surface treatments is an area suitable for small business activity.
Remanufacturing and repair. Aircraft structures are damaged by bird hits and impact damage from flying or runway debris. In light of the high cost of structural materials and the need to ensure that readiness has not been compromised, remanufacturing techniques that can be applied at the ALC level would be
extremely useful. These techniques would have to be simple, easy to use, environmentally compliant, and relatively inexpensive. Because they would be used by routine service personnel with minimal education, they would have to be easy to learn, easily transferable, and consistent in quality. Remanufacturing and repair technologies are promising candidates for many SBIR programs, especially for the aging aircraft program.
Composites. The development of high-strength, stiff, easy-to-manufacture composites that can be bonded or attached to similar or dissimilar structures would be of immense value to the Air Force at the ALC level. An understanding of how composites could be used in various environmental conditions, the interfacial strength, and the degradation rates of interfaces would also be of great benefit. The focus of the Air Force's repair technology program is on highly reliabile and long-lasting bonded repair of metallic structures using composite materials. Methods of qualifying bonds, new materials for bonding, and methods of establishing acceptable levels of strength created during bonding could be good candidates for SBIR projects.
Miniature sampling methods. Small samples that provide representative bulk data is another area of significant interest, especially for composites or precipitation-hardened alloys. In such materials, the interface/environment effects may increase stress levels, decreasing the fatigue or corrosion-fatigue life. Reliable methods of sampling and analyzing data could help to establish and improve safety factors in design.
Cost ownership models. The cost of maintaining an aircraft throughout its lifetime and the ability to make intelligent decisions based on the relationship between useful service life, readiness, and cost of upkeep will require the development of cost ownership models. Most aging aircraft in the fleet have already outlived their planned service life, and the cost of upkeep for the fleet for the next 20 to 25 years is not known; many issues that will affect operation and maintenance costs or even safety have not been identified. The Air Force does not have cost ownership and usage models to help plan the retirement of aircraft, develop maintenance interval guidelines, and make early budget allocations in an austere environment. A number of the available cost models currently being successfully adapted by a number of Air Force groups for their analyses of cost of ownership and economic service life originated in SBIR programs, and the SBIR community could play an important role in developing or adapting these models for aging aircraft.
Recommendation. The committee recommends that more emphasis should be placed on using the Small Business Innovation Research (SBIR) program in the near term to solve problems related to localized corrosion (including galvanic corrosion and corrosion fatigue) and nondestructive evaluation and inspection (NDE/NDI). Solutions to the problems of (1) modeling and understanding galvanic corrosion, stress-corrosion cracking, corrosion fatigue, and all the other insidious forms of corrosion and (2) developing tools for NDE/NDI and software to analyze data in these areas should be solicited from the small business community. Because many of the innovations will be specific to the Air Force, the end user (in the Air Force) should be involved in the Phase I and Phase II award process. In addition, if the innovation is Air Force-specific, non-SBIR funding for Phase III may be an Air Force responsibility.