Materials Reliability Analysis
Sandia National Laboratories has the programmatic responsibility to determine the effects of processing and aging on the performance and reliability of nonnuclear portions of nuclear weapons in the enduring stockpile. It is the behavior of constituent materials that fundamentally establishes the performance and reliability of nonnuclear components. The microstructural mechanisms that underlie materials behavior must be understood and controlled through processing to ensure that as-fabricated products meet reliability requirements. Moreover, the materials aging mechanisms must be understood and quantified to provide the basis for predicting weapon reliability throughout their design lifetime. The materials understanding and reliability approach also has been applied to components in other high-consequence systems including aging aircraft and spacecraft, nuclear power plants, and delivery and control systems.
Materials Reliability Approach Materials reliability is defined as the probability that there is sufficient materials response available to meet demands of the system during all (e.g., operational, storage, transportation, etc.) conditions. This probability can be quantified by comparing the distribution of "available materials properties" to the distribution of "design requirements." The effects of aging can be incorporated into this approach by determining how the distribution of available materials properties changes as a function of time or environment. This approach provides the framework for evaluating the reliability of the full range of behavior (e.g., mechanical, electrical, magnetic) required for high-consequence systems to function properly.
Materials reliability can be quantified by comparing the distribution of “available materials properties” to the distribution of “design requirements.” Ongoing Materials Reliablility Studies From the thousands of materials and materials interfaces used in the nonnuclear portion of weapons, Sandia has used a risk-management approach to identify those materials and interfaces that must be understood more fully.
- The degradation of solder materials due to thermo-mechanical fatigue and intermetallic compound growth is being quantified. Materials models are developed and used to predict the long-term performance of solder interconnects.
Vesicles of concentric porous silica shells formed by evaporation-induced self-assembly in an aerosol. - The materials mechanisms controlling the reliability and aging of microelectromechanical system (MEMS) devices in the as-manufactured state and under dormant storage conditions are being investigated.
- Corrosion (as shown above) can affect electronic components by removing material (causing an open circuit) or adding corrosion product (causing a short circuit). The conditions required for corrosion and their kinetics are quantified and compared to electrical requirements to determine the impact on system reliability.
- Electrical contacts used in switches and other electromechanical devices can degrade due to contamination, corrosion, and fretting/wear. Contacts in returned hardware are being evaluated and degradation mechanisms measured.
Vesicles of concentric porous silica shells formed by evaporation-induced self-assembly in an aerosol. - Electromechanical devices including switches, motors, and environmental sensing devices critically depend on lubricant performance. The kinetics of lubricant degradation due to oxidation, wear, migration and other mechanisms are being determined.
- Stress voiding of aluminum interconnect lines in integrated circuits (ICs) can occur during long-term dormant storage as shown above. The coalescence of vacancies driven by diffusion and residual stress is being quantified in weapon ICs.
- Polymeric materials perform critical functions both at the component and system levels; they provide electrical insulation, environmental seals, shock/vibration mitigation, and structural roles. The rates of property changes due to oxidation, thermal degradation, and other mechanisms are being determined.
- Although glasses and ceramics chemically are very stable, they are sensitive to process-induced defects and long-term aging effects. The stability of glass and ceramic hermetic seals is being measured.
Accomplishments
- Measurements of the ferroelectric material used in a weapon fireset eliminated safety concerns that there might be age-induced "self-poling."
- Careful measurements of the desiccant and gas atmosphere in the W80 weapon system determined that the life of the desiccant could be extended significantly. This work provided the basis for eliminating a major maintenance activity and saved tens of millions of dollars in refurbishment costs.
- Materials studies have provided important fundamental reliability information for Life Assessment Reports for the W76 and the W80 weapons systems.
- Elastomer o-ring lifetimes have been predicted based on physical and chemical mechanisms. "Inferior" material supplied by specific vendors has been identified.
- Wire-insulation lifetime has been determined for specific aircraft and power-plant systems.
Contacts: Jill Glass, (505) 845-8050, sjglass@sandia.gov
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