Sandia National Laboratories is working to fill gaps in the fundamental understanding of materials science through an ambitious long-term, multidisciplinary project called Predicting Performance Margins, or PPM. From the atomic level to full-scale components, the research links variability in materials’ atomic configurations and microstructures with how actual parts perform.
PPM, which launched in 2010, aims to identify how material variability affects performance margins for an engineering component or machine part. The goal is a science-based foundation for materials design and analysis—predicting how a material will perform in specific applications and how it might fail compared with its requirements, then using that knowledge to design high-reliability components and systems. Materials are such things as alloys, polymers or composites; components are switches, engines or aircraft wings, for example, while systems can be entire airplanes, appliances or even bridges.
The PPM approach has become a prototype for tackling other difficult materials issues. Materials science researchers recently used the approach in a proposal to understand brittle materials, establishing a multidisciplinary project to develop the fundamental science while delivering improvements during the project to those who use these materials. That way, users don’t have to wait years to reap benefits from the fundamental work. Future studies that could benefit from the approach include the aging of polymers and foams, friction between electrical contacts and failures in glass-to-metal seals and in solders and interconnects.
Too often, we are unable to predict precisely how a material will behave, and instead we must rely on expensive performance tests. Capturing variability by testing alone is too expensive and not predictive.—Amy Sun, program manager
PPM simultaneously tackles fundamental materials science issues at the atomic and microstructural scales and engineering problems at the visible scale. The program draws on expertise across Sandia’s campuses in New Mexico and California to study materials’ behavior at different scales, applying materials, physical and chemical sciences, nanoscience and engineering.
From the bottom up, the program studies how atoms undergo rearrangement that initiates defects in response to mechanical stresses and strains (nanoscale); how these crystalline defects evolve, multiply and interact (mesoscale); and finally, how an ensemble of polycrystals works in concert to govern deformation and failure of a component (macroscale).
Researchers use advanced characterization techniques such as 3-D microscopy and focused ion beam and digital image correlation, as well as quantum and atomistic simulations and mesoscale material mechanics.
PPM also looks at how manufacturing processes determine the microstructure of a material and examines test data and failure statistics to better understand the relationship between microstructures and how engineering materials perform.
One pilot study involves laser welds, which are used widely in engineered systems. Weld performance can be unpredictable because a weld’s microstructure isn’t homogenous and geometric imperfections such as cracks and pores can be introduced in the welding process. The aim is to understand a basic engineering question: how the microscopic variability of a weld impacts the mechanical reliability of a welded component.
We could say, “If you weld it with this margin of overdesign, you’re probably OK, you’re probably safe.” But as a materials scientist, you’re not going to be happy with that answer.—Amy Sun