Interpreting temperature evolution of a bulk-metallic glass during cyclic loading through spatial–temporal modeling

Infrared (IR) imaging represents an innovative sensing modality to study the interior structure of metallic glasses such that hidden defects causing fracture can be identified and handled in a controlled way. In this paper, the compression-compression-fatigue study is performed on a bulk-metallic glass (BMG), and the fatigue-damage evolution is recorded by an IR camera. Since IR images can only capture the surface temperature on the material, how to obtain the temperature-evolution information of internal defects through the interpretation of the surface temperature remains a challenging problem. In this paper, we consider the surface-temperature readings as a result of multiple heat sources (e.g., defects) emitting energy simultaneously from inside the BMG with each heat source having its own unique temperature-evolution pattern. This concept is a key enabler to go beyond what is immediately measureable on the surface of the material. We interpret the surface-temperature evolution over time across the spatial domain using a linear-mixing model and presents a robust unsupervised unmixing algorithm such that joint effects of hidden events (i.e., heat sources) can be identified, providing the prevailing support to the understanding of the IR images of BMGs during cyclic loading. In addition, we tackle the challenging issue of the structural characterization of defects through functional imaging techniques using a thermal-electric analog. Thus, the fatigue deformation and fracture behavior can be further studied. Moreover, the fatigue mechanisms of BMGs will be suggested.