The condition of internal or hidden material layers or interfaces is monitored and used for control of a process that changes a condition of a material system. The material system has multiple component materials, such as layers or embedded constituents, or can be represented with multiple layers to model spatial distributions in the material properties. The material condition changes as a result of a process performed on the material, such as by cold working, or from functional operation. Sensors placed proximate to the test material surface or embedded between material layers are used to monitor a material property using magnetic, electric, or thermal interrogation fields. The sensor responses are converted into states of the material condition, such as temperature or residual stress, typically with a precomputed database of sensor responses. The sensor responses can also be used to determine properties of the test material, such as electrical conductivity or magnetic permeability, prior to conversion to the material state. The states are used to support control decisions that control the process or operation causing the material condition to change.