On a simultaneous use of fiber-Bragg-gratings and strain-gages to determine the stress-free temperature Tsf during GLARE manufacturing

Abstract

Process-induced residual stresses in fiber-metal laminates depend on the stress-free temperature, which refers to the moment during the manufacturing process where a resilient mechanical connection between metal and fiber-reinforced epoxy layers is established. The stress free temperature is often determined reversely by evaluating distortions of FML specimens with asymmetric layup. The present paper focusses on an in situ strain-measurement-based procedure, which allows for the direct determination of the stress-free temperature during manufacturing. The paper reports on a combined application of strain-gage and fiber-Bragg sensors, during manufacturing of a GLARE laminate in an oven environment. The experiment setup allowed for the simultaneous measuring of strains in both constituents along the entire fabrication process. The in situ technique gives insight into mechanical interactions of the GLARE constituents during processing. As will be shown, the stress free temperature can be identified from the monitored strains and therefrom, the material’s residual stress state is quantified.