Investigation of Strain History in Autoclave Process for Composite Laminates Subjected to Tool–Part Interaction Using <scp>FBG</scp> Sensors

ABSTRACT During the autoclave process, the curing deformation of composite components is recognized as a key factor affecting the forming quality. In this paper, an online monitoring system for cure‐induced strain in the full curing process is established based on Fiber Bragg Grating (FBG) and thermocouple sensor principles. By real‐time monitoring of temperature and strain data during the curing process of pure resin, the effectiveness of the system is demonstrated. On this basis, the strain formation and evolution mechanisms at different process stages of composite laminates under aluminum tool are analyzed. The effects of tool characteristics such as tool materials and tool surface states on the strain are studied. Results indicate that both the resin of the composite and tool properties are the main influencing factors of strain changes. In the heating and holding stages, resin flow, thermal expansion, and curing reactions are the main reasons, while tool shrinkage plays a dominant role in strain changes during the cooling stage. The differences in stiffness, bonding capacity with components, and thermal expansion coefficient of different tool materials have a significant impact on the strain changes. At the same time, the maximum interaction between the tool and the component occurs on the surface of the tool with a layer of release agent. In order to reduce the problem of strong interaction between the tool and the part brought about by too little release agent, the number of layers of release agent should not be less than three layers.