Method for in-situ measurement of near-consolidation zone temperature profiles for laser-based Automated Fiber Placement (InSiTe)

• Applicant: Professor Dr.-Ing. Berend Denkena
• Subject Area: Plastics Engineering ; Metal-Cutting and Abrasive Manufacturing Engineering
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 508102410

Laser-based Automated Fiber Placement (AFP) enables the in-situ production of fiber composite structures using thermoplastic matrix materials, thus eliminating the need for an energy-intensive autoclave process. In addition, further advantages arise from improved recyclability as well as interlocking joining techniques. The challenge is to achieve mechanical properties equivalent to the autoclave process. The joint strength is set by thermal-mechanical process control, which is ideally based on knowledge of the thermal-mechanical conditions in the joining zone. Known models can then be used to predict the interlaminar strengths, so that time-consuming and cost-intensive test methods can be minimized and, if necessary, quality can be improved during the process. One problem here is the in-process measurement of the temperature history in the joining zone. While the temperature before and after the joining zone can be recorded by IR thermography, for example, the actual joining zone is covered by the consolidation roller. Thermocouples or fiber optic sensors inserted into the laminate measure the temperature only selectively and are used exclusively for model validation, although they also act as interference points and therefore overestimate or underestimate the temperature. Accordingly, no method currently exists to obtain empirical knowledge about the temperature history within the joining zone in the continuous AFP process. For this reason, a new measuring method was designed in our own preliminary work, in which the consolidation roller is equipped with fiber-optic Rayleigh sensors. This creates a strain-sensitive shell surface that is in continuous contact with the joining zone and thus enables the detection of thermal-mechanical conditions.Therefore, the aim of this project is to explore the thermal-mechanical sensitivity of Rayleigh sensors embedded in a shape-adaptive consolidation roller typical for AFP, thus enabling the measurement method for temperature sensing in laser-based AFP. To this end, experimental studies of fiber embedding and the resulting thermal and mechanical sensitivities will be conducted. The findings will be used to compensate for mechanical as well as thermal disturbances so that the remaining strains are thermal strains. In further investigations, a model-based method for calibrating the sensitive consolidation roll will be developed by correlating the thermal strains with the temperature curves. Combining the disturbance compensation with the model-based calibration will enable temperature detection in a continuous roller-based manufacturing process, such as laser-based AFP.

• DFG Programme: Research Grants
• Co-Investigator: Dr.-Ing. Carsten Schmidt